Mycobacterium Tuberculosis: Etiological Agent of Tuberculosis
Pp. 5-13 (9)
The Mycobacteria genus, member of the Mycobacteriacea family and
Actinomycetales order, are nonmotile, nonsporulating, acid-fast bacilli, 2-4 μ in length
and 0.2-0.5 μ in width. Their waxy cell wall, rich in mycolic acid plays an important
role in its resistance to many antibiotics. The Mycobacterium genus can be separated
into two major groups. One group includes the Mycobacterium tuberculosis complex
and the other includes non-tuberculous (also known as environmental) mycobacteria.
The Mycobacterium tuberculosis complex includes M. tuberculosis (Mtb), M. canettii,
M. africanum, M. microti, M. bovis, M.caprae and M. pinnipedii. Mycobacteria are
facultative intracellular bacteria that multiply within phagocytic cells. In addition to the
ability to acquire new resistance through the acquisition of chromosomal mutations,
Mtb has a variety of intrinsic resistance mechanisms that allow active neutralization of
antibiotic actions. Mtb intrinsic drug resistance can be divided into two categories:
passive resistance and specialized resistance mechanisms; besides the cell wall barrier
that helps slow down the penetration of antibiotics, Mtb operates multiple specialized
resistance mechanisms that allow active detoxification of drugs once they reach the
cytoplasmic space. Mtb, acquired drug resistance is caused by spontaneous random
mutations in chromosomal genes, facilitating the selection of resistant strains during
sub-optimal drug therapy. Clinically, drug resistance in Mtb represents the selection of
random genetic mutations, not a change caused by exposure to the medication.
Acquired resistance, Actinomicetales, Chromosome, Detoxification, Genus,
Intrinsic resistance, M. africanum, M. bovis, M. canettii, M.caprae and M. pinnipedii, M.
microti, M. tuberculosis, Mutations, Mycobacteria.
Clínica y Laboratorio de Tuberculosis Hospital General Tijuana, México.