Biofilm formation by Escherichia coli in hypertonic sucrose media

High osmotic environments produced by NaCl or sucrose have been used as reliable and traditional methods of food preservation. We tested, Escherichia coli as an indicator of food-contaminating bacterium, to determine if it can form biofilm in a hyperosmotic environment. E. coli K-12 IAM1264 did not form biofilm in LB broth that contained 1 M NaCl. However, the bacterium formed biofilm in LB broth that contained 1 M sucrose, although the planktonic growth was greatly suppressed. The biofilm, formed on solid surfaces, such as titer-plate well walls and glass slides, solely around the air–liquid interface. Both biofilm forming cells and planktonic cells in the hypertonic medium adopted a characteristic, fat and filamentous morphology with no FtsZ rings, which are a prerequisite for septum formation. Biofilm forming cells were found to be alive based on propidium iodide staining. The presence of 1 M sucrose in the food environment is not sufficient to prevent biofilm formation by E. coli.