These findings may indicate that plasmid encoded α-hemolysins have evolved from one source and separately from the chromosomal hemolysin operons. In order find more to explore this possibility we compared

plasmid α-hly from unrelated E. coli strains of human, mouse, canine and porcine origin for similarities the regulatory and structural genes and their click here adjacent sequences. Plasmid encoded α-hly determinants were found similar to each other in their genes (hlyR, hlyC, hlyA and hlyD) as well as in the adjacent sequences upstream and downstream of the α-hly-operon. Plasmid encoded hlyC and hlyA genes showed typical alterations in the nucleotide and in the amino acid sequence compared to their chromosomally encoded homologues. Moreover, chromosomally encoded α-hly genes were found different for the regions encompassing the α-hly-operon. The finding that chromosomal hlyC and hlyA genes clustered separately and showed greater sequence diversity compared to the plasmid homologues suggests that plasmid α-hly-genes have emerged more recently in E. coli and thus accumulated fewer changes compared SCH 900776 chemical structure to the chromosomal α-hly genes. It was previously suggested that α-hly genes were acquired by strains of E. coli by horizontal gene transfer [25, 27, 30]. This hypothesis is supported by the location of chromosomally

encoded hemolysin genes on pathogenicity islands [13, 14, 16, 17] and the flanking of plasmid encoded α-hly genes by transposable elements [20, 21]. A truncated IS911 element located downstream of the hlyD gene was found Flucloronide in all α-hly plasmids investigated in our study indicating that the plasmid encoded α-hly determinants may have descended from a common progenitor [31]. We do not know much about the genetic similarity between the α-hly plasmids investigated in this study, except that they show differences in size (48-157 kb) and conjugation ability. Further investigation of plasmid backbone sequences could reveal if they have descended from a common progenitor. At present, we

cannot exclude that the α-hly determinant was transposed independently to different plasmids in E. coli. Interestingly, plasmid pEO14 differed largely from all other α-hly-plasmids investigated in this study. The nucleotide sequence analysis of its α-hly genes and the adjacent sequences revealed close similarity to chromosomal α-hly genes. Because the α-hly genes present on plasmid pEO14 shows all features of chromosomal α-hly operon it is likely that it was generated by recombination between a plasmid and chromosomal α-hly loci in E. coli. A similar event might have been involved in generation of a truncated α-hly segment in plasmid Vir68 that has been analyzed for its complete nucleotide sequence [GenBank CP001162]. The chromosomally located α-hly genes of the E. cloacae strain KK6-16 showed similarities to E. coli plasmid encoded α-hly determinants.