A Novel VanA-Carrying Plasmid in a Clinical Isolate of Enterococcus avium

Bernasconi, Odette Joëlle; Principe, Luigi; Viaggi, Valentina; Luzzaro, Francesco; Endimiani, Andrea (2019). A Novel VanA-Carrying Plasmid in a Clinical Isolate of Enterococcus avium. International journal of antimicrobial agents, 53(6), pp. 876-877. Elsevier 10.1016/j.ijantimicag.2019.04.006

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Objectives. Vancomycin resistance among enterococci represents an important medical challenge. This phenotype is frequently associated to the expression of the vanA trait and is usually observed in Enterococcus faecalis/faecium. In contrast, the VanA phenotype has been very rarely reported in Enterococcus avium. VanA mobilization is enabled mainly by transposition of Tn1546 which displays structural variability. Here, we aimed to explore in detail the whole-genome of a vancomycin-resistant E. avium isolate (LC0559/18).
Methods. LC0559/18 was recovered from a rectal swab of an ICU-patient hospitalized in Northern Italy. Vancomycin-resistant enterococci were searched with selective plates. Species identification and antimicrobial resistance profile were assessed by MALDI-TOF/MS and VITEK2, respectively. Whole-genome sequencing (WGS) was obtained merging data of both HiSeq (Illumina) and MinION (Oxford Nanopore) platforms.
Results. LC0559/18 showed MICs >16 mg/L and 16 mg/L for vancomycin and teicoplanin, respectively. WGS analysis indicated the presence of two plasmids. pLC0559/18-1 (40’456bp) was of replicon type rep17 and harbored vanA, aph(3’)III, ant(6)-Ia antimicrobial resistance genes (ARGs). The vanA cassette was on a Tn1546-B2 variant reported to date only in E. faecium. This variant includes presence of element IS1216, as well as absence of transposase ORF1 and resolvase ORF2 of the native Tn1546. Moreover, Tn1546-B2 of LC0559/18 was carried by a novel plasmid backbone. pLC0559/18-2 (52’156bp) was repUS7 positive and did not harbor ARGs.
Conclusions. We report a new plasmid backbone of rarely reported vancomycin-resistant E. avium and provide detailed characteristics of its vanA genetic environment. In turn, this highlights further mobilization of Tn1546 among this genus.

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