Community acquired bacterial infections Flashcards
Name some examples of cocci bacteria
Staphylococci, streptococci, sarcina and tetrad
Name some examples of bacilli bacteria?
Coccobacillus, bacillus, diplobacilli, palisades, streptobacili
Name the common virulence factors
Secretion systems Flagella Pili Capsule Endospores - resistant to heat, cold, desiccation and chemical resistant Exotoxins
What are the different types of exotoxins?
Neurotoxins- Act on nerves or motor endplates to cause paralysis e.g. tetanus and botulinum toxin
Enterotoxins- GI tract to cause diarrhoea- inhibit NaCl resorption, activate NaCl secretion or kill intestinal epithelial cells- commune end result is osmotic pull of fluid into the intestine which causes diarrhoea
Pyrogenic exotoxins- stimulate release of cytokines and can cause rash, fever and toxic shock syndrome
Tissue invasive exotoxin
Miscellaneous exotoxin
How does infectious diarrhoea occur?
Bacteria colonise and bind to the GI tract, continuously releasing their enterotoxin locally. Diarrhoea will continue until bacteria are destroyed by the immune system or antibiotics
Give some examples of infectious diarrhoea diseases?
Vibro cholera
Escherichia coli
Campylobacter jejuni
Shigella dysenteriae
Describe the process of food poisoning?
Bacteria grow in food and release enterotoxin into the food. The enterotoxin is ingested resulting in diarrhoea and vomiting for less than 24 hours
Give some examples of food poisoning bacteria?
Staphylococcus aureus and bacillus cereus
What are endotoxins?
Lipid A part of LPS, component of gram negative bacterium
What is septic shock?
Sepsis that results in dangerous drops in blood pressure and organ dysfunction
What is septic shock also known as?
Endotoxin shock because endotoxin often triggers the immune response that results in sepsis and shock (but adverse effects in gram-positive bacteria or even fungi can trigger adverse immune response)
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 systems provide an opportunity to identify outbreaks- report to a central system to identify the spread
Good and timely reporting systems are instrumental
What was the E coli outbreak in Germany 2011 caused by?
Entero-aggregative shiga-toxin producing e coli
What did the E.coli outbreak lead to?
Gastroenteritis and haemolytic-uremic syndrome
What was the e.coli outbreak spread by?
Consumption of sprouts
What is haemolytic-uremic syndrome?
Acute renal failure, haemolytic anaemia and thrombocytopenia
Who is HUS normally found in?
Children
What is the normal reservoir for HUS?
Cattle
How does infection occur of HUS in humans?
Inadvertent ingestion of decal matter and secondary through contact with infected humans- very rare in adults
What do you need to define an outbreak?
Cause, characteristics, scale, time-frame, source, illness, involvement of different strains, symptoms to look for etc
What can you do once you know the genome of the bacteria to detect the outbreak strain?
Do PCR in stool samples etc
What is the structure of shiga/vero toxin?
Subunit a (StxA) is non covalently associated with a pentamer of protein B (StxV)
What is the role of StxA?
Enzymatically active domain- it is an enzyme that cleaves the 28S ribosomal RNA in eukaryotic cells leads to inhibition of protein synthesis
What is the StxB pentamer responsible for?
Binding to host cell receptors
What are bacterial ribosomes a substrate for and what is the effect?
StxA and it will result in decreased proliferation of susceptible bacteria which might affect the commensal microflora in the gut
What are shiga toxins encoded on?
A bacteriophage (highly mobile genetic element which contributes to horizontal gene transfer
What caused the outbreak in Germany?
Horizontal gene transfer of shiga toxin from EHEC strain to EAEC strain of coli, which also has a virulence factor- aggregative adherence fimbriae (AAF) which is required for adhesion to to enterocytes in gut. It also stimulates a strong IL-8 response which allows biofilm formation and additional virulence factors.
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 diseases and zoonoses
Emerging and vector borne diseases
Vaccine preventable diseases
Antimicrobial resistance and healthcare associated infections
Give examples of respiratory tract infections?
Influenza (human, avian and animal)
Legionnaire’s disease
Tuberculosis
What type of bacteria is legionella pneumophila?
Gram-negative bacterium
Where is legionella pneumophila?
