STUDIES ON THE ACTION OF SOME ANTIBIOTICS ON CHOLERA VIBRIOS

Abstract

The minimum inhibitory concentrations (MIC) of chloramphenicol, tetracycline and penicillin for cholera vibrios were found to be 1.5μg/ml, 2.5μg/ml and 30μg/ml, respectively. No strains were found completely or partially resistant to either chloramphenicol or tetracycline at their MIC but a number of strains were partially resistant to these antibiotics at lower concentrations. The incidence of partially resistant strains to tetracycline was higher and it was found increasing year to year. There was no significant difference between V. eltor and V. cholerae in their sensitivity to other two of these antibiotics.
The action of chloramphenicol, tetracycline and penicillin was studied in growth kinetic experiments using normal vibrio cells as well as protoplasts. All the three antibiotics caused a sharp fall in viable count of V. cholerae as well as V. eltor during the first 4hr of incubation. Penicillin-treated vibrios of both types then resumed growth and in 24hr multiplied to the same extent as control cultures. V. eltor cells treated with chloramphenicol or tetracycline resumed very slow growth after 4hr and this continued up to 24hr whereas the vibriocidal action of the two antibiotics on V. cholerae cells continued to be exerted for up to 24hr.
Similar concentrations of the three antibiotics totally inhibited the growth of protoplasts of both V. eltor and V. cholerae. Unlike in the case of normal cells, the inhibition of growth of protoplasts by penicillin was found to be irreversible. These findings have been discussed in relation to likely sites of action of the antibiotics on the vibrio cells.