Search

Citrobacter rodentium is the causative agent of transmissible murine colonic hyperplasia and contains a locus of enterocyte effacement (LEE) similar to that found in enteropathogenic Escherichia coli (EPEC). EPEC espB is necessary for intimate attachment and signal transduction between EPEC and cultured cell monolayers. Mice challenged with wild-type C. rodentium develop a mucosal immunoglobulin A response to EspB. In this study, C. rodentium espB has been cloned and its nucleotide sequence has been determined. C. rodentium espB was found to have 90% identity to EPEC espB. A nonpolar insertion mutation in C. rodentium espB was constructed and used to replace the chromosomal wild-type allele. The C. rodentium espB mutant exhibited reduced cell association and had no detectable fluorescent actin staining activity on cultured cell monolayers. The C. rodentium espB mutant also failed to colonize laboratory mice following experimental inoculation. The espB mutation could be complemented with a plasmid-encoded copy of the gene, which restored both cell association and fluorescent actin staining activity, as well as the ability to colonize laboratory mice. These studies indicate that espB is necessary for signal transduction and for colonization of laboratory mice by C. rodentium.

An unusual bacterial pathogen of laboratory mice has been previously classified as an atypical biotype of Citrobacter freundii. Designated C. freundii biotype 4280, this bacterium is the etiologic agent of transmissible murine clonic hyperplasia. An eaeA gene has been shown to be present in this organism and to be necessary for virulence in laboratory mice. However, other biotypes of C. freundii lack DNA homology with the eaeA gene. Because of the recent reclassification in which five named species and three unnamed species, all previously considered C. freundii, were described, we determined the taxonomic status of C. freundii biotype 4280. With a battery of biochemical tests and DNA relatedness studies, three isolates of C. freundii biotype 4280 were shown to be members of an unnamed Citrobacter species, designated species 9. In total, six isolates of Citrobacter species 9, but none of the type strains of the other eight named species or of the two remaining unnamed species of Citrobacter, were shown to possess DNA homology with both the eaeA and the eaeB genes. Species 9 was named Citrobacter rodentium sp. nov.