Gram Stains

Copyright © 1991 by Dave McCluggage, DVM and NCS
The Bird Hospital
Boulder, CO
All Rights Reserved

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A gram stain is a rough (an I do mean very rough) estimate of the bacterial flora on the place the swab was taken (i.e., mouth, crop, feces, trachea, choanal slit, etc.). Gram stains are inexpensive and rapid, but they are not very helpful in the majority of cases. A culture is a more precise estimate of what bacteria are present. Cultures are always good, but I think we need to look at cost effectiveness here. Cultures are somewhat expensive and often tell us little more than we know to start with. It is my belief that a culture and sensitivity is often not the best place to start with in many cases. The test is far overused for its cost effectiveness. Cultures have these problems:

1. The true site of the infection is rarely cultured, and instead we culture feces and hope to find the bacteria that is affecting (for e.g.) the liver.
2. Negative cultures don't say things are all ok, just that we didn't grow up anything that time (ie. we often get a false sense of security).
3. If we get a "bad" bacteria, we have no knowledge that that bacteria is actually the bad guy - he could have just been passing through the body or even normal flora for that individual.
4. Many disease causing organisms are not culturable, this includes anaerobic bacteria, and viruses - in fact, it is likely that the majority of infections are being caused by organisms that can not be cultured. So we are relying on a test that going by the odds should not give us the true answer.
5. The presence of a gram negative bacteria does not mean that the bird is sick; blood tests and x-rays are needed for that.

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