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Growth inhibition of multiresistant enterococci by interferon-gamma-activated human uro-epithelial cells
Colin R Mackenzie1, Christian Hucke1, Dorothee MÜller1
1Institute for Medical Microbiology and Virology, Heinrich-Heine University, Universitätsstraße 1, 40225 Düsseldorf, Germany.
Abstract:
Nosocomial infections with enterococci are an increasing problem in modern medical practice due to the development of resistance to a wide range of antibiotics, including the glycopeptides vancomycin and teicoplanin. An increasing number of vancomycin-resistant enterococci (VRE) have been cultured from clinical specimens -- especially from patients undergoing immunosuppressive therapy -- and bacteraemia caused by these VRE, subsequent to colonisation of epithelial surfaces, is a significant cause of mortality in such patients. Recent evidence showed that the induction of indoleamine 2,3 dioxygenase (IDO) by interferon-gamma (IFN-gamma) inhibited growth of group B streptococci by depleting the essential amino acid L-tryptophan. This study describes the IFN-gamma-induced expression of IDO -- shown at a transcriptional level by Northern blot analysis, at translational level by Western blot and also at a functional level by L-tryptophan degradation to L-kynurenine -- in the uro-epithelial cell line RT4. The depletion of L-tryptophan resulted in growth inhibition of enterococci, and this was confirmed by abrogation of the inhibitory effect by re-supplementation with excess L-tryptophan. Multiresistant enterococci, including vancomycin-resistant strains resistant to all commercially available antibiotics, were inhibited by the IFN-gamma-induced expression of IDO and subsequent L-tryptophan degradation. This may be an important mechanism in the local restriction of colonisation of the urinary tract by endogenous enterococci and in inhibiting the spread of the bacteria beyond the epithelial barrier.
Insights
Interferon-gamma (IFN-gamma) induces indoleamine 2,3 dioxygenase (IDO) in uro-epithelial cells, depleting L-tryptophan and inhibiting enterococci growth. This mechanism combats antibiotic-resistant infections, including vancomycin-resistant enterococci (VRE).
Area of Science:
- Microbiology
- Immunology
- Molecular Biology
Background:
- Nosocomial infections caused by enterococci are a growing concern due to increasing antibiotic resistance, particularly to vancomycin and teicoplanin.
- Vancomycin-resistant enterococci (VRE) infections, especially in immunocompromised patients, lead to significant mortality, often originating from epithelial surface colonization.
- Previous research indicated that interferon-gamma (IFN-gamma) induces indoleamine 2,3 dioxygenase (IDO), inhibiting group B streptococci by depleting L-tryptophan.
Purpose of the Study:
- To investigate the IFN-gamma-induced expression of IDO in uro-epithelial cells.
- To determine if IDO-mediated L-tryptophan depletion inhibits the growth of enterococci, including VRE strains.
- To explore the potential of this mechanism in controlling endogenous enterococcal colonization and spread.
Main Methods:
- IFN-gamma-induced IDO expression was analyzed at transcriptional (Northern blot), translational (Western blot), and functional (L-tryptophan degradation to L-kynurenine) levels in the RT4 uro-epithelial cell line.
- Enterococcal growth inhibition was assessed in the presence of IDO-induced L-tryptophan depletion.
- The inhibitory effect was confirmed by observing the abrogation of inhibition upon re-supplementation with L-tryptophan.
Main Results:
- IFN-gamma successfully induced IDO expression in RT4 cells, confirmed by Northern blot, Western blot, and functional assays measuring L-tryptophan degradation.
- L-tryptophan depletion mediated by IDO resulted in significant growth inhibition of enterococci.
- This inhibitory effect was reversed by adding excess L-tryptophan, confirming the specificity of the mechanism.
- Multiresistant enterococci, including vancomycin-resistant strains, were effectively inhibited by IFN-gamma-induced IDO activity.
Conclusions:
- The IFN-gamma-induced IDO pathway in uro-epithelial cells effectively inhibits enterococcal growth by depleting essential L-tryptophan.
- This mechanism presents a potential host defense strategy against colonization and spread of endogenous enterococci, including multidrug-resistant strains.
- This finding offers a novel perspective on combating VRE infections within the urinary tract and beyond the epithelial barrier.