The extent of genetic differentiation among 80 Escherichia coli isolates collected from turkeys with acute colisepticemia was assessed based on allelic variation at 20 enzyme-encoding loci detected by multilocus enzyme electrophoresis. Isolates were polymorphic at 117 loci and were classified into 32 multilocus genotypes, delineating clones, that differed on average at 36% of the loci. In the total sample, 29 (36%) of the isolates belonged to one of two closely related clones, differing only in a single electromorph, and 11 of these isolates were serogroup O78. Most isolates fell into one of 4 genetically distinct clusters of strains. Three of these clusters represent E. coli clone complexes that have been previously identified in avian diseases and a fourth cluster which is specific to coliseptecimia in turkeys. Most (73%) isolates produced aerobactin, whereas none produced hemolysins. Assays for detecting K1 capsules. including the use of polyclonal antisera, monoclonal antibodies, and K1-specific bacteriophages, gave variable resutls, but showed that overall 18% of the strains from colisepticemia were K1 encapsulated with most of the K1+ isolates found in one clone cluster. The results show that many cases of colisepticemia in turkey flocks are caused by a small number of pathogenic clones representing at least three distinct clone complexes.
Bibliographical noteFunding Information:
We thank Marie Wolfe, Michael Davis, and Anita Marcase for technical assistance, Dr. Alan Cross for providing the Kl-specific bacteriophages, and Dr. Lydia Crosa for providing strains and notes for the aerobactin bioassay. The research was supported in part by a Intercollege Competitive Grant from the College of Agriculture at The Pennsylvania State University and by grant AI 24566 from the National Institutes of Health.