Antimicrobial Susceptibility of Bacteroides fragilis group isolates derived from clinical specimens in Southeast Austria

E. Ullrich, H.P. Ziegler, A. J. Grisold, G. Feierl, E. Leitner

all: Institute of Hygiene, Medical University of Graz, Universitaetsplatz 4, 8010 Graz, Austria Background Routine susceptibility testing of anaerobic bacteria is Two B. fragilis isolates from this group were classified as MDR. Table 2. Antimicrobial susceptibility of the two MDR B. fragilis isolates not recommended in polymicrobial infections but From the investigated 11 isolates derived from PAI, 45.5% (5; 1 Antimicrobial agent Etest MIC range 1. MDR B.fragilis 2. MDR B.fragilis should be considered for specific clinical situations and B. fragilis, 4 BNFI) showed resistance to clindamycin and 27.3% (µg/ml) in monomicrobial infections. For empiric therapy (3; 2 B. fragilis, 1 BNFI) to moxifloxacin. In the 10 MI isolates MIC Int* MIC Int* strategies resistance-surveillance is recommended due the highest resistance rates were found for moxifloxacin with (µg/ml) (µg/ml) to an increase of resistance especially in Bacteroides 60% (6; 3 B. fragilis, 3 BNFI) and clindamycin with 50% (5; 2 B. amoxicillin-clavulanic 0.016 - 256 >256 R 32 R fragilis group isolates (BFGI). The aim of this study was fragilis, 3 BNFI). Within the 110 BFGI resistance rates were as acid to determine antibiotic susceptibility of clinical BFGI in followed (table 1): 50.9% for clindamycin (56; 19 B. fragilis, 37 piperacillin-tazobactam 0.016 - 256 >256 R 8 S southeast Austria. BNFI), followed by moxifloxacin with 35.5% (39; 21 B. fragilis, imipenem 0.002 - 32 >32 R 8 I 18 BNFI). For piperacillin/tazobactam a resistance rate of 10% Material and methods (11; 1 B. fragilis, 10 BNFI) was observed in contrast to meropenem 0.002 - 32 >32 R >32 R In total 110 non-duplicate clinical BFGI were analyzed, amoxicillin/clavulanic acid with 7.3% (8; 4 B. fragilis, 4 BNFI). moxifloxacin 0.002 - 32 >32 R 2 S collected at the Institute of Hygiene, Medical Low resistance rate was detected for metronidazole with 2.7% cefoxitin 0.002 - 32 >32 R 64 R University of Graz from June to December 2014. From (3; all BNFI) and carbapenems with 1.8% (2; all B. fragilis). clindamycin 0.016 - 256 2 S >256 R the 110 isolates 80.9% (89) derived from polymicrobial These two strains, isolated from wounds were non-susceptible metronidazol 0.016 - 256 0.5 S 0.25 S aerobic/anaerobic infections (PAAI), 10% (11) from to nearly all tested beta-lactams including the carbapenems. polymicrobial anaerobic infections (PAI) and 9.1 % (10) *Int, Interpretation: according to EUCAST, except for moxifloxacin and cefoxitin CLSI guideline Additionally one of the two isolates was resistant to M11-A8 was used. S, susceptible; R, resistant; I, intermediate from monomicrobial infections (MI). The species clindamycin, the other one to moxifloxacin (table 2). distribution of the 110 isolates was 46.4% (51) Conclusion Bacteroides fragilis and 53.6% (59) Bacteroides non- Table 1. In vitro activity of eight antimicrobial agents against B. fragilis and BNFI (n=110) This surveillance study shows that the resistance levels for fragilis isolates (BNFI). Etest (bioMérieux) or MIC test Antimicrobial agent Etest MIC % of resistance (n) % of resistance(n) BFGI are still increasing whether in polymicrobial or strips (Liofilchem) with the protocol for anaerobic range B. fragilis (n=51) BNFI* (n=59) monomicrobial infections. Based on our findings clindamycin bacteria were used to determine the MICs of the (µg/ml) and moxifloxacin showed remarkable resistance, following drugs: amoxicillin/clavulanic acid, amoxicillin-clavulanic acid 0.016 - 256 7.8 (4) 6.8 (4) consequently, they should not be recommended for empiric piperacillin/tazobactam, imipenem, meropenem, piperacillin-tazobactam 0.016 - 256 2.0 (1) 16.9 (10) treatment. The resistance rates for carbapenems are still low, moxifloxacin, cefoxitin, clindamycin and imipenem 0.002 - 32 2.0 (1) 0.0 (0) but there must be an increasing awareness to multidrug metronidazole. Interpretation was done according to resistance among BFGI. EUCAST guidelines for Gram-negative anaerobes meropenem 0.002 - 32 3.9 (2) 0.0 (0) except for cefoxitin and moxifloxacin, where the CLSI moxifloxacin 0.002 - 32 41.2 (21) 30.5 (18) guideline M11-A8 was applied. cefoxitin 0.002 - 32 5.9 (3) 27.1 (16) Results clindamycin 0.016 - 256 37.3 (19) 62.7 (37) Within the 89 isolates from PAAI 51.7% (46; 16 B. metronidazol 0.016 - 256 0.0 (0) 5.1 (3) Figure 1. B. fragilis on fragilis, 30 BNFI) were resistant to clindamycin and *BNFI: B. thetaiotaomicron (n=19), B. ovatus (n=14), B. vulgatus (n=11), Parabacteroides Brucella Agar, 33.7% (30; 16 B. fragilis, 14 BNFI) to moxifloxacin. distasonis (n=6), B. uniformis (n=5), B. caccae (n=2), B. stercoris (n=2) bioMérieux©

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