Extraintestinal strains of Escherichia coli possess a variety of
virulence factors that enable them to cause disease. These strains express a group 2 capsular
polysaccharide which is important in the pathogenic process. Extraintestinal strains evaluated to date are also capable of producing the group 1 capsular
polysaccharide colanic acid. The blood isolate CP9 (O4/K54/H5) constitutively produces the group 2, K54
capsule but can be induced to produce
colanic acid. In this report we assess whether
colanic acid contributes to the pathogenesis of this extraintestinal pathogen. CP9 and its derivatives that are deficient in their ability to produce
colanic acid (TR94), the K54 group 2
capsule +/-
colanic acid (CP9.137, TR1374) and the O4 specific
antigen +/-
colanic acid (CP921,CP925) were used to test whether the group 1
capsule colanic acid conferred protection against the bactericidal effects of serum and recombinant
bactericidal/permeability-increasing protein (rBPI-23) in vitro. Additionally, CP9, CP9.137 and TR94 were evaluated in the rat
granuloma pouch, an in vivo model for localized
infection, and by intraperitoneal inoculation into mice, a systemic
infection model. In summary, the inability of CP9 to produce
colanic acid in the presence or absence of its K54 and O4
antigens had no effect on its ability to survive these host defenses in vitro and did not affect its virulence in these two in vivo models of
infection.