Sequencing of the rpoB Gene in Legionella pneumophila and Characterization of Mutations Associated with Rifampin Resistance in the Legionellaceae

Rifampin in combination with erythromycin is a recommended treatment for severe cases of legionellosis. Mutations in the rpoB gene are known to cause rifampin resistance in Escherichia coli and Mycobacterium tuberculosis, and the purpose of the present study was to investigate a possible similar resistance mechanism within the members of the family Legionellaceae. Since the RNA polymerase genes of this genus have never been characterized, the DNA sequence of the Legionella pneumophila rpoB gene was determined by the Vectorette technique for genome walking. A 4,647-bp DNA sequence that contained the open reading frame (ORF) of the rpoB gene (4,104 bp) and an ORF of 384 bp representing part of the rpoC gene was obtained. A 316-bp DNA fragment in the center of the L. pneumophila rpoB gene, corresponding to a previously described site for mutations leading to rifampin resistance in M. tuberculosis, was sequenced from 18 rifampin-resistant Legionella isolates representing four species (L. bozemanii, L. longbeachae, L. micdadei, and L. pneumophila), and the sequences were compared to the sequences of the fragments from the parent (rifampin-sensitive) strains. Six single-base mutations which led to amino acid substitutions at five different positions were identified. A single strain did not contain any mutations in the 316-bp fragment. This study represents the characterization of a hitherto undescribed resistance mechanism within the family Legionellaceae

Identity of streptococcal blood isolates and oral isolates from two patients with infective endocarditis.

The purpose of this study was to isolate streptococcal strains from the oral cavities of streptococcal endocarditis patients and compare these strains biochemically and genetically with the corresponding streptococcal blood isolates. Total identity was observed between the blood and oral cavity isolates from the two patients studied

Immunochemical characterization of and isolation of the gene for a Borrelia burgdorferi immunodominant 60-kilodalton antigen common to a wide range of bacteria.

By crossed immunoelectrophoresis and Western blotting (immunoblotting), it was shown that Borrelia burgdorferi expresses the 60-kilodalton Common Antigen (CA) that is cross-reactive with an equivalent antigen in a wide range of remotely related bacteria. B. burgdorferi CA is strongly immunogenic. A B. burgdorferi genomic library was constructed by using a plasmid cloning system. Escherichia coli recombinants were screened for expression of immunodominant B. burgdorferi antigens. One of the recombinant clones expressed the 60-kilodalton CA of B. burgdorferi. The DNA region encoding B. burgdorferi CA was localized on a 2.3-kilobase fragment of the plasmid pKH1. CA may have pathogenetic implications in Lyme borreliosis, since the CA of mycobacteria recently has been shown to play a role in the etiology of experimental autoimmune arthritis. The extensive cross-reactivity of this antigen may account for the low diagnostic specificity of the currently used serological tests in Lyme borreliosis