Staph and Strep (Bacteria) Flashcards
How does Staph present in blood agar?
Staph is Beta Hemolytic gram + cocci.
When seeing “Beta Hemolytic gram + cocci” what are you thinking?
Think both Group A strep as well as staph aureus.
What are the 3 staph organisms of clinical relevance?
Staph Aureus, Staph Epidermitidis and Staph Saprophyticus.
How can we differentiate staph aureus from other bacteria and what does this feature allow staph to do?
Aureus is the only staph that is coagulase positive, allowing the plasma to clump up and clot. Also, staph can ferment mannitol and turn it yellow.
What is the easiest way to differentiate between Staph and Strep?
Catalase test, Staph is Catalase Positive, Strep is catalase neg. Catalase will cleave hydrogen peroxide, so if it is positive for catalase, when H2O2 is dropped into the colonies it will bubble.
How does staph saprophyticus and epidermitidis differ from aureus?
Aureus is beta hemolytic, the other 2 are gamma hemolytic (another way of saying there is no hemolysis). Further, they are both coagulase negative whereas aureus is coagulase positive.
How does one tell the difference between Staph Epidermidis and Saprophyticus (and also aureus)?
Aureus is coagulase + and Beta hemolytic, the other 2 are coag neg and gamma hemolytic. Between Saphro and Epi, Epi is sensitive to the ABX NOVOBIOCIN, whereas Saphro is NOT SENSITIVE.
What is the claim to fame of Staph Saprophyticus?
It can cause uncomplicated UTI’s in young recently sexually active women.
Which Staph organisms can cause UTI’s?
Usually it is saprophyticus in young sexually active women, however if there is cathoder involvement and an immunocomprimised patient, it can also be Staph Epidermidis which is an opportunistic infection.
What are the features of strep in terms of catalase, coagulase, and hemolysis tests?
Strep pyo (group A) and group B strep are all catalase, coagulase negative, and they are both beta hemolytic.
How does one differentiate group A from group B strep?
From ABX sensitivity just like between Staph saprophyticus and epidermidis. However the ABX in this case is BACITRACIN. Group A is SENSITIVE to Bacitracin, group B is RESISTANT to Bacitracin.
How does staph epi and saphro react with their distinguishing ABX? Strep group A and group B with their distinguishing ABX?
Epi is sensitive to Novobiocin, Saphro is resistant. Group A is sensitive to Bacitracin, Group B is resistant.
What should be the first organism we should think of upon hearing “alpha hemolytic gram + cocci?
Strep Pneumoniae. However, the viridens strep also fits this description.
If both S. pneumo and viridens are catalase and coagalase neg and both alpha hemolytic, how does one differentiate the two?
By sensitivity to the ABX Optochin, strep pneumo IS SENSITIVE, viridens is NOT SENSITIVE TO OPTOCHIN.
What 2 groups of strep are PYR +?
Group A strep and Enterococcus (Group D).
