Could anyone provide some advice for a novice microbiologist about a
Staphylococcal isolate? The blood cultures were collected into a FAN
bottle (The patient had recently received antibiotics). BacTiAlert
signalled positive six days after the blood culture was collected. Gram
positive cocci were seen. Slide coagulase was positive. A
thermonuclease was set up directly from the blood culture bottle. It was
negative at 4 hours, and remained negative. Positive and negative
controls worked well. A tube coagulase was set up, and was positive, so
we were happy to call this S. aureus.
Interestingly the thermonuclease was positive from colonies growing in
TSB.
My question is why was the direct thermonuclease negative? Also why did
the BactiAlert take six days to signal positive? (I presume the answer to
the second question is that the patient was on antibiotics).
