Cytotoxic activity and adherence of S. marcescens to epithelial cells

Serratia marcescens can be found in the subgingival biofilm of certain subjects and these oral isolates are genotypicaly more similar to diseased associated than to environmental strains, suggesting that the oral cavity could be a reservoir of potentially pathogenic isolates. However, the virulence factors associated with oral isolates are not known. Objectives: to compare the adhesion ability and cytotoxic activity of oral isolates of S. marcescens on KB epithelial cells with these traits in isolates from human diseases and environment. Methods: 48 isolates of S. marcescens (8 environmental- E, 18 from extra-oral infections-EO, and 21 from subgingival plaque-O) were evaluated in a cytotoxicity assay. Culture supernatants from standardized cultures (~ 1.4 x 109 CFU/ml) were added to KB monolayers at 60-70% confluence. After 96 h of incubation, cell viability was determined by staining with neutral red and absorbance measured at 540nm. Adhesion of 55 isolates (10 E, 22 EO and 23 O) was evaluated by inoculating 2.2 x 108CFU S. marcescens/ml to KB cells monolayer in 24-wells tissue plates. After 2 h incubation, the number of adherent bacteria was determined by viable counts, and the percentage of adherent cells estimated. Results: The cytotoxic effect was variable among the isolates. Only 6 isolates (2 E, 1 EO and 3 O) were highly cytotoxic, and there was no difference in the cytotoxic effect according to the origin of the strain (Mann-Whitney, p>0.05) . All strains were able to adhere to KB cells. 15 of 23 oral (69.6%), 13 of 22 extraoral (59.0%) and 3 of 10 environmental isolates (30.0%) exhibited >1.5 x 105 adherent cells/well. Conclusion: S. marscencens isolates from the oral cavity differ in their ability to adhere to epithelial cells and in their cytotoxic activities, however these traits can not be considered as markers for diseased-associated strains.

CNPq 110845/2005-6