Community and Hospital acquired bacterial infection Flashcards
What are the different types of bacteria with reference to their shape/size classification?
Cocci ( circle) - Staphylococci is like a snooker ball triangle whereas, streptococci are like a caterpillar, many circles to form one line
Bacilli - Looks like a tic tac, palisades are when they are aggregated by long edge whereas, streptobacilli are like a caterpillar of tic tacs
Budding or appendaged bacteria - stalk or hypha
Other - vibrio, comma’s form, enlarged rod, club rod, filamentous ( string),
What are the components of a bacterial cell?
Capsule Cell wall - Projections coming off Pili Plasma membrane cytoplasm DNA ribosomes (70S) Flagellum
What are the 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, desiccation and chemical resistant i.e. Bacillus sp. and Clostridium sp. Biofilms (organized aggregates of bacteria embedded in polysaccharide matrix – antibiotic resistant) i. e. Pseudomonas aeruginosa i.e. Staphylococcus epidermidis
What are the different types of exotoxins?
Neurotoxins (act on nerves or motor endplate) i.e. Tetanus or Botulinum toxins
Enterotoxins (act on the GI tract)
1) Infectious diarrhea
i. e. Vibrio cholera, Escherichia coli, Shigella dysenteriae and Campylobacter jejuni
2) Food poisoning
i. e. Bacillus cereus or Staphylcoccus aureus
Pyrogenic exotoxins (stimulate release of cytokines) i.e. Staphylcoccus aureus or Streptococcus pyogenes
Tissue invasive exotoxin (allow bacteria to destroy and tunnel through tissue)
enzymes that destroy DNA, collagin, fibrin, NAD, red or white blood cells
i.e. Staphylococcus aureus, Streptococcus pyogenes and Clostridium perfringens
Miscellaneous exotoxin (specific to a certain bacterium and/or function not well understood) i.e. Bacillus anthracis and Corynebacterium diphtheriae
What is an endotoxin?
Only found in gram negative bacteria, outer membrane lipopolysaccharide, Lipid A part of LPS.
If people have blood stream infections with lots of gram negative bacteria, antibiotics will cause lysis of bacteria and possibly release the LPS/endotoxins leading to toxic/septic shock syndrome
Exotoxins are proteins
What’s the difference between gram negative and positive?
Gram negative have an outer membrane which is a lipopolysaccharide membrane whereas gram positive have a peptidoglycan rich outer layer
What is an outbreak?
an outbreak is a sudden increase in occurrences of a disease in a particular time and place. It may affect a small and localized group or impact upon thousands of people across an entire continent. Four linked cases of a rare infectious disease may be sufficient to constitute an outbreak.
How can an outbreak be identified?
Surveillance systems provide an opportunity to identify outbreaks
Good and timely reporting systems are instrumental to identify outbreaks
What outbreak occurred in 2011?
Germany E.coli outbreak
Describe the outbreak a little bit
Causative agent: Outbreak was caused by an entero-aggregative
Shiga-toxin producing E. coli O104:H4 strain
Illness: gastroenteritis and hemolytic-uremic syndrome (HUS)
Source: The consumption of sprouts was identified as the most likely vehicle of infection
Time frame: 1 May 2011- 4 July 2011
Scale: Total of 3816 Cases (54 death) in Germany
845 (22%) of these were with hemolytic-uremic syndrome
Smaller outbreak in France
Incubation period was around 8 days with a medium of 5 days from the onset of diarrhea to development of the hemolytic-uremic syndrome
What is hemolytic-uremic syndrome?
first described in children in the 1950th
characterized by a triad of acute renal failure, hemolytic anemia and thrombocytopenia
usually found in children and usually caused by the Shiga toxin producing E. coli strain O157:H7
EHEC strains - enterohemorrhagic E. coli
reservoir are normally ruminants – mostly cattle
human infection occurs through the inadvertent ingestion of fecal matter and secondary through contact with infected humans
usually the hemolytic-uremic syndrome is very rare in adults
How can PCR be used to detect an outbreak strain?
Once you have genome code sequence of the disease Multiplex PCR (more than one target sequence amplified by using multiple primer pairs in reaction mixture) looks for characteristic features Can be done via stools samples
What is a shiga toxin?
An AB5 toxin
One fragment that has enzymatic toxic activity
Subunit a (StxA) is non-covalently associated with a
pentamer of protein B (StxB)
StxA is enzymatically active domain
StxB pentamer is responsible for binding to host cell receptors
StxA is an enzyme that cleaves the 28S ribosomal RNA in eukaryotic cells
leads to inhibition of protein synthesis
Bacterial ribosomes are also a substrate for StxA and this will result in decreased proliferation of susceptible bacteria
might affect the commensal microflora in the gut
Shiga toxin does not only block protein synthesis in eukaryotic cells but also affects several other cellular processes
Where are shiga toxins encoded on?
Encoded on a bacteriophage
Highly mobile genetic elements which contributes to horizontal gene transfer (acquisition of genetic material from organism that isn’t parent and is usually of a different species)
Toxins are highly expressed when the lytic cycle of the phage is activated
Which areas can enteroaggregative E.coli colonise?
Both small and large bowels
Dependent on virulence factors and strain you are dealing with
Shiga toxin also found in the small bowel hence this strain was really pathogenic
Where are genes coding for aggregative adherence fimbriae found on EAEC
Plasmid
What is the function of AAF?
required for adhesion to enterocytes
stimulates a strong IL-8 response (neutrophil chemotactic factor)
Allows biofolm production
What additional virulence factors does EAEC have?
Leads to disruption of actin cytoskeleton - exfoliations
How can communicable diseases be grouped?
1) Respiratory tract infections
2) Sexually transmitted infections, including HIV and blood-borne viruses
3) Food- and waterborne diseases and zoonoses
4) Emerging and vector-borne diseases
5) Vaccine-preventable diseases
6) Antimicrobial resistance and healthcare-associated infections
List respiratory infections
2 of which are bacterial
Influenza
Animal influenzas, including avian influenza
SARS - Severe acute respiratory syndrome
Legionnaires’ disease (legionellosis) Legionella pneumophila (Gram -)
Tuberculosis Mycobacterium tuberculosis (Gram +)
