Outer Membrane Protein A Conservation among Isolates Suggests Its Potential as a Protective Antigen and Diagnostic Target.

Scrub typhus threatens one billion people in the Asia-Pacific area and cases have emerged outside this region. It is caused by infection with any of the multitude of strains of the bacterium . A vaccine that affords heterologous protection and a commercially-available molecular diagnostic assay are lacking. Herein, we determined that the nucleotide and translated amino acid sequences of outer membrane protein A (OmpA) are highly conserved among 51 isolates. Molecular modeling revealed the predicted tertiary structure of OmpA to be very similar to that of the phylogenetically-related pathogen, , including the location of a helix that contains residues functionally essential for infection. PCR primers were developed that amplified DNA from all strains, but not from negative control bacteria. Using these primers in quantitative PCR enabled sensitive detection and quantitation of DNA from organs and blood of mice that had been experimentally infected with the Karp or Gilliam strains. The high degree of OmpA conservation among strains evidences its potential to serve as a molecular diagnostic target and justifies its consideration as a candidate for developing a broadly-protective scrub typhus vaccine.