Lecture 1: Gram Positive Bacteria Flashcards
What is the meaning of Gram-Positive?
Gram-positive is a way bacteria can be classified. This classification is based off the structure of their cell wall.
What is the structure of a gram-positive bacterium’s cell wall?
it is composed of a thick dense peptidoglycan layer.
What antibodies are responsible for acute responses and long-term responses?
IgM is responsible for the acute response
IgG is part of the adaptive immune response
What differences are there between gram-positive peptidoglycan and gram-negative peptidoglycan?
Gram-positive has pentaglycine cross-linkages, making it stronger and more dense.
Gram-negative bacteria has direct linkages, making the peptidoglycan layer weaker and less dense.
What is the most common gram-positive bacteria?
Staphylococcus.
What is staphylococcus?
A gram-positive genus of bacteria that usually form grape like clusters of cocci.
The characteristics are:
- Facultative anaerobe
- Prokaryotic
- Gram-positive
- Non-spore forming
- Non-motile (not conventionally)
Where does the name Staphylococcus come from?
The word Staphyle means a bunch of grapes in greek, and the word Kokkos means berry.
What direction does staphylococcus divide in?
What direction does streptococcus divide in?
Staphylococci divide in all directions, forming grape like clusters.
Streptococci divide in one direction only and thus form chains.
What class of drug does penicillin belong to?
Beta-Lactams.
What two species of staphylococcus are most associated with human disease?
Staphylococcus aureus and Staphylococcus epidermidis
What differences are there between staphylococcus aureus and staphylococcus epidermidis?
Staphylococcus aureus has more virulence factors and causes more diseases. Epidermidis is more opportunistic.
Epidermidis is not capable of haemolysis, aureus is capable of alpha, beta, and gamma.
What enzyme does penicillin inhibit?
Transpeptidase, the enzyme which performs the final step of cell wall synthesis, by forming pentaglycine linkages between peptidoglycan chains. This makes the cell wall weak and more easily broken, killing the bacterium.
What does staphylococcus aureus derive its name from?
They get the name because they are gold in colour as they contain lots of yellow carotenoids (large family of molecules that can be very useful for pigmentation, antioxidation, and some function as provitamins).
Which Staphylococci species produce catalase?
All species, with 2 very minor exceptions.
What is a difference in colony appearance between Staphylococcus aureus and Staphylococcus epidermidis?
Aureus will have a yellowish tint to it rather than white in epidermidis.
How does Staphylococcus aureus’ salt resistance affect the location of normal flora?
It will be present in areas that get sweaty such a groin or armpits.
Why is staphylococcus very contagious?
Because they can survive desiccation while strongly attached to dead skin cells that flake off to form dust (despite not being spore forming).
They can also survive radiation and high temperatures (up to around 65 degrees C).
Produces catalase, which breaks down H2O2, thus dealing with a dangerous radical creating molecule),
What is C. diff?
Clostridium difficile.
The normal flora in human guts that overtakes other bacteria when antibiotics used for a long duration. Causes bad diarrhoea and sickness.
What is Staphylococcus aureus?
The most common species of Staphylococcus that are special due to being coagulase positive, with the only other member of the genus sharing this trait being staphylococcus intermedius.
What defences does Staphylococcus aureus have against the immune system?
It can defend against phagocytosis.
Protein A coated, this binds IgG stems and inhibits complement cascade.
Has bound coagulase on surface - forms fibrin clots around bacteria, hiding it.
Slime/capsules made of polysaccharide that prevents chemotaxis and endocytosis by leukocytes.
How specifically does Staphylococcus aureus use coagulase?
Coagulase is a protein that binds to and activates the protein prothrombin to become the active enzyme thrombin. Thrombin catalyses the conversion of fibrinogen into fibrin, which forms threads and attaches to red blood cells, clotting the blood.
Staphylococcus aureus uses this to form blood clots around infections, protecting it from cells of the immune system.
What is Staphylococcus epidermidis?
An opportunistic bacteria that’s defining feature is relying on slime (high molecular weight polysaccharides) to attach to fomites. Using this slime they form colonies coated in this slime (biofilms).
What groups of streptococcus are there?
Group A
Group B
Group C
Group G
What is group A streptococcus?
Strep A refers to Streptococcus pyogenes, with strep throat being a illness commonly associated.
Strep A is normally found on the skin and in the throat.
Streptococcus pyogenes is aerotolerant.
Strep A has a wide array of virulence factors
It is the streptococcus group that is associated with the most diseases.
These include:
- Strep Throat (pharyngitis)
- Tonsillitis
- Scarlet Fever
- Impetigo
- Pneumonia
- Rheumatic Fever
- Post-Streptococcal
Glomerulonephritis (PSGN)
More serious conditions that arise from strep A, known as invasive group A streptococcus infections, these include:
- Bacteraemia (infection of
bloodstream)
- Septic arthritis
- Meningitis
- Streptococcal toxic shock syndrome
(STSS)
