Background Rates of mortality and readmission are high in patients hospitalised with acute exacerbations of chronic obstructive pulmonary disease (AECOPD). In this population, the prognostic value of the Medical Research Council Dyspnoea Scale (MRCD) is uncertain, and an extended MRCD (eMRCD) scale has been proposed to improve its utility. Coexistent pneumonia is common and, although the CURB-65 prediction tool is used, its discriminatory value has not been reported. Methods Clinical and demographic data were collected on consecutive patients hospitalised with AECOPD. The relationship of stable-state dyspnoea severity to inhospital mortality and 28-day readmission was assessed. The discriminatory value of CURB-65, MRCD and eMRCD, in the prediction of in-hospital mortality, was assessed and compared. Results 920 patients were recruited. 10.4% died inhospital and 19.1% of the 824 survivors were readmitted within 28 days of discharge. During their stable state prior to admission, 34.2% of patients were too breathless to leave the house. Mortality was significantly higher in pneumonic than in non-pneumonic exacerbations (20.1% vs 5.8%, p<0.001). eMRCD was a significantly better discriminator than either CURB-65 or the traditional MRCD scale for predicting in-hospital mortality, and was a stronger prognostic tool than CURB-65 in the subgroup of patients with pneumonic AECOPD. Conclusions The severity of dyspnoea in the stable state predicts important clinical outcomes in patients hospitalised with AECOPD. The eMRCD scale identifies a subgroup of patients at a particularly high risk of inhospital mortality and is a better predictor of mortality risk than CURB-65 in exacerbations complicated by pneumonia. BACKGROUND

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Gene replacement by homologous recombination is a powerful tool for fundamental studies of gene function, as well as allowing specific attenuation of pathogens, but has proved difficult to achieve for Mycobacterium tuberculosis. We have used a plasmid-based test system to demonstrate the occurrence of homologous recombination in the tuberculosis vaccine strain Mycobacterium bovis BCG, and we have successfully replaced a target gene in BCG by homologous recombination, using a shuttle plasmid. Specific inactivation of selected genes will facilitate study of virulence factors and drug resistance as well as allowing rational attenuation of M. tuberculosis for the production of new vaccines.

The causative agents of leprosy and tuberculosis, Mycobacterium leprae and Mycobacterium tuberculosis, have a lipid-rich cell envelope which contributes to virulence and antibiotic resistance. Acyl coenzyme A carboxylase, which catalyzes the first committed step of lipid biosynthesis, consists in mycobacteria of two subunits, one of which is biotinylated. Genes from M. leprae and M. tuberculosis encoding a biotinylated protein have been cloned and sequenced. Analysis of the derived protein sequences demonstrated the presence of biotin-binding sites and putative ATP-bicarbonate interactions sites, consistent with the proteins having a biotin carboxylase function as well as their being biotin carrier proteins.

We have constructed a mycobacterial integrative vector by placing two copies of the insertion sequence IS900 flanking a kanamycin-resistance gene into a 'suicide' vector unable to replicate in mycobacteria. The Mycobacterium leprae gene encoding the M. leprae 18 kDa protein was cloned between the two copies of IS900 to provide expression signals. Constructs were introduced into Mycobacterium species smegmatis, vaccae and bovis BCG by electroporation and selection for kanamycin resistance. The expression of the 18 kDa gene was analysed by Western blotting. Integration of the vector into the M. smegmatis chromosome was analysed by Southern blotting. One to five copies of the vector were detected in each transformant. The SIV gag p27 gene and the foot-and-mouth disease virus VP1 140-160 epitope were successfully cloned into the 18 kDa gene and expression in M. smegmatis was obtained.