Streptococcae Flashcards
Role of the catalase test
Streptococcae are catalase negative (unlike enterococcus) - they can’t convert hydrogen peroxide to water and oxygen
Role of blood agar test
Can be subcategorised into beta (complete haemolysis), alpha (partial haemolysis -green) and gamma (non-haemolytic)
Main types of beta haemolytic streptococae
Lancefield groups A (pyogenes) and B (agalactia)
What is the purpose of the Lancefield grouping?
To differentiate between beta haemolytic streptococcae i.e. group A and group B, based on their ability to agglutinate
What is another name for group A strep?
Streptococcus pyogenes
What is another name for group B strep?
Streptoccus agalactia
What is another name for streptococcus agalactia?
Group B strep
What is another name for streptoccus pyogenes?
Group A strep
What is the difference between type 1 and 2 necrotising fasciitis?
Type 1 = polymicrobial (streptococcus, staphylococcus, enterobacteriae
Type 2 = caused by group A strep (streptococcus pyogenes)
What causes toxic shock syndrome?
Streptococcus pyogenes (group A strep) - predominately caused by the exotoxins A and C which cause endothelial damage and fever
What causes scarlet fever?
Group A streptococcus (streptoccus pyogenes)
Normal habitat of group A strep
Oropharynx
Normal habitat of group B strep
GI tract, female genital tract (30% of women are carriers)
What percentage of women are GBS carriers?
20-40% (but carriage is intermittent), occurs more frequently in black African ethnic groups
Which streptococci fall into the alpha haemolytic group?
Partial haemolysis = Enterococcus, strep pneumonia, strep viridans
How is “early onset” neonatal GBS infection defined?
Within 7 days of delivery
Risk of recurrent GBS carriage for a mother who has previously GBS detected in another pregnancy
50% will experience recurrence
When should GBS treatment be given during pregnancy?
If the patient has a GBS positive UTI. Not if they have a positive vaginal or rectal swab.
Recommended management for a patient who is known GBS positive who ruptures their membranes at term
Give intrapartum antibiotic prophylaxis and induce labour
What should be given to a patient if she requires intrapartum antibiotic prophylaxis but is allergic to penicillin?
If mild allergy - give clindamycin or a cephalosporin
If severe allergy- give vancomycin
Rate of neonatal GBS disease
5 in 10,000 births
How does streptococcus pneumoniae appear on blood agar?
Partial haemolysis (alpha haemolytic group)-green ring around the colony
How does streptococcus pneumoniae appear under the microscope?
diplococcus- “draughtsman shaped colonies”
Which streptococcus species is described as forming “draughtsman shaped” colonies
Streptoccocus pneumoniae
