Lecture 5 Mycobacteria Flashcards
How much of the worlds population is affected by TB
1/3
How many million deaths are caused by TB every year
2.5 million deaths
Which city has the highest incidence of TB
Mumbai
TB has been classed as a DDW, what does this mean
Disease of the developing world
What was the number of infections of tb in 2013 in the UK
7892
M tuberculosis accounts for what percentage of all TB infections in the U.K.
98%
Who are at risk of catching TB
Travellers to endemic countries/regions, close contact with infected, immunosuppressed, elderly, homeless, drug abusers and alcoholics
Which bacterium uses humans as reservoir and causes TB (high virulence)
Mycobacterium tuberculosis
Name two species of microorganisms that can use animal reservoirs and their virulence for humans
M canetti (unsure of animal) and high virulence M bovis (cows) high virulence get bovine TB
Which microorganism uses armadillos (alongside humans) as a reservoir, and what is the condition called?
M leprae, causes leprosy with high virulence
M avium-intracellulare and M. Abscessus both have low virulence for humans. What is their reservoir and in what conditions do they cause human disease
Reservoir in environment or birds. As environmental hard to kill for resistance reasons, but cause. A TB-like lung infection or disseminated infection in AIDS patients
Describe major characteristics of the mycobacterial cell
Acid fast: cell envelope is 60% long chain branched hydrocarbons (waxy)
Mycolic acid - most abundant and big virulence factor
Trehalose dimycolate (TDM) or cord factor - two mycolic acids with trehalose sugar head group.
Cell wall prevent dessication - essential for intracellular survival
What is the normal growth duration for mycobacterium to divide once
15-20 hrs
State the structure of the mycobacterial cell wall from inner to outer
Inner membrane
Periplasm
Peptidoglycan with arabinogalactan overlay
Bound mycolic acids
Outer membrane
Characteristic free lipids
Running vertically through whole cell wall and linked to cytoplasmic membrane is lipoarabinomannan
What is does the overlay of arabinogalactin linked to
(overlay is covalently linked to outer layer composed of mycolic acid, glycophospholipids and cord Factor)
What is the complex between the mycolic acid, arabinogalactan and peptidoglycan called
Mycolatearabinogalactan-peptidoglycan-complex (MAPc)
Describe stage 1 of m tuberculosis pathogenesis
Inhalation of infectious particles as DROPLET NUCLEI, approx 3 bacilli needed
Describe stage 2 of m tuberculosis (MTB) pathogenesis including a rough timeline
7-21 days
MTB multiplies in macs due to inhibition of phagolysosome fusion by cord factor
Macrophages secrete IL-12 and present MTB antigen on surface
Eventually bursting with high TB levels and release the microorganisms
Describe stage 3 of m tuberculosis pathogenesis
IL-12 stimulates CD4 and CD8 T cells to infiltrate and recognise MTB antigen and are activated.
CD4 release inflammatory factors - Gamma interferon resulting in tubercule formation (primary lesion)
Describe stage 4 of m tuberculosis pathogenesis
MTB continues to multiply within inactivated/poorly activated macrophages and tubercule expands into granuloma
This is a fully encapsulated, immune maintained vessel to prevent wider dissemination
Describe stage 5 of m tuberculosis pathogenesis
Primary lesion heals: GHON FOCUS - type of granuloma
Dormant lesion, contains MTB, may reactivate
What does a ghon focus look like an an X-ray?
White bunches of grapes within he lung
What receptors on alveolar macrophages allow for entry of MTB
Surface complement receptors, scavenger receptors and Fcg receptors
What cell other than alveolar macrophages can take up mycobacteria
DC cells which travel to the draining lymph nodes to activate t cells which contribute to tubercule and granuloma formation.
Spread of MTB by which arteries can lead to miliary tuberculosis
Pulmonary
Which patients often will obtain miliary tuberculosis
Immunocompromised or small children
FILL IN THE GAPS. Although MTB often inhibits phagolysosome fusion, some are degraded and presented to T cells by MHC class II. In the presence of _/_ produced by macrophages and _, the T cells will differentiate into _. These _ cells produce pro inflammatory cytokines _ and _ which in combination with IFNgamma and _ produced by macrophages themselves, further activate bactericidal effectors of macrophages such as _, _ and autophagy induction.
1- IL-12 2-IL-18 3- Dendritic cells 4- Th1 cells. 5 - th1 cells 6- IFNgamma 7- TNFalpha 8- IL-1 9- defensins 10- nitric oxide production
After inhalation of droplet nuclei, what are the three pathways of disease that can occur and the percentage of people in each
No infection = 50%
Latent TB infection/ active infection = 25-50%
When does a tb infeciton become latent
At the granulomatous lesion form and bacteria cease to grow and the lesion calsifies (90% of infection cases)
In an active tb infection what happens after a granulomatous lesion is formed.
