Biochemical and genetic characteristics of Cronobacter sakazakii biofilm formation

Cronobacter sakazakii is a wide-spread opportunistic foodborne pathogen that can form biofilms on a number of different substances, creating food safety risk. However, there is little information about biofilm characteristics for this species. In this study, biofilm formation of 14 foodborne C. sakazakii strains was examined. Transposon mutants of the strain (IQCC10423), the isolate with the greatest biofilm activity, were prepared. A total of 12 mutants were developed with >40% reduction in biofilm formation ability. Eight of these mutants were successfully sequenced with genes putatively identified for: biofilm formation, fundamental cellular processes, phage tail complete protein and uncertain functional protein. The morphology of the biofilm showed that the wild type strain formed a thick biofilm and mutants formed less extracellular polymeric substances (EPSs). Raman spectroscopy was employed to confirm less biofilm formation by different bacterial mutants and demonstrate a similar chemical composition, but different contents of EPS. Wild type biofilms contained a high level of carotenoids, with the distribution of carotenoids mapped using confocal Raman imaging. We demonstrate that various selective functional genes are responsible for the forming ability of C. sakazakii biofilms, which may have the potential to cause risks to food safety.