Alternative vanHAX promoters and increased vanA-plasmid copy number resurrect silenced glycopeptide resistance in Enterococcus faecium. (26th December 2020)

• Record Type: Journal Article
• Authors: Wagner, Theresa Maria; Janice, Jessin; Sivertsen, Audun; Sjögren, Ingegerd; Sundsfjord, Arnfinn; Hegstad, Kristin
• Is Part Of: Journal of antimicrobial chemotherapy. Volume 76:Number 4(2021)
• Page Start: 876
• Page End: 882
• Publication Date: 2020-12-26
• Subjects: Anti-infective agents -- Periodicals; Chemotherapy -- Periodicals; 615.58
• DOI: 10.1093/jac/dkaa541
• Languages: English
• ISSNs: 0305-7453

Abstract

Abstract: Background: Vancomycin variable enterococci (VVE) are van -positive isolates with a susceptible phenotype that can convert to a resistant phenotype during vancomycin selection. Objectives: To describe a vancomycin-susceptible vanA -PCR positive ST203 VVE Enterococcus faecium isolate (VVE Swe -S) from a liver transplantation patient in Sweden which reverted to resistant (VVE Swe -R) during in vitro vancomycin exposure. Methods: WGS analysis revealed the genetic differences between the isolates. Expression of the van- operon was investigated by qPCR. Fitness and stability of the revertant were investigated by growth measurements, competition and serial transfer. Results: The VVE Swe -R isolate gained high-level vancomycin (MIC >256 mg/L) and teicoplanin resistance (MIC = 8 mg/L). VVE Swe -S has a 5′-truncated vanR activator sequence and the VVE Swe -R has in addition acquired a 44 bp deletion upstream of vanHAX in a region containing alternative putative constitutive promoters. In VVE Swe -R the vanHAX -operon is constitutively expressed at a level comparable to the non-induced prototype E. faecium BM4147 strain. The vanHAX operon of VVE Swe is located on an Inc18-like plasmid, which has a 3–4-fold higher copy number in VVE Swe -R compared with VVE Swe -S. Resistance has a low fitness cost and the vancomycin MIC of VVE Swe -R decreased during in vitro serial culture without selection. The reduction in MIC was associated with a decreased vanA -plasmid copy number. Conclusions: Our data support a mechanism by which vancomycin-susceptible VVE strains may revert to a resistant phenotype through the use of an alternative, constitutive, vanR -activator-independent promoter and a vanA -plasmid copy number increase.