Achromobacter Infections and Treatment Options

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1 Achromobacter Infections and Treatment Options

2 Burcu Isler 1

2,3

3 Timothy J. Kidd Downloaded from

4 Adam G. Stewart 1,4

5 Patrick Harris 1,2

6 1,4

David L. Paterson http://aac.asm.org/

7 1. University of Queensland, Faculty of Medicine, UQ Center for Clinical Research,

8 Brisbane, Australia

9 2. Central Microbiology, Pathology Queensland, Royal Brisbane and Women’s Hospital,

10 Brisbane, Australia on August 18, 2020 at University of Queensland

11 3. University of Queensland, Faculty of Science, School of Chemistry and Molecular

12 Biosciences, Brisbane, Australia

13 4. Infectious Diseases Unit, Royal Brisbane and Women’s Hospital, Brisbane, Australia

15 Editorial correspondence can be sent to:

16 Professor David Paterson

17 Director

18 UQ Center for Clinical Research

19 Faculty of Medicine

20 The University of Queensland

21 Level 8, Building 71/918, UQCCR, RBWH Campus

22 Herston QLD 4029 AUSTRALIA

23 T: +61 7 3346 5500 Downloaded from

24 F: +61 7 3346 5509

25 E: [email protected]

26 http://aac.asm.org/

29 on August 18, 2020 at University of Queensland

40 Abstract

41 Achromobacter is a genus of non-fermenting Gram negative bacteria under order

42 Burkholderiales. Although primarily isolated from respiratory tract of people with cystic Downloaded from 43 fibrosis, Achromobacter spp. can cause a broad range of infections in hosts with other

44 underlying conditions. Their rare occurrence and ever-changing taxonomy hinder defining

45 their clinical features, risk factors for acquisition and adverse outcomes, and optimal

46 treatment. Achromobacter spp. are intrinsically resistant to several antibiotics (e.g. most http://aac.asm.org/ 47 cephalosporins, aztreonam and aminoglycosides), and are increasingly acquiring resistance to

48 carbapenems. Carbapenem resistance is mainly caused by multidrug efflux pumps and

49 metallo-β-lactamases, which are not expected to be overcome by new β-lactamase

50 inhibitors. Among the other new antibiotics, cefiderocol and eravacycline were used as on August 18, 2020 at University of Queensland

51 salvage therapy for a limited number of patients with Achromobacter infections. In this

52 article, we aim to give an overview of the antimicrobial resistance in Achromobacter species,

53 highlighting the possible place of new antibiotics in their treatment.

54 Introduction

55 Taxonomy. Genus Achromobacter was first established in 1923 by the Committee of the

56 Society of American Bacteriologists (today the American Society for Microbiology) as “non-

57 pigment forming, motile or non-motile Gram negative bacteria occurring in water and soil”

58 (1). Close resemblance of genus Achromobacter to genus Alcaligenes, both of which are

59 members of the Alcaligenaceae family of the order Burkholderiales, prompted reassignment

60 of several Achromobacter species to genus Alcaligenes and vice versa. Genus Achromobacter

61 currently comprises 19 officially designated species, most of which were characterized within

62 the last decade (2). Fifteen species to date have been isolated from clinical specimens,

63 including Achromobacter xylosoxidans, Achromobacter denitrificans, Achromobacter

64 ruhlandii, Achromobacter piechaudii (3), Achromobacter animicus, Achromobacter

65 mucicolens, Achromobacter pulmonis (4), Achromobacter insolitus, Achromobacter spanius

66 (5), Achromobacter deleyi (6), Achromobacter aegreficans, Achromobacter insuavis, Downloaded from 67 Achromobacter anxifer, Achromobacter dolens (7) and Achromobacter marplatensis (8).

68 Worldwide, A. xylosoxidans is the most common species recovered from clinical samples,

69 including those derived from persons with cystic fibrosis (CF). Distribution of other species

70 show geographical diversity. A. ruhlandii is the second most common species in the Americas http://aac.asm.org/ 71 (9-11), whereas A. dolens and A. insuavis are more prevalent in Europe (12-14). Clinical

72 significance of species variation is not well characterized.

73 Identification. Genus Achromobacter is an obligately aerobic, non-fermentative; oxidase and

74 catalase positive; indole, urease and DNase negative bacteria (15). Achromobacter spp. are on August 18, 2020 at University of Queensland

75 frequently misidentified as other common (i.e., Pseudomonas aeruginosa, Stenotrophomonas

76 maltophilia, Burkholderia cepacia complex, Acinetobacter spp.), and rare (i.e., Pandoraea spp.

77 and Ralstonia spp.) non-fermenting Gram negative bacilli with conventional methods due to

78 biochemical similarities (16-18). Furthermore, most Achromobacter species were referred as

79 A. xylosoxidans with conventional methods. More accurate speciation became possible with

80 the utilization of the genotypic methods such as nrdA gene sequencing and the multilocus

81 sequence typing (MLST) (8, 9). However, for many routine clinical microbiology laboratories

82 sequence-based identification using these techniques is not feasible. Matrix-assisted laser

83 desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) was successful at

84 distinguishing Achromobacter from other non-fermenters at the genus level (17, 19, 20).

85 Identification to the species level has been hampered by the limited number of species

86 included in the MALDI-TOF databases (e.g., two and six species for VITEK MS V3.0 and MALDI

87 Biotyper IVD-CE, respectively) (21). MALDI-TOF was successful at identifying most species (i.e.

88 ≥ 90%) accurately when its database was expanded using 18 and 9 different Achromobacter

89 species in two different studies (21). Correct identification rates with the default MALDI

90 Biotyper database in these studies were 51% and 66%, respectively, misidentification mainly Downloaded from 91 stemming from referring the species not involved in the database as A. xylosoxidans (22).

92 These results are promising, and their incorporation into the commercial databases will

93 facilitate a more accurate identification at the species level. Until then, confirmation of the

94 MALDI-TOF results with genotypic methods is warranted for correct species identification. http://aac.asm.org/

95 Host predisposition and clinical spectrum. Achromobacter spp. are predominantly recovered

96 from persons with CF as chronic respiratory pathogens, and are common causes of CF post-

97 lung transplant infections with poor outcomes (23-25).

98 Outside the context of CF, data on the clinical spectrum of Achromobacter infections come on August 18, 2020 at University of Queensland

99 from case reports and case series. Pneumonia and bacteremia are the two most common

100 clinical presentations of Achromobacter infections in non-CF hosts (26). Infections of the skin

101 and soft tissue, urinary tract, intraabdominal organs, central nervous system (CNS), eye and

102 ear are less frequently reported, endocarditis and bone infections being very rare (27-34).

