Abstract
Background:
Cronobacter species is the most significant foodborne pathogens in infant milk formula (IMF). These pathogens have been incriminated in sever form of neonatal meningitis, sepsis and necrotizing enterocolitis with high mortality rate.
Aim:
The current study was performed to demonstrate the effect of heat stress on Cronobacter spp. (C. sakazakii and C. pulveris) in reconstituted IMF (RIMF).
Methods:
The reconstituted formula was inoculated with five C. sakazakii isolates and four C. pulveris isolates separately. The nine isolates of Cronobacter spp. were heated in RIMF at 48, 52, 56, 60, 64 and 66°C. The D- and z-values were determined by using linear regression analysis.
Results:
The D˗values of all isolates of C. sakazakii (CS1, CS3, CS4, CS5 and CS6) at 48°C, 52°C, 56°C, 60°C, 64°C, 66°C ranged from 7.29 ˗ 23.47, 2.77˗15.50, 0.62˗1.04, 0.62˗1.02, 0.62˗1.00, 0.62˗1.00 min, respectively, while the z˗ values extended from 2.50˗4.28°C. The D˗ values of C. pulveris isolates (CP1, CP2, CP3, CP4) ranged from 7.60 ˗ 22.32, 1.42 ˗ 8.45, 0.62 ˗ 1.08, 0.62 ˗ 0.78, 0.62 ˗ 0.78, 0.62 ˗ 0.79 min. at 48°C, 52°C, 56°C, 60°C, 64°C, 66°C, respectively and the calculated z-values ranged from 3.33 ˗ 4.89°C.
Conclusion:
This study may contribute to improve the understanding of behavior of C. sakazakii and C. pulveris isolates in RIMF at various heat stress temperature and may participate in effective control of this pathogens in infant’s foods production.

Key words: Cronobacter sakazakii, Cronobacter pulveris, Thermo-tolerance, D˗ value, z˗ value, Infant milk formula