Studies on the effect of antibiotic substances on leptospires and their cultivation from material with a high bacterial count.

Leptospira species are difficult to isolate from sperm specimens because rapid growth of the contaminant flora will kill the pathogen. The resistance of 5 Leptospira strains to 5 different antibiotics was examined with a view to an inhibition of such contaminant growth. Neomycin (10, 20, 30 mg/l), vancomycin (5, 8, 10 mg/l), nalidixic acid (50, 75, 100 mg/l), streptomycin (5, 8, 10 mg/l) and chloramphenicol (5, 10, 20 mg/l) were added separately to Korthof's culture medium containing rabbit serum. The comparative growth rates of the leptospires were evaluated. Against the control medium, all 5 antibiotics were found to have an adverse influence on the multiplication phase. In conformity with literature data, vancomycin (10 mg/l) and nalidixic acid (50 mg/l) were found to have the lowest effect. In the cases of streptomycin and chloramphenicol, there was a high reduction of the leptospiral count and even a complete lack of multiplication. A combination of vancomycin (10 mg2l) and nalidixic acid (50 mg/l) was used for the recovery of leptospires from porcine sperm. To inhibit a growth of Ps. aeruginosa, 5000 U/l polymyxin B were added. The strongly inhibitory action of polymyxin B on leptospiral growth could be eliminated by subculturing in a medium free from inhibitory substances after 2 days.