Determination of the clonal structure of avian Escherichia coli strains by isoenzyme and ribotyping analysis

Forty-nine avian Escherichia coli strains isolated from different outbreak cases of septicemia (24), swollen head syndrome (14) and omphalitis (11), and 20 strains isolated from poultry with no signs of the mentioned illnesses, for a total of 69 strains, were typed by isoenzyme profile and ribotyping analysis by restriction fragment length polymorphism (RFLP). Isoenzyme analysis discriminated better among strains (0-0.07 degree of genetic dissimilarity) than ribotyping analysis (0- 0.02 degree of genetic dissimilarity). The enzyme profiles of the E. coli isolates allowed the identification of 33 clones that were organized into six main clusters (A-F). Cluster A comprised 87% of the pathogenic strains and had no commensal strains, while commensal strains were assigned to clusters B-F. The ribotyping analysis resulted in a more heterogenous distribution of strains but most of those that cause the same type of infection were kept close together. Taken as a whole, these results demonstrate that pathogenic clones are more similar to one another when compared with commensal strains and suggest a correlation between the genetic background and the pathogenic characteristics of avian pathogenic E. coli strains.502636