[Microbiology] Re: group A strept beta haemolysis

John Gentile yjgent at cox.net
Sun Dec 11 22:34:05 EST 2005

On 2005-12-10 22:35:22 -0500, "streptoA" <sindhulina at hotmail.com> said:

> Is there any way to find out if beta strept are b haemolytic other than
> by actually plating on sheep blood agar? We find it a little difficult
> to get sheep blood. So we manage with chocolate agar from other blood.
> Just a thought that it would make diagnosis so much easier if there was
> a easier way - like a biochemical test of some kind, or something.
> Anyone wih any ideas on this, please get back to me.

Without seeing the hemolysis and doing some kind of biochemical or disk 
test I doubt if you could accurately identify any kind of beta Strep. 
There are rapid Strep kits available that will take a swab of the 
throat and after an extraction identify the presence or absence of 
Strep antigens. Most of these kits are limited to Group A.

You mentioned other blood - I have used Columbia agar with Horse blood 
for many years and can tell you that hemolysis for Group A Strep is 
very good. However there are other organisms that can also appear 
hemolytic on HB that would be non hemolytic on sheep blood.

Are you also using a "Taxo A" disk? This is a test disk that can be 
placed on the culture and a zone of inhibition almost always indicates 
the presence of Group A Strep. We also confirm that zone with a latex 
agglutination kit.
John Gentile, MS M(ASCP)
Laboratory Information Manager
Providence, VAMC

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