Lecture 19 - Streptococcus Flashcards
How do symptoms get caused by a microorganism?
Virulence factors can directly damage cells
Host immune response to virulence factors can lead to host cell damage
Describe the appearance of streptococci in terms of:
-Gram stain
-Shape
-Arrangement
Gram positive cocci in chains
How are different Streptococci classified?
By the degree of Haemolysis they do
What is Haemolysis?
The break down of Red Blood cells
Why do streptococcus bacteria benefit from doing haemolysis?
How does this affect their virulence?
The more able they are to do haemolysis the more easily they can break down the RBC and obtain their iron
This makes thee bacteria more able to replicate and produce virulence factors
More ability to do haemolysis = more virulent
What are the 3 broad groups of Streptococci based on their ability to do haemolysis?
Alpha haemolysis (viridans streptococci) = partial haemolysis
Beta haemolysis (complete/full haemolysis)
Non-haemolytic
What is an example of an Alpha haemolysis classified streptococci (viridans streptococci)?
Streptococcus pneumoniae
What is an example of a streptococci that is classified as a Beta Haemolytic organism?
How does this organism show on a blood agar?
Streptococcus pyogenes
Halo around the colony due to full break down of the red blood cells
What is an example of a streptococcus organism classified as non-haemolytic?
What does this mean in terms of its virulence?
Enterococcus faecalis
Have a lower virulence since they have a less ability to obtain iron
What is being tested for in serological classification of bacteria?
Antibodies and antigens
What is the most virulent streptococcus species?
Streptococcus pyogenes
What are 3 species of Streptococcus in the Beta haemolytic group? (Full haemolysis)
Streptococcus pyogenes
Strep agalactiae
Strep dysgalactiae
Where are Strep bovis, Strep mutans and strep salivarius commonly found?
What disease are they commonly associated with?
In the mouth
Endocarditis
What lancefield group is streptococcus pyogenes?
Group A Beta Haemolytic streptococcus
What are the 4 groups by which streptococci are classified in based on their physiological properties?
Pyogenic
Viridans
Enterococcal
Lactic
What is meant by streptococci being Pyogenic?
Pus forming
What is meant by streptococci being viridans?
Don’t fall into the other categories
What is meant by streptococci being enterococcal?
Are bile tolerant
Penicillin resistant
Gut dwelling (faecal sources)
What is meant by streptococci being lactic?
From diary sources
What is the main virulence factor of streptococcus pyogenes?
What does this virulence factor do?
M protein
Makes streptococcus pyogenes resistant to phagocytosis
Why is the M protein a very important virulence factor of streptococcus pyogenes?
It is the antigen normally presented to the host
We develop antibodies to the M protein
So if we have had an infection from a streptococcus pyogenes with the same M protein as a previous infection we should be immune to it
What disease is very common in children between 5-15 yrs as a result of streptococcus pyogenes infection?
Streptococcal pharyngitis
How is streptococcal pyogenes causing streptococcal pharyngitis spread?
What type of environment does it spread the best in?
Droplet infection
Overcrowded areas
Why is it often best not to give antibiotics to treat streptococcus pharyngitis?
Normally resolves by itself
If give antibiotics host immune system does not make antibodies for it so vulnerable to future infection
What are the clinical features of streptococcal pharyngitis?
Abrupt onset sore throat
Malaise
Inflamed tonsils
Can have pus/abscesses on tonsils
If throat swab done -> Group A strep
What are some complications associated with streptococcus pyogenes infection?
Scarlet fever
Abscesses in head and neck region
Acute rheumatic fever
Acute post-streptococcal glomerulonephritis
How can streptococcal pharyngitis lead to scarlet fever?
How does it spread?
The infected strain of Streptococcus pyogenes produces pyrogenic exotoxin
Exotoxin spreads locally or Haematogenous
How is scarlet fever treated?
Antibiotics
What can happen if an abscess in the head and neck leads to the infection spreading to the internal carotid artery?
Infection will then spread to the brain
What are some head and neck complications of streptococcal pharyngitis?
Sinusitis
Otitis media (middle ear infection)
Meningitis
Brain abscess
What is special about the state of the streptococcal pharyngitis infection (S.pyogenes) with Acute Rheumatic fever and Acute post-streptococcal glomerulonephritis?
How do these disease get caused then?
No bacteria present at the time the diseases occur
Due to autoimmune response:
-M protein antibodies cross react with host antigens
What is acute Rheumatic fever?
Condition which causes inflammation of the:
-heart
-joints
-CNS
What is acute post-streptococcal glomerulonephritis?
Why does it happen?
Acute inflammation of renal glomerulus
M antibodies target healthy kidney cells
Antigen-antibody complexes clog up in the glomerulus
What group of Streptococci leads to rheumatic fever?
Why dont we see rheumatic fever in the UK?
Group A strep infection (Strep. pyogenes)
Don’t have the rheumatic strain of streptococcus pyogenes here that causes it
What 4 skin infections are commonly caused by streptococcus pyogenes?
Impetigo
Erysipelas
Cellulitis
Necrotising fasciitis
Who does impetigo most commonly infect?
How does it normally look on a patient?
Childhood (2-5yrs)
Honey comb appearance around mouth
How is impetigo usually treated?
Topical antibiotics like mupirocin
What is Impetigo a common cause of?
Glomerulonephritis
What is Erysipelas?
Dermis infection with lymphatic involvement affecting face and lower limbs
When do the lower limbs typically get affected by erysipelas?
Secondary to invasion of skin via trauma, skin disease or local fungal infection
What is cellulitis?
What is a major risk factor for cellulitis?
Infection of skin and subcutaneous tissue
IV drug injectors
What is necrotising fasciitis?
How quickly does it happen?
Infection of deep subcutaneous tissues and fascia
Rapid extensive necrosis
What are the signs of necrotising fasciitis?
Severe pain
Blistering formation
A skin break has happened
How is necrotising fasciitis caused by streptococcus pyogenes infection treated?
IV antibiotics (Penicillin or amoxicillin)
Debridement of dead tissue
What is Streptococcal toxic shock syndrome?
What causes the negative effects?
When you have a deep tissue infection with Strep pyogenes (Group A strep) which then enters the blood stream
Causes:
-bacteriaemia
-vascular collapse
-organ failure
Bacterial exotoxins lead to T cells producing non specific inflammatory response leading to vascular collapse
What are some virulence factors of streptococcus pyogenes that isn’t the M protein?
How do they function?
Hyaluronic acid capsule (inhibits phagocytosis since so similar to human connective tissue)
Pyrogenic exotoxins (cleaves IgG bound to group A strep)
