Staphylococcus aureus plasmids of animal origin, a vector of antibiotic resistance
Résumé
Staphylococcus aureus is a human and animal opportunistic pathogen that has demonstrated the capacity to develop resistance to a wide range of antibiotics. Its ability to acquire antibiotic resistance genes (ARGs) is closely associated with the large proportion of mobile genetic elements (MGEs)
present in its genome (between 15 to 20%) and its capacity to exchange genetic material with its environment1. We recently conducted an in silico analysis of MGEs and their linked ARGs on a dataset of 1257 S. aureus genomes isolated from animals, obtained from the NCBI database. As this
analysis suggested the central role of plasmids in the dissemination of antibiotic resistance, our aim here was to provide further evidence from the field by characterizing 340 S. aureus isolates collected from different animal species by the Resapath network2 in France from 2010 to 2021.
Their antibiotic resistance genes were detected by PCR, their plasmid content was identified by PFGE and finally the plasmid/resistance gene associations were established with Southern Blot.
Data showed that almost all isolates (304/340, 89.4%) carried at least one resistance gene, of which 60% contained blaZ gene (beta-lactam resistance), 55% tet(M) (tetracycline resistance) and 40% aac(6')-aph(2'') (aminoglycoside resistance). The diversity of ARGs in these S. aureus field isolates
was similar to that found in our in silico analyses. A large proportion of isolates (55%) contained at least one plasmid, with an average of three plasmids per isolate. The plasmid sizes varied between 2kb and 160kb, but isolates mostly carried plasmids whose size was either 25kb-35kb (27%) or 4.3kb
(21%). Southern Blot analyses showed that 40% of S. aureus plasmids carried at least one of the four ARGs aadD, erm(C), str, or tet(K). Contrarily to in silico data, tet(M) was only found localized on the chromosome. A large diversity of ARG/plasmid associations (42 different profiles) was observed.
Each gene was found to be more commonly associated with a specific size of plasmid: str, tet(K) anderm(C) were located on small (<5kb) plasmids while aadD was found either associated with medium-size plasmids (25kb) or associated with erm(C) on a small 9kb plasmid.
This study confirmed that plasmids play an important role in antimicrobial resistance in S. aureus, as suggested by in silico analyses. Short- and long-read sequencing are ongoing on a subset of isolates carrying representative patterns of plasmids in order to refine their characterization. Further research is needed to uncover the mechanisms behind the wide dissemination of these plasmids and to explain their epidemic success.
Domaines
BactériologieOrigine | Fichiers éditeurs autorisés sur une archive ouverte |
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