Mixed species biofilms of Candida albicans and Staphylococcus epidermidis

Competitive inter-species interactions underlie the increased antimicrobial tolerance in multispecies brewery biofilms

Genetic diversity often enhances the tolerance of microbial communities against antimicrobial treatment. However the sociobiology underlying this antimicrobial tolerance remains largely unexplored. Here we analyze how inter-species interactions can increase antimicrobial tolerance. We apply our approach to 17 industrially relevant multispecies biofilm models, based on species isolated from 58 contaminating biofilms in three breweries. Sulfathiazole was used as antimicrobial agent because it showed the highest activity out of 22 biofilm inhibitors tested. Our analysis reveals that competitive interactions dominate among species within brewery biofilms. We show that antimicrobial treatment can reduce the level of competition and therefore cause a subset of species to bloom. The result is a 1.2-42.7-fold lower percentage inhibition of these species and increased overall tolerance. In addition, we show that the presence of Raoultella can also directly enhance the inherent tolerance of Pseudomonas to antimicrobial treatment, either because the species protect each other or because they induce specific tolerance phenotypes as a response to competitors. Overall, our study emphasizes that the dominance of competitive interactions is central to the enhanced antimicrobial tolerance of the multispecies biofilms, and that the activity of antimicrobials against multispecies biofilms cannot be predicted based on their effect against monocultures.

The innovation of cryo-SEM freeze-fracturing methodology demonstrated on high pressure frozen biofilm

In this study we present an innovative method for the preparation of fully hydrated samples of microbial biofilms of cultures Staphylococcus epidermidis, Candida parapsilosis and Candida albicans. Cryo-scanning electron microscopy (cryo-SEM) and high-pressure freezing (HPF) rank among cutting edge techniques in the electron microscopy of hydrated samples such as biofilms. However, the combination of these techniques is not always easily applicable. Therefore, we present a method of combining high-pressure freezing using EM PACT2 (Leica Microsystems), which fixes hydrated samples on small sapphire discs, with a high resolution SEM equipped with the widely used cryo-preparation system ALTO 2500 (Gatan). Using a holder developed in house, a freeze-fracturing technique was applied to image and investigate microbial cultures cultivated on the sapphire discs. In our experiments, we focused on the ultrastructure of the extracellular matrix produced during cultivation and the relationships among microbial cells in the biofilm. The main goal of our investigations was the detailed visualization of areas of the biofilm where the microbial cells adhere to the substrate/surface. We show the feasibility of this technique, which is clearly demonstrated in experiments with various freeze-etching times.

Bacterial-derived exopolysaccharides enhance antifungal drug tolerance in a cross-kingdom oral biofilm

Fungal-bacterial interactions generate unique biofilms that cause many infections in humans. Candida albicans interact with Streptococcus mutans in dental biofilms associated with severe childhood tooth-decay, a prevalent pediatric oral disease. Current modalities are ineffective and primarily based on antimicrobial monotherapies despite the polymicrobial nature of the infection. Here, we show that the combination of clinically used topical antifungal fluconazole with povidone iodine (PI) can completely suppress C. albicans carriage and mixed-biofilm formation without increasing bacterial killing activity in vivo. We unexpectedly found that the inclusion of PI enhanced fluconazole efficacy by potently disrupting the assembly of a protective bacterial exopolysaccharide (EPS) matrix through inhibition of α-glucan synthesis by S. mutans exoenzyme (GtfB) bound on the fungal surface. Further analyses revealed that the EPS produced in situ directly bind and sequester fluconazole, reducing uptake and intracellular transportation of the drug. Conversely, inhibition of GtfB activity by PI, enzymatic degradation of the α-glucan matrix or co-culturing with gtfB-defective S. mutans re-established antifungal susceptibility. Hence, topical antifungal has limitations in mixed oral biofilms due to enhanced C. albicans tolerance to fluconazole afforded by the shielding effect of bacterial-derived EPS. The data provide new insights for treatment of C. albicans in cross-kingdom biofilms, indicating that EPS inhibitors may be required for enhanced killing efficacy and optimal anti-biofilm activity.

