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Table 1 Performances of Penicillin G zone diameter, nitrocefin disk test, Zone edge test and Penicillin G MIC determination (Vitek 2®) for the detection of penicillinase production in 182 S. epidermidis isolates and comparison of zone edge test results between the 5 investigators

From: Performance of penicillinase detection tests in Staphylococcus epidermidis: comparison of different phenotypic methods

Phenotypic method for penicillinase detection TP (N) FP (N) TN (N) FN (N) Total (N) Se (%) Sp (%) PPV (%) NPV (%)
Diameter 54 0 127 1 182 98 100 100 99
Nitrocefin 50 0 127 5 182 91 100 100 96
Zone edge test 54 20 107 1 182 98 84 73 99
MIC 51 1 126 4 182 93 99 98 97
zone edge test reading/investigators
 Investigator 1 54 21 106 1 182 98 83 72 99
 Investigator 2 54 19 108 1 182 98 85 74 99
 Investigator 3 53 43 84 2 182 96 66 55 98
 Investigator 4 55 28 99 0 182 100 78 66 100
 Investigator 5 54 5 122 1 182 98 96 93 99
 Final result 54 20 107 1 182 98 84 73 99
  1. blaZ PCR was used as the reference method
  2. TP true positive, FP false positive, TN true negative, FN false negative, Se Sensitivity, Sp Specificity, PPV Positive Predictive Value, NPV Negative Predictive Value, (N) Number of isolates