Staphylococcus aureus Hyaluronidase Is a CodY-Regulated Virulence Factor

Abstract

ABSTRACTStaphylococcus aureusis a Gram-positive pathogen that causes a diverse range of bacterial infections. InvasiveS. aureusstrains secrete an extensive arsenal of hemolysins, immunomodulators, and exoenzymes to cause disease. Our studies have focused on the secreted enzyme hyaluronidase (HysA), which cleaves the hyaluronic acid polymer at the β-1,4 glycosidic bond. In the study described in this report, we have investigated the regulation and contribution of this enzyme toS. aureuspathogenesis. Using the Nebraska Transposon Mutant Library (NTML), we identified eight insertions that modulate extracellular levels of HysA activity. Insertions in thesigBoperon, as well as in genes encoding the global regulators SarA and CodY, significantly increased HysA protein levels and activity. By altering the availability of branched-chain amino acids, we further demonstrated CodY-dependent repression of HysA activity. Additionally, through mutation of the CodY binding box upstream ofhysA, the repression of HysA production was lost, suggesting that CodY is a direct repressor ofhysAexpression. To determine whether HysA is a virulence factor, a ΔhysAmutant of a community-associated methicillin-resistantS. aureus(CA-MRSA) USA300 strain was constructed and found to be attenuated in a neutropenic, murine model of pulmonary infection. Mice infected with this mutant strain exhibited a 4-log-unit reduction in bacterial burden in their lungs, as well as reduced lung pathology and increased levels of pulmonary hyaluronic acid, compared to mice infected with the wild-type, parent strain. Taken together, these results indicate thatS. aureushyaluronidase is a CodY-regulated virulence factor.