Isolation of Enterococcus faecalis clinical isolates that efficiently adhere to human bladder carcinoma T24 cells and inhibition of adhesion by fibronectin and trypsin treatment

Enterococcus faecalis: an overlooked cell invader

SUMMARYEnterococcus faecalis and Enterococcus faecium are human pathobionts that exhibit a dual lifestyle as commensal and pathogenic bacteria. The pathogenic lifestyle is associated with specific conditions involving host susceptibility and intestinal overgrowth or the use of a medical device. Although the virulence of E. faecium appears to benefit from its antimicrobial resistance, E. faecalis is recognized for its higher pathogenic potential. E. faecalis has long been considered a predominantly extracellular pathogen; it adheres to and is taken up by a wide range of mammalian cells, albeit with less efficiency than classical intracellular enteropathogens. Carbohydrate structures, rather than proteinaceous moieties, are likely to be primarily involved in the adhesion of E. faecalis to epithelial cells. Consistently, few adhesins have been implicated in the adhesion of E. faecalis to epithelial cells. On the host side, very little is known about cognate receptors, except for the role of glycosaminoglycans during macrophage infection. Several lines of evidence indicate that E. faecalis internalization may involve a zipper-like mechanism as well as a macropinocytosis pathway. Conversely, E. faecalis can use several strategies to prevent engulfment in phagocytes. However, the bacterial and host mechanisms underlying cell infection by E. faecalis are still in their infancy. The most recent striking finding is the existence of an intracellular lifestyle where E. faecalis can replicate within a variety of host cells. In this review, we summarize and discuss the current knowledge of E. faecalis-host cell interactions and argue on the need for further mechanistic studies to prevent or reduce infections.

Pathogenicity of Enterococci

Enterococci are unusually well adapted for survival and persistence in a variety of adverse environments, including on inanimate surfaces in the hospital environment and at sites of infection. This intrinsic ruggedness undoubtedly played a role in providing opportunities for enterococci to interact with other overtly drug-resistant microbes and acquire additional resistances on mobile elements. The rapid rise of antimicrobial resistance among hospital-adapted enterococci has rendered hospital-acquired infections a leading therapeutic challenge. With about a quarter of a genome of additional DNA conveyed by mobile elements, there are undoubtedly many more properties that have been acquired that help enterococci persist and spread in the hospital setting and cause diseases that have yet to be defined. Much remains to be learned about these ancient and rugged microbes, particularly in the area of pathogenic mechanisms involved with human diseases.

[Pathogenicity of Enterococci]

Enterococci belong to the group of lactic acid bacteria (LAB), and inhabit the gastrointestinal tracts of a wide variety of animals from insects and to human, and the commensal organism in humans and animals. The commensal/probiotic role of enterococci has evolved through thousands of years in mutual coexistence. Enterococcus have many favorable traits that have been appreciated in food fermentation and preservation, and many serve as probiotics to promote health. While lactobacillus have been shown to confer numerous benefits on and often regarded as health bringing organisms, enterococci have become more recognized as emerging human pathogens in recent years. Mac Callum and Hastings characterized an organism, now known to be Enterococcal faecalis, which was isolated from a lethal case of endocarditis on 1899. The report was the first detailed description of its pathogenic capabilities. Over the past few decades, multi-drug resistance enterococci have become as important health-care associated pathogen, and leading causes of drug resistance infection. The modern life style including the broad use of antibiotics in medical practice and animal husbandry have selected for the convergence of potential virulence factors to the specific enterococcus species such as E. faecium and E. faecalis. The development of modern medical care of intensive and invasive medical therapies and treatments for human disease, and existence of severe compromised patients in hospitals has contributed to the increased prevalence of these opportunistic organisms. The virulence factors converged in E. faecalis and E. faecium which have been isolated in nosocomial infections, include antibiotic resistance, extracellular proteins (toxins), extrachromosome and mobile genetic elements, cell wall components, biofilm formation, adherence factors, and colonization factor such as bacteriocin, etc. In these potential virulence factors, I presented characteristics of enterococcal conjugative plasmid, cytolysin, collagen binding protein of adhesion, bacteriocins, and drug resistances. I made reference to our original reports, and review books for this review. The review books are "Enterococci: from Commensals to Leading Causes of Drug Resistant Infection, NCBI Bookshelf. A service of the National Library of Medicine, National Institute of Health. Ed. by Michael S Gilmore, Don B Clewell, Yasuyoshi Ike, and Nathan Shankar", and "The Enterococci: Pathogenesis, Molecular Biology, and Antibiotic Resistance, Gilmore M., Clewell D., Courvadin P., Dunny G., Murray B., Rice L., (ed) 2002. ASM Press".

