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Microbiology II > MYCROBACTERIA > Flashcards

MYCROBACTERIA Flashcards

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1
Q

What are the typical growth conditions for Mycobacterium species?

A

Mycobacterium species are generally aerobic, although some may grow in reduced oxygen concentrations

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2
Q

Do Mycobacterium species form spores?

A

No, Mycobacterium species are non-spore forming, except for M. marinum

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3
Q

Major mycobacterium species

A

M . tuberculosis
M. bovis
M. bovis Bcg
M. africunum
M. caprae
M canetti
M . microti
M. pinnipedi

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3
Q

Describe the morphology of Mycobacterium cells

A

Mycobacterium cells are very thin, slightly curved or straight rods. Some species may also display branching morphology.

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4
Q

morphology of mycobacterium

A

Displays a branching morphology
Only genus of in the mycobacteriaceae family

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5
Q

Non-tuberculous mycobacteria: early pigmented, rapid growing mycobacterium spp

A

M canariasense
M. cosmeticum
M. monacense

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5
Q

what is M pinnipedi

A

Bacterium that affects marine mammals such as seals and sea lions. Not typically associated with human infections except in cases of close contact with infected animals

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6
Q

what is M africumun

A

Primarily found in west and central Africa. A cause of tuberculosis

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7
Q

what is M. bovis

A

Causative agent of bovine tuberculosis (Btb), bacterial infection that primarily affects cattle, can also affext othe ranimals including humans

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7
Q

what is M microti

A

Affects rodents such as voles and mice. It can also causeinfections in humans like tb, lymphadenitis

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7
Q

Slow growing nonphotochromogens (does not produce pigments when exposed to light)

A

M avium complex
M intracellulare
M celatum

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7
Q

3 examples of Early pigmented rapid growing mycobacteria

A
  • M. canariasense
  • M. cosmeticum
  • M. monacense
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7
Q

3 examples of Slow glowing nonphotochromogens

A

M. avium complex
M. intracellulare
M. celatum

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7
Q

what is the disadvantage of mycobacterium having N-glycolylmuramic acid instead of N-acetylmuramic acid

A

Because of this cell structure, Mycobacteria are difficult to stain with commonly used basic aniline dyes, such as those used in Gram staining. Nevetheless, they are considered gram positive.

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8
Q

explain the composition of hydrophobic cell structure of mycobacterium

A

That greasy cell wall—rich in mycolic acids—creates a formidable barrier. It’s like wrapping themselves in cling film made of lipids.

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8
Q

what does the cell structure of mycobacterium contain

A

contains N-glycolylmuramic acid instead of N-acetylmuramic acid, and it has a very high lipid content which creates a hydrophobic permeability barrier

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8
Q

Why are Mycobacteria difficult to stain using basic aniline dyes like those used in Gram staining?

A

Due to their unique cell wall composition, Mycobacteria resist staining with basic aniline dyes. These dyes cannot easily penetrate the hydrophobic barrier created by mycolic acids. Consequently, Mycobacteria do not follow the typical Gram staining behavior.

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8
Q

What is the key difference in the cell wall composition of Mycobacteria compared to other bacteria?

A

Mycobacteria have a cell wall that contains N-glycolylmuramic acid instead of the more common N-acetylmuramic acid found in most bacterial cell walls. This difference contributes to their distinct properties

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8
Q

How does the high lipid content in the Mycobacterial cell wall affect its permeability

A

: The high lipid content, particularly the presence of mycolic acids, creates a hydrophobic permeability barrier. This barrier makes it challenging for hydrophilic molecules (like water-soluble dyes) to penetrate the cell wall.

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8
Q

What is acid-fastness, and how does it relate to mycobacteria?

A

Acid-fastness is a unique property exhibited by mycobacteria due to their cell wall structure. When stained with a basic fuchsin dye and subjected to decolorization with acidified alcohol (usually 3% hydrochloric acid), mycobacteria resist decolorization. This means that even after prolonged exposure to the dye and subsequent treatment, the color remains steadfast within their cells.

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9
Q

Despite their staining challenges, how are Mycobacteria classified in terms of Gram reaction?

A

Despite their staining difficulties, Mycobacteria are considered gram positive. This classification is based on their cell wall structure and other biochemical features, even though they don’t conform to the standard Gram staining protocol.

