Microbiology Division, US Food and Drug Administration, National Center for Toxicological Research, Jefferson, AR 72079, USA.
J Antimicrob Chemother. 2012 Jan;67(1):101-10. doi: 10.1093/jac/dkr414. Epub 2011 Oct 18.
To determine the fluoroquinolone resistance determinants in Salmonella enterica serovar Schwarzengrund from imported foods.
Antibiotic susceptibility of Salmonella Schwarzengrund to 16 antibiotics was examined using disc agar diffusion and Etest. Quinolone resistance determinants were examined by sequence analysis of gyrA, gyrB, parC and parE, PCR amplification of qnrA, qnrB and qnrS, and expression of acrB, ramA, marA, soxS and rob using quantitative RT-PCR. The contribution of efflux pump activities to antibiotic resistance was determined by the addition of carbonyl cyanide m-chlorophenylhydrazone (CCCP). The effect of ramR deletion on ciprofloxacin resistance was determined by complementing with wild-type ramR.
Salmonella strains 30 and 487 were susceptible to ciprofloxacin and had a single mutation in gyrA as compared with strain 75, which was highly resistant to ciprofloxacin and had a double mutation in gyrA. Increased expression of ramA was associated with high resistance to ciprofloxacin. Strain 75 had a deletion of 315 bp in the ramR gene, which regulates ramA expression. Overexpression of ramA was possibly related to a loss of ramR. Introduction of ramR decreased the MIC of ciprofloxacin from 48 to 24 mg/L. The addition of CCCP did not reduce antibiotic resistance. To our knowledge, this study reports for the first time the natural deletion of ramR in Salmonella Schwarzengrund.
This study indicates that fluoroquinolone-resistant Salmonella are prevalent in imported food. Double mutations in gyrA and a loss of ramR were associated with high-level quinolone resistance in multidrug-resistant Salmonella Schwarzengrund strain 75.
确定进口食品中肠炎沙门氏菌 Schwarzengrund 血清型的氟喹诺酮耐药决定因素。
采用纸片琼脂扩散法和 Etest 检测肠炎沙门氏菌 Schwarzengrund 对 16 种抗生素的药敏性。通过对 gyrA、gyrB、parC 和 parE 进行序列分析、qnrA、qnrB 和 qnrS 的 PCR 扩增以及 acrB、ramA、marA、soxS 和 rob 的定量 RT-PCR 检测，检测喹诺酮耐药决定因素。通过添加羰基氰化物 m-氯苯腙（CCCP）来确定外排泵活性对抗生素耐药性的贡献。通过用野生型 ramR 互补来确定 ramR 缺失对环丙沙星耐药性的影响。
与对环丙沙星高度耐药且 gyrA 有双突变的菌株 75 相比，菌株 30 和 487 对环丙沙星敏感，gyrA 只有一个突变。ramA 高表达与对环丙沙星的高度耐药有关。菌株 75 在调节 ramA 表达的 ramR 基因中缺失 315 bp。ramA 的过度表达可能与 ramR 的缺失有关。引入 ramR 使环丙沙星的 MIC 从 48 降至 24 mg/L。加入 CCCP 并不能降低抗生素的耐药性。据我们所知，本研究首次报道了肠炎沙门氏菌 Schwarzengrund 中 ramR 的天然缺失。
本研究表明，氟喹诺酮耐药性沙门氏菌在进口食品中普遍存在。gyrA 的双突变和 ramR 的缺失与多药耐药性肠炎沙门氏菌 Schwarzengrund 菌株 75 高水平的喹诺酮耐药性有关。
