The Impact of Enterococcus spp. in the Immunocompromised Host: A Comprehensive Review

Abstract

The immunocompromised host is usually vulnerable to infectious diseases due to broad-spectrum treatments and immunological dysregulation. The Enterococcus genus consists of normal gut commensals, which acquire a leading role in infective processes among individuals with compromised immune systems. These microorganisms may express a potential virulence and resistance spectrum, enabling their function as severe pathogens. The Enterococcus spp. infections in immunocompromised hosts appear to be difficult to resolve due to the immunological response impairment and the possibility of facing antimicrobial-resistant strains. As regards the related risk factors, several data demonstrated that prior antibiotic exposure, medical device insertion, prolonged hospitalization and surgical interventions may lead to Enterococcus overgrowth, antibiotic resistance and spread among critical healthcare settings. Herein, we present a comprehensive review of Enterococcus spp. in the immunocompromised host, summarizing the available knowledge about virulence factors, antimicrobial-resistance mechanisms and host-pathogen interaction. The review ultimately yearns for more substantial support to further investigations about enterococcal infections and immunocompromised host response.

Keywords: Enterococcus; immunocompromised host; infection; pathogenicity.

Figure 1

Italian VRE isolate proportion, by year.

Figure 2

(A) Sicilian Enterococcus Vancomycin-resistant isolate proportion per species (ENTFAE = Enterococcus faecalis and ENTFCM = Enterococcus faecium according to RETE MIC Dashboard acronyms). (B) Sicilian Enterococcus faecium and faecalis Vancomycin-resistant isolate proportion per year. Downloaded from https://qlik.qualitasiciliassr.it/anonimo/single/?appid=85ada16c-4b41-4bc6-9ca1-405b8243d0c2&sheet=6ad6f3ac3369-41c5-bd72-792243f9091b&opt=ctxmenu,currsel, accessed on 29 November 2023.

Figure 3

Principal mechanisms of enterococcal antibiotic resistance. The acronyms “Vat” and “Vgb” indicates streptogramins resistance genes, while “MsrC” identifies a macrolides resistance marker. The acronyms “GdpD”, “LiaF” and “cls” indicate regulation system components whose mutations contribute to daptomycin resistance. Finally, the “PBP5” acronym identifies a penicillin-binding protein which express reduced β-lactams affinity. This figure was created by the authors using Biorender.com (app.biorender.com, accessed on 10 December 2023).

Figure 4

Visual illustration of principal E. faecalis and E. faecium virulence factors. (this figure was created by the authors using Biorender.com, app.biorender.com, accessed on 10 December 2023).