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MYCOBACTERIUM
K
R
MICRO
NOTES
1
Introduction
 Mycobacterium tuberculosis is an infectious microorganism that causes Tuberculosis
in humans. It is a type of Mycobacteria which include 2 species that cause diseases in
humans Mycobacterium tuberculosis and Mycobacterium leprae (which causes
Leprosy)
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Mycobacterium tuberculosis
 Mycobacterium tuberculosis is a species of pathogenic bacteria in the family
Mycobacteriaceae and the causative agent of tuberculosis. First discovered in 1882 by Robert Koch,
M. tuberculosis has an unusual, waxy coating on its cell surface primarily due to the presence of
mycolic acid.
Domain: Bacteria
Phylum: Actinobacteria
Class: Actinobacteria
Order: Mycobacteriales
Family: Mycobacteriaceae
Genus: Mycobacterium
Species: M. tuberculosis
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Characteristics of Mycobacterium tuberculosis
 M. tuberculosis are straight or slightly curved rod, they may be in groups or single.
 They are non motile, non-sporing and non capsulating.
 Non-Acid fast rods and granules from young culture is also reported to produce tuberculosis. This bacilli are
called Much’s granules.
 They are aerobic and grow slow colony appears in within 2 to 6 weeks, Optimum temperature 37℃ and pH 6.4
to 7.
 They form dry, rough, raised and irregular colonies, white to yellowish in color.
 They are Obligate parasites that depend on others to survive
 They are Opportunist pathogens that can cause serious infections when the immune system is suppressed by
the presence of disease or drugs (in immunosuppression)
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Mycobacterium tuberculosis Epidemiology
 Tuberculosis was originated in East Africa about 3 million years ago. A growing pool of evidence suggests that the
current strains of M. tuberculosis is originated from a common ancestor around 20,000 – 15,000 years ago.
 Mycobacterium tuberculosis is the second infectious diseases causing morbidity and mortality in the developing
world and 1/3 of the worlds population is infected with Mycobacterium Tuberculosis with 30 million people have
active tuberculosis. There are about 9 million new cases every year and 3 million people die of Mycobacterium
Tuberculosis disease yearly.
 Tuberculosis is a global pandemic, killing someone approximately every 22 seconds — about 1.4 million in 2019
alone
 World TB Day 2021- 24 March
 Global efforts to combat TB have saved an estimated 63 million lives since the year 2000. The theme of World TB
Day 2021 - 'The Clock is Ticking' –conveys the sense that the world is running out of time to act on the
commitments to end TB made by global leaders
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Mycobacterium tuberculosis
Morphology/Structure
 The structure of Mycobacterium tuberculosis when viewed under the microscope shows
slender rods (this why they are called Bacilli rods). This bacterium is difficult to staining
but once stained, it becomes resistant to decolorization by diluted mineral acids this is
the reason why Mycobacterium tuberculosis is called Acid Fast bacilli (AFB).

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Resistance of Mycobacterium tuberculosis
to heat and chemicals
 It is relatively resistant to heat but becomes destroyed when heated to 60 degrees Celsius for 20 minutes.
 It can survive in sputum for about 20 to 30 hours
 Mycobacteria are relatively resistant to disinfectants and can survive after exposure to any of these chemicals:
5% Phenol, 15% Sulphuric acid, 3% Nitric acid, 5% Oxalic acid and 4% sodium hydroxide (NaOH)
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Symptoms and Signs of Mycobacterium
tuberculosis infection
 Low grade fever
 Cough: may be productive of blood stained sputum
 Drenching night sweats
 Weight loss
 Anemia
 Fatigue
 Hemoptysis (coughing of blood)
 Dyspnea (difficulty in breathing)
 Other symptoms are dependent on the part of the body affected outside of the lungs such as in Extra pulmonary
tuberculosis
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Mycobacterium tuberculosis transmission
 Droplet infection: this occurs through person to person transmission by inhalation of aerosols when an
infected person coughs, speaks, signs or laughs
 Contamination of skin abrasion this occurs mostly in laboratory workers.
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Stages
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Pathology and causes
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Signs and symptoms
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Laboratory Diagnosis of Mycobacterium
tuberculosis infection
 Culture of needed specimen
 Tuberculin skin test (mantoux test)
 Chest X ray for pulmonary tuberculosis
 Polymerase chain reaction (PCR) test
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Types of specimen that can be collected for
culturing Mycobacteria tuberculosis
 Sputum
 Urine
 Body fluids such as pleural fluid, peritoneal fluid, synovial fluid etc
 Gastric lavage
 Blood
 Tissue biopsy
 The type of specimen collected is based on the organ or part of the body affected by tuberculosis.
