A rapid and simple screening method of Cronobacter spp. in cell suspension and tofu

BACKGROUND: Cronobacter spp. causes illnesses such as neonatal meningitis, sepsis and necrotising enterocolitis that can be fatal in infants and neonates. Thus it is of great concern to the food industry, which requires a simple and miniaturised method for the rapid detection of Cronobacter spp. in food. RESULTS: A simple and rapid method was developed for the quantitative estimation of Cronobacter spp. Cell suspension cultures and tofu inoculated with Cronobacter spp. as well as a mixed culture (Cronobacter spp. and other micro-organisms) were serially diluted twofold on microtitre plates. Kim and Rhee broth, containing salicin, was added to each well. After 16-18 h of incubation the colour of broth in the wells changed from purple to yellow owing to salicin fermentation by Cronobacter spp. Bacterial counts were predicted by analysing the end points (the last well number in a series of positive wells). The coefficients of determination (r²) between the conventional plating method and the current method had high degrees of correlation (0.954-0.963), suggesting that the latter method offers a reasonable quantification of Cronobacter spp. CONCLUSION: The simple method developed in this study could be used for the efficient and rapid screening of Cronobacter spp. in the food industry.