Roles of outer membrane protein W (OmpW) on survival, morphology, and biofilm formation under NaCl stresses in Cronobacter sakazakii

Cronobacter sakazakii is an important foodborne pathogen associated with rare but severe infections through consumption of powdered infant formula. Tolerance to osmotic stress in Cronobacter has been described. However, the detailed factors involved in tolerance to osmotic stress in C. sakazakii are poorly understood. In this study, roles of outer membrane protein W (OmpW) on survival rates, morphologic changes of cells, and biofilm formation in C. sakazakii under different NaCl concentrations between wild type (WT) and OmpW mutant (ΔOmpW) were determined. The survival rates of ΔOmpW in Luria-Bertani medium with 3.5% or 5.5% NaCl were reduced significantly, and morphological injury of ΔOmpW was significantly increased compared with survival and morphology of WT. Compared with biofilm formation of the WT strain, biofilms in ΔOmpW were significantly increased in Luria-Bertani with 3.5% or 5.5% NaCl using crystal violet staining assay after 48 and 72 h of incubation. Detection of biofilms using confocal laser scanning microscopy and scanning electron microscopy further confirmed the changes of biofilm formation under different NaCl stresses. This study demonstrates that OmpW contributes to survival of cells in planktonic mode under NaCl stresses, and biofilm formation is increased in ΔOmpW in response to NaCl stress.