Streptococci Flashcards
T/F: Streptococci are obligate anaerobes
FALSE - All strep are FACULATIVE ANAEROBES
All Streptococci are GM ___ cocci in ______ (arrangement).
Gm + in CHAINS
Streptococci are catalase ______
Negative
Group A Streptococci are also referred to as:
Streptococcus Pyogenes
Group A strep are classified as ____-Hemolytic, which means:
Beta hemolytic, means that they completely lyse red cells or produce a large clear zone on blood agar
the beta hemolytic streptococci are classified into groups A - O based on _________ _____________. *Bonus, which one is an ‘exception’.
They are classified based on complex carbs of the cell wall that act as antigen. Group D is an exception because it is NOT Beta hemolytic. Remember, Group A = Strep Pyogenes
Group A strep a further subdivided based on what feature?
They are divided based on immunological analysis of their M PROTEIN, of which there are 90+ serotypes.
M Protein appears on the surface of the bacteria.
Group A strep are transmitted by __________ and a (small/large) inoculum is required to infect
Respiratory droplets; a large inoculum is required. 5-10% of ppl carry strep pyogenes in nasopharynx
What are streptolysins and what do they do?
These are hemolytic enzymes that cause the beta hemolysis of Group A Strep
Streptolysin O:
an Oxygen-labile streptolysin that can induce anti-streptolysin-O antibody titers; these titers can be used in diagnosis
Streptolysin S:
A poorly antigenic streptolysin that is stable in oxygen
Streptokinase:
An enzyme that triggers blood proteolysis that DESTROYS FIBRIN CLOTS
What 2 factors contribute to Strep pyogenes ANTIPHAGOCYTIC activity?
- Hyaluronic acid capsule - without this they would not be pathogenic!
- M Proteins - more M protein = less phagocytosis. Also, Ab against an M protein = immunity to that strain.
What are SpeA SpeB and SpeC, and what two clinical presentations are they responsible for
These are proteases produced by Strep Pyogenes. They are also considered EXOTOXINs which can act as SUPERANTIGENS.
They cause:
1. The rash of Scarlet Fever
2. Streptococcal Toxic Shock Syndrome
5 invasive syndromes caused by strep pyogenes are:
- Puerperal fever - infected uterus at birth, now uncommon
- Acute pharyngitis/tonsilitis - fever, h/a, chills…treat soon to prevent rhematic fever
- Impetigo - superficial skin infection, infected via lesion
- Erysipelas - severe Cellulitis of dermis + underlying tissue
- Necrotizing Fasciitis - highly invasive strain produces a rapidly progressing destructive infection.
Rheumatic fever might occur _____ week(s) after an untreated strep infection; Acute glomerulonephritis might occur ___ week(s) later
Rheumatic fever - 2-3 weeks after strep throat
Glomerulo - 1 week after skin isolate infections
T/F: Penicillin resistance is never a problem with Streptococcus Pyogenes
TRUE! All Strep pyogenes are penicillin sensitive!!!
T/F: Group A strep are sensitive to bacitracin
TRUE. Strep pyogenes are Bacitracin sensitive!
T/F: Group B strep have Beta hemolysin
TRUE, but it is known to have a smaller zone of hemolysis than Group A
T/F: Group B strep are sensitive to Bacitracin
FALSE. Group B strep are resistant to bacitracin
What group of streptococci (A-O) does Strep. Agalactiae belong to ?
Group B
Group B strep can be part of the ______ or _______ normal flora
Vaginal or Colonic
Two patterns of Group B strep infection:
- Early onset - infection of bay @ birth from vaginal canal -> septicaemia, meningitis, pneumonia, death
- Late onset disease - infant to infant spread, has lower mortality
Why a re neonattes more susceptible to group B strep @ birth>
Lack of maternal Ab
