Production and Partial Purification of Heat-Stable Enterotoxin (A) Produced by Enterotoxigenic Escherichia coli Rajiha I. Al-Nuaimy, Zaid K. Kamona, Maha F. Al-Taee

Abstract

A total of (25) stool samples were collected from children and adults (2- 4) years old
suffering from diarrhea to isolate E. coli strains that produce heat-stable enterotoxin a (STa),
and after performing microscopic examination, cultural characterization and biochemical
identification only (11) isolates showed positive E. coli. STa activity was estimated by using
suckling mouse assay (SMA) and from these (11) isolates only (5) showed STa activity and
the one with the highest STa activity was selected for large scale production of STa, which
was followed by partial purification using ion-exchange chromatography (normal phase)
using DEAE sephadex A-50 column. After purification and determination of protein
concentration by using the standard curve of bovine serum albumin, the concentration of
toxin-protein was estimated as (1.08) mg/ml. The specific activity varied from (350) U/mg
protein at the first step of purification to (2366.6) U/mg protein at the final step, while the
final purification of the toxin was about (6.76) fold and with a yield of (18.25) %.