Genotypic differences in the Chlamydia pneumoniae tyrP locus related to vascular tropism and pathogenicity.

Chlamydia pneumoniae is an obligate intracellular pathogen that causes respiratory infections and has been associated with cardiovascular disease. We compared respiratory and cardiovascular isolates to find genetic differences associated with pathogenicity. A polymorphic region encoding a tyrosine/tryptophan permease was found to differ between disease isolates. Respiratory strains contained multiple copies of the tyrP gene, and vascular strains contained a single copy. Single-nucleotide polymorphism analysis revealed the duplication to be a phylogenetically old event. Gene amplification was associated with higher mRNA levels and higher uptake of the substrate tyrosine, indicating an amino-acid transport-related phenotype associated with the tyrP genotype. Vascular strains, despite their reduced ability to transport tyrosine, do not appear to have a reduced growth rate in vitro. We hypothesize that the important difference between strains of vascular and respiratory origin may lie in the increased tendency of vascular strains to elicit persistent infection that is triggered by amino-acid starvation.