Analysis of the Fluoroquinolone Antibiotic Resistance Mechanism of Salmonella enterica Isolates

Abstract

Quinolone-resistant Salmonella strains were isolated from patient samples, and several quinolone-sensitive strains were used to analyze mutations in the quinolone resistance-determining region (QRDR) of gyrA, gyrB, parC, and parE and to screen for plasmid-mediated quinolone resistance. Among the 21 strains that showed resistance to nalidixic acid and ciprofloxacin (MIC 0.125-2.0 μg/ml), 17 strains had a mutation in QRDR codon 87 of gyrA, and 3 strains had a single mutation (Ser83 → Phe). Another cause of resistance, efflux pump regulation, was studied by examining the expression of acrB, ramA, marA, and soxS. Five strains, including Sal-KH1 and Sal-KH2, showed no increase in relative expression in an analysis using the qRT-PCR method (p < 0.05). In order to determine the genes involved in the resistance, the Sal-9 isolate that showed decreased susceptibility and did not contain a mutation in the gyrA QRDR was used to make the STM (MIC 8 μg/ml) and STH (MIC 16 μg/ml) ciprofloxacin-resistant mutants. The gyrA QRDR Asp87 → Gly mutation was identified in both the STM and STH mutants by mutation analysis. qRT-PCR analysis of the efflux transporter acrB of the AcrAB-TolC efflux system showed increased expression levels in both the STM (1.79-fold) and STH (2.0-fold) mutants. In addition, the expression of the transcriptional regulator marA was increased in both the STM (6.35-fold) and STH (21.73-fold) mutants. Moreover, the expression of soxS was increased in the STM (3.41-fold) and STH (10.05-fold) mutants (p < 0.05). Therefore, these results indicate that AcrAB-TolC efflux pump activity and the target site mutation in gyrA are involved in quinolone resistance.

Quinolone susceptibility and genetic characterization of Salmonella enterica subsp. enterica isolated from pet turtles

“…Previously, qnrA , qnrB , qnrS , and aac(6')-Ib-cr plasmid-mediated resistance genes were reported in quinolone-resistant, non-typhoidal Salmonella [36]. The Qnr protein induces resistance to nalidixic acid, thereby decreasing or limiting susceptibility to fluoroquinolones [31].…”

“…Moreover, Asai et al [34] could detect qnrS among 0.08% of the S. enterica isolates of food-producing animals while Kim et al [33] reported qnrB4 and qnrS1 in 3.2% of the isolates from poultry. Prevalence of qnr genes in S. enterica human clinical isolates was also reported as low in recent studies [3536]. …”

“…In addition to above two sites, a recent study reported gyrA mutations of Ala-131 position in poultry and human isolates [30]. Another study could detect mutations in parC in addition to the gyrA mutations but in very low rate compared to gyrA [36]. Besides, Ser83-Phe substitution was detected in Salmonella spp.…”

Emerging coexistence of three PMQR genes on a multiple resistance plasmid with a new surrounding genetic structure of qnrS2 in E. coli in China

“…PCR amplification, DNA sequencing, and sequence analysis PCR assays were conducted targeting QRDRs of the gyrA, gyrB, parC, and parE genes with primer pairs as previously reported [17]. The genomic DNA was extracted using the QIAGEN Midi Kit (Qiagen, Hilden, Germany).…”

Correlation between gyrA and CmeR Box Polymorphism and Fluoroquinolone Resistance in Campylobacter jejuni Isolates in China

“…To investigate the molecular basis of high FQ resistance in the C. jejuni isolates, we analyzed the full gene sequences encoding the DNA gyrase subunits (gyrA and gyrB) (9,10) and the topoisomerase IV subunits (parC and parE) (11,12), which are known targets of FQ, the regulatory protein CmeR, and the sequence of the promoter region of cmeABC, which encodes an efflux pump (13,14), by DNA sequencing as previously described (15,16). The MICs of ciprofloxacin against the 39 isolates which represent different sequence variants were tested according to CLSI guidelines (17,28).…”