Virulence factors and antibiotic susceptibility in enterococci isolated from oral mucosal and deep infections

Living together: The role of Candida albicans in the formation of polymicrobial biofilms in the oral cavity

The oral cavity of humans is colonized by diversity of microbial community, although dominated by bacteria, it is also constituted by a low number of fungi, often represented by Candida albicans. Although in the vast minority, this usually commensal fungus under certain conditions of the host (e.g., immunosuppression or antibiotic therapy), can transform into an invasive pathogen that adheres to mucous membranes and also to medical or dental devices, causing mucosal infections. This transformation is correlated with changes in cell morphology from yeast-like cells to hyphae and is supported by numerous virulence factors exposed by C. albicans cells at the site of infection, such as multifunctional adhesins, degradative enzymes, or toxin. All of them affect the surrounding host cells or proteins, leading to their destruction. However, at the site of infection, C. albicans can interact with different bacterial species and in its filamentous form may produce biofilms-the elaborated consortia of microorganisms, that present increased ability to host colonization and resistance to antimicrobial agents. In this review, we highlight the modification of the infectious potential of C. albicans in contact with different bacterial species, and also consider the mutual bacterial-fungal relationships, involving cooperation, competition, or antagonism, that lead to an increase in the propagation of oral infection. The mycofilm of C. albicans is an excellent hiding place for bacteria, especially those that prefer low oxygen availability, where microbial cells during mutual co-existence can avoid host recognition or elimination by antimicrobial action. However, these microbial relationships, identified mainly in in vitro studies, are modified depending on the complexity of host conditions and microbial dominance in vivo.

Exploring the prevalence of antibiotic resistance patterns and drivers of antibiotics resistance of Salmonella in livestock and poultry-derived foods: a systematic review and meta-analysis in Bangladesh from 2000 to 2022

Background

Antimicrobial resistance (AMR) is a severe public health problem that Bangladeshis are dealing with nowadays. However, we wanted to investigate the pooled prevalence of Salmonella and AMR in Salmonella strains isolated from livestock- and poultry-derived foods between 1 January 2000 and 31 August 2022.

Methods

The metafor and metareg packages in the R programming language were used to conduct all analyses. We used a random-effect or fixed-effect model for pooled prevalence of Salmonella and AMR to Salmonella, depending on the heterogeneity test for each antibiotic. The heterogeneity was examined using stratified analyses, the meta-regression approach and sensitivity analysis.

Results

The combined prevalence of Salmonella in livestock and poultry-derived food in Bangladesh is 37%, according to the 12-research considered (95% CI: 23%-52%). According to subgroup analysis, neomycin had the lowest prevalence of resistance (4%, 95% CI: 1%-13%), whereas tetracycline had the highest prevalence of resistance (81%, 95% CI: 53%-98%). According to univariate meta-analysis and correlation analysis, the prevalence of Salmonella increased with the study period (β = 0.0179; 95% CI: 0.0059-0.0298, P = 0.0034; R² = 46.11%) and without this, none of aforementioned variables was significantly associated with the detected heterogeneity and there was a positive relationship (r = 0.692, P = 0.001) between the Salmonella prevalence and study period.

Conclusions

AMR is rising alarmingly in Bangladesh by livestock-derived food consumption. However, monitoring and evaluating antibiotic sensitivity trends and developing effective antibiotic regimens may improve Salmonella infection inhibition and control in Bangladesh. Policymakers should be concerned about food handling practices. Doctors should be concerned when using prescribing antibiotics.

Cross-kingdom interaction between Candida albicans and oral bacteria

Candida albicans is a symbiotic fungus that commonly colonizes on oral mucosal surfaces and mainly affects immuno-compromised individuals. Polymicrobial interactions between C. albicans and oral microbes influence the cellular and biochemical composition of the biofilm, contributing to change clinically relevant outcomes of biofilm-related oral diseases, such as pathogenesis, virulence, and drug-resistance. Notably, the symbiotic relationships between C. albicans and oral bacteria have been well-documented in dental caries, oral mucositis, endodontic and periodontal diseases, implant-related infections, and oral cancer. C. albicans interacts with co-existing oral bacteria through physical attachment, extracellular signals, and metabolic cross-feeding. This review discusses the bacterial-fungal interactions between C. albicans and different oral bacteria, with a particular focus on the underlying mechanism and its relevance to the development and clinical management of oral diseases.

Enterococcus faecalis and Candida albicans dual-species biofilm: establishment of an in vitro protocol and characterization

Enterococcus faecalis is the most important agent of persistent apical periodontitis, and recently, Candida albicans has also been implicated in periapical infections. This study aimed to optimize an in vitro E. faecalis and C. albicans dual-species biofilm protocol for endodontic research. Different physicochemical conditions for biofilm formation were tested. Susceptibility assays to antimicrobials, biochemical composition and an ultra-morphological structure analyses were performed. Reproducible dual-species biofilms were established in BHI medium at 35 °C, for 48 h and in a microaerophilic atmosphere. An increase in biomass and chitin content was detected after vancomycin treatment. Structural analysis revealed that the dual-species biofilm was formed by both microorganisms adhered to the substrate. The proposed protocol could be useful for the study of interkingdom relationships and help to find new strategies against periapical infections.

