Mobile Elements Acquired DNA and Antimicrobial Resistance

A total of 47 insertion sequences are present in E.faecalis V583; only 38 of these are considered functional, and of these 26 are present in the chromosome, 10 of them belonging to the IS256 family. There are two main clusters of IS elements, one of which is associated with the pathogenicity island (G+C content 32.2%), while the other is associated with a separate region of atypical nucleotide composition (G+C content 31%). The disparate G+C content of these regions combined with the presence of mobile DNA elements suggests origination by horizontal gene transfer. From EF1855 to EF1874, six either full or partial IS elements are present. Also present in this region are panB, panC, and panD, (EF1860-EF1858), which encode three of the four steps of the pantothenate biosynthesis pathway. Homology comparisons show a greater relationship of these enzymes to counterparts in clostridia, rather than other lactic acid bacteria. There are three homologues present in the rest of the genome of the remaining enzyme in this pathway, one of which is encoded on the pathogenicity island. Also in this atypical nucleotide region are homologues of the Streptococcus pneumoniae VncRS two-component signal transduction system (EF1863-EF1864) and the Vex secretion ABC transporter (EF1867-EF1869). Previously mutations in the VncRS locus in S. pneumoniae had been linked to vancomycin tolerance, and it was hypothesized that VncR functioned as a repressor of autolytic functions [14]; however, a second study suggested that VncRS is involved in the regulation of a proximal ABC transporter, Vex [15]. More recent work has cast further doubt on the role of the VncRS two-component system, and its function is at present undetermined [16]. Homologues of the Vex transport system are also present in both E. faecium and Streptococcus agalactiae, and in both of these organisms the genes have greater than 88%

1) All genes referred to in this chapter as being present on the pathogenicity island are annotated according to the gene locus described in E. faecalis MMH594, which contains the full length island [9] (GenBank accession number AF454824).

identity at the nucleotide level to E.faecalis. A homologue of the VncS sensor kinase is present in both E.faecalis and S. agalactiae, again sharing greater than 88% identity at the nucleotide level, but is absent from E.faecium. This degree of similarity suggests a common source for these genes in these three organisms (Table 7.1).

Table 7.1 Mobile and/or exogenously acquired DNA in the E.faecalis V583 genome.

Locus

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