Interactions of helium, oxygen, and nitrous oxide affecting bacterial growth.

Helium at pressures of 20 to 70 atm in the presence of air found to stimulate growth of Streptococcus faecalis, Escherichia coli, and Staphylococcus aureus, mainly by increasing the rate of exponential growth. However, at these same pressures, helium potentiated the growth-inhibitory actions of oxygen and nitrous oxide (N2O). Oxygen was found to act essentially as an anesthetic gas in inhibiting growth of S. faecalis; its potency was approximately the same as that of N2O, and it acted additively in combination with N2O to inhibit the streptococcus. Oxygen proved to be more potent than N2O in inhibiting the growth of E. coli and S. aureus, and each gas potentiated the action of the other. Oxygen sensitivity was correlated with N2O sensitivity. Overall, our findings indicate that bacterial growth inhibition by anesthetic gases does not accurately reflect narcotic action.