Browsing by Author "Khateb, Aiah"

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    The Role of Staphylococcal Protein A (SPA) in the Virulence of Staphylococcus aureus Infections.
    (2014-05-05) Khateb, Aiah; Zhang, Kunyan
    Staphylococcus aureus infections have spread globally and caused significant morbidity and mortality. Previous studies have indicated several functions that Staphylococcal Protein A (SPA) plays to enhance S. aureus virulence. To evaluate the role of SPA in S. aureus with respect to virulence and other biological functions, the chimeric clones were constructed by replacing the spa gene of a high-virulence S. aureus strain with the spa from a non/low-virulence strain, and vice versa. Three representative MRSA strains, a high-virulence CA-MRSA strain USA300 (spa t008), a typically low-virulence hospital-associated MRSA strain CMRSA6 (spa t037) and an avirulent colonization strain M92 (non-typeable spa) with different genetic backgrounds (ST8, ST239 and ST239, respectively) were selected. Expression of the spa gene was confirmed by western blot. The chimeric clone was evaluated by its growth curve, immunoglobulin (IgG) binding capacity, biofilm formation, and virulence using the Caenorhabditis elegans nematode infection model, and compared with the wild type (WT) donor strains. The chimeric clone USA300spa▲:: CMRSA6 spa, which had the background of a high virulence strain USA300 with the native spa gene being replaced by the spa gene of a low virulence strain CMRSA6, showed a slower growth rate, and a significantly decreased SPA expression with a 24-fold dramatic reduction in SPA IgG-Fc binding capacity. There was a 3.4-fold increase in the biofilm formation and a 62% reduction in the nematocidal activity, when compared to the parent strain WT-USA300. The other two opposite chimeric clones (M92 spa▲::USA300 spa and M92spa▲::CMRSA6spa) were constructed from an avirulent colonization strain M92, with the native spa gene being replaced with the spa genes of a high virulence strain USA300 and a low virulence strain CMRSA6, respectively. Both chimeric clones (M92 spa▲::USA300 spa and M92spa▲::CMRSA6spa) showed slight changes in growth rates, significantly increased SPA expression with 1.6- and 0.7-fold increase in SPA IgG-Fc binding capacity, respectively. No significant change was observed in the biofilm formation and the nematocidal activity of both chimeric clones when compared to the parent strain WT-M92. In conclusion, replacing the spa gene of S. aureus strain altered its biological characteristics, behavior and virulence. This study resultssuggests that spa plays an important role in the virulence and pathogenicity of S. aureus infections.