Genus = MycobacteriaGenus = Mycobacteria

Consultant Microbiologist & Head of the Bacteriology

By: Prof. A.M.Kambal By: Prof. A.M.Kambal

Genus = MycobacteriaGenus = Mycobacteria

Definition:Definition:

Acid – Fast Bacilli / Acid and Alcohol fast bacilli, non – motile. Aerobic bacilli difficult to stain by gram stain - But stained by Z – N stain. Acid fastness due to Mycolic acid in cell wall.

ClassificationI- Parasitic

a) M. tuberculosis complex:

(i) M.t.b. (hominis) – humans

(ii) M. bovis – cattle cause

(iii) M. africanum – human tuberculosis

(vi) Others

b) M. lepraeII- Saprophytic (Environmental)

E.g. M. kansasii

M. avium - intracellulare

M. tberculosis (M.t.b.) (hominis)(humans)

Optimum Temperature: 37 % Takes 6-8 weeks on average to see colonies Medium Complex. Commonly used one is

egg – based called Loweinstein – Jensen (L.J).

Pathogenesis: Causes TB mainly affect lung but also other organs.

Route – respiratory – inhalation of infected droplet nuclei.

Infection - Pulmonary TB 2 Types:Infection - Pulmonary TB 2 Types:

I- Primary TB bacilli settle in the lungs usually the Right lung in the middle lobe.

Granulomatous inflammation Lesion called tubercle in the sub pleural space Spread to regional mediastinal lymph nodes Similar lesions occur

Pulmonary TB (Continued)

Further spread of bacilli to other organs in the body

In 90 – 95 % of people with primary infection, the tubercle heals.

In the remaining 5-10 % the infection does not heal, secondary to immunosuppression and leads to active disease in multiple organs and is then referred to as miliary tuberculosis.

(II) Secondary TB (open / infectious) Usually in the lungs especially apex of the right

lung. It maybe by:

a) Reactivation (Endogenous) - as a result of suppression of host”s defence system by:

Diabetes

Steroid and other immunosuppressive

Malignant disease e.g. Leukemia

b) Reinfection (Exogenous)

In secondary TB. There is excessive tissue destruction of the lung leading to formation of cavities.

Patient Complain of:a) Coughb) Loss of weightc) Feverd) Cough of blood, i.e. Haemoptysis

Secondary TB (Open Infections) Continued

In secondary TB too, the disease process may become as progressive as in primary TB and lead to miliary TB.

Tuberculosis: (a) Chest X-ray of a patient with tuberculosis bronchopneumonia. (b) Chest X-ray of the same patient 10 months

after antituberculous therapy. (Courtesy of Dr. R.S.Kennedy)

Pathogenesis of Pulmonary Tb

Infection

Non-Immune Host (tuberculin –ve)

Asymptomatic Primary Symptomatic Infection Primary Infection

Tuberculin +ve

Reactivation TB Resolution Progressive

(Majority) Disease

Apical Lung disease Bronchopneumonia

Miliary TB

TB Meningitis

Urinary TB

Bone TB

Chronic Progressive Disease

Virulence factor The bacilli survive and multiply in the macrophages

Epidemiology: Pulmonary TB is a communicable disease.

i) Sources of infection in the community are the open pulmonary lesions (usually seen in adults).

Epidemiolgy (Continued)

(ii) Environmental Factors : - over crowding, poor ventilation and housing

(iii) Populations at special risk:- Health workers – Doctors

NursesLaboratory StaffImmunosuppressed patients

(iv) Underlying Diseases: Sarcoidosis Pneumoconiosis Diabetes

Laboratory DiagnosisLaboratory Diagnosis

i) Specimen - Sputum, Urine, CSF etc.

3 successive specimens

ii) Direct Microscopy - Acid alcohol – fast bacilli by Z.N. stain of auramine fluorescent.

Fluorescent Auramine Gel - More sensitive

less specific

iii) Culture - Loweinstein Jensen Media (4 – 8 weeks)

iv) Guinea Pig - inoculation - Kill guinea pig after 6 – 8 weeks.

Mycobacterium tuberculosis (approx. x 1000)

Mycobacterium tuberculosis (approx. x 1000)

Treatment: Prolonged, multiple and combined treatment schedule:

i) Ethambutol (or Pyrazinamide)

plus

Isoniazid for 2 mos.

plus

Rifampicin

ii) Then continue with Isoniazid and

Rifampicin for 4 more months.

iii) Total duration of treatment 9 months.

Prevention And ControlPrevention And ControlControl:1. Isolate all open pulmonary cases and treat effectively.

2. Trace all contacts of the index case by:

a) Tuberculin testing: This is a T-cell mediated hypersensitivity reaction.

Interpretation: Positive Tests: Patient has at least previously come into contact with M.tb and developed infection.

Negative: Patient has not previously come into contact with a case of tuberculosis and has not therefore developed the primary infection.

PreventionPrevention1) Vaccination: Live attenuated vaccine called

Bacilli – Calmette Guerin (BCG) given to all newborn babies.

N.B. B.C.G. not given to those already tuberculin positive.

Immunity in T.B. is cell mediated and protection given by B.C.G. is about 10 years.

