Effects of Nitrogen Dioxide on Resistance to Klebsiella pneumoniae in Mice

Abstract

We studied the effects of nitrogen dioxide (NO₂) exposure on host resistance in mice. Mice were exposed continuously in inhalation chambers to 0.5, 1.0, or 1.5 ppm NO₂ for 3 months or to 5 ppm NO₂ for 3 days. Chamber NO₂ concentrations were monitored continuously by a Thermoelectron chemiluminescent analyzer verified by the Saltzman procedure in accordance with Federal Register procedures. After the NO₂ exposure, the mice were placed in an infectivity chamber and exposed to aerosolized cultures of Klebsiella pneumoniae for 15 minutes. Chamber clouds contained 55.2 ± 9.3 organisms (1–3 μ in size) per liter of air. The animals were removed from the infectivity chamber and observed for 15 days, after which percent mortalities and relative mean survival times (RMST) were determined. Control mice and mice exposed to 0.5, 1.0, or 1.5 ppm NO₂ for 3 months did not differ significantly in mortality or RMST. In mice exposed to 5 ppm NO₂ for 3 days, percent mortality was significantly higher and RMST was significantly lower. Lung index (lung weight/body weight) and body weight did not differ significantly after exposure to 0.5, 1.0, and 1.5 ppm NO₂ for 3 months or to 5 ppm NO₂ for 3 days. These results indicate that inhalation of 5 ppm NO₂ for 3 days depresses host resistance to K. pneumoniae, whereas inhalation of 1.5 ppm NO₂ for up to 3 months does not.

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