Abstract:ObjectiveTo study virulence factors and drug resistance mechanism of linezolidintermediate Enterococcus faecalis(E. faecalis) isolated from patients with bloodstream infection.MethodsTwo linezolidintermediate 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 linezolidintermediate 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 linezolidintermediate 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 nonsusceptible to such antimicrobial agents, and the treatment strategy needs further study.