103 Most Achromobacter infections are either hospital acquired or health care associated, and

104 often develop in relation to foreign devices (35). Achromobacter infections do not solely

105 occur in immunocompromised hosts as previously thought. Patients with devices, (e.g.,

106 catheters and endotracheal tubes), underlying conditions (e.g., diabetes mellitus, chronic

107 renal failure, chronic heart diseases) and with current or previous hospitalization or health-

108 care exposure are at risk (26, 36).

109 Antibiotic resistance mechanisms

110 The two main intrinsic resistance mechanisms of Achromobacter species comprise multidrug

111 efflux pumps and chromosomal OXA-114-like β-lactamases (Table 1). Extended spectrum β-

112 lactamases (ESBLs), AmpC type β-lactamases and metallo-β-lactamases (MBLs) have been Downloaded from 113 detected in Achromobacter isolates and appear to contribute to resistance to β-lactams,

114 including carbapenems.

115 Multidrug efflux pumps. Achromobacter species harbor two well characterized multidrug

116 efflux pumps and several putative efflux pump genes (37). AxyABM efflux pump is found in http://aac.asm.org/

117 all publicly available Achromobacter genomes and share common properties with the

118 MexAB-OprM efflux pump of P. aeruginosa (38). AxyABM plays a major role in the extrusion

119 of cephalosporins other than cefepime and cefuroxime, and of aztreonam, but does not

120 appear to be the sole mechanism of resistance for these agents as aztreonam and on August 18, 2020 at University of Queensland

121 cephalosporin susceptibilities were not restored after AxyABM inhibition in vitro (39).

122 AxyABM inhibition resulted in decreases in cefotetan, cefoxitin, cefotaxime, ceftriaxone and

123 aztreonam Minimum Inhibitory Concentrations (MICs) from >256 µg/ml to 32, 128, 12, 12

124 and 16 µg/ml, respectively (39). Ceftazidime MIC dropped from 4 to 1.5 µg/ml, whereas

125 cefuroxime, cefepime, amikacin, colistin, tigecycline and carbapenem (i.e., meropenem and

126 imipenem) MICs remained unchanged. Changes in fluoroquinolone MICs were not significant

127 (drop from 0.75 µg/ml to 0.5 and 0.38 µg/ml for ciprofloxacin and levofloxacin, respectively).

128 The second efflux pump AxyXY-OprZ has a broader spectrum, and is involved in the extrusion

129 of aminoglycosides, cefepime, carbapenems, fluoroquinolones, tetracyclines, and

130 erythromycin to varying degrees (40). AxyXY-OprZ is the main resistance determinant that

131 accounts for high-level intrinsic aminoglycoside resistance in Achromobacter spp. For other

132 antibiotics (e.g., cefepime, ceftazidime, carbapenems, tetracyclines and fluoroquinolones)

133 AxyXY-OprZ appears to be a contributor to the resistance rather than being the main

134 resistance mechanism. Inhibition of AxyXY-OprZ restored susceptibilities to all

135 aminoglycosides and tigecycline (40). Imipenem and meropenem MICs dropped from 4 to 1 Downloaded from 136 µg/ml and 12 to 2 µg/ml, respectively, for a carbapenem resistant strain, whereas the drop

137 was one-fold for a carbapenem susceptible strain. Fluoroquinolone MICs were reduced 2 to

138 4-fold for fluoroquinolone resistant strains, but susceptibilities were not restored. AxyXY-

139 OprZ inhibition resulted in one-fold and zero to 4-fold drop in ceftazidime and cefepime http://aac.asm.org/ 140 MICs, respectively without restoring susceptibilities to these agents. A previous study found

141 AxyXY-OprZ to be present only in certain strains with phenotypic aminoglycoside resistance

142 (i.e., A. xylosoxidans, A. ruhlandii, A. dolens, A. insuavis, A. denitrificans, A. insolitus and A.

143 aegrifaciens) and absent in aminoglycoside susceptible strains (i.e., A. mucilocens, A. on August 18, 2020 at University of Queensland

144 animicus, A. piechaudii and A. spanius) (41), whereas a pan-genome analysis from 2016

145 demonstrated AxyXY-OprZ to be present in all publicly available genomes (38). The reason of

146 the inconsistency between these studies is unclear.

147 Whether the production of efflux pumps is induced under antibiotic pressure is a question

148 that remains to be answered. In vitro tobramycin exposure lead to mutations in the AxyXY-

149 OprZ regulator resulting in MIC increases in its substrate antibiotics in laboratory strains (42).

150 The same mutation was observed in a clinical strain from a CF patient after tobramycin

151 exposure, but this patient had been exposed to several other antibiotics during her chronic

152 colonization, and it is uncertain which of these, if any, induced the mutation (42). In contrast,

153 successive strains with increased antibiotic MICs from four other patients did not have the

154 same mutation, suggesting the involvement of other genetic mechanisms in AxyXY-OprZ

155 regulation (42). Finally, no association could be demonstrated between antibiotic exposure

156 and resistance development for meropenem, ticarcillin clavulanic acid, and colistin in

157 Achromobacter isolates from a single CF patient (43).

158 β-lactamases. Achromobacter species produce a constitutive chromosomal β-lactamase, Downloaded from

159 namely OXA-114, with activity against penicillin G, early cephalosporins, piperacillin and

160 ticarcillin. OXA-114-like enzymes are efficient piperacillin hydrolyzers in vitro. Ticarcillin is

161 hydrolyzed to a lesser degree, whereas extended spectrum cephalosporins, such as

162 ceftazidime, cefotaxime, or cefepime are not substrates of OXA-114-like enzymes (44). http://aac.asm.org/

163 Hydrolytic activity of OXA-114 against imipenem is very poor.

164 The contribution of OXA-114 to phenotypic piperacillin resistance of Achromobacter isolates

165 is unclear as piperacillin susceptibility is common among OXA-114 positive Achromobacter

166 isolates (45). Piperacillin hydrolysis by OXA-114 does not appear to be inhibited by on August 18, 2020 at University of Queensland

167 tazobactam. In their study in which OXA-114 was discovered, Doi et al. demonstrated all five

168 OXA-114 positive Achromobacter strains to be susceptible to piperacillin (MICs 1-4 µg/ml),

169 and addition of tazobactam dropped piperacillin MICs one-fold except for the strain with

170 piperacillin MIC of 4 µg/ml, for which no MIC change was observed (44). Likewise, piperacillin

171 and piperacillin-tazobactam MICs were similar (MIC50/90 32/>128 µg/ml, range 4->128 for

172 both antibiotics) in another collection of 94 CF isolates (16).

