Dr David Patterson dlpaters at medeserv.com.au
Thu Jul 4 04:05:47 EST 1996

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 

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).

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