Microbiology 3: bacteria Flashcards
structural difference in organisation of cell contents between bacteria and eukaryotic cells
Bacteria do not have organelles (different to eukaryotes)
Outline the location of DNA in bacteria
hey just have their genetic material and ribosomes floating in the cytoplasm, as well as a cell wall
What kind of appendages coul dbacteria have? Does this affec virulence
Hypha/stalks Yes may do
Normal 3 tpes of naceria
Cocci, bacilli, spiral
List the common virulence features for bacteria
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 Exotoxin Endotoxin
How does flagella and pili contribute to virulence
Flagella (movement, attachment) Pili (important adherence factors)
How does capsule contribute to virulence Example
Capsule (protect against phagocytosis) i.e. Streptococcus pneumoniae
How does endospores contribute to virulence Examle
Endospores (metabolically dormant forms of bacteria) heat, cold, desiccation and chemical resistant i.e. Bacillus sp. and Clostridium sp.
How does biofilms contribute to virulence. Examples
(organized agregrates of bacteria embedded in polysaccahride matricesi. e. Pseudomonas aeruginosa i.e. Staphylococcus epidermidis
3 types of exotoxin
Neurotoxin Enterotoxin Tissue invasive exotoxin Miscellaneous exotoxin Pyrogenic exotoxin
Outline neurotoxin wiht examples
act on nerves or motor endplate i.e. Tetanus or Botulinum toxins
Outline 2 types of enterotoxin withexamples
- Infectious diarrhea Vibrio cholera, Escherichia coli, Shigella dysenteriae and Campylobacter jejuni 2. Food poisoning Bacillus cereus or Staphylcoccus aureus
THEY ACT ON THE GI TRACT
Outline pyrogenic exotoxins
Stimulate cytokine release Staphylcoccus aureus or Streptococcus pyogenes
Outline Tissue invasive exotoxin
allow bacteria to destroy and tunnel through tissue i.e. Staphylococcus aureus, Streptococcus pyogenes Clostridium perfringens
Which enzymes might tissue invasive exotoxin involve
enzymes that destroy DNA, collagin, fibrin, NAD, red or white blood cells
Examples of miscellaneous exotoxin, and what is different about them
specific to a certain bacterium and/or function not well understood Bacillus anthracis and Corynebacterium diphtheriae
What is endotoxin released by
Only produced by Gram-negative bacteria
What is endotoxin
Not a protein but it’s the the lipid A moiety of LPS
Differentiate gram positive and gram negative
Gram +ve= big cell wall, 1 lipid bilayer Gram -ve= small cell wall, 2 lipid bilayers
What is seen on the lipid bilayer of
On the lipid bilayer of gram negative bacteria, we see LPS and sugars – these are endotoxins
What can happen if lots of the LPS is shed
Then it can cause endotoxic shock Normally shed in steady amounts
Why can giving antibiotics to gram neg bacteria be dangerous
when bacteria lyse they release large quantities of LPS/ Endotoxin Leads to septic shock
Define septic shock
Sepsis that results in dangerous drops in blood pressure and organ dysfunction is called septic shock. It is also referred to as endotoxin shock because endotoxin often triggers the immune response that results in sepsis and shock.
Differentiate endotoxin shock and septic shock
different effectors molecules in Gram-positive bacteria or even fungi can trigger this adverse immune response – so the term septic shock is inclusive (of endotoxin shock and other shocks too)
What is haemolytic-uraemic syndrome
triad of acute renal failure, hemolytic anemia and thrombocytopenia
What usually causes haemolytic-uraemic syndrome
Shiga toxin producing E. coli strain
Define outbreak
An outbreak is 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.
What are E.coli strains which release shiga toxin known as
EHEC enterohemorrhagic E. coli
Reservoirs for EHEC
reservoir are normally ruminants – mostly cattle
When does human infection with EHEC often occur
occurs through the inadvertent ingestion of fecal matter and secondary through contact with infected humans
Who does HUS affect more
usually the hemolytic-uremic syndrome is very rare in adults
What can be done with genetics in an outbreak
You can sequence the gene in the bacteria to find the virulent genes You can then do PCR on people to confirm this e.g on stool samples
Give an example of how bacteriophage transfer can cause increased virulence
E.g. EHEC contains shiga toxin causing HUS enteroaggregative E. coli (EAEC) contains 2 plasmids Baceriophage can infect the EHEC and transfer the shiga toxin genetic info to the EAEC
What 2 plasmids are contained in EAEC
pAA-type plasmids - contains the aggregative adhesion fimbrial operon ESBL plasmid - harbors the genes encoding for extended-spectrum b-lactamases (i.e. beta lactam resistant)
What is the result of transfer of EHEC to EAEC
EAHEC Now the bacteria which was aggregating and beta-lactam resistant (EAEC) also contains a shiga toxin
Composition of shiga toxin
have an AB5 subunit composition Subunit a (StxA) is non-covalently associated with a pentamer of protein B (StxB).
What is the function of subunit A and the B subunits in shiga toxin
StxA is enzymatically active domain. StxB pentamer is responsible for binding to host cell receptors.
Mechanism of subunit A action
enzyme that cleaves the 28S ribosomal RNA in eukaryotic cells ,,, inhbits protein synthesis
Why can a shiga toxin bacteria infection affect gut microbiota
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
Why is shiga toxin a mobile genetic element
Shiga toxins are encoded on a bacteriophage highly mobile genetic elements and contributes to horizontal gene transfer Toxins are highly expressed when the lytic cycle of the phage is activated (so that the gene can be taken up by lots of E coli)