173 Presence of acquired β-lactamases such as ESBLs (i.e. blaCTX-M, blaVEB-1), AmpC type β-

174 lactamases (i.e., blaAmpC, blaCMY−2) and carbapenemases (i.e. blaIMP, blaVIM) in Achromobacter

175 isolates were reported from several countries, including Greece, Italy, France, Japan, and

176 Korea (46-55). In addition to IMP and VIM which are among the most common MBLs

177 worldwide, another rarer MBL, namely Tripoli MBL (TMB), was discovered in the

178 chromosome of an A. xylosoxidans strain from Tripoli, Libya (56). Amino acid structure of

179 TMB was similar to that of DIM and GIM MBLs of P. aeruginosa, with a lower hydrolytic

180 activity against cephalosporins and carbapenems. Meropenem and imipenem MICs were 4

181 and 2 µg/ml, respectively, for the isolate harboring TMB (56). Downloaded from

182 Spread of acquired β-lactamases, particularly MBLs, is concerning as none of the currently

183 available β-lactamase inhibitors can overcome the β-lactam resistance caused by MBLs.

184 Aztreonam, the only β-lactam antibiotic resistant to MBL hydrolysis, is a substrate of the

185 AxyABM efflux pump. Proportion of MBLs among carbapenem resistant Achromobacter http://aac.asm.org/

186 isolates is not well described despite increasing carbapenem resistance rates. Achromobacter

187 strains with elevated carbapenem MICs should be screened for the presence of these MBLs

188 while keeping in mind that resistance to carbapenems may occur via other resistance

189 mechanisms (e.g., AxyXY-OprZ, unidentified β-lactamases). Some in vitro studies on August 18, 2020 at University of Queensland

190 demonstrated that mutations in transcription regulators of unnamed β-lactamases, or

191 increased expression of a putative β-lactamase gene (i.e., blaAXC) may contribute to

192 carbapenem resistance in Achromobacter spp. (43, 57, 58). Comparative genomic analysis of

193 carbapenem susceptible and resistant strains is essential to elucidate the genetic

194 mechanisms behind carbapenem resistance of genus Achromobacter.

195 Other. A. xylosoxidans contains at least 50 intrinsic resistance genes, including class A-D β-

196 lactamases (five new β-lactamases), efflux pump systems (seven new RND-type efflux

197 pumps), aminoglycoside acetyltransferase and phosphotransferases, dihydrofolate

198 reductases and others; more than half of which show significant similarities with that of P.

199 aeruginosa (37). Furthermore, clinical isolates carry additional β-lactam, aminoglycoside, and

200 sulphonamide resistance genes as compared to the environmental isolates (37, 38).

201 Presence of plasmid-mediated acetyltransferases (i.e. aac-(6′)-Ib-cr) and other plasmidic (i.e.

202 oqxA, qnrA, and oqxB) and chromosomal (i.e. gyrA and parC) fluoroquinolone resistance

203 genes were demonstrated in clinical Achromobacter isolates from Serbia (59), and Downloaded from 204 environmental Achromobacter isolates from Brazil (60). Their contribution to phenotypic

205 fluoroquinolone resistance in Achromobacter strains awaits further evaluation.

206 Antibiotic susceptibility

207 Optimal genus-specific susceptibility testing methods and widely accepted susceptibility http://aac.asm.org/

208 breakpoints are not defined for Achromobacter spp. CLSI provides MIC breakpoints for

209 Achromobacter spp. under the “other non-Enterobacterales” category, but most of the

210 previous studies used various antimicrobial susceptibility testing methods and susceptibility

211 breakpoints (Table 2) (61, 62). Despite these heterogeneities, some common phenotypic on August 18, 2020 at University of Queensland

212 susceptibility patterns emerge among Achromobacter isolates. Wild type strains appear to

213 demonstrate phenotypic resistance to narrow spectrum penicillins, first and second

214 generation cephalosporins, ceftriaxone, cefotaxime, aztreonam, tetracycline and

215 aminoglycosides; whereas they may remain susceptible to ceftazidime, cefepime, piperacillin,

216 carbapenems, sulfonamides, fluoroquinolones, doxycycline, tigecycline and colistin.

217 Contemporary isolates, particularly those from chronically colonized CF patients are often

218 resistant to most of these antibiotics, particularly to fluoroquinolones (63). Trimethoprim-

219 sulfamethoxazole, ceftazidime, piperacillin, and carbapenems are the most active agents

220 against Achromobacter isolates. However, acquired resistance to these are increasingly being

221 reported (64). Proportion of ceftazidime susceptible isolates was 71% in a US collection

222 (susceptibility breakpoint ≤8 µg/ml, CLSI other non-Enterobacterales; MIC50/90 8/32 µg/ml)

223 (65). In another collection from Europe, trimethoprim-sulfamethoxazole MIC50/90 was 0.5/8

224 µg/ml (susceptibility breakpoint ≤ 2 µg/ml, CLSI other non-Enterobacterales) and it was one

225 of the two most active agents against 59 Achromobacter isolates, the other being imipenem

226 (MIC50/90 of 2/8 µg/ml) (66). Several studies showed imipenem to be more active than Downloaded from 227 meropenem against Achromobacter isolates (63, 65, 66). This was also observed in P.

228 aeruginosa isolates and was demonstrated to be caused by the overexpression of the mexAB

229 efflux pumps (67). A similar mechanism may be responsible for the discordant carbapenem

230 susceptibilities in Achromobacter spp. Conversely, some other studies report meropenem http://aac.asm.org/

231 (MIC50/90 0.125/1 µg/ml) to be more active than imipenem (MIC50/90 1/4 µg/ml) (68) (Table 2)

232 and the genetic determinants of this phenotype is not characterized.

233 Studies that present data on tigecycline susceptibility are limited. MIC50/90 values were 2-4/4-

234 16 µg/ml in three different studies (69-71). In an in vitro study comparing the activities of on August 18, 2020 at University of Queensland

235 four tetracyclines against Achromobacter isolates, tigecycline and minocycline demonstrated

236 lower MICs (MIC50/90 2/4 and 2/8 µg/ml, respectively), as compared to doxycycline and

237 tetracycline (MIC50/90 16/64 and 256/256 µg/ml, respectively) (71). Colistin may remain active

238 in vitro against Achromobacter isolates. According to EUCAST antimicrobial wild type

239 distributions, colistin modal MIC was 4 µg/ml for 150 A. xylosoxidans isolates obtained from

240 three undefined sources and the MIC range was 0.5-16 µg/ml except for the three isolates

241 with an MIC of 512 µg/ml (72).

