Transport of daptomycin resistance genes between animals and humans as a possible mechanism for development of de novo daptomycin resistance in enterococci.

Transport of daptomycin resistance genes between animals and humans as a possible mechanism for development of de novo daptomycin resistance in enterococci To the Editor Zoonoses that can be transmitted from livestock to humans have increasingly been reported [1]. Geenen et al. determined the prevalence of livestock-associated methicillin-resistant Staphylococcus aureus (MRSA) on Dutch broiler farms and in people living and/or working on these farms and concluded that people in contact with live broilers are at risk for MRSA carriage worldwide [2]. Another emerging infection that may be associated with livestock is dap-tomycin non-susceptible Enterococcus (DNSE) [3]. Arias et al. described mutations that set the genetic basis for in vivo daptomycin resistance in enterococci that were exposed to daptomycin [4]. These mutations may have originated from recombination between adjacent repetitive nucleotide sequences [4]. However, little is known about the mechanisms of development of daptomycin resistance in patients without prior exposure to daptomycin (de novo DNSE) [5]. The genes encoding antibiotic resistance may derive from commensal bacteria that constitute a reservoir of resistance genes for pathogenic bacteria [6]. The level of resistance encountered in commensal bacteria may be a good indicator for selection pressure by antibiotic use and for resistance problems to be expected in pathogens [6]. Antibiotic use for animal growth promotion may hasten the appearance of antibiotic-resistant bacteria that, like zoonotic bacteria, might contaminate meat products and reach the intestinal tract of humans [6, 7]. Antimicrobial usage in animals has a major role in the selection of bacterial resistance and the transport of resistance genes via the food chain to humans [6, 7]. These resistant bacteria can transfer their antibiotic resistance genes, located on mobile genetic elements, to other bacteria, including human enterococci [6, 7]. Enterococci are members of the gastrointestinal tract consortium in humans and most other organisms [8, 9]. Acquired resistance in Enterococcus spp. is mediated by transferable transposons or plas-mids encoding resistance cassettes [8, 9]. Multidrug-resistant enterococci can be found in food and animal species [8, 9]. Previous studies have shown that food and animal species other than E. faecium and E. fae-calis can efficiently transfer antibiotic resistance to human strains in inter-specific matings [8, 9]. Of note, vancomycin-resistant enterococci emerged in farm animals in Europe, but became widespread in US hospitals within just a few years [8, 9]. The potential development of environmental reservoirs of antibiotic resistance in farmland is a concern [7, 8]. Thus, a …