Development of a rapid assay methodology for antimicrobial susceptibility testing of Staphylococcus aureus.

Development of a new phenotypic technique for rapid antimicrobial susceptibility testing (AST) of methicillin-resistant Staphylococcus aureus is presented. The new technique combines bacterial culturing and specific immunometric detection in a single separation-free process. The technique uses dry chemistry reagents and the recently developed two-photon excitation detection technology, which allows online detection of bacterium-specific growth. The performance of the new technique was evaluated by monitoring the growth of S. aureus reference strains and determining their susceptibility to oxacillin. In the direct analysis of clinical specimens, method specificity and tolerance to interferences caused by other bacteria present in the sample are pivotal. Other bacteria can compete with the bacteria of interest for nutrients, for example. Specificity and tolerance were studied against Staphylococcus epidermidis reference strains. The results suggest that the new technique could allow rapid AST directly from clinical samples within 6 to 8 h. Such a rapid and simple testing methodology would be a valuable tool in clinical microbiology because it would shorten the turnaround times of microbiologic analyses. Advantages of the new approach in relation to conventional methods are discussed.