Group A Beta Strep Incubation Time

Michelle halcyon at horizon.hit.net
Fri Oct 3 19:35:59 EST 1997


Carles Alonso i Tarrés wrote:
> 
> On 19 Sep 97 02:51:34 GMT, "Lynn Gerber" <lgerbe29 at cybertrails.com>
> wrote:
> 
> >There is a bit of controversy at our laboratory as to the length of time a
> >culture for group A beta strep should be incubated.  We are using a
> >selective strep media which inhibits much of the normal flora.  The
> >controversy is whether the negative plates should be kept for more than 24
> >hours.  In Bailey and Scott's Diagnostic Microbiology, 9th edition, it
> >states that overnight incubation can be used for presumptive
> >identification.  No references are given.  Anyone out there have any
> >opinions, references, etc. regarding this topic?
> >Lynn Gerber
> 
>Hello Lynn,
 In our lab we use just plain blood agar for the detection of Group A
Strep  (well for the detection of everything actually).  We usually keep
a culture based on the source.  From a throat we keep a culture 18-24
hours, but I think that is because the normal flora will overgrow the
plate if kept longer and then Strep would be hard to detect unless it is
in a large quantity.  A wound culture--which can also grow Strep--we
keep 48 hours.  It would seem that if overgrowth of normal flora is not
a concern, then 48 hours would be best.
Michelle



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