Survival and Growth of Enterobacter sakazakii in Infant Cereal as Affected by Composition, Reconstitution Liquid, and Storage Temperature

摘要

Invasive infections caused by Enterobacter sakazakii have occurred predominantly in low-birth-weight neonates and infants younger than 2 months of age. However, infections have also occurred in healthy infants up to 8 months of age and in immunocompromised children up to 4 years of age. The ability of E. sakazakii to survive and grow in infant cereals as affected by composition of the cereal, composition of the reconstitution liquid, and temperature is unknown. A study was done to determine the survival and growth characteristics of E. sakazakii initially at populations of 0.005 and 0.52 CFU/ml of infant rice cereal, oatmeal cereal, or rice with mixed fruit cereal reconstituted with water, milk, or apple juice. Reconstituted cereals were stored at 4, 12, 21, and 30℃, and populations were monitored for up to 72 h. Growth did not occur in reconstituted cereals stored at 4℃ or in cereals reconstituted with apple juice and stored at 12℃. Populations ( ≥1 CFU/ml) were detected in cereals reconstituted with water or milk and stored at 12, 21, and 30℃ for 24, 8, and 4 h, respectively. The composition of infant cereals did not markedly affect the survival or growth of E. sakazakii in reconstituted cereals. Populations of E. sakazakii in reconstituted cereal decreased with increases in populations of mesophilic aerobic microflora up to 8 to 9 log CFU/ml, which was concurrent with decreases in pH. E. sakazakii, initially at 2.62 log CFU/ml of rice cereal reconstituted with apple juice (pH 4.32), survived at 4℃ for at least 14 days. The pathogen grew at 21 and 30℃ within 2 days and then decreased to undetectable levels (<1 CFU/10 ml) in cereal stored at 21℃ for 5 days or 30℃ for 4 days. Initially, at 7.32 log CFU/ml, E. sakazakii was detected in rice cereal stored at 4℃ for 50 days. It is recommended that reconstituted infant cereals stored at 21 or 30℃ be discarded within 4 h after preparation or stored at ≤4℃, temperatures at which E. sakazakii will not grow.