242 Azithromycin is a macrolide agent commonly used in CF patients to improve lung function

243 and reduce P. aeruginosa exacerbations, mainly provide by its immunomodulatory and anti-

244 inflammatory properties (73, 74). Achromobacter species are intrinsically resistant to

245 azithromycin, and whether CF patients colonized with Achromobacter spp. would benefit

246 from indirect antimicrobial effects of azithromycin is unclear. An in vitro study demonstrated

247 enhanced Achromobacter killing in the presence of azithromycin when tested in mammalian

248 tissue culture media rather than the standard bacterial growth media, which needs to be

249 confirmed on larger collections and in vivo studies (75). Downloaded from

250 Susceptibility data on different Achromobacter species is limited. A. ruhlandii strains may

251 exhibit a more resistant phenotype as demonstrated during a pandrug resistant A. ruhlandii

252 epidemic in Denmark, and more recently in an Argentinian collection, where most imipenem

253 resistant strains belonged to A. ruhlandii (i.e., imipenem MIC was > 4 µg/ml for 3/7, 1/26, and http://aac.asm.org/

254 0/8 of A. ruhlandii, A. xylosoxidans and other Achromobacter spp. [A. dolens, A. insuavis, A.

255 pulmonis and A. spiritinus], respectively) (11). In an early study, where species were identified

256 using biochemical methods, A. denitrificans strains (n=11) demonstrated a more susceptible

257 phenotype as compared to A. xylosoxidans strains (n=24) (i.e., resistance to ceftazidime, on August 18, 2020 at University of Queensland

258 meropenem and trimethoprim-sulfamethoxazole was 7, 17 and 27% among 24 A.

259 xylosoxidans isolates, whereas all 11 A. denitrificans remained susceptible to these agents)

260 (76). Antibiotic susceptibility testing of large collections of isolates identified using reference

261 methods is essential for a more clear picture of the susceptibility variation among different

262 Achromobacter species.

263 Achromobacter genomes appear to harbor various resistance genes that are involved in the

264 resistance to several antibiotics to varying degrees. However, genetic mechanisms and

265 environmental factors influencing resistance gene expression is not well characterized.

266 Despite common resistance phenotypes among Achromobacter strains, (e.g., resistance to

267 aminoglycoside, aztreonam, and cephalosporins except ceftazidime), rare reports of strains

268 with varying degrees of susceptibility to these agents are also present (76, 77). These

269 inconsistencies may be caused by many factors including the variation in gene expression

270 level, presence of other unidentified resistance mechanisms, inaccurate identification of the

271 non-fermenting Gram negative bacilli, and variation in antibiotic susceptibility testing

272 methods. Downloaded from

273 Treatment

274 Treatment of Achromobacter infections in CF patients is challenged by the intrinsic and

275 acquired resistance to several first line antibiotics. Efficacy of different treatment regimens

276 on the outcomes of Achromobacter infections is unknown. Its rare occurrence, co-presence http://aac.asm.org/

277 with more pathogenic non-fermenters (e.g., P. aeruginosa) and poorly understood clinical

278 features hamper the evaluation of treatment efficacy on patient outcomes. Despite being

279 regarded as a non-pathogenic colonizer of the CF respiratory tract in earlier studies,

280 Achromobacter species may cause frequent exacerbations and devastating post-lung on August 18, 2020 at University of Queensland

281 transplant infections in CF patients (78). There are no standard treatment protocols for CF

282 Achromobacter infections, and treatment usually consists of systemic and/or inhaled

283 antibiotics. Addition of inhaled antibiotics may provide some benefit as compared to systemic

284 therapy alone, but the evidence comes from observational studies with few patients. In a

285 study from Denmark, addition of inhaled antibiotics (i.e., ceftazidime, colistin, tobramycin) to

286 active systemic therapy resulted in Achromobacter clearance after three years in 10 of 17

287 (59%) patients as compared to one of six (17%) patients without inhaled antibiotics (79).

288 Similar results were observed among those who received inactive systemic antibiotics. The

289 outcomes in this study may be influenced by factors other than the inhaled therapy per se,

290 and small numbers do not allow to adjust for confounders. Controlled clinical studies are

291 needed to evaluate the effect of inhaled antibiotics and of different systemic antibiotics for

292 the treatment of Achromobacter infections (79). Until then, treatment of Achromobacter

293 respiratory infections will need to be evaluated on a case by case basis, taking into account

294 several factors including infection severity, infection frequency, suppressive antibiotics

295 received and in vitro antibiotic susceptibility. Downloaded from

296 Treatment of Achromobacter infections outside the context of CF depends on the site of

297 infection and patient factors in addition to disease severity. Favorable clinical outcomes were

298 observed with β-lactams, including ceftazidime, piperacillin-tazobactam, carbapenems, and

299 trimethoprim-sulfamethoxazole for bloodstream infections (80). In a series of 10 cancer http://aac.asm.org/

300 patients with Achromobacter bacteremia, all had favourable outcomes with β-Iactams (e.g.,

301 ceftazidime, piperacillin, ticarcillin) and/or trimethoprim-sulfamethoxazole, including six

302 patients who received monotherapy with one of these agents. It is important to note that

303 four of six patients with monotherapy had their central venous catheter (CVC) removed on August 18, 2020 at University of Queensland

304 which may have contributed to the favourable outcomes. Similarly, successful outcomes

305 were observed with foreign device associated CNS infections treated with ceftazidime or

306 doripenem in addition to foreign device removal (81, 82). In another case series, 15 elderly

307 patients (median age 89) with hospital acquired Achromobacter pneumonia were successfully

308 treated with piperacillin-tazobactam, meropenem and imipenem monotherapies (n=9) (45).

309 Five patients died on day-30 and four of these were receiving combination therapies (e.g.,

310 meropenem or piperacillin-tazobactam plus ceftazidime or minocycline).

311 Achromobacter infections in non-CF hosts can be managed with appropriate source control

312 and treatment with a single β-lactam antibiotic (e.g., ceftazidime, piperacillin-tazobactam)

313 with in vitro activity against the infecting strain. Carbapenems should be spared where

314 possible. Trimethoprim-sulfamethoxazole alone may be considered for less severe infections

315 such as urinary tract infections, but data is very limited for its use in severe infections. For the

316 strains with elevated β-lactam MICs, combination with an active non-β-lactam antibiotic such

317 as trimethoprim-sulfamethoxazole, tetracyclines, fluoroquinolones or colistin may be

318 considered but the evidence behind this recommendation is very poor. Downloaded from

319 New therapeutic options against Achromobacter infections

320 Cefiderocol is a new generation cephalosporin with in vitro activity against carbapenem

321 resistant Gram negative non-fermenters such as P. aeruginosa, A. baumannii and

322 Burkholderia spp. (83, 84). Although in vitro data on cefiderocol activity against http://aac.asm.org/

323 Achromobacter spp. are limited (85), it was used to treat nine patients with MDR

324 Achromobacter infections as part of the compassionate use programme (Table 4). Most were

325 CF respiratory tract infections (four with lung transplant) (86). One of the cases was

326 chronically colonized with A. xylosoxidans and developed A. xylosoxidans bacteremia post- on August 18, 2020 at University of Queensland