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Types of Culture Media for growing
Mycobacterium tuberculosis
 Solid media
 Liquid media
 Culture Media is like a broth containing all the needed ingredients for the
appropriate growth of specific microorganisms. Because of this, there are different
types depending on the ingredient added to it.
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Types of Solid Culture Media used for
culturing Mycobacterium tuberculosis
 Egg containing Solid culture media: this include: Lowenstein-Jensen Medium, Petragnini medium and Dorset
medium
 Blood containing Solid culture media: example is the Tarshis medium
 Serum containing solid culture media: example is the Loefflers serum slope
 Potato containing culture media: example is the Pawlowskys medium
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Types of Liquid Culture Media used for
culturing Mycobacterium tuberculosis
 Dubos Media
 Middlebrooks Media
 Proskauer & Becks Media
 Sulas Media
 Sauton Media
 Culturing Mycobacterium tuberculosis can therefore be carried using any of these media: either the liquid media
or solid media.
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Mycobacterium tuberculosis Treatment
 The treatment guideline for infection by mycobacterium tuberculosis is the same as for pulmonary tuberculosis. It
involves the use of Rifampicin, Isoniazid, Ethambutol and Pyrazinamide. Treatment is based on the category of
the patient using the W.H.O classification.
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Mycobacterium tuberculosis infection
prevention
 Prevention is done by vaccination of children at birth using the BCG vaccine. This vaccine protects against
Tuberculosis and even when infected, it will be milder and it will prevent against having skeletal TB,
meningeal and miliary Tuberculosis forms.
 Bacillus Calmette–Guérin vaccine is a vaccine primarily used against tuberculosis. It is named after its
inventors Albert Calmette and Camille Guérin. In countries where tuberculosis or leprosy is common, one
dose is recommended in healthy babies as soon after birth as possible.
 The vaccine was originally developed from Mycobacterium bovis, which is commonly found in cows. While
it has been weakened, it is still live.
 Wearing N95 mask.
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Mycobacterium leprae
 Mycobacterium leprae is a bacterium that causes leprosy, also known as "Hansen’s disease", which is a chronic
infectious disease that damages the peripheral nerves and targets the skin, eyes, nose, and muscles.
 Leprosy can occur at all ages from infancy to elderly, but is curable in which treatments can avert disabilities. It
was discovered in 1873 by the Norwegian physician Gerhard Armauer Hansen, who was searching for the bacteria
in the skin nodules of patients with leprosy.
Domain: Bacteria
Phylum: Actinobacteria
Order: Corynebacteriales
Family: Mycobacteriaceae
Genus: Mycobacterium
Species: M. leprae
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Characteristics of Mycobacterium leprae
 M. leprae is a straight or slightly curved rod, (1-8 mm X 0.2 -0.5 mm) in size with parallel sides and rounded ends.
 They are arranged singly, in parallel bundles in a packet or in globular masses.
 Polar bodies and other intracellular elements may be present.
 The bacteria show considerable morphological variations. They exhibit cubical, lateral or branching forms.
 They are non-motile, non-spore forming.
 They are Gram positive and stains readily than M. tuberculosis.
 They are acid fast bacilli but less thus 5 % H2SO4 is used for decolorization during staining procedures.
 In stained smears, the live leprae bacilli appear solid and uniformly stained whereas the dead appear fragmented and granular.
 The bacilli are seen singly or in groups, intracellularly or lying free outside the cell.
 They frequently are bound together by a lipid like substances the glia.
 These masses of bacteria lying together is called ‘globi’ that present a ‘cigar bundle’ appearance.
 The globi appears in Virchow’s ‘lepra cell’ or ‘foamy cell’ which are large undifferentiated histocytes.
 M. leprae is an obligate intracellular parasite that multiplies preferentially in tissues at cooler temperature.
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Epidemiology
 About 208,000 people worldwide are infected with leprosy, according to the World Health Organization,
most of them in Africa and Asia. About 100 people are diagnosed with leprosy in the U.S. every year, mostly
in the South, California, Hawaii, and some U.S. territories.
 30 January, World Leprosy Day 2021 is “Beat Leprosy, End Stigma and advocate for Mental Wellbeing.”
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Mode of transmission:
 Leprosy is an exclusively human disease but is not very contagious.
