I am not sure of the reliability of this source but there are a couple of good referecnes to E. coli, like the K-99 strain, in the context of scours.
Scours -- What is it? Calf scours is a broad, descriptive term referring to diarrhea in calves. Calf scours is not a specific disease with a specific cause, but is actually a clinical sign of a disease complex with many possible causes.
Scours occur when normal movement of water into and out of the digestive tract is disrupted, resulting in water loss and dehydration. Loss of body fluids through diarrhea is accompanied by loss of body salts. This fluid and electrolyte loss produces a change in body chemistry that can lead to severe depression in the calf and eventual death. Rehydration therapy of scouring calves with water and supplemental electrolytes can help alleviate effects of dehydration and help restore a normal electrolyte balance.
Noninfectious scours (nutritional scours) are usually caused by changes to the feeding program. While usually not severe enough to cause death, noninfection scours can weaken the calf and make it more susceptible to infectious scours. Infectious scours are the biggest problem and are caused primarily by viruses, bacteria and protozoa. Identifying the infectious agent causing scours is an important part of developing a sound prevention program.
Infectious Scours -- Bacterial Agents
These bacterial agents produce toxins that degrade the intestinal lining. The calf responds to these toxins by pumping large amounts of water into the intestinal tract as if trying to flush out the toxin.
E. coli organisms are part of the normal flora of the intestinal tract. Many strains are harmless to the calf, but certain strains can cause moderate to severe scours and even death. E. coli typically produces a secretory diarrhea resulting from the intestinal epithelial cells being switched from an absorption mode to a secretion mode. E. coli is often referred to as "white" scours and is the most common cause of calf scours.
3 Types Enteric. This is the most common type. The main clinical sign is severe diarrhea. The calf rapidly becomes weak and dehydrated with an initial fever that rapidly returns to normal (or subnormal). Dehydration can lead to death.
Enterotoxigenic. (K-99 strain) This infection runs a rapid, fatal course. Toxins cause so much fluid to be pumped into the intestine that the calf usually dies before external signs of diarrhea are present. This type of scours is one of the few that occur within the first 3 days of life.
Septicemic. This type acts like Salmonella by invading the blood stream and penetrating body tissues causing a general infection. Gross lesions are usually minimal. This is a rapid form of E. coli, often with no evidence of diarrhea. Colostrum deprived calves usually die of this form of E. coli.
Occurrence: E. Coli affects calves within the first 10-14 days of age, usually within the first week.
E. Coli is commonly found in conjunction with rota- and coronavirus.
Other: Since only about 60% of the electrolyte solution is absorbed by the scouring calf, effective treatment requires increased frequency of treatment to replenish fluids and electrolytes lost during diarrhea. Consequently, diarrhea may appear to be worsening even though treatment is effective.
http://www.merricks.com/tech_calfscours.html