**1. Introduction**

*Campylobacter* spp. are Gram-negative, microaerophilic bacteria, and the most common cause of bacterial foodborne illness in the world [1–4]. Among 17 *Campylobacter* species, *Campylobacter jejuni* and *Campylobacter coli* are the major causative agents of foodborne illness in human [5–7]. Animal species such as chicken, cattle and wild birds are reservoirs for *Campylobacter* [8,9]. *Campylobacter* infection causes watery diarrhea, fever, bloody stools, abdominal pain, and some complications such as Guillain-Barré syndrome (GBS) and Reiter's syndrome in severe case [10]. Facciolà et al. [10] suggested that it is difficult to find the contamination sources because *Campylobacter* outbreaks were sporadic and caused by cross-contamination.

Recently, campylobacteriosis have increased dramatically in South Korea. Until 2002, there were no *Campylobacter* outbreaks, but 831 people were infected by *Campylobacter* in 2016 [11]. In Switzerland, campylobacteriosis have also been increased, and healthcare cost for the patients was \$7.5 million per year, expected to increase steadily [12]. *Campylobacter* have several virulence factors such as flagellin, capsular polysaccharides, and cytotoxins [13]. Regarding cytotoxin production, *Campylobacter* can produce cytolethal distending toxin (CDT), which is encoded by *cdtA*, *cdtB,* and *cdtC* genes [14–16]. This toxin can induce the host cell distension, then lead to cell death [17]. In severe cases, antibiotic (erythromycin, ciprofloxacin, tetracycline, etc.) treatment is necessary to treat *Campylobacter* infection, but *Campylobacter* spp. have recently begun to show resistance to several antibiotics [18–20]. In a previous study, 159 *Campylobacter* isolates from poultry samples in China were examined for antibiotic resistance and 94% (149 isolates) of *Campylobacter* isolates were resistant to tetracycline, doxycycline, and erythromycin [18]. Thus, *Campylobacter* isolates need to be investigated for antibiotic susceptibility.

To analyze the genetic correlation among bacterial isolates, restriction-based, amplification-based, and sequencing-based methods have been used [21]. Restriction-based methods include plasmid analysis, restriction fragment length polymorphism (RFLP) analysis, and pulsed-field gel electrophoresis (PFGE). Amplification-based methods are amplified fragment length polymorphisms (AFLP), random amplified polymorphic DNA PCR (RAPD-PCR), and repetitive element PCR (Rep-PCR). Sequencing-based methods include multilocus sequence typing (MLST) and single-nucleotide polymorphism (SNP) analysis. Rep-PCR can assign molecular fingerprints according to the repetitive sequences in bacterial genomes [22,23]. Compared to other PCR typing methods, Rep-PCR has advantages: processing is rapid and it has the ability to analyze small amounts of DNA [21,24]. Abay et al. [25] also suggested that Rep-PCR was more powerful for typeability of *Campylobacter* than PFGE.

The objective of this study was to investigate the prevalence of *Campylobacter* in poultry carcasses in wet markets, determine antibiotic susceptibility patterns, the presence of *cdt* genes, and analyzed the genetic diversity between the *Campylobacter* isolates.
