Staphylococcus aureus biofilm organization modulated by YycFG two-component regulatory pathway

Staphylococcus aureus (S. aureus) infection accounts for more than 50% of the osteomyelitis cases. Currently, methicillin-resistant S. aureus (MRSA) strains present an urgent medical problem. The YycFG two-component regulatory system (TCS) can allow bacteria to rapidly adapt to physical, chemical, and biological stresses. To define the role of YycFG in modulation virulence of S. aureus in osteomyelitis, we isolated clinical MRSA strains and compared these with ATCC29213 methicillin-sensitive S. aureus (MSSA).

In the present study, 13 MRSA strains from chronic osteomyelitis tissues were isolated. The in-depth sequencing of 16S rRNA amplicons of the samples was conducted. Bacterial growth was monitored, and biofilm biomass was determined by crystal violet microtiter assay. Furthermore, quantitative RT-PCR analysis was adopted to identify the expression of yycF/G/H and icaA/D in MRSA and MSSA strains. Analysis of variance with one-way ANOVA was used for statistical analysis.

The in-depth sequencing of 16S rRNA amplicons of the clinical samples indicated a polymicrobial infection, with the phylum Firmicutes made up 13% of the microbial population. The MRSA strains showed an accelerated growth rate compared to the MSSA strains. Of note, MRSA biofilms showed an accumulation of an intercellular polysaccharides matrix and enhanced biomass upon microscopic examination. Furthermore, MRSA strains had a higher expression of the yycF/G/H and icaA/D genes and adhesion force.

These data suggested the roles of intercellular polysaccharide in S. aureus pathogenesis, indicating a possible association between YycFG pathways and MRSA strain virulence.