Community Acquired Bacterial Infections

Question 1

Define virulence factor.

Answer 1

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

Question 2

List 5 common bacterial virulence factors and include their function.

Answer 2

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

Question 3

Give examples of bacteria that possess the following virulence factors:

a. Capsule
b. Endospores
c. Biofilms

Answer 3

Capsule: S. pneumoniae
Endospores: Bacillus + Clostridium
Biofilms: P. aeruginosa + S. epidermidis

Question 4

What are exotoxins?

Answer 4

Toxins released by a living bacterial cell into its surrounding

Question 5

What are the 4 different types of exotoxin? Give examples of bacteria that produce such toxins.

Answer 5

Neurotoxins: Botulinum toxin, Tetanus
Enterotoxins: Infectious diarrhoea –Vibrio cholerae, E. coli, Shigella
+ Food poisoning –Bacillus cereus, S. aureus
Pyrogenic toxins: S. aureus, S. pyogenes
Tissue invasive toxins: S. aureus, S. pyogenes

Question 6

What is an endotoxin? What is the pattern of release?

Answer 6

Lipid A moiety of lipopolysaccharide found on outer membrane of Gram-negative cells
Shed in steady amounts from living bacteria

Question 7

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

Answer 7

Antibiotics can cause lysis of bacteria, releasing endotoxins into the circulation in large quantities
This can trigger an immune response that leads to septic SHOCK

Question 8

What is an outbreak?

Answer 8

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

Question 9

How can an outbreak be identified?

Answer 9

Surveillance

Good + timely reporting systems are necessary

Question 10

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

What were the symptoms of infection?

Answer 10

Enteroaggregative shiga toxin producing E. coli

Gastroenteritis + Haemolytic uraemia syndrome

Question 11

What was special about the E. coli strain that caused the 2011 outbreak?

Answer 11

It was an EAEC strain that had acquired the ability to produce shiga toxin
Shiga toxin production is a feature of EHEC
Thus, produced a new strain = EAHEC

Question 12

Describe the structure of shiga toxin.

Answer 12

An A subunit non-covalently associated with a pentamer of protein B

Question 13

Describe the action of shiga toxin.

Answer 13

Subunit A = enzymatically active domain
Subunit B = binds 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. commensals)

Question 14

How was the shiga toxin gene transferred between bacteria?

Answer 14

Bacteriophage

Question 15

What is the important virulence factor in EAEC?

Answer 15

Aggregative adherence fimbriae (AAF): required for adhesion to enterocytes

Question 16

What type of bacterium is Legionella pneumophila and what is the route of infection?
Which cells does it infect and grow in?

Answer 16

Gram negative
Transmitted through inhalation of contaminated aerosols
Grows in Alveolar Macrophages

Question 17

What is the important virulence factor for L. pneumophila? Describe this

Answer 17

Type IV secretion system

Allows injection of toxic proteins from cytoplasm into vacuoles of macrophages

Question 18

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

Answer 18

Mycolic acid outer membrane; prevents normal antibiotics from getting into the cell

Question 19

State 3 bacterial sexually transmitted diseases including the species of bacteria that cause the diseases. What type of bacteria are these?

Answer 19

Chlamydia: Chlamydia trachomatis
Syphilis: Treponema pallidum
Gonorrhoea: Neisseria gonorrhoeae
All gram negative

Question 20

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

Answer 20

Blindness (due to eye infection)

Question 21

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

Answer 21

Interacts with non-ciliated epithelial cells in urogenital tract

Question 22

What are the important virulence factors of N. gonorrhoeae?

Answer 22

Pili allow adhesion

Antigenic variation: escapes detection + clearance by the immune system

Question 23

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

Answer 23

Campylobacter jejuni

Question 24

What is the route of infection of Campylobacter and Salmonella?

Answer 24

Ingestion of undercooked poultry

Question 25

State 4 important virulence factors of Campylobacter jejuni.

Answer 25

Adhesion + invasion factors Flagella motility Type IV secretion system Toxin

Question 26

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

Answer 26

Young children (0-4 years)

Question 27

What is an important virulence determinant of Salmonella sp.?

Answer 27

Type III secretion system | Allows injection of toxic proteins into eukaryotic cells

Question 28

What are the important virulence factors of Vibrio cholerae?

Answer 28

Cholera toxin | Type IV fimbria

Question 29

Explain how cholera toxin works.

Answer 29

Has A + B subunits A = active toxin B = allows entry of toxin into epithelial cell A subunit activates adenylate cyclase, thus increasing production of cAMP cAMP binds to CFTR + causes Cl- efflux Water follows ion movement Results in massive movement of water into intestinal lumen

Question 30

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

Answer 30

Immunocompromised Elderly Pregnant + their foetus

Question 31

What are some special features of Listeria?

Answer 31

Can enter non-phagocytic cells + cross tight barriers (e.g. intestinal barrier, BBB + maternal-foetal barrier)

Question 32

Name 2 bacterial vector-borne diseases.

Answer 32

Q fever | Plague

Question 33

List 6 vaccine-preventable diseases caused by bacteria

Answer 33

``` Diphtheria Invasive pneumococcal infections Invasive meningococcal infections Invasive Haemophilus influenzae Pertussis Tetanus ```

Question 34

What is the mode of action of each type of exotoxin?

Answer 34

Neurotoxins act on nerves/ motor endplates Enterotoxins act on GI tract Pyrogenic exotoxins stimulate release of cytokines Tissue invasive exotoxins allow bacteria to destroy + tunnel through tissue

Question 35

What are the usual consequences of Salmonella and Campylobacter infection?

Answer 35

Salmonella sp. can cause outbreaks | Campylobacter tends to be sporadic cases

Question 36

What is cholera? What can it lead to?

Answer 36

Acute, severe diarrhoea disease | Without prompt dehydration, leads to death within hours