Lecture 4 - Mycobacteria Flashcards
What shape are the mycobacterium
Rod shaped
How do the mycobacterium live in regards to oxygen
Obligate aerobes
Do mycobacterium produce spores and have a caspsule
No
What size are mycobacterium
2-4um
What phylum does mycobacteria belong to
actinobacteria
What is special about the actinobactera
High G and C content and filamontous
How many hours is the generation time
15-20hours
How is the cell wall different to gram-/+ bacteria
HIGH LIPID CONTENT
How much of the mycobacteria cell wall is lipid
60%
What is the main glycolipid part of the membrane
MYCOLIC ACID
Name 2 other lipids found in the membrane
Surface acyl lipids, lipoarabinomannan, phosphatidyl inositol mannosides (PIM), CORD FACTOR (TDM)
Why is the cell wall structure of mycobacteria important
Intracellular survival, confers resistance e,.g many antimicorbials, heat, chemicals, drying STAINS.
Acid fast
What is meant by acid fast
Once stained the organisms resist dilute acid or ethanol based de colourisation!!
What is the stain for mycobacteria
Ziehl neelson stain
Describe the ziehl neelson stain
1- stain with hot concentrated carbol fuschin (all cells pink)
2- de stain with 1% acid-alcohol (HCl/ethanol) or 20% H2SO4 (mycbacteria stay red, others colourless
3- counterstain with methylene blue (mycobacterial cells remain pink others are blue e.g. Wbc are blue)
Name 4 species of mycobacteria
M. Tuberculosis, M. Bovis, M. Avium intracellulare, M. Leprae (Hansen’s bacillus)
What disease does M. Avium intracellulare cause and what are the symptoms
Disseminated TB in immunocompromised patients e.g. HIV
Symptoms:
Lung infection - spread t bones, joints, blood, meninges, renal system. DEATH
Describe the symptoms of leprosy
Folded lesions on face and limbs, disfiguration, loss of peripheral nerves, secondary infection
How can you get M. Bovis and what are the symptoms
From unpasteurised milk
Asymptotic often, pneumonia like symptoms. Weight loss, temp. Cough, blood in sputum
SAME AS FOR M.TUBERCULOSIS
How much of world popn have TB
1/3
Why was there a huge decrease in HIV patients from the 1950’s (50,000) to mid 1980’s (6000) in the UK
Introduction of vaccinations to prevent against TB infection
Why may there be a steady increase once again in the no of TB cases in the UK
Antibiotic resistance of bacteria
Also more HIV cases so more risk of infection
What are predisposing factors of TB infection
- close contact with large popn of people I.e schools, nursing homes. Prisons
- poor nutrition
- IV drug use
- alcoholism
- HIV infection MAIN predisposing factor of TB infection. 10% of all HIV + positive individuals have TB (400x rate associated with general public)
How large are the droplet nuclei
5um
How many droplet nuclei are released when someone talks for 5 mins, coughs, sneezes?
3,000 for each.
Sneezing 3000 up to ten feet away
The droplet nuclei once in the air die within 5 minutes. True or false
False
A few hours
What does the small size of the droplet nuclei allow for
Bypass mucociliary lining
What are the 5 stages of a TB infection
1- droplet nuclei inhales
2- (7-21 days) MTB multiplies within macrophages (intracellular), macs secrete IL-12 and present MTB antigen on surface, eventually burst through liberating MTB
3- IL-12 stimulates T cells to infiltrate, recognise MTB antigen, become activated (sensitised) and start to release inflammatory factors (IFN gamma); tubercule formation (primary lesion)
4- MTB continues to multiple within unacfivated/poorly activated macs and tubercule expands
5- primary lesion heals - GHON focus (dormant lesion, contains MTB, may reactivate
What in healthy people ‘heals ‘ primary lesion
Cell mediated response
What are the symptoms of primary tuberculosis
LRTI- cough (sputum with blood), weight loss, night sweats, fatigue, fever
May spread to other body parts: meningitis, blood poisoning, kidney infection, joint infection
How many people experience primary tuberculosis and how is the body prepared for attacking re exposure
10% and patients hypersensitised e,g, CMI (T- lymphocytes)
How many people are asymptomatic due to cell mediated response keeping the infection under control
90%
What is secondary tuberculosis
Reactivation
Give examples of how secondary tuberculosis is associated with impairment of CMI
Steroid therapy, immunosuppressive drugs, cancer chemotherapy, old age, HIV.
What happens to the dormant primary focus during secondary tuberculosis
Dormant primary focus becomes necrotic (cheesy) and liquefies distributing thousands of M, tuberculosis MTB into the lungs
What is the appropriate clinical sample for lab diagnosis of pulmonary (respiratory) TB?
Sputum
What category microorganism is m.tuberculosis
Category 3
What are category 3 microorganisms
Cause severe human diseases, serious hazard to employees, risk of spread in community BUT EFFECTIVE TREATMENT.
How is the sputum processed in a lab diagnosis of pulmonary (respiratory) TB?
Class 3 lab under a class 1 safety cabinet, under negative pressure, 0.74m3/sec
When was consumption first described and who by
1970- Benjamin Martin
“Wonderfully minute living creatures”
When was the cause of consumption discovered
1882 - caused by infectious agent Kochs bacillus
Recently UCL proved that Granvilles mummy had TB instead of ovarian cancer by finding what
TB DNA in lung, femur, gall bladder
What magnification is used to view sputum smears stained by ZN
1000x light microscopy
How many microbes per ml is required to visualise one organism
10^4 microbes in 1ml
What is the incredibly specialist agar that sputum is culture on
Lowenstein-Jensen slopes (LJ slopes)
What does LJ slopes contain
Egg, glycerol, minerals, potato flour, antibiotics, malachite green
How many weeks and what temp do you incubate the sputum
37deg for up to 12 weeks
Describe the colonies in m.tuberuclosis
Generally grown 4-6 weeks,
- yellow/buff coloured colonies, irregular in shape
- colonies ZN positive
- form distinctive serpentine cords when stained.
Who discovered the serpentine cords
Robert Koch.
What makes the cells to grow in serpentine cords
Cord factor - trehalose 6,6’ dimycolate
How long is the treatment regime for TB
six months - toxic anti mycobacterial drugs
What is the combo of drugs
Isoniazid
Rifampicin
Pyrazinamide
Ethambutol
What are side effects of TB treatment
Hepatitis (inflammation of liver), gastrointestinal disturbances
What vaccination is used to prevent TB
BCG vaccination (1953)
What is the vaccination made of and how is it obtained
Live attenuated form of m.bovis.
230 passages over glycinerated bile potato medium in vitro.
How effective is the vaccination and how long does it last
50-80% effective, last 10-15 years
What changed about the vaccine from 2005
Targeted vaccination introduced to high risk e,g,
Babies born in areas of uk where TB prevalence is high e.g, London
At risk employees e,g. Healthcare workers
What is the principle of the Mantoux test ( tuberculin skin testing)
TST detects delayed type 4 hypersensitivity. If previous infection, sensitised T cells circulate that respond to re- exposure to TB antigen
What is the procedure of the Mantoux test
Inject 0.1ml of tuberculin purified protein derivative (PPD) into inner surface of forearm. (intradermal injection). Injection produce pale elevation of skin (wheal) 6-10mm diameter.
What is the interpretation of the TST
Examined between 48 and 72 hours,measure induration (mm); positive if induration is >10mm
VACCINATION GENERATE POSITIVE RESPONSE
Are mycobacterium multicellular or unicellular?
Unicellular
