Need Help With Experiment
bg005d at uhura.cc.rochester.edu
Tue Apr 23 16:57:33 EST 1996
In <Pine.SUN.3.93.960423100223.4925B-100000 at eskimo.com> KM <mirza at eskimo.com> writes:
>On Wed, 17 Apr 1996, David R. Boone wrote:
>> Terry J. Peek wrote:
>> > I am trying to differentiate between Serratia marcescens and a gram pos. cocci
>> > that I suspect is Staph epidermidis or S. aureus. I've placed the culture on
>> > 10% NaCl agar. I'll check the results later this morning. What is the best way
>> > to seperate these organisms using the resources of a small college lab? Is my
>> > first step in the right direction? Any suggestions would be appreciated.
>> > Thanks. Terry
>> There are lots of differences between Serratia marcescens and the two cocci you
>> mentioned. If you know an organism is one of these three species, it is
>> relatively easy to distinguish Serratia marcescens. Many strains of Serratia
>> marcescens when grown as surface colonies produce a red pigment (in contrast,
>> Staphylococcus epidermidis is usually light colored and Staphylococcus aureus is
>> usually dark yellow or golden (the species epithet refers to gold). The color of
>> colonies is really not very taxonomically significant (in fact, <90% of Serratia
>> marcescens strains produce the red pigment), but if you want a quick and dirty
>> discriminator, this may be it. From a taxonomic standpoint, probably the most
>> reliable differentiating characteristics are morphological: Serratia are
>> gram-negative rods, whereas staphylococci are gram-positive cocci, often arranged
>> in grape-like clusters.
>> David R. Boone
>> Professor of Environmental Microbiology
>> Oregon Graduate Institute, Portland
>> boone at ese.ogi.edu
>I am puzzled at the 90% of S.marcescens and production of pigment.
>Prof.Boone where is that reference, my understanding of pig production was
>a lot smaller than 90%.
>May be in the envoirnment isolates are differeent, I am a clinical man,
>my observation of clinical isolates is a lot different.
>Hope to hear ur reply.
The most selective way to discriminate would be to plate on Maconkey agar.
The crystal violet is selective for gram-negative organisms. If it is indeed
S. marscenses, the culture will grow. If they are Gram-positive, no growth
will be seen on the plates. Hektoen-enteric plates serve the same function.
Brent Gilbert (bg005d at uhura.cc.rochester.edu)
"If you choose not to decide, you still have made a choice" -Neil Peart
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