The hyaluronate lyase of Staphylococcus aureus – a virulence factor?

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Abstract
The hyaluronate lyase (HL) gene ofStaphylococcus aureus8325-4 (hysA) was inactivatedin vitrowith the insertion of the erythromycin determinant,ermC, from plasmid pE194. ThehysA : : ermCmutation was introduced intoS. aureusvia a temperature-sensitive shuttle vector, where it underwent homologous recombination with the wild-type (w.t.) allele. The insertion ofermCin the chromosomalhysAlocus was confirmed by Southern blot hybridization and the loss of HL activity was demonstrated macroscopically by a plate assay. The importance of HL for pathogenicity was assessed by comparing the virulence of the HL−mutant strain to that of the w.t. in an established mouse abscess model ofS. aureusinfection. A significantly higher cell recovery was obtained from lesions infected with the w.t. strain compared to the lesions infected with the HL−strain (P=0·01). Although the lesion areas from both groups were not significantly different (P=0·9) they were of different morphology. A colorimetric assay was used to measure HL activity from culture supernatants of theS. aureus8325-4 strains w.t., WA250 (agr) and PC1839 (sar) grown in a chemically defined medium. HL activity reached a maximum in the w.t. strain during mid-exponential phase (t=5 h) and while it showed a 16-fold decrease in theagrmutant it increased 35-fold in thesarmutant background. These results strongly suggest that HL is a virulence factor which is important in the early stages of subcutaneous infections.