Streptococcal colonization of host mucosal surfaces: A study of biofilm formation and dispersal

Group A Streptococcus (GAS) is a Gram-positive pathogen that is the causative agent of a variety of human diseases. Infections include pharyngitis, otitis media, sepsis, a toxic-shock syndrome, necrotizing fasciitis, and the postinfectious sequelae acute rheumatic fever and acute rheumatic heart disease. Thus, rather than exploit a singular niche, GAS has evolved to colonize and disseminate within several physiologically distinct anatomical sites of the human host. Such versatility requires the ability to coordinately regulate the expression and production of numerous factors in rapid response to host and environmental signals in order to facilitate attachment, replication, and eventual dispersal (dissemination). Experimental evidence suggests that GAS forms biofilms during the colonization of a surface. A biofilm is a bacterial sessile community encased in an extracellular matrix and attached to a substratum or interface. Biofilms are inherently tolerant to host defenses and antibiotic therapies and often involved in chronic illness due to impaired clearance. It is estimated that upwards of 60% of all bacterial infections involve biofilms. Presently, little is known about GAS biofilm matrix composition, or the regulation of biofilm formation and dispersal.;Our evidence indicated that allelic replacement of the GAS transcriptional regulator srv resulted in a significant reduction in GAS biofilm formation. Thus, we hypothesized that srv is required for GAS biofilm formation, and that biofilms are required for colonization of the host mucosa. Our research revealed that complementation of srv in the srv mutant background restored biofilm formation indicating that srv is required for biofilm formation. Furthermore, we discovered that the biofilm null phenotype of the srv mutant was due to the constitutive production of a GAS cysteine protease (SpeB). Allelic replacement of speB in the srv mutant background or chemical inhibition of SpeB restored GAS biofilm formation. We further demonstrated that GAS formed biofilms in vivo in both chinchillas and human patients. Finally, we demonstrated that biofilms may not be required for infection of the host, but that biofilm dispersal may lead to more severe disease. Under this model, Srv regulation of SpeB mediates biofilm formation/dispersal.