Analysis of the DNA region mediating increased thermotolerance at 58°C in Cronobacter sp. and other enterobacterial strains.

Cronobacter spp. are opportunistic pathogens associated with serious infections in neonates. The increased stress tolerance, including thermoresistance, of some Cronobacter strains can promote their survival in production facilities and thus raise the possibility of contamination of dried infant milk formula, which has been identified as a potential source of infection. In this study, we characterized a DNA region which is present in some Cronobacter strains and which contributes to their prolonged survival at 58°C. The 18 kbp long region containing 22 open reading frames was sequenced in Cronobacter sakazakii ATCC 29544. The major feature of the region contained a cluster of conserved genes, most of them having significant homologies with bacterial proteins involved in some type of stress response, including heat, oxidation and acid stress. The same thermoresistance DNA region was detected in strains belonging to the genera Cronobacter, Enterobacter, Citrobacter and Escherichia and its presence positively correlated with increased thermotolerance.