Virulence factors of Mycobacterium bovis

Virulence factors of Mycobacterium bovis are the special properties that en able it to infect, survive, multiply and cause disease in an animal host. A n understanding of these factors will lead to new strategies including an e ffective vaccine to control bovine tuberculosis. A few factors have already been identified and two broadly different approaches to discover other vir ulence factors are now being used. In the first approach, libraries of rand om M. bovis mutants are produced, the likely attenuated mutants are identif ied using a screening technique and the interrupted genes in selected mutan ts are identified. in the second approach, genes encoding putative virulenc e factors are selected by a range of different methods and then inactivated , usually by allelic exchange, to produce likely attenuated mutants of M. b ovis. In both approaches, loss of virulence by a mutant must be determined in an animal model. Subsequently, the mutant must be complemented back to v irulence with an active form of the identified gene in order to demonstrate that loss of virulence was not due to polar effects of the mutation on nea rby genes. It is almost certain that most of the virulence factors of M. bo vis are the same as those of the classical human tuberculosis organism, Myc obacterium tuberculosis, as both organisms can cause identical clinical dis ease in humans and are genetically very similar. Many putative virulence ge nes are now being investigated and only the inherent slowness with which my cobacterial work proceeds, delays the inevitable arrival of an exciting new phase in the understanding of mycobacterial disease. (C) 2001 Harcourt Pub lishers Ltd.