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Unit 13 > Microbiology TB lecture > Flashcards

Microbiology TB lecture Flashcards

1
Q

In microbiology what does the term facultative mean?

A

The ability of an organism to adapt to different environmental conditions. Often use host resources to their advantages but also able to live independently.
For example faculative anerobe - can produce ATP with and without the presence of oxygen.

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2
Q

What in mircobiology is meant by non-motile?

A

Organisms of cells that are not capable of movement on their own.
Do not possess the means to move through their environment independently aka lack flagella

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3
Q

What in microbiology is meant by a obligate aerobe?

A

Organisms that require oxygen to survive and grow.

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4
Q

What is a ghon focus in microbiology?

A

1-2cm
Cheese looking with pulmonary parenchymal nodule with a necrotic centre usually close to the pleura

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5
Q

What is a ghon complex in microbiology?

A

Ghon focus associated with enlarged hilar lymph nodal involvement

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6
Q

What is a ranke complex in TB microbiology?

A

A ghon complex undergoes progressive fibrosis and calcification

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7
Q

What is meant by host tropism in microbiology?

A

Specificity of a pathogen for infecting particular hosts or tissues within those hosts/

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8
Q

What is meant by an acid fast bacillus in microbiology?

A

Bacterium that has a unique, waxy lipid layer in its cell wall made predominantly of mycolic acid.
This characteristic makes resistant to decolorisation during staining procedures hence the name acid-fast.

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9
Q

What are the characteristics of a mycobacterium tuberculosis?

A

Non motile
Non -sporing
Obligate aerobe
Facultative intracellular organism (can live inside or outside host cells including macrophages)
Can remain dormant for decades (latent TB infection)

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10
Q

What are the staining and identification characteristics of myobacterium tuberculosis?

A

Slightly curved baciluus shape
Gram stain poorly
Stains fluorescence yellow on auramine
Or pink on Ziehl-Neelson.

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11
Q

What is a mycobacterium tuberculosis complex?

A

Genetically related groups of mycobacterium species that can cause tuberculosis in humans or animals.
99.5% similar but differ widely in host tropism, phenotype and pathogenicity.

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12
Q

What is the growth rate of myobacterium tuberculosis?
What is this relevant?

A

tD 18-24 hrs under ideal conditions
This is very slow compared to other microbes such as E.coli and S,aureus. Means a patient can be infected for a long time before symptoms start to show as need time to replicate and increase in number to cause sufficient damage.

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13
Q

What are the main types of mycobacterium tuberculosis complex that can cause TB in humans?

A

Mycobacterium tuberculosis (cause 85%)
Mycobacterium africanum
Mycobacterium canettii
Mycobacterium bovis
Mycobacterium orygis.

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14
Q

What are the different geographic distributions or myobacterium causes of TB in humans?

A

Mycobacterium tuberculosis - worldwide
M. Afrincanum - W and central Africa
M. canettii - horn of Africa
M. bovis - associated with areas of unpastuerised milk usage or from cattle such as bison, elk consumption.
M. orygis - from deer, diary cattle, humans

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15
Q

What mycobacterium species tends to be used in vaccination?

A

Attenuated strain of M.bovis is used in human vaccinations
Shares significant genetic and antigenic similarities to Mtb.

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16
Q

What are the features of the mycobacterium cell wall? (broad ideas)

A

Contains an inner membrane
Has a peptoglycan middle layer - thicker than gram neg but thinner than gram positive
Does not have an outer membrane
Has a unique outer cell wall which is rich in mycolic acids responsible for most of virulence.
Hence has features of gram negative and positive so does not gram stain well.

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17
Q

What are some specific molecules found within the mycoplasma cell wall?

A

Cell membrane made from phospholipids
Periplasmic space - contains high lipid content including lipomannan and liporabinomannan
Then peptoglycan layer
Followed by arabinogalactan
Then mycolic acid
Then free acids and glycoproteins including trehalose dimycolate before the capsule layer.

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18
Q

What is the distinguishing fetaure of the periplasmic space/cell wall of myobacteria?

A

Has a high lipid content around 60% including lipomannan and lipoarabinomannan
Has features of both gram +ve and -ve walls.

