Effect of Gramicidin Suspended in Mineral Oil on Streptococci of Bovine Mastitis

Gramicidin, an alcohol-soluble, water-insoluble substance extracted from cultures of an aerobic sporulating bacillus, has been found to exert a marked bactericidal effect against Gram positive microorganisms, both in vitro and in vivo. 1 When injected by way of the cistern into infected quarters of cows suffering from mastitis caused by Streptococcus agalactiae (Lancefield serological group B), gramicidin apparently cured a number of the infections. 2

The method originally used for the administration of gramicidin in the treatment of bovine mastitis consisted in diluting 60-240 mg of the bactericidal substance in 1000 cc of aqueous media and injecting this material into the cistern of the infected quarter. As reported earlier, this method of administration caused an intense swelling of the treated quarter, accompanied by a marked elevation of temperature. Although this reaction lasted only a few hours, it was severe enough to prevent repeated treatments on successive days.

It has now been found that sterile mineral oil is a suitable, non-irritating vehicle for the administration of gramicidin. Of 42 quarters treated with gramicidin-oil mixtures, only 4, which had received 120-160 mg of bactericidal substance, exhibited a severe reaction. On the second and third day following treatment, the fore milk in 3 of these quarters was tinged with blood, whereas the secretion of milk was suppressed for 4 days in a fourth quarter. The reaction in the remaining 38 quarters was milder than in those injected with gramicidin in water.

On the basis of present experience, the following technique of treatment appears the most satisfactory. 2-3 cc of an alcoholic solution of gramicidin, containing 40 mg per cc, are emulsified in 15 cc of sterile double distilled water and the emulsion mixed thoroughly in 25 cc of heavy mineral oil.