Hyaluronidase expression and biofilm involvement in Staphylococcus aureus UAMS-1 and its sarA, agr and sarA agr regulatory mutants

Abstract

In a previous study, two proteins identified as hyaluronidases were detected in spent media by MS and found to be in greater quantity in the sarA and sarA agr mutant strains when compared with the parent and agr mutant strains of Staphylococcus aureus UAMS-1. In the present study, spent media and total RNA were isolated from UAMS-1 and its regulatory mutants and analysed for hyaluronidase activity and steady-state hyaluronidase (hysA) RNA message levels. Hyaluronidase activity was observed throughout all time points examined regardless of the regulatory effects of sarA and agr but activity was always substantially higher in the sarA and sarA agr mutant strains than in the UAMS-1 parent and agr mutant strains. Northern analysis did not detect hysA message for either the UAMS-1 parent or the agr mutant strains at any time point examined, while steady-state hysA message levels were detected throughout growth for the sarA mutant strain, but only at exponential and early post-exponential growth for the sarA agr mutant strain. An in vitro biofilm plate assay, pre-coated with human plasma as a source of hyaluronic acid, demonstrated no significant increase in biofilm for a sarA mutant strain of S. aureus UAMS-1 defective in hyaluronidase activity when compared with the sarA mutant strain. These data indicate that, while hysA message levels and hyaluronidase activity are elevated in the sarA mutant strains of S. aureus UAMS-1, the increase in activity did not contribute to the biofilm-negative phenotype observed in the sarA mutant strain of S. aureus UAMS-1.