 Nasal secretions and discharges from nodular lesions are the most likely
infections materials for family contacts.
 Transmission of leprosy is generally via:
 Inhalation of an infectious aerosol
 By direct contact with skin
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Pathogenesis:
 Lepra bacilli enter the body usually through respiratory system.
 It has low pathogenicity, only a small proportion of infected people develop signs of the disease.
 After entering the body, bacilli migrate towards the neural tissues and binds to Schwann cells (Scs).
 Schwann cells are major target for infection by M. leprae leading to injury of nerve, demyelination and consequent disability.
 M. leprae invades Schwann cells by specific laminin-binding protein of 2.1 KDa in addition to Phenolic glycolipid-1 (PGL-1).
 Bacteria can also be found in macrophages, muscles cells and endothelial cells of blood vessels.
 After entering the Schwann cells or macrophages, fate of the bacterium depends on the resistance of infected individuals towards the
infecting organism.
 Bacilli start multiplying slowly (about 12-14 days for one bacterium to divide into two) within cells, get liberated from the destroyed cells
and enter other unaffected cells.
 Till this stage, person remains free from signs and symptoms of leprosy.
 As the bacilli multiply, bacterial load increases in the body and infection is recognized by the immunological system.
 Lymphocytes and histiocytes invades the tissue.
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 At this stage clinical manifestation may appear as involvement of nerves with impairment of sensation and skin patch. If it is not
diagnosed then it is determined by the strength of patient’s immune response.
 Specific and effective cell mediated immunity (CMI) provides protection to a person against leprosy.
 When specific CMI is effective in eliminating/controlling the infection in the body, lesions heal spontaneously or it produces
paucibacillary (PBL) type of leprosy.
 If CMI is deficient the disease spreads uncontrolled and products multi-bacillary (MB) leprosy with multiple system involvement.
 Sometimes the immune response is abruptly altered, either following treatment (Multiple drug therapy) or due to improvement of
immunological status which results in inflammation of skin and or nerves and even other tissue called as leprosy reaction.
 In person with good CMI, granuloma formation occurs in cutaneous nerve.
 This nerve swells and gets destroyed often only a few fascicles of the nerve are infiltrated, but inflammation within the epineurium causes
compression and destruction of unmyelinated sensory and autonomic fiber.
 Myelinated motor fibers are the last to get affected producing motor impairments.
 Severe inflammation may result in caseous necrosis within the nerve.
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 Clinical manifestation of sensory loss occurs when nearly 30% of sensory fibers are destroyed.
 Good CMI limits the disease to nerve Schwann cell resulting in occurrence of the pure neural leprosy.
 M. leprae may escape from nerve to adjacent skin at any time and cause classical skin lesions.
 In persons with depressed CMI, bacilli entering the Schwann cells multiply rapidly and destroy the nerve.
 Also, bacilli liberated by Schwann cells that also infected and destroyed are engulfed by histiocytes.
 Histiocytes with bacilli inside them become wandering macrophages.
 Bacilli multiply inside these macrophages and travel to other tissues, through blood, lymph or tissue third.
 Toll like receptors (TLRs) play important role in the pathogenesis of leprosy. TLRs such as TLR-1 and TLR-2 are found
on the surface of Schwann cells, especially in patients with tuberculoid leprosy. M. leprae activates this receptor on
Schwann cells, which is suggested to be responsible for the activation of apoptosis gene and which enhances the
onset of nerve damage seen in the mild disease.
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Clinical features:
 Incubation period:
 The incubation period varies from few months as long as 30 years and average 2-5 years.
 Clinical forms of leprosy:
 There are two major extreme or polar forms of leprosy-tuberculoid form and lepromatous leprosy.
 Many patients occupy an intermediate position on the spectrum, which may be classified as borderline
tuberculoid (BT), mid-borderline (BB) or borderline lepromatous (BL).
 The type of disease is a reflection of the immune status of the host. It is therefore not permanent and varies
with chemotherapy and alterations in host resistance.
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1. Tuberculoid leprosy:
 This is a localized form of the disease and found in patients with high degree of resistance where cell mediated
immunity is intact and the skin is infiltrated with helper TH1 cells.
 There is usually only a single or very few well defined skin- lesions.
 The lesions may appear as a flattered area with raised edges and erythematous edges and a dry hairless center.
 It is without feeling and less pigmented than the surrounding skin.