Role of extracellular polymeric substances in polymicrobial biofilm infections of Staphylococcus epidermidis and Candida albicans modelled in the nematode Caenorhabditis elegans

Biofilms are formed by communities of microorganisms living in a self-produced extracellular polymeric matrix attached to a surface. When living in a biofilm microorganisms change phenotype and thus are less susceptible to antibiotic treatment and biofilm infections can become severe. The aim of this study was to determine if the presence of multikingdom microorganisms alters the virulence of a biofilm infection in a host organism. The coexistence of Candida albicans and Staphylococcus epidermidis in biofilm was examined in the nematode model Caenorhabditis elegans. It was evaluated if the hyphal form of C. albicans and extracellular polymeric substances (EPS) formed by S. epidermidis increases biofilm virulence. Survival assays were performed, where C. elegans nematodes were exposed to S. epidermidis and C. albicans. Single inoculation assays showed a decreased survival rate after 2 days following exposure, while dual inoculation assays showed that a clinical S. epidermidis strain together with C. albicans significantly increased the virulence and decreased nematode survival. EPS seem to interfere with the bacterial attachment to hyphae, since the EPS overproducing S. epidermidis strain was most virulent. The clinical S. epidermidis paired with C. albicans led to a severe infection in the nematodes resulting in reduced survival.

Candida Biofilms: Threats, Challenges, and Promising Strategies

Candida species are fungal pathogens known for their ability to cause superficial and systemic infections in the human host. These pathogens are able to persist inside the host due to the development of pathogenicity and multidrug resistance traits, often leading to the failure of therapeutic strategies. One specific feature of Candida species pathogenicity is their ability to form biofilms, which protects them from external factors such as host immune system defenses and antifungal drugs. This review focuses on the current threats and challenges when dealing with biofilms formed by Candida albicans, Candida glabrata, Candida tropicalis, and Candida parapsilosis, highlighting the differences between the four species. Biofilm characteristics depend on the ability of each species to produce extracellular polymeric substances (EPS) and display dimorphic growth, but also on the biofilm substratum, carbon source availability and other factors. Additionally, the transcriptional control over processes like adhesion, biofilm formation, filamentation, and EPS production displays great complexity and diversity within pathogenic yeasts of the Candida genus. These differences not only have implications in the persistence of colonization and infections but also on antifungal resistance typically found in Candida biofilm cells, potentiated by EPS, that functions as a barrier to drug diffusion, and by the overexpression of drug resistance transporters. The ability to interact with different species in in vivo Candida biofilms is also a key factor to consider when dealing with this problem. Despite many challenges, the most promising strategies that are currently available or under development to limit biofilm formation or to eradicate mature biofilms are discussed.

Molecular mechanisms of biofilm-based antibiotic resistance and tolerance in pathogenic bacteria

Biofilms are surface-attached groups of microbial cells encased in an extracellular matrix that are significantly less susceptible to antimicrobial agents than non-adherent, planktonic cells. Biofilm-based infections are, as a result, extremely difficult to cure. A wide range of molecular mechanisms contribute to the high degree of recalcitrance that is characteristic of biofilm communities. These mechanisms include, among others, interaction of antimicrobials with biofilm matrix components, reduced growth rates and the various actions of specific genetic determinants of antibiotic resistance and tolerance. Alone, each of these mechanisms only partially accounts for the increased antimicrobial recalcitrance observed in biofilms. Acting in concert, however, these defences help to ensure the survival of biofilm cells in the face of even the most aggressive antimicrobial treatment regimens. This review summarises both historical and recent scientific data in support of the known biofilm resistance and tolerance mechanisms. Additionally, suggestions for future work in the field are provided.

