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
What is the role of optochin in differentiating species of streptococcus?
Streptococcus is sensitive to optochin, unlike other streptococcus species in the alpha haemolytic group
What is the role of aesculin in differentiating species of streptococcus?
Derived from horsechesnut, when hydrolysed, it forms a dark brown ring. Enterococcus (both alpha haemolytic and gamma haemolytic strains) are aesculin positive
optochin sensitive, bile soluble streptococcus
Streptococcus pneumonia
optochin resistant, bile insoluble streptococcus
Streptococcus viridans
aesculin positive streptococcus
Enterococcus
Which gram positive bacteria are catalase positive?
Staph aureus and enterococcus
Group F streptococcae (name and disease)
Streptococcus anginosus, forms Liver abscesses
