Resistance to antibiotics by microbial pathogens.

Resistance to antibiotics by microbial pathogens is worldwide cause for concern. That also applies to the major mastitis-causing organisms. The question is what is the current status – should we be concerned? Should we consider alternatives? On consulting the literature the following seems to summarize current thought and evidence.

Antibiotics are used extensively in the dairy industry, not only to combat mastitis but also other diseases and occasionally to improve performance. Antibiotics differ in countries but the majority of commercial products contain penicillin, cephalothin, streptomycin, gentamicin or tetracycline and are used for control of a variety of gram-positive and gram-negative organisms. Many species and their strains cause mastitis, but the prominent species are Staphylococcus aureus, Escherichia coli, Streptococci, Corynebacterium and Klebsiella.

Antibiotics are often administered routinely to entire herds to prevent mastitis during the dry period instead of selectively. Further increases in antibiotic use result when an increase in the disease or SCC occur, which in turn increases the potential for increased bacterial resistance. A third problem is that in some instances non-specific antibiotics are administered which could be less effective against particular infections but provide the opportunity for increased resistance. Thus, clearly the opportunity is provided that mastitis-causing organisms may develop resistance to the primary antibiotic products in use. The argument is augmented by reports of farmers suggesting less efficiency of these products in combating mastitis or increases in SCC.

Based on studies worldwide, scientific evidence does not support widespread, emerging resistance among mastitis causing organisms to antibiotic drugs, even though many of these drugs have been used in the dairy industry for treatment and prevention of mastitis for several decades. However, there nevertheless is concern as some strains of particular species, a number of gram-negative bacteria and Klebsiella spp do show limited resistance, the latter which is alarming since Klebsiella can affect human health. Being the case, prudent use of antibiotics in consultation with experienced veterinarians and dedicated managerial recommendations to limit the incidence of mastitis should be followed on dairy farms. Also, innovative and non-antibiotic methods of controlling mastitis pathogens, such as by bacteriophage and bacteriocin therapy (work initiated in South Africa), should be encouraged.

Literature cited:                                                                                                                                Basdew, I.H. et al., 2013. Biological control of bovine mastitis using bacteriophage therapy. www.formatex.info/microbiology3/book/386-393.pdf

Botrel, M.A. et al., 2010. Distribution and antimicrobial resistance of clinical and subclinical mastitis pathogens in dairy cows in Rhône-Alpes, France. Foodborne Pathog. Dis. 7, 479-487

Daka, D., 2012. Antibiotic-resistant Staphylococcus aureus isolated from cow’s milk. www.ann-clinmicrob.com/content/11/1/26

Moroni, P. 2013. Klebsiella – Dairy study reveals rising antibiotic resistance and produces new test to help treat mastitis. http://www.vet.cornell.edu/news/Klebsiella.cfm

Oliver, S.P. & Murinda, S.E., 2012. Antimicrobial resistance of mastitis pathogens. Vet. Clin.North Am. Food Anim. Pract. 28, 165-185

Pieterse, R., 2010. Bacteriocins – Exploring alternatives to antibiotics in mastitis. www.ncbi.nim.nih.gov)NCBI)Literature)PubMed Central (PMC)

Pritchard, D.E., 2006. Antimicrobial resistance of mastitis pathogens. Proc. of the 2006 NMC Annual Meeting., 0306nlet.pdf

Saini, V. et al., 2012. Antimicrobial resistance profiles of common mastitis pathogens on Canadian dairy farms. J. Dairy Sci. 95, 4319-4332.

Swartz, R. et al., 1984. Antibiotic susceptibility patterns of mastitis pathogens isolated from Bloemfontein dairy herds. J.S. Afr. Vet. Ass. 55, 187-193