Prevalence and Antibiotic Susceptibility Trends of Selected Enterobacteriaceae, Enterococci, and Candida albicans in the Subgingival Microbiota of German Periodontitis Patients: A Retrospective Surveillance Study

The periodontal microbiota is ecologically diverse and may facilitate colonization by bacteria of enteric origin (Enterobacteriaceae, Enterococci) and co-infections with Candida albicans, possibly producing subgingival biofilms with high antimicrobial tolerance. This retrospective surveillance study followed periodontitis-associated superinfection profiles in a large patient sample. From 2008 to 2015, biofilm samples from deep periodontal pockets were collected from a total of 16,612 German adults diagnosed with periodontitis. The presence of selected Enterobacteriaceae, Enterococci, and Candida albicans was confirmed in overnight cultures. Antimicrobial susceptibility of these clinical isolates was tested by disk diffusion with antibiotics routinely used for treatment of oral infections, e.g., amoxicillin (AML), amoxicillin/clavulanic acid (AMC), doxycycline (DO), and ciprofloxacin (CIP). The mean annual prevalence of patients harboring Enterobacteriaceae in periodontal plaques was 11.5% in total and ranged from 2.5% for Enterobacter cloacae to 3.6% for Klebsiella oxytoca, 1.1% for Klebsiella pneumoniae, 2.8% for Serratia marcescens, and 1.5% for Serratia liquefaciens. In comparison, the mean detection rates for microbiota typically found in the oral cavity were higher, e.g., 5.6% for Enterococcus spp. and 21.8% for Candida albicans. Among the Enterobacteriaceae, species harboring intrinsic resistance to AML (Enterobacter spp., Klebsiella spp., Serratia spp.) were predominant. Non-susceptibility to AMC was observed for Serratia spp. and Enterobacter cloacae. By contrast, Enterococcus spp. only showed non-susceptibility to DO and CIP. Trends for increasing resistance were found to AML in Serratia liquefaciens and to DO in Enterococcus spp. Trend analysis showed decreasing resistance to AMC in Serratia liquefaciens and Klebsiella oxytoca; and to DO in Serratia marcescens, liquefaciens, and Enterobacter cloacae. This study confirms the low but consistent presence of Enterobacteriaceae and Enterococci among the subgingival microbiota recovered from periodontitis specimen. Although their pathogenetic role in periodontal lesions remains unclear, their presence in the oral cavity should be recognized as a potential reservoir for development and spread of antibiotic resistance in light of antibiotic usage in oral infections.

Antibacterial and anti-biofilm activity of silver nanoparticles on multi-drug resistance pseudomonas aeruginosa isolated from dental-implant

Aim

The aim of this study was to isolate multi-drug-resistant p. aeruginosa from dental implant, and control the growth and biofilm of isolated p. aeruginosa by silver nanoparticles.

Materials and methods

Thirty specimens from patients with Peri-implantitis were taken for isolation of p. aeruginosa. Bacterial samples were obtained from the infected peri-implant pocket with sterile paper points (size 30-45 mm). Samples were cultured for isolation of Multi-drug resistance P. aeruginosa. Phenotypical identification was done by the VITEK 2 system. DNA was extracted from the isolates and 16S rDNA-based PCR assay was used to confirm the identification. Susceptibility of isolated p. aeruginosa to 16 antibiotics was evaluated using the VITEK 2 system. The growth inhibition of isolated bacteria by AgNPs was tested by disk-diffusion method. The microtiter plate assay was used to estimate the capacity of P. aeruginosa to from biofilms. Antibiofilm activity of AgNPs was determined by microtiter plate assay.

Results

Three P. aeruginosa were successfully isolated from 30 clinical specimens. P. aeruginoas isolates were resistance to most of used antibiotics. Silver nanoparticles exerted an inhibitory effect on all isolated bacteria. All tested concentration of AgNP_S exhibited a greatest anti-biofilm activity against multi-drug resistance (MDR) p. aeruginosa.

Conclusion

Current findings highlight the role of AgNP_S in growth inhibition of P. aeruginosa and reveal a potential application of AgNPS in eradication of p. aeruginosa biofilms.

Coexistence of Candida albicans and Enterococcus faecalis increases biofilm virulence and periapical lesions in rats

The present study utilized an in vitro dual-species biofilm model and an in vivo rat post-treatment endodontic disease (PTED) model to investigate whether co-infection of Candida albicans and Enterococcus faecalis would aggravate periapical lesions. The results showed that co-culturing yielded a thicker and denser biofilm more tolerant to detrimental stresses compared with the mono-species biofilm, such as a starvation-alkalinity environment, mechanical shear force and bactericidal chemicals. Consistently, co-inoculation of E. faecalis and C. albicans significantly increased the extent of in vivo periapical lesions compared with mono-species infection. Specifically, coexistence of both microorganisms increased osteoclastic bone resorption and suppressed osteoblastic bone formation. The synergistic effects also up-regulated inflammatory cytokines including TNF-α and IL-6. In summary, coexistence of C. albicans and E. faecalis increased periapical lesions by enhanced biofilm virulence.

Antibiofilm Efficacy of Luteolin Against Single and Dual Species of Candida albicans and Enterococcus faecalis

Candida albicans and Enterococcus faecalis biofilm-associated infections have been a huge challenge to the medical community. However, the efficacy of natural products against mixed biofilms of C. albicans and E. faecalis still remains largely unexploited. The aim of this study was to evaluate the efficacy of luteolin against planktonic cell growth, adhesion, and biofilm formation of C. albicans and E. faecalis in single and mixed cultures in vitro. The results showed that the minimum inhibitory concentrations of luteolin against planktonic cells of C. albicans, E. faecalis, and mixed cultures were 32 and 64 μg ml^–1, respectively. The results displayed that a remarkable variation in biofilm biomass, viability, structure, and composition of single and dual-species biofilms formed by mono- and dual-species biofilms of C. albicans and E. faecalis in the presence of luteolin was confirmed by mainly crystal violet staining assay (CVSA), optical microscope, field emission scanning electron microscope (FESEM), and confocal laser scanning microscope (CLSM). The tolerance of luteolin-treated single- and dual-species biofilms to antibiotics was found to obviously decrease, and the loss of biofilm matrix components (mainly polysaccharides and proteins) was revealed by CLSM. Moreover, luteolin was effective at inactivating biofilm cells, as well as destructing preformed biofilm structures by single and dual species by CVSA, FESEM, and CLSM. Collectively, these data indicate the potential of luteolin as a promising antibiofilm agent for the therapeutic management of biofilm-related infections induced by single and dual species of C. albicans and E. faecalis.

