Transcript Prof. Kambal-Mycobacteria (Undergraduate)

Genus = Mycobacteria
By: Prof. A.M.Kambal
Consultant Microbiologist
& Head of the Bacteriology
Genus = Mycobacteria
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.
Classification
I-
Parasitic
a)
b)
M. tuberculosis complex:
(i)
M.t.b. (hominis) – humans
(ii) M. bovis – cattle cause
(iii) M. africanum – human tuberculosis
(vi) Others
M. leprae
II- 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:
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
Secondary TB (Open Infections) Continued
b) Reinfection (Exogenous)
 In secondary TB. There is excessive tissue destruction
of the lung leading to formation of cavities.
Patient Complain of:
a)
Cough
b)
Loss of weight
c)
Fever
d)
Cough of blood, i.e. Haemoptysis
 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
(Majority)
Disease
Apical Lung disease
Chronic Progressive Disease
Progressive
Bronchopneumonia
Miliary TB
TB Meningitis
Urinary TB
Bone TB
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
Nurses
Laboratory Staff
Immunosuppressed patients
(iv) Underlying Diseases:
Sarcoidosis
Pneumoconiosis
Diabetes
Laboratory 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 Control
Control:
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.
1.
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.
Prevention
1) 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. 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 leprosy
Seen 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:
Diagnosis:
Z/N stain of
Similar to tuberculin test
(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.
Epidemiology
 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 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 Mycobacteria
(Atypical / Saprophytic / Mycobacteria other than
Tuberculosis (MOTT))
 Members are found in the environment
E.g. Soil, water and others may be found
and other animals.
in
birds
 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
Mycobacteria are not communicable (Continued)
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.
Negative Tuberculin Test
 No
induration, either due to:
 no previous infection
 pre-hypersensitivity stage
 lost TB sensitivity with loss of Ag.
 AIDS,
anergic, susceptible to infection
Secondary TB (Continue)
 Clinically:
fever, cough, hemoptysis.
 Source: - endogenous (reactivation)
- exogenous (reinfection)
Immunity to Tuberculosis
 Cell-mediated
immunity associated with
delayed hypersensitivity reaction.
 Detected by tuberculin test.
 Takes 2-10 weeks to react to tuberculin.
Negative Tuberculin Test
 No
induration, either due to:
 no previous infection
 pre-hypersensitivity stage
 lost TB sensitivity with loss of Ag.
 AIDS,
anergic, susceptible to infection
Quantiferon G test
 It
measures the amount of interferon
produced by lymphocytes in patients
latently infected by M.tuberculosis
 Compared to TST IT IS NOT AFFECTED by
atypical mycobacterial infection