Walsh Fiona, Willcock Joanne, Amyes Sebastian
Department of Medical Microbiology, Medical School, University of Edinburgh, Edinburgh EH8 9AG.
J Antimicrob Chemother. 2003 Sep;52(3):345-53. doi: 10.1093/jac/dkg348. Epub 2003 Aug 13.
Resistance to macrolides in Streptococcus pneumoniae is usually mediated by methylation of 23S ribosomal RNA, encoded by the erm(B) methylation gene, or by efflux mediated by the mef(A) gene. Changes in the L4 and L22 ribosomal proteins have also been associated with macrolide resistance and reduced telithromycin activity. This study generated in vitro mutants from three parent strains of S. pneumoniae: 02J1175 [mef(A) +], 02J1095 [erm(B) +] and NCTC 13593 (macrolide susceptible). The erm(B) and the erm(B) upstream region, the mef(A) genes and the mef(A) upstream and downstream regions, the 23S rRNA genes encoding domains II and V and the L4 and L22 genes of the telithromycin-resistant strains were all amplified by PCR and all, except the mef(A) upstream and downstream regions, were sequenced. No changes were present in any of the genes of the mef(A) + mutants. No changes were found in the erm(B) genes, the 23S rRNA genes or the L4 protein genes of the erm(B) + mutants. However, a Lys-94 to Gln-94 amino acid mutation did occur in a mutant derived from erm(B) + with a telithromycin MIC of >32 mg/L. A 210 base pair deletion in the erm(B) upstream region was also present in this strain. We believe this is the first incidence of a Lys-94 to Gln-94 change in L22 associated with telithromycin resistance and also the first time that such a large deletion in the erm(B) upstream region has been identified in S. pneumoniae.
肺炎链球菌对大环内酯类药物的耐药性通常由erm(B)甲基化基因编码的23S核糖体RNA甲基化介导，或由mef(A)基因介导的外排作用介导。L4和L22核糖体蛋白的变化也与大环内酯类耐药性及替利霉素活性降低有关。本研究从三株肺炎链球菌亲本菌株中产生了体外突变体：02J1175 [mef(A) +]、02J1095 [erm(B) +]和NCTC 1,3593（对大环内酯类药物敏感）。通过PCR扩增了erm(B)及其上游区域、mef(A)基因及其上下游区域、编码结构域II和V的23S rRNA基因以及替利霉素耐药菌株的L4和L22基因，除mef(A)上下游区域外，其余均进行了测序。mef(A) +突变体的任何基因均未出现变化。erm(B) +突变体的erm(B)基因、23S rRNA基因或L4蛋白基因均未发现变化。然而，在一株来自erm(B) +且替利霉素最低抑菌浓度>32 mg/L的突变体中，确实发生了Lys-94至Gln-94的氨基酸突变。该菌株的erm(B)上游区域还存在210个碱基对缺失。我们认为这是首次发现L22中与替利霉素耐药性相关的Lys-94至Gln-94变化，也是首次在肺炎链球菌中鉴定出erm(B)上游区域如此大的缺失。
