Microbial growth patterns in intravenous fat emulsions

Microbial growth patterns were studied in intravenous fat emulsions under conditions that simulated touch contamination before or during administration. Commercially available emulsions of 10% and 20% soybean oil and 10% safflower oil in 500-ml bottles were inoculated with two concentrations of each of four organisms; a coagulase-negative Staphylococcus isolated from a venipuncture site, Escherichia coli, Pseudomonas aeruginosa, and Candida albicans. The bottles were kept at room temperature, and samples were taken by direct puncture of the i.v. port at 0, 3, 6, 12, 24, 48, and 72 hours, diluted, and plated. Emulsions were visually inspected daily. Growth of the coagulase-negative Staphylococcus was minimal for 48 hours. E. coli showed substantial growth within 12 hours in all three emulsions. Growth patterns for Ps. aeruginosa were similar in all emulsions, and growth approximated that of E. coli within 48 hours. The growth rate of C. albicans was intermediate between that of Staphylococcus and those of E. coli and Ps. aeruginosa. Growth of C. albicans was greater in 10% safflower oil emulsion than in the other emulsions. No physical changes were observed. The coagulase-negative Staphylococcus showed less growth than C. albicans, Ps. aeruginosa, and E. coli. Substantial growth within 12 hours was seen only with E. coli. C. albicans exhibited preferential growth in 10% safflower oil emulsion.