Gentamicin as a bactericidal antibiotic in tissue culture.

The effects of gentamicin on cellular physiology were studied in a total of 9 mammalian cell lines, using the following parameters: cell morphology and viability (cytotoxicity), proliferation, culture medium acidification, lactic acid production, lactate dehydrogenase release, virus susceptibility, and effects on karyotype. With regard to cytotoxicity no gross differences could be found in the sensitivity of the diploid and aneuploid cells investigated, as judged by morphological criteria. However, cells exposed to the antibiotic in the lag-log phase of growth showed damage at lower concentrations (1000 mug/ml) than cells treated in the stationary phase (2000 mug/ml). As regards the influence of gentamicin on cell growth and metabolsim, dose-response relationship were found proving that the antibiotic causes a depression of proliferation, a striking increase in lactate production, an elevated LDH release, and changes in pH behaviour. All these parameters were unaffected by concentrations up to 125 mug/ml. No gross changes in chromosome morphology and number could be detected in huploid cell line after 10 passages with 50 mug/ml gentamicin in lieu of the usual penicillin plus streptomycin combination. The minimal bactericidal concentrations (MBC) were determined in cell-free media and in tissue cultures against 4 species of bacteria. The MBC of gentamicin was generally lower as compared with the penicillin plus streptomycin combination. In some instances MBC was higher in the presence than in the absence of ti-sue culture cells. Comparison of the bactericidal efficiency against 31 strains of 7 species of bacteria of gentamicin (50 mug/ml) and penicillin plus streptomycin (100 units plus 100 mug/ml) in cell cultures proved that gentamicin is superior for control of bacterial growth in tissue culture.