Susceptibility to cephalosporins of bacteria causing intramammary infections in dairy cows with a high somatic cell count in Germany.

Abstract

The objective of this cross-sectional study was to determine the minimal inhibitory concentrations of cephalosporins of the first (cefalonium and cefapirin) and fourth generation (cefquinome) against bacteria isolated from intramammary infections in dairy cows with elevated somatic cell counts in Germany. Additionally, possible regional differences of the minimal inhibitory concentrations within Germany should be evaluated. In total, 6936 quarter milk samples from cows with a somatic cell count >200,000cells/ml were taken in 43 herds. The concentrations of the first generation cephalosporins inhibiting at least 90% of the isolates of a pathogen (MIC90) were ≥64μg/ml against Gram-negative bacteria and enterococci whereas the respective MIC90 against the other Gram-positive bacteria were ≤4μg/ml. The MIC90 of cefquinome were ≥16μg/ml against Gram-negative bacteria, bacilli and enterococci, and ≤2μg/ml against the other Gram-positive bacteria. Only the minimal inhibitory concentrations against coagulase-negative staphylococci differed significantly between regions in parametric survival models with shared frailties for the herds. However, the minimal inhibitory concentrations of cefquinome against staphylococci were higher than the minimal inhibitory concentrations of the tested cephalosporins of the first generation. Therefore, cefquinome should not be the first choice to treat staphylococcal mastitis in dairy cows.