In-vitro antibiotic susceptibility of E. coli isolated from acute and chronic bovine mastitis with reference to clinical efficacy.

131 strains of E. coli isolated from coliform mastitis were examined for susceptibility to 8 antibiotics. Colistin, gentamycin, and polymyxin B were the most active drugs based upon MIC determination. In milk, ampicillin showed the highest bactericidal activity followed by polymyxin B and colistin. All strains examined were sensitive to colistin, gentamycin, and polymyxin B.