The importance of fungal pathogens and antifungal coatings in medical device infections

In recent years, increasing evidence has been collated on the contributions of fungal species, particularly Candida, to medical device infections. Fungal species can form biofilms by themselves or by participating in polymicrobial biofilms with bacteria. Thus, there is a clear need for effective preventative measures, such as thin coatings that can be applied onto medical devices to stop the attachment, proliferation, and formation of device-associated biofilms. However, fungi being eukaryotes, the challenge is greater than for bacterial infections because antifungal agents are often toxic towards eukaryotic host cells. Whilst there is extensive literature on antibacterial coatings, a far lesser body of literature exists on surfaces or coatings that prevent attachment and biofilm formation on medical devices by fungal pathogens. Here we review strategies for the design and fabrication of medical devices with antifungal surfaces. We also survey the microbiology literature on fundamental mechanisms by which fungi attach and spread on natural and synthetic surfaces. Research in this field requires close collaboration between biomaterials scientists, microbiologists and clinicians; we consider progress in the molecular understanding of fungal recognition of, and attachment to, suitable surfaces, and of ensuing metabolic changes, to be essential for designing rational approaches towards effective antifungal coatings, rather than empirical trial of coatings.

Modulation of Staphylococcus aureus Response to Antimicrobials by the Candida albicans Quorum Sensing Molecule Farnesol

In microbial biofilms, microorganisms utilize secreted signaling chemical molecules to coordinate their collective behavior. Farnesol is a quorum sensing molecule secreted by the fungal species Candida albicans and shown to play a central physiological role during fungal biofilm growth. Our pervious in vitro and in vivo studies characterized an intricate interaction between C. albicans and the bacterial pathogen Staphylococcus aureus, as these species coexist in biofilm. In this study, we aimed to investigate the impact of farnesol on S. aureus survival, biofilm formation, and response to antimicrobials. The results demonstrated that in the presence of exogenously supplemented farnesol or farnesol secreted by C. albicans in biofilm, S. aureus exhibited significantly enhanced tolerance to antimicrobials. By using gene expression studies, S. aureus mutant strains, and chemical inhibitors, the mechanism for the enhanced tolerance was attributed to upregulation of drug efflux pumps. Importantly, we showed that sequential exposure of S. aureus to farnesol generated a phenotype of high resistance to antimicrobials. Based on the presence of intracellular reactive oxygen species upon farnesol exposure, we hypothesize that antimicrobial tolerance in S. aureus may be mediated by farnesol-induced oxidative stress triggering the upregulation of efflux pumps, as part of a general stress response system. Hence, in mixed biofilms, C. albicans may influence the pathogenicity of S. aureus through acquisition of a drug-tolerant phenotype, with important therapeutic implications. Understanding interspecies signaling in polymicrobial biofilms and the specific drug resistance responses to secreted molecules may lead to the identification of novel targets for drug development.

Proteus vulgaris and Proteus mirabilis Decrease Candida albicans Biofilm Formation by Suppressing Morphological Transition to Its Hyphal Form

PURPOSE

Candida albicans (C. albicans) and Proteus species are causative agents in a variety of opportunistic nosocomial infections, and their ability to form biofilms is known to be a virulence factor. In this study, the influence of co-cultivation with Proteus vulgaris (P. vulgaris) and Proteus mirabilis (P. mirabilis) on C. albicans biofilm formation and its underlying mechanisms were examined.

MATERIALS AND METHODS

XTT reduction assays were adopted to measure biofilm formation, and viable colony counts were performed to quantify yeast growth. Real-time reverse transcriptase polymerase chain reaction was used to evaluate the expression of yeast-specific genes (rhd1 and rbe1), filament formation inhibiting genes (tup1 and nrg1), and hyphae-related genes (als3, ece1, hwp1, and sap5).

RESULTS

Candida biofilm formation was markedly inhibited by treatment with either living or heat-killed P. vulgaris and P. mirabilis. Proteus-cultured supernatant also inhibited Candida biofilm formation. Likewise, treatment with live P. vulgaris or P. mirabilis or with Proteus-cultured supernatant decreased expression of hyphae-related C. albicans genes, while the expression of yeast-specific genes and the filament formation inhibiting genes of C. albicans were increased. Heat-killed P. vulgaris and P. mirabilis treatment, however, did not affect the expression of C. albicans morphology-related genes.

