Purpose: To investigate the occurrence of vancomycin-variable enterococci (VVE) in a hospital in central Italy. Methods: vanA positive but vancomycin-susceptible Enterococcus faecium isolates (VVE-S) were characterized by antibiotic susceptibility tests, molecular typing (PFGE and MLST), and WGS approach. The reversion of VVE-S to a resistant phenotype was assessed by exposure to increasing vancomycin concentrations, and the revertant isolates were used in filter mating experiments. qPCR was used to analyze the plasmid copy number. Results: Eleven putative VVE-S were selected. WGS revealed two categories of vanA cluster plasmid located: the first type showed the lack of vanR, the deletion of vanS, and an intact vanH/vanA/vanX cluster; the second type was devoid of both vanR and vanS and showed a deletion of 544-bp at the 5'-end of the vanH. Strains (n = 7) carrying the first type of vanA cluster were considered VVE-S and were able to regain a resistance phenotype (VVE-R) in the presence of vancomycin, due to a 44-bp deletion in the promoter region of vanH/vanA/vanX, causing its constitutive expression. VVE-R strains were not able to transfer resistance by conjugation, and the resistance phenotype was unstable: after 11 days of growth without selective pressure, the revertants were still resistant but showed a lower vancomycin MIC. A higher plasmid copy number in the revertant strains was probably related to the resistance phenotype. Conclusion: We highlight the importance of VVE transition to VRE under vancomycin therapy resulting in a potential failure treatment. We also report the first-time identification of VVE-S isolates pstS-null belonging to ST1478.

Genetic analysis of vancomycin-variable Enterococcus faecium clinical isolates in Italy / Coccitto, Sonia Nina; Cinthi, Marzia; Simoni, Serena; Pocognoli, Antonella; Zeni, Guido; Mazzariol, Annarita; Morroni, Gianluca; Mingoia, Marina; Giovanetti, Eleonora; Brenciani, Andrea; Vignaroli, Carla. - In: EUROPEAN JOURNAL OF CLINICAL MICROBIOLOGY & INFECTIOUS DISEASES. - ISSN 0934-9723. - 43:4(2024), pp. 673-682. [10.1007/s10096-024-04768-0]

Genetic analysis of vancomycin-variable Enterococcus faecium clinical isolates in Italy

Coccitto, Sonia Nina
Primo
;
Cinthi, Marzia
Secondo
;
Simoni, Serena;Pocognoli, Antonella;Morroni, Gianluca;Mingoia, Marina;Giovanetti, Eleonora;Brenciani, Andrea
Penultimo
;
Vignaroli, Carla
Ultimo
2024-01-01

Abstract

Purpose: To investigate the occurrence of vancomycin-variable enterococci (VVE) in a hospital in central Italy. Methods: vanA positive but vancomycin-susceptible Enterococcus faecium isolates (VVE-S) were characterized by antibiotic susceptibility tests, molecular typing (PFGE and MLST), and WGS approach. The reversion of VVE-S to a resistant phenotype was assessed by exposure to increasing vancomycin concentrations, and the revertant isolates were used in filter mating experiments. qPCR was used to analyze the plasmid copy number. Results: Eleven putative VVE-S were selected. WGS revealed two categories of vanA cluster plasmid located: the first type showed the lack of vanR, the deletion of vanS, and an intact vanH/vanA/vanX cluster; the second type was devoid of both vanR and vanS and showed a deletion of 544-bp at the 5'-end of the vanH. Strains (n = 7) carrying the first type of vanA cluster were considered VVE-S and were able to regain a resistance phenotype (VVE-R) in the presence of vancomycin, due to a 44-bp deletion in the promoter region of vanH/vanA/vanX, causing its constitutive expression. VVE-R strains were not able to transfer resistance by conjugation, and the resistance phenotype was unstable: after 11 days of growth without selective pressure, the revertants were still resistant but showed a lower vancomycin MIC. A higher plasmid copy number in the revertant strains was probably related to the resistance phenotype. Conclusion: We highlight the importance of VVE transition to VRE under vancomycin therapy resulting in a potential failure treatment. We also report the first-time identification of VVE-S isolates pstS-null belonging to ST1478.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11566/326571
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