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19
Q

What is the role of mycolic acid in the mycoplasma cell wall?

A

Mycolic acid are long chain fatty acids in bacterial cell wall.
Creater a waxy coat below capsule
Makes cell less permeable and highly resistant to antibiotics.

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20
Q

What is the role of peptoglycan in mycoplasma cell wall?

A

Made from alternating NAG and NAM
Confers rigidity and maintains shape.

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21
Q

What is the role of arabinogalactan in the mycoplasma cell wall?

A

Helps the bacteria to survive inside macrophages.
Amy interfere with host immune function, recognition process and phagosome maturation.

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22
Q

What is the role fo TDM Trehalose dimycolate (cord factor) in the mycoplasma cell wall?

A

Is an outer layer just deep to the capsule
Helps evade immune response
Triggers cytokine release
Causes chronic granulomas. (prevents phagosomal vesicle fusion)
Causes Mycobacteria to arrange together in slim cord like fashion.

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23
Q

What does mycoplasm look like under the microscope?

A

Cord factor helps clump together, give a string or thread-like appearance as robs clump together.

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24
Q

What is the global impact of TB?

A

10.6 million infected with TB worldwide
8.4% of those live with HIC
13th leading cause of death worldwide
2nd leading infectious killer after COVID-19
1.1 million deaths
1/3 of the worlds population are infected with TB and at risk of developing active TB.

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25
Q

What is the key public health element related to TB infections?

A

All mycobacterium tuberculosis complexes organisms are notifiable to Public Health England under the 2010 Health Protection Regulations.
Must be notified due to highly infectious and risk of drug resistance means contact tracing should occur.

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26
Q

How has the incidence of TB changed over time?
Suggest some reasons why?

A

Overall TB incidence has decreased dramatically over the last 100 years.
Mainly due to development of antibiotics, public health campaigns and improvements in housing and sanitation.
However some spikes in 1980s due to HIV epidemic, MDR inc and inc international travel
Another spike in 2011, followed by a decline caused by increased screening in high incidence countries.

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27
Q

What is TB sanitorium?
What is the history behind them?

A

Historical concept: A hospital typically in the countryside where people can go to rest and recover after a particularly long illness.
Encouraged fresh air exposure.
Need created by 1840s and 1850s epidemic
First purpose built sanitorium was Brompton Hospital in 1854
First antibiotic streptomycin was discovered in 1943. (aminoglycoside)

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28
Q

What is the historical use of x-ray and plombage in TB diagnosis and treatment?

A

Historical treatment used prior to discovery of antibiotics for TB in 1943.
Cavity created in upper zone of chest cavity under ribs, filled with material such as lucite balls, ping pong balls etc - aim was to make the elung collapse - theory was that a collapsed lung would heal quicker.

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29
Q

What is the liklihood of developing active TB from a TB infection?

A

ONly 5-10% of infected develop active disease. These tend to have a weak immune system, HIV, malnutrition or be pregnant.
Majority never have any clinical symptoms

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30
Q

What are the outcomes after exposure to TB?

A

10-30% are infected
Of these 10% develop active TB, remaining 90% develop latent TB
Latent TB has a 5-10% lifetime risk of reactivation

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31
Q

What is meant by TB reactitvation?

A

When a latent TB infection transitions to an active TB resulting in disease
This may be called Post primary or secondary TB
Can occur many years after infection to loss of immune control.

32
Q

What are the key features of latent TB?

A

Asymptomatic
Not infectious to others
No TB disease
Can last lifetime of host

33
Q

What are the key features of active TB?

A

Symptoms are ill
Likely to die if untreated (usually in 1-2yrs)
Infectious to others.

34
Q

What are the two different infection sites of TB?

A

Pulmonary containment
Extrapulmonary TB

35
Q

What is meany by pulmonary containment TB?

A

When infection starts in the lungs
THis is 85% of cases
May spread to others parts of the body.

36
Q

What is meant by extra-pulmonary TB?

A

15% of cases
Tends to not be contagious
Occurs more frequently in immunosuppressed individuals
Sites of infection include: military (disseminated rash), lymph nodes (lymphadenitis), peritoneuam TB in adbomen, spine bone and joints such as in Potts disease, neuroTB (cause meningitis), skin (lupus vulgaris), genitourinary system.

