Transcriptional Regulation oficaADBCby both IcaR and TcaR inStaphylococcus epidermidis
ABSTRACTS. epidermidisis a primary cause of biofilm-mediated infections in humans due to adherence to foreign bodies. A major staphylococcal biofilm accumulation molecule is polysaccharide intracellular adhesin (PIA), which is synthesized by enzymes encoded by theicaADBCoperon. Expression of PIA is highly variable among clinical isolates, suggesting that PIA expression levels are selected in certain niches of the host. However, the mechanisms that govern enhancedicaADBCtranscription and PIA synthesis in these isolates are not known. We hypothesized that enhanced PIA synthesis in these isolates was due to function of IcaR and/or TcaR. Thus, twoS. epidermidisisolates (1457 and CSF41498) with differenticaADBCtranscription and PIA expression levels were studied. Constitutive expression of bothicaRandtcaRdemonstrated that both repressors are functional and can completely repressicaADBCtranscription in both 1457 and CSF41498. However, it was found that IcaR was the primary repressor for CSF41498 and TcaR was the primary repressor for 1457. Further analysis demonstrated thaticaRtranscription was repressed in 1457 in comparison to CSF41498, suggesting that TcaR functions as a repressor only in the absence of IcaR. Indeed, DNase I footprinting suggests IcaR and TcaR may bind to the same site within theicaR-icaAintergenic region. Lastly, we found mutants expressing variable amounts of PIA could rapidly be selected from both 1457 and CSF41498. Collectively, we propose that strains producing enhanced PIA synthesis are selected within certain niches of the host through several genetic mechanisms that function to repressicaRtranscription, thus increasing PIA synthesis.IMPORTANCEStaphylococcus epidermidisis a commensal bacterium that resides on our skin. As a commensal, it protects humans from bacterial pathogens through a variety of mechanisms. However, it is also a significant cause of biofilm infections due to its ability to bind to plastic. Polysaccharide intercellular adhesin is a significant component of biofilm, and we propose that the expression of this polysaccharide is beneficial in certain host niches, such as providing extra strength when the bacterium is colonizing the lumen of a catheter, and detrimental in others, such as colonization of the skin surface. We show here that fine-tuning oficaADBCtranscription, and thus PIA synthesis, is mediated via two transcriptional repressors, IcaR and TcaR.