Mycobacterium tuberculosis

Publisher Summary Mycobacterium tuberculosis is the causative agent of tuberculosis (TB). Recent years have seen the resurgence of TB, particularly where there is a high prevalence of human immunodeficiency virus (HIV) infection. Most mycobacteria are saprophytes in soil or water and are harmless to humans; however, at some point thousands of years ago, M. tuberculosis became a significant human pathogen. The origins of tuberculosis are both ancient and obscure. Mycobacteria are aerobic to microaerophilic Gram-positive members of the actinomycete family. M. tuberculosis occurs as straight rods which, unlike other members of the actinomycete group, produce neither aerial hyphae nor spores. A marked characteristic of mycobacteria is that they behave anomalously during staining with arylmethane dyes. Recent developments have, however, limited the value of sputum-based AFB staining methods. The rise in the numbers of HIV-infected people in particular has posed significant problems. Many of those who are HIV-infected may become co-infected with normally non-pathogenic mycobacteria such as Mycobacterium avium (M. avium) or they may develop extra pulmonary tuberculosis for which sputum smears would be unhelpful.