Laboratory Diagnosis of Staphylococcus spp. Infections

Staphylococcus spp. are among the most common human pathogens identified from clinical samples in microbiology laboratories. S. aureus is the most clinically relevant species, followed by some coagulase-negative Staphylococcus spp. (CoNS) such as S. saprophyticus and, to a lesser extent, S. epidermidis, S. haemolyticus, and S. lugdunensis. Different methods are available for the laboratory diagnosis of Staphylococcus spp. infections. The aim of this tutorial is to provide a practical approach for students and laboratory technicians to identify Staphylococcus species from clinical samples, guiding the step-by-step execution using abbreviated algorithms for phenotypic identification and presenting guidance for when to perform additional miscellaneous tests or pursue other microorganisms. Commercial semi-automated and automated phenotypic identification systems are also addressed, as they can speed up identification, particularly of CoNS species. Finally, molecular methods (proteotypic and genotypic) are briefly discussed as alternative or complementary approaches to identification by conventional or automated phenotypic methods. Despite the advantages of molecular methods, it is highly unlikely they will replace biochemical tests entirely, as phenotypic methods (mainly biochemical test-based methods) will remain as backup identification strategies when the latest technology fails. Therefore, future technicians in the field still have to be taught and gain experience with these older, valuable methods.