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Flashcards in Community Acquired Bacterial Infections Deck (35)
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Define virulence factor.

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


List some common bacterial virulence factors and include their function.

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


Give examples of bacteria that possess the following virulence factors:
a. Capsule
b. Endospores
c. Biofilms

a. Capsule
S. pneumoniae
b. Endospores
Bacillus sp.
Clostridium sp.
c. Biofilms
P. aeruginosa
S. epidermidis


What are exotoxins?

A toxin released by a living bacterial cell into its surrounding


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

 Botulinum toxin
 Tetanus
 Infection 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
 C. perfringens


What is an endotoxin?

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


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

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


What is an outbreak?

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


How can an outbreak be identified?

Good and timely reporting systems are necessary


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

Enteroaggregative shiga toxin producing E. coli


What were the symptoms of infection by this bacterium?

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


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

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


Describe the structure of shiga toxin.

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


Describe the action of shiga toxin.

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)


How was the shiga toxin gene transferred between bacteria?



What is the important virulence factor in EAEC?

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


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

Gram negative
It is transmitted through inhalation of contaminated aerosols


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

Alveolar macrophages


What is the important virulence factor for L. pneumophila?

Type IV secretion system


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

It has a mycolic acid outer membrane – this prevents normal antibiotics from getting into the cell


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

Chlamydia - Chlamydia trachomatis
Syphilis –Treponema pallidum
Gonorrhoea –Neisseria gonorrhoeae


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

Blindness (due to eye infection)


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

It interacts with non-ciliated epithelial cells


What are the important virulence factors of N. gonorrhoeae?

Antigenic variation escapes detection and clearance by the immune system


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

Campylobacter jejuni


What is the route of infection of Campylobacter and Salmonella?

Ingestion of undercooked poultry


State some important virulence factors of Campylobacter jejuni.

Adhesion and invasion factors
Type IV secretion system


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

Young children (0-4 years)


What is an important virulence determinant of Salmonella sp.?

Type III secretion system
NOTE: Salmonella sp. can cause outbreaks whereas Campylobactertends to be sporadic cases


What are the important virulence factors of Vibrio cholerae?

Cholera toxin
Type IV fimbria