Thermal resistance of Enterobacter sakazakii in reconstituted dried-infant formula

Enterobacter sakazakii, designated a unique species in 1980, has been implicated in a rare but severe form of neonatal meningitis, with dried-infant formula being implicated as the mode of transmission. The high mortality rate (40-80%) and the lack of information about this organism led to a study of the heat resistance of Ent. sakazakii in reconstituted dried-infant formula. Ten Canadian Ent. sakazakii strains (5 clinical and 5 food isolates) were used to determine the heat resistance of this organism at 52, 54, 56, 58 and 60 degrees C in reconstituted dried-infant formula. D-values of 54.8, 23.7, 10.3, 4.2 and 2.5 min were obtained for each temperature, respectively. The overall calculated z-value was 5.82 degrees C. In a comparison of the D-values of several members of the Enterobacteriaceae in dairy products, Ent. sakazakii appeared to be one of the most thermotolerant organisms. The importance of process control during manufacture and the use of aseptic procedures during the preparation, use and storage of dried-infant formula is discussed.