Pharmaceutical Research Center, Meiji Seika Kaisha, Ltd., 760 Morooka-cho, Kohoku-ku, Yokohama, Japan.
Int J Antimicrob Agents. 2010 Apr;35(4):333-7. doi: 10.1016/j.ijantimicag.2009.11.011. Epub 2010 Jan 13.
To clarify the molecular mechanisms of fosfomycin resistance in clinical isolates of Escherichia coli, the murA, glpT, uhpT, uhpA, ptsI and cyaA genes were sequenced from six fosfomycin-resistant isolates. Two strains were found to harbour a mutation in the murA gene that leads to an amino acid substitution (Asp369Asn or Leu370Ile) in the target protein. The remaining four strains carried specific mutations in the glpT gene; one strain possessed a mutation and the other three strains possessed truncated versions of the GlpT transporter owing either to the presence of insertion sequences or a deletion in the coding region of the gene. Two of the strains with truncated GlpT had also lost the entire uhpT gene, which encodes another fosfomycin transporter. Uptake of specific substrates for the transporters was either totally blocked or reduced in strains possessing truncated forms of GlpT or those lacking the uhpT gene. Escherichia coli strains expressing an amino-acid-substituted MurA were at least eight-fold more resistant to fosfomycin than the strain overproducing wild-type MurA. In conclusion, novel amino acid substitutions in MurA or the loss of function of transporters were identified as mechanisms of fosfomycin resistance in clinical isolates of E. coli.
为了阐明临床分离大肠杆菌中磷霉素耐药的分子机制，对 6 株磷霉素耐药分离株的 murA、glpT、uhpT、uhpA、ptsI 和 cyaA 基因进行了测序。发现 2 株菌 murA 基因发生突变，导致靶蛋白氨基酸替换（Asp369Asn 或 Leu370Ile）。其余 4 株菌 glpT 基因存在特异性突变；1 株菌发生突变，另外 3 株菌因插入序列的存在或基因编码区缺失，导致 GlpT 转运体截短。2 株 GlpT 截短的菌株也失去了编码另一种磷霉素转运体的完整 uhpT 基因。转运体特异性底物的摄取在 GlpT 截短或 uhpT 基因缺失的菌株中完全受阻或减少。表达氨基酸替换 MurA 的大肠杆菌菌株对磷霉素的耐药性至少比野生型 MurA 过表达菌株高 8 倍。总之，MurA 中的新型氨基酸取代或转运体功能丧失被确定为大肠杆菌临床分离株磷霉素耐药的机制。
