Accuracy of different methods for identification of Staphylococcus haemolyticus

Abstract

Objectives: Staphylococcus haemolyticus is associated with device-related infections in immunocompromised individuals and acts as a reservoir for antibiotic resistance genes. It is also the species with the highest antibiotic resistance rates. However, identification is still difficult in most clinical laboratories. Simplified biochemical tests give variable results while newer methods such as MALDI-TOF MS and automated systems may not be readily available. Aim: To compare the performance of the simplified biochemical scheme, BD-Phoenix automated system, and PCR for nuc gene for the identification of S. haemolyticus with MALDI-TOF MS as the gold standard. Methods: This study included 427 coagulase-negative staphylococci (CoNS) isolates of which 356 were identified as S. haemolyticus and 71 as other species by MALDI-TOF MS. These isolates were subjected to a simplified biochemical scheme using tests like the fermentation of maltose, sucrose, trehalose, mannose, urease, xylose, ornithine, and susceptibility to novobiocin. Conventional PCR targeting the nuc gene and BD-Phoenix were also used for identification. The accuracy of these methods was assessed in comparison with MALDI-TOF MS. Results: The sensitivity and specificity of biochemical tests, BD- Phoenix and nuc PCR were 97.5% and 97.2%: 97.8% and 100%: 100% and 100% respectively. Inaccurate identification was observed for some of the isolates (2.2% by BD- Phoenix and 2.5% by biochemical tests). These isolates were identified as S. haemolyticus by the other methods. Conclusion: Identification of S. haemolyticus by biochemical tests and BD-Phoenix had good accuracy comparable to PCR as well as MALDI-TOF MS. This simplified biochemical scheme can be easily implemented even in laboratories with limited resources. J Microbiol Infect Dis 2021; 11(1):8-14.