Genetic structure of natural populations of Escherichia coli in wild hostson different continents

Current knowledge of genotypic and phenotypic diversity in the species Esch erichia coli is based almost entirely on strains recovered from humans or z oo animals. In this study, we analyzed a collection of 202 strains obtained from 81 mammalian species representing 39 families and 14 orders in Austra lia and the Americas, as well as several reference strains; we also include d a strain from a reptile and 10 from different families of birds collected in Mexico. The strains were characterized genotypically by multilocus enzy me electrophoresis (MLEE) and phenotypically by patterns of sugar utilizati on, antibiotic resistance, and plasmid profile. MLEE analysis yielded an es timated genetic diversity (H) of 0.682 for 11 loci. The observed genetic di versity in this sample is the greatest yet reported for E. coli, However, t his genetic diversity is not randomly distributed; geographic effects and h ost taxonomic group accounted for most of the genetic differentiation. The genetic relationship among the strains showed that they are more associated by origin and host order than is expected by chance. In a dendrogram, the ancestral cluster includes primarily strains from Australia and ECOR strain s from groups B and C, The most differentiated E. coli in our analysis are strains from Mexican carnivores and strains from humans, including those in the ECOR group A. The kinds and numbers of sugars utilized by the strains varied by host taxonomic group and country of origin. Strains isolated from bats were found to exploit the greatest range of sugars, while those from primates utilized the fe,vest, Toxins are more frequent in strains from rod ents from both continents than in any other taxonomic group. Strains from M exican wild mammals were, on average, as resistant to antibiotics as strain s from humans in cities. On average, the Australian strains presented a low er antibiotic resistance than the Mexican strains. However, strains recover ed from hosts in cities carried significantly more plasmids than did strain s isolated from wild mammals. Previous studies have shown that natural popu lations of E. coil harbor an extensive genetic diversity that is organized in a limited number of clones. However, knowledge of this worldwide bacteri um has been limited. Here, we suggest that the strains from a wide range of wild hosts from different regions of the world are organized in an ecotypi c structure where adaptation to the host plays an important role in the pop ulation structure.