JMM Editor’s Choice: Serratia marcescens cytoxicity

This study brings original findings about pathogenicity of Serratia marcescens, an opportunistic bacterial pathogen responsible for numerous hospital-acquired infections (particularly pneumonia) and ocular infections. The authors investigated mechanisms of cytotoxicity against human epithelial cells mediated by a major regulator of virulence (FlhDC) in S. marcescens. They demonstrated that two FlhDC-regulated genes (phlA and shlA coding for phospholipase A and cytolysin ShlA, respectively) were cytotoxic to airway and ocular surface cell lines. They showed that ShlA was the key determinant of FlhDC-mediated cytotoxicity whereas differences were observed in patterns of human epithelial cell susceptibility to PhlA.

Differential susceptibility of airway and ocular surface cell lines to FlhDC-mediated virulence factors PhlA and ShlA from Serratia marcescens

Serratia marcescens is a bacterial pathogen that causes ventilator-associated pneumonia and infections of the eyes. Two proteins, FlhC and FlhD, have been implicated as virulence determinants. However, the mechanisms by which these proteins regulate bacterial cytotoxicity to different cell types remains unclear.

Wild-type and mutant bacteria and bacterial secretomes were used to challenge airway and ocular surface cell lines. Pathogenesis was further tested using a Galleria mellonella infection model.

This study indicates that the S. marcescens FlhDC-regulated secreted proteins PhlA and ShlA, but not flagellin, are cytotoxic to airway and ocular surface cells and demonstrates differences in human epithelial cell susceptibility to PhlA.