Enterotoxin production and resistance to antimicrobial agents in porcine and bovine Escherichia coli strains.

A select group of porcine and bovine Escherichia coli strains capable of causing diarrheal disease in neonatal pigs and calves, respectively, were tested for enterotoxin production and resistance to 23 different antimicrobial agents. Thirty-four of the 39 porcine strains tested were enterotoxigenic; that is, they synthesized heat-stable (ST), together with heat-labile (LT), enterotoxin; ST toxin alone, or LT toxin alone. Fourteen of the 15 bovine strains tested produced ST toxin only, whereas 1 strain elaborated LT toxin only. All of the strains were multiple drug resistant. Among the porcine strains, 2 were resistant to 6 of the antimicrobial agents, and 1 was resistant to 18 of the drugs. All of these strains were resistant to cloxacillin, lincomycin, and penicillin G. None of them was resistant to chloramphenicol, colistin, gentamicin, polymyxin B, or nalidixic acid. One of the bovine strains was resistant to 7 of the drugs, and 1 strain was resistant to 17 of these antimicrobial agents. All of the bovine strains exhibited resistance to cloxacillin, lincomycin, novobiocin, pencillin G, sulfathiazole, sulfamethizole, and triple sulfa (sulfadiazine, sulfamerazine, and sulfamethazine). None of these strains showed resistance to gentamicin, nalidixic acid, nitrofurazone, or nitrofurantoin.