CONCLUSION

These results suggest that secretory products from P. vulgaris and P. mirabilis regulate the expression of genes related to morphologic changes in C. albicans such that transition from the yeast form to the hyphal form can be inhibited.

An Update on Candida tropicalis Based on Basic and Clinical Approaches

Candida tropicalis has emerged as one of the most important Candida species. It has been widely considered the second most virulent Candida species, only preceded by C. albicans. Besides, this species has been recognized as a very strong biofilm producer, surpassing C. albicans in most of the studies. In addition, it produces a wide range of other virulence factors, including: adhesion to buccal epithelial and endothelial cells; the secretion of lytic enzymes, such as proteinases, phospholipases, and hemolysins, bud-to-hyphae transition (also called morphogenesis) and the phenomenon called phenotypic switching. This is a species very closely related to C. albicans and has been easily identified with both phenotypic and molecular methods. In addition, no cryptic sibling species were yet described in the literature, what is contradictory to some other medically important Candida species. C. tropicalis is a clinically relevant species and may be the second or third etiological agent of candidemia, specifically in Latin American countries and Asia. Antifungal resistance to the azoles, polyenes, and echinocandins has already been described. Apart from all these characteristics, C. tropicalis has been considered an osmotolerant microorganism and this ability to survive to high salt concentration may be important for fungal persistence in saline environments. This physiological characteristic makes this species suitable for use in biotechnology processes. Here we describe an update of C. tropicalis, focusing on all these previously mentioned subjects.

Efficacy of carboxymethyl chitosan against Candida tropicalis and Staphylococcus epidermidis monomicrobial and polymicrobial biofilms

Polymicrobial biofilms with fungi and bacteria are the leading cause for the failure of medical devices and related infections. In this study, antibiofilm activities of carboxymethyl chitosan (CM-chitosan) on monomicrobial and polymicrobial biofilms of Staphylococcus epidermidis and Candida tropicalis in vitro were evaluated. CM-chitosan was effective as a sole agent, inhibiting both monomicrobial and polymicrobial biofilms in microplates and also on the silicone surface in short- and long-term periods. Biofilm architecture was investigated by scanning electron microscopy and confocal laser scanning microscopy was used to examine living/dead organisms within biofilm. CM-chitosan inhibited planktonic growth as well as adhesion. Further biofilm formation was inhibited by CM-chitosan added at 90min or 12h after biofilm initiation. CM-chitosan may serve as a possible antibiofilm agent to limit monomicrobial and polymicrobial biofilm.

Heavy metal tolerance and removal potential in mixed-species biofilm

The aim of the study was to examine heavy metal tolerance (Cd²⁺, Zn²⁺, Ni²⁺ and Cu²⁺) of single- and mixed-species biofilms (Rhodotorula mucilaginosa and Escherichia coli) and to determine metal removal efficiency (Cd²⁺, Zn²⁺, Ni²⁺, Cu²⁺, Pb²⁺ and Hg²⁺). Metal tolerance was quantified by crystal violet assay and results were confirmed by fluorescence microscopy. Metal removal efficiency was determined by batch biosorption assay. The tolerance of the mixed-species biofilm was higher than the single-species biofilms. Single- and mixed-species biofilms showed the highest sensitivity in the presence of Cu²⁺ (E. coli-MIC 4 mg/ml, R. mucilaginosa-MIC 8 mg/ml, R. mucilaginosa/E. coli-MIC 64 mg/ml), while the highest tolerance was observed in the presence of Zn²⁺ (E. coli-MIC 80 mg/ml, R. mucilaginosa-MIC 161 mg/ml, R. mucilaginosa-E. coli-MIC 322 mg/ml). The mixed-species biofilm exhibited better efficiency in removal of all tested metals than single-species biofilms. The highest efficiency in Cd²⁺ removal was shown by the E. coli biofilm (94.85%) and R. mucilaginosa biofilm (97.85%), individually. The highest efficiency in Cu²⁺ (99.88%), Zn²⁺ (99.26%) and Pb²⁺ (99.52%) removal was shown by the mixed-species biofilm. Metal removal efficiency was in the range of 81.56%-97.85% for the single- and 94.99%-99.88% for the mixed-species biofilm.

