Antibiotic susceptibility of 259 Listeria monocytogenes strains isolated from food, food-processing plants and human samples in Germany

Background: The objective of this study was to evaluate the susceptibility of 259 Listeria monocytogenes strains isolated from food and food-processing environments and patient samples in Germany to 14 antibiotics widely used in veterinary and human medicine. L. monocytogenes strains were isolated mainly from milk and milk products and classified according to their molecular serotypes IIa (n = 112), IIb (n = 41), IIc (n = 36), IVa (n = 1), IVb (n = 66), and IVb-v1 (n = 3). Methods: Susceptibility tests were performed by using the automated 96-well based microdilution system Micronaut-S. Ampicillin, benzylpenicillin, ceftriaxone, ciprofloxacin, daptomycin, erythromcyin, gentamicin, linezolid, meropenem, rifampicin, tetracycline, tigecycline, trimethoprim/sulfamethoxazole and vancomycin were tested in at least five different concentrations. Results: Among the 259 strains under study, 145 strains revealed multidrug-resistance (resistance to ≥3 antibiotics) and predominantly belonged to serotype IV (59%). Strains were mainly resistant to daptomycin, tigecycline, tetracycline, ciprofloxacin, ceftriaxone, trimethropim/sulfamethoxazole and gentamicin. Conclusions: Antibiotic resistance in general and multidrug-resistance in particular were more prevalent in L. monocytogenes strains isolated in Germany compared to similar reference stocks from other European countries and the USA but similar to stocks from China. Keywords: Antibiotic resistance, Antimicrobials, Germany, Listeria monocytogenes, Susceptibility testin