Explorative study on Lactobacillus species and their acid-producing capacity and anti-microbial activity in head and neck cancer patients

OBJECTIVE

To determine acid-producing capacity and anti-microbial activity of Lactobacillus species collected pretreatment and post treatment in head and neck cancer patients.

MATERIAL AND METHODS

Lactobacillus isolates from 21 patients pretreatment and post treatment were identified using molecular methods. The patients' stimulated salivary secretion was determined pretreatment, and 6 and 12 months post treatment and caries lesions/new filled surfaces registered at 24 months post treatment. The acid-producing capacity of the Lactobacillus isolate was analyzed using a colorimetric fermentation test in microtiter plates. The anti-microbial activity of the isolates against Streptococcus mutans associated with caries, and against the mucosal pathogens Staphylococcus aureus, Candida albicans, and Enterococcus faecalis was analyzed by determining inhibitory zones on agar plates.

RESULTS

The most frequent species were L. paracasei (n = 21), L. casei/rhamnosus (n = 17) and L. fermentum (n = 10). Sixty-seven percent of the patients harbored L. paracasei either at 6 or 12 months post radiotherapy. The corresponding figures for L. casei/rhamnosus and L. fermentum were 62% and 33%. L. paracasei strains showed the best acid-producing capacity and L. fermentum strains the lowest. Strong acid-producing capacity was most common among isolates collected at 6 months post treatment. Seventy-two percent of the strains showed an anti-microbial activity against S. mutans, one strain against S. aureus and none against C. albicans or E. faecalis.

CONCLUSION

The most frequent species isolated from head and neck cancer patients both pretreatment and post treatment were L. paracasei, L. casei/rhamnosus, and L. fermentum. L. paracasei showed the best acid-producing capacity and the highest proportion with anti-microbial activity against S. mutans.

Antimicrobial susceptibility and virulence of Enterococcus spp. isolated from periodontitis-associated subgingival biofilm

BACKGROUND

This study evaluated the prevalence, virulence and antimicrobial susceptibility of enterococci isolated from the subgingival microbiota of patients with different periodontal status.

METHODS

Subgingival biofilm was obtained from individuals with periodontal health (PH) (n = 139), gingivitis (n = 103), and periodontitis (n = 305) and cultivated on selective media. Isolated strains were identified by mass spectrometry. Antimicrobial sensitivity was determined by disk diffusion, virulence genes by polymerase chain reaction, and the subgingival microbiota by checkerboard. Differences among groups were assessed by Kruskal-Wallis, Mann-Whitney, and Chi-square tests.

RESULTS

Enterococcus spp. were isolated from 7.4% of all samples; 53.7% were Enterococcus faecalis. They were more prevalent in periodontitis (9.8%) and gingivitis (7.8%) than PH (2.2%; P <0.05), but no differences among stages of disease severity were observed. High rates of low susceptibility/resistance (>64%) to at least one antimicrobial were observed. Predominant virulence factors included ace (64.3%), asa (39.3%), and esp (35.7%). Fusobacterium nucleatum was prevalent in the subgingival microbiota of enterococci+ individuals, whereas Dialister pneumosintes was found in low frequency in patients with bopD+ enterococci. Oral streptococci were prevalent (>70%) in patients carrying enterococci susceptible to doxycycline (P <0.05), usually bopD- and esp- (P <0.01).

CONCLUSIONS

E. faecalis is increased in periodontitis-associated biofilm. Oral enterococci carry virulence genes and express resistance to some antibiotics commonly used in dentistry, such as ciprofloxacin and erythromycin. Specific subgingival taxa are associated with oral enterococci, suggesting they may interact with species of the dysbiotic periodontitis biofilm, constituting a potential source of factors to tissue destruction, antibiotic resistance dissemination, and poor response to periodontal therapy.

Interactions between Candida albicans and Enterococcus faecalis in an Organotypic Oral Epithelial Model

Candida albicans as an opportunistic pathogen exploits the host immune system and causes a variety of life-threatening infections. The polymorphic nature of this fungus gives it tremendous advantage to breach mucosal barriers and cause oral and disseminated infections. Similar to C. albicans, Enterococcus faecalis is a major opportunistic pathogen, which is of critical concern in immunocompromised patients. There is increasing evidence that E. faecalis co-exists with C. albicans in the human body in disease samples. While the interactive profiles between these two organisms have been studied on abiotic substrates and mouse models, studies on their interactions on human oral mucosal surfaces are non-existent. Here, for the first time, we comprehensively characterized the interactive profiles between laboratory and clinical isolates of C. albicans (SC5314 and BF1) and E. faecalis (OG1RF and P52S) on an organotypic oral mucosal model. Our results demonstrated that the dual species biofilms resulted in profound surface erosion and significantly increased microbial invasion into mucosal compartments, compared to either species alone. Notably, several genes of C. albicans involved in tissue adhesion, hyphal formation, fungal invasion, and biofilm formation were significantly upregulated in the presence of E. faecalis. By contrast, E. faecalis genes involved in quorum sensing, biofilm formation, virulence, and mammalian cell invasion were downregulated. This study highlights the synergistic cross-kingdom interactions between E. faecalis and C. albicans in mucosal tissue invasion.

