Community Acquired Bacterial Infections Flashcards
Define virulence factor.
Molecules produced by pathogens that contribute to the pathogenicity of the organism
List 5 common bacterial virulence factors and include their function.
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
Give examples of bacteria that possess the following virulence factors:
a. Capsule
b. Endospores
c. Biofilms
Capsule: S. pneumoniae
Endospores: Bacillus + Clostridium
Biofilms: P. aeruginosa + S. epidermidis
What are exotoxins?
Toxins released by a living bacterial cell into its surrounding
What are the 4 different types of exotoxin? Give examples of bacteria that produce such toxins.
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
What is an endotoxin? What is the pattern of release?
Lipid A moiety of lipopolysaccharide found on outer membrane of Gram-negative cells
Shed in steady amounts from living bacteria
Why can treating patients with Gram-negative infection sometimes worsen their condition?
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
What is an outbreak?
A greater than normal/ than expected number of individuals infected with a particular infection in a given time period or place
How can an outbreak be identified?
Surveillance
Good + timely reporting systems are necessary
What was the 2011 E. coli outbreak in Germany caused by?
What were the symptoms of infection?
Enteroaggregative shiga toxin producing E. coli
Gastroenteritis + Haemolytic uraemia syndrome
What was special about the E. coli strain that caused the 2011 outbreak?
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
Describe the structure of shiga toxin.
An A subunit non-covalently associated with a pentamer of protein B
Describe the action of shiga toxin.
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)
How was the shiga toxin gene transferred between bacteria?
Bacteriophage
What is the important virulence factor in EAEC?
Aggregative adherence fimbriae (AAF): required for adhesion to enterocytes
What type of bacterium is Legionella pneumophila and what is the route of infection?
Which cells does it infect and grow in?
Gram negative
Transmitted through inhalation of contaminated aerosols
Grows in Alveolar Macrophages
What is the important virulence factor for L. pneumophila? Describe this
Type IV secretion system
Allows injection of toxic proteins from cytoplasm into vacuoles of macrophages
What feature of Mycobacterium tuberculosis makes it more difficult to treat?
Mycolic acid outer membrane; prevents normal antibiotics from getting into the cell
State 3 bacterial sexually transmitted diseases including the species of bacteria that cause the diseases. What type of bacteria are these?
Chlamydia: Chlamydia trachomatis
Syphilis: Treponema pallidum
Gonorrhoea: Neisseria gonorrhoeae
All gram negative
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?
Interacts with non-ciliated epithelial cells in urogenital tract
What are the important virulence factors of N. gonorrhoeae?
Pili allow adhesion
Antigenic variation: escapes detection + clearance by the immune system
What is the most commonly reported infectious GI disease in the EU?
Campylobacter jejuni
What is the route of infection of Campylobacter and Salmonella?
Ingestion of undercooked poultry
State 4 important virulence factors of Campylobacter jejuni.
Adhesion + invasion factors
Flagella motility
Type IV secretion system
Toxin
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
Allows injection of toxic proteins into eukaryotic cells
What are the important virulence factors of Vibrio cholerae?
Cholera toxin
Type IV fimbria
Explain how cholera toxin works.
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
Which subsets of the population are at risk of infection by Listeria monocytogenes?
Immunocompromised
Elderly
Pregnant + their foetus
What are some special features of Listeria?
Can enter non-phagocytic cells + cross tight barriers (e.g. intestinal barrier, BBB + maternal-foetal barrier)
Name 2 bacterial vector-borne diseases.
Q fever
Plague
List 6 vaccine-preventable diseases caused by bacteria
Diphtheria Invasive pneumococcal infections Invasive meningococcal infections Invasive Haemophilus influenzae Pertussis Tetanus
What is the mode of action of each type of exotoxin?
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
What are the usual consequences of Salmonella and Campylobacter infection?
Salmonella sp. can cause outbreaks
Campylobacter tends to be sporadic cases
What is cholera? What can it lead to?
Acute, severe diarrhoea disease
Without prompt dehydration, leads to death within hours