Frequency of ace, epa and elrA Genes in Clinical and Environmental Strains of Enterococcus faecalis

Surface proteins play an important role in the pathogenesis of enterococcal infections. Some of them are candidates for a vaccine, e.g., the frequency of endocarditis in rats vaccinated with Ace protein was 75 % as 12 opposed to 100 % in those who weren't. However, there are other components of enterococcal cells, such as Epa antigens or internalin-like proteins, which may be used in the prophylaxis of infections caused by them. However, also other virulence factors and resistance to antibiotics are important during enterococcal infection. Therefore, the relevance of ace, epa, elrA, other virulence genes, as well as resistance to antibiotics was investigated. 161 Enterococcus faecalis strains isolated from teaching hospitals in Lodz, cultured according to standard microbiological methods, were investigated for the presence of genes encoding surface proteins by PCR. Results were analyzed with χ(2) test. The elrA gene was found in all clinical and environmental strains, the ace gene was also widespread among E. faecalis (96.9 %). Both tested epa genes were found in the majority of isolates (83.25 %). There was correlation between the presence of esp and ace genes (p = 0.046) as well as between epa and agg genes (p = 0.0094; χ(2) test). The presence of the genes encoding surface proteins investigated in our study in the great majority of isolates implies that they would appear to be required during E. faecalis infection. Therefore, they could be excellent targets in therapy of enterococcal infections or, as some studies show, candidates for vaccines.

Antibiotic resistance and adhesion properties of oral Enterococci associated to dental caries

BACKGROUND

Enterococci are increasingly associated with opportunistic infections in Humans but the role of the oral cavity as a reservoir for this species is unclear. This study aimed to explore the carriage rate of Enterococci in the oral cavity of Tunisian children and their antimicrobial susceptibility to a broad range of antibiotics together with their adherence ability to abiotic and biotic surfaces.

RESULTS

In this study, 17 E. faecalis (27.5%) and 4 E. faecium (6.5%) were detected. The identified strains showed resistance to commonly used antibiotics. Among the 17 isolated E. faecalis, 12 strains (71%) were slime producers and 5 strains were non-producers. Among the 4 E. faecium, 2 strains were slime producers. All the tested strains were able to adhere to at least one of the two tested cell lines. Our result showed that 11 E. faecalis and 2 E. faecium strains adhered strongly to Hep-2 as well as to A549 cells.

CONCLUSIONS

Drugs resistance and strong biofilm production abilities together with a high phenotypic adhesion to host cells are important equipment in E. faecalis and E. faecium which lead to their oral cavity colonization and focal infections.

Characterization of the invasion of porcine endothelial cells by Streptococcus suis serotype 2

Streptococcus suis serotype 2 is an important swine pathogen associated mainly with meningitis. In a previous study, we demonstrated the ability of S. suis serotype 2 to adhere to and invade immortalized porcine brain microvascular endothelial cells (PBMECs) forming the blood-brain barrier. The aim of the current work was to further characterize the mechanism(s) by which S. suis invades porcine endothelial cells. The ability of several S. suis strains to interact with PBMECs was not found to correlate with their geographic origin, virulence, host of origin, or suilysin production. Characterization studies demonstrated that proteinaceous adhesins/invasins, cell wall components, lipoteichoic acid, and serum components (including fibronectin) were involved in interactions between S. suis and PBMECs. In addition to PBMECs, S. suis was able to adhere to and invade 2 porcine aortic endothelial cell lines and primary PBMECs.

