Abstract
The use of antibiotics on a mass scale, particularly in farming, and their release into the environment has led to a rapid emergence of resistant bacteria. Once emerged, resistance determinants are spread by horizontal gene transfer among strains of the same as well as disparate bacterial species. Their accumulation in free-living as well as livestock and community-associated strains results in the widespread multiple-drug resistance among clinically relevant species posing an increasingly pressing problem in healthcare. One of these clinically relevant species is Staphylococcus aureus, a common cause of hospital and community outbreaks. Among the rich diversity of mobile genetic elements regularly occurring in S. aureus such as phages, pathogenicity islands, and staphylococcal cassette chromosomes, plasmids are the major mean for dissemination of resistance determinants and virulence factors. Unfortunately, a vast number of whole-genome sequencing projects does not aim for complete sequence determination, which results in a disproportionately low number of known complete plasmid sequences. To address this problem we determined complete plasmid sequences derived from 18 poultry S. aureus strains and analyzed the prevalence of antibiotic and heavy metal resistance determinants, genes of virulence factors, as well as genetic elements relevant for their maintenance. Some of the plasmids have been reported before and are being found in clinical isolates of strains typical for humans or human ones of livestock origin. This shows that livestock-associated staphylococci are a significant reservoir of resistance determinants and virulence factors. Nevertheless, nearly half of the plasmids were unknown to date. In this group we found a potentially mobilizable plasmid pPA3 being a unique example of accumulation of resistance determinants and virulence factors likely stabilized by a presence of a toxin–antitoxin system.
Highlights
Growing antibiotic resistance among clinically relevant bacteria is currently becoming a grave concern of global health
Based on their novelty and prevalence among analyzed strains, the plasmids were divided into three distinct groups: (I) poultry-associated plasmids; (II) plasmids of previously known sequences occurring in S. aureus strains of diverse host-specificity; and (III) plasmids entirely unknown to date and characterized in this study (Table 4)
A vast number of sequencing projects do not aim for complete sequence determination, which frequently requires a considerable amount of extra workload
Summary
Growing antibiotic resistance among clinically relevant bacteria is currently becoming a grave concern of global health. Community and livestock-associated S. aureus populations are of utmost importance for genetic elements exchange, in particular for dissemination of antibiotic determinants, and reservoirs of potentially life-threatening strains (Vandenesch et al, 2003; Armand-Lefevre et al, 2005; Voss et al, 2005; Nimmo, 2012; Planet et al, 2013; Strauß et al, 2017). For all these reasons S. aureus is listed by the World Health Organization as one among several bacterial species of high clinical relevance. The spread of other antibiotic resistance determinants is not to be underestimated
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