THE GENETIC-STRUCTURE OF ESCHERICHIA-COLI POPULATIONS IN FERAL HOUSE MICE

Escherichia coli was isolated from feral house mice (Mus domesticus) d uring the course of a mouse plague in the state of Victoria, Australia . Two farms were sampled over a period of 7 months and a total of 447 isolates were collected. The isolates were characterized using the tec hniques of randomly amplified polymorphic DNA and multi-locus enzyme e lectrophoresis. The mean genetic diversity of this E. coli population (H = 0.24) was found to be substantially lower than the diversity of a n E. coli population reported elsewhere for a single human host. Analy sis of the allozyme data revealed that there were significant differen ces in the relative abundance of genotypes between the two localities sampled and among sample dates. Overall, however, spatial and temporal effects accounted for less than 5% of the genotypic diversity. Allele frequencies and the relative abundance of the more common genotypes d id not differ between male and female hosts. The number of genotypes a nd genotype diversity increased as the age of the host increased, sugg esting that the mice are continuing to acquire new E. coli clones thro ughout their life. The frequency of some alleles changed with respect to host age, which indicates that clone acquisition may not be a rando m process. It is argued that the low level of genetic diversity observ ed in this population of E. coli reflects the boom and bust nature of mouse population density in this region of Australia.