Effect of desiccation, starvation, heat, and cold stresses on the thermal resistance of Enterobacter sakazakii in rehydrated infant milk formula

Abstract

Enterobacter sakazakii has been implicated in outbreaks of meningitis, septicemia, and necrotizing enterocolitis in immunocompromised and premature neonates. In this study, the effect of desiccation stress, starvation stress, heat shock and cold shock on thermal inactivation of E. sakazakii in rehydrated infant milk formula was evaluated. Stressed cells were mixed with rehydrated infant milk formula at 52, 54, 56, and 58°C for various time periods. The D- and z-values were determined by using linear regression analysis. Z)-values for unstressed E. sakazakii at 52, 54, 56 and 58°C were 15.33, 4.53, 2.00 and 0.53 min, respectively. Desiccation and heat stress, but not starvation or cold stress, caused significant reduction in Z)-values. For example, D52 was 15.33 min for unstressed cells compared with 8.72 and 7.36 after desiccation and heat stress. Z-values of 53 desiccated, starved, heat shocked and cold shocked E. sakazakii were not significantly different from unstressed cells (4.22°C). The results of this study may be of use to regulatory agencies, infant milk producers and infant caregivers to design heating processes to eliminate E. sakazakii that may be present in infant milk formula