Streptococci Flashcards
What type of bacteria is streptococci?
Gram positive cocci
Strep - chains
What is haemolysis classification?
Breakdown of RBC in agar
Alpha - partial haemolysis - green appearance
Beta - complete haemolysis - yellow appearance
Non-haemolytic
What classification of haemolysis is streptococcus pyrogenes?
Beta
Describe beta haemolysis
Complete haemolysis
Yellow apearance
Describe alpha haemolysis
Partial haemolysis
Green appearance
Example of alpha haemolysis bacteria
Streptococci pneumoniae
Example of beta haemolysis bacteria
Streptococcus pyogenes
What type of haemolytic strep have the lowest virulence?
Non-haemolytic
Describe streptococcus pyogenes
Lancefield group A beta haemolytic
Streptococcus - gram positive cocci chains
What can streptococcus pyogenes cause?
Bacterial pharyngitis
Tonsillitis
Scarlett fever
Rheumatic fever
Cellulitis
TSS
Impetigo
Treatment of streptococcus pyogenes
Penicillin V
Clarithromycin if resistance to penicillin
Virulence factors of streptococci pyogenes
- Hyaluronic acid capsule - inhibit phagocytosis
- M protein - disrupts respiratory burst of neutrophils
- Streptokinase - breaks down blood clots
- DNAases - degrade DNA
- pyrogenic exotoxin - cleave igG
Complications of streptococcal pharyngitis
Scarlet fever
Suppurative (pus) complications
Acute rheumatic fever
Acute post-streptocccal glomerulonephritis
What is scarlet fever due to?
Infection of streptococcal pyrogenic exotoxin strain of streptoccal pyogenes
Signs + symptoms of scarlet fever
High fever
Sepsis
Rash
Arthritis
Jaundice
Suppurative complications of streptococcal pharyngitis
Forming/discharging pus
- peritonsillar cellulits/abscess
- retropharyngeal abscess
- mastoiditis
- sinusitis
- otitis media
- meningitis
- brain abscess
What is peritonsillar abscess?
What is it a complication of?
Area of pus filled tissue next to tonsil
Streptococcal pharyngitis
What is a retropharngeal abscess?
What is it a complication of?
Collection of pus deep in back of throat
Streptococcal pharyngitis
What is otitis media?
What is it a complication of?
Middle ear infection
Streptococcal pharyngitis
What skin infections can streptocccus pyrogenes cause?
Impetigo
Cellulitis
Necrotising fasciitis
Erysipelas
What is impetigo?
What is it caused by?
Skin infection forming pustules and yellow crusty sores
Glomerunephritis from streptococcus pyogenes
When is impetigo normally seen?
Childhood
2-5 years
What is acute rheumatic fever?
Inflammation of heart, joints, CNS…
What is erysipelas?
What is it caused by?
Dermis infection with lymphatic involvement
Raised areas of erythema
Streptococcus pyogenes
Presentation of erysipelas
Raised areas of erthyema on face + lower limbs
What type of erysipelas frequently follows pharyngits?
Facial lesion
What is lower limb erysipelas usually secondary to?
Invasion of skin via trauma, skin disease or local fungal infection
What is necrotising fasciitis?
Infection of deeper subcutaneous tissue + fascia
Rapid extensive necrosis
Outline toxic shock syndrome
Caused by entirely of strep pyogenes into bloodstream after deep tissue infection > bacteriaemia > vascular collapse > organ failure
What is the severity of TTS determined by?
Endotoxin released by bacteria
Triggering T cells to give non-specific systemic inflammatory response > vascular collapse
Treatment of necrotising fasciitis
IV antibiotics - penicillin
Antibody transfusion
What organism is associated with TSS?
MRSA
Strep pyogenes
What organism of Coagulase positive?
Staphylococcus aureus
What does it mean if a bacteria is Coagulase positive?
- Staphylococcus auerus converts fibrinogen > fibrin
- Causes clot formation
