sspecies are the most significant foodborne pathogen in infant milk formula (IMF). These pathogens have been incriminated in severe forms of neonatal meningitis, sepsis, and necrotizing enterocolitis with a high mortality rate. This study was performed to elucidate the effect of heat stress on spp. ( and ) in reconstituted IMF (RIMF). The reconstituted formula was inoculated with five isolates and four isolates separately. The nine isolates of spp. were heated in RIMF at 48°C, 52°C, 56°C, 60°C, 64°C, and 66°C. The - and -values were determined by using linear regression analysis. The -values of all isolates of (CS1, CS3, CS4, CS5, and CS6) at 48°C, 52°C, 56°C, 60°C, 64°C, and 66°C were in the ranges 7.29-23.47, 2.77-15.50, 0.62-1.04, 0.62-1.02, 0.62-1.00, 0.62-1.00 minutes, respectively; while, the -values extended from 2.50°C to 4.28°C. The - values of isolates (CP1, CP2, CP3, CP4) were in the ranges 7.60-22.32, 1.42-8.45, 0.62-1.08, 0.62-0.78, 0.62-0.78, 0.62-0.79 minutes at 48°C, 52°C, 56°C, 60°C, 64°C, 66°C, respectively and the calculated -values ranged from 3.33°C to 4.89°C. This study may contribute to improving the understanding of the behavior of and isolates in RIMF at various heat stress temperatures and may participate in the effective control of these pathogens in infant food production.