The lesion liquifies and spread bacteria to blood and organs and the bacteria can be coughed up in sputum.
The end result is often death if left untreated. A latent infeciton can become active upon immunosuppression
What is the predicted outcome for primary tuberculosis (primary exposure) in an immunoCOMPETENT host
Cell mediated immunity prevent spread of MTB, minimal or no symptoms (90% of people)
MTB remain LATENT
REACTIVATION MAY OCCUR
What is the predicted outcome for primary tuberculosis (primary exposure) in an immunocompromised host
Primary focus worsens, pneumonia develops (LRTI link here)
Systematic dissemination (lymph nodes, meninges, upper parts of the lung)
Symptoms result from host Cell mediated immunity response and get chronic inflammation.
Does M tuberculosis have an endotoxin or exotoxin
NO
Non replicating persistence is a term applicable to which type of tb
LATENT INFECTION
When does resactivation of an initial infection occur within (years) of tb
Within 2 years but may occur at any time after
Why does secondary TB (reactivatin of latent tb) occur
Associated with impairment of cell mediated immunity such as steroid therapy, immunosuppressive drugs, cancer or HIV
Also local disturbance of dormant tubercules
What is involved in secondary TB
Breakdown of latent tubercules, and immune system can’t maintain it and keep the bacteria encased. As break down bacteria can access nutrients and oxygen and burst out of granuloma. At break down get CASEOUS NECROTIC LESION - good for bacteria to disseminate.
The switch from hypoxic core to oxygen environment of lungs is essential to reactivation of tb in secondary tb
true
Why does tb occur in HIV patients
Immunocompromised as depleted cd4+ helper cells so impairs cell mediated immunity.
How many AIDS patients in sub saharan Africa have developed TB
2/3q
In developed nations what are we recently seeing regarding aids and tb
Prone to rapid primary infection and rapid reactivation
Advanced AIDS patients very susceptible to M avium-intracellulare which is environmental and hard to kill
Disseminated complex (MAC) infection: chronic, fever, M Adium wasting, multiple organ involvement and death
What percentage of tb patients are symptomatic in form of primary tuberculosis and what percent are asymptomatic
10% symptomatic with primary
90% asymptomatic
What are the symptoms of lower respiratory tract TB
Cough sputum with blood Tissue destruction in lungs result in cavitation and can lead to loss of lung volume and erosion of bronchial arteries Significant weight loss Night sweats Fatigue Fever
What are the symptoms of TB spread to other body parts (miliary TB)
Meningitis
Septicaemia
Kidney infection
Joint infections; pott disease (curvature of the spine)
What is PPD used in mantoux text
Purified protein derivative - from mycobacteria
What clinical diagnosis tools can be used to identify TB (NOT LAB)
Symptoms
Radiological changes on chest x ray
Tuberculin skin test (TST) or Mantoux - inject with PPD
How does the mantoux test work
Inject a patient with PPD and if previously exposed to TB get very strong immune response - length of induration can tell you if exposed to TB before (room for false positive)
What laboratory diagnosis can be used for TB
Non culture: Interferon gamma release assay
Nucleic acid amplification and PCR - molecular detection
Microscopy
Culture - LJ slopes
What is pcr useful for in tb diagnosis
Detect presence of multi drug resistant tuberculosis (drug resistance correlated with characteristic mutations in specific genes)
What are the clinical samples used to establish a lab diagnosis for pulmonary, renal, mengitis from TB and checks to see if it has disseminated
Pulmonary - early morning sputum Renal - Complete early morning urine Meningitis - CSF aspirate Dissemination check - lymph node biopsy, blood/bone marrow aspirate IGRA test - whole blood
What category is m tuberculosis
Category 3 bacteria
What is the theory of IGRA test
A persons t cells previously exposed to tb infection produce high levels of IFN gamma when re-exposed to same antigen (memory)
False positive if had BcG vaccine - as ‘previous exposure’
What patients have IGRA test performed
Blood sample from patient with possible or latent TB re exposed to same mycobacterial antigen
What genomic seq are the antigens encoded for the IGRA test
Antigens used rate encoded in region of difference (RD)1 - genomic sequence absent from most MOTT (e.g BcG, environmental mycobacteria)
Name some RD1 encoded antigens for IGRA
Early secretary antigenic target (ESAT-6)
Culture filtrate protein (CFP-10)
Name 2 commercial kits available for IGRA
T-SPOT. TB = ENUMERATE IFNgamma secreting t cells (more sensitive)
QuantiFERON-TB Gold - INF gamma secretion measured (less sensitive as not enumerate cells)
What stain is used to detect TB
Ziehl-Neelson stain
What is the lower limit of detection of ZN stain
5 x 10^3 organisms/ml
When would a fluorescent auramine stain be used for TB non culture
Using fluorescent microscopy to get results within an hour
Why do negative smears from microscopy not rule out a tb infection
Because low numbers of microorganisms in samples
What is the overal sensitivity of microscopy for tb detection
<50%
What can ZN stain not detect
Not differentiate between mycobacteria species, just know the genus with red staining.
