UNIQUE CHROMOSOMAL REGIONS ASSOCIATED WITH VIRULENCE OF AN AVIAN PATHOGENIC ESCHERICHIA-COLI STRAIN

The avian pathogenic Escherichia coli strain (chi)7122 (serotype O78:K 80:H9) causes airsacculitis and colisepticemia in chickens, To identif y genes associated with avian disease, a genomic subtraction technique was performed between strain (chi)7122 and the E. coli K-12 strain (c hi)289, The DNA isolated using this method was found only in strain (c hi)7122 and was used to identify cosmid clones carrying unique DNA fro m a library of (chi)7122 that were then used to map the position of un ique DNA on the E. coli chromosome, A total of 12 unique regions were found, 5 of which correspond to previously identified positions for un ique DNA sequence in E. coli strains, To assess the role each unique r egion plays in virulence, mutants of (chi)7122 were constructed in whi ch a segment of unique DNA was replaced with E. coli K-12 DNA by cotra nsduction of linked transposon insertions in DNA flanking the unique s equence, The resulting replacement mutants were assessed for inability to colonize the air sac and cause septicemia in 2-week-old white Legh orn chickens, Two mutants were found to be avirulent when injected int o the right caudal air sac of 2-week-old chickens, One avirulent mutan t, designated (chi)7145, carries a replacement of the rfb locus at 44 min, generating a rough phenotype, The second mutant is designated (ch i)7146, and carries a replacement at position 0.0 min on the genetic m ap, Both mutants could be complemented to partial virulence by cosmids carrying sequences unique to (chi)7122.