Bacterial growth and endotoxin production in lipid emulsion

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Abstract
Klebsiella pneumoniae serotypes 21 and 24 and Enterobacter cloacae were responsible for an outbreak of polymicrobial bacteremia associated with the receipt of lipid emulsion. Since it is recommenced that lipid emulsion be kept refrigerated between uses, a study was undertaken to determine the growth characteristics of these organisms in lipid emulsion at 5.degree. and 25.degree. C and to examine the use of alternative measurements (pH and endotoxin) to determine contamination by viable and nonviable microorganisms. The bacteria survived but did not proliferate at 5.degree. C; no endotoxin was detected; the pH was unchanged. After a 2 h lag phase, all 3 organisms proliferated rapidly when incubated at 25.degree. C and reached concentrations of .gtoreq. 107 CFU[colony-forming units]/ml at 24 h. A decrease in pH was detected after proliferation to 107 CFU/ml. Endotoxin was detected after proliferation reached 102 CFU/ml. The amount of endotoxin elaborated by the 3 organisms differed and ranged from 0.013 ng/8 .times. 102 CFU/ml-1.3 ng/2 .times. 103 CFU/ml at 8 h. Thus, these microorganisms do not proliferate at refrigerator temperature in lipid emulsion, but can reach significant levels at room temperature. It is, therefore, important to keep lipid emulsion refrigerated between uses. When lipid emulsion contamination is suspected, endotoxin and pH determinations should be considered as possible adjunctive tests while results of bacterial cultures are pending. The results of the present study are applicable to only selected gram-negative bacteria and may not apply to gram-positive bacteria and fungi. These data demonstrate that measurement of pH and detection of endotoxin is quite useful when lipid emulsion contamination occurs with selected gram-negative bacteria.