Culture filtrates prepared from a strain of Escherichia coli associated
with calf diarrhoea were shown to produce fluid accumulation in ligated
segments of calf intestine. No activity could be demonstrated in vitro in
the other experimental systems in which these culture filtrates were tested.
The material was therefore examined using Thiry-Vella loops prepared in
Thiry-Vella loops were found to be a useful test preparation for the study
of enterotoxin activity, and were used to examine the effect of enterotoxio
extracts on net fluid, electrolyte and glucose absorption. It was found
that a significant shift towards secretion of fluid, sodium, bicarbonate
and chloride occurred in each case in which they were examined. Potassium
was not consistently affected, and glucose absorption was unchanged.
The effects of enterotoxin on unidirectional fluxes of water and sodium
were studied using isotopic labels. It was found that the net effect on
water movement resulted from an increase in exsorption. However, the net
effect on sodium movement was mainly the result of decreased insorption. It
was suggested that this indicated a complex mechanism for enterotoxin activity.
Culture filtrates prepared from strains of E.coli isolated from diarrhoeic
but non-septicaemic calves provoked a greater volume of fluid exudate than
did filtrates from strains in septicaemic or healthy animals. It was
suggested that enterotoxin production may be a graded phenomenon, and moreover,
may be commonly encountered in organisms associated with diarrhoea in calves.
Using Thiry-Vella loops as a test preparation, it was shown that enterotoxic
activity was distinct from bacterial endotoxin, and that the activity was
dialysable using Visking tubing. Ultrafiltration showed that most of the
activity was contained in the 1000 to 10,000 molecular weight fraction. The
material was stable when heated at 100°C, but showed partial loss of activity
when heated at 121°C for two hours.
Evidence of systemic absorption of enterotoxin was obtained in one animal,
but could not be confirmed in another. Attempts to inhibit enterotoxin
activity with drugs were not successful.
Mucosal lactase was assayed in material from healthy calves and from calves
which had died after scouring. Lactase activity was shown to be depressed in
the latter group. Normal calves were shown to be able to digest at least
twice the normal lactose intake before changes were seen in faeces weight and
dry matter, but despite this, lactose tolerance tests showed that there was a
significant regression of peak blood glucose rise on faecal dry-matter content.
It was therefore suggested that scouring calves may be unable to fully utilise
dietary lactose. No effect of enterotoxin on lactase activity could be