Phenotypic and Molecular Characterization of Plasmid-Mediated Virulence and Antimicrobial Resistance Traits among Multidrug Resistant Enterococcus spp. in Egypt

Enterococcus spp. are remarkable multidrug resistant (MDR) bacteria that are causing serious healthcare-associated infections. The current study investigated the frequency of Enterococcus spp., antimicrobial susceptibility, biofilm formation and the presence of some plasmid-mediated virulence characters and antimicrobial resistance determinants in enterococcal isolates from Egyptian hospitals in Cairo. Enterococcus bacterial isolates were recovered from different clinical specimens and identified using biochemical testing and KB005A HiStrep™ identification kit. Kirby-Bauer disc diffusion method and/or broth microdilution method were used to determine the antimicrobial susceptibility patterns. Phenotypic assays were performed to study biofilm formation and cytolysin and gelatinase production. PCR assays targeting the plasmid-carried genes aac(6’)-aph(2’), aph(3)-IIIa, vanA, agg and cylA were performed. In this study, 50 isolates of diverse Enterococcus spp. were identified with E. faecium was the most frequently isolated one. High resistance profiles were determined against tested antimicrobials and all isolates were MDR. Moderate biofilm formation was detected in 20% of isolates, 18% showed complete blood hemolysis and 12% produced gelatinase. All isolates carried the tested aminoglycosides resistance genes, while vanA was found only in 4 isolates (8%). The virulence genes agg and cylA were detected in 4% and 32% of isolates, respectively. In conclusion, E. faecium was the most prevalent species. The entire isolates set were MDR and the plasmid-carried aminoglycoside resistance genes were extensively disseminated among MDR isolates. Thus, regular surveillance studies, from the area of study or other geographical regions in Egypt, and strict infection control measures are required to monitor the emerging MDR enterococci.

Molecular Detection of Multidrug Resistant Salmonella Species Isolated from Broiler Farm in Bangladesh

Multidrug resistant (MDR) Salmonella are a leading cause of foodborne diseases and serious human health concerns worldwide. In this study we detected MDR Salmonella in broiler chicken along with the resistance genes and class 1 integron gene intl1. A total of 100 samples were collected from broiler farms comprising 50 cloacal swabs, 35 litter and 15 feed samples. Overall prevalence of Salmonella was 35% with the highest detected in cloacal swabs. Among the Salmonella, 30 isolates were confirmed as S. enterica serovar Typhimurium using molecular methods of PCR. Disk diffusion susceptibility test revealed that all the Salmonella were classified as MDR with the highest resistance to tetracycline (97.14%), chloramphenicol (94.28%), ampicillin (82.85%) and streptomycin (77.14%). The most prevalent resistance genotypes were tetA (97.14%), floR (94.28%), bla_TEM-1 (82.85%) and aadA1 (77.14%). In addition, among the MDR Salmonella, 20% were positive for class 1 integron gene (intl1). As far as we know, this is the first study describing the molecular basis of antibiotic resistance in MDR Salmonella from broiler farms in Bangladesh. In addition to tetA, floR, bla_TEM-1, aadA1 and intl1 were also detected in the isolated MDR Salmonella. The detection of MDR Salmonella in broiler chicken carrying intl1 is of serious public health concern because of their zoonotic nature and possibilities to enter into the food chain.

Identification of Novel Bacteriophages with Therapeutic Potential That Target Enterococcus faecalis

The Gram-positive opportunistic pathogen Enterococcus faecalis is frequently responsible for nosocomial infections in humans and represents one of the most common bacteria isolated from recalcitrant endodontic (root canal) infections. E. faecalis is intrinsically resistant to several antibiotics routinely used in clinical settings (such as cephalosporins and aminoglycosides) and can acquire resistance to vancomycin (vancomycin-resistant enterococci). The resistance of E. faecalis to several classes of antibiotics and its capacity to form biofilms cause serious therapeutic problems. Here, we report the isolation of several bacteriophages that target E. faecalis strains isolated from the oral cavity of patients suffering root canal infections. All phages isolated were Siphoviridae with similar tail lengths (200 to 250 nm) and icosahedral heads. The genome sequences of three isolated phages were highly conserved with the exception of predicted tail protein genes that diverge in sequence, potentially reflecting the host range. The properties of the phage with the broadest host range (SHEF2) were further characterized. We show that this phage requires interaction with components of the major and variant region enterococcal polysaccharide antigen to engage in lytic infection. Finally, we explored the therapeutic potential of this phage and show that it can eradicate E. faecalis biofilms formed in vitro on a standard polystyrene surface but also on a cross-sectional tooth slice model of endodontic infection. We also show that SHEF2 cleared a lethal infection of zebrafish when applied in the circulation. We therefore propose that the phage described here could be used to treat a broad range of antibiotic-resistant E. faecalis infections.

Emergence of multidrug resistance and extensive drug resistance among enterococcal clinical isolates in Egypt

Introduction

Enterococci commonly inhabit the gastrointestinal tract of both human and animals; however, they have emerged as a leading cause of several infections with substantial morbidity and mortality. Their ability to acquire resistance combined with intrinsic resistance to various antimicrobials makes treatment of enterococcal infections challenging.

Materials and methods

The aim of the study was to evaluate the antimicrobial resistance pattern, and assess the prevalence of multidrug resistance (MDR) and extensive drug resistance (XDR) among enterococcal isolates, collected from different clinical sources, in Mansoura University Hospitals, Egypt.

