Hemolysis determinant common to Escherichia coli strains of different O serotypes and origins

Ten Escherichia coli hemolytic strains, isolated from various types of human infection and belonging to at least six different O serotypes were analyzed. In all these strains, our results are consistent with the hly genetic determinant being located on the bacterial chromosome. An hly-specific probe (plasmid pAN215) was used to detect homologous fragments in the strains analyzed by the Southern blotting technique. It was found that all 10 strains contain sequences that hybridize against the probe (greater than 85% homology) and thus contain hly genetic determinants very similar to those found on Hly plasmids. These results strongly suggest that there is a unique ubiquitous genetic determinant responsible for the hemolytic phenotype in E. coli.