A rapid assay was designed for the detection of resistant strains of Staphylococcus aureus to antibiotic inhibitors of protein synthesis. The assay was based on the fact that a brief cell wall digestion with lysostaphin resulted in fragmentation of the chromosomal DNA by releasing the characteristic DNase stored in the cell wall. DNase activity was ascertained by visualization of the DNA fragments released from the isolated nucleoids. Lysostaphin-released DNase activity was found to be influenced by ribosomal protein synthesis. Inhibition of protein synthesis resulted in the prevention of lysostaphin-DNase induced DNA fragmentation when susceptible clinical strains were incubated with erythromycin, azithromycin, or doxycycline for 2 hr before enzymatic treatment. However, in nonsusceptible strains where protein synthesis was unsuccessfully inhibited, this suppression of lysostaphin-DNase was not, or only very slightly, evident. This assay was highly efficient, identifying resistance to erythromycin and azithromycin with 88-90.9% sensitivity and 100% specificity and with 100% sensitivity and specificity to gentamicin and doxycycline, within a 2 hr and 45 min period.
Keywords: DNA fragmentation; DNase; Staphylococcus aureus; antibiotic resistance; inhibitors of protein synthesis; rapid assay.