2例利奈唑胺中介粪肠球菌血流感染的毒力及耐药机制

Virulence determinants and drug resistance mechanisms of two linezolidintermediate Enterococcus faecalis isolates from bloodstream infection

摘要:

目的对血流感染患者临床分离的利奈唑胺中介粪肠球菌的毒力因子及耐药机制进行初步研究。 方法从2例血流感染患者血标本中分离2株利奈唑胺中介粪肠球菌，分析患者治疗经过，2株分离菌编号为A、B，测定其对利奈唑胺和万古霉素的最低抑菌浓度（MIC），采用聚合酶链反应（PCR）扩增毒力基因（esp、asa1、gelE、ace、agg、efaA、cylA、hyl）和利奈唑胺耐药相关基因，包括23SrRNA V 区基因、cfr、cfr(B)及optrA 基因片段，其中23SrRNA V 区基因扩增产物送测序并分析有无突变位点。结果2例患者培养出利奈唑胺中介粪肠球菌后均使用利奈唑胺治疗控制了临床症状。菌株A、B对万古霉素、替考拉宁、氨苄西林、呋喃妥因敏感，对利奈唑胺中介（MIC均为4 μg/mL），对万古霉素敏感（MIC分别为1 μg/mL和4 μg/mL）。2株菌均含有多种毒力因子，菌株A仅cylA、hyl为阴性，菌株B仅hyl、esp为阴性，其余毒力基因均为阳性。菌株A 的23SrRNA V区存在G2621T突变，菌株B未发现突变位点。菌株A和B耐药基因cfr、cfr(B)、optrA均为阴性。结论此研究中血流感染患者分离的利奈唑胺中介粪肠球菌对万古霉素和氨苄西林敏感，虽治疗结果提示利奈唑胺仍有效，但临床中选用利奈唑胺治疗需谨慎。靶位突变是该类药物重要的耐药机制，临床中治疗该类药物不敏感粪肠球菌感染需足够重视，其治疗策略仍需进一步探讨。

关键词:

利奈唑胺; 粪肠球菌; 细菌; 耐药机制; 毒力基因

Abstract:

ObjectiveTo study virulence factors and drug resistance mechanism of linezolidintermediate Enterococcus faecalis(E. faecalis) isolated from patients with bloodstream infection.MethodsTwo linezolidintermediate E. faecalis strains, namely A and B, were isolated from two patients with bloodstream infection, the treatment of two patients was analyzed. The minimum inhibitory concentration (MIC) of linezolid and vancomycin were determined. The virulence genes (esp, asa1, gelE, ace, agg, efaA, cylA, and hyl) and linezolid resistance genes (domain V region of the 23SrRNA, cfr, cfr［B］, optrA) were amplified by polymerase chain reaction (PCR). PCR products of domain V region of 23SrRNA gene were sequenced and analyzed.ResultsSymptoms of two patients who isolated two linezolidintermediate E. faecalis strains were controlled after accepted linezolid therapy. Strains A and B were both susceptible to vancomycin(MICs were 1μg/mL and 4μg/mL respectively）, teicoplain, ampicillin, and nitrofurantoin, while intermediate to linezolid（MIC were both 4μg/mL）. Two strains both contained multiple virulence factors, strain A were negative for cylA and hyl, strain B were negative for hyl and esp, but positive for other virulence genes. There was G2621T mutation in domain V region of 23SrRNA in strain A, and no variation was found in strain B. Drug resistance genes of cfr, cfr(B), and optrA were all negative in both strain A and B.ConclusionIn the present study, two linezolidintermediate E. faecalis strains isolated from patients with bloodstream infection were susceptible to vancomycin and ampicillin, although the treatment of linezolid in two patients is effective, the utilization of linezolid therapy in clinical practice still needs to be cautious. The mutation of target site is a significant resistance mechanism, it is necessary for us to pay more attention to these clinical strains which are nonsusceptible to such antimicrobial agents, and the treatment strategy needs further study.

Key words:

linezolid; Enterococcus faecalis; bacteria; resistance mechanism; virulence gene