Community and hospital acquired bacterial infections Flashcards
List some common virulence factors.
Diverse secretion systems.
Flagella (movement, attachment).
Pili (important adherence factors).
Capsule (protect against phagocytosis), i.e. Streptococcus pneumoniae.
Endospores (metabolically dormant forms of bacteria)- heat, cold, dessication and chemical resistant, i.e. Bacillus sp. and Clostridium sp.
Biofilms (organised aggregates of bacteria embedded in polysaccharide matrix- antibiotic resistant), i.e. Pseudomonas aeruginosa, Staphylococcus epidermidis.
Exotoxins- neurotoxins, enterotoxins and pyrogenic exotoxins.
Endotoxins.
List the different types of exotoxins.
Neurotoxins. Enterotoxins. Pyrogenic exotoxins. Tissue invasive exotoxins. Miscellaneous exotoxins.
What are neurotoxins?
Act on nerves or motor endplates to cause paralysis, i.e. tetanus or botulinum toxins.
What are enterotoxins?
Act on the GI tract to cause diarrhoea- inhibit NaCl resorption, activate NaCl secretion or kill intestinal epithelial cells, resulting in osmotic pull of fluid into the intestine.
Infectious diarrhoea (bacteria colonise and bind to the GI tract, continuously releasing their enterotoxin locally, i.e. Vibrio cholera, Escherichia coli, Shigella dysenteriae, Campylobacter jejuni.
Food poisoning (bacteria grow in food and release enterotoxin into the food- enterotoxin is ingested resulting in diarrhoea and vomiting for less than 24 hours), i.e. Bacillus cereus, Staphylococcus aureus.
What are pyrogenic exotoxins?
Stimulate release of cytokines and can cause rash, fever and toxic shock syndrome, i.e. Staphylococcus aureus, Streptococcus pyogenes.
What are tissue-invasive exotoxins?
Allow bacteria to destroy and tunnel through tissue, enzymes that destroy DNA, collagen, fibrin, NAD, red or white blood cells, i.e. Staphylococcus aureus, Streptococcus pyogenes, Clostridium perfringens.
What are miscellaneous exotoxins?
Specific to a certain bacterium and/or function not well understood, i.e. Bacillus anthracis, Corynebacterium diphtheriae.
What are endotoxins?
Only produced by Gram negative bacteria.
Not a protein- the lipid A moiety of LPS.
Shed in steady amounts from living bacteria.
Treating a patient who has a Gram negative infection with antibiotics can sometimes worsen the condition- when bacteria lyse they release large quantities of LPS/endotoxin, leading to septic shock.
What is septic shock?
Sepsis that results in dangerous drops in blood pressure and organ dysfunction.
a.k.a. endotoxin shock- endotoxin often triggers the immune response that results in sepsis and shock.
Different effector molecules in Gram positive bacteria or even fungi can trigger this adverse immune response, so the term septic shock is inclusive.
Most effective treatment is to find the site of infection, the microbe responsible and eradicate it.
Lung, abdomen and urinary tract are common places.
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 period of time, or a particular place, or both.
How can an outbreak be identified?
Surveillance provides an opportunity to identify outbreaks.
Good and timely reporting systems are instrumental to identify outbreaks.
What is haemolytic-uraemia syndrome characterised by?
A triad of acute renal failure, haemolytic anaemia and thrombocytopaenia.
What are the different types of communicable disease in Europe?
Respiratory tract infections.
Sexually transmitted infections, including HIV and blood-borne viruses.
Food- and waterborne disease and zoonoses.
Emerging and vector-borne diseases.
Vaccine-preventable diseases.
Antimicrobial resistance and healthcare-associated infections.
Give examples of respiratory tract infections.
Influenza.
Animal influenzas, including avian influenza.
SARS- severe acute respiratory syndrome.
Legionnaires’ disease (legionellosis)- Legionella pneumophila (Gram negative).
Tuberculosis- Mycobacterium tuberculosis (Gram positive).
What is Legionella pneumophila?
Gram negative bacterium.
Lives in amoeba in ponds, lakes, air conditioning units, whirlpools…
Infection route: inhalation of contaminated aerosols.
In humans, L. pneumophila will infect and grow in alveolar macrophages.
Human infection is ‘dead end’ for bacteria.
Important virulence factor: type IV secretion system.
What is the importance of type IV secretion system to Legionella pneumophila?
Allows L. pneumophila to infect and replicate in human macrophages.
Secretion of effector proteins by the type IV secretion system allow Legionella to replicate in a Legionella containing vacuole (LCV).
