Linear chromosomes of Lyme disease agent spirochetes: genetic diversity and conservation of gene order.

We have constructed physical and genetic maps of the chromosomes of 21 Lyme disease agent spirochetes from geographically diverse locations. All have linear chromosomes whose lengths range from 935 to 955 kbp, and all contain multiple linear plasmids in the 16- to 175-kbp size range. The locations of 11 gene clusters on the chromosomes of these different isolates are indistinguishable at the resolution achieved in this study, indicating that the members of this related group of species have highly conserved chromosomal gene orders. However, chromosomal restriction endonuclease cleavage site maps are unique for nearly all isolates. The 22 chromosomal maps currently available define eight classes of Lyme disease agents. Four of these correspond to the previously proposed species Borrelia burgdorferi, Borrelia garinii, Borrelia afzelii, and Borrelia japonica. In addition, the North American isolates 21038, DN127 c19-2, 25015, and CA55 typify four additional chromosomal types that are as phylogenetically distinct as the species listed above. These findings support the idea that comparison of restriction maps is currently the most robust and definitive method for determining overall chromosomal relationships among closely related bacteria. In the course of this work, we located on the chromosome the previously unmapped outer surface protein-encoding LA7 gene and genes homologous to the Escherichia coli priA, plsC, parE, and parC genes, and we have substantially refined the locations of the recA, fla, p22A, and flgE genes.

Telomeres of the linear chromosomes of Lyme disease spirochaetes: nucleotide sequence and possible exchange with linear plasmid telomeres.

Bacteria of the spirochaete genus Borrelia have linear chromosomes about 950 kbp in size. We report here that these linear chromosomes have covalently closed hairpin structures at their termini that are similar but not identical to those reported for linear plasmids carried by these organisms. Nucleotide sequence analysis of the chromosomal telomeric regions indicates that unique, apparently functional genes lie within a few hundred bp of each of the telomeres, and that there is an imperfect 26 bp inverted repeat at the two telomeres. In addition, we characterize a major chromosomal length polymorphism within the right telomeric regions of various Borrelia isolates, and show that sequences similar to those near the right telomere are often found on linear plasmids in B. burgdorferi (sensu stricto) isolates from nature. Sequences similar to a number of other regions of the chromosome, including those near the left telomere, were not found on B. burgdorferi plasmids. These observations suggest that there has been historical exchange of genetic information between the linear plasmids and the right end of the linear chromosome.

[The cost effectiveness of the study of the familial contacts of tuberculosis patients coinfected with the human immunodeficiency virus]. / Rentabilidad del estudio de los contactos familiares de enfermos con tuberculosis coinfectados por el virus de la inmunodeficiencia humana.

The investigation of contacts of patients with tuberculosis is a highly cost-effective measure to detect new cases of disease and infected individuals; nevertheless, its efficacy has not been contrasted with persons living with patients with tuberculosis (TB) coinfected with HIV. A total of 152 family contacts were studied corresponding to 84 HIV-positive tuberculosis patients. As a control group, 516 persons living with HIV-negative TB patients were included. Contacts were classified according to the bacteriologic status of the index case (IC): group I, contacts of patients with negative bacterioscopy and positive culture of respiratory specimens; group II, contacts of patients with negative bacterioscopy and positive culture of respiratory specimens, and group III, contacts of pulmonary and/or extrapulmonary TB patients with negative bacterioscopy and culture. Among IC coinfected with HIV there was a higher percentage of extrapulmonary clinical forms and therefore a lower proportion of bacillary forms, which accounted for a lower rate of infection among contacts of HIV-positive patients than among contacts of HIV-negative patients (20.4% vs 48.8%; OR: 3.7; 95% CI: 2.4-5.9). After controlling for bacteriologic status of the IC, differences remained when bacillary (group I) of HIV-coinfected patients were compared with those of patients not coinfected with HIV (35.9% vs 52.3%; OR: 2.1%; 95% CI: 1.2-5.9). Overall, 28 new TB cases were detected (4.2% of the total of studied persons living with TB patients) with no differences among contacts of both groups. The lower rate of infections among persons living with HIV-positive patients might be due not only to a lower number of pulmonary forms in HIV-coinfected IC and therefore less bacillary forms but also to a lower degree of crowding and a higher protection against exposure to their contacts.