Lives in amoeba in ponds, lakes, air conditioning units, whirlpools etc
What is the infection route of legionella pneumophila?
Inhalation of contaminated aerosols
What does L. pneumophila affect in humans?
It will infect and grow in alveolar macrophages
What is the important virulence factor in l.pneumophila?
Type IV secretion system which allows secretion of effector proteins to cytoplasm of host cells which allows legionella to replicate in a legionella containing vacuole within the host cell
What sort of bacteria are mycobacterium tuberculosis?
It groups with gram positive but are structurally very different as they have a cell wall with an extra lipid layer. This makes treatment more difficult
What is the latent state of TB?
Evidence of infection by immunological tests but no clinical signs and symptoms of active disease
What makes treatment of TB difficult?
There is often a mixture of active and latent so it is difficult to treat bacteria in different states
What is the treatment success rate of TB (for 1st and then second infection)?
It is 78% and decreases to 53% for 2nd infection as well as further decreasing to 32% in multi drug resistant TB
Give examples of sexually transmitted infections?
Chlamydia trachomatis infection Gonorrhoea Hepatitis B Hepatitis C HIV/AIDS Syphilis
What type of bacteria is chlamydia trachomatis and what does this mean?
It is an obligate intracellular gram negative pathogen so can’t culture it outside host cell
What is the most frequent STI in europe?
Chlamydia 350,000 cases/year
How is the infection rate of chlamydia changing?
Increasing
What percentage of the worlds blindness is chlamydia responsible for?
More than 3%
What type of bacteria is neisseria gonorrhoeae?
Gram negative diplococcus
How does neisseria gonorrhoeae establish infection?
It establishes infection in urogenital tract by interacting with non-ciliated epithelial cells
What is the important virulence factor for gonorrhoea?
Pili
Give some examples of food and waterborne diseases and zoonoses?
Campylobacter sp Salmonella sp Bacillus anthracis Vibro cholera Listeria monocytogenes
What is the most commonly reported GI infectious disease in the EU?
Campylobacteriosis (sporadic cases not outbreaks)
What is the highest risk group of campylobacter?
Children aged 0-4 years
What is infection of campylobacter most likely from?
Undercooked poultry
What is the virulence factor involved in campylobacter?
Adhesion and invasion factors, flagella motility, type IV secretion system, toxin
What is salmonella sp. caused by?
Undercooked poultry
What is the most at risk group of salmonella infection?
Small children aged 0-4
What is the important virulence factor involved in salmonella?
Type III secretion systems (encoded on pathogenicity islands= SPI)- two islands:
SPI1 is required for invasion
SPI2 is for intracellular accumulation
How is bacillus anthraces usually transmitted?
It is very rare and usually transmission to humans from animals e.g. sheep and cattle
Outbreak in 2009 in UK- IV drug users
How does bacillus anthraces cause infection?
Infectious particles endospores (high mortality if untreated)
What virulence factors are involved in bacillus anthracis?
Toxin and capsule (encoded on plasmids)
What is cholera?
Acute, severe diarrheal disease
What can happen without prompt rehydration in cholera?
Death can occur within hours of onset of symptoms
What is the important virulence factor in cholera?
Type IV fimbria Cholera toxin (carried on phages)
What else does type IV fimbria (TCP phage) serve as apart from a colonisation factor?
A receptor for CTX phage encoding cholera toxin- Both bacteriophages can integrate into bacterial genome and form episomal replication intermediates and this is dependent on secretin
What does the cholera toxin do?
Makes the cell produce cyclic AMP which activates transporters leading to efflux of chloride ions with water movement following
What is the risk group for listeria monocytogenes?
Immunocompromised, elderly, pregnant and their fetus
Why is listeria a big problem?
It can cross three tight barriers- intestinal, blood/brain and materno/fetal
What has studying listeria allowed understanding of?
Actin-based cell mobility
What emerging and vector borne diseases are there?
Plague (yersinia pestis, gram negative)
Q fever (coxiella burnetti, gram negative)
Smallpox (eradicated)
What do vaccine preventable diseases include?
Diphtheria Invasive haemophillus influenza disease Invasive meningococcal disease Invasive pneumococcal disease Pertussis Tetanus
