Abstract
The epithelium provides a crucial barrier to infection, and its integrity requires efficient wound healing. Bacterial cells and secretomes from a subset of tested species of bacteria inhibited human and porcine corneal epithelial cell migration in vitro and ex vivo. Secretomes from 95% of Serratia marcescens, 71% of Pseudomonas aeruginosa, 29% of Staphylococcus aureus strains, and other bacterial species inhibited epithelial cell migration. Migration of human foreskin fibroblasts was also inhibited by S. marcescens secretomes indicating that the effect is not cornea specific. Transposon mutagenesis implicated lipopolysaccharide (LPS) core biosynthetic genes as being required to inhibit corneal epithelial cell migration. LPS depletion of S. marcescens secretomes with polymyxin B agarose rendered secretomes unable to inhibit epithelial cell migration. Purified LPS from S. marcescens, but not from Escherichia coli or S. marcescens strains with mutations in the waaG and waaC genes, inhibited epithelial cell migration in vitro and wound healing ex vivo. Together these data suggest that S. marcescens LPS is sufficient for inhibition of epithelial wound healing. This study presents a novel host-pathogen interaction with implications for infections where bacteria impact wound healing and provides evidence that secreted LPS is a key factor in the inhibitory mechanism.
Highlights
Since P. aeruginosa and S. marcescens are the most common causes of contact-lens associated keratitis and are commonly isolated from chronic wounds[8], we tested a panel of P. aeruginosa and S. marcescens strains used in laboratory research and derived from clinical keratitis for the capacity to prevent corneal epithelial cell migration
The cornea is a relevant and useful model to study the impact of bacteria on wound healing
We hypothesized that bacterially derived factors modulate epithelial cell behavior, corneal epithelial wound healing
Summary
Secretomes from 15 out of 16 (94%) of the tested keratitis strains of S. marcescens inhibited HCLE cell migration (Supplementary Fig. S1). Based on Calcein AM staining several of the keratitis strains were cytotoxic when 500 μ l of normalized secretome was added to the wells, but inhibited migration without killing the HCLE cells when used at 25 μ l per well (Supplementary Fig. S1). Treatment of physical wounds with S. marcescens secretomes resulted in inhibited corneal cell migration (Supplementary Fig. S2).
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