Serratia marcescens invasion in epithelial cells: more than one bacterium per CHO cell?

MEDIAVILLA, M.G.; GARCÍA VÉSCOVI, E

Rosario

Congreso; L Reunión Anual de SAIB; 2014

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular

More than one Serratia marcescens (S.m.) are often seen inside CHO cells at short times p.i. (60 min) suggesting that two or more bacteria could simultaneously enter one CHO cell. Thus, we conducted invasion experiments combining two strains of wild type (wt) S.m. expressing GFP or mCherry. We compared invasion rates of these strains separately and in a 1:1 mix by fluorescence microscopy and measuring C.F.U.s. We observed the presence of both S.m./GFP and S.m./mCherry inside one CHO cell indicating that more than one bacterium is able to invade the same epithelial cell either in a cooperative or an independent uptake event. Moreover, percentages of invasion were similar for both strains alone (p>0.05) as well as in co-infection experiments where they resulted half of the total for each strain (p>0.05). Using this attribute, and having previously established that the flagellum is required for an initial bacterial attachment to the epithelial cell, we attempted to rescue S.m. flhD mutant defective in flagella expression and to infect CHO cells. The rates of invasion of S.m. flhD and wt were not modified by the presence of the other strain suggesting that the simultaneous entry of bacteria is not cooperative and the flagellar structure attached to the envelope of each invading bacterium is required to exert an anchoring function preceding the internalization process to the host cell.