Community acquired bacterial infections Flashcards

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1
Q

Define virulence factor.

A

Molecules produced by pathogens that contribute to the pathogenicity of the organism

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2
Q

List some common bacterial virulence factors and include their function.

A

Flagella – movement and attachment
Pili – adherence factors
Capsule – protects against phagocytosis
Endospores – metabolically dormant forms of bacteria – they are heat, cold, desiccation and chemical resistant
Biofilms – organised aggregates of bacteria embedded in a polysaccharide matrix => antibiotic resistant

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3
Q

Give examples of bacteria that possess/exhibit the following virulence factors:

a. Capsule
b. Endospores
c. Biofilms

A
a. Capsule 
= S. pneumoniae 
b. Endospores 
= Bacillus sp. 
= Clostridium sp. 
c. Biofilms 
= P. aeruginosa 
= S. epidermidis
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4
Q

What are exotoxins?

A

A toxin released by a living bacterial cell into its surrounding

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5
Q

What are the five different types of exotoxin and what do they each generally do? Give examples of bacteria that produce such toxins.

A

Neurotoxins (act on nerves or motor endplate)

  • Botulinum toxin
  • Tetanus

Enterotoxins (act on GI tract)
Infection diarrhoea – Vibrio cholerae, E. coli, Shigella
Food poisoning – Bacillus cereus, S. aureus

Pyrogenic toxins (stimulate release of cytokines)

  • S. aureus
  • S. pyogenes

Tissue invasive toxins

  • S. aureus
  • S. pyogenes
  • C. perfringens

Miscellaneous exotoxin

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6
Q

What is an endotoxin?

A

This is the lipid A part of lipopolysaccharide that is found on the outer membrane of Gram-negative cells (it is shed in steady amounts from living bacteria)

NOTE: so ONLY Gram-negative cells can produce endotoxins

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7
Q

Why can treating patients with Gram-negative infection sometimes worsen their condition?

A

Antibiotics can cause lysis of the bacteria meaning that the endotoxins are released into the circulation in large quantities
This can trigger an immune response that leads to SEPTIC SHOCK

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8
Q

What is an outbreak?

A

A greater than normal or greater than expected number of individuals infected or diagnosed with a particular infection in a given time period, or a particular place, or both

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9
Q

How can an outbreak be identified?

A

Surveillance

Good and timely reporting systems are necessary

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10
Q

Describe the set of criteria to be met for an epidemic case to be confirmed

A

Possible epidemic case:
- Any person that has developed the symptoms AND has met a laboratory criteria (e.g. isolation of agent).

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.

Confirmed epidemic case:
- Any person meeting criteria for a possible case AND has had strain isolated.

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11
Q

Describe how PCR may be used to identify the outbreak strain

A

The isolates can be screened by multiplex PCR for characteristic features of the outbreak strain.
- This can be done on stool samples for example (e. coli).

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12
Q

What was the 2011 E. coli outbreak in Germany caused by?

A

Enteroaggregative shiga toxin producing E. coli

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13
Q

Describe the structure of shiga toxin.

A

There is an A subunit that is non-covalently associated with a pentamer of protein B

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14
Q

Describe the action of shiga toxin.

A

Subunit A is the enzymatically active domain
Subunit B is responsible for binding to the host cell membrane
Subunit A cleaves 28S ribosomal RNA in eukaryotic cells thus inhibiting protein synthesis
Bacterial ribosomes are also a substrate for subunit A so it can lead to decreased proliferation of susceptible bacteria (e.g. commensal microflora of the gut)

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15
Q

How was the shiga toxin gene transferred between bacteria?

A

Bacteriophage

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16
Q

What is the important virulence factor in EAEC?

A

Aggregative adherence fimbriae (AAF) – this is required for adhesion to enterocytes and biofilm formation

17
Q

What type of bacterium is Legionella pneumophila and what is the route of infection?
State the disease name.

A

Gram negative
It is transmitted through inhalation of contaminated aerosols
Legionnaire’s disease

18
Q

Which cells within the human host does L. pneumophila infect and grow inside?

A

Alveolar macrophages

19
Q

What is the important virulence factor for L. pneumophila?

A

Type IV secretion system

20
Q

What features of Mycobacterium tuberculosis makes it more difficult to treat?

A

It has a mycolic acid outer membrane – this prevents normal antibiotics from getting into the cell
It can enter a dormant state for reactivation

21
Q

State three bacterial sexually transmitted diseases including the species of bacteria that cause the diseases.

A

Chlamydia - Chlamydia trachomatis (gram-ve obligate intracellular parasite)
Syphilis –Treponema pallidum
Gonorrhoea –Neisseria gonorrhoeae

22
Q

What is a major consequence of Chlamydia in the developing world?

A

Blindness (due to eye infection)

23
Q

How does N. gonorrhoeae establish infection in the urogenital tract?

A

It interacts with non-ciliated epithelial cells

24
Q

What are the important virulence factors of N. gonorrhoeae?

A
  • Pili

- Antigenic variation mechanisms

25
Q

What is the most commonly reported infectious GI disease in the EU?

A

Campylobacter jejuni

26
Q

What is the route of infection of Campylobacter and Salmonella?

A

Ingestion of undercooked poultry

27
Q

State some important virulence factors of Campylobacter jejuni.

A
  • Adhesion and invasion factors
  • Type IV secretion system
  • Toxins
28
Q

Which subset of the population has the highest incidence of Salmonella and Campylobacter infection?

A

Young children (0-4 years)

29
Q

What is an important virulence determinant of Salmonella sp.?

A

Type III secretion system

NOTE: Salmonella sp. can cause outbreaks whereas Campylobactertends to be sporadic cases

30
Q

What are the important virulence factors of Vibrio cholerae?

A

Cholera toxin

Type IV fimbria

31
Q

Explain how cholera toxin works.

A

It has A and B subunits
A is the active toxin
B allows entry of the toxin into the epithelial cell
The A subunit activates adenylate cyclase, thus increasing the production of cAMP
The cAMP then binds to CFTR and causes Cl- efflux
Water follows the ion movement so you get massive movement of water into the lumen of the intestine

32
Q

Which subsets of the population are at risk of infection by Listeria monocytogenes?

A

Immunocompromised
Elderly
Pregnant and their foetus

33
Q

What are some special features of Listeria?

A

They can enter non-phagocytic cells and cross tight barriers (e.g. BBB and maternal-foetal barrier)

34
Q

Name some bacterial vector-borne diseases.

A

Q fever

Plague

35
Q

List some vaccine-preventable diseases. Identify which are viral.

A
  • Diphtheria
  • Invasive pneumococcal infections
  • Invasive meningococcal infections
  • Pertussis
  • Tetanus
  • Invasive Haemophilus influenzae
  • Measles, Mumps, Rubella*
  • Polio*
  • Rabies*