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9
Q

why does mycobacteria grow more slowly than most other human pathogenic bacteria

A

because of their hydrophobic cell surface

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10
Q

advantages of mycobacteria over other bacterias

A

By growing slowly, they can withstand harsh conditions—like a microbial tortoise with a shell of resilience.

Persistence: When faced with antibiotics or immune attacks, mycobacteria hunker down. Their slow growth helps them evade threats.

Mycobacteria struggle to let nutrients in. Their hydrophobic surface repels water, which means fewer molecules can sneak through.

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11
Q

what is the growth rate of mycobacterium

A

A single cell’s generation time may range from approx. 20hrs to 36hrs for M. ulcerans. This slow growth results in the formation of visible colonies in 2 to 60 days at optimum temperature

12
Q

What is an interesting fact about mycobacterium

A

Everyone has tuberculosis in their system, they just dont show symptoms up until their immunity weakens, either due to old age or other diasease like HIV.

13
Q
A
13
Q

when and how does an individual gets TB infection after being exposed

A

The disease usually occurs some years after the initial infection, when the patient’s immune system breaks down for some reason other than the presence of tuberculosis bacilli in the lung.

14
Q

what percentage of people may fall sick after being exposed to mycobacterium

A

Inhalation of a single viable organism has been shown to lead to infection, 15 to 20% of people develop the disease

15
Q

what is the pathogenesis of M. bovis

A

After ingestion of milk from infected cows, Mycobacterium bovis may penetrate the gastrointestinal mucosa or invade the lymphatic tissue of the oropharynx.
Attenuated strain of M. Bovis, Calmette-Guerin (BCG) HAS BEEN USED TO IMMunise susceptible individuals against tuberculosis

16
Q

what is an increasing complicating factor in the management of TB

A

increasing incidence of co-infection with the human immune deficience virus(HIV

16
Q

how many people are infected with TB on earth

A

1.7 billion

17
Q

by statiscts how many people with HIV are HIV positive

A

ABOUT 1.1 million individuals living with HIV are associated with TB

18
Q

which people are common with TB

A

poor,
homeless,
intravenous drug users,
alcoholics,
the elderly
medically undeserved populations

19
Q

How do clinical manifestations of TB vary?

A

Clinical manifestations of TB can range from asymptomatic (no symptoms) to acutely symptomatic (with noticeable signs).

20
Q

What symptoms might symptomatic TB patients exhibit?

A

Symptomatic TB patients may present with systemic symptoms, pulmonary signs and symptoms, or signs related to other organ involvement (e.g., kidney symptoms). They can also have a combination of these features

21
Q

Can you distinguish Mycobacterium tuberculosis (MTB) complex infections from other conditions?

A

No, MTB complex infections are clinically, radiologically, and pathologically indistinguishable from other conditions

21
Q

what are the symptoms of of TB

A

include low grade fever, night sweats, fatigue, anorexia (loss of appetite) and weight loss

21
Q

What happens upon respiratory infection with MTB complex organisms

A

Upon respiratory infection, T cells and macrophages from the cellular immune system migrate to the lungs. The MTB complex organisms are then phagocytized by the macrophages.

22
Q

How do MTB complex organisms behave within macrophages?

A

Despite being phagocytized, these organisms are capable of intracellular multiplication within the macrophages

23
Q

What often occurs when the host encounters MTB complex infection?

A

The host is frequently unable to eliminate the MTB organisms. As a result, a systemic hypersensitivity to Mycobacterium antigens develops.

24
Q

what is the spectrum of TB/genesis of TB

A

Upon respiratory infection with MTB complex organisms, the cellular immune system T cells and macrophages migrate to the lungs, and the organisms are phagocytised by the macrophages
However, those organisms are capable of intracellular multiplication in the macrophages
Often the host is unable to eliminate the organisms, and the result is a systemic hypersensitivity to Mycobacterium antigens
Granulomas or a hard tubercle forms in the lung from the lymphocytes, macrophages, and cellular pathology, including giant cell formation (cellular fusion displaying multiple nuclei).
If the Mycobacterium antigen concentration is high, the hypersensitivity reaction may result in tissue necrosis, caused by enzymes released from the macrophages. In this case, no granuloma forms, and a solid or semisolid, caseous material is left at the primary lesion site

