1 Translational Renal Research Group, Harry Perkins Institute of Medical Research, Perth, Western Australia; 2 Renal Unit, Sir Charles Gairdner Hospital, Perth, Western Australia

Aim: To define the early changes in mesothelial gene expression in response to infection with Staphylococcus epidermidis.

Background: Peritonitis is responsible for the majority of peritoneal dialysis treatment failures and significant morbidity and mortality. Gram positive microorganisms account for 60-70% of PD peritonitis cases, with Staphylococcus epidermidis the most commonly isolated pathogen. Mesothelial cells lining the abdominal cavity orchestrate the initial host responses to infection however the effects of infection on mesothelial cells are not well characterized.

Methods: We systematically investigated the early mesothelial cell responses to infection with clinical and reference isolates of S. epidermidis using primary mesothelial cells and the mesothelial cell line Met-5A. Confluent mesothelial cells were challenged with 107 colony forming units of S. epidermidis for 1 hour before RNA was isolated using the RNeasy Plus Mini kit. Initial analyses were performed using an unbiased whole genome microarray, followed by assessment of a targeted panel of genes known to be involved in the human antibacterial response. Findings were then validated using qPCR.

Results: We identified 38 differentially regulated genes (adj. p-value < 0.05) representing 35 canonical pathways after 1 hour exposure to S. epidermidis. Including a number of genes not previously described in mesothelial cell responses to infection. Marked heterogeneity was observed between different clinical isolates of S. epidermidis, and between Met-5A and primary mesothelial cells.

Conclusions: Multiple unique pathways are activated within 1 hour by reference strains and clinical isolates of S. epidermidis. Identifying key differences in these responses and how they vary over time between common clinical pathogens will enhance our understanding of mesothelial cell biology and may define novel therapeutic targets.

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