IDENTIFICATION OF NOVEL CHROMOSOMAL LOCI AFFECTING YERSINIA-ENTEROCOLITICA PATHOGENESIS

Pathogenic species of the genus Yersinia have a marked tropism for lym phoid tissue during the early stages of infection. Bacterial survival at this site determines whether the disease is localized or progresses systemically, leading to a high rate of mortality. Several plasmid-en coded virulence genes are known to be required for survival and pathog enesis, but the contribution of chromosomal genes has been largely une xplored. This study represents the first intensive effort to character ize and determine the function of Yersinia chromosomal genes expressed in lymphoid tissue after intragastric infection. Strains harbouring c at fusions expressed in the host were isolated from Peyer's patch tiss ue of mice intragastrically infected and treated with chloramphenicol (Cm); genes identified in this manner were designated hre for host res ponsive element. The hre::cat strains that were Cm resistant in vivo ( in mouse tissue) and Cm sensitive in vitro (on laboratory media at 26 degrees C) were identified and shown to consist of 61 different alleli c groups. The hre::cat fusions from 48 of the allelic groups were clon ed and characterized by DNA sequence analysis. The results identified genes necessary for iron acquisition, protection from environmental st resses, biosynthesis of cell envelope components and other diverse met abolic activities. However, the DNA sequence of many clones had no hom ology to other known genes. Insertion mutations were constructed for f our hre genes and the resulting Y. enterocolitica mutants were tested in the mouse model for effects on pathogenesis. All of the mutant stra ins were affected for virulence when assayed for survival in host tiss ues and LD50 analysis.