Prevalence, quantification and antibiotic resistance of Listeria monocytogenes in poultry preparations

A total of 100 samples of fresh poultry preparations were obtained from 10 retail outlets in North-Western Spain. Listeria spp. were found in 73 samples. Isolates were identified through polymerase chain reaction (PCR) as Listeria monocytogenes (56 samples), Listeria innocua (32), Listeria grayi (3), Listeria seeligeri (1) and Listeria spp. (6). In 24 samples, several different Listeria species were found. The loads of L. monocytogenes detected by quantitative polymerase chain reaction (q-PCR) in the 56 positive samples ranged from < 2.15 log units (limit of detection) up to 5.96 log units. Neither the type of sample nor the retail outlet involved had any significant influence (P > 0.05) on concentrations of L. monocytogenes. A total of 163 L. monocytogenes isolates were tested (disc diffusion) against 15 antimicrobials of clinical significance. The average number of resistances per isolate was 5.83 +/- 1.64. All strains showed resistance to multiple antimicrobials (between 4 and 11). In all, 80 isolates (49.1%) showed a multi-drug resistant (MDR) phenotype, and two isolates (1.2%) showed an extensively drugresistant (XDR) phenotype. More than 50.0% of isolates showed resistance or reduced susceptibility to oxacillin, cefoxitin, cefotaxime, cefepime, rifampicin, ciprofloxacin, enrofloxacin or nitrofurantoin. This is a cause for concern because these substances are among the antibiotics used to treat human listeriosis, with rifampicin and fluoroquinolones frequently being used. The results from this research work show that poultry preparations are a potential major source of resistant L. monocytogenes strains, since these are present in some samples at high concentrations. This highlights the pressing need to handle poultry preparations correctly, so as to ensure they are sufficiently cooked and to avoid cross-contamination events.