Microbial Pathogenesis

Microbial Pathogenesis

We study the pathogenesis of microbes at a skin and mucosal surfaces to identify novel targets for therapy and disease prevention.

 


Defining key signaling pathways utilized by secreted staphylococcal toxins to induce inflammatory responses in epithelial cells.

Published microarray data was used to identify a network of genes up-regulated by human vaginal epithelial cells (HVECs) in response to Toxic Shock Syndrome Toxin-1 (TSST-1).

Laboratory experiments revealed that the ADAM17 proteolytic targets, amphireglin (AREG), transforming growth factor α (TGFα), syndecan-1 (SDC1), and tumor necrosis factor receptor 1 (TNFR1), are shed from human vaginal epithelial cells (HVECs) in response to TSST-1. TAPI-1 (an ADAM inhibitor) completely abrogates all observed shedding and the production of the cytokine interleukin-8 (IL-8). Knock-down studies show that ADAM17, but not the closely related ADAM10, is required for AREG, TGFα, and TNFR1 shedding. Both ADAM10 and ADAM17 contribute to SDC1 shedding and IL-8 production by HVECs in response to TSST-1. EGFR signaling is critical for up-regulation of IL-8 at the transcriptional level in response to TSST-1 and is also necessary for AREG, TGFα, and TNFR1 shedding. The model, depicted at right, describes the interactions of TSST-1, ADAMs, and the EGFR that lead to establishment of a proinflammatory positive feedback loop in epithelial cells, suggesting a localized role for staphylococcal superantigens in the initial stages of Toxic Shock Syndrome (TSS)


Role of virulence factors in mucosal biofilm formation

An ex vivo model of microbial biofilm was developed, in response to the need for a model that more closely simulates the host-pathogen interaction, using porcine mucosa as a substrate and infecting with important Gram positive and Gram negative pathogens, such as methicillin-resistant Staphylococcus aureus (MRSA) and Acinetobacter baumannii. Biofilms are sessile colonies of bacteria which adhere to and persist on organic and inert surfaces. The ability of bacteria to form biofilms is considered a virulence factor and, in fact, is central to the pathogenesis of some organisms. Clinically, biofilms are considered a primary cause of a majority of infections and bacteria in a biofilm are known to be significantly more resistant to antimicrobial treatment. However, the vast majority of the data on biofilm formation comes from traditional microtiter-based or flow displacement assays with no consideration given to host factors. These assays, which have been a valuable tool in high-throughput screening for biofilm-related factors, do not mimic a host-pathogen interaction and may contribute to an inappropriate estimation of the role of some factors in clinical biofilm formation.

We recently described an essential role for S. aureus alpha-toxin in mucosal biofilm formation (see publications).
SEM micrograph of MRSA biofilm on porcine vaginal mucosa (10,000 x)