Results

Antibiotic sensitivity testing revealed elevated levels of resistance among enterococcal clinical isolates (N=103). All E. faecium (N=32) and 74.6% of E. faecalis isolates(N=71) were MDR, while two E. faecalis and four E. faecium isolates were XDR. High level gentamicin resistance was detected in 79.6%, most of them carried the aac(6’)-Ie-aph(2’’)-Ia gene. High level streptomycin resistance was seen in 36.9%, of which 52.6% carried the ant(6’)-Ia gene. Resistance to macrolides and lincosamides were mediated by ermB (92.2%) and msrA/B (42.7%). tetK, tetL, andtetM genes were detected among tetracyclines resistant isolates. Resistance to vancomycin was detected in 15.5%, where vanB and vanC₁ gene clusters were detected in VRE isolates. Ten isolates (9.7%) were resistant to linezolid, eight of which harbored the optrA gene. Vancomycin and linezolid resistant enterococci were more likely to exhibit strong/moderate biofilm formation than vancomycin and linezolid sensitive ones.

Conclusion

Elevated levels of resistance to different classes of antimicrobial agents and emergence of MDR and XDR strains pose a major threat with limited therapeutic options for infections caused by this emerging pathogen.

Candida albicans induces mucosal bacterial dysbiosis that promotes invasive infection

Infectious complications are a common cause of morbidity and mortality in cancer patients undergoing chemotherapy due to increased risk of oral and gastrointestinal candidiasis, candidemia and septicemia. Interactions between C. albicans and endogenous mucosal bacteria are important in understanding the mechanisms of invasive infection. We published a mouse intravenous chemotherapy model that recapitulates oral and intestinal mucositis, and myelosuppression in patients receiving 5-fluorouracil. We used this model to study the influence of C. albicans on the mucosal bacterial microbiome and compared global community changes in the oral and intestinal mucosa of the same mice. We validated 16S rRNA gene sequencing data by qPCR, in situ hybridization and culture approaches. Mice receiving both 5Fu and C. albicans had an endogenous bacterial overgrowth on the oral but not the small intestinal mucosa. C. albicans infection was associated with loss of mucosal bacterial diversity in both sites with indigenous Stenotrophomonas, Alphaproteobacteria and Enterococcus species dominating the small intestinal, and Enterococcus species dominating the oral mucosa. Both immunosuppression and Candida infection contributed to changes in the oral microbiota. Enterococci isolated from mice with oropharyngeal candidiasis were implicated in degrading the epithelial junction protein E-cadherin and increasing the permeability of the oral epithelial barrier in vitro. Importantly, depletion of these organisms with antibiotics in vivo attenuated oral mucosal E-cadherin degradation and C. albicans invasion without affecting fungal burdens, indicating that bacterial community changes represent overt dysbiosis. Our studies demonstrate a complex interaction between C. albicans, the resident mucosal bacterial microbiota and the host environment in pathogenesis. We shed significant new light on the role of C. albicans in shaping resident bacterial communities and driving mucosal dysbiosis.

Comparison of genotypes, antimicrobial resistance and virulence profiles of oral and non oral Enterococcus faecalis from Brazil, Japan and the United Kingdom

OBJECTIVES

To determine whether phenotypic and genotypic differences amongst isolates ofEnterococcus faecalis relate to geographical and clinical origin.

METHODS

E. faecalis from primary endodontic infections in Brazilian patients (n = 20), oral infections in UK patients (n = 10), and non-oral infections in Japanese patients (n = 9) were studied. In addition, 20 environmental vancomycin resistant Enterococcus faecalis (VRE) isolates from a UK hospital were analysed. For all isolates, polymerase chain reaction (PCR) was used to detect genes associated with antibiotic resistance and virulence, whilst randomly amplified polymorphic DNA-PCR (RAPD-PCR) was used to produce molecular profiles.

RESULTS

Gelatinase gene (gelE) was prevalent amongst isolates (77-100%) and for oral isolates, genes of aggregation substances (agg), immune evasion protein (esp), cytolysin (cylB), tetracycline resistance (tetM; tetL) and erythromycin resistance (ermB) were detected to varying extent. Japanese non-oral isolates had a similar genetic profile to oral isolates, but with higher prevalence of ermB and cylB. All VRE isolates were positive for gelE, esp, agg, vanA, ermB and tetM, 95% were positive for cylB and 17% positive for tetL. All isolates were negative for ermA, asa373 vanB, vanC1 and vanC2/3. RAPD-PCR revealed clustering of VRE isolates.

CONCLUSIONS

RAPD-PCR analysis revealed extensive genetic variability among the tested isolates. Oral isolates carried antibiotic resistance genes for tetracycline and whilst they possessed genes that could contribute to pathogenicity, these were detected at lower incidence compared with non-oral and VRE isolates. RAPD-PCR proved to be a useful approach to elucidate relatedness of disparate isolates.

Candida Interactions with the Oral Bacterial Microbiota

The human oral cavity is normally colonized by a wide range of microorganisms, including bacteria, fungi, Archaea, viruses, and protozoa. Within the different oral microenvironments these organisms are often found as part of highly organized microbial communities termed biofilms, which display consortial behavior. Formation and maintenance of these biofilms are highly dependent on the direct interactions between the different members of the microbiota, as well as on the released factors that influence the surrounding microbial populations. These complex biofilm dynamics influence oral health and disease. In the latest years there has been an increased recognition of the important role that interkingdom interactions, in particular those between fungi and bacteria, play within the oral cavity. Candida spp., and in particular C. albicans, are among the most important fungi colonizing the oral cavity of humans and have been found to participate in these complex microbial oral biofilms. C. albicans has been reported to interact with individual members of the oral bacterial microbiota, leading to either synergistic or antagonistic relationships. In this review we describe some of the better characterized interactions between Candida spp. and oral bacteria.

