Preliminary Investigation...Congo Red Binding in Escherichia Coli

Infections by gram negative bacteria are among the most common problems encountered in psittacine birds. In particular, the bacteria Escherichia coli is responsible for considerable disease. However, apparently nonpathogenic strains of E. coli can also be isolated from the cloaca of healthy psittacine birds and there is controversy as to whether it is necessary to treat all birds that carry E. coli in their gastrointestinal tract. Currently, there is no readily available laboratory technique for assessing the disease causing potential (pathogenicity) of various trains of E. coli. The purpose of this project was to investigate the potential use of Congo Red dye binding as a screening test for determining the pathogenicity of E. coli isolated from the cloaca of psittacine birds. Congo Red is a dye that can be added to bacterial growth media. In the poultry industry, some studies have indicated that only pathogenic E. coli will bind this dye, resulting in a visible change in the color and appearance of the bacterial colony. Positive colonies are red and have a wrinkled surface while negative colonies are pink with a smooth surface. In poultry, only Congo Red positive E. coli will cause disease when inoculated into chicks; Congo Red negative colonies will not. Congo Red testing has been primarily used to identify potentially pathogenic strains of E. coli in hatcheries and brooders where aerosolized bacteria can be a significant problem for poultry chicks raised in concentrated environments. In our study, we investigated the incidence of Congo Red binding in E. coli isolated from the cloaca of psittacine birds and correlated the results with the subjective health status of the birds (see Table 1). Escherichia coli was isolated from 120/435 (27.6%) of the birds: 85.8% were Congo Red negative and 14. 2 % were Congo Red positive. Congo Red positive colonies were cultured only from clinically ill birds, however, Congo Red negative E. coli was isolated from both healthy and ill birds. It is possible that some ill birds harboring Congo Red negative E. coli were sick due to causes other than the E. coli. To absolutely determine if the Congo Red positive and negative E. coli strains were truly pathogenic and nonpathogenic would require that we inoculate each isolate into young birds and look for signs of disease. This study was not done due to the obvious ethical concerns of inducing illness in psittacine birds. These results suggest that there is some correlation between the isolation of Congo Red positive colonies and signs of clinical illness in psittacine birds, however, this finding was not consistent and this test would not be useful for screening cloaca cultures from psittacine birds. This study demonstrates that tests developed....