[Treatment with erythromycin of experimental legionellosis in guinea pigs infected by aerosol].

The infectious strain L. pneumophila serogroup 1 Philadelphia (ATCC 33152) was cultured on charcoal dialysed yeast extract agar medium (CDYE agar) which produces more virulent strains than those grown on classical agar media. The aerosol was dispersed in a depression chamber by means of a nebuliser and the density was controlled by a density probe. Male albinos Dunkin-Hartley guinea pigs weighing 250-300 g were exposed for 30 minutes to an aerosol dose of 1 LD50 (10(3) viable organisms) and 10 LD50 (10(4) viable organisms). Erythromycin lactobionate (Abbott) was administered subcutaneously 18 hours after the infection, at dosages of 270 mg/kg/day for 4 days in the animals treated with 1 LD50 and for 6 or 7 days in the animals treated with 10 LD50. The guinea pigs were observed for 9 days (weight, rectal temperature; serological and bacteriological tests (cardiac blood, lungs, spleen) and erythromycin assays (serum, lungs) were performed and compared in the treated animals, the non-treated infected control animals and the control animals which only received erythromycin. The percentage survival in the treated guinea pigs after inhalation of 1 LD50 and 10 LD50 (2 tests) were 100%, 75% and 87.5% respectively. Three weeks after treatment, the survivors had antibody titres from 32 to 1,024; the bacteriological cultures and erythromycin assays were negative. In this study, an improvement in the treatment of experimental Legionnaires' disease was observed in comparison with previous experiments. The increased dosage and duration and the early initiation of treatment resulted in survival rates of 75%.(ABSTRACT TRUNCATED AT 250 WORDS)