Showing papers by "Barbara J. B. Johnson published in 2001"

Borrelia lonestari Infection after a Bite by an Amblyomma americanum Tick

Abstract: Erythematous rashes that are suggestive of early Lyme disease have been associated with the bite of Amblyomma americanum ticks, particularly in the southern United States. However, Borrelia burgdorferi, the causative agent of Lyme disease, has not been cultured from skin biopsy specimens from these patients, and diagnostic serum antibodies usually have not been found. Borrelia lonestari sp nov, an uncultured spirochete, has been detected in A. americanum ticks by DNA amplification techniques, but its role in human illness is unknown. We observed erythema migrans in a patient with an attached A. americanum tick. DNA amplification of the flagellin gene flaB produced B. lonestari sequences from the skin of the patient that were identical to those found in the attached tick. B. lonestari is a probable cause of erythema migrans in humans.

Resistance to Lyme disease in decorin-deficient mice

Abstract: Microbial adhesion to the host tissue represents an early, critical step in the pathogenesis of most infectious diseases. Borrelia burgdorferi, the causative agent of Lyme disease (LD), expresses two surface-exposed decorin-binding adhesins, DbpA and DbpB. A decorin-deficient (Dcn–/–) mouse was recently developed and found to have a relatively mild phenotype. We have now examined the process of experimental LD in Dcn–/– mice using both needle inoculation and tick transmission of spirochetes. When exposed to low doses of the infective agent, Dcn–/– mice had fewer Borrelia-positive cultures from most tissues analyzed than did Dcn+/+ or Dcn+/– mice. When the infection dose was increased, similar differences were not observed in most tissues but were seen in bacterial colonization of joints and the extent of Borrelia-induced arthritis. Quantitative PCR demonstrated that joints harvested from Dcn–/– mice had diminished Borrelia numbers compared with issues harvested from Dcn+/+ controls. Histological examination also revealed a low incidence and severity of arthritis in Dcn–/– mice. Conversely, no differences in the numbers of Borrelia-positive skin cultures were observed among the different genotypes regardless of the infection dose. These differences, which were observed regardless of genetic background of the mice (BALB/c or C3H/HeN) or method of infection, demonstrate the importance of decorin in the pathogenesis of LD.

Mapping the ligand-binding region of Borrelia burgdorferi fibronectin-binding protein BBK32.

Abstract: The cellular attachment and entry of pathogenic microorganisms can be facilitated by the expression of microbial adhesins that bind fibronectin. We have previously described a Borrelia burgdorferi gene, bbk32, that encodes a 47-kDa fibronectin-binding protein. In this study, the ligand-binding region of BBK32 from B. burgdorferi isolate B31 was localized to 32 amino acids. The bbk32 gene was cloned and sequenced from three additional B. burgdorferi isolates representing different genospecies of B. burgdorferi sensu lato. All four bbk32 genes encoded proteins having fibronectin-binding activity when expressed in Escherichia coli, and the deduced proteins shared 81 to 91% amino acid sequence identity within the ligand-binding domain. In addition, the ligand-binding region of BBK32 was found to share sequence homology with a fibronectin-binding peptide defined for protein F1 of Streptococcus pyogenes. The structural and functional similarity between the ligand-binding region of BBK32 and the UR region of protein F1 suggests a common mechanism of cellular adhesion and entry for B. burgdorferi and S. pyogenes.