[Antibiotic resistance and siderophore production in enterococci].

Abstract

Introduction: Enterococci belong to the normal bacterial flora of the gastrointensinal tract of humans. Enterococci are regarded as harmless commensal, and are even believed to have probiotic characteristics. However, they can cause variety of infections, including endocarditis, bloodstream infections and urinary tract infections. During the past several decades, enterococci, and particularly Enterococcus faecalis and E. faecium, have been identified as an important cause of nosocomial infections. Enterococci are intrinsically resistant to a broad range of antimicrobials. Infection caused by resistant strains are difficult to treat. Iron is an essential element for bacteria, but is not easily available in host organisms. Enterococci are iron dependent bacteria. Competition for iron between the host and bacteria is an important factor determining the course of bacterial infections. A common strategy among bacteria living in iron-limited environments is the secretion of siderophores, which can bind poorly soluble iron and make it available to cells via active transport mechanisms. The aim of the presented study was to evaluate the correlation between antibiotic resistance and siderophore production of bacteria of the genus Enterococcus.

Methods: The study included 55 bacterial strains from genus Enterococcus belonging to two species--Enterococcus faecalis and E. faecium. Antimicrobial susceptibility tests were carried out using disc diffusion methods with guidelines of European Committee on Antimicrobial Susceptibility Testing (EUCAST). Total siderophore activity in the culture supernatants was measured using chrome azurol S. Hydroxamate siderophores were assayed using a chemical-specific assay.

Results: Antibacterial susceptibility pattern reveals that E. faecium is more resistant than E. faecalis. A significant correlation was found between resistance to fluoroquinolnes and siderophores production. Ciprofloxacin- and norfloxacin-resistant enterococal strains produced siderophores in large quantity.

Conclusions: One of the most common infections caused by enterococci are urinary tract infections. Fluoroquinolones are an important group of antimicrobial agents used in this type of infection. Fluoroquinolones resistance of enterococci associated with increased synthesis of siderophores result in the increased virulence that may decide on the severity of the infection and the effectiveness of the treatment.