Phenotypic and Genotypic Variations of Enterococcus Spp

Overview

Enterococci are Gram-positive facultative anaerobic cocci arranged in short and medium chains. Enterococci reside in the gastrointestinal tract and usually function commensally with humans. They can, however, cause several infections, such as urinary tract infections (UTIs), intra-abdominal infection, bacteremia, or endocarditis. Among many species identified, E. faecalis and E. faecium are the most common species capable of causing infection and posing a threat of antimicrobial resistance, with E. faecalis accounting for the majority of infections.

Enterococci are Gram-positive facultative anaerobic cocci arranged in short and medium chains. Enterococci reside in the gastrointestinal tract and usually function commensally with humans. They can, however, cause several infections, such as urinary tract infections (UTIs), intra-abdominal infection, bacteremia, or endocarditis. Among many species identified, E. faecalis and E. faecium are the most common species capable of causing infection and posing a threat of antimicrobial resistance, with E. faecalis accounting for the majority of infections. Pathogenic species of enterococci express many virulence factors such as adhesins, gelatinase, Enterococcus surface protein, aggregation substances and cytolysins along with biofilm formation. These factors enhance the ability of the pathogen to invade, attach and survive through the acquisition of nutrients in the host tissue. Their presence in drug resistant strains increases the severity of the infection Enterococci are intrinsically resistant to antibiotics such as aminoglycosides and β-lactam-based antibiotics. Moderate resistance to aminoglycosides is due to the intrinsic low permeability of the enterococcal cell wall to the large aminoglycoside molecules and is more prevalent in E. faecium than E. faecalis. Intrinsic β-lactam resistance is due to the overexpression of penicillin-binding proteins with low affinity for β-lactams, which makes E. faecalis more resistant to penicillin than E. faecium Moreover, enterococci can readily acquire resistance to antimicrobials, and vancomycin-resistant enterococci (VRE) are among the priority pathogens for which new antibiotics are needed. In addition, biofilm formation is one of the strategies for the enterococci to evade the host's immune response and the inhibitory or killing effects of antibiotics. This self-produced extracellular matrix also provides a suitable microenvironment for enterococci to grow and facilitates the transmission of mobile genetic elements (MGEs) between bacteria. Enterococcal biofilms have been implicated in indwelling device-related infections such as prosthetic valve endocarditis, prosthetic joint infections and catheter-related infections. Biofilm forming bacteria show resistance to many antibiotics and immune response which results in treatment failure. Given the difficulty of treating and eradicating biofilm associated infections, there is an unmet need for therapeutic options other than antibiotics to prevent biofilm formation. Nanoparticles are attracting attention given their very small size and various antibacterial properties. Nanoparticles can interact with bacteria per unit area, which can make the antibacterial activity of nanoparticles more powerful. Nanoparticles can also initiate several bactericidal pathways, such as disrupting the bacterial membrane and release of intracellular components, making it difficult for bacteria to become resistant.