Abstract
Data concerning the virulence and pathogenesis of South African strains of Staphylococcus aureus are limited. We investigated host–pathogen interactions of randomly selected clinical S. aureus isolates representing various clones. We characterized the ability of isolates to adhere to fibronectin, fibrinogen, collagens IV and VI, to invade host cells and to induce cell death in vitro. We analysed the possible association of these results with characteristics such as methicillin resistance, Panton–Valentine leucocidin (PVL) positivity and clonality. The S. aureus isolates displayed diversity in their abilities to adhere to various human ligands. All isolates were highly invasive except for ST121. PVL-negative isolates were significantly more invasive than the PVL-positive isolates (p 0.004). Isolates of CC5, CC30 and CC121 were non-cytotoxic, whereas isolates of CC22, CC8, CC15, CC45 and CC88 were very cytotoxic. No statistical association was identified between cell death and methicillin resistance, bacterial PVL status, clonality or patient HIV status. The vast majority of isolates were invasive and induced significant cell death. PVL-negative isolates were more invasive than PVL-positive isolates, while methicillin-resistant isolates were not found to be more invasive or cytotoxic than methicillin-susceptible isolates.
Highlights
Staphylococcus aureus is a facultative intracellular bacterium and a significant human pathogen
It possesses many surface factors that aid with host colonization and cellular invasion as well as secreted virulence factors involved in host cell death induction [1]
The aim of this research was to investigate the abilities of S. aureus isolates representative of clones causing infection in our patient population to adhere to immobilized ligands, to investigate their cellular invasiveness and host cell death induction abilities, and to identify any associations between adherence, invasiveness or cell death induction and bacterial characteristics, such as methicillin resistance, Panton–Valentine leucocidin (PVL) positivity and clonality
Summary
Staphylococcus aureus is a facultative intracellular bacterium and a significant human pathogen. Numerous bacterial surface proteins can be used during the process of adherence to host ligands and are called ‘microbial surface components recognizing adhesive matrix molecules’ or MSCRAMM, such as fibronectin-binding proteins A and B [6], staphylococcal protein A and clumping factors Another group of bacterial proteins which is involved in this process are the SERAM molecules, or the ‘secreted expanded repertoire adhesive molecules’ [7], such as the extracellular adherence protein (Eap). Adherence to fibronectin by S. aureus can be mediated by fibronectin-binding proteins A and B (FnbA/B), which aid in the binding of the organism to plasma clots [8] Both genes are fundamental for the invasion of eukaryotic cells [7]. Staphylococcus aureus possess two distinct fibrinogen-binding proteins, namely clumpingfactor A and B, of which clumping factor A is mainly used to adhere to substances containing fibrinogen [8]
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