Community Acquired Bacterial Infection

Question 1

What are some virulence factors? Give examples of bacteria

Answer 1

• Diverse secretion systems
• Flagella – for movement, attachment
• Pili – adherence
• Capsule – protect against phagocytosis - Streptococcus pneumoniae
• Endospores – metabolically dormant forms of bacteria - Bacillus sp. And Clostridium sp
• Biofilms – aggregates of bacteria embedded in polysaccharide matrix – antibiotic resistant - Pseudomonas aeruginosa and Staphylococcus epidermidis

Question 2

What are some different types of exotoxins? Give examples of bacteria

Answer 2

• toxins that damage biological systems:
• Neurotoxins – act on nerves or motor-end-plates- Tetanus or Botulinum toxins
• Enterotoxins – act on GIT:
  > Infectious diarrhoea – Vibrio cholera, E. coli, Shigella dysenteriae, Campylobacter jejuni
  > Food poisoning – Bacillus cereus, Staph. aureus
• Pyrogenic exotoxins – stimulate release of cytokines: Staph. aureus or Strep. pyogenes
• Tissue invasive exotoxins – enzymes that allow bacteria to tunnel through tissue: Staph. aureus, Strep. pyogenes, Clostridium perfringens
• Misc. exotoxins – specific to certain bacteria, function not well understood: Bacillus anthracis, Corynebacterium diphtheriae

Question 3

What are endotoxins?

Answer 3

– i.e. Lipid A in LPS from gram- bacteria
- Only produced by gram –ve bacteria
- NOT a protein – a lipid A moiety of LPS
> Shed in steady amounts from living bacteria
- When treating a patient with a gram-ve infection, the ABs can make them worse: Bacteria lyses -> release large quantities of LPS/endotoxins -> septic shock

Question 4

What is an outbreak?

Answer 4

a sudden increase in the incidence of a disease in a particular place at a particular time

Question 5

What is haemolytic-uraemic syndrome?

Answer 5

triad of acute renal failure, haemolytic anaemia and thrombocytopenia

Caused by EHEC – enterohaemorrhagic E. coli - Reservoir is usually in cattle

Question 6

How are outbreaks identified?

Answer 6

1. Possible epidemic case:
   - Any person that has developed the symptoms AND has met a laboratory criteria (e.g. isolation of agent)
2. Probable epidemic case:
   - Any person that has met the above criteria AND has been in epidemic country, consumed possibly contaminated food, been in close contact with a confirmed epidemic case
3. Confirmed epidemic case:
   - Any person meeting criteria for a possible case AND has had strain isolated
4. PCR :
   - The isolates can be screened by multiplex PCR for characteristic features of the outbreak strain

Question 7

What are the virulence factors for respiratory tract infections? Give examples of bacteria

Answer 7

Legionnaire’s disease – Legionella pneumophilia (gram-ve):
- Virulence factor – type IV secretion systems – legionella replicates in legionella containing vacuoles (LCVs) inside cells

Tuberculosis – Mycobacterium tuberculosis (gram+ve):
- Virulence factor – has an extra lipid layer & can enter a dormant state for reactivation

Question 8

What are the virulence factors of some STIs?

Answer 8

Chlamydia – Chlamydia trachomatis (gram-ve obligate intracellular parasite):
- Most common STI in Europe and causes >3% of the world’s blindness

Gonorrhoea – Neisseria gonorrhoeae (gram-ve):
- Virulence factors – pili, antigenic variation mechanisms

Question 9

What are the virulence factors of food and waterborne diseases and zoonoses?

Answer 9

Campylobacteriosis – Campylobacter sp. (mostly C. jejuni):
- virulence factors – adhesion, invasion factors, flagella motility, T4 secretion systems, toxins

Salmonellosis – Salmonella sp. (gram-ve):
- Virulence factors – T3 secretion systems encoded on pathogenicity islands - SPI1 for invasion, SPI2 for intracellular accumulation

Cholera – Vibrio cholera (gram-ve):
- Virulence factors – T4 fimbria, cholera toxin (increased cAMP -> opening of Cl- channels and expulsion of water from cells), carried on phages

Listeriosis – Listeria monocytogenes (gram+ve):
- Virulence factors – actin-based cell mobility

Question 10

What are some examples of emerging and vector-borne diseases?

Answer 10

Plague – Yersina pestis (gram-ve)
Q fever – Coxiella burnetti (gram-ve)
Smallpox (A VIRUS) – eradicated

Question 11

What are examples of vaccine preventable diseases? What bacteria causes them?

Answer 11

1. Diphtheria – Clostridium diphtheriae (gram+ve)
2. Invasive HA disease – Haemophilus influenzae (gram-ve)
3. Invasive meningococcal disease – Neisseria meningitides (gram-ve)
4. Invasive pneumococcal disease – Streptococcus pneumoniae (gram+ve)
5. Pertussis – Bordetella pertussis (gram-ve)
6. Tetanus – Clostridium tetani (gram+ve)