Identification of genomic differences between Escherichia coli strains pathogenic for poultry and E. coli K-12 MG1655.

摘要

Diseases of poultry caused by Escherichia coli result in significant economic losses every year. Specific virulence factors associated with E. coli strains pathogenic for poultry have been identified, but it is likely that others remain to be identified. The objective of this project was to identify novel virulence factors of avian E. coli. The signature-tagged mutagenesis technique was to be used for this purpose. Difficulties were encountered using that technique, and it was decided that suppression subtractive hybridization should be used to identify genomic differences between E. coli K-12 and avian E. coli pathogenic for poultry. A total of 62 fragments specific to two avian strains were identified. They were composed of sequences with homology to four types of fragments: plasmid sequences, phage sequences, sequences with known function and sequences without any currently known function. Two E. coli collections, a reference collection of diverse strains (ECOR) and a collection of 41 avian isolates, were screened for the presence of 25 of the 62 fragments. Eleven fragments were present in significantly more of the avian strains than of the ECOR strains. Some of the fragments were further characterized by sequencing the DNA flanking the fragments, and analyzing the sequences for the putative genes. One of the fragments was disrupted in the genome of an avian E. coli strain. The disruption mutant did not have reduced virulence in two animal models tested, which indicates that the disrupted gene may not be required for virulence. The role of the other fragment sequences in the virulence of avian E. coli has not yet been determined.