Staphylococcus aureus encodes for a secreted hyaluronidase, hysA. Hyaluronidases are bacterial enzymes that cleave hyaluronic acid (HA) at the β-1,4 glycosidic bond, yielding unsaturated disaccharides. Initially, little was known about the regulation of this enzyme as well as its roles in S. aureus physiology and pathogenesis. The goal of this dissertation was to determine the regulation of hysA, and to determine the biological and physiological roles of this enzyme.
Studies presented in Chapter II focus on determining the regulation of hysA and role of hysA in S. aureus pathogenesis. By screening the Nebraska Transposon Mutant Library (NTML) we identified 8 mutations that significantly altered HysA activity. Further analysis revealed that CodY directly represses hysA by binding to the CodY consensus binding sequence upstream of the hysA translational start site. Additionally, we found that a hysA mutant was attenuated in a neutropenic murine pneumonia model of infection and that there was reduced degradation of HA in the lungs of mice infected with the hysA mutant compared to wildtype by immunofluorescence.
Studies presented in Chapter III focus on examining if HA can be incorporated into the S. aureus biofilm matrix and if HysA is involved in biofilm dispersal. We show that HA is incorporated into the biofilm matrix both in vitro and in vivo by confocal microscopy and HA ELISA. Additionally, we found that HA can enhance biofilm formation of the hysA mutant as well as other staphylococcal species in vitro. We show that induction of hysA can prevent biofilm formation in the presence of HA and that exogenous addition of purified HysA can disperse established HA containing biofilms. Finally, we found that a hysA mutant has reduced dissemination in an implant-associated infection model. Together these studies support our hypothesis that HA is incorporated into staphylococcal biofilms and that HysA is involved in dispersing S. aureus from the biofilm.