Genetic characterization and virulence of enterotoxigenic Escherichia coli mutants which have lost virulence genes in vivo

Loss of K99 and STaP genes from enterotoxigenic Escherichia coli 431 during infection occurred by either plasmid curing or plasmid deletion. These mutants expressed the F41 adhesion and colonized neonatal pigs, but only those mutants that retained STaP caused diarrhea with significant weight loss.