The genetic structure of enteric bacteria from Australian mammals

A total of 246 isolates representing five species of the family Enterobacte riaceae, taken from a variety of Australian mammal species, were characteri zed using multi-locus enzyme electrophoresis. Genome diversity estimates va ried significantly among species, with the Klebsiella pneumoniae sample exh ibiting the lowest diversity and the Citrobacter freundii sample the highes t. Multi-locus linkage disequilibrium estimates revealed that alleles were non-randomly associated in all five species samples, but the magnitude of t he estimates differed significantly among species. Escherichia coli had the lowest linkage disequilibrium estimate and Klebisella oxytoca the largest. Molecular analyis of variance was used to determine the extent to which po pulation structure explained the observed genetic variation in a species. T wo population levels were defined: the taxonomic family of the host from wh ich the isolate was collected and the geographical locality where the host was collected. The amount of explained variation varied from 0% for K. oxyt oca to 22% for K. pneumoniae. Host locality explained a significant amount of the genetic variation in the C. freundii (12 %), E. coli (5 %), Hafnia a lvei (17 %) and K, pneumoniae (22 %) samples. Host family explained a signi ficant fraction of the variation in E. coli (6 %) H. alvei (7 %) and K. pne umoniae (20 %). Estimates of effective population size for all five species , based on the probability that two randomly chosen isolates will be identi cal, failed to reveal any relationship between the effective population siz e and the genetic diversity of a species.