Detection and Analysis of Naladixic Acid and Ciprofloxacin Resistance-Associated Genes and Mutations in Salmonella
HUANG Jinling, WANG Jiawei, NIU Qinya, LIAN Luxin, YIN Mingyuan, WU Yun, YANG Baowei
2019, 40(22):
320-330.
doi:10.7506/spkx1002-6630-20181015-128
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Objective: In this study, the serotype, antimicrobial susceptibility to nalidixic acid and ciprofloxacin, genes associated with quinolone and fluoroquinolone resistance of the foodborne pathogen Salmonella isolated in nine provinces and municipalities of China, including Shaanxi, Xinjiang and Guangdong, were identified and analyzed, aiming to better understand the development and transmission of antimicrobial resistance, and more broadly, to ensure food safety. Methods: Salmonella serovars were determined by the slide agglutination method, the antimicrobial susceptibility was tested by the agar dilution method, and nine genes associated with resistance to quinolone and fluoroquinolines were determined using PCR. Results: A total of 83 serotypes were identified from 814 Salmonella isolates. The most prevalent serotype was S. typhimurium (24.08%), followed by S. enteritidis (19.41%), S. indiana (13.27%) and S. derby (5.16%). Out of the 814 isolates, 553 (67.94%) and 219 (26.90%) resisted to nalidixic acid and ciprofloxacin, respectively. The average prevalence of oqxB positive isolates (31.82%) was significantly (P < 0.05) higher than that of qnrA (24.94%), oqxA (24.57%), qnrB (24.45%),qnrS (10.32%) and qepA (3.07%) positive isolates, and it showed no significant difference from that of aac(6’)-Ib positive isolates (27.52%). A difference could be found among five common serotypes, different sampling sites, different sample types and different geographical areas in the prevalence of the seven antibiotic resistance-associated genes. A total of 221 mutations were detected in gyrA, with the most prevalent one being Ser83Phe/Asp87Gly (21.27%), followed by Ser83Phe (16.29%), Asp87Gly (13.57%), Ser83Tyr (12.22%), Asp87Tyr (11.31%), Asp87Asn (10.41%), Ser83Phe/Asp87Asn (9.95%), Ser83Tyr/Asp87Gly (2.71%), Asp87Val (0.90%), Gly75Phe (0.45%), Asp87Asn/Ile89Val (0.45%), and Asp87Asn/Val90Gly (0.45%). A total of 217 mutations were detected in parC, the most prevalent one being Ser80Arg (64.49%),followed by Thr57Ser (35.05%) and Ser80Arg/Gly72Phe (0.47%). Conclusion: The serovars of Salmonella isolates from the nine provincial regions were diverse, and the resistance to nalidixic acid and ciprofloxacin was highly prevalent. oqxA, oqxB, qepA, qnrA, qnrB, qnrS and aac(6’)-Ib were prevalent in Salmonella, and multiple mutations could be detected in both gyrA and parC. The existence of these antibiotic associated genes and mutations in the quinolone resistance-determining region (QRDR) may play important roles in nalidixic acid and ciprofloxacin resistance.