Purpose: The current study was carried out to detect Salmonella spp. contamination on chicken carcasses produced at major poultry slaughterhouses in South Korea.
Methods: To determine the seasonal prevalence, serotypes, and antibiotic resistance patterns of Salmonella, a total of 120 chicken carcasses were collected through twelve individual samplings (20 chickens per month) in summer 2014 and winter 2015.
Results: A total of 18 chicken samples (15%) were found to be contaminated with Salmonella, with a higher rate of contamination observed during summer (14 isolates, 11.7%) than during winter (4 isolates, 3.3%). Among these isolates, S. enterica serotype Typhimurium was the most prevalent, followed by Salmonella Hadar, Bareilly, and Virchow. A single strain among 5 MDR isolates was resistant to 10 antibiotics, including third-generation cephalosporins. This cephalosporin-resistant strain exhibited the extended-spectrum β-lactamase phenotype and harbored the gene encoding CTX-M-15, the most prevalent ESBL enzyme worldwide. Based on molecular subtyping using an automated rep-PCR system (DiversiLab), all Salmonella isolates except the ESBL-producing strain showed low genetic heterogeneity, with more than 95% similarity in their rep-PCR banding patterns. The ESBL-producing isolate was distinguished by molecular subtyping patterns and distinct antibiotic resistance profiles.
Significance: Given that poultry slaughterhouses are considered the last stage in the chicken production chain, the occurrence of Salmonella including ESBL-producing strains in individually packaged chickens highlights the necessity for regular monitoring of Salmonella strains in poultry slaughterhouses.