ANTIMICROBIAL RESISTANCE OF PRAUSNITZII A. Rintala, E. Munukka, E. Eerola, P. Huovinen Department of Medical Microbiology and Immunology, University of Turku, Finland

INTRODUCTION METHODS Antibiotic-induced alterations in the gut raise the Antimicrobial susceptibility of three F. prausnitzii strains was determined: disease risk by disrupting gut homeostasis and thus • DSM-17677 (Leibniz-Institut DSMZ, Germany) increasing the susceptibility to pathogen • ATCC-27766 (American Type Culture Collection, USA). colonization. Faecalibacterium prausnitzii (F. • AREM-1 (isolated from faeces of a healthy Finnish subject) prausnitzii) is one of the most abundant Table 1. MIC values for F. prausnitzii strains. Values were read after 24 and 48 hours of incubation. Represented values are from the 48 hour time point. MIC values for all antimicrobial agents were in a healthy human gut. F. prausnitzii was Minimal inhibitory concentrations (MICs) for ten antimicrobials were determined by E- previously described as a Gram-negative bacterium determined at least two times. Results were mainly identical, differences are marked in the table as test® method (bioMérieux) on modified Fastidious Anaerobe Agar plates. To control the two values. belonging to genus , but has since suitability of the growth medium for MIC testing, values of a performance standard MIC 2002 (1) been classified as a Gram-positive thetaiotaomicron ATCC-29741 (American Type Culture Collection, USA) were member of cluster IV. F. prausnitzii is also determined. Antibiotic (range [mg/L]): DSM-17677 ATCC-27766 AREM-1 an important producer of butyrate and has been Benzylpenicillin (0.002 – 32) 0.75 0,094 0.094 suggested to enhance intestinal homeostasis and Ceftriaxone (0.002 – 32) > 32 > 32 12 / > 32 gut health (2,3). Ciprofloxacin (0.002 – 32) > 32 > 32 6 / 12

Clindamycin (0.016 – 256) < 0.016 < 0.016 < 0.016 The aim of this study was to investigate the RESULTS antimicrobial susceptibility of different F. Colistin (0.016 – 256) 24 32 32 prausnitzii strains. The antimicrobial resistance of The studied F. prausnitzii strains showed resistance to ceftriaxone, ciprofloxacin and Erythromycin (0.016 – 256) 0.094 / 0.125 0.19 / 0.125 2 health-promoting bacteria has gained little colistin, and borderline susceptibility to gentamicin (Table 1). Gentamicin (0.016 – 256) 1 2 1 interest, even though antibiotic use can lead to The modified agar plate was found to be suitable for MIC testing; values of the control (0.016 – 256) 0.032 0.023 < 0.016 intestinal dysbiosis by disturbing the symbiotic and strain Bacteroides thetaiotaomicron ATCC-29741 were within the ranges determined by Tetracycline (0.016 – 256) 0.19 0.25 0.094 CLSI (results not shown). commensal microbiota. Vancomycin (0.016 – 256) 0.75 0.50 0.50

CONCLUSIONS Many of the commonly used antimicrobials have a potential to reduce or even eliminate F. prausnitzii from the . Of the tested antimicrobials, F. prausnitzii was highly-resistant only to ceftriaxone, ciprofloxacin and colistin. The resistant patterns support the definition of F. prausnitzii being Gram-positive.

The antibiotic resistance among beneficial bacteria may be as important as in pathogens. If the beneficial bacteria like F. prausnitzii are susceptible to the used antimicrobial agent, antibiotic treatment may decrease the amount of these bacteria, exposing the gut to dysbiosis. When necessary to use antimicrobial drugs, it would be beneficial to use antimicrobials that the symbiotic bacteria are resistant to, so the antibiotic course would not cause depletion of these bacteria. Further studies are needed to elucidate the role of F. prausnitzii in the antimicrobial-associated intestinal dysbiosis.

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