Molecular analysis of ciprofloxacin resistance among non-typhoidal Salmonella with reduced susceptibility to ciprofloxacin isolated from patients at a tertiary care Hospital in Kuala Lumpur, Malaysia

Abstract

We investigated the prevalence of non-typhoidal Salmonella (NTS) with "reduced susceptibility to ciprofloxacin" (RS-Cip) (minimum inhibitory concentration [MIC], 0.12-1.0 μg/mL) as well as their resistance genes in 75 NTS isolates (53 from stool, 21 from blood, and 1 from urine) from patients at a tertiary care Malaysian hospital between January and December 2009. RS-Cip was detected in 24/75 (32.0z) isolates. Using the ciprofloxacin MIC interpretive criteria for Salmonella in the Clinical and Laboratory Standards Institute 2013 guidelines, 51/75 (68.0z) isolates were found to be sensitive, 22/75 (29.3z) were intermediate, and 2/75 (2.7z) were resistant to ciprofloxacin. The 24 isolates that were intermediate or resistant to ciprofloxacin were the same isolates categorized as having RS-Cip. Among the 23 tested isolates with RS-Cip, the qnrS gene was detected in 17/23 (73.9z) and single gyrA mutations were detected in 6/23 (26.1z) (Asp87Tyr [n = 3], Asp87Asn [n = 2], and Ser83Phe [n = 1]). A parC (Thr57Ser) mutation was detected in 13/23 (56.5z) isolates, coexisting with either a qnrS gene or a gyrA mutation. The high incidence of the qnrS gene among isolates with RS-Cip needs to be monitored because qnr genes can spread via plasmids and aid in the emergence of increased resistance levels.