Relationship between the Tsh autotransporter and pathogenicity of avian Escherichia coli and localization and analysis of the tsh genetic region

The temperature-sensitive hemagglutinin Tsh is a member of the autotranspor ter group of proteins and was first identified in avian-pathogenic Escheric hia coli (APEC) strain chi 7122. The prevalence of tsh was investigated in 300 E. coli isolates of avian origin and characterized for virulence in a 1 -day-old chick lethality test. Results indicate that among the tsh-positive APEC isolates, 90.6% belonged to the highest virulence class. Experimental inoculation of chickens with chi 7122 and an isogenic tsh mutant demonstra ted that Tsh may contribute to the development of lesions within the air sa cs of birds but is not required for subsequent generalized infection manife sting as perihepatitis, pericarditis, and septicemia. Conjugation and hybri dization experiments revealed that the tsh gene is located on a CoIV-type p lasmid in many of the APEC strains studied, including strain chi 7122, near the colicin V genes in most of these strains. DNA sequences flanking the t sh gene of strain chi 7122 include complete and partial insertion sequences and phage-related DNA sequences, some of which were also found on virulenc e plasmids and pathogenicity islands present in various E. coli pathotypes and other pathogenic members of the Enterobacteriaceae, These results demon strate that the tsh gene is frequently located on the CoIV virulence plasmi d in APEC and suggest a possible role of Tsh in the pathogenicity of E. col i for chickens in the early stages of infection.