Diagnosis of staph

lamb L.A.M.Buisman at chello.nl
Fri May 4 09:37:48 EST 2001

In endocarditis cases two or three cultures are not always enough. Low numbers, and it is
impossible to predict the moment that bacteria get into the bloodstream.
We do culture streptococci in endocarditis after longer then 7 days. But that could be
due to the rotten medium in the Vital bottles. And of course Propionibacterium, that we
used to underestimate in the good old days, when an antibiotic panel consisted of three
antibiotics. Gramnegatives: strepto-tetra-chlor.


Dilworth wrote:

> 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
> sets.
> 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
> growths.
> 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)
> Microbiology
> 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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