Evaluation of HiaureusTM Coagulase Confirmation Kit in Identification of Staphylococcus aureus

Abstract

Introduction: Staphylococcus aureus is a facultative anaerobic Gram positive coccal bacterium whose incidence ranges to different infections. It is a cause of various uncomplicated skin infections, abscesses, septicaemia/bacteraemia, gastroenteritis, endocarditis, toxic shock syndrome and food intoxications. Various methods with varied time, sensitivities, specificities and costs are available, but may not be used as a reliable test for the identification and differentiation of S. aureus. Therefore, there is a need to evaluate newer tests. Aim: To compare the conventional tests with a commercial available kit for reliable, cost effective identification and confirmation of S. aureus. Materials and Methods: The current prospective study was conducted in the Department of Clinical Pathology, Haffkine Institute for a period of six months. A total of 341 clinical isolates of staphylococci isolated from pus, urine, blood culture and sterile body fluids were subjected to conventional tests like Tube Coagulase Test (TCT) using Rabbit Plasma (RP) and Human Plasma (HP), culture media such as Mannitol Salt Agar (MSA) and Deoxyribonuclease (DNase) media in parallel to HiaureusTM Coagulase Confirmation Kit (HACCK), a commercially available kit for identification of S. aureus. Amplification of the femA gene was used as a comparative reference point test to calculate the sensitivity, specificity and concordance values of the conventional tests. Results: Amongst the coagulase based tests, HACCK was 100% sensitive and specific. The TCT using RP was 98.58% sensitive while TCT using HP was less sensitive (95.37%). A total of 100% specificity was observed for TCT using RP while TCT using HP was 96.68% specific. The MSA and DNase media were 97.86% vs 96.44% and 96.67% vs 91.67% sensitive and specific respectively. The combination tests had varying sensitivity and specificity ranges. The HACCK demonstrated 100% concordance with femA amplification and was labelled as an ideal perfect test (κ=1) with MSA as an alternative test for S. aureus identification. Conclusion: The HACCK can be used as an exclusive, reliable and cost effective test for identification of S. aureus. Alternatively, in view of the cost factor MSA either as a single test or in combination with TCT using HP could be used as screening tests and confirm discordant results with HACCK.

Keywords

• deoxyribonuclease
• mannitol
• plasma
• polymerase chain reaction
• rabbit