Community Acquired Infection Flashcards
What are common virulence factors and its associated bacteria?
x Diverse secretion systems
x Flagella - for movement, attachment
x Pili - adherence
x Capsule - protect against phagocytosis
• i.e. Streptococcus pneumoniae
x Endospores - metabolically dormant forms of bacteria
• i.e. Bacillus sp. & Clostridium sp.
x Biofilms - aggregates of bacteria embedded in polysaccharide matrix (AB resistance)
• i.e. Pseudomonas aeruginosa & Staphyloc. epidermidis
What are exotoxins?
Toxins that damage biological systems
Give examples of exotoxins
x Neurotoxins - act on nerves of MEP
• i.e. Tetanus OR Botulinum toxins
x Enterotoxins - act on GIT
• i.e. infectious diarrhoea - Vibrio cholera, E.coli. Shigella dysenteriae, Campylobacter jejuni
• i.e. food poisoning - Bacillus cereus, Staph, aureua
x Pyrogenic exotoxins - stimulate release of cytokines
• i.e. Staph. aureus OR Strep. pyogenes
x Tissue invasive exotoxin - enzymes that allow bacteria to TUNNEL through tissue
• i.e. Staph. aureus, Strep. pyogenes, Clostridium perfringens
x Miscellaneous exotoxins - specific to certain bacteria, function NOT well understood
• i.e. Bacillus anthracis, Corynebacterium diphtheriae
What are endotoxins?
ONLY produced by gram -VE bacteria
NOT a protein
• it is a lipid A moiety of LPS
• shed in steady amounts from living bacteria
When treating a patient with a gram -VE bacteria infection, ABs can make it worse
• bacteria lyses = releases large quantities of LPS/endotoxins = septic shock
An example of an endotoxin?
Lipid A in LPS from gram-bacteria
Define outbreak
A sudden increase in the incidence of a disease in a particular place at a particular time
Give an example of an outbreak
E-COLI OUTBREAK!
Haemolytic-uraemic syndrome
• TRIAD of acute RF, haemolytic anaemia & thrombocytopenia
Caused by EHEC - enterohaemorrhagic E.coli
Outbreak was the result of a fusion of EHEC & EAHC strains to form the EAHEC strain
Difference between Possible vs. Probable vs. Confirmed Epidermic case?
Possible Epidemic Case
• any person that have developed the symptoms AND has met a laboratory criteria (e.g. isolation of agent)
Probably Epidemic Case
• Any person that has met the above criteria AND been in an epidemic country, consumed possibly contaminated food, been in close contact w. a confirmed epidemic case
Confirmed Epidemic Case
• Any person meeting criteria for possible case AND has had strain isolated
What is used to identify outbreak strains
PCR
Explain how outbreak strains are identified giving an example
Isolated can be screened by MULTIPLEX PCR for characteristic features of the outbreak strain
• can be done of stool samples for e.g. (e-coli)
• can determine if strain is outbreak strain or not
Give an example of indentifying an outbreak strain
Example - E-coli outbreak
• unique combination of genomic features containing characteristics from BOTH EHEC & EAEC suggested the new strain EAHEC
EAEC - 2 plasmids
• pAA-type plasmid - contain aggregative adhesion fimbrial operon
• ESBL plasmid - gene encoding for extended-spectrum beta-lactamases
EHEC - prophage encoding the Shiga toxin
• characteristic of EHEC strains
Explain the Shiga/Vero Toxin
Shiga toxins have an AB5 subunit composition
• StxA is the enzymatic portion - cleaves RNA = inhibits protein synthesis & might affect gut commensal bacteria
• StxB is the pentamer that binds to HOST CELL RECEPTORS
These toxins are encoded on bacteriophages
• contribute to horizontal gene transfer SO can be given to other bacteria types in phages
What is the virulence factor of EAEC
AAF - Aggregative Adherence Fimbriae
• required for adhesion to enterocytes & stimulates IL-8 response
• also allows a biofilm formation
Can colonise the larger & small bowel = affects gut flora
How can an outbreak be identifies?
x Surveillance
x Good and timely reporting systems
x PCR
2 examples of respiratory tract infections?
(1) Legionnaire’s Disease
• Legionella pneumophilia (gram -VE)
(2) Tuberculosis
• Mycobacterium tuberculosis (gram +VE)
