THE EFFECT OF DRY Cow TREATMENT ON ANTIBIOTIC RESISTANCE OF FECAL ESCHERICHIA COLI AND OF MAMMARY QUARTER ISOLATES

摘要

Dry cow therapy (DCT) is an important strategy for managing bovine mastitis. Antibiotics in DCT preparations potentially exert antimicrobial resistance (AR) pressure on commensal bacteria such as Escherichia coli in treated cows' gut as a consequenceof passive transport of molecules out of the mammary gland at the beginning of the dry period (3) followed by biliary excretion (1) into the gut. A cycle of fecal shedding and oral inoculation of AR E. coli may lead to a generally increased circulation of AR genetic elements in the farm environment. The National Antimicrobial Resistance Monitoring System (NARMS, United States) suggests some AR pressure on E. coli in dairies (2). Escherichia coli circulating in the dairy environment and carrying geneticelements of AR can potentially serve as reservoirs and traffickers of AR elements for human bacterial pathogens (4). It is not known if a single cycle of DCT exerts enough pressure on commensal gut E. coli or on post-calving intramammary S. aureus or coagulase-negative staphylococci (CNS) to make a practical impact on observable AR expression.