Elevated body temperature restricts growth of Haemophilus influenzae type b during experimental meningitis

Elevation of the environmental temperature appeared to counteract the temperature-depressing effects of urethane anesthetic and allowed rabbits intracisternally infected with Haemophilus influenzae type b to mimic the development of a fever following infection. Elevated core body temperature (greater than 39 degrees C) was associated with an inhibition of the growth of H. influenzae in cerebrospinal fluid (CSF) during the first 12 h postinfection, whereas bacterial growth was essentially unrestricted in rabbits with reduced (approximately 37 degrees C) body temperature. Bacterial densities 24 h postinfection were different, hyperthermic animals having log 6.0 +/- 0.4 CFU/ml of CSF and hypothermic rabbits having log 8.2 +/- 0.8 CFU/ml of CSF (P less than 0.05, Wilcoxon rank sum test). However, the growth of this bacterium in vitro, in either pooled rabbit CSF or brain heart infusion broth, was not inhibited at 39 degrees C. These results suggest that elevated body temperature associated with the development of fever during meningitis may be associated with restriction of the growth of H. influenzae in vivo but that this effect is apparently not due to an innate inability of the bacterium to grow at elevated temperatures.