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Microbiology > Community Acquired Bacterial Infections > Flashcards

Community Acquired Bacterial Infections Flashcards

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
  1. Flagella – movement and attachment
  2. Pili – adherence
  3. Capsule – protects against phagocytosis
  4. Endospores – metabolically dormant forms of bacteria – they are heat, cold, desiccation and chemical resistant
    5, Biofilms – organised aggregates of bacteria embedded in a polysaccharide matrix – antibiotic resistant
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3
Q

Give examples of bacteria that possess the following virulence factors:

a. Capsule
b. Endospores
c. Biofilms

A

Capsule
Streptococcus pneumoniae

Endospores
Bacillus sp.
Clostridium sp.

Biofilms
Pseuodmonas aeruginosa
Staphylococcus 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 four main different types of exotoxin? Give examples of bacteria that produce such toxins.

A
  1. Neurotoxins -act on nerves or motor-end plates
    - Botulinum toxin
    - Tetanus
  2. Enterotoxins- act on GIT
    - Infection diarrhoea –Vibrio cholerae, E. coli, Shigella dysenteriae, C.jejuni
    - Food poisoning –Bacillus cereus, Staph. aureus
  3. Pyrogenic exotoxins- stimulate realise of cytokines
    - Staph. aureus
    - Strep. pyogenes
  4. . Tissue invasive toxins - enzymes that allow bacteria to tunnel through tissue
    - Staph. aureus
    - Strep. pyogenes
    - Clos. perfringens
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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
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

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

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9
Q

How can an outbreak be identified?

A

Surveillance
Good and timely reporting systems are necessary
PCR

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10
Q

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

A

outbreak due to fusion of EHEC and EAHC strains to form EAHEC

EHEC- enterhohaemorrhagic E.coli
EHAC- enteroaggregative E.coli

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11
Q

What were the symptoms of infection by this EHEC bacterium?

A

Gastroenteritis

Haemolytic uraemia syndrome (acute renal failure + haemolytic anaemia + thrombocytopenia

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12
Q

What was special about the bacterial strain that caused by outbreak?

A

The bacterial strain was an enteroaggregative E. coli strain (EAEC) that had acquired the ability to produce shiga toxin (through phagetransfer)
Shiga toxin production is a feature of Enterohaemorrhagic E. coli(EHEC)
This produced a new strain called Enteroaggregative haemorrhagic E. coli (EAHEC

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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

(AB5 subunit composition)

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14
Q

Describe the action of shiga toxin.

A

Subunit A is the enzymatically active domain (StxA)
Subunit B is pentamer 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) –

  1. this is required for adhesion to enterocytes and stimualtes IL-8 response
  2. AAF also allows biofilm formation
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17
Q

What type of bacterium is Legionella pneumophila and what is the route of infection?

A

Gram negative

It is transmitted through inhalation of contaminated aerosols

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 feature 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

21
Q

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

A

Chlamydia - Chlamydia trachomatis
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 escapes detection and clearance by the immune system

25
Q

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

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
Toxin

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
  1. Diphtheria (clostr. diptheriae)
    - gram +ve
  2. Invasive pneumococcal infections (strep. pneumoniae)
    - gram +ve
  3. Invasive meningococcal infections (neiss. meningitidis)
    - gram -ve
  4. Pertussis (bordetella pertussis)
    - gram -ve
  5. Tetanus (clos. tetani)
    - gram +ve
  6. Invasive Haemophilus influenza
    - gram -ve
Viral
Measles * 
Mumps* 
Rubella* 
Polio*
36
Q

What aspects of EHEC and EAEC did the PCR identify?

A

EAEC- 2 plasmids

  • pAA type plasmids which contain aggregative adhesion fibril operon
  • ESBL plasmids- gene for encoding for extended spectrum beta lactamase (AB resistance)

EHEC
-prophage encoding shiga toxin
prophage is when a bacteriophage inserts genome into circular bacteria DNA

37
Q

List two communicable respiratory tract infections, giving their virulence factors and route of infection by their bacterium.

A
  1. Legionnaire’s diseases ( legionella pneumophilila)
    - gram -ve
    - v factors are type 4 secretion systems
    - roi- inhalation of aerosols
  2. Tuberculosis (mycobacterium tuberculosis)
    - gram +ve
    - v factors are it has an extra lipid layer and can enter a dormant state for reactivation
38
Q

List three communicable sexually transmitted infections, giving their virulence factors and route of infection by their.

A
  1. Chlamydia (chlamydia trcahomatis)
    - gram -ve obligate intracellular parasite
    - most common STI in Europe and causes more than 3% worlds blindness
  2. Gonorrhoea (neisseria gonorrhoea)
    - gram -ve
    - UTI affecting non-ciliated epithelial cells
    - v factors are pili, antigenic variation mechanisms
  3. Syphilis ( treponema pallidum)
    - also gram -ve
39
Q

List four communicable food./waterbourne/zoonoses infections, giving their virulence factors and route of infection by their.

A
  1. Campylobacterosis mostly (C. jejuni)
    - most infectious GI disease in EU
    - gram -ve
    - small children 0-4 highest risk group
    - infection route via uncooked poultry, but does NOT causes outbreaks
    - v factors are adhesion, flagella, T4 secretion system
  2. Salmonellosis (salmonella species)
    -gram -ve
    - again uncooked poultry but DOES cause outbreaks
    - highest risk in small children 0-4
    - main v factor is T3 secretion system;
    SPI1 for invasion and SPI2 for intracellular accumulation
  3. Cholera (vibrio cholera)
    - gram -ve
    - acute severe diarrhoeal disease
    - main v factors are T4 fimbria and cholera toxin (increased cAMP- opening of Cl- channels and expulsion of water from cells)- carried on bacteriophages
  4. Listerosis ( listeria monocytogenes)
    - gram +ve
    - risk groups are immunocompromised and pregnant people
40
Q

State two emerging and vector borne disease?

A
  1. Plague (yersina pestis)
    - gram -ve
  2. Q fever (coxiella burnetti)
    - gram -ve

smallpox has been eradicated

41
Q

What infectious disease has mass vaccination eradicated?

A

Smallpox

Poliomyelitis

Microbiology (8 decks)

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