Diagnosis of staph

Dilworth bactitech at hortonsbay.com
Fri May 4 00:35:59 EST 2001

There's been a move in the US to go to a five day protocol over the last
ten years or so.  In the early 70's we held them for ten days (when we
were doing them all manually).  Then, we went to 7 days with the early
Bactecs (when they used to use the radioactive markers).  Then we went
to the five day protocol. 

There's also been a reduction from "x3" to "x2" in most cases, as some
statistics have found that the chances of finding a positive in the
third blood culture over the first two was infinitesimally small (did I
say that right?).  What I mean is that it isn't worth drawing the third
culture because you'll find what you need to know by only drawing two

I remember 25 years ago we got a significant gram negative out of some
bottles we were holding for fungus.  It grew in all three sets and was
sent to the state labs when we couldn't ID it (we tried for over a week,
I think).  It eventually went to the CDC in Atlanta for identification
and came back as DF-19, which probably has a name by now.  That's the
only thing significant I ever saw by holding blood cultures that long.  

Do you ever find anything significant in these long lived blood
cultures?  I can remember years ago ignoring Propionibacterium on ten
day old blood cultures (we did a final gram stain on them and saw them
there) as insignificant (per our Ph.D.) and signed them out as no

We're currently using a TREK blood culture system, that seems to be
growing those bugs well.  In the evenings all we do is put bottles on
and pull positives off, so I don't have experience in the day to day
operation of it, but everyone seems to like it.  We have three units and
they're full most of the time.  We're going to be getting a fourth
soon.  Sometimes we're putting 80-90 bottles on in one shift (45-50
sets) as we get BC's from four hospitals, so we're cranking them out in
huge numbers.  We don't have the time or personnel to do manual subbing,
either.  We can set the machine to hold the bottles longer if the
physician requests, and we routinely do this if the doc wants them held
for fungus.  It's just a matter of going into the software and manually
entering the number of days instead of taking the 5 day default.

I admit I'm partial to Bactec, as this is what I've used through the
years and really like it.  We had one of the little 50 bottle ones at my
last job (we didn't get a whole lot of them) that used the long neck
bottles.  It was very easy to work with and suited to a lab with low
volumes of blood cultures.  It sat on a table top and only took up about
3-4 feet of counter space, if that.

Judy Dilworth, M.T. (ASCP)

lamb wrote:
>> We culture blood for 7 days, except in case of endocarditis, then we culture for 3
> weeks.
> Not only for CNS, but also very low numbers of streptococci,  Propionibacterium and
> fastidious gramnegatives can be cultured that way. It is important then that many
> blood cultures are taken. Not only to rule out contamination.

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