Old World Aviaries

The truth about E. Coli

by Darrel K. Styles, DVM
The Schubot Center, Texas A&M University

How many of you have been frustrated at a veterinarian's diagnosis of E. coli in your birds? What is it? Where did it come from? Is it bad? Should it be treated? The answers to these perplexing questions are: a bacterium, the environment, maybe, and possibly. E. coli

To be more explicit, E. coli or Escherichia coli is a Gram-negative bacterium in the family Enterobacteriacae. These bacteria are normal inhabitants of the intestines of mammals, reptiles, and even some birds. In fact, without the presence of E. coli in our gut we would be overgrown by harmful bacteria and fungi, because E. coli protect us by populating our intestines and out-competing pathogens. Birds, especially psittacines, are less dependent on E. coli and rely on a more Gram-positive gut flora. However, our softbills, such as the passerines (finches, canaries, songbirds), columbiforms (pigeons and doves), galliforms (chicken-like birds), raptors (birds of prey), and ratites (emus and ostriches), have a high incidence of normal Gram-negative gut flora of many varieties including E. coli.

The distribution of E. coli in psittacines varies. It is infrequent in Amazons and macaws, sometimes found in greys, and common in cockatoos and Eclectus. In fact, E. coli can compose up to 30 percent of the gut flora of cockatoos. Cockatiels and budgies can carry a normal amount of E. coli but somewhat less than cockatoos.

Without question, E. coli can be a pathogen. But just because a bird is sick and E. coli is cultured does not necessarily implicate the bacterium as the inciting cause of illness.

E. coli is usually detected from a cloacal (vent) culture. It is best to take the culture directly from the cloaca rather than from a fecal sample. A fecal sample may be contaminated by another bird or animal, such as a rodent. Anytime E. coli is found in an internal culture other than the gastrointestinal tract, it should be considered pathogenic. E. coli can proliferate uncontrollably outside its normal home in the gut. However, some strains of E. coli can cause gastrointestinal disease. So, even in the gut, the bacterium may be pathogenic.

Once a positive culture for E. coli has been obtained, I use some loose guidelines on interpretation. First, if the bird is a juvenile of any species, I consider it significant but not always necessary to treat. If the bird is a cockatoo, the E. coli does not comprise more than about 30 percent of the gut flora, and the bird is performing normally on its feeding or weaning schedule, I usually do not treat. However, if the bird is an Amazon, I might treat depending on the health status of the bird. I would absolutely treat the E. coli if the bird is in any distress, such as that associated with weight loss or sick bird syndrome, regardless of species.

Second, if the bird is an adult, I again consider the species. If it is a cockatoo, Eclectus, or even a grey, the E. coli is not the major gut organism, and the bird is clinically normal, I do not treat. If the E. coli is isolated from an Amazon or macaw and the bird is doing well, I usually consider the E. coli as an indicator of contamination. Often, fruit will age or spoil, and flies can easily carry E. coli onto the fruit. The birds may ingest the fruit and establish an E. coli population in the gut. In this way the bacteria act as an indicator of hygiene. And, the E. coli can come from many sources including water. In a normal, healthy, adult Amazon or macaw, the bird typically will eliminate the bacteria when the source of contamination is removed.

To reiterate, most cockatoos normally carry some E. coli but it is unusual for an Amazon or macaw to do so. If the bird is a softbill, such as a finch, I use the same guidelines but bear in mind that Gram-negative flora are normal for most passerines.

Third, if a bird of any age or species is ill and I isolate E. coli, I treat the organism. Even if the E. coli is not the main cause of illness, it can further tax the bird's immune and nutrition resources.

Fourth, if E. coli is isolated from any source within the bird other than the GI tract, I consider it a pathogen and treat.

As we have seen, E. coli can act as a pathogen. Even seemingly innocuous strains of E. coli may revert or convert to pathogenic strains under appropriate circumstances. The recent events involving contaminated meat in fast-food restaurants are an excellent example. This leads us to conclude that E. coli may be a sheep, a wolf, or a wolf in sheep's clothing. However, at this stage of science, it is difficult to determine which strains of E. coli are pathogenic.

So, why not treat E. coli every time it is isolated from the gut? Try as you might, E. coli appears to be a normal inhabitant of a cockatoo's gut, and it will return shortly after treatment. Also, if the bird is healthy regardless of species, then E. coli may be an itinerate bacterium only and not well established, merely being an indicator of a source of contamination. Finally, indiscriminate antibacterial treatment is associated with other problems, such as fungal overgrowth, maldigestion, inherent difficulty in dosing the drug, and selecting for resistant strains of bacteria. In fact, the inappropriate use of the penicillin- and tetracycline-based antibiotics has selected for resistance to these drugs in many strains of avian E. coli.

If it is determined to be a problem, treatment for E. coli depends on the sensitivity of the bacterium to the appropriate antibiotic. E. coli may vary widely in its sensitivity pattern because many different strains exist. Treatment should always be under the supervision of a veterinarian. I have seen many examples of aviculturists having problems with resistant strains of bacteria due to indiscriminate use of antibiotics.

In summary, the isolation of E. coli from your bird does not necessarily indicate a disease state. This information needs to be properly interpreted by your avian veterinarian.


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