The genetic diversity of predominant Escherichia coli strains isolated from cattle fed various amounts of hay and grain

When the 16S rDNA of predominant Escherichia coli strains from cattle was d igested with HhaI and HaeIII, the strains could be subdivided into four ope rational taxonomic units. When genomic DNA was digested with XbaI, strains could be grouped into 24 pulsed-field gel electrophoresis genotypes (> 95% Dice similarity) and five clades (> 20% Dice similarity). Diet (hay versus grain) and gastrointestinal compartment (rumen versus colon) did not have a large impact on diversity. However, both analyses indicated that the cows (n = 2) had different E. coli populations. When all 22 colonic strains were inoculated into a maltose-limited chemostat, only a single genotype persis ted. Based on these results, the genetic diversity of E. coli in the cattle is very great and this bacterium can occupy different niches. (C) 2000 Fed eration of European Microbiological Societies. Published by Elsevier Scienc e B.V. All rights reserved.