Suppression of biofilm formation in Staphylococcus aureus by targeting Staphylococcal accessory regulator X expression using siHybrids

Abstract

Nosocomial infections are becoming increasingly prevalent due to the ability of bacteria to adhere to implanted medical devices. Over 600,000 prosthetic joint replacements are performed yearly in the United States, with approximately 2% of those cases developing infections. The implantation of cardiac valves has increased by 42%, but with a corresponding 210% increased infection rate of Staphylococcus gram‐positive bacteria. S. aureus accounts for up to 73% of these infections. The ability of bacteria to adhere to the hard surfaces of medical devices is due to production of a biofilm, which is initiated by the secretion of polysaccharide intercellular adhesion (PIA) molecules. In Staphylococcal species, PIA production and regulation is controlled by the icaADBC (ica) operon, a sequence of four genes that are all involved in the production of PIA molecules. The icaA gene produces an N‐acetyl‐glucosaminyltransferase like protein, with the icaD gene product enhancing its activity. The icaC gene encodes a membrane protein that initiates the production of longer chains of polysaccharides and their translocation to the cell surface, while the icaB product is responsible for deacetylating the poly‐N‐acetylglucosamine ica transcript.The ica locus has several known activators and repressors. One of the best‐characterized factors is the staphylococcal accessory regulator A (sarA), which functions as an activator of the locus. Research has shown that when sarA transcripts are suppressed, biofilm growth is repressed. SarX is closely homologous to SarA and is believed to share similar, activating functions; however, the product of the sarX locus is not as well characterized. We investigated if sarX function can be suppressed through the use of sequence specific siHybrids, and if so, whether suppressing sarX has a repressing effect on biofilm development in Staphylococcus aureus. We hypothesized that suppression of sarX will cause repression of biofilm formation. S. aureus was passively transformed with siHybrids and the resulting biofilm growth was measured using crystal violet staining. RNA was isolated from transformed bacteria to determine if levels of sarX transcripts had changed. SiHybrid treatment groups were compared to three controls: an untreated S. aureus positive control, a sterile media negative control, and an E. coli negative control. The results indicated that repressing biofilm growth through the suppression of sarX transcripts with siHybrids led to a seventeen to forty percent decrease in biofilm formation. An ANOVA with a p‐value of 0.5 was used to determine significance. Inhibition of S. aureus at the molecular level, by targeting the RNA transcripts of the icaADBC activator, sarX, presents a novel treatment for nosocomial infections.