327 lung transplant (A. xylosoxidans susceptible to cefiderocol (MIC 0.12 µg/ml), piperacillin-

328 tazobactam, trimethoprim-sulfamethoxazole, imipenem and colistin). He was put on

329 extended infusion piperacillin-tazobactam therapy, with no improvement. At this stage,

330 cefiderocol was added to the treatment and continued for 28 days with a favorable clinical

331 response. However, a relapse of pneumonia occurred 14 days after discharge and he was put

332 on cefiderocol plus imipenem this time, which was continued for 42 days. The patient was

333 reported to be doing well at 8-month follow-up (24). The second case was chronically

334 colonized with A. xylosoxidans pre-transplant (intermediate susceptibility to piperacillin-

335 tazobactam and resistant to all other drugs tested) and was treated with cefiderocol (MIC 1

336 µg/ml) post-transplant (6 weeks) together with meropenem (5 weeks) as part of the planned

337 peri-transplant treatment regimen. The patient was reported to be well at 4-months follow

338 up, although still colonized with A. xylosoxidans (24). An implantable cardioverter-

339 defibrillator-associated bacteremia case and post-operative wound infection complicated

340 with osteomyelitis were two other complicated cases treated with cefiderocol with favorable

341 outcomes (cefiderocol MICs were not reported) (86). Cefiderocol was always used in Downloaded from 342 combination, in one case together with meropenem-vaborbactam and phage therapy. These

343 results are promising, particularly for the CF patients infected with carbapenem resistant

344 Achromobacter infections. However, an FDA warning for increased all-cause mortality with

345 cefiderocol in patients with carbapenem-resistant Gram negative bacterial infections is in http://aac.asm.org/ 346 place due to the higher death rate in the cefiderocol arm as compared to the best available

347 therapy in a recent randomized controlled trial of cefiderocol for the treatment of serious

348 carbapenem resistant Gram negative infections (86).

349 Eravacycline is a new tetracycline stable against most tetracycline efflux pumps of on August 18, 2020 at University of Queensland

350 Enterobacteriaceae. However, it is extruded by AdeABC pump of A. baumannii, which is an

351 RND type efflux pump similar to AxyXY-OprZ of Achromobacter. Whether eravacyline is a

352 substrate of the AxyXY-OprZ pump or not remains unknown. Limited in vitro data

353 demonstrate some activity of eravacycline against 19 Achromobacter spp. isolates from

354 IGNITE1 and IGNITE4 clinical trials (MIC50/90 was 1/8 µg/ml, range 0.06-8 µg/ml) (87).

355 Eravacycline was also used for the treatment of seven patients with MDR Achromobacter

356 spp. respiratory tract infections (Table 5) (personal communication, Tetraphase

357 Pharmaceuticals) (87). It is difficult to evaluate the impact of eravacycline on patient

358 outcomes as it was often used in combination with other antibiotics, except two cases where

359 the favorable outcome may have been provided exclusively by eravacycline. The first case

360 was a 30 year old CF patient, previously treated with meropenem-vaborbactam and colistin

361 twice due to A. xylosoxidans growth in sputum (clinical syndrome not specified). In the

362 current episode, she was treated with eravacycline for 7 days which was replaced with

363 tigecycline for the last 4 days of the treatment (MICs not reported). She had favorable

364 outcomes (i.e., did not have in hospital mortality or 30-day readmission due to infection,

365 further details of the “favorable outcome” are not reported). The second case was a 22 year Downloaded from 366 old CF patient, who had A. xylosoxidans growth in the bronchial wash and was treated with

367 eravacycline (MIC 2 µg/ml) from day 2-11 and day 14-18 of hospitalization and had favorable

368 outcomes. Among the other agents that were included in the treatment regimen of the

369 second case, only colistin had MICs within susceptible range, but it was started at day 10. http://aac.asm.org/

370 Clinical experience with eravacycline for the treatment of Gram negative bacterial infections

371 in general is limited. Although eravacycline was not tested in randomized trials for the

372 treatment of pneumonia, an FDA warning for higher all-cause mortality for the treatment of

373 pneumonia was issued for tigecycline, predecessor of eravacycline, which warrants caution on August 18, 2020 at University of Queensland

374 with eravacycline, as well.

375 β-lactam/β-lactamase inhibitors. Acquired carbapenem resistance occur via MBLs in

376 Achromobacter species, limiting the utility of new β-lactam/β-lactamase inhibitors against

377 carbapenem resistant Achromobacter isolates. Despite vaborbactam being inactive against

378 MBLs, meropenem-vaborbactam was used to treat Achromobacter infections in a number of

379 cases (Table 5) (87). One of them was a 29 year old CF patient with A. xylosoxidans growth in

380 sputum (clinical syndrome was not specified). Meropenem-vaborbactam was used in

381 combination with colistin, yielding favorable clinical outcomes, which could have been

382 provided by meropenem per se or colistin, rather than meropenem-vaborbactam (antibiotic

383 MICs were not reported). This patient had a subsequent episode of A. xylosoxidans growth in

384 sputum, which was treated with eravacycline followed by tigecycline. Meropenem-

385 vaborbactam monotherapy was also used to treat an 80 year old patient with bronchiectasis

386 and A. xylosoxidans growth in sputum, with favorable outcomes. Meropenem and

387 meropenem-vaborbactam susceptibilities were not reported for this isolate, either. For the

388 two other cases with meropenem-vaborbactam use, meropenem-vaborbactam MIC values Downloaded from 389 were 8 and 32 µg/ml and the drug was used as part of combination therapies against

390 polymicrobial infections (87). In vitro activity of meropenem-vaborbactam was

391 demonstrated to be slightly higher than that of meropenem against Achromobacter spp.

392 Meropenem-vaborbactam was active against 86% of 100 CF-derived A. xylosoxidans, A. http://aac.asm.org/

393 ruhlandii and A. dolens isolates (MIC50/90 ≤0.5/8 µg/ml, range ≤0.5 to 32 µg/ml; susceptibility

394 breakpoint ≤4 µg/ml); whereas meropenem alone was active against 72% of the isolates

395 (MIC50/90 1/>32 µg/ml, range ≤0.5 to >32 µg/ml; susceptibility breakpoint ≤4 µg/ml) (65). The

396 reason behind this difference remains unknown as vaborbactam is not expected to enhance on August 18, 2020 at University of Queensland

397 the activity of meropenem against Achromobacter species.

398 Among the other new β-lactam/β-lactamase inhibitors, in vitro activity of imipenem-

399 relebactam against 345 Achromobacter spp. isolates was somewhat favorable, as 44% of the

400 isolates were inhibited at a concentration of 1 µg/ml and 95% were inhibited at 4 µg/ml (MIC

401 range 0.12 to >32 µg/ml) (personal communication, Merck & Co.). Imipenem MICs for these

402 isolates are not reported and additional benefit of relebactam to imipenem is unknown.

