Effects of isoflurane on bacterial growth

Anaesthetic agents have been implicated in the development of postoperative pneumonia, but the direct effect of volatile anaesthetics on bacterial gro wth has given contradictory results. The effects of isoflurane on the growt h of Staphylococcus aureus and Escherichia coil were investigated under con ditions similar to those of clinical practice, using standardized microbiol ogical methods. An open anaesthetic circuit was adjusted to the normal vent ilatory settings of an adult patient. A spray, installed on the inspiratory side of the circuit, ensured the delivery of isoflurane at 1.5 minimal alv eolar concentration. The bacterial strains studied were both wild-type and reference strains. Bacterial inoculums were prepared to obtain a bacterial exponential growth of 10(3) colony-forming units per mt in 10 mL of nutriti ve broth. Each strain was studied with and without exposure to isoflurane a nd measured by the usual criteria of bacterial growth, and by bacterial reg rowth after exposure to isoflurane. Under experimental conditions close to clinical practice, exposure to isoflurane did not alter bacterial growth of S aureus and E. coil, or their bacterial regrowth when isoflurane exposure is over.