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Distinguishable Epidemics of Multidrug-Resistant Salmonella Typhimurium DT104 in Different Hosts

Science  27 Sep 2013:
Vol. 341, Issue 6153, pp. 1514-1517
DOI: 10.1126/science.1240578

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Sourcing Antibiotic Resistance

It is widely assumed that antibiotic resistance in farm animals contributes in a major way to antibiotic resistance in humans. Mather et al. (p. 1514, published online 12 September; see the Perspective by Woolhouse and Ward) analyzed hundreds of genome sequences from Salmonella isolates collected from both livestock and patients in Scotland between 1990 and 2004. The relative contributions of animal-derived and human-derived sources of infection were quantified and the phylogenetic diversity of resistance profiles was matched with bacterial phylogenies. The results suggest that most human infections are caught from other humans rather than from livestock and that humans harbor a greater diversity of antibiotic resistance.

Abstract

The global epidemic of multidrug-resistant Salmonella Typhimurium DT104 provides an important example, both in terms of the agent and its resistance, of a widely disseminated zoonotic pathogen. Here, with an unprecedented national collection of isolates collected contemporaneously from humans and animals and including a sample of internationally derived isolates, we have used whole-genome sequencing to dissect the phylogenetic associations of the bacterium and its antimicrobial resistance genes through the course of an epidemic. Contrary to current tenets supporting a single homogeneous epidemic, we demonstrate that the bacterium and its resistance genes were largely maintained within animal and human populations separately and that there was limited transmission, in either direction. We also show considerable variation in the resistance profiles, in contrast to the largely stable bacterial core genome, which emphasizes the critical importance of integrated genotypic data sets in understanding the ecology of bacterial zoonoses and antimicrobial resistance.

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