Factors Affecting Terramycin Activity in Milk, Broth, Buffer, and Water

Studies were conducted to determine the effect of heat, storage, total solids content, bacterial metabolism, and various gases upon the degree of terramycin inactivation in milk, broth, buffer, and water. Terramycin activity was determined by a modified disk assay technique and the acid inhibition method. The rate of heat inactivation of the antibiotic at 143 and 160 F. for 50 rain. followed the first-order reaction in milk and buffer but not in water. When autoclaved at 15 lb., the antibiotic was inactivated completely within 5 rain. in all three media. The Z values for complete thermal inactivation curves for terramycin, aureomycin, streptomycin, and penicillin in milk were 48, 51.5, 36, and 49, respectively. Terramycin was more heat-susceptible than the three other antibiotics. Heat inactivation of terramycin in reconstituted milk of different solids concentrations was inversely related to the solids content. During storage terramycin lost its potency at a faster rate in the unheated than in the heated system. This may have been owing to natural microorganisms and their enzymes in the unheated media, because it was observed that the loss of terramycin potency in a broth inoculated with a raw milk bacterial suspension was directly related to bacterial multiplication. When sterile milk containing terramycin was exposed constantly to nitrogen, oxygen, or air, the antibiotic lost its potency, the greatest loss occurring with oxygen. Terramycin (oxytetracycline), an analogue of the tetracycline antibiotics, has been shown to possess a marked effect against various microorganisms, including gram-positive, gram-negative, aerobic, and anaerobic bacteria and many viruses When used as a therapeutic agent, it has been shown also to possess a low degree of toxicity (4). It is, therefore, used singly or in combination with other antibiotics, for the treatment of various diseases.