Tipping the Balance: C. albicans Adaptation in Polymicrobial Environments

Candida albicans is a pleiomorphic fungus which co-exists with commensal bacteria in mucosal and skin sites of mammalian hosts. It is also a major co-isolated organism from polymicrobial systemic infections, with high potential for morbidity or mortality in immunocompromised patients. Traditionally, resident mucosal bacteria have been thought to antagonize C. albicans in its ability to colonize or cause infection. However, recent investigations have revealed synergistic relationships with certain bacterial species that colonize the same mucosal sites with C. albicans. Such relationships broaden the research landscape in pathogenesis but also contribute to clinical challenges in the prevention or treatment of mucosal candidiasis. This review sheds light on interactions of C. albicans and mucosal bacteria, with special emphasis on the effects of the resident bacterial microbiota on C. albicans physiology as they relate to its adaptation in mucosal sites as a commensal colonizer or as a pathogenic organism.

Comparative genome analysis reveals key genetic factors associated with probiotic property in Enterococcus faecium strains

BACKGROUND

Enterococcus faecium though commensal in the human gut, few strains provide a beneficial effect to humans as probiotics while few are responsible for the nosocomial infection. Comparative genomics of E. faecium can decipher the genomic differences responsible for probiotic, pathogenic and non-pathogenic properties. In this study, we compared E. faecium strain 17OM39 with a marketed probiotic, non-pathogenic non-probiotic (NPNP) and pathogenic strains.

RESULTS

E. faecium 17OM39 was found to be closely related with marketed probiotic strain T110 based on core genome analysis. Strain 17OM39 was devoid of known vancomycin, tetracycline resistance and functional virulence genes. Moreover, E. faecium 17OM39 genome was found to be more stable due to the absence of frequently found transposable elements. Genes imparting beneficial functional properties were observed to be present in marketed probiotic T110 and 17OM39 strains. Genes associated with colonization and survival within gastrointestinal tract was also detected across all the strains.

CONCLUSIONS

Beyond shared genetic features; this study particularly identified genes that are responsible for imparting probiotic, non-pathogenic and pathogenic features to the strains of E. faecium. Higher genomic stability, absence of known virulence factors and antibiotic resistance genes and close genomic relatedness with marketed probiotics makes E. faecium 17OM39 a potential probiotic candidate. The work presented here demonstrates that comparative genome analyses can be applied to large numbers of genomes, to find potential probiotic candidates.

Quantification of carious pathogens in the interdental microbiota of young caries-free adults

Background

The majority of caries lesions in adults occur on the proximal tooth surfaces of the posterior teeth. A comprehensive study of the composition of the oral microbiota is fundamental for a better understanding of the etiology of interdental caries.

Methods

Twenty-five caries-free subjects (20–35 years old) were enrolled in the study. The interdental biofilm of four interdental sites were collected. The real-time polymerase chain reaction (PCR) methodology were used to quantify (i) the following bacteria: Streptococcus spp., Streptococcus mutans, Lactobacillus spp., Enterococcus spp., and Enterococcus faecalis; (ii) the fungus Candida albicans; and (iii) total bacteria.

Results

Streptococcus spp. was the most abundant species, followed by Lactobacillus spp. and Enterococcus spp. Streptococcus spp. and Lactobacillus spp. were detected at all tested sites and Enterococcus spp. at 99% of sites. S. mutans was detected at only 28% of the tested sites and C. albicans was detected at 11% of sites. E. faecalis was never detected. In 54.5% of the biofilm inhabited by C. albicans, S. mutans was present. Moreover, 28% of the ID sites co-expressed S. mutans and Lactobacillus spp. The studied pathogens were organized into two correlated groups of species. Strikingly, the fungus C. albicans and the bacteria Enterococcus spp. cluster together, whereas Streptococcus spp., S. mutans and Lactobacillus spp. form one distinct cluster.

Conclusion

The interdental biofilm of young caries-free adults is comprised of pathogens that are able to induce interproximal caries. That several of these pathogens are implicated in heart disease or other systemic diseases is an argument for the disruption of interdental biofilms using daily oral hygiene.

Emergent multisystemic Enterococcus infection threatens endangered Christmas Island reptile populations

Multisystemic infections with a morphologically unusual bacterium were first observed in captive critically endangered Lister’s geckos (Lepidodactylus listeri) on Christmas Island in October 2014. Since then the infection was identified in another captive critically endangered lizard species, the blue-tailed skink (Cryptoblepharus egeriae) and two species of invasive geckos; the four clawed gecko (Gehyra mutilata) and Asian house gecko (Hemidactylus frenatus), in a wide geographic range across the east side of the island. The Gram and periodic acid-Schiff positive cocci to diplococci have a propensity to form chains surrounded by a matrix, which ultrastructurally appears to be formed by fibrillar capsular projections. The bacterium was associated with severe and extensive replacement of tissues, but minimal host inflammatory response. Attempts to grow the organism in culture and in embryonated eggs were unsuccessful. Molecular characterisation of the organism placed it as a novel member of the genus Enterococcus. Disease Risk Analyses including this organism should now be factored into conservation management actions and island biosecurity.

Prevalence and Genetic Diversity of Enterococcus faecalis Isolates from Mineral Water and Spring Water in China

Enterococcus faecalis is an important opportunistic pathogen which is frequently detected in mineral water and spring water for human consumption and causes human urinary tract infections, endocarditis and neonatal sepsis. The aim of this study was to determine the prevalence, virulence genes, antimicrobial resistance and genetic diversity of E. faecalis from mineral water and spring water in China. Of 314 water samples collected from January 2013 to January 2014, 48 samples (15.3%) were contaminated E. faecalis. The highest contamination rate occurred in activated carbon filtered water of spring water (34.5%), followed by source water of spring water (32.3%) and source water of mineral water (6.4%). The virulence gene test of 58 E. faecalis isolates showed that the detection rates of asa1, ace, cylA, gelE and hyl were 79.3, 39.7, 0, 100, 0%, respectively. All 58 E. faecalis isolates were not resistant to 12 kinds of antibiotics (penicillin, ampicillin, linezolid, quinupristin/dalfopristin, vancomycin, gentamicin, streptomycin, ciprofloxacin, levofloxacin, norfloxacin, nitrofurantoin, and tetracycline). Enterobacterial repetitive intergenic consensus-PCR classified 58 isolates and three reference strains into nine clusters with a similarity of 75%. This study is the first to investigate the prevalence of E. faecalis in mineral water and spring water in China. The results of this study suggested that spring water could be potential vehicles for transmission of E. faecalis.

