Internal Medicine_Infectious Diseases_2 Flashcards
Bacteria_Non-Coag Staph
What type of bacteria are Staphylococcus epidermidis and Staphylococcus saprophyticus?
Both are gram-positive cocci.
What test distinguishes Staphylococcus epidermidis and S. saprophyticus from Staphylococcus aureus?
They are coagulase-negative, whereas S. aureus is coagulase-positive.
When performing a coagulase test, the presence or absence of coagulase can be observed by adding a bacterial culture to a test tube containing coagulase-reacting plasma. If the bacteria are coagulase negative, a visible clot will not form in the plasma. Both Staphylococcus epidermidis and Staphylococcus saprophyticus are coagulase-negative, differentiating them from Staphylococcus aureus, which is coagulase-positive.
What enzyme do S. epidermidis and S. saprophyticus produce to convert hydrogen peroxide into water and oxygen that helps distinguish staphylococcus from streptococcus ?
Catalase.
Both Staphylococcus epidermidis and Staphylococcus saprophyticus are catalase-positive. The production of this enzyme helps differentiate staphylococci from streptococci, which are catalase-negative.
What enzyme produced by S. epidermidis and S. saprophyticus hydrolyzes urea into carbon dioxide and ammonia?
Urease.
Where is S. epidermidis commonly found in the body?
It is part of the normal flora of the skin and mucous membranes.
Why is S. epidermidis a common contaminant of blood cultures?
Because it is part of the skin flora.
What medical devices is S. epidermidis associated with due to biofilm production?
- Prosthetic joints (causing prosthetic joint infections).
- Catheters (causing catheter-associated infections).
- Prosthetic heart valves (causing prosthetic valve endocarditis).
What substance allows S. epidermidis to adhere to prosthetic devices and evade the immune system?
Biofilms (extracellular polysaccharide matrix).
How can S. epidermidis be distinguished from S. saprophyticus in the lab?
S. epidermidis is novobiocin-sensitive, whereas S. saprophyticus is resistant.
What is the drug of choice for treating S. epidermidis infections?
Vancomycin (due to frequent resistance to nafcillin and methicillin), especially for endocarditis.
What infections are commonly caused by S. saprophyticus?
- Uncomplicated urinary tract infections in young, sexually active females (honeymoon cystitis).
- Acute bacterial prostatitis.
What is S. saprophyticus resistant to that helps distinguish it from S. epidermidis?
Novobiocin.
Novobiocin susceptibility can be used to differentiate between the two.
Staphylococcus epidermidis is sensitive to novobiocin, whereas Staphylococcus saprophyticus is resistant.