 The lesions are commonly found on the face limbs, buttocks or elsewhere but not in the axilla, perineum or
scalp.
 Neural involvement is common that is pronounced leading to deformities, particularly in the hands and feet.
Affected nerves show marked thickening.
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2. Borderline tuberculoid leprosy:
 Lesions in this form of leprosy are similar to those seen in the tuberculoid leprosy, but are smaller and more
numerous.
 Skin lesions are few, asymmetric and with nearly complete anesthesia, peripheral nerves are thickened and
involved asymmetrically.
 This form of leprosy may remain at this stage or can regress to the tuberculoid form or it can progress to
lepromatous form.
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3. Mid- borderline leprosy:
 Skin lesions in this type of leprosy consists of numerous unequally shaped plagues that
are less well defined than in the tuberculoid types.
 These skin lesions are distributed asymmetrically. Anesthesia is moderate and the
disease can remain in this stage can improve or worsen.
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4. Borderline lepromatous leprosy:
 Skin lesions are moderate to numerous.
 They are slightly asymmetrical with slight or no anesthesia.
 Peripheral nerves are enlarged moderately and symmetrical. Like the other forms
of borderline leprosy, the disease may remain in this stage, improve or worsen.
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5. Lepromatous leprosy:
 It is generalized form of the disease and found in individuals where the host resistance is low due to specific defect in their cellular
response to M. leprae antigen.
 The bacteria disseminate in hematogenous manner although the disease does not appear to manifest in deeper organs.
 The lesions are small and many.
 They are shining with no loss of feeling.
 Superficial nodular lesions develop which consists of granulation tissue containing a dense collection of vacuolated cells to
different stages of development from mononuclear cells to lepra cells.
 The nodules ulcerate become secondarily infected and cause distortion and mutilation.
 Facial disfigurement is commonly observed.
 The skin of the face and forehead becomes thickened and corrugated giving rise to typical leonine face.
 The lateral part of eyebrows may be lost.
 Other disfigurement of lesions includes pendulous ear lobes, hoarseness of voice, perforation of nasal septum and nasal collapse.
 The reticuloendothelial system, eyes, kidneys and bones are also involved.
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 The lepromatous type is more infective than other types.
 Patients often have a hemolytic anemia, a raised erythrocyte sedimentation rate
due to abnormal serum albumin and globulin levels.
 Antinuclear factor and rheumatoid factor may be found in serum and LE cells can
sometimes be selected in blood buffy coat preparation.
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Diagnosis and Treatment
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Prevention
 Prevention of contact with droplets from nasal and other secretions from patients with untreated M.
leprae infection is currently the most effective way to avoid the disease. Treatment of patients with
appropriate antibiotics stops the person from spreading the disease.
 Animals (chimpanzees, mangabey monkeys, and nine-banded armadillos) rarely transfer M. leprae to
humans. Nonetheless, it is not advisable to handle such animals in the wild. These animals are a source
for endemic infections.
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Reference
 Satish Gupte, Medical Microbiology, 3rd edition, Jaypee brothers Medical publishers,
New Delhi, Page no 222-239.
 Apurba Sankar Sastry, Sandhya Bhat K, Essential of practical Microbiology, The Health
Science Publishers, New Delhi, Page no 97-101.
 Satish Gupte, The Short Textbook Of Medical Microbiology, 8th edition, Jaypee Brothers,
Medical publishers, New Delhi, Page no 188-200.
