الفهرس 
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Abstract
Colibacillosis occurs in all species of newborn farm animals and is a major
cause of losses in tills age group Enterotoxigenic Eschen•chia coli (ETEC) and is
a major cause of diarrhea in newly born calves. The heat stable enterotoxin (STa)
,
is one of two major types of enterotoxins produced by Enterotoxigenic
Escherichia coli (ETEC) in neonatal animals, human, infants, and travelers to
under developed countries.
In tills study a total of 100 diarrhoeic and apparently healthy buffalo calves
were clinically and bacteriologycally investigated for the isolation of k99+ E. coli
strains by slide agglutination test using k99 specific antiserum.
Out of 56 diarrheic and apparently healthy buffalo calves, E. coli organisms
were isolated from 36 (64.3%) and 18 (40.9%), respectively, while k99+ E. coli
organisms were detected in 15 diarrhoeic (41.6%) and 3 apparently healthy
calves (16.6%), respectively.
Concerning the isolation and characterization of heat - stable enterotoxin,
the reversed - phase high performance liquid chromatography (RP - HLPC) has
been used in STa- purification. To overcome the non antigenic nature of E. coli
heat - stable, it has been coupled to a protein carrier (succinilated BSA - coupling
To evaluate the immunogensity of the purified STa, the neutralization titer in
suckling mice of sera obtained from rabbits was determined. Six rabbits were
immunized with STa crosslinked to succinilated BSA. Four out of the six rabbits
failed to produce antibodies against STa. Positive rabbits were kept for
boostering to maintain a high titer of antibodies which can be used in other
iagnostic tests. The gut - weight - to - remaining - body - weight ratio of 2 - 3
ay old infant mice was recorded after inoculation them with succinilated STa -
SA and sera obtained from rabbits before they have been immunized (Baseline).
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Regarding the first rabbit before it had been immunized the gut - weight - to -
remaining - body - weight ratio 0.0925. After boostering of the 1 st rabbit with
succinilated STa - BSA, the ratio was 0.075, 0.0614, 0.0639. 0.0621, 0.0645 for
the first, second, third, fourth, fifth and sixth booster respectively serum from the
second rabbit, demonstrated a the gut - weight - to - remaining - body - weigh
ratio 0.0923. at baseline serum neutralizations results obtained after boostering
the second rabbit with succinilated BSA - STa, the ratio of 0.0871, 0.0772,
0.0639, 0.0639, 0.0631 for the first, second, third, fourth, fifth and sixth booster
doses respectively. Boostering was continued till the 17th booster dose to
maintain a high titer of STa antibodies in the immunized rabbits. In vitro
characterization of STa specific enterocyte receptors was carried out by using
indirect immunoflurescent technique using STa and STa - specific antibodies.
Enterocyte cells from different parts of the small intestine was used. This test
reveled that there was a direct relationship between the fluorescence intensity and
STa concentration (M.U.) and also revealed that posterior jejunum
’possess more fluorescence intensity (Glaring yellow green fluorescence +4)
anterior jejunum (dull yellow green fluorescence +2), then the ileal part (dim
yellow green fluorescence + 1)
STa antibodies produced in the immunized rabbits were used ELISA that
utilized enterocyte cells from a control calf (anterior and posterior jejunum and
ileum). It was shown that, there was a direct relationship between the optical
density as measured by ELISA and the amount of STa (M.U.) added to the wells.
Concerning enterocytes from the anterior jejunum, the optical densities were
0.287, 0.289, and 0.291 for STa concentration of 1000, 5000, and 10.000 (M.U.)
respectively. Regarding enterocytes from the posterior jejunum, the optical
densities were 0.0467, 0.475 and 0.485 for STa concentrations 1000, 5000 and
10.000 (M.U.) respectively. The optical densities of the ileal enterocytes were
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0.271, 0.280 and 0.293 for STa concentrations 1000, 5000 and 10,000 (M.D.)
respectively.