Analysis of the Fluoroquinolone Antibiotic Resistance Mechanism of Salmonella enterica Isolates

• Published in: Journal of microbiology and biotechnology Vol. 26; no. 9; pp. 1605 - 1612
• Main Authors: Kim, Soo-Young, Lee, Si-Kyung, Park, Myeong-Soo, Na, Hun-Taek
• Format: Journal Article
• Language: English
• Published: Korea (South) 한국미생물·생명공학회 28.09.2016
• Subjects: Anti-Bacterial Agents - pharmacology; Drug Resistance, Bacterial - genetics; Fluoroquinolones - pharmacology; Humans; Microbial Sensitivity Tests; RNA, Messenger - analysis; RNA, Messenger - genetics; RNA, Messenger - metabolism; Salmonella enterica - drug effects; Salmonella enterica - genetics; Salmonella Infections - microbiology; 생물학; marA; Salmonella enterica; QRDR; quinolone resistance; AcrAB-TolC
• ISSN: 1017-7825; 1738-8872
• DOI: 10.4014/jmb.1602.02063

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.