Species-related differences in the incidence of gram-negative bacteria isolated from the cloaca of clinically normal psittacine birds.

Cloacal swabs from 506 clinically normal psittacine birds of 22 species were aerobically cultured for bacteria and yeasts. In 45 (9%) samples, no microbial organisms were recovered. Gram-positive bacteria were recovered from 474 (91%) samples. The incidences of gram-negative bacteria and yeasts were: Escherichia coli 157 (31%), Enterobacter sp. 21 (4%), Klebsiella sp. 3 (0.6%), Pseudomonas sp. 4 (0.8%), and yeasts 26 (5%). Differences were noted in the recovery rate of E. coli among the various species of birds cultured. Escherichia coli was recovered from 101 of 168 cockatoos (60%) of the genus Cacatua but from only 18% of 338 non-Cacatua species. As all birds were housed in the same facility under similar conditions, this difference in the incidence rate of E. coli cannot be explained on the basis of differences in husbandry or diet alone.