National Mastitis Council Research Committee Report Bovine Mastitis Pathogens and Trends in Resistance to Antibacterial Drugs

Bovine mastitis is the single most common cause for antibacterial use in lactating dairy cattle (18, 24). Treatment of this disease is also the most common cause of illegal antibacterial residues in marketed milk (10). Antibacterial therapy of bacterial-induced diseases in cattle has been incriminated as a catalyst for resistance in bacteria isolated from treated animals, other animals within the herd, and food derived from cattle for human consumption (2, 15, 30, 37, 41). Additionally, antibacterial use has been suggested as a selective force in determining the bacterial ecology of bovine mastitis (25). Numerous studies have determined the antibacterial susceptibility patterns of mastitis pathogens isolated from clinical studies or submissions to diagnostic laboratories (1, 3, 6, 7, 8, 9, 12, 22, 23, 27). Overall, susceptibility patterns for various bacteria are similar between studies, but few studies have compared trends in susceptibility patterns over a period of several years from the same laboratory and geographical region (11, 20, 21, 26).