Lecture 19 - Streptococcus Flashcards by Callum Donoher

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

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Describe the appearance of streptococci in terms of:
-Gram stain
-Shape
-Arrangement

Gram positive cocci in chains

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How are different Streptococci classified?

By the degree of Haemolysis they do

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What is Haemolysis?

The break down of Red Blood cells

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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

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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

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What is an example of an Alpha haemolysis classified streptococci (viridans streptococci)?

Streptococcus pneumoniae

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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

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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

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What is being tested for in serological classification of bacteria?

Antibodies and antigens

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What is the most virulent streptococcus species?

Streptococcus pyogenes

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What are 3 species of Streptococcus in the Beta haemolytic group? (Full haemolysis)

Streptococcus pyogenes
Strep agalactiae
Strep dysgalactiae

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Where are Strep bovis, Strep mutans and strep salivarius commonly found?

What disease are they commonly associated with?

In the mouth

Endocarditis

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What lancefield group is streptococcus pyogenes?

Group A Beta Haemolytic streptococcus

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What are the 4 groups by which streptococci are classified in based on their physiological properties?

Pyogenic
Viridans
Enterococcal
Lactic

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What is meant by streptococci being Pyogenic?

Pus forming

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What is meant by streptococci being viridans?

Don’t fall into the other categories

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What is meant by streptococci being enterococcal?

Are bile tolerant
Penicillin resistant
Gut dwelling (faecal sources)

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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)