Evaluation of Environmental Resistance of Cronobacter spp.

Powdered infant formula (PIF) is the main source of Cronobacter spp. contamination, among which the addition of raw and auxiliary materials and the processing environment are the most important routes of transmission. In order to effectively prevent and control Cronobacter spp. to ensure the safety of dairy products, eight strains of Cronobacter spp. isolated from PIF and its processing environment were used as the research objects. Their heat resistance, acid and alkali resistance, dryness resistance and permeability resistance were studied, and the differences of environmental resistance of different strains were analyzed. The results showed that Cronobacter spp. had different heat resistance. The strains isolated from the end products had relatively stronger heat resistance. Cronobacter spp. generally had the characteristics of acid resistance but not alkali resistance. Under the acidic conditions at pH1.5, all strains could still survive being treated for 30 s. Cronobacter spp. had strong resistance to desiccation. The bacterial count of all strains decreased from an initial concentration of 10⁸ CFU/mL to 10⁵ CFU/mL over the course of the 7-month test at room temperature with a relative air humidity of 20.7%. The slow decreasing trend indicated that Cronobacter spp. had a strong ability to resist dry environment. Cronobacter spp. had a strong resistance to osmosis. We found that all strains grew slowly when the concentration of NaCl was over 8% and the tolerance of Cronobacter spp. to sorbitol was stronger than that to NaCl under isotonic conditions.