Molecular Cloning and Characterization of the Ehrlichia chaffeensis Variable-Length PCR Target: an Antigen-Expressing Gene That Exhibits Interstrain Variation

Authors

John W. Sumner, Centers for Disease Control and Prevention, Atlanta
James E. Childs, Centers for Disease Control and Prevention, AtlantaFollow
Christopher D. Paddock, Centers for Disease Control and Prevention, Atlanta

Date of this Version

1999

Comments

Published in JOURNAL OF CLINICAL MICROBIOLOGY, 0095-1137/99 May 1999, p. 1447–1453

Abstract

A clone expressing an immunoreactive protein with an apparent molecular mass of 44 kDa was selected from an Ehrlichia chaffeensis Arkansas genomic library by probing with anti-E. chaffeensis hyperimmune mouse ascitic fluid. Nucleotide sequencing revealed an open reading frame (ORF) capable of encoding a 198-aminoacid polypeptide. The ORF contained four imperfect, direct, tandem 90-bp repeats. The nucleotide and deduced amino acid sequences did not show close homologies to entries in the molecular databases. PCR with primers whose sequences matched the sequences flanking the ORF was performed with DNA samples extracted from cell cultures infected with nine different isolates of E. chaffeensis, blood samples from seven patients with monocytic ehrlichiosis, and Amblyomma americanum ticks collected in four different states. The resulting amplicons varied in length, containing three to six repeat units. This gene, designated the variable-length PCR target, is useful for PCR detection of E. chaffeensis and differentiation of isolates.