Culebras Esther, Rodríguez-Avial Iciar, Betriu Carmen, Picazo Juan J
Servicio de Microbiología, Hospital Clínico San Carlos, Plaza Cristo Rey s/n, Madrid, 28040, Spain.
J Antimicrob Chemother. 2005 Nov;56(5):836-40. doi: 10.1093/jac/dki337. Epub 2005 Sep 26.
To study the regulatory region of a constitutively expressed erm(A) gene in Streptococcus agalactiae clinical isolates.
Thirty clinical isolates of S. agalactiae which were cross-resistant to erythromycin and clindamycin and with a clindamycin MIC higher than that of erythromycin were studied by PCR, sequencing and molecular typing.
PCR analysis revealed that all the strains harboured the erm(A) gene, either alone (26 isolates) or in combination with erm(B) (four isolates). Sequencing of the region upstream of erm(A) showed that all isolates possessed two types of genetic alteration. Most of the strains showed point mutations in the second leader peptide (mainly A137C) and, in four isolates (two clones), an insertion fragment with high homology to IS1381 and transposase genes was detected. Epidemiological analysis of strains indicated several clonal origins of isolates.
The mutations described here are thought to result in increased or constitutive expression of the erm(A) gene.
研究无乳链球菌临床分离株中组成型表达的erm(A)基因的调控区。
对30株对红霉素和克林霉素交叉耐药且克林霉素最低抑菌浓度高于红霉素的无乳链球菌临床分离株进行聚合酶链反应（PCR）、测序和分子分型研究。
PCR分析显示，所有菌株均携带erm(A)基因，单独携带erm(A)基因的有26株，与erm(B)基因共同携带的有4株。erm(A)基因上游区域测序表明，所有分离株均存在两种类型的基因改变。大多数菌株在第二个前导肽中出现点突变（主要是A137C），在4株分离株（两个克隆）中检测到与IS1381和转座酶基因具有高度同源性的插入片段。菌株的流行病学分析表明分离株有多个克隆起源。
此处描述的突变被认为导致erm(A)基因表达增加或组成型表达。
