Community Acquired Bacterial Infections Flashcards
(53 cards)
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
Pseudomonas aeruginosa
Staphylococcus epidermidis
What are exotoxins?
A toxin released by a living bacterial cell into its surrounding
What are the five different types of exotoxin? Briefly describe what they do
Neurotoxins - act on nerves or motor endplate to cause paralysis
Enterotoxins - act on the GI tract to cause diarrhea and vomiting
Pyrogenic exotoxins - stimulate release of cytokines to cause rash, fever and toxic shock
Tissue invasive toxins - allow bacteria to destroy and tunnel through tissue
Miscellaneous exotoxin - specific to becterium/function not well understood
What is an endotoxin?
This is the lipid A part of lipopolysaccharide (LPS) that is found on the outer membrane of Gram-negative cells
Gram negative bacteria shed this all the time
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?
Surveillance
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 was special about the bacterial strain that caused by 2011 E.coli outbreak in Germany?
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?
Bacteriophage
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
Incredibly slow growing
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 Neisseria gonorrhoeae establish infection in the urogenital tract?
It interacts with non-ciliated epithelial cells
What are the important virulence factors of Neisseria gonorrhoeae?
Pili
Antigenic variation escapes detection and clearance by the immune system
What are the 2 most commonly reported infectious GI diseases in the EU?
Campylobacter jejuni
Salmonella sp.
