The genetic structure of enteric bacteria from Australian mammals

A total of 246 isolates representing five species of the family Enterobacteriaceae, taken from a variety of Australian mammal species, were characterized using multi-locus enzyme electrophoresis. Genome diversity estimates varied significantly among species, with the Klebsiella pneumoniae sample exhibiting the lowest diversity and the Citrobacter freundii sample the highest. Multi-locus linkage disequilibrium estimates revealed that alleles were non-randomly associated in all five species samples, but the magnitude of the 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 population structure explained the observed genetic variation in a species. Two population levels were defined: the taxonomic family of the host from which the isolate was collected and the geographical locality where the host was collected. The amount of explained variation varied from 0% for K. oxytoca to 22% for K. pneumoniae. Host locality explained a significant amount of the genetic variation in the C. freundii (12 %), E. coli (5 %), Hafnia alvei (17 %) and K, pneumoniae (22 %) samples. Host family explained a significant fraction of the variation in E. coli (6 %) H. alvei (7 %) and K. pneumoniae (20 %). Estimates of effective population size for all five species, based on the probability that two randomly chosen isolates will be identical, failed to reveal any relationship between the effective population size and the genetic diversity of a species.