A small rod-shaped bacillus that grows very slowly and causes tuberculosis (TB).

Mycobacterium tuberculosis (Mtb) survives within human macrophages. It can establish very long-lasting infections, often without causing any symptoms (latent TB). Treatment of TB is highly challenging, requiring several antibiotics for several months. Mtb is slow growing and difficult to culture, and identification increasingly relies on molecular diagnostics.

Although Mtb does not acquire antibiotic resistance through genetic exchange, some chromosomal mutations confer resistance to commonly used antibiotics such as rifampicin. Drug-resistant TB infections are a growing public health challenge. Multidrug-resistant TB (MDR-TB), strains resistant to rifampicin and isoniazid, requires longer and more intensive antibiotic treatment, with high treatment failure rates. Extremely drug-resistant TB (XDR-TB) is resistant to rifampicin, isoniazid, fluoroquinolones and at least one second-line drug (amikacin, capreomycin or kanamycin).