Inactivation of the flagellin gene of Salmonella enterica serotype enteritidis strongly reduces invasion into differentiated Caco-2 cells.

A nonflagellated mutant of Salmonella enterica serotype Enteritidis was constructed by disrupting the flagellin gene (fliC). Northern blot analysis indicated that the mutation did not affect expression of the downstream fliU gene. Infection experiments with differentiated Caco-2 cells revealed that the mutant was about 50-fold less invasive than the wild-type strain, while bacterial adherence was unaffected. Complementation of the mutant with an intact fliC copy restored flagella formation and efficient bacterial invasion. Our data demonstrate that the fliC gene of S. enterica serotype Enteritidis is essential for the invasion of Caco-2 cells.

A serological study of cohorts of young dogs, naturally exposed to Ixodes ricinus ticks, indicates seasonal reinfection by Borrelia burgdorferi sensu lato.

Thirty-three family dogs were monitored for antibodies to Borrelia burgdorferi sensu lato over a 3-year period. Serum samples were collected before and during the season of high tick activity. Antibody levels were measured with an ELISA based on whole-cell antigens and an ELISA with a purified recombinant flagellin (r410). Antibody levels measured with the whole-cell ELISA increased after the first exposure to ticks. Following the first seasonal period of tick quiescence, antibody levels decreased, and subsequently increased again in the second tick season. Thereafter whole-cell ELISA titres persisted at moderate levels and did not decrease between tick seasons. The recombinant flagellin ELISA did not show a strong response in the first tick season, but did in the second tick season and levels of antibodies continued to fluctuate thereafter. We conclude that most dogs in this study developed an antibody response against Borrelia burgdorferi sensu lato after their first tick infestation and were thereafter repeatedly immunologically stimulated, probably reinfected, during the consecutive tick seasons.

Structural and functional analysis of two Campylobacter jejuni flagellin genes.

The purpose of this study was to characterize the flagellin gene of Campylobacter jejuni and to study the structure of this protein and the regulation of its synthesis. A part of the flagellin gene of C. jejuni strain 81116 was recently cloned by us. This DNA fragment was used as a probe to isolate the other homologous flagellin sequences from genomic libraries. The flagellin nucleotide sequence was determined from overlapping clones. Two copies of the flagellin gene were identified: genes fla A and fla B consisted of 1731 base pairs each, occurred as tandem repeats, and were 95% identical. Only mRNA that was transcribed from gene A was detected in flagellate cells. sigma 28-specific promoter sequences were found upstream of the transcription initiation site. Analysis of the flagellin protein sequence showed that the amino-terminal and the carboxyl-terminal regions were highly similar to other bacterial flagellins. The conserved regions can form alpha-helices with a nonpolar backbone at one side. We suggest that because these domains were conserved (i) they may be involved in polymerization or transport of flagellins or both, and (ii) they are important for maturation and stability of the flagellum.