Deletion of <i>psm-mec</i> in MRSA clinical isolates increases the PSMα production, <i>agrA</i> expression, and colony spreading, whereas decreases biofilm formation.

Abstract

<p>(<b>A, B</b>) The amounts of PSMα3 (A) and Hld + PSMα1 (B) of 18 MRSA isolates and its <i>psm-mec-</i>deleted mutants were measured. White bar represents the clinical isolate used as the parent strain. Black bar represents the <i>psm-mec</i>-deleted mutant of the clinical isolate. The vertical axis represents the amount of PSMαs in arbitrary units based on A₂₁₅. Means ± standard deviations from three independent experiments are shown. Student t-test P-values between the parent strain and the <i>psm-mec</i>-deleted mutant are presented. NS, P>0.05. (<b>C</b>) Cell extracts (3.7 µg protein) of 15 h-cultures of clinical MRSA isolates and the <i>psm-mec</i>-deleted mutants were subjected to Western blotting by anti-AgrA IgG (Upper panel). Band intensities of AgrA were measured and are presented as relative values against that of the parent strain (Lower graph). Means ± standard deviations from three independent experiments are presented. Student t-test P-values between the parent strain and the <i>psm-mec</i>-deleted mutant are presented. NS, P>0.05. (<b>D</b>) Colony spreading abilities of clinical MRSA isolates and the <i>psm-mec</i>-deleted mutants were evaluated. Overnight cultures were spotted onto soft agar plates and incubated for 24 h at 37°C. The vertical axis represents diameters of giant colonies. Means ± standard deviations from three independent experiments are shown. Student t-test P-values between parent strain and the <i>psm-mec</i>-deleted mutant are presented. NS, P>0.05. (<b>E</b>) Biofilm formation of clinical MRSA isolates and <i>psm-mec</i>-deleted mutants were evaluated. Bacterial strains were grown on polystyrene plates for 3 days and the biofilm amounts were measured. White bar represents the clinical isolate used as the parent strain. Black bar represents the <i>psm-mec</i>-deleted mutant of the clinical isolate. Means ± standard deviations from four independent experiments are shown. NS, P>0.05.</p