Analysis of the Fluoroquinolone Antibiotic Resistance Mechanism of Salmonella enterica Isolates.
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.
Department of Biological Sciences, Konkuk University, Seoul 05029, Republic of Korea.
Soo-Young
SY
Kim
Department of Biosources and Food Science, Konkuk University, Seoul 05029, Republic of Korea.
Si-Kyung
SK
Lee
Department of Hotel Culinary Arts, Yeonsung University, Anyang 14011, Republic of Korea.
Myeong-Soo
MS
Park
Department of Biological Sciences, Konkuk University, Seoul 05029, Republic of Korea.
Hun-Taek
HT
Na
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D024841:Fluoroquinolones / Q000494:pharmacology*; D006801:Humans; D008826:Microbial Sensitivity Tests; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D012480:Salmonella Infections / Q000382:microbiology; D019779:Salmonella enterica / Q000187:drug effects* / Q000235:genetics*
D000900:Anti-Bacterial Agents; D024841:Fluoroquinolones; D012333:RNA, Messenger
AcrAB-TolC; QRDR; Salmonella enterica; marA; quinolone resistance