37
Q

What microbiology is required for the diagnosis of TB?

A

x2 sputum samples or BAL sample for Acid Fast Bacillus microscopy and culture. One sample must be a.m.
Samples must be decontaminated before culture as can contain resident flora.
Decontamination - include NaOH or H2SO4 to kill gram -ve bacteria, however can also kill up to 30% mycobacter risk of false negative.

38
Q

What are the key symptoms of TB?

A

Blood cough (hemoptysis)
Fever
Chest pain
Chills
Long term cough
Fatigue
Night sweats
Weight loss.

39
Q

What is the required for the diagnosis of TB?

A

A combination of clinical (signs and symptoms) and chest x-ray findings (air space consolidation), with or without acid fast bacilli (sputum sample)

40
Q

What do TB positive cultures look like?

A

Are very slow to grow, taking more than 8w on LJ media or MBA
Taking 2-4w on BacT/ALERT 3D
Colonies are raised, irregular, dry and white or yellow in appearance

41
Q

What do positive Acid Fast Bacillus (AFB) smears look like?

A

Auramine stain - yellow (using fluorescent microscopy)
Ziehl Neelson stain - pink
Low sensitivity
Must have at least 5-10K bacilli p/mm of specimen to allow detection.

42
Q

What radiographic features are positive in TB diagnosis?

A

Often order a CXR
Lymph nodes greater than 1cm indicates lymphadenopathy
Calcifications in the lungs can indicate granuloma formations

43
Q

What tests are less commonly ordered but still useful when looking to diagnose TB?

A

Molecular:
GeneXpert-TB (PCR), NAATs (pcr), MALDI-TOF MS, Whole genome sequencing

Others:
Lymph node biopsy (for granulomas) and Urine test for Mtb sheds.

44
Q

What is the Interferon-Gamma Release Assay test for TB diagnosis?

A

Is a blood test for mycobacterium tuberculosis.
Requires one appointment to take blood.
Patients blood is stimulated with synthetic antigens and the amount of INFy produced by T cell or no. active T cells is measured.

45
Q

What are the advantages and limitations of an IGRA test for TB?

A

+ only requires one patient appointment so less lost to follow up
+ not effected by previous BCG vaccination
+ results do not require subjective interpretation
- expensive
- requires specific labs and experts to perform and interpret results
- not recommended for children under 5yrs due to insufficient immune response.
- unable to differentiate between latent and active TB infection
- only detects mycobacterium tuberculosis

46
Q

What is the TST (skin test) for diagnosing TB?

A

A small amount of TB antigen is injected under the skin and measure the immune response 48-72 hours later.
Is a delayed type Hypersensitivity reaction, antigen take up and presented, activate CD4+, cytokines activate vasculature, phagocytes recruited, fluid leak causing odeamse, inflammation including NO and ROS.
Measure size of induration of skin, above 15mm is positive.
A positive reaction indicates TB infection exposure.

47
Q

What are the advantages and limitation of the TST skin test to diagnose TB?

A

+ low cost
+ widely available
+ can be used in all age groups and population
- requires two visits, people can be lost for follow up before results obtained
- results can be influenced by previous BCG vaccination leading to false positives
- subjective deciding size od induration.
- specific for mycobacterium tuberculosis.

48
Q

What are the four fates of inhlaed TB bacilli?

A
  1. initial host response can kill all bacteria - no chance of developing active TB
  2. Organism begins to multiply immediately - primary TB
  3. Bacilli becomes dormant and nerve causes disease - latent TB
  4. Latent organisms eventually grow with resultant clinical disease - reactivation of TB.
49
Q

What is the basic mechanism by which the immune system eliminates TB bacteria on inhalation>

A

Phagocytosis of bacteria by alveolar macrophages
Triggers by various phagocytic receptors including mannose, FcyR and CR3.
Subject to variety of killing mechanisms in the phagosome, including fusion of lysosome

50
Q

What is the basic mechanism by which primary active TB occurs?

