Antimycobacterial Drugs –Used for Treatment of

Tuberculosis

By,Ishaque P.KBiochemistry & MolecularbiologyPondicherry University

Introduction to Mycobacteria

• Aerobic bacilli

• Gram positive – Do not stain well with Gram stain

• Acid fast – Bind phenol based dyes (carbol fuchsin) and resist acid alcohol decoloration (Ziehl-Neelsen stain).

• Non spore forming

• Non motile, rods with varying sizes (1-10μm)

• Catalase positive

• Many mycobacteria produce pigments on culture

• Relatively simple growth medium required

• Rapid (<7 days) or slow growing (weeks or months)

• Most of them are pathogens, they are slow growing

Mycobacterium species of clinical importance• Mycobacterium tuberculosis : TB in humans

but also cats, dogs, pigs, chickens, parrots, canaries, guinea pigs and mice

• Mycobacterium bovis : bovine tuberculosis, also TB in man, other ruminants, pigs and more rarely in horses, dogs, cats.

• Mycobacterium avium subsps.Paratuberculosis : Johne’s disease in cattle, sheep, goats and deer .

• Mycobacterium avium complex : TB in birds, poultry very susceptible. Pigs susceptible but not cattle. Sporadic cases in horses, dogs and cats. Opportunist in man (AIDS – M. avium intracellulare)

• M. Leprae - Leprosy (man, mice, armadillos)• M. lepraemurium, M. ulcerans, M. kansasii,

M. fortuitum and M. Chelonae Skin ulceration and lymph node involvement in many different species, Chronic RTI

• Cell wall components

• Mycolic acids – resist phagocytic digestion.

• Sulfatides – prevent phagocyte activation and phagosome-lysosome fusion.

• Trehalose di-mycolate (cord factor) – Inhibits phagocyte chemotaxis, activation, phagosome-lysosome fusions and digesion.

• Lipoarabinomannan (LAM) – prevents phagocyte activation and digestion within the phagocyte.

• Mycosides – prevent intracellular killing and digestion

• Cell wall antigens in general induce DTH

• Other factors include SOD (superoxide dismutase) and heat shock proteins.

Virulence factors of Mycobacteria

General Features• Thick, waxy and complex• Higher fluidity in more

external regions than internal regions

• Relatively impermeable to hydrophilic solutes

• Contain porins (selective cationic channels)

Main Components• Peptidoglycan - contains

N-glycolylmuramic acid instead of N-acetylmuramic acid

• Arabinogalactan• Mycolic Acids (60% of

cellular envelope)• Lipoarabinomannan (LAM)

Mycobacterial (acid-fast) cell wall

Diagnosis of Mycobacterial infection• Immunological detection • ‘tuberculin’ testing- using PPD (purified

protein derivative) from the relevant bacterial species.

• Gama interferon assay• Laboratory Diagnosis - Microscopy

(e.g. Ziehl Neelsen staining, rhodamine/auramine fluorescent stain) of appropriate specimens from site of infection

• Culture – of lymph node, tissue lesions, sputum, aspirates, milk

• Decontamination of specimens with sodium hydrochloride, sodium triphosphate, oxalic acid

• Lowenstein Jensen medium (slants) incubated for up to 8 weeks

• Genomic detection (e.g. PCR)