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


Health & Medicine

Mycobacteria