 https://www.jotscroll.com/forums/11/posts/159/mycobacterium-tuberculosis-
morphology-acid-fast-stain-characteristics.html
 https://www.osmosis.org/learn/Mycobacterium_tuberculosis_(Tuberculosis)
 https://www.osmosis.org/learn/Mycobacterium_leprae
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Mycobacterium Mycobacterium tuberculosis

  • 2. Introduction  Mycobacterium tuberculosis is an infectious microorganism that causes Tuberculosis in humans. It is a type of Mycobacteria which include 2 species that cause diseases in humans Mycobacterium tuberculosis and Mycobacterium leprae (which causes Leprosy) K R MICRO NOTES 2
  • 3. Mycobacterium tuberculosis  Mycobacterium tuberculosis is a species of pathogenic bacteria in the family Mycobacteriaceae and the causative agent of tuberculosis. First discovered in 1882 by Robert Koch, M. tuberculosis has an unusual, waxy coating on its cell surface primarily due to the presence of mycolic acid. Domain: Bacteria Phylum: Actinobacteria Class: Actinobacteria Order: Mycobacteriales Family: Mycobacteriaceae Genus: Mycobacterium Species: M. tuberculosis K R MICRO NOTES 3
  • 4. K R MICRO NOTES 4
  • 5. Characteristics of Mycobacterium tuberculosis  M. tuberculosis are straight or slightly curved rod, they may be in groups or single.  They are non motile, non-sporing and non capsulating.  Non-Acid fast rods and granules from young culture is also reported to produce tuberculosis. This bacilli are called Much’s granules.  They are aerobic and grow slow colony appears in within 2 to 6 weeks, Optimum temperature 37℃ and pH 6.4 to 7.  They form dry, rough, raised and irregular colonies, white to yellowish in color.  They are Obligate parasites that depend on others to survive  They are Opportunist pathogens that can cause serious infections when the immune system is suppressed by the presence of disease or drugs (in immunosuppression) K R MICRO NOTES 5
  • 6. Mycobacterium tuberculosis Epidemiology  Tuberculosis was originated in East Africa about 3 million years ago. A growing pool of evidence suggests that the current strains of M. tuberculosis is originated from a common ancestor around 20,000 – 15,000 years ago.  Mycobacterium tuberculosis is the second infectious diseases causing morbidity and mortality in the developing world and 1/3 of the worlds population is infected with Mycobacterium Tuberculosis with 30 million people have active tuberculosis. There are about 9 million new cases every year and 3 million people die of Mycobacterium Tuberculosis disease yearly.  Tuberculosis is a global pandemic, killing someone approximately every 22 seconds — about 1.4 million in 2019 alone  World TB Day 2021- 24 March  Global efforts to combat TB have saved an estimated 63 million lives since the year 2000. The theme of World TB Day 2021 - 'The Clock is Ticking' –conveys the sense that the world is running out of time to act on the commitments to end TB made by global leaders K R MICRO NOTES 6
  • 7. K R MICRO NOTES 7
  • 8. Mycobacterium tuberculosis Morphology/Structure  The structure of Mycobacterium tuberculosis when viewed under the microscope shows slender rods (this why they are called Bacilli rods). This bacterium is difficult to staining but once stained, it becomes resistant to decolorization by diluted mineral acids this is the reason why Mycobacterium tuberculosis is called Acid Fast bacilli (AFB).  K R MICRO NOTES 8
  • 9. Resistance of Mycobacterium tuberculosis to heat and chemicals  It is relatively resistant to heat but becomes destroyed when heated to 60 degrees Celsius for 20 minutes.  It can survive in sputum for about 20 to 30 hours  Mycobacteria are relatively resistant to disinfectants and can survive after exposure to any of these chemicals: 5% Phenol, 15% Sulphuric acid, 3% Nitric acid, 5% Oxalic acid and 4% sodium hydroxide (NaOH) K R MICRO NOTES 9
  • 10. Symptoms and Signs of Mycobacterium tuberculosis infection  Low grade fever  Cough: may be productive of blood stained sputum  Drenching night sweats  Weight loss  Anemia  Fatigue  Hemoptysis (coughing of blood)  Dyspnea (difficulty in breathing)  Other symptoms are dependent on the part of the body affected outside of the lungs such as in Extra pulmonary tuberculosis K R MICRO NOTES 10
  • 11. Mycobacterium tuberculosis transmission  Droplet infection: this occurs through person to person transmission by inhalation of aerosols when an infected person coughs, speaks, signs or laughs  Contamination of skin abrasion this occurs mostly in laboratory workers. K R MICRO NOTES 11
  • 12. Stages K R MICRO NOTES 12
  • 13. K R MICRO NOTES 13
  • 14. K R MICRO NOTES 14
  • 15. K R MICRO NOTES 15
  • 16. Pathology and causes K R MICRO NOTES 16
  • 17. Signs and symptoms K R MICRO NOTES 17
  • 18. K R MICRO NOTES 18
