Structure, function, and regulation of the plasmid-encoded hemolysin determinant of Escherichia coli.

Abstract

In 1967, H. William S. Smith first reported on the extrachromosomal nature of hemolysin formation in Escherichia coli (1). Shortly thereafter it was demonstrated that transmissible plasmids carrying the information for the hemolytic phenotype were present in E. coli strains which were isolated from among the fecal flora of various animals. Since then a large number of hemolytic (Hly) plasmids have been characterized (2–5), clearly establishing the early assumption of the extrachromosomal nature of this property. These Hly plasmids belong to various incompatibility groups although the incJ2 and FVI groups are predominant. Their molecular sizes range from 60 kilobases (kb) to over 160 kb (2–5). As we have shown by hybridization with cloned hly genes, even those Hly plasmids which are structurally rather unrelated share extensive homology in their hemolysin determinants, suggesting that the hemolysin determinant may represent a discrete genetic entity that can undergo recombination without extended sequence homology. Association of the hemolytic phenotype with other known extrachromosomal phenotypes of IS. coli such as antibiotic resistance, heavy metal resistance, enterotoxin production, or colonization factor antigens appears to be very rare and has tiever been observed in our laboratory. Recently it became apparent, however, that most hemolytic IS. coli strains isolated from humans, especially from patients suffering from urinary tract infections, bear the hemolysin determinant on the chromosome (6,7). It was shown in several animal model systems (8,9,20) that chromosomal hly-determinants contribute to virulence whereas little effect could be demonstrated for plasmid-encoded hly-determinants.KeywordsGalactosidase ActivityHeavy Metal ResistanceHemolysin GeneAmino Terminal FragmentTransmissible PlasmidThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.