| Summary: | 碩士 === 國立中興大學 === 微生物暨公共衛生學研究所 === 101 === Multi-drug resistant (MDR) Salmonella has been the major issue in animals and humans, which comprises resistance of ampicillin, chloramphenicol, streptomycin, sulfamethoxazole, tetracycline (ACSSuT), and quinolones. The expression of AcrAB-TolC efflux pump is an important antimicrobial-resistant factor, which may be associated with MDR development of Salmonella. The expression of transcriptional activator RamA regulates the promoter strength of acrA, acrB and tolC genes and affects AcrAB-TolC expression. The ramA-deleted or -removed mutants would decrease AcrAB-TolC expression and resistant levels to multiple drugs. The ramR gene is located upstream of ramA, which is a transcriptional repressor of ramA and negatively regulates ramA expression. RamR binding site is overlapped with ramA promoter region. Mutation, insertion or deletion of ramR gene or RamR binding site could significantly increase ramA expression. In this study, a total of 463 isolates of nine Salmonella serovars are molecular typed by ramR (including ramR-A intergenic region) and ramA sequences to study the individual role of these mutants in MDR of ACSSuT and quinolone resistance. Real time two-step RT-PCR by SYBR green was applied to measure relative expression of ramA, acrA, acrB and tolC genes. Our results indicated that a total of 27 ramR genotypes and 3 ramA genotypes were found in the Salmonella isolates, and most of which were firstly reported worldwide. Only mutants with partially deleted ramR gene, with more than one amino acid change or insertion subsequently causing a premature stop codon were associated with higher ramA expression. The ramA mutants themselves were not associated with higher acrA, acrB and tolC expressions, but isolates with higher expression of ramA were significantly associated with higher acrA and acrB expressions. Comparing to non-MDR isolates, higher acrA and acrB expressions were identified in MDR isolates. Moreover, in serovars of Typhimurium, Choleraesuis, Albany and Newport, proportions of isolates with higher acrA and acrB expression were significantly higher in MDR and quinolone-resistant (QR) groups, respectively.
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