  • 19. Laboratory Diagnosis of Mycobacterium tuberculosis infection  Culture of needed specimen  Tuberculin skin test (mantoux test)  Chest X ray for pulmonary tuberculosis  Polymerase chain reaction (PCR) test K R MICRO NOTES 19
  • 20. K R MICRO NOTES 20
  • 21. Types of specimen that can be collected for culturing Mycobacteria tuberculosis  Sputum  Urine  Body fluids such as pleural fluid, peritoneal fluid, synovial fluid etc  Gastric lavage  Blood  Tissue biopsy  The type of specimen collected is based on the organ or part of the body affected by tuberculosis. K R MICRO NOTES 21
  • 22. Types of Culture Media for growing Mycobacterium tuberculosis  Solid media  Liquid media  Culture Media is like a broth containing all the needed ingredients for the appropriate growth of specific microorganisms. Because of this, there are different types depending on the ingredient added to it. K R MICRO NOTES 22
  • 23. Types of Solid Culture Media used for culturing Mycobacterium tuberculosis  Egg containing Solid culture media: this include: Lowenstein-Jensen Medium, Petragnini medium and Dorset medium  Blood containing Solid culture media: example is the Tarshis medium  Serum containing solid culture media: example is the Loefflers serum slope  Potato containing culture media: example is the Pawlowskys medium K R MICRO NOTES 23
  • 24. Types of Liquid Culture Media used for culturing Mycobacterium tuberculosis  Dubos Media  Middlebrooks Media  Proskauer & Becks Media  Sulas Media  Sauton Media  Culturing Mycobacterium tuberculosis can therefore be carried using any of these media: either the liquid media or solid media. K R MICRO NOTES 24
  • 25. Mycobacterium tuberculosis Treatment  The treatment guideline for infection by mycobacterium tuberculosis is the same as for pulmonary tuberculosis. It involves the use of Rifampicin, Isoniazid, Ethambutol and Pyrazinamide. Treatment is based on the category of the patient using the W.H.O classification. K R MICRO NOTES 25
  • 26. Mycobacterium tuberculosis infection prevention  Prevention is done by vaccination of children at birth using the BCG vaccine. This vaccine protects against Tuberculosis and even when infected, it will be milder and it will prevent against having skeletal TB, meningeal and miliary Tuberculosis forms.  Bacillus Calmette–Guérin vaccine is a vaccine primarily used against tuberculosis. It is named after its inventors Albert Calmette and Camille Guérin. In countries where tuberculosis or leprosy is common, one dose is recommended in healthy babies as soon after birth as possible.  The vaccine was originally developed from Mycobacterium bovis, which is commonly found in cows. While it has been weakened, it is still live.  Wearing N95 mask. K R MICRO NOTES 26
  • 27. Mycobacterium leprae  Mycobacterium leprae is a bacterium that causes leprosy, also known as "Hansen’s disease", which is a chronic infectious disease that damages the peripheral nerves and targets the skin, eyes, nose, and muscles.  Leprosy can occur at all ages from infancy to elderly, but is curable in which treatments can avert disabilities. It was discovered in 1873 by the Norwegian physician Gerhard Armauer Hansen, who was searching for the bacteria in the skin nodules of patients with leprosy. Domain: Bacteria Phylum: Actinobacteria Order: Corynebacteriales Family: Mycobacteriaceae Genus: Mycobacterium Species: M. leprae K R MICRO NOTES 27
  • 28. Characteristics of Mycobacterium leprae  M. leprae is a straight or slightly curved rod, (1-8 mm X 0.2 -0.5 mm) in size with parallel sides and rounded ends.  They are arranged singly, in parallel bundles in a packet or in globular masses.  Polar bodies and other intracellular elements may be present.  The bacteria show considerable morphological variations. They exhibit cubical, lateral or branching forms.  They are non-motile, non-spore forming.  They are Gram positive and stains readily than M. tuberculosis.  They are acid fast bacilli but less thus 5 % H2SO4 is used for decolorization during staining procedures.  In stained smears, the live leprae bacilli appear solid and uniformly stained whereas the dead appear fragmented and granular.  The bacilli are seen singly or in groups, intracellularly or lying free outside the cell.  They frequently are bound together by a lipid like substances the glia.  These masses of bacteria lying together is called ‘globi’ that present a ‘cigar bundle’ appearance.  The globi appears in Virchow’s ‘lepra cell’ or ‘foamy cell’ which are large undifferentiated histocytes.  M. leprae is an obligate intracellular parasite that multiplies preferentially in tissues at cooler temperature. K R MICRO NOTES 28
  • 29. K R MICRO NOTES 29
