Two hundred and twenty four strains of E. coli have been isolated from watercourses, and human, bovine, equine, and ovine faeces in a rural area of Queensland, Australia. These have been subjected to biochemical, serological, and genetic studies. Only the normal variation in biochemical properties were encountered.
Fifty percent of the recognized 0 antigens have been detected. Strains having the same serotype have been isolated from two contiguous sites only when these sites were very close geographically. The antigens 08 and 088 were predominant, but not overwhelmingly so.
Considerable serological diversity was also shown by strains isolated from members of a single dairy herd. Twenty four percent of known 0 antigens were detected. No individual 0 antigen was dominant.
Molecular studies have been performed. Base compositions of strains were determined by the UV absorbance - thermal denaturation profile. Hybridization studies were made using the spectral method. Results from this method and the hydroxyapatite method were found to be in excellent agreement.
Forty two Escherichia, Shigella, and alkalescens-dispar strains were studied by the hydroxyapatite method. Alkalescens-dispar strains could not be distinguished from E.coli strains. Shigella strains were distinguishable from E. coli but still show a high degree of genetic relatedness with E. coli.
Studies by the spectral method of fifteen wildtype strains of E. coli having the 08 or 088 antigen in common show that strains have nucleotide sequence similarities ranging from 79% to 101% with a reference strain. Molecular weights for these strains range from 2.30 X 109 to 2.72 X 109 daltons.
The molecular weights of strains with the O88 antigen were significantly larger than those with the 08 antigen. Their (G+C) contents were significantly lower. ....................................