Antibiotic sensitivities and elimination of mycoplasmas from infected cell cultures

Invaluable or irreplaceable cell lines infected with mycoplasmas can be cured. We have had success with a protocol that utilizes a combination of anti-mycoplasma immune serum and pretested antibiotics. A panel of antibiotics was evaluated by examining inhibition of agar growth of a variety of cell culture mycoplasmas. Resistant strains were found with certain drugs and intraspecies heterogeneity was seen in drug response. For these reasons drug regimens must be tailored to individual strains. When possible, two effective antibiotics were chosen to minimize chances of outgrowth of drug-resistant subpopulations. Cell lines were diluted and cultured in treatment cocktail consisting of growth medium plus antibiotics and antiserum. After a short exposure, cells were subcultured into fresh growth medium. Routine culturing practices were resumed and mycoplasma monitoring was begun. This procedure has been effective in curing eight cell lines, of which five were monolayers and three were suspension cultures. Mycoplasmas from four species comprised the contaminants. Two cures were of mixed infection caused by strains of two mycoplasma species. No failures have been encountered with this procedure thus far. Cultures have remained free of mycoplasmas and have retained properties of interest.