Stapleton Paul, Adams Victoria, Pike Rachel, Lucas Victoria, Roberts Graham, Mullany Peter, Rowbury Robin, Wilson Michael, Richards Hilary
Department of Biology, University College London, Gower Street, London, UK.
Int J Antimicrob Agents. 2004 Nov;24(5):439-43. doi: 10.1016/j.ijantimicag.2004.06.003.
Streptococcus oralis 264-3, Streptococcus mitis 254-1 and S. mitis 264-1, isolated from the oral cavities of two children were each found to carry the tet(M) gene but exhibited different degrees of reduced susceptibility to tetracycline (tetracycline MICs of 2, 8 and 64 mg/L, respectively). The aim of this study was to determine the molecular basis for the different levels of tetracycline resistance (Tc(R)) observed. Escherichia coli HB101 carrying the cloned tet(M) genes exhibited similar levels of tetracycline susceptibility to those observed in the parental streptococcal strains (MICs of 1, 16, and 64 mg/L for tet(M) genes from S. oralis 264-3, S. mitis 254-1 and S. mitis 264-1, respectively). DNA sequencing revealed that S. oralis 264-3 had a tet(M) gene highly homologous to tet(M) carried by Tn916 from Enterococcus faecalis (99.6% identity), while the intermediate- and high-level Tc(R) strains had tet(M) sequences that resembled the tet(M) gene of Tn5251 from Streptococcus pneumoniae (99.3% and 99.4% identity, respectively). No differences were observed in the upstream attenuator structure for each of the strains and differences in reduced tetracycline susceptibilities could be attributed to changes in the deduced amino acid sequences of the Tet(M) proteins.
从两名儿童口腔中分离出的口腔链球菌264 - 3、缓症链球菌254 - 1和缓症链球菌264 - 1均被发现携带tet(M)基因，但对四环素的敏感性降低程度不同（四环素MIC分别为2、8和64mg/L）。本研究的目的是确定观察到的不同水平四环素抗性（Tc(R)）的分子基础。携带克隆tet(M)基因的大肠杆菌HB101对四环素的敏感性水平与亲代链球菌菌株中观察到的相似（来自口腔链球菌264 - 3、缓症链球菌254 - 1和缓症链球菌264 - 1的tet(M)基因的MIC分别为1、16和64mg/L）。DNA测序显示，口腔链球菌264 - 3具有与粪肠球菌Tn916携带的tet(M)基因高度同源的tet(M)基因（同一性为99.6%），而中度和高度Tc(R)菌株的tet(M)序列类似于肺炎链球菌Tn5251的tet(M)基因（分别为99.3%和99.4%同一性）。各菌株的上游衰减器结构未观察到差异，四环素敏感性降低的差异可归因于Tet(M)蛋白推导氨基酸序列的变化。
