GROWTH OF MICROORGANISMS IN PROPOFOL, THIOPENTAL, AND A 1 1 MIXTURE OF PROPOFOL AND THIOPENTAL/

To assess and compare the growth of four microorganisms in solutions o f intravenous anesthetics, known quanta of Staphylococcus aureus, Esch erichia coli, Pseudomonas aeruginosa, and Candida albicans were inocul ated into propofol, thiopental, a 1:1 mixture of propofol and thiopent al, and normal saline. All microorganisms were taken from standard sto ck cultures and incubated for 24 h (48 h for C. albicans). Growth of m icroorganisms in each drug was compared by counting the number of colo ny forming units (CFUs) grown from a subculture of each inoculated ane sthetic at 0, 3, 6, 12, and 24 h. The study shows that propofol strong ly supports the growth of E. coli and C. albicans but is bacteriostati c toward S. aureus and weakly bactericidal toward P. aeruginosa. In co ntrast, both thiopental and the 1:1 mixture of propofol and thiopental behaved differently, exhibiting markedly bactericidal properties towa rd E. coli, S. aureus, and P. aeruginosa and a bacteriostatic effect o n C. albicans. This finding supports recommendations that a strict ase ptic technique should be used when handling propofol and that the cont ents of an ampoule should be used within 6 h of aspirating. The measur ed high PH of both thiopental and the 1:1 mixture of propofol and thio pental compared to propofol alone suggest pH to be a major factor in d etermining whether a given drug will support microbial growth.