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Growth of Enterobacter sakazakii in Reconstituted Infant Formula as Affected by Composition and Temperature

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The ability of Enterobacter sakazakii to cause infections in infants, coupled with its documented presence in some lots of commercially manufactured powdered infant formula, raises a concern about the potential for its growth in reconstituted formula, with consequent increased safety risk. A study was done to determine these characteristics in four commercial milk-based powdered infant formulas and two soy-based formulas reconstituted with water and inoculated with a 10-strain mixture of E. sakazakii at populations of 0.02 and 0.53 CFU/ml (ca. 13 CFU/100 g and ca. 409 CFU/100 g of powdered formula, respectively). Reconstituted formulas were stored at 4, 12, 21, and 30°C, and populations were monitored up to 72 h. E. sakazakii did not grow in formulas stored at 4°C, although it was detected by enrichment of all formulas 72 h after reconstitution. Initially at a population of 0.02 CFU/ml, E. sakazakii grew to populations ≥1 log CFU/ml of reconstituted formulas held at 12, 21, and 30°C for 48, 12, and 8 h, respectively. At an initial population of 0.53 CFU/ml, the pathogen grew to populations 1 log CFU/ml in reconstituted infant formula held at 12 and 21°C for 24 and 8 h, respectively, and to populations 2.55 to 3.14 log CFU/ml when held at 30°C for 8 h. Populations initially at 0.02 and 0.53 CFU/ml of reconstituted formula increased to ≤0.25 and 0.4 log CFU/ml, respectively, when formulas were held at 30°C for 4 h. Growth was not greatly influenced by the composition of formulas. Results show that the hang time for reconstituted infant formula held at temperatures in neonatal intensive care units should be no longer than 4 h. Portions of reconstituted infant formula not fed to infants should be stored at ≤4°C, a temperature at which E. sakazakii will not grow.

Document Type: Research Article

Affiliations: 1: Center for Food Safety and Department of Food Science and Technology, University of Georgia, 1109 Experiment Street, Griffin, Georgia 30223-1797, USA; USDA, ERRC-ARS, 600 East Mermaid Lane, Wyndmoor, PA 19038-8551, USA 2: Center for Food Safety and Department of Food Science and Technology, University of Georgia, 1109 Experiment Street, Griffin, Georgia 30223-1797, USA

Publication date: 2007-09-01

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