Emerging role of Enterococcus spp in catheter-related infections: biofilm formation and novel mechanisms of antibiotic resistance

Enterococci are gram-positive bacteria that are part of the normal human intestinal flora and can colonize the upper respiratory tract, biliary tract and vagina of otherwise healthy people. Although their virulence is relatively low, recently enterococci have emerged as significant nosocomial pathogens and are currently the 4th leading cause of hospital-acquired infections, including those associated with intravascular catheter and biliary stent implants. The frequent use of these medical devices is often associated with severe complications, including catheter-related bloodstream infections (CRBSIs) and biliary stent occlusions, because of microbial biofilm formation on the device surface. Furthermore, other than a high level of resistance to penicillin, ampicillin and aminoglycosides, a dramatic increase in vancomycin resistance of enterococci has been recently observed in most clinical settings. Clinical strains exhibiting novel mechanisms of acquired resistance to antimicrobials are frequently isolated. In addition, enterococci have a great ability to transmit these resistance traits to other species and even to other genera. Due to their associated morbidity and mortality, enterococcal infections related to medical devices currently represent a major challenge for clinicians, especially for the management of critically ill patients, resulting in prolonged hospitalization and additional health costs.

Inhibition of uropathogenic Escherichia coli by cranberry juice: a new antiadherence assay

A combination of microplate technology and turbidity assessment for testing the adherence of P-fimbriated Escherichia coli to human uroepithelial cell line T24, validated with the addition of the known inhibitor 4-O-alpha-D-galactopyranosyl-alpha-D-galactopyranose (galabiose), resulted in a high-throughput, biologically relevant assessment of cranberry (Vaccinium macrocarpon). P-fimbriated ATCC E. coli strains 25922, 29194, and 49161 were inhibited by galabiose. ATCC 29194, a representative urine isolate containing the papGII allele (Class II fimbrial adhesin) and demonstrating the most significant inhibition in the presence of galabiose, was chosen for further testing. In this assay, a low-polarity fraction of cranberry juice cocktail demonstrated dose-dependent inhibition of E. coli adherence. Reported here, for the first time in V. macrocarpon, are 1-O-methylgalactose, prunin, and phlorizin, identified in an active fraction of cranberry juice concentrate. This in vitro assay will be useful for the standardization of cranberry dietary supplements and is currently being used for bioassay-guided fractionation of cranberry juice concentrate.

Variable phenotypes of enterocolitis in interleukin 10-deficient mice monoassociated with two different commensal bacteria

BACKGROUND & AIMS

To explore the hypothesis that selective immune responses to distinct components of the intestinal microflora induce intestinal inflammation, we characterized disease kinetics and bacterial antigen-specific T-cell responses in ex germ-free interleukin 10 -/- and wild-type control mice monoassociated with Enterococcus faecalis , Escherichia coli , or Pseudomonas fluorescens .

METHODS

Colitis was measured by using blinded histological scores and spontaneous interleukin 12 secretion from colonic strip culture supernatants. Interferon gamma secretion was measured from mesenteric or caudal lymph node CD4 + T cells stimulated with bacterial lysate-pulsed antigen-presenting cells. Luminal bacterial concentrations were measured by culture and quantitative polymerase chain reaction.

RESULTS

Escherichia coli induced mild cecal inflammation after 3 weeks of monoassociation in interleukin 10 -/- mice. In contrast, Enterococcus faecalis-monoassociated interleukin 10 -/- mice developed distal colitis at 10-12 weeks that was progressively more severe and associated with duodenal inflammation and obstruction by 30 weeks. Neither bacterial strain induced inflammation in wild-type mice, and germ-free and Pseudomonas fluorescens-monoassociated interleukin 10 -/- mice remained disease free. CD4 + T cells from Enterococcus faecalis- or Escherichia coli-monoassociated interleukin 10 -/- mice selectively produced higher levels of interferon gamma and interleukin 4 when stimulated with antigen-presenting cells pulsed with the bacterial species that induced disease; these immune responses preceded the onset of histological inflammation in Enterococcus faecalis -monoassociated mice. Luminal bacterial concentrations did not explain regional differences in inflammation.

