Diarrhea in Neonatal Piglets Caused by K99⁺ST⁺ Enterotoxigenic Escherichia coli

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Enterotoxigenic Escherichia coli strains were isolated from the feces of 34.4% of 64 diarrheaic neonatal piglets on seven farms. Of a total of 518 isolates, 86 (16.6%) were enterotoxigenic and grouped into four phenotypes: K99⁺ST⁺ (K99 pilus antigen and heat-stable enterotoxin producing, 36 strains), ST⁺ (37 strains), K88⁺LT⁺(K88 pilus antigen and heat-labile enterotoxin producing, 11 strains), and K88⁺ST⁺ (2 strains). K99⁺ST⁺ and ST⁺ isolates showed multiple drug resistance and most of those (58.3% and 56.8% respectively) belonged to O serogroup 101. A K99⁺ST⁺ isolate proved to be capable of inducing diarrhea and death in hysterectomy-produced colostrum-deprived piglets when orally inoculated.