| Summary: | This study analyzed the genetic diversity of ciprofloxacin (CIP) nonsusceptibility and the relationship between two major mechanisms and minimum inhibitory concentrations (MICs) of CIP in nontyphoidal <i>Salmonella</i> (NTS). Chromosomal mutations in quinolone resistance-determining regions (QRDRs) and plasmid-mediated quinolone resistance (PMQR) genes were searched from ResFinder, ARG-ANNOT, and PubMed for designing the sequencing regions in <i>gyrA</i>, <i>gyrB</i>, <i>parC</i>, and <i>parE</i>, and the 13 polymerase chain reactions for PMQR genes. We found that QRDR mutations were detected in <i>gyrA</i> (82.1%), <i>parC</i> (59.0%), and <i>parE</i> (20.5%) but not in <i>gyrB</i> among the 39 isolates. Five of the 13 PMQR genes were identified, including <i>oqxA</i> (28.2%), <i>oqxB</i> (28.2%), <i>qnrS</i> (18.0%), <i>aac</i>(6′)-<i>Ib</i>-<i>cr</i> (10.3%), and <i>qnrB</i> (5.1%), which correlated with the MICs of CIP within 0.25–2 μg/mL, and it was found that <i>oxqAB</i> contributed more than <i>qnr</i> genes to increase the MICs. All the isolates contained either QRDR mutations (53.8%), PMQR genes (15.4%), or both (30.8%). QRDR mutations (84.6%) were more commonly detected than PMQR genes (46.2%). QRDR mutation numbers were significantly associated with MICs (<i>p</i> < 0.001). Double mutations in <i>gyrA</i> and <i>parC</i> determined high CIP resistance (MICs ≥ 4 μg/mL). PMQR genes contributed to intermediate to low CIP resistance (MICs 0.25–2 μg/mL), thus providing insights into mechanisms underlying CIP resistance.
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