2) Chemoprophylaxis: Isoniazid is given to those who are tuberculin positive but who don’t have disease.

M. LepraeM. Leprae

This is the cause of leprosy in humans. It affects the skin,

peripheral nerves and the nasal mucosa. M. leprae is weakly acid fast.

Culture: Can not be grown in artificial media in the lab.

Grown in animals:

(i) Foot pad of mice or

(ii) The armadillo

Infection is acquired mainly by inhalation of respiratory droplets.

Outcome of the infection depends on the status of patient’s cell mediated immune response:

1) Tuberculoid leprosySeen in patients with competent T-cell function and there is slow and progressive development.

2) Lepromatous leprosy

In such patients the cell mediated immune system is very poor and the bacilli are therefore able to multiply and spread through blood without any inhibition by the patient’s immune system. The lesions are contagious. i.e. Infectious.

Disease is more severe in the Lepromatous form.

Lepromin test: Similar to tuberculin test

Diagnosis:Z/N stain of (i) Nasal scrapings or

(ii) Ear lobe aspirate and look for AFB

Leprosy. Mutilation of fingers due to trophic changes associated with anaesthesia caused by infection of peripheral nerves.

Treatment:

R (i) Dapsone - but many strains now resistant

(ii) Dapsone + Rifampicin - Duration about 1-2

years.

Vaccination:

Combination killed M. leprae + B.C.G..

EpidemiologyEpidemiology

Source of infection usually a case of leprosy

Requires close and prolonged contact for infection to occur

Believed that most infections are acquired in childhood

Laboratory DiagnosisLaboratory Diagnosis

i) Specimen - Sputum, Urine, CSF, etc.

ii) Direct Microscopy - Acid Alcohol – fast bacilli by Z.N. stain of auramine &

fluorescent.

iii) Culture - Lowenstein Jensen Media (4-8 weeks)

iv) Guinea Pig - Inoculation - Kill g. pig after 6-8 weeks.

Environmental MycobacteriaEnvironmental Mycobacteria(Atypical / Saprophytic / Mycobacteria other than (Atypical / Saprophytic / Mycobacteria other than

Tuberculosis (MOTT))Tuberculosis (MOTT))

Members are found in the environment

E.g. Soil, water and others may be found in birds and other animals.

They all grow on L.J. media and some will also grow on Blood Agar. Some are slow growing just as M. tuberculosis but others grow fast within 5-7 days.

Environmental Mycobacteria (Continued)

Some produce yellowish or orange pigment only when growing in the presence of light and are called PHOTOCHROMOGENS; others will produce pigment whether grown in light or darkness and are called SCOTOCHROMOGENS, and other do not produce any pigment at all. They are called NONCHROMOGENS. Atypical mycobacteria are opportunistic and do not produce disease in the normally healthy person.

Infections by these mycobacteria are not communicable

1) M. avium – intracellulare – cause tuberculosis in birds. Infections in human only under special circumstances in AIDS patients.

It is slow growing Non chromogenic Causes pulmonary disease in immunocompromised

specially AIDS patients. Often resistant to many anti TB drugs.

2) M. kansasii - usually found in soil. Photochromogenic Slow growing Optimum temperature 37°C

3) M. scrofulaceum Scotochromogenic Slow growing

Optimum temperature 25°C

4) M. fortuitum Fast grower – within 5-7 days Causes infection in soft tissue.

E.g. Skin, muscles, forming abscesses.

Mycobacteria are not communicable (Continued)

Negative Tuberculin TestNegative Tuberculin Test

No induration, either due to:No induration, either due to: no previous infectionno previous infection pre-hypersensitivity stagepre-hypersensitivity stage lost TB sensitivity with loss of Ag.lost TB sensitivity with loss of Ag.

AIDS, anergic, susceptible to infectionAIDS, anergic, susceptible to infection

Secondary TBSecondary TB (Continue) (Continue)

Clinically: fever, cough, hemoptysis.Clinically: fever, cough, hemoptysis. Source: - endogenousSource: - endogenous (reactivation)(reactivation)

- - exogenous exogenous (reinfection(reinfection))

Immunity to TuberculosisImmunity to Tuberculosis

Cell-mediated immunity associated with Cell-mediated immunity associated with delayed hypersensitivity reaction.delayed hypersensitivity reaction.

Detected by Detected by tuberculin testtuberculin test.. Takes 2-10 weeks to react to tuberculin.Takes 2-10 weeks to react to tuberculin.

Negative Tuberculin TestNegative Tuberculin Test

No induration, either due to:No induration, either due to: no previous infectionno previous infection pre-hypersensitivity stagepre-hypersensitivity stage lost TB sensitivity with loss of Ag.lost TB sensitivity with loss of Ag.

AIDS, anergic, susceptible to infectionAIDS, anergic, susceptible to infection

Quantiferon G test Quantiferon G test

It measures the amount of interferon It measures the amount of interferon produced by lymphocytes in patients produced by lymphocytes in patients latently infected by M.tuberculosis latently infected by M.tuberculosis

Compared to TST Compared to TST IT IS NOT AFFECTEDIT IS NOT AFFECTED by by atypical mycobacterial infectionatypical mycobacterial infection