Serotyping and genotyping of encapsulated Escherichia coli K1 sepsis isolates with a monoclonal IgG anti K1 antibody and K1 gene probes.

Among infectious diseases caused by E. coli the capsular type K1 plays a predominant role. E. coli K1 isolates account for 80% of cases of E. coli neonatal meningitis and 30% of E. coli sepsis strains. Serotyping of K1 strains has conventionally relied upon the use of K1-specific bacteriophages or serum agar methods with polyvalent anti K1 serum. In the study present here, 187 E. coli sepsis isolates have been analysed for production of the K1 antigen using K1 phages, K1 serum agar plates and Latex agglutination and ELISA using an IgG2a anti K1 monoclonal antibody. In total, 33 sepsis isolates (about 18%) were identified as K1 positive, with three of these strains proving negative in all tests except those exploiting the monoclonal antibody. That these three strains elaborate the K1 antigen was confirmed by Southern blot experiments using cloned K1 antigen production genes as probes. The failure of the three strains in all the tests except those that use monoclonal antibody could be explained by apparent disruption of K1 gene sequences that encode functions essential for the export of capsular material to the cell surface. The superiority of tests based on monoclonal antibodies above the conventional methods for detection of K1 antigen is evident.