Inhibitory effects of chitosan on Cronobacter malonaticus cells and biofilm formation

Cronobacter malonaticus is one of foodborne pathogens associated with life-threating infections in newborns and adults. Controlling C. malonaticus in food samples is important to achieve microbial safety. In this study, inhibitory effects of chitosan with low molecular weight (LMW) and high molecular weight (HMW) on growth of C. malonaticus cells and biofilm formation were determined. Results indicated that minimum inhibitory concentration (MICs) of 0.165% (w/v) and 0.225% (w/v) for LMW and HMW were observed respectively. Compared to control group, both LMW and HMW with 1/4 MIC and 1/2 MIC could significantly inhibit growth of C. malonaticus cells, and caused the release of intracellular nuclear acid of C. malonaticus cells. Furthermore, the cell shrinkage, injury of cell membrane, the disruption of cell integrity, and deformation of cells were also found by scanning electron microscope (SEM) and transmission electron microscope (TEM) after treatment of 1/2 MIC of LMW and HMW chitosan. Finally, we demonstrated that chitosan with LMW and HMW significantly inhibited the biofilm formation in C. malonaticus compared to control groups. The findings provide valuable information for application of chitosan to control C. malonaticus in food samples.