Staphylococcus aureus Hyaluronidase Is a CodY-Regulated Virulence Factor

Abstract

Staphylococcus aureus is a Gram-positive pathogen that causes a diverse range of bacterial infections. Invasive S. aureus strains 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 ␤-1,4 glycosidic bond. In the study described in this report, we have investigated the regulation and contribution of this enzyme to S. aureus pathogenesis. Using the Nebraska Transposon Mutant Library (NTML), we identified eight insertions that modulate extracellular levels of HysA activity. Insertions in the sigB operon, 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 of hysA, the repression of HysA production was lost, suggesting that CodY is a direct repressor of hysA expression. To determine whether HysA is a virulence factor, a ⌬hysA mutant of a community-associated methicillin-resistant S. 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 that S. aureus hyaluronidase is a CodY-regulated virulence factor.

Hyaluronan Modulation Impacts Staphylococcus aureus Biofilm Infection

“…Given that S. aureus systemic infections can readily arise from skin or mucosal sites, it is reasonable to infer that the active invasion of host tissue is a key facet of S. aureus pathogenicity. Consistent with this view, S. aureus hysA mutants exhibit a hypovirulent phenotype in models of acute pulmonary and cutaneous infection (22,23). In addition, hyaluronidases from numerous Gram-positive pathogens have been shown to promote tissue penetrance of bacteria, toxins, and large-molecular-mass dyes in the vicinity of the challenge site (25,57).…”

“…Within the context of intense homeostatic stress such as nutrient deprivation, HysA might play a multifunctional role as a mediator of biofilm dispersal and tissue invasion, which are both vital to a recolonization effort. Coupling the proposed HysA behaviors with nutritional distress, we recently showed that the global regulator CodY represses hysA expression (22) in response to nutrient levels in the cell. Thus, CodY could control biofilm dissemination in a nutrient-dependent manner and facilitate S. aureus survival when facing a resource-depleted environment (i.e., nutritional immunity [52]).…”

“…S. aureus produces a hyaluronidase, encoded by the gene hysA, that is conserved across all S. aureus lineages (21). Our group and others have shown that HysA is a virulence factor in a variety of infection models (22,23), which is thought to be due to its role in facilitating local spread of the infection. However, it has become increasingly clear that hyaluronidases have additional functions that benefit pathogen survival in the host.…”

Staphylococcus aureus: Immunopathogenesis and Human Immunity

“…Mice infected with mutant strains carrying mutation of the CodY binding box exhibited a 4-log-unit reduction in bacterial burden in their lungs, reduced lung pathology and increased levels of pulmonary hyaluronic acid, compared to mice infected with the wild-type, parent strain. These results can give insight into the possible reduction of the strain virulence, especially in patients with lung infection (25).…”

Resilience in the Face of Uncertainty: Sigma Factor B Fine-Tunes Gene Expression To Support Homeostasis in Gram-Positive Bacteria

“…The transcription of S. aureus hyaluronidase, encoded by hysA, is controlled by the accessory gene regulator (Agr) quorum-sensing system (86,87). Work by Ibberson et al (88) suggests that B (as well as CodY) downregulates agr and therefore indirectly and negatively controls hyaluronidase activity in S. aureus. Based on the observation that sigB and codY mutants express higher levels of hyaluronidase activity, hysA is proposed to be under direct positive control by the effectors of Agr and negatively modulated by CodY and B (88).…”