  • 30. Epidemiology  About 208,000 people worldwide are infected with leprosy, according to the World Health Organization, most of them in Africa and Asia. About 100 people are diagnosed with leprosy in the U.S. every year, mostly in the South, California, Hawaii, and some U.S. territories.  30 January, World Leprosy Day 2021 is “Beat Leprosy, End Stigma and advocate for Mental Wellbeing.” K R MICRO NOTES 30
  • 31. K R MICRO NOTES 31
  • 32. Mode of transmission:  Leprosy is an exclusively human disease but is not very contagious.  Nasal secretions and discharges from nodular lesions are the most likely infections materials for family contacts.  Transmission of leprosy is generally via:  Inhalation of an infectious aerosol  By direct contact with skin K R MICRO NOTES 32
  • 33. Pathogenesis:  Lepra bacilli enter the body usually through respiratory system.  It has low pathogenicity, only a small proportion of infected people develop signs of the disease.  After entering the body, bacilli migrate towards the neural tissues and binds to Schwann cells (Scs).  Schwann cells are major target for infection by M. leprae leading to injury of nerve, demyelination and consequent disability.  M. leprae invades Schwann cells by specific laminin-binding protein of 2.1 KDa in addition to Phenolic glycolipid-1 (PGL-1).  Bacteria can also be found in macrophages, muscles cells and endothelial cells of blood vessels.  After entering the Schwann cells or macrophages, fate of the bacterium depends on the resistance of infected individuals towards the infecting organism.  Bacilli start multiplying slowly (about 12-14 days for one bacterium to divide into two) within cells, get liberated from the destroyed cells and enter other unaffected cells.  Till this stage, person remains free from signs and symptoms of leprosy.  As the bacilli multiply, bacterial load increases in the body and infection is recognized by the immunological system.  Lymphocytes and histiocytes invades the tissue. K R MICRO NOTES 33
  • 34.  At this stage clinical manifestation may appear as involvement of nerves with impairment of sensation and skin patch. If it is not diagnosed then it is determined by the strength of patient’s immune response.  Specific and effective cell mediated immunity (CMI) provides protection to a person against leprosy.  When specific CMI is effective in eliminating/controlling the infection in the body, lesions heal spontaneously or it produces paucibacillary (PBL) type of leprosy.  If CMI is deficient the disease spreads uncontrolled and products multi-bacillary (MB) leprosy with multiple system involvement.  Sometimes the immune response is abruptly altered, either following treatment (Multiple drug therapy) or due to improvement of immunological status which results in inflammation of skin and or nerves and even other tissue called as leprosy reaction.  In person with good CMI, granuloma formation occurs in cutaneous nerve.  This nerve swells and gets destroyed often only a few fascicles of the nerve are infiltrated, but inflammation within the epineurium causes compression and destruction of unmyelinated sensory and autonomic fiber.  Myelinated motor fibers are the last to get affected producing motor impairments.  Severe inflammation may result in caseous necrosis within the nerve. K R MICRO NOTES 34
  • 35.  Clinical manifestation of sensory loss occurs when nearly 30% of sensory fibers are destroyed.  Good CMI limits the disease to nerve Schwann cell resulting in occurrence of the pure neural leprosy.  M. leprae may escape from nerve to adjacent skin at any time and cause classical skin lesions.  In persons with depressed CMI, bacilli entering the Schwann cells multiply rapidly and destroy the nerve.  Also, bacilli liberated by Schwann cells that also infected and destroyed are engulfed by histiocytes.  Histiocytes with bacilli inside them become wandering macrophages.  Bacilli multiply inside these macrophages and travel to other tissues, through blood, lymph or tissue third.  Toll like receptors (TLRs) play important role in the pathogenesis of leprosy. TLRs such as TLR-1 and TLR-2 are found on the surface of Schwann cells, especially in patients with tuberculoid leprosy. M. leprae activates this receptor on Schwann cells, which is suggested to be responsible for the activation of apoptosis gene and which enhances the onset of nerve damage seen in the mild disease. K R MICRO NOTES 35
  • 36. Clinical features:  Incubation period:  The incubation period varies from few months as long as 30 years and average 2-5 years.  Clinical forms of leprosy:  There are two major extreme or polar forms of leprosy-tuberculoid form and lepromatous leprosy.  Many patients occupy an intermediate position on the spectrum, which may be classified as borderline tuberculoid (BT), mid-borderline (BB) or borderline lepromatous (BL).  The type of disease is a reflection of the immune status of the host. It is therefore not permanent and varies with chemotherapy and alterations in host resistance. K R MICRO NOTES 36
