Antimicrobial Resistance Profiles, Virulence Genes, and Genetic Diversity of Thermophilic Campylobacter Species Isolated From a Layer Poultry Farm in Korea

Thermophilic species are among the major etiologies of bacterial enteritis globally. This study aimed at assessing the antimicrobial resistance (AMR) profiles, virulence genes, and genetic diversity of thermophilic species isolated from a layer poultry farm in South Korea. One hundred fifty-three chicken feces were collected from two layer poultry farms in Gangneung, South Korea. The species were isolated by cultural techniques, while PCR and sequencing were used for species confirmation. Antimicrobial susceptibility testing for six antimicrobials [ciprofloxacin (CIP), nalidixic acid (NAL), sitafloxacin (SIT), erythromycin (ERY), tetracycline (TET), and gentamicin (GEN)] was carried out by broth microdilution. Three AMR and nine virulence genes were screened by PCR. Genotyping was performed by A-restriction fragment length polymorphism (RFLP) and multilocus sequence typing (MLST). Of the 153 samples, spp. were detected in 55 (35.9%), with and being 49 (89.1%) and six (10.9%), respectively. High-level resistance was observed for CIP (100%), NAL (100%), and TET ( , 93.9%; : 83.3%). No resistance was observed for SIT. The missense mutation (C257T) in A gene was confirmed by sequencing, while the (O) gene was similar to known sequences in GenBank. The rate of multidrug-resistant (MDR) strains was 8.2%, and they all belonged to . All isolates possessed five virulence genes ( B, II, A, F, and J), but none possessed , while the rates for other genes ( A, B, and A) ranged between 33.3 and 95.9%. The A-RFLP yielded 26 A types ( : 21 and : five), while the MLST showed 10 sequence types (STs) for and three STs for , with CC-607 (STs 3611) and CC-460 (ST-460) being predominant. Among the 10 STs of , three were newly assigned. The findings of this study highlight the increased resistance to quinolones and TET, the virulence potential, and the diverse genotypes among strains isolated from the layer poultry farm.