Fitness cost of vancomycin-resistant Enterococcus faecium plasmids associated with hospital infection outbreaks

• Published in: Journal of antimicrobial chemotherapy 2021-10, Vol.76 (11), p.2757-2764
• Main Authors: Tedim, Ana P, Lanza, Val F, Rodríguez, Concepción M, Freitas, Ana R, Novais, Carla, Peixe, Luísa, Baquero, Fernando, Coque, Teresa M
• Format: Article
• Language: English
• Subjects: Bacterial Proteins - genetics; Cross Infection - epidemiology; Disease Outbreaks; DNA Transposable Elements; Enterococcus faecium - genetics; Gram-Positive Bacterial Infections - epidemiology; Humans; Plasmids; Vancomycin - pharmacology
• ISSN: 0305-7453; 1460-2091
• DOI: 10.1093/jac/dkab249

Abstract Background Vancomycin resistance is mostly associated with Enterococcus faecium due to Tn1546-vanA located on narrow- and broad-host plasmids of various families. This study’s aim was to analyse the effects of acquiring Tn1546-carrying plasmids with proven epidemicity in different bacterial host backgrounds. Methods Widespread Tn1546-carrying plasmids of different families RepA_N (n = 5), Inc18 (n = 4) and/or pHTβ (n = 1), and prototype plasmids RepA_N (pRUM) and Inc18 (pRE25, pIP501) were analysed. Plasmid transferability and fitness cost were assessed using E. faecium (GE1, 64/3) and Enterococcus faecalis (JH2-2/FA202/UV202) recipient strains. Growth curves (Bioscreen C) and Relative Growth Rates were obtained in the presence/absence of vancomycin. Plasmid stability was analysed (300 generations). WGS (Illumina-MiSeq) of non-evolved and evolved strains (GE1/64/3 transconjugants, n = 49) was performed. SNP calling (Breseq software) of non-evolved strains was used for comparison. Results All plasmids were successfully transferred to different E. faecium clonal backgrounds. Most Tn1546-carrying plasmids and Inc18 and RepA_N prototypes reduced host fitness (–2% to 18%) while the cost of Tn1546 expression varied according to the Tn1546-variant and the recipient strain (9%–49%). Stability of Tn1546-carrying plasmids was documented in all cases, often with loss of phenotypic resistance and/or partial plasmid deletions. SNPs and/or indels associated with essential bacterial functions were observed on the chromosome of evolved strains, some of them linked to increased fitness. Conclusions The stability of E. faecium Tn1546-carrying plasmids in the absence of selective pressure and the high intra-species conjugation rates might explain the persistence of vancomycin resistance in E. faecium populations despite the significant burden they might impose on bacterial host strains.