TnphoA-mediated disruption of K54 capsular polysaccharide genes in Escherichia coli confers serum sensitivity.
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. Transposon mutagenesis (TnphoA) was used to generate isogenic capsule-negative mutants. CP9 was resistant to the bactericidal effects of serum, growing in 80% serum. In contrast, all of the capsule-negative mutants 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) CFU/ml were used. The killing of the capsule-negative strains was mediated through the alternative complement pathway and not by lysozyme or beta-lysins. The protective effect of the K54 capsule against the bactericidal 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.
Bacterial Pathogenesis Unit, National Institute of Allergy and Infectious Diseases, Bethesda, Maryland 20892.
T A
TA
Russo
M C
MC
Moffitt
C H
CH
Hammer
M M
MM
Frank
D023181:Antimicrobial Cationic Peptides; D016667:Bacterial Capsules / Q000235:genetics*; D001770:Blood Bactericidal Activity; D001798:Blood Proteins; D003176:Complement C3 / Q000378:metabolism; D003170:Complement Pathway, Alternative; D004251:DNA Transposable Elements; D004926:Escherichia coli / Q000235:genetics* / Q000276:immunology; D005798:Genes, Bacterial; D006801:Humans; D009113:Muramidase / Q000502:physiology; D011506:Proteins / Q000502:physiology
D023181:Antimicrobial Cationic Peptides; D001798:Blood Proteins; D003176:Complement C3; D004251:DNA Transposable Elements; D011506:Proteins; C011679:beta lysin, human; D009113:Muramidase