Serious bloodstream infections are a significant complication in critically ill patients. The treatment of
these infections has become more difficult because of the increasing prevalence of multiresistant strains,
especially methicillin-resistant Staphylococcus aureus (MRSA). Rapid differentiation of low number of
MRSA from methicillin-susceptible S. aureus (MSSA) cells (101–102 cellsmL1) in blood is necessary for
fast effective antibiotic therapy. Currently, three groups of techniques, phenotyping, genotyping, and
mass spectrometry, are used for MRSA and MSSA strains differentiation. Most of these techniques are
time-consuming. PCR and other molecular techniques allow the detection and differentiation between
MSSA and MRSA directly from blood cultures. These methods alone are rapid and they have good
reproducibility and repeatability. Potential disadvantages of the genotyping methods include their
discrimination ability, technical complexity, financial costs, and difficult interpretation of the results.