PURPOSE. The aim of the work presented here was to establish the response of a corneal epithelial cell line (hTCEpi) to protein extracted from a bacterium (Bacillus oleronius) previously isolated from a Demodex mite from a rosacea patient. METHODS. The response of the corneal epithelial cell line to Bacillus proteins was measured in terms of alterations in cell migration and invasiveness. Changes in the expression of metalloproteinase genes and proteins were also assessed. RESULTS. The results indicated increased cell migration (14.5- fold, P ¼ 0.001) as measured using 8-lm PET inserts (BD Falcon) in a transwell assay and invasiveness (1.7-fold, P ¼ 0.003) as measured using 8-lm Matrigel (BD Biocoat) invasion inserts in a 24-well plate assay format, following exposure to the Bacillus proteins. Cells exposed to the Bacillus protein showed a dose-dependent increase in expression of genes coding for matrix metalloprotease (MMP)-3 (61-fold) and MPP-9 (301-fold). This dose-dependent increase in gene expression was also reflected in elevated levels of MMP-9 protein (1.34- fold, P ¼ 0.033) and increased matrix metalloprotease activity (1.96-fold, P¼0.043) being present in the culture supernatant. Cells also displayed reduced levels of b-integrin (1.25-fold, P ¼ 0.01), indicative of increased motility and elevated levels of vinculin (2.7-fold, P ¼ 0.0009), suggesting altered motility. CONCLUSIONS. The results indicate that exposure of corneal epithelial cells to Bacillus proteins results in an aberrant wound healing response as visualized using a scratch wound assay. These results suggest a possible link between the high density of Demodex mites on the eyelashes of ocular rosacea patients and the development of corneal ulcers. (Invest Ophthalmol Vis Sci. 2012;53:3250–3259) DOI:10.1167/ iovs.11-9295