Abstract:

Objective To compare the phenotypic methods for β-lactamase detection in Staphylococcus aureus. Methods A total of 38 isolates with penicillin minimum inhibitory concentration（MIC）≤0.12 μg/mL and 15 isolates with penicillin MIC≥0.25 μg/mL were collected. Penicillin zone edge test（P1 and P10）,nitrocefin test and clover test were used for β-lactamase detection. Polymerase reaction chain（PCR） was used for amplifying blaZ gene. The gene detection method was used as standard,and the difference among these methods were evaluated. Results Among the 38 isolates with MIC≤0.12 μg/mL,by penicillin zone edge test（P10）,2 isolates produced 27 mm diameter of inhibition zone. Totally,15 isolates were positive for blaZ gene,including 2 isolates with MIC=0.12 μg/mL and 13 isolates with MIC≥0.25 μg/mL. Among the 15 isolates,the penicillin zone edge test showed all sensitive（100%）. The nitrocefin test and clover test detected 14 isolates,and the sensitivity was 93.3%. There were 38 isolates being negative for blaZ gene,the nitrocefin test and penicillin zone edge test detected 2 isolates,and the specificity was 94.7%,while clover test detected 3 isolates,and the specificity was 92.1%.Conclusions The phenotypic methods mentioned above are specific and sensitive,which can be used according to clinical needs.

Key words: Staphylococcus aureus, β-lactamase;, Minimum inhibitory concentration, blaZ gene, Penicillin z one edge test, Nitrocefin test, Clover test