Evaluation of the capability of three phenotypic tests used alone or in combination for identification of Staphylococcus aureus

Abstract

Objective To evaluate the capability of three tests used alone or in combination for identification of Staphylococcus aureus.Methods Identification of Staphylococcus aureus by the detection of spa gene with PCR and the Vitek-2 system were selected as the reference methods.Comparison of three phenotypic tests including DNase,mannitol fermentation and tube coagulase test was carried out to analyze the sensitivity,specificity,positive/negative predictive value,positive/negative likelihood ratio and Youden index.The consistency,cost and related indexes of the assays were analyzed between the combined phenotypic tests and the reference methods.Results In the present study,324 isolates of Staphylococci,including 293 Staphylococcus aureus and 31 non-Staphylococcus aureus,were collected.Single biochemical test could not identify Staphylococcus aureus efficiently.Comparison between the reference methods and the combined three biochemical tests by Kappa statistic analysis indicated that an overall Kappa value was 0.9441,and the algorithm of combined test was less costly.The sensitivity and specificity of this algorithm were 100％ and 90.3％,respectively.Conclusion The cost-effective algorithm of combined DNase,mannitol fermentation and tube coagulase test could efficiently distinguish Staphylococcus aureus from other Staphylococcus species. Key words: Staphylococcus aureus; Bacterial identification; Cost-effective; Biochemical test