ANSES, Laboratory for Animal Health in Normandy, Physiopathology and Epidemiology of Equine Diseases Unit, Goustranville, France.
ANSES, Laboratory for Animal Health in Normandy, Physiopathology and Epidemiology of Equine Diseases Unit, Goustranville, France.
J Glob Antimicrob Resist. 2020 Dec;23:137-144. doi: 10.1016/j.jgar.2020.08.006. Epub 2020 Sep 28.
Study of the rifampicin resistance of Rhodococcus equi strains isolated from French horses over a 20-year period.
Rifampicin susceptibility was tested by disk diffusion (DD) and broth macrodilution methods, and rpoB gene sequencing and MLST were performed on 40 R. equi strains, 50.0% of which were non-susceptible to rifampicin.
Consistency of results was observed between rifampicin susceptibility testing and rpoB sequencing. Strains non-susceptible to rifampicin by DD had a substitution at one of the sites (Asp516, His526 and Ser531) frequently encountered and conferring rifampicin resistance. High-level resistance was correlated with His526Asp or Ser531Leu substitutions; low-level resistance was correlated with Asp516Tyr substitution, a novel substitution for R. equi. Strains susceptible to rifampicin by DD showed no substitution in the three sites, except for two strains carrying, respectively, the His526Asn and Asp516Val substitutions (previously correlated with low-level rifampicin resistance). Both strains were isolated from an animal from which ten other strains were also isolated and found to be rifampicin-non-susceptible by DD. MLST showed the presence of 10 STs (including the novel ST43), but no association was observed with rifampicin resistance.
This study confirms that certain substitutions in RpoB are more likely to confer high- or low-level rifampicin resistance, describes a new substitution conferring rifampicin resistance in R. equi and suggests non-clonal dissemination of rifampicin-resistant strains in France. Standard DD may miss strains with a low-level rifampicin-resistant substitution; further studies are needed to remedy the absence of R. equi-specific clinical breakpoints.
研究 20 年来从法国马匹中分离出的马红球菌菌株的利福平耐药性。
采用纸片扩散法（DD）和肉汤微量稀释法检测利福平的敏感性，并对 40 株马红球菌进行 rpoB 基因测序和 MLST，其中 50.0%对利福平不敏感。
利福平药敏试验和 rpoB 测序结果一致。DD 法不敏感的菌株在经常遇到的三个位点（Asp516、His526 和 Ser531）之一发生取代，导致利福平耐药。高水平耐药与 His526Asp 或 Ser531Leu 取代有关；低水平耐药与 Asp516Tyr 取代有关，这是马红球菌的一种新取代。DD 法敏感的菌株在这三个位点均未发生取代，除了两株分别携带 His526Asn 和 Asp516Val 取代（以前与低水平利福平耐药相关）。这两株均从一只动物中分离出来，从该动物中还分离出了另外 10 株对 DD 不敏感的菌株。MLST 显示存在 10 个 ST （包括新的 ST43），但与利福平耐药无关。
本研究证实，RpoB 中的某些取代更可能导致高水平或低水平的利福平耐药性，描述了一种新的取代，赋予马红球菌利福平耐药性，并提示法国利福平耐药菌株的非克隆传播。标准 DD 可能会错过低水平利福平耐药性取代的菌株；需要进一步研究来弥补缺乏马红球菌特异性临床折点的问题。