In some patients, the disease may spread via the lymph system or hematogenously, leading to meningeal or military TB. Often in patients with depressed or ineffective cellular immunity
Disseminated tuberculosis may involve organs besides the lungs like Genitourinary tract, lymph nodes (cervical lymphadenitis), CNS (meningitis), Bone and joint (arthritis and osteomyelitis), peritoneum, pericardium, larynx and pleural lining (pleuritis)
Disseminated tuberculosis may be diagnosed by a positive tuberculin skin test

25
Q

What is the purpose of the Tuberculin Skin Test (TST)

A

The TST is used to determine whether an individual has been infected with Mycobacterium tuberculosis (MTB), the bacterium responsible for tuberculosis (TB).

26
Q

What does the TST rely on

A

The TST relies on the principle of delayed hypersensitivity cell-mediated immunity

27
Q

How is the TST administered

A

A purified protein derivative (PPD) of tuberculin (an extract from MTB) is injected intracutaneously (just under the skin).

28
Q

When is the TST read

A

The TST is read after 48 to 72 hours.

29
Q

What signs indicate a positive TST result?

A

An infected individual typically shows erythema (redness) at the injection site, but the most important sign is induration (firmness due to immune cell influx).

30
Q

How is the size of induration interpreted

A

Interpretation varies based on risk factors:
- ≥5 mm: Positive for high-risk individuals.
- ≥10 mm: Positive for moderate-risk individuals.
- ≥15 mm: Positive for low-risk individuals

31
Q

Methods uswd in TB diagnosis

A
  1. Tuberculin skin test
  2. Enzyme linked immunosorbent assay
  3. Elisa
  4. Genexpert
  5. Microscopy
  6. Fluorochrome stain
  7. Culture
32
Q

enzyme linked immunosorbent assay in TB diagnosis

A

It is called QuantiFERON-TB Gold
The assay measures a component of the cell-mediated immune response to MTB to diagnose latent tuberculosis infection and tuberculosis disease
It is based on the quantification of interferon-gamma released from sensitised lymphocytes in heparinized whole blood that has been incubated overnight with a mixture of synthetic peptides stimulating two proteins in MTB

33
Q

ELISA in TB diagnosis

A

The test assesses responses to multiple antigens
It can be performed in a single patient visit
It is less subject to reader bias and error
An important feature is that the results of the assay are unaffected by previous BCG vaccination

33
Q

explain microscopy/acid fast staining in TB diagnosis

A

The cell wall of Mycobacteia contain long-chain, cross-linked fatty acids called Mycolic acids.
Mycolic acids complex basic dyes, contributing to the characteristic of acid-fastness that distinguishes mycobacteria from other bacteria
The mycolic acids and lipids in the mycobacterial cell wall probably account for the unusual resistance of these organisms to the effects of drying and harsh decontaminating agents in addition to the property of acid-fastness
Acid-fastness is affected by the age of colonies, the medium on which growth occurs, and exposure to ultraviolet light.
Three types of staining procedures are used in the laboratory for rapid detection and confirmation of acid-fast bacilli: fluorochrome, Ziehl-Neelsen, Kinyoun
Smears for all methods are prepared in the same way
Visualization of AFB in sputum or other clinical material should be considered only presumptive evidence of tuberculosis, because staining does not specifically identify M. tuberculosis.

34
Q

why carbol fuchsin requires heating

A

Carbolfuchsin requires heating of the slide for better penetration of the stain into the mycobacterial cell wall (

to fix the stain so that is should not be washed off

35
Q

Close Relative of M. tuberculosis

A

M. leprae

36
Q

what are culture challenges of M leprae

A

t has not yet been successfully cultivated in vitro (outside the human or animal host).
However, researchers have found ways to propagate M. leprae in specific animal models.

37
Q

Leprosy (Hansen’s Disease):

A

Leprosy, also called Hansen’s disease, is a chronic infectious disease.
It primarily affects the skin, mucous membranes, and peripheral nerves.
Historically, leprosy was associated with severe social stigma due to disfigurement caused by nerve damage.

38
Q

which animals are used to culture M leprae

A
  1. Armadillos: M. leprae can be cultivated in armadillos. These animals serve as a reservoir for the bacterium.
  2. Mice Footpads: Another method involves inoculating M. leprae into the footpads of mice, where it can multiply.
39
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A
40
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Microbiology II (4 decks)

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