Characterization of vancomycin-resistant Enterococcus faecium causing infections in one Portuguese hospital (2022-2024)

Abstract

Background: Vancomycin-resistant Enterococcus faecium (VREfm) are leading nosocomial pathogens linked to high mortality rates and costs [1,2]. VREfm are also included in the WHO global priority list of antibiotic-resistant bacteria for which new antibiotics are urgently needed [3]. Their epidemiology is puzzling within Europe and VREfm data in Portuguese hospitals are lacking since the 2000s. Objective: We aimed to characterize the antibiotic susceptibility of VREfm obtained from one hospital in the Porto metropolitan area during 2022-2024. Methods: Thirty-seven pure cultures obtained from diverse clinical specimens were sent by the hospital in blood agar plates and inoculated onto Slanetz-Bartley agar. Colonies with different morphologies (typical of Enterococcus spp.) were further cultivated onto BHI agar. To specifically select VREfm, PCR screening of vanA/vanB genes was performed along with a species-specific gene, gluP, to distinguish Enterococcus faecium and Enterococcus lactis (former E. faecium clade B) [4]. Antibiotic susceptibility was performed by disk diffusion or broth microdilution (linezolid) (EUCAST/CLSI). WGS (Illumina-NovaSeq) was performed on the linezolid-resistant isolate. Results: All VREfm harbored the vanA gene and were multidrug-resistant (MDR: resistant to ≥ 3 antibiotics of different families). All isolates were resistant to ampicillin, ciprofloxacin, vancomycin and teicoplanin. Most to erythromycin (94%) and quinupristin-dalfopristin (88%), and less to tetracycline (16%), streptomycin (15%), high-level gentamicin (6%), or linezolid (3%; MIC=8mg/L). None of the isolates were resistant to chloramphenicol. The linezolid resistant isolate (sequence type 80) carried a G2576T mutation in the 23s rRNA gene. Preliminary findings indicated that three cultures (9%) exhibited colonies with different susceptibility to streptomycin (n=2) and quinupristin-dalfopristin (n=1). Conclusions: Contemporaneous VREfm isolates are MDR, demanding dependence on last-resort alternatives, and vanA continues to be the dominant gene in local VREfm. Continuing surveillance of linezolid susceptibility and the need for different approaches investigating colony-level diversity are needed to optimize treatment, infection control and antibiotic stewardship.