Assessment of virulence potential of uncharacterized Enterococcus faecalis strains using pan genomic approach - Identification of pathogen-specific and habitat-specific genes

Enterococcus faecalis, a leading nosocomial pathogen and yet a prominent member of gut microbiome, lacks clear demarcation between pathogenic and non-pathogenic strains at genome level. Here we present the comparative genome analysis of 36 E. faecalis strains with different pathogenic features and from different body-habitats. This study begins by addressing the genome dynamics, which shows that the pan-genome of E. faecalis is still open, though the core genome is nearly saturated. We identified eight uncharacterized strains as potential pathogens on the basis of their co-segregation with reported pathogens in gene presence-absence matrix and Pathogenicity Island (PAI) distribution. A ~7.4 kb genomic-cassette, which is itself a part of PAI, is found to exist in all reported and potential pathogens, but not in commensals and other uncharacterized strains. This region encodes four genes and among them, products of two hypothetical genes are predicted to be intrinsically disordered that may serve as novel targets for therapeutic measures. Exclusive existence of 215, 129, 4 and 1 genes in the blood, gastrointestinal tract, urogenital tract, oral cavity and lymph node derived E. faecalis genomes respectively suggests possible employment of distinct habitat-specific genetic strategies in the adaptation of E. faecalis in human host.

Enterococcal Infective Endocarditis following Periodontal Disease in Dogs

In humans, one of the major factors associated with infective endocarditis (IE) is the concurrent presence of periodontal disease (PD). However, in veterinary medicine, the relevance of PD in the evolution of dogs’ endocarditis remains poorly understood. In order to try to establish a correlation between mouth-associated Enterococcus spp. and infective endocarditis in dogs, the present study evaluated the presence and diversity of enterococci in the gum and heart of dogs with PD. Samples were collected during necropsy of 32 dogs with PD and visually diagnosed with IE, which died of natural causes or euthanasia. Enterococci were isolated, identified and further characterized by Pulsed-Field Gel Electrophoresis (PFGE); susceptibility to antimicrobial agents and pathogenicity potential was also evaluated. In seven sampled animals, PFGE-patterns, resistance and virulence profiles were found to be identical between mouth and heart enterococci obtained from the same dog, allowing the establishment of an association between enterococcal periodontal disease and endocarditis in dogs. These findings represent a crucial step towards understanding the pathogenesis of PD-driven IE, and constitute a major progress in veterinary medicine.

Enterococcus faecalis from Food, Clinical Specimens, and Oral Sites: Prevalence of Virulence Factors in Association with Biofilm Formation

Enterococci have gained significance as the cause of nosocomial infections; they occur as food contaminants and have also been linked to dental diseases. E. faecalis has a great potential to spread virulence as well as antibiotic resistance genes via horizontal gene transfer. The integration of food-borne enterococci into the oral biofilm in-vivo has been observed. Therefore, we investigated the virulence determinants and antibiotic resistance of 97 E. faecalis isolates from the oral cavity, food, and clinical specimens. In addition, phenotypic expression of gelatinase and cytolysin were tested, in-vitro biofilm formation was quantified and isolates were compared for strain relatedness via pulsed field gel electrophoresis (PFGE). Each isolate was found to possess two or more virulence genes, most frequently gelE, efaA, and asa1. Notably, plaque/saliva isolates possessed the highest abundance of virulence genes, the highest levels of phenotypic gelatinase and hemolysin activity and concurrently a high ability to form biofilm. The presence of asa1 was associated with biofilm formation. The biofilm formation capacity of clinical and plaque/saliva isolates was considerably higher than that of food isolates and they also showed similar antibiotic resistance patterns. These results indicate that the oral cavity can constitute a reservoir for virulent E. faecalis strains possessing antibiotic resistance traits and at the same time distinct biofilm formation capabilities facilitating exchange of genetic material.

Identification and characterization of vancomycin-resistant Enterococcus species frequently isolated from laboratory mice

To determine the prevalence of drug resistant bacteria colonizing laboratory mice, we isolated and characterized vancomycin-resistant Enterococcus species (VRE) from commercially available mice. A total of 24 VRE isolates were obtained from 19 of 21 mouse strains supplied by 4 commercial breeding companies. Of these, 19 isolates of E. gallinarum and 5 isolates of E. casseliflavus possessing the vanC1 and vanC2/3 genes intrinsically, exhibited intermediate resistance to vancomycin respectively. In addition, these isolates also exhibited diverse resistant patterns to erythromycin, tetracycline, and ciprofloxacin, whereas the use of antibiotics had not been undertaken in mouse strains tested in this study. Although 6 virulence-associated genes (ace, asa, cylA, efaA, esp, and gelE) and secretion of gelatinase and hemolysin were not detected in all isolates, 23 of 24 isolates including the isolates of E. casselifalvus secreted ATP into culture supernatants. Since secretion of ATP by bacteria resident in the intestinal tract modulates the local immune responses, the prevalence of ATP-secreting VRE in mice therefore needs to be considered in animal experiments that alter the gut microflora by use of antibiotics.

