I need help

Austin Reade rbs at hfx.andara.com
Fri Mar 24 21:41:03 EST 2000

Not being a clinical microbiologist I have not used blood agar for anything
other than foodborne Listeria id work so I just looked up its composition.
According to an American Society of Microbiology general micro text, it is
essentially tryptic soy agar (also known as trypticase soy agar and
soybean-casein digest agar) with the blood added to this base.

This isn't the sort of medium one would "normally" (there are always
exceptions I'm sure) use for environmental air surveys.  TSA without the
blood works well as someone noted already.  However, if you are looking
particularly for molds it would be better to use one of the numerous malt
extract agar formulations supplemented with antibiotics to suppress
bacteria, and rose bengal to prevent excessive spread of mold colonies.  We
also use a medium called DG18 which is a low water activity formulation
designed to select for xerophilic/xerotolerant molds which can often be
found in air samples and which don't compete well on high water activity

Of course if you are looking for airborne bacteria which can hydrolyse blood
cells then I guess blood agar makes a lot of sense.

I receive isolates of fungi from a pharmaceutical company for ID and these
are always on blood agar plates.  In order to identify to species the
isolates are always transferred to different media (MEA, CYA, etc) as their
morphology on blood is unusual (to me at least).

Austin Reade, PhD, RSM(CCM)
Reade BioSciences Inc                 phone (902)423-8369
1136 Cartaret Street                       fax (902)423-8313
Halifax, NS, B3H 3P3 Canada      email rbs at hfx.andara.com

David Lawton <dhlawton at clara.co.uk> wrote in message
news:0rSC4.3987$pQ5.90150 at nnrp3.clara.net...
> The brain's not working this evening - I do know what oligotrophic
> are, just not used to using the posh name.
> Yeast extract agar is recommended for water samples in the UK.
> For general air samples tryptone soya agar is often recommended, however
> our routine use we find no trouble using blood agar. Depends of cause why
> you're taking the air samples
> I still wouldn't call blood agar isn't a selective medium though.
> A medium that doesn't grow an organism as well as another one doesn't mean
> it's selective.
> To my mind a selective media is something where an ingredient is added to
> make it selective for a specific organism or group of organisms.
> If you added, for example, nalidixic acid and colistin then you have a
> selective medium.
> --
> David Lawton
> "lamb" <L.A.M.Buisman at cable.A2000.nl> wrote in message
> news:38DBC8FB.8DCCDF6A at cable.A2000.nl...
> > David Lawton wrote:
> >
> > > As I know nothing about oligtrophic bugs I can't comment,
> > > but being highly pedantic, for air samples wouldn't blood agar be
> considered
> > > a non - selective medium
> > > especially when compared with nutrient agar.
> >
> > For culturing watersamples nutrient agar or R2A is recommended. We find
> > 100-1000 fold increase in colony count compared to blood agar.
> > Air samples can show fantastic amounts of growth on bloodagar. Usually
> whole
> > lot gets overgrown with molds.
> >
> > Loes
> >
> >

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