[Characterization of strains of Escherichia coli isolated from calves with neonatal diarrhea].

Thirty fecal samples of diarrheic calves from a beef herd with previous history of neonatal diarrhea were cultured for isolation of Escherichia coli K99 (+) and for enterotoxigenic tests. The age distribution of sampled calves was: 1 animal less than 6 days old, 21 between 7-15 days old and 8 between 16-30 days old. Although most strains were classified as Isaacson et al (16) biotype four, they were negative for detection of K99 antigen by slide agglutination test. The assay for heat-stable (ST) and heat-labile (LT) enterotoxins by intragastric infant mouse inoculation and ELISA tests, respectively, were negative. More than 93% of the E. coli strains were sensitive to ampicillin, colistin, gentamycin and nitrofurantoin .