Prophages in enterococcal isolates from renal transplant recipients: renal failure etiologies promote selection of strains

Infections caused by commensal bacteria may be fatal for the patients under immunosuppressive therapy. This results also from difficulty in identification of high risk strains. Enterococcal infections are increasingly frequent but despite many studies on virulence traits, the difference between commensal and pathogenic strains remains unclear. Prophages are newly described as important elements in competition between strains during colonization, as well as pathogenicity of the strains. Here we evaluate a difference in presence of pp4, pp1, and pp7 prophages and ASA (aggregation substance) gene expression in enterococcal isolates from renal transplant recipients (RTx) with different etiology of the end-stage renal failure. Prophages sequence was screened by PCR in strains of Enterococcus faecalis isolated from urine and feces of 19 RTx hospitalized at Medical University of Gdansk and 18 healthy volunteers. FLOW-FISH method with use of linear locked nucleic acid (LNA) probe was used to assess the ASA gene expression. Additionally, ability of biofilm formation was screened by crystal violet staining method. Presence of prophages was more frequent in fecal isolates from immunocompromised patients than in isolates from healthy volunteers. Additionally, both composition of prophages and ASA gene expression were related to the etiology of renal disease.

Dicationic imidazolium-based ionic liquids: a new strategy for non-toxic and antimicrobial materials

Dicationic imidazolium-based ILs: a potent strategy for applications requiring non-toxic materials with antimicrobial activity.

Presence of virulence factors in Enterococcus faecalis and Enterococcus faecium susceptible and resistant to vancomycin

Despite the increasing importance of Enterococcus as opportunistic pathogens, their virulence factors are still poorly understood. This study determines the frequency of virulence factors in clinical and commensal Enterococcus isolates from inpatients in Porto Alegre, Brazil. Fifty Enterococcus isolates were analysed and the presence of the gelE, asa1 and esp genes was determined. Gelatinase activity and biofilm formation were also tested. The clonal relationships among the isolates were evaluated using pulsed-field gel electrophoresis. The asa1, gelE and esp genes were identified in 38%, 60% and 76% of all isolates, respectively. The first two genes were more prevalent in Enterococcus faecalis than in Enterococcus faecium, as was biofilm formation, which was associated with gelE and asa1 genes, but not with the esp gene. The presence of gelE and the activity of gelatinase were not fully concordant. No relationship was observed among any virulence factors and specific subclones of E. faecalis or E. faecium resistant to vancomycin. In conclusion, E. faecalis and E. faecium isolates showed significantly different patterns of virulence determinants. Neither the source of isolation nor the clonal relationship or vancomycin resistance influenced their distribution.

Antimicrobial resistance and virulence traits of Enterococcus faecalis from primary endodontic infections

OBJECTIVES

To determine the phenotypic and molecular characteristics of Enterococcus faecalis recovered from primary endodontic infections in Brazilian patients.

METHODS

Twenty isolates of E. faecalis recovered from 43 Brazilian patients with primary endodontic infections were identified by biochemical profiling (API20Strep) and 16S rDNA sequencing. Antimicrobial susceptibility was ascertained by agar dilution, using the recommended protocol of the Clinical and Laboratory Standards Institute (CLSI). PCR with validated primers was used to detect genes associated with antibiotic resistance and specific virulence factors.

RESULTS

All isolates were deemed susceptible to penicillin G, erythromycin and vancomycin. However, nine isolates had a minimum inhibitory concentration of 4μg/mL to vancomycin (the resistance breakpoint). Fourteen isolates (70% of isolates) were also resistant to tetracycline with MICs of >64μg/mL. PCR products for tetracycline resistance genes were detected in test isolates, while erythromycin and vancomycin resistance genes were not evident. Gelatinase, aggregation substance and enteroccocal surface protein genes were detected in 20, 18 and 12 isolates, respectively.

CONCLUSIONS

Endodontic E. faecalis isolates exhibit high level of resistance to tetracycline, an antibiotic that has use in local treatment of dental infections. This opens up a much-needed debate on the role and efficacy of this antibiotic for oral infections. Furthermore, these isolates were shown to possess genes that could contribute to pathogenicity in the pulp cavity.

Photodynamic and antibiotic therapy impair the pathogenesis of Enterococcus faecium in a whole animal insect model

Enterococcus faecium has emerged as one of the most important pathogens in healthcare-associated infections worldwide due to its intrinsic and acquired resistance to many antibiotics, including vancomycin. Antimicrobial photodynamic therapy (aPDT) is an alternative therapeutic platform that is currently under investigation for the control and treatment of infections. PDT is based on the use of photoactive dye molecules, widely known as photosensitizer (PS). PS, upon irradiation with visible light, produces reactive oxygen species that can destroy lipids and proteins causing cell death. We employed Galleria mellonella (the greater wax moth) caterpillar fatally infected with E. faecium to develop an invertebrate host model system that can be used to study the antimicrobial PDT (alone or combined with antibiotics). In the establishment of infection by E. faecium in G. mellonella, we found that the G. mellonella death rate was dependent on the number of bacterial cells injected into the insect hemocoel and all E. faecium strains tested were capable of infecting and killing G. mellonella. Antibiotic treatment with ampicillin, gentamicin or the combination of ampicillin and gentamicin prolonged caterpillar survival infected by E. faecium (P = 0.0003, P = 0.0001 and P = 0.0001, respectively). In the study of antimicrobial PDT, we verified that methylene blue (MB) injected into the insect followed by whole body illumination prolonged the caterpillar survival (P = 0.0192). Interestingly, combination therapy of larvae infected with vancomycin-resistant E. faecium, with antimicrobial PDT followed by vancomycin, significantly prolonged the survival of the caterpillars when compared to either antimicrobial PDT (P = 0.0095) or vancomycin treatment alone (P = 0.0025), suggesting that the aPDT made the vancomycin resistant E. faecium strain more susceptible to vancomycin action. In summary, G. mellonella provides an invertebrate model host to study the antimicrobial PDT and to explore combinatorial aPDT-based treatments.