Analysis of the role of flagella in the heat-labile Lior serotyping scheme of thermophilic Campylobacters by mutant allele exchange.

Flagellin mutations originally constructed in Campylobacter coli VC167 (serotype LIO8) by a gene replacement mutagenesis technique (P. Guerry, S. M. Logan, S. Thornton, and T. J. Trust, J. Bacteriol. 172:1853-1860, 1990) were moved from the original host into Campylobacter strains of a number of other Lior serogroups by a natural transformation procedure. This is the first report of the use of this transformation method to transfer a mutated locus among Campylobacter strains. Flagellin mutants were constructed in a number of heat-labile LIO serotypes and were serotyped and analyzed by immunoelectron microscopy with LIO typing antisera. In six cases, isogenic nonflagellated mutants were able to be serotyped in the same serogroup as their parent, and immunogold electron microscopy confirmed that antibodies in the typing antisera bound to components on the surface of both parent and mutant cells. However, in only one case, a strain belonging to serogroup LIO4, was a nonflagellated mutant untypeable, and immunogold electron microscopy showed that antibodies bound to the flagella filament of the parent but not to the cell surface. Furthermore, after introduction and expression as a flagellar filament of a LIO8 flagellin gene in this mutant, the strain could not be serotyped. These results indicate that a nonflagellar antigen is often the serodeterminant in the heat-labile Lior serotyping scheme.