Food Safety and Evaluation Laboratory, Department of Food Bioscience and Technology, Korea University, Anam-dong 5-ga, Seongbuk-gu, Seoul 136-713, Republic of Korea.
Int J Food Microbiol. 2011 Mar 15;146(1):52-6. doi: 10.1016/j.ijfoodmicro.2011.01.037. Epub 2011 Feb 2.
Sixteen Salmonella strains resistant to nalidixic acid isolated from kimbab, the most popular ready-to-eat (RTE) food in Korea, and chicken meat were selected for this study. The resistant strains were shown to have high minimal inhibitory concentrations (MICs) against nalidixic acid (5124096 μg/mL). Among them, 4 Salmonella enterica serovar Haardt isolates showed multi-drug resistance (MDR) patterns with reduced susceptibility to fluoroquinolone (0.5 μg/mL of ciprofloxacin MICs). The mechanisms of quinolone resistance in the nalidixic acid resistant strains were characterized by PCR and sequence analysis. The presence of plasmid-mediated quinolone resistance (PMQR) genes and amino acid changes in the quinolone resistance determining region (QRDR) were investigated by PCR-based detection and sequencing, and the efflux pump inhibition test was also done using phe-arg-β-naphthylamide (PAβN). Although PMQR genes were not detected in any of the tested strains, the QRDR mutations were found in this study: single mutation in gyrA (Asp87Tyr, Asp87Gly, and Asp87Asn), double mutations in gyrA (Ser83Thr) and parC (Thr57Ser), and single mutation in parC (Thr57Ser). MICs of nalidixic acid were reduced by 2- to 32-folds by the efflux pump inhibitor, PAβN. Pulsed-field gel electrophoresis (PFGE) was carried out to confirm the epidemiological relationship between the nalidixic acid resistant strains. The PFGE patterns were classified into 6 groups at cutoff level of 70100% correlation on the dendrogram. Some strains of serotype Haardt and Enteritidis showed several values of genomic identity in accordance with strains, sources, and isolation year. We suggest that point mutation on QRDR and efflux pump systems involved in antimicrobials had independent effects on drug-resistance regardless of bacterial genomic variation.
从韩国最受欢迎的即食 (RTE) 食品紫菜卷和鸡肉中分离出 16 株耐萘啶酸的沙门氏菌菌株，用于本研究。这些耐药菌株对萘啶酸（5124096μg/mL）显示出高最小抑菌浓度 (MIC)。其中，4 株肠炎沙门氏菌哈代分离株表现出多药耐药 (MDR)模式，对氟喹诺酮类药物（环丙沙星 MIC 为 0.5μg/mL）的敏感性降低。通过 PCR 和序列分析，对耐萘啶酸菌株的喹诺酮类耐药机制进行了特征分析。通过基于 PCR 的检测和测序研究了质粒介导的喹诺酮耐药 (PMQR) 基因和喹诺酮耐药决定区 (QRDR) 中的氨基酸变化，并使用 phe-arg-β-萘基酰胺 (PAβN) 进行了外排泵抑制试验。尽管在测试的菌株中均未检测到 PMQR 基因，但在本研究中发现了 QRDR 突变：gyrA 中的单个突变（Asp87Tyr、Asp87Gly 和 Asp87Asn）、gyrA（Ser83Thr）和 parC（Thr57Ser）中的双突变以及 parC 中的单个突变（Thr57Ser）。外排泵抑制剂 PAβN 将萘啶酸的 MIC 降低了 2-32 倍。进行脉冲场凝胶电泳 (PFGE) 以确认耐萘啶酸菌株的流行病学关系。在聚类图上，70%100%相关的截止水平，PFGE 模式分为 6 组。一些哈代和肠炎血清型的菌株与菌株、来源和分离年份相符，显示出几个基因组同一性值。我们认为，QRDR 和参与抗生素的外排泵系统的点突变对耐药性有独立的影响，而与细菌基因组变异无关。
