Tuberculosis

Question 1

Mycobacterium tuberculosis

Answer 1

• an acid fast bacterium
• requires a special staining technique called ziehl - neelson
• must be in the presence of oxygen to survive. It can also survive in low oxygen levels
• very slow growing with a doubling time of 15-20 hours.
• mycobacterium species have a wax like and virtually impermeable cell wall

Question 2

Acid fast properties of Tuberculosis

Answer 2

• Mtb cell envelope provides a protective barrier against drug host defence mechanisms.

cell wall has 3 essential macromolecules :
- peptidoglycan
- arabinogalactan
- mycolic acids

porins are required to transport small hydrophilic molecules through the outer membrane of the cell wall.

Question 3

Tuberculosis

Answer 3

• disease caused by mycobacterium tuberculosis
• droplet transmission over a prolonged time meaning its airborne
• slow rate of growth once infected
• ability to lie dormant for decades
• pulmonary disorder but can cause a systemic infection.

Question 4

Infection cycle of mycobacterium tuberculosis

Answer 4

• bacilli enters the alveoli through inhaled droplets
• immune system begins to fight infection
• primary infection = host mounts a response, formation of aggregates of activated macrophage leading to a tubercle
• Mtb can survive this and grow within the macrophage, even with an ongoing immune response
• if a pt has poor resistance, bacterial growth is not controlled and pulmonary TB becomes acute.
• TB can survive both the low pH and effects of reactive ROS and RNI in lysosomes of phagocytes

Question 5

Response of Mtb to the granuloma enviornment

Answer 5

• extremely successful pathogen is able to persist in this latent infection
• enters a dormant and non replicating state
• undergoes extensive and appropriate gene regulation to establish this dormant state responding to the signals of infection

Question 6

symptoms of tb

Answer 6

SYMTPOMS OF TB IN THE LUNGS MAY INCLUDE :
- cough that has lasted 3 weeks or longer
- weight loss
- presence of blood in sputum
- weakness and fatigue
- fever and chills
- night sweats

SYMPTOMS OF DISSEMINATED TB :
- abdominal pain and swelling
- chills/fever
- coughs and sob
- joint pain
- pale skin due to anaemia
- infect any number of organs

Question 7

Diagnosis - test for bacilli

Answer 7

• test sputum or tissue samples
• long used method
• mycobacteria are acid fast bacilli due to their appearance after staining and clearing with acid. However, it cannot distinguish between live and dead bacteria and it a requires a high bacterial load.

Question 8

Growth in culture

Answer 8

• more expensive
• takes very long
• more sensitive to technical difficulties
• requires strong infrastructure, qualified staff, and equipment

Question 9

Tuberculin skin test

Answer 9

PURIFIED PROTEIN DERIVATIVE
- protein from Mtb
- injected under skin
- looks for a reaction under the arm and to see if antibodies are present
- shows prior exposure to Mtb
- reactive to antibodies raised against BCG vaccine

Question 10

Vaccine

Answer 10

BCG is a widely used vaccine for TB
- no longer part of routine NHS vaccination programme but reserved for adults and children considered to be at increased risk of contact with Tb.
- vaccine is only partially effective.