A

Mtb not cleared quickly by alveolar macrophages
Reproduce exponentially inside the macrophage and the alveolar space
TB cord factor (trehalose dimycolate) triggers inflammatory response and regulates marcophage function
Results in cytokine release, Macrophage and immune cell recruitment.
Immune cell particularly macrophages surrounded infected alveolar macrophages, forms a granuloma
Is a cell-mediated type 4 hypersensitivity reaction.

51
Q

What is the structure of a granuloma in TB?

A

Is a ceasating granuloma
Macrophages, dead tissue and bacteria form central or granuloma
Helper T cells, B cells, NKC, DC etc form a ring round macrophages
Macrophages rings will contain epitheliod cells, foams cells and Lagnerhans giant cells (horse shoe shaped many nuclei arrangement) closer to the outside, due to attempts of macrophage to adaptive to better phagocytose or contain infection.

52
Q

What happens to the granuloma in its maturation phase during active TB?

A

Centre of granuloma dies (bacteria toxins or hypoxia) form a caseous necrosis - this is known as a ghon focus (melty cheese like on gross appearance)
Some bacteria is not contained by granuloma and enter local lymph nodes (lymphadenopathy) forming a Ghon complex.
Gohn complex becomes latent but granuloma still contains viable bacteria.
This individual is not contagious or symptomatic as MTb contained so does not enter airway
In strong immune system tissue undergoes fibrosis and calcification and the complex heals leaving a small cavity and scar which is seen on an x-ray ranke complex.

53
Q

How can pulmonary TB become miliary TB?
What are the consequences of this?

A

Bacteria can proliferate inside alveolar macrophages and migrate from the lungs to the bloodstream to other tissues causing miliary TB.
Forms granulomas and areas of caseous necrosis in other organs including liver, spleen etc

54
Q

Explain what is meant by ghon focus, ghon complex and ranked complex?

A

Ghon focus - granuloma with caesating necrosis centre
Ghon focus - above granuloma and lymph node involvement
Ranke complex - calcified ghon lesion and potentially lymph node.

55
Q

What are the three different types of granulomas that can be present in the lungs of a person with TB?
** check with relation to caesating **

A

Primary or active
Latent
Reactivation
(note multiple types can be present in the same person at the same time)

56
Q

How does secondary/reactivated TB occur?

A

Granulomas doesn’t heal/calcify and still contains viable bacteria
Immunosuppression - Matured TB granuloma ruptures, free bacterium cause latent TB to reactivate
New outbreak results in more caseous necrosis
This normally occurs in the lung apices
THis is why we treat and screen for latent TB.

57
Q

What are the different TB virulence factors?

A

Mycolic acid - interupts phagocytosis
Cord factor - damage macrophages
Sulfatides - prevent phagosome/lysosome fusion
Catalase peroxidase - provide resistance to oxidative killing in macrophages.
LAM - induce cytokines

58
Q

What are some risk factors for TB?

A

Socioeconomic status - poverty, overcrowding, poor living conditions, lack of adequate healthcare, incarceration
Overall health/immune system status: immune suppression, HIV co-infection, diabetes, TB within last 2 years, transplant patients, malignancy.
Alcoholism
Smoking
Drug users
Mental health - delay seeking, mis doses
Health Care workers - inc exposure to Category 3 organisms such as Mycobacterium tuberculosis.
Genetic predisposition

59
Q

What medications should be given to a patient with active TB without central nervous system involvement?

A

Rifampicin, isoniazid (with pyridoxine), pyrazinamide and ethambutol for 2 months (RIPE)
Then Isoniazid (with pyridoxine) and rifampicin for a further 4 months

60
Q

What medications should be given to a patient with active TB with central nervous system involvement?

A

Rifampicin, isoniazid (with pyridoxine), pyrazinamide and ethambutol for 2 months.
Isoniazid (with pyradoxine) and rifampicin for a further 10 months.

61
Q

Why is pyridoxine given alongside isoniazid in TB patient?

A

Insoniazid - may cause peripheral neuropathy due to Vitamin B6 deficiency
Pyridoxine is a VitB6 supplement.

62
Q

What are the different treatment options for latent TB?

A

3 months isoniazid (with pyridoxine) and rifampicin
Or
6 months isoniazid with pyridoxine.

