PREVALENCES OF RESISTANCE TO 7 ANTIMICROBIALS AMONG FECAL ESCHERICHIA-COLI OF SWINE ON 34 FARROW-TO-FINISH FARMS IN ONTARIO, CANADA

Fecal specimens were composited and a hydrophobic-grid membrane-filter method was used to measure antimicrobial resistance to ampicillin 16 mu g/ml, carbadox 30 mu g/ml, gentamicin 4 mu/ml, nitrofurantoin 32 mu g/ml, spectinomycin 16 mu g/ml, sulfisoxazole 32 mu g/ml and tetracyc line 8 mu g/ml among 8119 Escherichia coli isolates from 68 fecal samp les collected on 34 farrow-to-finish swine farms marketing over 500 ho gs/yr. The overall prevalences of resistance to antimicrobials among t hese isolates were: ampicillin 29%, carbadox 3.5%, gentamicin 0.6%, ni trofurantoin 27%, spectinomycin 28%, sulfasoxizole 38% and tetracyclin e 71%. Thirty to seventy-six per cent of the variations in prevalences were explained by between-farm differences. (C) 1998 Elsevier Science B.V.