Comparative efficacy of five antibiotics on experimental airborne legionellosis in guinea-pigs

The efficacy of preventive and curative treatment of experimental airborne legionellosis in guinea-pigs was studied for erythromycin, rifampicin, minocycline, doxycycline and pefloxacin. The aerosol was produced from a strain of Legionella pneumophila serogroup 1 and dispersed in a chamber maintained below atmospheric pressure. Guinea-pigs were exposed for 30 min to 1 or 10 LD50 (10(3) or 10(4) viable inhaled organisms). Treatment was preventive or curative. Antibiotic concentrations in lungs and serum were evaluated during treatment. The action of the antibiotics on guinea-pigs infected by 1 LD50 resulted in 100% survival. For the 10 LD50 infection, pefloxacin, minocycline and erythromycin were more active (with 87.5% survivors) than doxycycline (75%) and rifampicin (62.5%). Preventive treatment with pefloxacin or doxycycline gave 100% protection, compared with 87.5% for rifampicin, 50% for erythromycin and 37.5% for minocycline. In this study, treatment of experimental legionellosis was improved, compared with previous publications, by early administration of antibiotics and increased dosage and duration.