Streptococci Flashcards
What sort of bacteria are strep and how do they normally appear
Gram positive cocci
Found in chains which can be short or long
What are the three classifications of strep and how do they differ
Alpha haemolysis - partial haemolysis
Beta haemolysis - full haemolysis
Non-haemolytic (gamma) - no haemolysis occurs
How do streptococcus pneumoniae appear and how is this relevent to the virulence of the bacteria
Have a wet appearance due to capsule around the bcateria and are alpha haemolysis strep
Capsule causes neutrophils to choke when they try to phagocytise bacteria - increase virulence
What sort of bacteria is strep pyogenes
Beta haemolysis strep
It is also a pus forming streph -> causes abscess formation
Is a lancefield group A bacteria
What is the Lancefield classification of strep
Classification of beta-haemolytic strep based on the cell wall antigens
What is strep pharyngitis, what does it cause and why is it beneficial to leave it untreated
A step pyogenes bacteria spread by droplets
Causes tonsil inflammation and bacterial sore throat
Untreated patients develop M protein specific antibody, protecting patients in the future
Describe scarlet fever
Complication of strep pharyngitis - specific extoxin strain
Caused by local or haematogenous spread
Characterised by high fever, spesis, arthritis, jaundice
What are some suppurative complications of strep pharyngitis
Peritonsillar cellulitis/abscess
Retropharyngeal abscess
Mastoiditis
Sinusitis
Otitis media
Meningitis
Brain abscess
Describe acute rheumatic fever
Immunological complication of strep pharyngitis
There is inflammation of heart, joints or CNS
Cannot treat with antibiotics due to it being immunological, so treatment is to reduce the response
If it affects the heart it can cause turbulent heart flow which can result in endocarditis
Describe acute post-streptococcal glomerulonephritis
An autoimmune complication from strep pharyngitis
It is acute inflammation of the renal glomerulus
Caused by antigen-antibody complexes in the glomerulus, which are retained in the glomerulus resulting in inflammation
Describe impetigo
Childhood infection
Caused by skin colonisation by strep pyogenes, followed by intradermal innoculation
Commonly causes glomerulonephritis
Describe erysipelas
Dermis infection with lymphatic involvement by strep pyogenes
Affect face and lower limbs
Face lesions usually preceded by pharyngitis
Lower limb infection usually secondary to invasion of skin via trauma, skin disease or fungal infection
Describe cellulitis
Skin and subcutaneous tissue infection by strep pyogenes or staph aureus
Usually only affects one leg
Caused by trauma to the skin or due to injury by dermatophytes
Impaired lymphatic drainage and illicit injecting drug use are risk factors
Describe necrotising fasciitis
Infection of deeper subcutaneous tissue and fascia - by strep pyogenes or due to combination of bacteria
There is rapid and extensive necrosis with the area becoming mush
Usually secondary to skin break and symptoms are severe pain, discolouration, bruising, blisters
Give antibiotics and antibodies (IV Ig molecules), can result in surgery and possible amputation
Exotoxins are secreted by the bacteria, causing the necrosis
Describe strep toxic shock syndrome
Caused by entry of group A strep into deeper tissues and bloodstream
Strep release exotoxins which stimulate T-cells producing a massive systemic inflammatory response
Signs - deep tissue infection by strep pyogenes, bacteraemia, vascular collapse, organ failure
