Antimicrobial Resistance of Mastitis Pathogens

Antibiotics are used extensively in the dairy industry to combat disease and to improve animal performance. Antibiotics such as penicillin, cephalosporin, streptomycin, and tetracycline are used for the treatment and prevention of diseases affecting dairy cows caused by a variety of gram-positive and gram-negative bacteria. Antibiotics are often administrated routinely to entire herds to prevent mastitis during the dry period. An increase in the incidence of disease in a herd generally results in increased use of antimicrobials, which in turn increases the potential for antibiotic residues in milk and the potential for increased bacterial resistance to antimicrobials. Continued use of antibiotics in the treatment and prevention of diseases of dairy cows will continue to be scrutinized. It is clear that strategies employing the prudent use of antimicrobials are needed. This clearly illustrates the importance of effective herd disease prevention and control programs. Based on studies published to date, scientific evidence does not support widespread, emerging resistance among mastitis pathogens to antibacterial drugs even though many of these antibiotics have been used in the dairy industry for treatment and prevention of disease for several decades. However, it is clear that use of antibiotics in dairy cows can contribute to increased antimicrobial resistance. While antimicrobial resistance does occur, we are of the opinion that the advantages of using antibiotics for the treatment of mastitis far outweigh the disadvantages. The clinical consequences of antimicrobial resistance of dairy pathogens affecting humans appear small. Antimicrobial resistance among dairy pathogens, particularly those found in milk, is likely not a human health concern as long as the milk is pasteurized. However, there are an increasing number of people who choose to consume raw milk. Transmission of an antimicrobial-resistant mastitis pathogen and/or foodborne pathogen to humans could occur if contaminated unpasteurized milk is consumed, which is another important reason why people should not consume raw milk. Likewise, resistant bacteria contaminating meat from dairy cows should not be a significant human health concern if the meat is cooked properly. Prudent use of antibiotics in the dairy industry is important, worthwhile, and necessary. Use of antibiotics at times when animals are susceptible to new infection such as the dry period is a sound management decision and a prudent use of antibiotics on the farm. Strategies involving prudent use of antibiotics for treatment encompass identification of the pathogen causing the infection, determining the susceptibility/resistance of the pathogen to assess the most appropriate antibiotic to use for treatment, and a sufficient treatment duration to ensure effective concentrations of the antibiotic to eliminate the pathogen. As the debate on the use of antibiotics in animal agriculture continues, we need to consider the consequences of, “What would happen if antibiotics are banned for use in the dairy industry and in other food-producing animals?” The implications of this question are far reaching and include such aspects as animal welfare, health, and well-being and impacts on food quantity, quality, and food costs. This question should be an important aspect in this ongoing and controversial debate!