Ta. Russo et al., TNPHOA-MEDIATED DISRUPTION OF K54 CAPSULAR POLYSACCHARIDE GENES IN ESCHERICHIA-COLI CONFERS SERUM SENSITIVITY, Infection and immunity, 61(8), 1993, pp. 3578-3582
To assess whether non-K1, group 2 capsular serotypes are important in
conferring serum resistance to extraintestinal isolates of Escherichia
coli, a K54 blood isolate (CP9) was evaluated as a model pathogen. Tr
ansposon mutagenesis (TnphoA) was used to generate isogenic capsule-ne
gative mutants. CP9 was resistant to the bactericidal effects of serum
, growing in 80% serum. In contrast, all of the capsule-negative mutan
ts had an increased sensitivity to 80% normal human serum, undergoing
a 2- to 3-log kill over 3 h when starting inocula of 10(4) to 10(7) CF
U/ml were used. The killing of the capsule-negative strains was mediat
ed through the alternative complement pathway and not by lysozyme or b
eta-lysins. The protective effect of the K54 capsule against the bacte
ricidal activity of serum was not through inhibition of the complement
cascade, nor did it appear to be through a difference in the binding
of C3.