Efficient inhibition of Cronobacter biofilms by chitooligosaccharides of specific molecular weight

Biofilms enable Cronobacter spp. to contaminate food, infect infants and resist different environmental stresses, especially desiccation, which is the main reason why Cronobacter can survive in powdered infant formula (PIF) for a long time. Considering the high lethality of Cronobacter infection in infants, it is important to find efficient and safe inhibitors of Cronobacter biofilms. In this study, we found that chitooligosaccharides (COS) with a molecular weight of 2000 Da efficiently inhibited Cronobacter biofilms, especially in skim milk broth. The minimum biofilm inhibitory concentration (MBIC₇₇) of COS was as low as 20 μg/mL, which is lower than that reported in most previous studies. Besides, the elimination rate of COS for Cronobacter mature biofilms was 50% when the concentration was 10 mg/mL. COS could significantly inhibit soluble polysaccharide secretion and biofilm cell growth, as well as change the cell membrane permeability of Cronobacter. These might be the possible reasons for COS's efficient inhibition of Cronobacter biofilms. However, during the inhibition, five important genes-related to biofilm formation-flhD, flgJ, luxR, ompA, and wcaJ-were all up-regulated after COS treatment, except the gene bcsA. In summary, our findings showed that COS could be used as an efficient and safe inhibitor against Cronobacter biofilms for better control of Cronobacter contamination and infection.