Introduction. Fluoroquinolone (FQ) resistant Salmonella are classified as high priority pathogens by WHO. FQ resistance among Salmonella Typhi has emerged rapidly and is predominantly mediated by mutations in the topoisomerase genes gyrA, and parC. Mutations in GyrA result in classical FQ resistance (DCS-NAR) i.e. decreased susceptibility to ciprofloxacin (MIC of 0.12 to 0.5 µg ml−1) (DCS) and resistance to nalidixic acid (NAR). Previously a nalidixic acid disc test was proposed for detection of DCS. Recently isolates with non-classical FQ resistance caused by plasmid-mediated quinolone resistance (PMQR) and mutations in GyrB have emerged. These mechanisms also result in DCS but are nalidixic acid susceptible (NAS) and thus pose diagnostic challenges. CLSI and EUCAST have recommended use of 5 µg pefloxacin discs for detection of DCS in Salmonella . Hypothesis. The CLSI and EUCAST recommendations for use of 5 µg pefloxacin for detection of DCS has not been validated on typhoidal Salmonella and resistance mediated by GyrB mutation in Salmonella species. Aim. The aim of the present study was to validate the performance of the 5 µg pefloxacin discs to detect isolates of S. Typhi with DCS with special reference to GyrB mutations. Methodology. A total of 180 clinical isolates of Salmonella Typhi (2005–2014) were investigated for genetic mechanisms of resistance. Zone diameters for nalidixic acid (30μg), ciprofloxacin (5μg) and pefloxacin (5µg) and minimum inhibitory concentration (MIC) for ciprofloxacin were determined using CLSI guidelines. Performance of the three discs was evaluated to detect FQ resistance in S. Typhi. Results. Topoisomerase mutations in GyrB +/ ParC and GyrB were detected in 112 and 34 isolates respectively. Different mutations have a varied effect on the MIC for ciprofloxacin. The current breakpoints for susceptible (≤0.06 µg ml−1) and non-susceptible (≥0.125 µg ml−1), failed to detect all isolates with a resistance mechanism. Performance of both ciprofloxacin and pefloxacin discs were excellent compared to nalidixic acid in differentiating isolates with non-classical resistance mediated by GyrB from wild-type. Conclusion. The pefloxacin disc can be used to detect FQ resistance among S. Typhi. This is the first report of validation of pefloxacin for detection of FQ resistance in S. Typhi mediated by GyrB mutation.

中文翻译：

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培氟沙星用于检测伤寒沙门氏菌中氟喹诺酮 (FQ) 耐药性的验证，特别参考 GyrB 突变

介绍。氟喹诺酮 (FQ) 耐药性沙门氏菌被世卫组织列为高度优先病原体。伤寒沙门氏菌的FQ 抗性迅速出现，主要由拓扑异构酶基因gyrA和parC 的突变介导。GyrA 突变导致经典 FQ 抗性 (DCS-NAR)，即降低对环丙沙星的敏感性（MIC 为 0.12 至 0.5 µg ml -1 ) (DCS) 和耐萘啶酸 (NAR)。以前建议使用萘啶酸圆盘试验来检测 DCS。最近出现了由质粒介导的喹诺酮耐药 (PMQR) 和 GyrB 突变引起的具有非经典 FQ 耐药性的分离株。这些机制也会导致 DCS，但对萘啶酸敏感 (NAS)，因此对诊断提出了挑战。CLSI 和 EUCAST 建议使用 5 µg 培氟沙星圆片检测沙门氏菌中的 DCS 。假设。使用5微克培氟沙星的检测DCS的CLSI和EUCAST建议尚未得到验证的伤寒沙门氏菌和GyrB的中介导的突变性沙门氏菌种。目的。 本研究的目的是验证5微克的培氟沙星盘上的性能，以检测的分离物小号。带有 DCS 的伤寒，特别提到 GyrB 突变。方法。研究了总共 180 株伤寒沙门氏菌（2005-2014）临床分离株的耐药遗传机制。萘啶酸 (30μg)、环丙沙星 (5μg) 和培氟沙星 (5μg) 的区域直径和环丙沙星的最小抑制浓度 (MIC) 使用 CLSI 指南确定。评估三个圆盘的性能以检测S 中的FQ 电阻。伤寒。结果。 GyrB +/ ParC 和 GyrB 中的拓扑异构酶突变分别在 112 和 34 株中检测到。不同的突变对环丙沙星的 MIC 有不同的影响。易感（≤0.06 µg ml -1）和非易感（≥0.125 µg ml -1）的当前断点未能检测到所有具有耐药机制的分离株。与萘啶酸相比，环丙沙星和培氟沙星圆片的性能在​​区分具有由 GyrB 介导的非经典耐药性的分离株与野生型方面都非常出色。结论。培氟沙星圆盘可用于检测S之间的 FQ 抗性。伤寒。这是第一份验证培氟沙星用于检测S中 FQ 耐药性的报告. 由 GyrB 突变介导的伤寒。