Comparison of loss of serum resistance by defined lipopolysaccharide mutants and an acapsular mutant of uropathogenic Escherichia coli O75:K5

• Published in: Infection and immunity 1998-09, Vol.66 (9), p.4244-4253
• Main Authors: BURNS, S. M, HULL, S. I
• Format: Article
• Language: English
• Subjects: Bacterial Capsules; Bacteriology; Biological and medical sciences; Complement System Proteins - immunology; Escherichia coli; Escherichia coli - genetics; Escherichia coli - immunology; Fundamental and applied biological sciences. Psychology; Genetic Complementation Test; Humans; Lipopolysaccharides - immunology; Microbiology; Molecular and Cellular Pathogenesis; Mutation; O Antigens - immunology; Pathogenicity, virulence, toxins, bacteriocins, pyrogens, host-bacteria relations, miscellaneous strains; Phenotype; Polysaccharides, Bacterial - genetics; Polysaccharides, Bacterial - immunology
• ISSN: 0019-9567; 1098-5522
• DOI: 10.1128/IAI.66.9.4244-4253.1998

In order to determine the importance of the O75 O antigen versus the K5 capsular antigen and the bimodal distribution of lipopolysaccharides (LPSs) in protection from complement-mediated lysis, mutants were made by insertion of a cat or an aphA gene in or in place of genes necessary for the synthesis of LPS and/or the K antigen of an O75(+) K5(+) uropathogenic Escherichia coli strain, GR-12. Mutations were made in the following genes: the rfbD gene (required for the synthesis of TDP-rhamnose), the rfbKM genes (necessary for the synthesis of GDP-mannose), the rol gene (regulating O-antigen length), the kfiC gene (encoding a putative glycosyltransferase), and the kfiC-rfbD genes. The resulting phenotypes were rough (O75(-)), core plus one partial O-antigen subunit, random distribution of O-antigen chain lengths, acapsular (K5(-)), and O75(-) K5(-), respectively. All five mutants and GR-12 were analyzed for survival in 80% serum. The GR-12 parent was resistant, exhibiting a 500% increase in numbers. The rol, rfbKM, rfbD, and kfiC-rfbD mutants were sensitive, experiencing 99%, 99.9%, 99.9%, and at least 99.999% killing, respectively, in the first hour. The kfiC mutant, however, increased in numbers in the first hour but experienced delayed sensitivity, decreasing in viability by 80% in the third hour. Single mutants were complemented with the wild-type gene in trans, showing restoration of the wild-type phenotype and serum resistance. Therefore, the O75 antigen is more important for survival in serum than the K5 antigen, and regulation of the O75 O-antigen chain length is crucial for protection of the bacteria from complement-mediated lysis.