TB a summary

TB - overview for Biology AS OCR unit F222

1. TB
summarised

2. TB
Caused by Mycobacterium tuberculosis, a bacterium.
The bacteria are prokaryotic cells
Every year 1.6 million people die from this disease.

3. Prokaryotic Cell Structure
As you can see, the structure is very different from plant and animal cells that we
have already learnt about.
Capsule is a layer of
mucilage which may unite
bacteria into colonies.
Pili are protein rods
concerned with cell-cell
attachment. The sex
pilus is involved in DNA
transfer
Plasma membrane is a
typical phospholipid
bilayer.
Plasmids are small pieces
of circular DNA which
replicate independently of
the main genome.
Cell wall has a rigid framework of
murein, a polysaccharide cross-linked
by peptide chains.
Genetic material is composed
of a circle of double-stranded
DNA which is not enclosed
within a nucleus.
Ribosomes smaller than those
in eukaryotes and not
supported by an endoplasmic
reticulum.
Food stores are typically
lipid droplets glycogen
granules.
Flagellum is
responsible for motility
of many bacteria.

4. Development of TB
Spread by a person who
has TB coughing or
sneezing droplets of
mucus containing the
bacterium in the air.
Droplets are breathed in
by another person and
the Mycobacterium infects
the lungs.
Also can be caught by
drinking unpasteurised
milk from cows infected
with Mycobacterium bovis.
TB infected sputum

5. TB infection
Usually infects lungs, but can infect almost any
organ in the body.
Symptoms – fever, weight loss, persistent cough and
very tired. This is the primary infection.
Healthy immune system – disease may not spread
any further.
If the disease does develop, patient will cough up
blood-stained sputum due to damaged lung tissue.
Chest pain and night sweats will also be present.

6. Diagnosis
Chest X-ray; infected
area looks cloudy.
Sputum sample –
examined in a
laboratory to see if TB
bacteria is present.
TB can spread to other
organs such as the heart,
bones, pancreas, thyroid
and skeletal muscles

7. TB links
Increased likelihood of developing TB if:
Live in damp, overcrowded conditions
Abuse alcohol / drugs
Infected with HIV
Suffering from other medical conditions that make the
body less able to resist disease (e.g. diabetics)

8. Treatment of TB
Like all bacterial infections TB can be treated
successfully using antibiotics. Isoniazid is the drug of
choice.
The problem:
The drugs need to be taken over six to nine months to be
effective. Initially the patient feels ill so takes the
medication and the most susceptible strains of
Mycobacterium are destroyed. As the patient feels better
they stop taking the medication, however the more resistant
Mycobacterium strains are still present in the body ; these
multiply and spread to others. These bacteria are likely to
be the resistant ones.

9. Treatment – the solution
To try to stop resistance developing, TB patients are
usually given a cocktail of three or four different drugs
– hopefully at least one of these will be effective.
A scheme called DOTS (Direct Observation Therapy)
has been developed. Here patients are watched while
they take their medication, this ensures they complete
the course of treatment. DOTS also enable the patients
health to be monitored.
Vaccination – BCG (Bacille-Calmet-Guerin) vaccine,
This is an attenuated vaccine – it contains a live but
weakened strain of Mycobacterium bovis.