OBJECTIVE To detect ?-lactamase of ampicillin-resistant Enterococcus in order to choose drugs for clinical treatment.METHODS According to CLSI's guideline,antimicrobial susceptibility tests were performed:to detect ?-lactamase with nitrocefin,to detect blaZ by PCR and to detect mutation of pbp4 by single-strand conformation polymorphism(SSCP).RESULTS The resistant rates of E.faecium and E.faecalis to ampicillin,penicillin,high level gentamicin,high level streptomycin,levofloxacin,erythromycin,tetracycline,and chloramphenicol were 100%,100%;86%,76%;46%,44%;84%,74%;100%,94%;54%,58%;and 42%,36%;to rifampicin 62%,58%;and to vancomycin both 0%,respectively.The positive rate of ?-lactamase in 50 E.faecalis strains with paper disk method and test tube method was 8% and 26%;and that of blaZ by PCR was 88%.But in 50 E.faecium strains the results were 0% and 2%,respectively.There was no significant mutation by SSCP and sequencing in E.faecalis.CONCLUSIONS The positive rate to ?-lactamase in E.faecalis is markedly higher than in E.faecium.The method of PCR is better than that of nitrocefin.The positive rate of test tube method is higher than paper disk method with nitrocefin.

Objective To study the relationship of ampicillin resistance and?lactamase production, and gene mutation on pbp5 gene fragment in Enterococcus faecium. Methods?lactamase production was tested with nitrocefin, the pbp5 gene fragment of 57 isolates of ampicillin-resistant Enterococcus faecium (ARE. faecium) was amplified by PCR, the mutation of amplified pbp5 gene was detected by single-strand conformation polymorphism(SSCP), the specific mutation types were confirmed by sequencing. Results?lactamase was negative in 57 isolates of ARE. faeciums; there were 3-6 gene mutation sites on pbp5 gene fragment, and the frequent mutation sites were the position 485 ,499 and 466'. Conclusion The gene mutation of pbp5 gene fragment may play an important role in the ARE. faecium.