CONCLUSIONS

Different commensal bacterial species selectively initiate immune-mediated intestinal inflammation with distinctly different kinetics and anatomic distribution in the same host.

Tissue-specific adherent Enterococcus faecalis strains that show highly efficient adhesion to human bladder carcinoma T24 cells also adhere to extracellular matrix proteins

The ability of Enterococcus faecalis clinical isolates to adhere to immobilized extracellular matrixes (ECMs) coating the walls of microtiter plates was examined by microscopy. The ECMs consisted of fibronectin, laminin, collagen types I, II, IV, and V, fibrinogen, and lactoferrin. With the exception of fibrinogen, each isolate showed a different level of adherence to each of the ECMs. No significant level of adherence to fibrinogen was observed for any isolate. The tissue-specific adhesive strains AS11, AS12, AS14, AS15, HT11, and HT12, which showed highly efficient adherence to human bladder carcinoma T24 cells and human bladder epithelial cells, showed strong adherence to fibronectin, laminin, and collagen type I, II, IV, and V ECMs, and the levels were greater than 10(4) cells/mm2 of well surface coated by ECM. None of the isolates that showed little adherence to human bladder carcinoma T24 cells showed efficient adherence to all the ECMs. The levels of adherence of gelatinase-producing isolates to the collagens were lower than the levels of adherence of gelatinase-negative isolates. When tissue-specific adhesive strains that adhered strongly to each ECM were preincubated with fibronectin, the adherence of the strains to fibronectin was inhibited, but the adherence of the strains to collagen type IV was not inhibited. Likewise, preincubation with collagen type IV inhibited adherence to collagen type IV but not adherence to fibronectin. All of the E. faecalis isolates were shown to carry the ace gene by PCR analysis performed with specific primers for collagen binding domain A of ace. The ace gene encodes Ace (adhesin of collagen from enterococci). The prtF gene of group A streptococci, which encodes the fibronectin binding protein of group A streptococci, was not detected in the tissue-specific adhesive strains by Southern analysis performed with the prtF probe of the Streptococcus pyogenes JRS4 strain. Mutants with altered collagen binding were isolated by insertion of Tn916 into the chromosome of tissue-specific adhesive strain AS14. The number of mutant adhesive bacterial cells that adhered to collagen and also to laminin was 1 or 2 orders lower than the number observed for the wild-type strain, but the level of adherence to fibronectin remained the same as that of the wild-type strain.

Upregulation of retinoic acid-inducible gene-I in T24 urinary bladder carcinoma cells stimulated with interferon-gamma

Urinary bladder epithelial cells play an important role in the host defense against urinary tract infections. Interferon-gamma (IFN-gamma) is a potent cytokine that regulates immune responses by inducing multiple genes in many types of cells including urinary bladder epithelial cells. Retinoic acid-inducible gene-I (RIG-I) is a member of the DExH-box family, which is involved in various reactions related to RNA metabolism, and is induced in leukemic cells by retinoic acid or in endothelial cells by lipopolysaccharide. We have studied the expression of RIG-I in T24 cells, a cell line derived from human urinary bladder epithelial carcinoma cells. IFN-gamma stimulated T24 cells to express RIG-I mRNA and protein in concentration- and time-dependent manners. Immunohistochemical analysis revealed the expression of RIG-I in the urinary bladder epithelium from a patient with chronic urinary tract infection and in a bladder epithelial carcinoma. We conclude that RIG-I may play some role in inflammatory reactions in the urinary tract epithelium.

Clinical isolates of Enterococcus faecium exhibit strain-specific collagen binding mediated by Acm, a new member of the MSCRAMM family

