Background: The Direct Repeat locus of the Mycobacterium tuberculosis complex (MTC) is a member of the CRISPR (Clustered regularly interspaced short palindromic repeats) sequences family. Spoligotyping is the widely used PCR-based reverse-hybridization blotting technique that assays the genetic diversity of this locus and is useful both for clinical laboratory, molecular epidemiology, evolutionary and population genetics. It is easy, robust, cheap, and produces highly diverse portable numerical results, as the result of the combination of (1) Unique Events Polymorphism (UEP) (2) Insertion-Sequence-mediated genetic recombination. Genetic convergence, although rare, was also previously demonstrated. Three previous international spoligotype databases had partly revealed the global and local geographical structures of MTC bacilli populations, however, there was a need for the release of a new, more representative and extended, international spoligotyping database.

Most multidrug-resistant (MDR) Mycobacterium tuberculosis isolates in Russia belong to the Beijing or Latino-American and Mediterranean (LAM) spoligotype families. The objective of this study was to investigate possible associations between genotype and the frequencies of mutations that confer drug resistance in a population that has two large families of circulating strains. Spoligotyping, IS6110 restriction fragment length polymorphism typing, and sequencing of the katG and rpoB genes, were performed for 217 consecutive MDR M. tuberculosis isolates from patients. The rpsL and rrs genes were also sequenced for selected streptomycin-resistant isolates. Of the 217 MDR isolates, 99 (46%) belonged to the LAM family, 92 (42%) to the Beijing family, 21 (10%) to the Haarlem family and four (2%) to the T family. There was one unique spoligotype. Mutations in the katG gene were identified in 207 (95%) isolates, all of which had mutations in codon 315. Mutations in the rpoB gene were identified in 200 (92%) isolates; 75% of LAM isolates carried a mutation in codon 516, whereas 71% of Beijing isolates carried a mutation in codon 531. In the 33 isolates resistant to streptomycin 50 mg/L, the 43AGG rpsL mutation was found in 27% of Haarlem, 75% of Beijing and 0% of LAM isolates, and rrs mutations were found in 17% (516C-->T) of Beijing and 100% (513A-->C) of LAM isolates. Overall, there appeared to be a correlation between the genotype and specific mutations conferring resistance to rifampicin or streptomycin in the Beijing and LAM families. The biological implications of this correlation remain to be explored.

The genotypic characteristics and drug susceptibility profiles of clinical isolates of Mycobacterium tuberculosis recovered from prison hospital patients in the Tula region (central Russia) during 2001 and 2002 are reported. The emergence of multi-drug-resistant tuberculosis (TB) poses a major health risk to the population, with economic implications for TB control. Prisons serve as a continuous source of TB transmission. The results showed that members of the LAM and Beijing families are major contributors to the epidemiological picture of TB in the population studied. The two families of strains accounted for most of the drug-resistant TB in the population. The genotypic characteristics of the M. tuberculosis predominant LAM strain that was responsible for 31 % of TB cases in this setting are presented.

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Lethal factor (LF), a zinc-dependent protease of high specificity produced by Bacillus anthracis, is the effector component of the binary toxin that causes death in anthrax. New therapeutics targeting the toxin are required to reduce systemic anthrax-related fatalities. In particular, new insights into the LF catalytic mechanism will be useful for the development of LF inhibitors. We evaluated the minimal length required for formation of bona fide LF substrates using substrate phage display. Phagebased selection yielded a substrate that is cleaved seven times more efficiently by LF than the peptide targeted in the protein kinase MKK6. Site-directed mutagenesis within the metal-binding site in the LF active center and within phage-selected substrates revealed a complex pattern of LF-substrate interactions. The elementary steps of LF-mediated proteolysis were resolved by the stopped-flow technique. Pre-steady-state kinetics of LF proteolysis followed a four-step mechanism as follows: initial substrate binding, rearrangement of the enzyme-substrate complex, a rate-limiting cleavage step, and product release. Examination of LF interactions with metal ions revealed an unexpected activation of the protease by Ca 2؉ and Mn 2؉ . Based on the available structural and kinetic data, we propose a model for LF-substrate interaction. Resolution of the kinetic and structural parameters governing LF activity may be exploited to design new LF inhibitors.Anthrax is an infectious disease caused by the encapsulated, spore-forming bacterium Bacillus anthracis. Systemic forms of the disease, such as inhalational anthrax, are characterized by nonspecific early symptoms, rapid progression, and lethality approaching 100% (1). The lethality of inhalational anthrax is high even with antibiotic treatment and is caused by accumulation of secreted anthrax toxin (2), which consists of three proteins as follows: protective antigen (PA), 2 lethal factor (LF), and edema factor. PA binds to membrane receptors, forms pore complexes, and translocates LF and edema factor into the host cell (3, 4). The PA⅐LF complex is known as the lethal toxin, a virulence factor with pleiotropic action that facilitates establishment of the B. anthracis infection. LF is a Zn 2ϩ -dependent metalloprotease related to the thermolysin family that cleaves mitogen-activated protein kinase kinases (5).Although the complete mechanism by which LF causes fatal intoxication is still unclear, inhibition of LF proteolytic activity may be an efficient means of preventing anthrax lethality. A better understanding of the LF catalytic mechanism will facilitate rational design and optimization of LF inhibitors with potential clinical applicability. Recent structural (6, 7), mechanistic (8), and in vivo studies (9, 10) of LF point to a sophisticated catalytic mechanism involving accurate recognition of multiple target substrates.Here we use substrate phage display and stopped-flow fluorimetry kinetics to examine both the substrate specificity and elementary steps of substrate processi...