Mycobacteria

Dr. Ashish V. Jawarkar

Mycobacterium• Name from Myco and Bacteria, Fungus like bacteria

• Because it forms mould like growth on liquid cultures

Mycobacteria that infect humans

• M. Tuberculosis – TB

• M. Leprae – Leprosy

• Non tuberculous mycobacteria / atypical mycobacteria

Mycobacterium Tuberculosis

• Morphology• Growth characteristics• Biochemical reactions• Resistance• Pathogenicity and virulence• Epidemiology• Diseases caused• Laboratory diagnosis• Treatment

Morphology

• Neither gram positive, nor negative

• Acid fast

• They have mycolic acid in their cell wall which makes them acid fast

• Difficult to decolorise with organic acids

Slightly curved rods

Non motile

Non capsulated

Growth characteristics

• Obligate aerobes

• Grow slowly – generation time 15 hours

• Colonies appear in two weeks

• Optimum temperature is 37 deg

• Solid media most commonly used – LJ media

Biochemical teststo differentiate MTB from atypical

mycobacteria• Niacin test –

– adding cyanogen bromide+aniline + ethanol = canary yellow color

• Paranitrobenzoic acid– MTB cannot grow in presence of this

• Catalase peroxidase test– MTB is weakly positive

• Aryl sulfatase test– Negative for MTB

Treatment and Resistance

• DOTS – directly observed treatment shortcourse– HRZE for 4 months– HR for 2 months

• H – isoniazid R – rifampicin Z - Pyrazinamide

• E - Ethambutol

MDR-TB

• Resistant to isoniazid and rifampicin

XDR-TB

• Resistant to all drugs

Pathogenicity and virulence

• Its pathogenicity is due to complex lipids like mycolic acid in cell wall.. This makes it– Acid fast– Resistant to antibiotics– Resistant to disinfectants like acid and alkalis– Resistant to immune system– Resistant to destruction by macrophages

Epidemiology

• Source – Humans with TB• Spread – droplet nuclei – inhaled• India – more than 40 percent population – that is

nearly half of us are infected• Only saved due to our immunity• To stop TB – RNTCP – revised national

tuberculosis control program has been started – offering DOTS to nearly 15 million patients daily – free of charge

Tuberculosis

• Pulmonary

• Extra pulmonary

Pulmonary

Lab diagnosis

• Sample – sputum for pulmonary, biopsy for extrapulmonary sites

• Stain – Zn stain

• Culture – LJ media

• Raised ESR

• PCR – polymerase chain reaction

Montoux test

• PPD/tuberculin is injected into skin

• Look for induration of skin

Treatment

• DOTS

Mycobacterium leprae

• Causes leprosy

• Seen in developing countries like India only

• Slightly curved rods

• Singly or in groups

• Cigar bundle appearance

• Lepra cells

Growth characteristics

• Cannot be cultivated in vitro on any media

• Grown in foot pad of armadillo

Biochemical reactions

• Cannot be grown..

• Cannot know biochemical reactions

Resistance

• Not known

• ----

Epidemiology

• Human disease only

• Source – nasal secretions

• Entry – respiratory tract / skin

• Not highly communicable

Diseases caused

• Leprosy

• Affects skin and nerves

• Hypoaesthetic patch, thickened nerves

• Lion face, saddle nose, autoamputation

• Two main types – tuberculoid leprosy, lepromatous leprosy

Tuberculoid leprosyaka paucibacillary leprosy

Tuberculoid leprosy

Multibacillary leprosy/lepromatous leprosy

AUTO AMPUTATION

Lab Diagnosis• Sample – biopsy from nasal mucosa, skin

lesions, ear lobes

• Stained with modified ZN stain – use 5% H2SO4 instead of 20%

• Cannot be cultured

LEPROMIN TEST

• Method is similar to tuberculin test

• Injected antigen is lepromin

• Reaction is read at – 48 hours – fernandez– 3-4 weeks - mitsuda

• MDT

Treatment

• Multi drug therapy consisting of– RIFAMPICIN

– DAPSONE

NOT COVERED

• ATYPICAL MYOBACTERIA – Can be asked for short note – 5 marks

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