ColV increases the virulence of Escherichia coli K1 strains in animal models of neonatal meningitis and urinary infection.

Isogenic Escherichia coli strains, differing in their expression of K1 antigen and ColV plasmid, were studied for their ability to produce disease. Newborn rats were used to test the ability of these strains to colonize the intestine and to produce bacteremia and meningitis; adult rats were used to test their ability to produce urinary tract infection. Colonization of intestine and bladder by K1+ ColV+ E. coli was associated with rapid induction of bacteremia and higher mortalities compared with colonization with K1+ ColV- strains. These findings suggest that the ColV plasmid could play a role in the pathogenesis of human infections.