B-248. Group A Streptococcus Forms Complex Surface-Attached Communities In Vitro and In Vivo Which Are Suggestive of a Biofilm

A. L. Roberts, C. D. Doern, R. C. Holder, J. Nelson, W. Hong, W. E. Swords, S. D. Reid;
Wake Forest Univ. Hlth. Sci., Winston-Salem, NC.

Group A Streptococcus (GAS) is a Gram-positive pathogen which is a common etiological agent of upper respiratory tract infections. Penicillin is the preferred antimicrobial therapy for GAS; however, since the 1970s, approximately 30% of GAS cases have resisted penicillin treatment. The reason for this high failure rate is unknown. This failure, combined with the ability of GAS to persist in a carrier state, suggests a mechanism of protection. Recent evidence suggests that GAS may form biofilms, a community of microorganisms characterized by an adhesive and perhaps protective matrix. Biofilms produced by other pathogenic species have been linked to chronic infection states such as carriage, and biofilms have been found to be inherently tolerant to antibiotics. Previous work in our laboratory led to the identification of a transcriptional regulator, Srv (streptococcal regulator of virulence). Microarray analysis of the Δsrv strain indicated that the transcription of ~50 genes encoding proven and putative extracellular proteins was down regulated, suggesting that the Δsrv strain may display an altered biofilm phenotype. To test this hypothesis, static and continuous flow models of biofilm formation were used to compare biofilm phenotypes of clinical GAS isolates and the Δsrv strain. Biofilm formation varied among the clinical strains tested and microscopic analyses revealed the presence of 3D structures encased in an extracellular matrix. LIVE/DEAD staining indicated the presence of living cells within the biofilm. Biochemical analyses demonstrated that extracellular DNA and protein were needed for GAS biofilm formation. The Δsrv strain was limited in its ability to form biofilms, a trait that was restored following complementation in trans. To test the hypothesis that similar structures could be formed in vivo, a chinchilla model of otitis media was used. Robust surface attached streptococcal communities were observed in the chinchilla middle ear. Taken together, these results indicate that GAS exhibits the capacity to form biofilms in vitro and in vivo and that Srv may have a role in regulating biofilm development.