Two Novel Point Mutations in Clinical Staphylococcus aureus Reduce Linezolid Susceptibility and Switch on the Stringent Response to Promote Persistent Infection
A and B) Growth characteristics of parental strain JKD6210 (normal MRSA), the clinical SCV strain (JKD6229), and the allelic exchange relA mutant containing the F128Y mutation (JKD6301). Reduced growth rate in MH broth (A) and reduced colony size on HBA agar (B) is demonstrated for the SCV strain JKD6229. The relA mutant JKD6310 demonstrates reduced growth rate in broth and on solid media, but is not as impaired as the clinical SCV strain. The growth curves were significantly different for all strains (P<0.001). An analysis of cellular attachment/invasion after 1 hour incubation demonstrates a reduced rate of attachment in JKD6229 and JKD6301 compared to JKD6210 (C), however an analysis of cellular invasion after 2 hours incubation (D), demonstrates significantly greater invasion for the SCV strain JKD6229 compared to JKD6210 and JKD6301. Results are presented as mean±SD of triplicates from at least three independent experiments. **, P≤0.01; ***, P≤0.001.