A comparison of microbial growth in alfaxalone, propofol and thiopental

OBJECTIVES: To compare the growth of Staphylococcus aureus and Escherichia coli in alfaxalone with that in propofol and thiopental and to evaluate contaminant microbial growth in these agents under two different conditions of storage and handling.

METHODS: Known quanta of S aureus and E coli were inoculated into separate 5 ml samples of propofol, thiopental and alfaxalone. Quantitative bacterial analysis was performed at intervals over a 14 day period. Commercial preparations of propofol, thiopental and alfaxalone were stored and handled using "dirty" or "clean" techniques. Microbial quantification and identification was performed over a 14 day period.

RESULTS: S aureus and E coli grew rapidly in propofol after six hours. Both bacteria were killed by thiopental. S aureus numbers slowly declined in alfaxalone; E coli growth was rapid after 24 hours. In "dirty" and "clean" groups of intravenous anaesthetics, 9.3 and 7.4 per cent of samples, respectively, were positive for microbial growth; none were considered to represent colonisation of bottles.

CLINICAL SIGNIFICANCE: Alfaxalone supports growth of some microorganisms but less readily than propofol. Bacterial colonisation of intravenous anaesthetic bottles is uncommon, but contamination as syringes are prepared for injection occurs regardless of storage and handling technique.