Genetics of antibiotic resistance in campylobacter coli isolated from swine in Thailand

Abstract

This study was performed in a total of eighty-three Campylobacter coli strains isolated from swine, of which minimal inhibitory concentrations (MICs) for erythromycin, ciprofloxacin, nalidixic acid and tetracycline were known. All of the isolates were investigated for the presence of tetO and class 1 integrase. Forty-four erythromycin-resistant isolates were tested for mutations in 23S rRNA gene. Sixty isolates resistant to ciprofloxacin and/or nalidixic were examined for mutations in gyrA and gyrB genes. Most of the tetracycline-resistant isolates (97%, 65/67) possessed tet(O). Four isolates (4.8%, 4/83) harbored class 1 integrons and all of them produced a 1,000-bp amplicon in a 5′-3′ conserved sequence PCR directed toward amplification of the gene cassettes. DNA sequencing demonstrated that all four isolates possessed the aminoglycoside resistance gene, aadA9. Most of erythromycin-resistant isolates (77%, 34/44) contained mutations in 23s RNA. Five of point mutations were found, of which the most common type was A2230G (70%, 31/44). For nalidixic acid and/or ciproflocxacin resistant strains, all carried mutations in Quinolone Resistance Determining Region (QRDR) of gyrA and 8.5% (5/60) contained mutations in QRDR of gyrB. The predominant mutation in gyrA was C257T (93%, 56/60) that converted threonine at position 86 to isoleucine. The point mutations in gyrB was A1144C (7%, 4/60) that converted lysine at position 381 to glutamic acid.