Friday, March 28, 2003

Hot Shit from Science
Enterococci, such as E. faecalis, are also prominent members of the GI tract microbial consortium. However, enterococci have gained notoriety because they can cause infections, primarily among hospitalized patients, that are extremely difficult to treat owing to antibiotic resistance. Strains of enterococci from GI tracts of healthy humans rarely carry genetic elements conferring additional antibiotic resistance or overt virulence. The most problematic enterococcal isolates from infected patients, namely those harboring genes for resistance to multiple antibiotics, appear to constitute a rogue subgroup of the species that, in addition to antibiotic resistance, has also acquired a number of genes conferring infectivity and virulence. Paulsen et al. report the genome sequence of such an infection-derived isolate of E. faecalis, strain V583, which caused the first vancomycin-resistant enterococcal infection reported in the United States.

As a multiple antibiotic-resistant clinical isolate, this strain was found to be replete with mobile DNA elements, many of implied foreign origin. These mobile DNA elements include a pathogenicity island--a large mobile genetic element consisting of a number of virulence-associated genes--a transposon carrying the complex of genes that mediate vancomycin resistance, three plasmids conferring resistance to other antibiotics, and a host of insertion sequences. These mobile elements constitute over a quarter of the genome of this strain. The occurrence of the pathogenicity island on the side of the chromosome opposite that of the vancomycin resistance transposon, as well as its occurrence in strains that predate the acquisition of vancomycin resistance, strongly suggest independent selection for antibiotic resistance and virulence traits.

[ref.s removed for clarity; cites: perspective: "The Thin Line Between Gut Commensal and Pathogen," Michael S. Gilmore and Joseph J. Ferretti, Science Mar 28 2003; report: "Role of Mobile DNA in the Evolution of Vancomycin-Resistant Enterococcus faecalis," I. T. Paulsen, et al., Science Mar 28 2003: 2071-2074.]

In other microbial news, SARS hits Canada and Connecticut as panic spreads in HK.


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