Effects of time, temperature, and preservative on bacterial growth in enteral nutrient solutions

Bacterial contamination and the effects of time, temperature, and preservative on bacterial growth in enteral nutrient solutions were studied. Bacteria were counted after 24-hour incubation of five samples of frozen Travasorb STD (Travenol Laboratories) from the pharmacy and five samples freshly reconstituted in the dietary department. Growth in samples of Travasorb STD prepared in the pharmacy was studied after (1) fresh mixing, 24-hour refrigeration, and 12 hours at room temperature, (2) freezing, thawing, and 12 hours at room temperature, and (3) freezing, thawing, 24-hour refrigeration, and 12 hours at room temperature. Duplicate samples of five products [Ensure (Ross Laboratories), Precision LR (Doyle Pharmaceuticals), Travasorb STD, Vital (Ross Laboratories), and Vivonex STD ( Norwich -Eaton)] were inoculated with Enterobacter cloacae, and growth curves for 24 hours were plotted. This challenge study was repeated using Travasorb STD as a control and Travasorb STD with potassium sorbate added. Bacterial contamination following reconstitution was not significantly different between pharmacy and dietary department samples. Growth after 12 hours at room temperature was not significantly different for the three sets of storage conditions. Logarithmic growth occurred only at room temperature. All products supported growth of E. cloacae, but growth was significantly lower in Vivonex STD (which contains potassium sorbate) and Precision LR. Growth was reduced by 70% versus control at 12 hours in Travasorb STD containing 0.036% potassium sorbate and by 90% with 0.2% potassium sorbate. Microbial growth in enteral nutrient solutions was dependent on the initial inoculum and the storage time at room temperature. Addition of potassium sorbate to these solutions may greatly reduce bacterial growth.