Antimicrobial resistance genes, virulence genes, and genetic diversity of Campylobacter isolated from chicken and swine farms in Jiangsu Province

Abstract:

[Background] Campylobacter spp. are a genus of the main pathogens causing foodborne diseases. They colonize the caeca of broilers and swine and can contaminate carcasses after slaughter during the processing, posing a risk of exposure to consumers and a serious threat to food safety and public health. [Objective] To investigate the antimicrobial resistance genes, virulence genes, and genetic diversity of 52 Campylobacter strains isolated from chicken and swine farms in Jiangsu Province by whole genome sequencing (WGS). [Methods] The agar dilution method was used to determine the minimal inhibitory concentrations (MICs) of Campylobacter isolates against eight antimicrobial agents. WGS was performed for the 52 Campylobacter strains. ResFinder of the Center for Genomic Epidemiology (CGE) was used to analyze the antimicrobial resistance genes. Virulence genes were identified from the core sequences downloaded from the virulence factor database (VFDB). Sequence type (ST) was determined in silico from the WGS data and isolates were assigned into clonal complex (CC) in PubMLST. [Results] Fifty-two Campylobacter strains were significantly resistant to ciprofloxacin, tetracycline, and nalidixic acid and sensitive to florfenicol, with the multidrug resistance rate of 57.69%. Sixteen acquired resistance genes belonging to six major categories were detected among with gyrA mutation associated with quinolones resistance and 23S rRNA gene mutation associated with macrolides resistance. In addition to the previously reported resistance genes to aminoglycosides, β-lactams, and tetracyclines (tetO), several new antimicrobial resistance genes emerging in Campylobacter in recent years were detected in this study, including ermB, ermA, fexA, optrA, tetL, and lnuC. A total of 120 virulence genes were detected in 52 strains of Campylobacter, among which the genes involved in adhesion, capsule synthesis, invasion, flagella, and chemotactic proteins had higher carrying rates. Campylobacter jejuni exhibited higher abundance of virulence genes than C. coli. MLST assigned 28 STs and 14 CCs (including 4 known CCs and 10 unknown CCs, among which CC-828 was the main one), indicating high genetic diversity among the isolates. [Conclusion] The Campylobacter isolated from chicken and swine farms in Jiangsu Province presented severe multidrug resistance. The resistance and virulence genes were complex, diverse, and widely distributed in Campylobacter strains. CC-828 was the main clonal complex, and the Campylobacter strains exhibited high genetic diversity. The results provide basic data for the monitoring of antimicrobial resistance of animal-derived Campylobacter in China.

Key words:Campylobacter;whole-genome sequencing;multidrug resistance;antimicrobial resistance gene;virulence gene