Recent developments in molecular biology of mycobacteria.

Molecular biology is beginning to revolutionise the study of tuberculosis and other mycobacterial diseases. DNA hybridization is used to classify strains at the generic and specific level and, when combined with the polymerase chain reaction, may rapidly detect very small amounts of mycobacterial DNA in clinical material. Restriction endonuclease mapping or the more refined restriction length polymorphism analysis is used to type strains at the sub-specific level for epidemiological purposes. Detection of plasmids is also an epidemiological aid and there is considerable interest in the role of plasmids as determinants of pathogenicity and virulence of some mycobacterial species. Genomic libraries provide a source of DNA probes for use in hybridization and restriction length polymorphism analysis and pure antigens in large quantities for experimental and diagnostic use. Vectors for the insertion of genes into mycobacteria provide a way of analysing genes relevant to virulence and protective immunity and a means of producing new vaccines for use against leprosy as well as tuberculosis. Finally, the ability to clone mammalian genes in bacteria enables immunological mediators to be produced in quantity for the elucidation of immune mechanisms in mycobacterial infections and possibly for therapeutic use.