Describe the principle of TB-REaD
Using a flourescent substrate, the device targets BlaC (beta lactamase) produced by the bacteria. Beta lactamase breaks open the fluorescent substrate to see fluorescence and light up sample quickly if MTB is present
How quickly can TB-REaD get results
20 minutes
What is the sensitivity and specificity of TB-REaD
Sensitivity is 86%
Specificity is 73%
What preparation is required for sputum samples of TB
Liquefaction of sputum using Sputasol
Concentration by centrifugation
Decontamination with 4% NaOH (sputum sample is non sterile)
What two types of culture media can be used for TB
Solid culture - Lowenstein Jensen slopes
Broth culture e.g. Bactec mycobacterial broth, or newer quicker method MGIT
What is the benefit of MGIT
MGIT - mycobacterial growth indicator test - use low volumes of growth media and high inoculum to force rapid positive/negative result in just over 2 weeks
How long can culture of TB take to grow and what components are in LJ slopes
37 degrees for up to 8 weeks for M tuberculosis
Eggs, salt, glycerol, potato flour and inhibitory agents such as malachite green and PENICILLIN, nalidixic acid
What does full biochemical ID of MTB involve
Biochemical characteristics: things MTB + for but other mycobacteria arent
Niacin
Nitrate reductase
Can take 4 weeks
What does full ID molecular of TB involve
PCR
Rapid ID molecular probes (result in 1-2 days) - species specific DNA probes or ribosomal rRNA based probes (10-100x more sensitive than DNA probes)
Which guidelines are followed for treatment of TB
British thoracic society
National institute for health and care excellence (NICE)
What is the management of active TB
2 phases
First two months have ISONIAZID, RIFAMPICIN, PYRAZINAMIDE & ETHAMBUTOL.
Next four months only have ISONIAZID AND RIFAMPICIN
What changes have been made to improve patient compliance over the long 6 month period
Directly observed therapy (DOT) following a patient risk assessment. DOT considered for patients having adverse factors on risk assessment such as homeless, or alcohols.
Why has DOT been introduced for TB treatment
To eliminate the infection properly and prevent drug resistance amongst tb strains
What percentage of tb strains in uk are resistant to one or more of the antibiotics
6-8%
What is MDR-TB and what are they resistant to
Multidrug resistant TB - resistant to isoniazid and rifampicin - best tb drugs.
Why has drug resistance in tb risen
Administration of improper treatment regimens by healthcare workers )solved by trained tb physicians)
Failure to complete treatment (solved using DOT)
When would the drug SHREZ be used and what does it contain
Multi drug resistant TB BASED ON SENSITIVITY TESTING
(Streptomycin + isonicotinyl hydrazine + rifampicin + ethambutol + pyrazinamide) wth moxifloxacin and cycloserine
Does does XDR-TB AND TDR-TB stand for
extensively drug resistant TB and totally drug resistant TB
What combination drug preparations have been developed to improve patient compliance
Rifater: initial phase isoniazid/RIFAMPICIN/pyrazinamide
Rifinah 300 or Rimactazid 300: continuous phase ISONIAZID/rifampicin
Describe Isoniazid target, MOA and side effects
Inhibit cell wall formation, (stop mycolic acid formation)
Pro-drug converted to isonictonic acid-NADH complex, bind to InhAat NADH inning site which facilitates mycolic acid synthesis
Hepatitis, peripheral neuropathy
Describe RIFAMPICIN target, MOA and side effects
Inhibit nucleic acid synthesis
Bind to RNA polymerase (block mRNA synthesis and subsequent nucleic acid synthesis)
Hepatitis (stains body fluids orange) and make cornea change colour
Describe pyrazinamide target, MOA and side effects
Cell acidification
Converted to pyrazinoic acid by pyrazinamidase which decreases pH and inhibits ribosomes
Hepatitis
Describe ethambutol target, MOA and side effects
Inhibit cell wall formation
Bund to arabinosyl transferases dirstupting cell wall component formation
Ocular toxicity which is reversible