403 Ceftazidime-avibactam and ceftazidime showed similar in vitro activities against

404 Achromobacter spp. isolates, MIC50/90 being 8/32 µg/ml for ceftazidime with and without

405 avibactam (65). Higher MICs (MIC50/90 128/>128) and lower susceptibility rates with

406 ceftazidime-avibactam were reported in other studies (88, 89). Avibactam combined with

407 either meropenem or aztreonam had poor activities against Achromobacter spp. (89).

408 Ceftolozane-tazobactam does not have any activity against Achromobacter species as

409 demonstrated in vitro (87, 90-92).

410 Plazomicin. Plazomicin is a new generation aminoglycoside which remains stable against most

411 aminoglycoside modifying enzymes, but is influenced by the efflux pumps of A. baumannii

412 and P. aeruginosa (93). Although data is lacking regarding the activity of AxyAX-OprZ of Downloaded from 413 Achromobacter against plazomicin, susceptibility of plazomicin to the MexXY efflux pump of

414 P. aeruginosa was demonstrated (94), making the inhibition of Achromobacter by plazomicin

415 unlikely.

416 Phage therapy. Achromobacter specific phages with a spectrum of 24 different http://aac.asm.org/

417 Achromobacter strains, including MDR strains were used for the treatment of a 17 year old

418 CF patient chronically colonized with A. xylosoxidans (95). The patient was put on a 20-day

419 oral and inhaler Achromobacter specific phage therapy, following a recent P. aeruginosa

420 infection episode and continuing Achromobacter colonization. Her symptoms and lung on August 18, 2020 at University of Queensland

421 capacity improved after a 20-day phage therapy, which was repeated quarterly for a year.

422 Achromobacter specific phages may be a promising option for the treatment of chronic

423 colonization and infection with Achromobacter in CF population.

424 Conclusion

425 Treatment of Achromobacter infections pose a clinical challenge. Intrinsic resistance to

426 several antibiotic classes mediated mainly by multidrug efflux pumps and chromosomal β-

427 lactamases accompanied by acquired carbapenem resistance caused by MBLs leave very few

428 treatment options for their treatment. New β-lactam/β-lactamase inhibitor combinations

429 with anti-carbapenemase activity do not provide much benefit as serine carbapenemase

430 production is not the main mechanism of resistance in Achromobacter spp. Among the other

431 new antibiotics, eravacycline and cefiderocol may have a role for the treatment of MDR

432 Achromobacter infections. The need for more clinical, microbiological and genomic data is

433 obvious for the management of MDR Achromobacter infections, which can only be provided

434 by multicentre studies due to the rarity of these infections. Furthermore, whole genome

435 sequencing of environmental isolates in addition to clinical collections would facilitate Downloaded from 436 characterization of the population structure and identification of antimicrobial resistance

437 mechanisms of Achromobacter species.

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767 Chemother 32:276-8. http://aac.asm.org/

768 on August 18, 2020 at University of Queensland

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769 TABLES

770 Table 1. Antibiotic resistance mechanisms http://aac.asm.org/ Multidrug efflux pumps Spectrum AxyABM Cephalosporins (except cefuroxime and cefepime), and aztreonam AxyXY-OprZ Aminoglycosides, tetracyclines including tigecycline, fluoroquinolones, erythromycin, cefepime, carbapenems β-lactamases OXA-114-like (chromosomal) Piperacillin, ticarcillin, benzylpenicillin, cephalothin ESBL (CTX-M, VEB-1) and AmpC (CMY-2, All β-lactams except carbapenems AmpC)

Plasmidic (IMP and VIM) and chromosomal All β-lactams except aztreonam on August 18, 2020 at University of Queensland (TMB-1) carbapenemases Other aac-(6′)-Ib-cr, qnrA, oqxA, oqxB Fluoroquinolones, aminoglycosides gyrA, parC Fluoroquinolones 771

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780 Table 2. Antibiotic susceptibility of Achromobacter isolates

Antibiotic http://aac.asm.org/ TZP CAZ IPM MEM SXT CIP AST S% S% Year, region Metho S% MIC50/90 (breakpoi MIC50/90 (breakpoi MIC50/90 S% MIC50/90 S% MIC50/90 S% MIC50/90 Ref and source d (breakpoint) (range) nt) (range) nt) (range) (breakpoint) (range) (breakpoint) (range) (breakpoint) (range) USA, 2013- 2018, CF respiratory 13% (≤16) ≤2/128 8/32 2/8 1/>32 ≤0.5/4 (65) (n=100) BMD (≤2->128) 29% (≤8) (1->32) - (≤0.5->32) 28% (≤4) (≤0.5->32) - (≤0.5->8) - - Spain, 2007- 2017, bloodstream 77% (≤2 36% (≤1 and (77) (n=13) Aut 77% (≤16) - 69% (≤8) - and ≤4) - 92% (≤2) - 54% (≤2) - ≤0.5) - Hungary, 2013-2016,

various on August 18, 2020 at University of Queensland (96) (n=171) DD 90% (≤16) - 38% (≤8) - 50% (≤4) - 86% (≤2) - 83% a - <25% (≤0.5) - West Indies, 2006-2016, (26) HAI (n=79) Aut 75%a - 79% a - 84% a - - - 91% a - 13% a - Europe, 2003- 2016, CF respiratory (66) (n=59) BMD - - - 8/128 - 2/8 - 2/32 - 0.5/8 8/32 Brazil, NR, CF respiratory 0·032– (10) (n=94) E-test - - 88% (≤8) 256 90% (≤4) 0·25–≥32 - - 90% (2) 0·032–256 76% (1) 0·38–4 Brazil, NR, CF respiratory 100% 100% (10) (n=28) E-test - - (≤8) 0·75–12 (≤4) 0·125–1 - - 79% (2) 0·023–32 43% (1) 0·38–6 France, 2010- 2015, Various non- respiratory (97) (n=63) DD 100% (≤16) - 92% (≤8) - 83% (≤2) - 97% (≤2) - - - 24% (1) UK, 2015, CF respiratory Variou (13) (n=15-81) s 89% (≤16) - 44% (≤8) - 88% (≤4) - 54% (≤2) - 67% a - 4% (≤0.5) France, 2014, CF respiratory (63) (n=109) - 88% (≤16) - - - 79% (≤4) - 72% (≤2) - - - 23% (≤0.5) 35

