Enterococcal surface protein Esp is not essential for cell adhesion and intestinal colonization of Enterococcus faecium in mice.

BACKGROUND: Enterococcus faecium has globally emerged as a cause of hospital-acquired infections with high colonization rates in hospitalized patients. The enterococcal surface protein Esp, identified as a potential virulence factor, is specifically linked to nosocomial clonal lineages that are genetically distinct from indigenous E. faecium strains. To investigate whether Esp facilitates bacterial adherence and intestinal colonization of E. faecium, we used human colorectal adenocarcinoma cells (Caco-2 cells) and an experimental colonization model in mice. RESULTS: No differences in adherence to Caco-2 cells were found between an Esp expressing strain of E. faecium (E1162) and its isogenic Esp-deficient mutant (E1162Deltaesp). Mice, kept under ceftriaxone treatment, were inoculated orally with either E1162, E1162Deltaesp or both strains simultaneously. Both E1162 and E1162Deltaesp were able to colonize the murine intestines with high and comparable numbers. No differences were found in the contents of cecum and colon. Both E1162 and E1162Deltaesp were able to translocate to the mesenteric lymph nodes. CONCLUSION: These results suggest that Esp is not essential for Caco-2 cell adherence and intestinal colonization or translocation of E. faecium in mice.

Identification of a novel genomic island specific to hospital-acquired clonal complex 17 Enterococcus faecium isolates.

Hospital-acquired clonal complex 17 (CC17) Enterococcus faecium strains are genetically distinct from indigenous strains and are enriched with resistance genes and virulence genes. We identified a genomic island in CC17 E. faecium tentatively encoding a metabolic pathway involved in carbohydrate transport and metabolism, which may provide a competitive advantage over the indigenous E. faecium microbiota.

Enterococcal surface protein Esp is important for biofilm formation of Enterococcus faecium E1162.

Enterococci have emerged as important nosocomial pathogens with resistance to multiple antibiotics. Adhesion to abiotic materials and biofilm formation on medical devices are considered important virulence properties. A single clonal lineage of Enterococcus faecium, complex 17 (CC17), appears to be a successful nosocomial pathogen, and most CC17 isolates harbor the enterococcal surface protein gene, esp. In this study, we constructed an esp insertion-deletion mutant in a clinical E. faecium CC17 isolate. In addition, initial adherence and biofilm assays were performed. Compared to the wild-type strain, the esp insertion-deletion mutant no longer produced Esp on the cell surface and had significantly lower initial adherence to polystyrene and significantly less biofilm formation, resulting in levels of biofilm comparable to those of an esp-negative isolate. Capacities for initial adherence and biofilm formation were restored in the insertion-deletion mutant by in trans complementation with esp. These results identify Esp as the first documented determinant in E. faecium CC17 with an important role in biofilm formation, which is an essential factor in infection pathogenesis.

Human bocavirus in stool: A true pathogen or an innocent bystander?

Human bocavirus (HBoV) is a parvovirus that was discovered only a decade ago and currently includes four genotypes. HBoV-1 is predominantly found in the respiratory tract, whereas HBoV-2, HBoV-3, and HBoV-4 are mainly detected in stool. HBoV-1 is known to be associated with respiratory tract infections. In stool, the prevalence of HBoV (1-4) is similar between patients with gastro-intestinal symptoms and healthy controls in most studies. Furthermore, often other viruses are concurrently present. Both findings suggest that HBoV in stool is an innocent bystander rather than a true pathogen. Nevertheless, several gaps in knowledge on the role of HBoV in stool remain to be addressed. All studies were performed in primarily immunocompetent patients. The role of HBoV in immunocompromised patients remains unknown.

Rapid and generic identification of influenza A and other respiratory viruses with mass spectrometry.

The rapid identification of existing and emerging respiratory viruses is crucial in combating outbreaks and epidemics. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) is a rapid and reliable identification method in bacterial diagnostics, but has not been used in virological diagnostics. Mass spectrometry systems have been investigated for the identification of respiratory viruses. However, sample preparation methods were laborious and time-consuming. In this study, a reliable and rapid sample preparation method was developed allowing identification of cultured respiratory viruses. Tenfold serial dilutions of ten cultures influenza A strains, mixed samples of influenza A virus with human metapneumovirus or respiratory syncytial virus, and reconstituted clinical samples were treated with the developed sample preparation method. Subsequently, peptides were subjected to MALDI-TOF MS and liquid chromatography tandem mass spectrometry (LC-MS/MS). The influenza A strains were identified to the subtype level within 3h with MALDI-TOF MS and 6h with LC-MS/MS, excluding the culturing time. The sensitivity of LC-MS/MS was higher compared to MALDI-TOF MS. In addition, LC-MS/MS was able to discriminate between two viruses in mixed samples and was able to identify virus from reconstituted clinical samples. The development of an improved and rapid sample preparation method allowed generic and rapid identification of cultured respiratory viruses by mass spectrometry.

Contribution of the enterococcal surface protein Esp to pathogenesis of Enterococcus faecium endocarditis.

The enterococcal surface protein Esp, specifically linked to nosocomial Enterococcus faecium, is involved in biofilm formation. To assess the role of Esp in endocarditis, a biofilm-associated infection, an Esp-expressing E. faecium strain (E1162) or its Esp-deficient mutant (E1162Δesp) were inoculated through a catheter into the left ventricle of rats. After 24 h, less E1162Δesp than E1162 were recovered from heart valve vegetations. In addition, anti-Esp antibodies were detected in Esp-positive E. faecium bacteremia and endocarditis patient sera. In conclusion, Esp contributes to colonization of E. faecium at the heart valves. Furthermore, systemic infection elicits an Esp-specific antibody response in humans.

Enterococcal surface protein transiently aggravates Enterococcus faecium-induced urinary tract infection in mice.

The role that the enterococcal surface protein Esp plays in the capacity of Enterococcus faecium to adhere to uroepithelial cells and the role that it plays in urinary tract infection and peritonitis was investigated in vitro and in vivo, respectively, using Esp-expressing E. faecium (E1162) and its isogenic Esp-deficient mutant (E1162 Delta esp). Esp expression enhanced in vitro binding to bladder and kidney epithelial cells. In mice, higher numbers of E1162 were cultured from kidneys and bladders after the induction of urinary tract infection, compared with E1162 Delta esp numbers. This was accompanied by a higher frequency of bacteremia, higher cytokine levels in kidney tissue, and renal insufficiency. Esp had no effect on the course of E. faecium peritonitis.