Biofilm formation and associated gene expression changes in Cronobacter from cereal related samples in China

Cronobacter is an important foodborne pathogen that can cause severe neonatal meningitis, necrotizing enterocolitis, and bacteremia. Currently, there is limited knowledge of biofilm formation in Cronobacter. In the present study, biofilm formation ability and associated gene expression changes in Cronobacter from cereal related samples was carried out systematically. Our results from 307 Cronobacter isolates analyzed for 48 h showed strong biofilm-forming ability in 14 strains (4.6%), moderate in 47 strains (15.3%), weak in 142 strains (46.2%), and no such ability in the remaining 104 strains (33.9%). Further studies on five strains with strong biofilm-forming ability showed that maximum biofilm formation in Cronobacter occurred after 24 h of cultivation, reaching a peak around 48 h-72 h, reducing gradually thereafter. Kyoto encyclopedia of genes and genomes (KEGG) analysis revealed that differentially expressed genes (DEGs) involved in flagellar assembly, oxidative phosphorylation, ribosome, photosynthesis, O-Antigen nucleotide sugar biosynthesis, citrate cycle (tricarboxylic acid cycle, TCA) and bacterial chemotaxis were enriched in biofilm forming cells. The genes involved these enrichment pathways were mostly downregulated when compared to planktonic cells. Several transcriptional regulator genes such as csrA and bolA, and the cell surface composition regulator gene glgS were significantly upregulated. 12 of 13 (92.3%) selected genes was found to be in agreement with the RNA-Seq of planktonic and biofilm cells by Quantitative real-time PCR analysis, thus increasing confidence in our data. Our research lays a sound theoretical basis for further studies on mechanisms regulating biofilm formation and provides a foundation for development of new food safety measures, clinical disease prevention and control.