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Serbia, 2012- 2013, Mostly respiratory DD, (47) (n=69) BMD 84% (≤16) - 97% (≤8) - 77% (≤4) - 94% (≤2) - 54% (2) - 88% (1) Argentina, http://aac.asm.org/ 1996-2013, CF respiratory (11) (n=41) AD - 0.06-32 0.25-64 - - 0.03-128 - 0.06-64 - 0.03-256 - 0.5-64 Spain, 2007- 2012, Skin and soft tissue (n=12- (29) 14) Aut 93% a - 100% a - 79% a - - - 92% a - 21% a - France, 2011- 2012, Hospital (66%), domestic (18%) and outdoor on August 18, 2020 at University of Queensland (98) (16%) (n=50) DD 100% (≤16) - 98% (≤8) - 70% (≤4) - 100% (≤2) - - - 2% (≤0.5) - Argentina, NR, CF respiratory (46) (n=24) AD 0.3-4 - 4-32 - 0.5-4 0.125-4 - 0.13-256 2-64 China, 2008- 2011, Respiratory (36) (HAI) (n=41) Aut 90% (≤16) - 71% (≤8) - 44% (≤2) - 56% (≤2) - 85% (2) - 34% (≤0.5) - Argentina, 1995-2008, Various 0.5/4 8/16 1/4 0.125/1 0.25/32 0.5->64 (68) clinical (n=92) AD - (0.06-32) - (1-256) (0.5-256) (0.016-8) (0.03-128) (4-16) France, 2008, Various 2/≥32 0.5/≥32 (70) clinical (n=25) E-test - - - - 72% (≤2) (1-≥32) 76% (≤2) (0.06-≥32) - - - - Italy, 2003- 2008, CF sputum (99) (n=53) DD 100% (<4) - 81% (<8) - 81% (<2) - 81% (<1) - 81% (<0.5) - 81% (<2) - Italy, 2003- 2007 CF (10 respiratory 29% 0) (n=42) Aut 64% (≤64) b - (≤16) - 74% (≤8) - - - 38% (≤2) - 12% (≤2) -

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Spain, 1994- 2006, Urinary 100% (28) tract (n=9) Aut 100% (≤16) - 89% (≤8) - (≤4) - - - 78% (≤0.5) - 22% (≤1) - Italy, 2002- 2004, CF http://aac.asm.org/ (10 sputum 1) (n=62) c Aut 85% (≤16) - 44% (≤8) - 84% (≤4) - 68% (≤2) - 53% (≤0.5) - 20% (≤1) - USA, 1989- 2003, (10 bloodstream 2) (n=9-48) BMD 100% (≤16) - 92% (≤8) - 87% (≤4) - 100% (≤2) - 94% (≤0.5) - 23% (≤1) - Latin America, 1997-2002, SENTRY (10 surveillance 3) (n=25) BMD 76% (≤16) 1/64 64% (≤8) 8/>16 84% (≤4) 2/8 88% (≤2) 0.25/8 68% (≤0.5) ≤0.5/>2 32% (≤1) 2/>2 USA, 2001, CF respiratory 32/128 64/128 4/>16 8/>16 >8/>8

(16) (n=94) BMD 55% (≤16) (4->128) 45% (≤8) (2->64) 59% (≤4) (1->16) 51% (≤2) (0.5->16) 0% (≤0.5) >16/>16 19% (≤1) (0.5->8) on August 18, 2020 at University of Queensland Spain, 1991- 2000, bloodstream 100% (35) (n=12-54) BMD 95% (≤16) - - - (≤4) - 95% (≤2) - 10% (≤0.5) - 10% (≤1) - USA, 1991- 1996, various 100% 100% 1/1 2/2 (76) (n=11) BMD 100% (≤16) ≤1/≤1 (≤8) 2/2 (1-8) (≤4) (0.5-1) - - 100% (≤0.5) ≤2.5/5 9% (≤1) (1-4) USA, 1991- 1995, various ≤1/≤1 4/16 1/8 8/>8 (76) (n=24) BMD 100% (≤16) (≤1-2) 83% (≤8) (2-16) 83% (≤4) (0.5-8) - - 83% (≤0.5) ≤2.5/>160 4% (≤1) (1->8) USA, 1990, bloodstream (10 and sputum 4/>64 2/4 0.03/0.03 2/4 4) (n=14) BMD - - - (1->64) - (0.25-4) - - - (0.0075-0.06) - (0.5-8) USA, 1983- 1988, bloodstream 2/4 2/4 0.03/0.06 2/4 (80) (n=10) BMD - - - (2->32) - (0.5-4) - - - (0.03-0.12) - (0.12-4) Belgium, (10 1983-1988, 0.5/64 b 4/16 0.5/2 0.5/2 0.12/16 4/16 5) various (n=33) BMD - (0.5->128) - (1-64) - (0.25-4) - (0.25-2) - (0.12-64) - (1-64) 781

Abbreviations TZP, piperacillin-tazobactam; CAZ, ceftazidime; IPM, imipenem; MEM, meropenem; SXT, trimethoprim-sulfamethoxazole; CIP, ciprofloxacin; MIC, minimum inhibitory concentration (µg/ml); AST, antibiotic susceptibility

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testing; R, resistant; DD, disk diffusion; AD, agar dilution; BMD, broth microdilution; Aut, automated systems; CF, cystic fibrosis; HAI, hospital-acquired infection; -, not reported.

a Susceptibility breakpoints used are not specified.

b Piperacillin susceptibility http://aac.asm.org/

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800 Table 3. In vitro activities of new antibiotics against Achromobacter isolates 38

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ERV FDC MEM MVB CAZ CZA

http://aac.asm.org/

Number Year(s) of

Ref collected Region isolates MIC50/90 (range) MIC50/90 (range) MIC50/90 (range) % R MIC50/90 (range) % R MIC50/90 (range) % R MIC50/90 (range) % R

(65) 2013-2018 USA 100 - - 1/>32 (≤0.5->32) 72 ≤0.5/8 (≤0.5->32) 86 8/32 (1->32) 71 8/32 (1->32) 78

(85) - USA 15 - <0.03/0.125 (<0.03-16) 1/16 (0.125-16) - - - - - 4/32 (1->64) -

2013-2014, a 2016-2017 Global 19 1/8 (0.06-8) ------

b,c d b b (87) 2017-2019 USA 14 2 (1-2) S - - 64 (0.25-256) - - - 8 (2-16) - on August 18, 2020 at University of Queensland

(92) - France 11 - - 32/128 (0.5->128) 9 - - 128/>128 (32->128) - 128/>128 (16->128) -

(88) - France 30 ------128/256 40 128/256 40 801

Abbreviations ERV, eravacycline; FDC, cefiderocol; MEM, meropenem; MVB, meropenem-vaborbactam; CAZ, ceftazidime; CZA, ceftazidime-avibactam; MIC, minimum inhibitory concentration (µg/ml); AST, antibiotic susceptibility

testing; -, not reported.

a Personal communication, Tetraphase Pharmaceuticals

b Mean value

c MIC for 3 isolates

d Interpretation based on P. aeruginosa disk diffusion breakpoints provided by Shionogi (breakpoint not provided).

