Comparison of the nucleotide sequences of 16S rRNA, 444 Ep-ank, and groESL heat shock operon genes in naturally occurring Ehrlichia equi and human granulocytic ehrlichiosis agent isolates from Northern California

Abstract

We examined 11 naturally occurring isolates of Ehrlichia equi in horses and two human granulocytic ehrlichiosis agent isolates in California for sequence diversity in three genes. Ehrlichia equi isolates were from Sierra (n = 6), Mendocino (n = 3), Sonoma (n = 1), and Marin (n = 1) counties, and human granulocytic ehrlichiosis (HGE) agent isolates were obtained from Humboldt county. PCR with specific primers for 16S rRNA, 444 Ep-ank and groESL heat shock operon genes successfully produced amplicons for all 13 clinical samples. The 444 Ep-ank gene of the HGE agent and E. equi isolates from northern California is different from the eastern U.S. isolates BDS and USG3. The translated amino acid sequence of the groESL heat shock operon gene fragment is identical among E. equi, the HGE agent, and E. phagocytophila, with the exception of the northern Californian equine CASOLJ isolate. Microheterogeneity was observed in the 16S rRNA gene sequences of HGE agent and E. equi isolates from northern California. These results suggest that E. equi and the HGE agent found in California are similar or identical but may differ from the isolates of equine and human origin found in the eastern United States.

FIG. 1

Map of California showing the counties where equine and human isolates were collected for PCR to detect E. equi (●) and HGE agent (■).

FIG. 2

PCR amplicons of 16S rRNA (928 bp), 444 Ep-ank (444 bp), and groESL heat shock operon (1,715 bp) genes from naturally infected with granulocytic ehrlichiae in horses from Sierra (CASIGR, CASIPE, CASIJA, CASICH, CASIRN, and CASITL), Mendocino (CAMEBS, CAMELI, and CAMEDO), Sonoma (CASOLJ), and Marin (CAMAWI) counties, California, and in a human from Humboldt county, California (CAHU-HGE1 and CAHU-HGE2). M, Molecular marker; C, double-distilled water; P, positive HGE agent control.