A collagen-binding adhesin of Enterococcus faecium, Acm, was identified. Acm shows 62% similarity to the Staphylococcus aureus collagen adhesin Cna over the entire protein and is more similar to Cna (60% and 75% similarity with Cna A and B domains respectively) than to the Enterococcus faecalis collagen-binding adhesin, Ace, which shares homology with Acm only in the A domain. Despite the detection of acm in 32 out of 32 E. faecium isolates, only 11 of these (all clinical isolates, including four vancomycin-resistant endocarditis isolates and seven other isolates) exhibited binding to collagen type I (CI). Although acm from three CI-binding vancomycin-resistant E. faecium clinical isolates showed 100% identity, analysis of acm genes and their promoter regions from six non-CI-binding strains identified deletions or mutations that introduced stop codons and/or IS elements within the gene or the promoter region in five out of six strains, suggesting that the presence of an intact functional acm gene is necessary for binding of E. faecium strains to CI. Recombinant Acm A domain showed specific and concentration-dependent binding to collagen, and this protein competed with E. faecium binding to immobilized CI. Consistent with the adherence phenotype and sequence data, probing with Acm-specific IgGs purified from anti-recombinant Acm A polyclonal rabbit serum confirmed the surface expression of Acm in three out of three collagen-binding clinical isolates of E. faecium tested, but in none of the strains with a non-functional pseudo acm gene. Introduction of a functional acm gene into two non-CI-binding natural acm mutant strains conferred a CI-binding phenotype, further confirming that native Acm is sufficient for the binding of E. faecium to CI. These results demonstrate that acm, which encodes a potential virulence factor, is functional only in certain infection-derived clinical isolates of E. faecium, and suggest that Acm is the primary adhesin responsible for the ability of E. faecium to bind collagen.

Characterization of a white bass (Morone chrysops) embryonic cell line with epithelial features

The genus Morone is an important one for U.S. aquaculture, but there has been no available cell line from this genus. We report here a cell line (the WBE line) derived from white bass embryos that has been grown for more than 80 passages over 21 mo in Dulbecco modified Eagle medium supplemented with fetal bovine serum. The WBE line showed epithelial features with positive immunohistochemical staining for cytokeratin and intercellular junctions when observed by electron microscopy. The doubling time, transformation characteristics, response to cryopreservation, and karyotype were determined. The WBE line was also tested by polymerase chain reaction to verify the species of origin and to screen for mycoplasma infection. This epithelial cell line may prove useful for the study of host-pathogen interactions that occur at the epithelial surface in this commercially important fish species.

In vitro adhesive properties and virulence factors of Enterococcusfaecalis strains

Twenty-nine Enterococcus faecalis isolates from patients with endocarditis or bacteremia or from stools of healthy volunteers were investigated for their ability to adhere to Int-407 and Girardi heart cell lines and for the presence of known enterococcal virulence factors. Eight strains (27.6%) adhered predominantly to Int-407 cells. The adherence of enterococci was enhanced by proteolytic digestion, suggesting that some cell binding components become surface-exposed after treatment with trypsin. The occurrence of known potential virulence factors of enterococci among these strains was determined and was as follows: enterococcal surface protein (72.4%), gelatinase (58.6%), aggregation substance (48.3%) and cytolysin (17.2%). Bacterial adherence was not significantly associated with any of these virulence factors.

Role of Enterococcus faecalis surface protein Esp in the pathogenesis of ascending urinary tract infection

Enterococcus faecalis bacteria isolated from patients with bacteremia, endocarditis, and urinary tract infections more frequently express the surface protein Esp than do fecal isolates. To assess the role of Esp in colonization and persistence of E. faecalis in an animal model of ascending urinary tract infection, we compared an Esp(+) strain of E. faecalis to its isogenic Esp-deficient mutant. Groups of CBA/J mice were challenged transurethrally with 10(8) CFU of either the parent or mutant strain, and bacteria in the urine, bladder, and kidneys were enumerated 5 days postinfection. Significantly higher numbers of bacteria were recovered from the bladder and urine of mice challenged with the parent strain than from the bladder and urine of mice challenged with the mutant. Colonization of the kidney, however, was not significantly different between the parent and mutant strains. Histopathological evaluations of kidney and bladder tissue done at 5 days postinfection did not show marked histopathological changes consistent with inflammation, mucosal hyperplasia, or apoptosis, and there was no observable difference between the mice challenged with the parent and those challenged with the mutant. We conclude that, while Esp does not influence histopathological changes associated with acute urinary tract infections, it contributes to colonization and persistence of E. faecalis at this site.