Amelioration of experimental bacterial meningitis by levamisole: evidence of a direct effect on the infecting bacteria.

The immune-modulating effects of levamisole were evaluated in vivo in rabbits with experimental meningitis due to Escherichia coli and in vitro in assays of ingestive and digestive functions of polymorphonuclear leukocytes. Intracisternal treatment of rabbits with 0.5 ml of levamisole (400 micrograms/ml) 48 and 24 hr before infection resulted in a longer survival time (mean, 49.3 hr) than either control (mean, 21.3 hr; P < 0.01) or intravenously treated animals (mean, 18.3 hr; P < 0.05). However, treatment of the organism by incubation in levamisole (100 micrograms/ml) resulted in survival times significantly longer than that of intracisternally treated animals (mean, 98.5 hr; P < 0.05). A reduction of 5 logs of viable bacteria 22 hr after infection was noted by previous therapy of either the animal or the bacteria. No antibiotic effect was demonstrated. In vitro studies revealed increased ingestion by polymorphonuclear leukocytes (P < 0.02) and digestion (P < 0.05) of bacteria incubated in levamisole. These results suggest that levamisole may alter the bacteria, enhance killing, and produce salutary in vivo effects.