Vancomycin-resistant Enterococcus faecium: research of virulence factors through innovative methods

The increasing prevalence of multidrug-resistant (MDR) bacteria poses serious challenges to global health. Infections caused by MDR bacteria present limited or even no therapeutic options. Among MDR bacteria, vancomycin resistant enterococci (VRE) are well-known, highly transmissible, nosocomial pathogens able to persistently colonize the gut of patients and to cause a range of infections that are typically difficult to treat (e.g. complicated urinary tract infections, intra- abdominal infections and endocarditis). WHO has listed vancomycin-resistant Enterococcus faecium (VREfm) among pathogens with high priority in its global priority list of antibiotic-resistant bacteria, underscoring the paucity of available and effective treatment options (WHO, 2017). As well as being resistant to vancomycin, VREs (mainly E. faecium) usually exhibit resistance to a wide range of other antibiotics, including intrinsic resistance to cephalosporins, lincosamides and aminoglycosides. Many clinical isolates are resistant to penicillins. Furthermore, reports of acquired resistance to last-line agents such as linezolid and daptomycin are increasing. The European Antimicrobial Resistance Surveillance Network (EARS-Net) published by ECDC reported an increasing prevalence of vancomycin-resistant E. faecium in Europe in the last five years (ECDC, 2024.). It is crucial to implement the infection control measures designed to limit the spread of VREfm and to develop tight monitoring plans to better understand the epidemiology, genetic diversity and risk factors associated with VREfm infections. We conducted several studies with the aim: 1. to provide information of recent epidemiology of vancomycin-resistant Enterococcus faecium bloodstream infections in the Foggia area involving the hospital “Policlinico Riuniti”; 2. to evaluate the in vitro activity of oritavancin and comparator antibiotics against a collection of clinical isolates of VRE; 3. to investigate the ability to form biofilm of a collection of clinical isolates of VRE; 4. to characterize E. faecium resistant to vancomycin, tigecycline, and eravacycline; 5. to study the epidemiology and genetic diversity of VRE isolates of Foggia area by the comparison of clinical isolates of VRE with VRE isolated from environmental samples, through the collaboration with the Istituto Zooprofilattico Sperimentale della Puglia e della Basilicata; 6. to develop an in vitro model of infective endocarditis as a preliminary step for setting up biofilm cultures that can mimic the endocardial vegetations produced by Enterococcus spp. strains. Our study confirms a high prevalence of vancomycin-resistant E. faecium in clinical setting of Foggia area. Continuous surveillance programs are need to monitor the prevalence in the future and provide appropriate data to act a strict infection control plan. In addition, through WGS, we were able to trace the clones circulating in clinical and environmental area, confirming the higher prevalence of sequence types predominant in hospitals worldwide and linked to numerous outbreaks. Furthermore, genomic data have allowed for profiling virulence traits (biofilm production) and antibiotic resistance genes, identifying new genetic determinants, in vancomycin-resistant Enterococcus faecium. The new lipoglycopeptide oritavancin can be considered a valid therapeutic option to treat infection caused by vancomycin-resistant Enterococcus faecium. The developed in vitro model of infective endocarditis represents an efficient tool capable to simulate the endocardial vegetations produced by Enterococcus spp. Strains, so as to study the treatment on new antibiotic molecules. During the doctoral period, the research activity was focused also on the study of other multidrug resistant bacteria of clinical concern.