Antibiotics in Milk—A Review

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Abstract
The widespread use of antibiotics has contributed to the control of diseases and the nutritional well-being of livestock. However, the use of antibiotics in the treatment of mastitis has created problems for the milk processor and consumer. Following treatment of mastitis with antibiotics, they may occur in the milk in sufficent concentrations to inhibit dairy starter microorganisms and cause economic losses to the cheese and fermented milk industries. Penicillin in very small concentrations in milk may cause reactions in highly sensitive individuals. Nationwide surveys revealed that penicillin was the primary antibiotic found in the central milk supply. Ten surveys covering a 9-yr. period (prior to 1960) in which 7,201 samples were tested, found 377 (5.2%) to contain antibiotics. The application of testing methods by regulatory and dairy personnel during 1960 resulted in a significant reduction in antibiotic-adulterated milk. Analyses of approximately 770,000 producer milk samples showed an incidence of 0.54%; a tenfold decrease. When antibiotics are used to treat mastitis, dairymen should follow the prescribed recommendations for withholding milk for human use following treatment. Data compiled on intramammary infusions, intramuscular injections, and oral administration of antibiotics and their vehicles illustrate that wide variations exist concerning the relative persistence of the amount of antibiotics found in milk. The persistence of antibiotics in milk differs from cows in early-, mid-, and late-lactation. Some recent studies using highly sensitive methods indicate that antibiotics are transferred from treated to untreated quarters, but with penicillin this transfer is slight and of short duration and not likely to present a problem. When adulterated milk leaves the farm, it is subjected to various processes in the milk plant. Antibiotics in milk are relatively stable to pasteurization temperatures and above, as well as to low temperatures (0.10[degree] F). Under refrigeration temperatures up to 7 days of storage, in raw and pasteurized milk there tends to be a loss in antibiotic activity. Large quantities of milk are necessary to dilute milk from treated quarters, since cultures may be retarded if the concentration of penicillin is approximately 0.05 unit ml or greater. Several substances were found that will inactivate penicillin. The most promising, penicillinase, can be used to hydrolyze penicillin in milk and in penicillin allergy cases. Larger quantities of inoculum and use of resistant cultures are an aid in the production of cheese made from milk that contains antibiotics. The presence of antibiotics in milk constitutes and adulteration under the Federal Food, Drug and Cosmetic Act. Educational and testing programs participated in by the Extension Service, veterinarians, dairy inspectors, sanitarians, fieldmen conferences, dairy schools, and government agencies were helpful and cooperative, but the primary responsibility continues to rest with dairymen.