Ontario weanling pigs who are exposed Enterotoxigenic Escherichia coli (ETEC) suffer from diarrhea. The diarrhea occurs because the ETEC permits bacteria to colonize the intestine, and enterotoxins induce hypersecretion of electrolytes and fluid into the lumen of the intestine. One of the most dominent serogroups that ETEC belongs to is O149. Experiments were carried out  to characterize urease genes that had been detected in strains of O149:F4 enterotoxigenic E. coli that had been associated with unusually severe outbreaks of diarrhea in weaned pigs in Ontario. The infection studies were designed to determine whether the urease genes contributed to the virulence of the O149 ETEC. The mutant that was tested was clearly reduced in virulence. However, complementing the mutation did not result in a restoration of virulence as the strain’s capacity to colonize remained severely impaired. Thus the studies failed to show that urease plays a role in virulence.