Isolates of Escherichia coli which produce Vero cytotoxin (VTEC) were obtained during 1983-1989 from calves raised in 5 north-central states of the USA. All of the calves experienced intestinal epithelial colonization by VTEC, diarrhea or both; twelve of the calves had bloody diarrhea. Twenty one isolates were serogroup O111 and the others were O103, O69, O45, 026, O5, or non-typable (4 isolates). All but one of the isolates hybridized with the CVD419 probe which identifies most VTEC strains. Thirty two isolates hybridized with the VT1 probe, 3 with both the VT1 and VT2 probes, and one with neither probe. The culture filtrate of the VT probe negative isolate was partially neutralized by SLT I monoclonal antibody. For the other isolates, the results of toxin neutralization by anti-SLT I and anti-SLT II monoclonal antibodies corresponded exactly with the VT1 and VT2 probe hybridization results. Three of the strains adhered in a localized manner to HEp-2 cells and Intestine 407 cells.

The bovine respiratory disease complex (BRDC) is the most common disease problem in feedlot cattle, accounting for 65-75% of feedlot morbidity and mortality. The annual cost of BRDC to the cattle industry has been estimated at $167.2 million to $232.4 million (Perino, 1992). BRDC is caused by a complex interaction of stresses and microorganisms on the host animal. In most outbreaks, it is not possible to diagnose with certainty which infectious agents are present by clinical examination alone. Diagnosis of infectious causes of BRDC has primarily been done on tissue samples obtained from postmortem examinations. This method has resulted in a low diagnosis rate for viral infections. In addition, antibiograms done on bacterial isolates from the lungs of treated dead cattle or chronically ill cattle are of questionable value since these samples were obtained from "treatment failures". We have adopted a new program combining nasal swabs and tracheal swabs to improve viral diagnosis rates and provide more meaningful sensitivity data on bacterial isolates. The goal of this program is to provide more timely and accurate information so informed decisions can be made on treatment, vaccination, and herd health programs when BRDC outbreaks occur.