Decide based on patient clinical circumstances
If interactions of Rifamycins with HIV drugs or those after transplant concern then avoid
If concerns over hepatotoxicity then offer shorter term treatment with rifampicin.

63
Q

Why is the antibiotic course long for TB?

A

Mtb are very slow growing
Antibotics must be taken for a long time 4 to 6 months or longer.
Often continued after patient feel well
Otherwise TB tends to recur as it was not fully eliminated.

64
Q

What is the basic mechanism of action of rifampicin?**

A

Targets: DNA dependent RNA polymerase.
Action: Binds to beta subunit of bacterial DNA dependent RNA polymerase, a vital enxyme responsible for transcribing DNA into messenger RNA
Results in reduced RNA synthesis
Is an antibiotic.

65
Q

What is the basic mechanism of action of pyrazinamide?**

A

Is a pro-drug.
Converted into active form pyrazionoic acid by bacterial enxyme pyrazinamidase.
Targets: Fatty acid synthesis (FAS-1)
Action: inhibits the fatty acid synthase 1 enzyme, which is involved in the synthesis of mycolic acids
Disrupts membrane potential and interedest with energy production of the myocbacterial cells.
is an antibiotic

66
Q

What is the basic mechanism of isoniazid?**

A

Is an antibiotic
Is a pro-drug
Targets: InhA (enoyl reductase)
InhA is an enoyl-acylc carrier protein redctase enzyme that is part of the fatty acid synthase system in Mtb
Inhibitoin prevents synthesis of mycolic acids

67
Q

What is the basic mechanism of action of ethambutol? **

A

Is an antibiotic
Targets: L-arabinosyltransferase
Action: inhibition of L-arabinosyltransferase, enzymes involved in biosynthesis of arabinogalactan.
Reduced arabinogalactan leads to weakened cell wall integrity.

68
Q

What is MDR/RR-TB?

A

TB that is resistant to isoniazid and rifampicin

69
Q

How should you treat MDR/RR-TB?

A

Offer a treatment regime involving at least 6 drugs which the mycobacterium is likely to be sensitive to.
Test for resistant to second line drugs and treat accordingly
Use all class A if possible: levofloxacin, bedaquiline, linezoid
Add 1 or 2 group B: clofazimine, cycloserine, terizidone
Add group C when not effective to bring regime to 5 drugs: delamanid, imipenem, streptomycin and many more…

70
Q

What is the BCG vaccine?

A

The Bacillus Calmette Guerin Vaccine
Contains a live attenuated strain derived from M.bovis.
Only licsned vacine for TB in UK
70-80% effectiveness against severe forms of TB such as meningitis, less effective against respiratory
Provides protection for 15-60 years
Previously part of NHS routein vaccination for 10-14yr old. Since 2015, given on a risk based programme only.

71
Q

What is the law regarding the disclosure of HIV/TB status and confidentiality?

A

GMC states you may disclose information to a person who has close contact with a patient who has a serious communicable disease (including HIV/TB)
If the person is at risk of infection that will likely result in serious harm
The patients has not informed them and cannot be persuaded to do so

It is illegal for a patient to knowing spread HIV to another person without the victim being informing the victim of their HIV status.

72
Q

What is non-tuberculous mycobacteria?

A

A diverse group fo more than 200 mycobacterial species found in soil and water that do not cause tuberculosis.
Divided into rapidly growing (4-7days) and slow growing (more than 7 days) before colony is visible on media
Are not transmitted from person to person.

73
Q

What problems are associated with non-tuberculous mycobacteria?

A

Can cause severe pulmonary disease, skin and soft tissue infections especially in underlying lung disease or immunocompromised such as CF infected with MAC or MABSC
Diagnosis and treatment is challenging, tend to be resistant to antibiotics and require a combination over an extended period (over 1yr), high variability in clinical presentation and high mortality rates.

74
Q

What agar is used to grow non tuberculosis myocbacteria?

A

NTM elite
Reduces growing of other microbes and natural flora in CF patients, enables NTM to be identified rather than overgrown.

75
Q

Draw a diagram to show the structure of the mycobacterium tuberculosis cel wall?

A
76
Q

What is shown in this image of the lungs from a TB patient.

A

Gohn focus

Unit 13 (22 decks)

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