Figure 1

Flow scheme for PCR/ESI-MS genotyping and characterization of S. aureus . DNA from nasal swabs was distributed into eight wells of a microtiter plate, allowing 12 samples to be analyzed per plate. Each well contained two pairs of primers as indicated in Table 1. Following PCR and desalting, amplicons were analyzed by ESI-MS. Amplicon masses were used to calculate base compositions—the A, G, C, and T counts—of the PCR products. Comparison to a database of calculated base compositions of characterized strains allowed the determination of clonal complexes and USA types and of the presence or absence of genes for virulence factors, toxins and antibiotic resistance determinants.