Common origin of plasmid encoded alpha-hemolysin genes in Escherichia coliReportar como inadecuado

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BMC Microbiology

, 10:193

First Online: 19 July 2010Received: 30 March 2010Accepted: 19 July 2010


BackgroundAlpha α-hemolysin is a pore forming cytolysin and serves as a virulence factor in intestinal and extraintestinal pathogenic strains of E. coli. It was suggested that the genes encoding α-hemolysin hlyCABD which can be found on the chromosome and plasmid, were acquired through horizontal gene transfer. Plasmid-encoded α-hly is associated with certain enterotoxigenic ETEC, shigatoxigenic STEC and enteropathogenic E. coli EPEC strains. In uropathogenic E. coli UPEC, the α-hly genes are located on chromosomal pathogenicity islands. Previous work suggested that plasmid and chromosomally encoded α-hly may have evolved independently. This was explored in our study.

ResultsWe have investigated 11 α-hly plasmids from animal and human ETEC, STEC and EPEC strains. The size of α-hly plasmids ranges from 48-157 kb and eight plasmids are conjugative. The regulatory gene hlyR located upstream of the hlyCABD gene operon and an IS911 element located downstream of hlyD are conserved . Chromosomally-encoded α-hly operons lack the hlyR and IS911 elements. The DNA sequence of hlyC and hlyA divided the plasmid- and chromosomally-encoded α-hemolysins into two clusters. The plasmid-encoded α-hly genes could be further divided into three groups based on the insertion of IS1 and IS2 in the regulatory region upstream of the α-hly operon. Transcription of the hlyA gene was higher than the housekeeping icdA gene in all strains rq 4.8 to 143.2. Nucleotide sequence analysis of a chromosomally located α-hly determinant in Enterobacter cloacae strain indicates that it originates from an E. coli α-hly plasmid.

ConclusionOur data indicate that plasmids encoding α-hly in E. coli descended from a common ancestor independent of the plasmid size and the origin of the strains. Conjugative plasmids could contribute to the spread of the α-hly determinant to Enterobactercloacae. The presence of IS-elements flanking the plasmid-encoded α-hly indicate that they might be mobile genetic elements.

Electronic supplementary materialThe online version of this article doi:10.1186-1471-2180-10-193 contains supplementary material, which is available to authorized users.

Ylanna Burgos and Lothar Beutin contributed equally to this work.

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Autor: Ylanna Burgos - Lothar Beutin


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