  • 37. 1. Tuberculoid leprosy:  This is a localized form of the disease and found in patients with high degree of resistance where cell mediated immunity is intact and the skin is infiltrated with helper TH1 cells.  There is usually only a single or very few well defined skin- lesions.  The lesions may appear as a flattered area with raised edges and erythematous edges and a dry hairless center.  It is without feeling and less pigmented than the surrounding skin.  The lesions are commonly found on the face limbs, buttocks or elsewhere but not in the axilla, perineum or scalp.  Neural involvement is common that is pronounced leading to deformities, particularly in the hands and feet. Affected nerves show marked thickening. K R MICRO NOTES 37
  • 38. K R MICRO NOTES 38
  • 39. 2. Borderline tuberculoid leprosy:  Lesions in this form of leprosy are similar to those seen in the tuberculoid leprosy, but are smaller and more numerous.  Skin lesions are few, asymmetric and with nearly complete anesthesia, peripheral nerves are thickened and involved asymmetrically.  This form of leprosy may remain at this stage or can regress to the tuberculoid form or it can progress to lepromatous form. K R MICRO NOTES 39
  • 40. 3. Mid- borderline leprosy:  Skin lesions in this type of leprosy consists of numerous unequally shaped plagues that are less well defined than in the tuberculoid types.  These skin lesions are distributed asymmetrically. Anesthesia is moderate and the disease can remain in this stage can improve or worsen. K R MICRO NOTES 40
  • 41. 4. Borderline lepromatous leprosy:  Skin lesions are moderate to numerous.  They are slightly asymmetrical with slight or no anesthesia.  Peripheral nerves are enlarged moderately and symmetrical. Like the other forms of borderline leprosy, the disease may remain in this stage, improve or worsen. K R MICRO NOTES 41
  • 42. 5. Lepromatous leprosy:  It is generalized form of the disease and found in individuals where the host resistance is low due to specific defect in their cellular response to M. leprae antigen.  The bacteria disseminate in hematogenous manner although the disease does not appear to manifest in deeper organs.  The lesions are small and many.  They are shining with no loss of feeling.  Superficial nodular lesions develop which consists of granulation tissue containing a dense collection of vacuolated cells to different stages of development from mononuclear cells to lepra cells.  The nodules ulcerate become secondarily infected and cause distortion and mutilation.  Facial disfigurement is commonly observed.  The skin of the face and forehead becomes thickened and corrugated giving rise to typical leonine face.  The lateral part of eyebrows may be lost.  Other disfigurement of lesions includes pendulous ear lobes, hoarseness of voice, perforation of nasal septum and nasal collapse.  The reticuloendothelial system, eyes, kidneys and bones are also involved. K R MICRO NOTES 42
  • 43.  The lepromatous type is more infective than other types.  Patients often have a hemolytic anemia, a raised erythrocyte sedimentation rate due to abnormal serum albumin and globulin levels.  Antinuclear factor and rheumatoid factor may be found in serum and LE cells can sometimes be selected in blood buffy coat preparation. K R MICRO NOTES 43
  • 44. K R MICRO NOTES 44
  • 45. K R MICRO NOTES 45
  • 46. K R MICRO NOTES 46
  • 47. Diagnosis and Treatment K R MICRO NOTES 47
  • 48. Prevention  Prevention of contact with droplets from nasal and other secretions from patients with untreated M. leprae infection is currently the most effective way to avoid the disease. Treatment of patients with appropriate antibiotics stops the person from spreading the disease.  Animals (chimpanzees, mangabey monkeys, and nine-banded armadillos) rarely transfer M. leprae to humans. Nonetheless, it is not advisable to handle such animals in the wild. These animals are a source for endemic infections. K R MICRO NOTES 48
  • 49. Reference  Satish Gupte, Medical Microbiology, 3rd edition, Jaypee brothers Medical publishers, New Delhi, Page no 222-239.  Apurba Sankar Sastry, Sandhya Bhat K, Essential of practical Microbiology, The Health Science Publishers, New Delhi, Page no 97-101.  Satish Gupte, The Short Textbook Of Medical Microbiology, 8th edition, Jaypee Brothers, Medical publishers, New Delhi, Page no 188-200.  https://www.jotscroll.com/forums/11/posts/159/mycobacterium-tuberculosis- morphology-acid-fast-stain-characteristics.html  https://www.osmosis.org/learn/Mycobacterium_tuberculosis_(Tuberculosis)  https://www.osmosis.org/learn/Mycobacterium_leprae K R MICRO NOTES 49
  • 50. K R MICRO NOTES 50