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826 Table 4. Achromobacter infections treated with cefiderocol a

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Age and Causative Treatment Case Sex Infection type Underlying condition pathogen Susceptibility Concomitant antibiotics duration (days) Outcome http://aac.asm.org/ Bacteremia, Susceptible to TZP 28+42 (with a 1 28, M pneumonia CF, lung transplant A. xylosoxidans and SXT TZP, IPM, DOX 14- day break) Patient well at 8-month follow-up

Intermediate to TZP, Patient well at 4-month follow-up, Respiratory tract resistant to all other CAZ, CST (nebulized), DOX, asymptomatically colonized with A. 2 17, F colonization CF, lung transplant A. xylosoxidans drugs tested IPM, SXT 42 xylosoxidans. Pneumonia, 2+13 empyema (post- Achromobacter (with a 59-day 3 56, F op) CF, lung transplant spp. - TZP, CST break) Discharged (rehabilitation facility)

Respiratory tract Achromobacter Discharged (home) with clinical 4 28, F infection CF, lung transplant spp. - CST, SXT 15 improvement

Respiratory tract CF, chronic ERV, AZM, C/T, CST Discharged (home) with clinical 5 41, M infection bronchiectasis A. denitrificans XDR (nebulized) 67 improvement on August 18, 2020 at University of Queensland

Respiratory tract Achromobacter Discharged (home) with clinical 6 10, F infection CF, asthma spp. Pan-resistant MVB, bacteriophage therapy 21 improvement

Respiratory tract 7 70, F infection Chronic bronchiectasis A. xylosoxidans - - 26 Discharged (rehabilitation facility)

Severe left ventricle ICD associated dysfunction, lung Patient well with oral suppressive 8 66, M bacteremia adenocarcinoma A. xylosoxidans - TZP, TGC 11 minocycline therapy A. xylosoxidans [with P. aeruginosa (VIM+), A. Postoperative wound baumannii infection with (OXA-23+), E. Patient well with complete resolution of 9 28, F Osteomyelitis osteomyelitis cloacae (KPC+)] - CST, TGC, CZA 20 bone infection 827

Abbreviations CF, cystic fibrosis; IPM, imipenem; TZP, piperacillin-tazobactam; SXT, trimethoprim-sulfamethoxazole; DOX, doxycycline; CAZ, ceftazidime; CST, colistin; ERV, eravacycline; AZM, azithromycin; C/T, ceftolozane-

tazobactam; MVB, meropenem-vaborbactam; TGC, tigecycline; CZA ceftazidime-avibactam; ICD, intracardiac device; XDR, extensively drug resistant; -, not reported.

a Table modified from reference (86)

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848 Table 5. Achromobacter infections treated with eravacycline and meropenem-vaborbactama

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Case Age and sex Infection type Underlying Susceptibility (MIC) Treatment regimen ERV or MVB Concomitant Outcome condition treatment microorganism(s) in duration (days) respiratory culture 1b 40, M Sinusitis CF MDR ERV single therapy 22 None Favorable c http://aac.asm.org/ 2 b 41, M Respiratory CF FDC 0.06 µg/ml, ERV 2 µg/ml ERV D1-31, FDC D10-31, C/T D4-10, 31 MDR P. aeruginosa Favorable tract MEM D5-10, DLX D10-31 3 63, M Respiratory COPD TZP 16 µg/ml, TOB 8 µg/ml, TZP D1-2, MIN D2-9, 24-34, CST D6-9 5 MDR P. aeruginosa, Patient died in tract MEM ≥16 µg/ml, MIN 4 and D35-37, CIP D9-27, CZA D22-35, SXT MDR S. maltophilia, hospital µg/ml, CST 2 µg/ml, CIP 4 D27-34, ERV D29-34 MRSA µg/ml, CAZ 8 µg/ml SXT ≤20 µg/ml, ERV - 4 45, F Respiratory Chronic CZA 4 µg/ml, MVB 8 µg/ml, CZA D1-15 and D23-27, MVB D22-23, 4 Enterobacter cloacae Patient died in tract respiratory TZP 8- ≥128 µg/mld D42, TZP D42-57 and D61-79 and D114- complex in separate hospital failure 121, ERV D106-108 and D112-114 culture 5 75, F Respiratory COPD, chronic MEM susceptiblee MEM D1-4, ERV D4-13 9 None Infection related tract bronchiectasis readmission in 30 days 6 30, F Respiratory CF MDR ERV D1-7, TGC D7-11 7 None Favorable

tract on August 18, 2020 at University of Queensland 7 22, M Respiratory CF TOB ≥16 µg/ml, FEP ≥64 TOB D1-5, FEP D1-5, ERV D2-11, and 13 Group A Favorable tract µg/ml, ERV 2 µg/ml, SXT 40 D14-18, SXT D5-25, TZP D5-7, CST D10- Streptococcus µg/ml, TZP 256 µg/ml, CST 0.5 18 µg/ml 8 80, F Respiratory Chronic MDR MVB single therapy 20 None Favorable tract bronchiectasis 9 40, M Respiratory CF CST 0.12 µg/ml, MVB 32 MVB+CST combination therapy 14 MDR P. aeruginosa Favorable tract µg/ml 10 29, F Respiratory CF MDR MVB+CST combination therapy 10 None Favorable tract 11 26, M Respiratory CF MEM 4 µg/ml MEM D1-2, MIN D1-5, MVB D3-5, CPT 2 MRSA, E. coli Favorable tract D5-16 849

Abbreviations MIC, minimum inhibitory concentration; CF, cystic fibrosis; COPD, chronic obstructive pulmonary disease; MDR, multidrug resistant; D, day; MRSA, methicillin resistant staphylococcus aureus;

FEP, cefepime; FDC, cefiderocol; CIP, ciprofloxacin; CZA, ceftazidime-avibactam; C/T, ceftolozane-tazobactam; CST, colistin; ERV, eravacycline; MEM, meropenem; MVB, meropenem-

vaborbactam; MIN, minocycline; TZP, piperacillin-tazobactam; TGC, tigecycline; SXT, trimethoprim-sulfamethoxazole; TOB, tobramycin; DLX, delafloxacin; CPT, ceftaroline.

a Table modified from reference (87). A. xylosoxidans and A. denitrificans were the causative pathogens for cases 1-10 and case 11, respectively.

b Case 1 and 2 are the same patient.

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c Favorable is defined as patient alive until discharge and not readmitted within 30 days due to infection.

d MIC was provided as a range for TZP in the original table and the reason was not specified. http://aac.asm.org/

e MIC was not provided.

850 on August 18, 2020 at University of Queensland