Staged Reimplantation of a Total Hip Prosthesis After Co-infection with Candida tropicalis and Staphylococcus haemolyticus: A Case Report

Fungal prosthetic joint infection is a rare complication in total joint arthroplasty. There are no established guidelines for management of these infections. We present a case of a 53-year-old male with a hip joint prosthesis co-infected with Candida tropicalis and Staphylococcus haemolyticus. A two-stage exchange arthroplasty was performed. The patient underwent implant removal, debridement, irrigation with saline solution and application of cement spacer impregnated with vancomycin followed by aggressive antimicrobial treatment in first stage. Complete eradication of infection was demonstrated by negative culture of sonicated cement spacer fluid and negative 16S rRNA and 18S rRNA gene PCR of sonicate fluid, synovial fluid and periprosthetic tissue samples. He underwent second-stage revision hip arthroplasty after 9 months of the first stage. At the latest follow-up, there was no evidence of recurrence of infection. This case illustrates the utility of sonication of biomaterials and molecular techniques for microbiological confirmation of absence of infection in staged surgeries which is required for a successful outcome.

Transcriptional Profiling of C. albicans in a Two Species Biofilm with Rothia dentocariosa

Biofilms on silicone rubber voice prostheses are the major cause for frequent failure and replacement of these devices. The presence of both bacterial and yeast strains has been suggested to be crucial for the development of voice prosthetic biofilms. Polymicrobial biofilms that include Candida albicans and Rothia dentocariosa are the leading cause of voice prosthesis failure. An in vitro biofilm comprising these two organisms was developed on silicone rubber, a material used for Groningen button voice prosthesis. We found that this biofilm environment was not conducive for C. albicans growth or differentiation. Global transcriptional analyses of C. albicans biofilm cells grown with R. dentocariosa revealed that genes with functions related to cell cycle progression and hyphal development were repressed >2-fold. The mixed species biofilms were more compact and less robust compared to C. albicans mono-species biofilms, even when developed under conditions of continuous nutrient flow. Under these conditions R. dentocariosa also significantly inhibited C. albicans biofilm dispersal. Preferential adherence of R. dentocariosa to candidal hyphae was mediated by the adhesin Als3.

Candida-Bacteria Interactions: Their Impact on Human Disease

Candida species are the most common infectious fungal species in humans; out of the approximately 150 known species, Candida albicans is the leading pathogenic species, largely affecting immunocompromised individuals. Apart from its role as the primary etiology for various types of candidiasis, C. albicans is known to contribute to polymicrobial infections. Polymicrobial interactions, particularly between C. albicans and bacterial species, have gained recent interest in which polymicrobial biofilm virulence mechanisms have been studied including adhesion, invasion, quorum sensing, and development of antimicrobial resistance. These trans-kingdom interactions, either synergistic or antagonistic, may help modulate the virulence and pathogenicity of both Candida and bacteria while uniquely impacting the pathogen-host immune response. As antibiotic and antifungal resistance increases, there is a great need to explore the intermicrobial cross-talk with a focus on the treatment of Candida-associated polymicrobial infections. This article explores the current literature on the interactions between Candida and clinically important bacteria and evaluates these interactions in the context of pathogenesis, diagnosis, and disease management.

Should the biofilm mode of life be taken into consideration for microbial biocontrol agents?

Almost one‐third of crop yields are lost every year due to microbial alterations and diseases. The main control strategy to limit these losses is the use of an array of chemicals active against spoilage and unwanted pathogenic microorganisms. Their massive use has led to extensive environmental pollution, human poisoning and a variety of diseases. An emerging alternative to this chemical approach is the use of microbial biocontrol agents. Biopesticides have been used with success in several fields, but a better understanding of their mode of action is necessary to better control their activity and increase their use. Very few studies have considered that biofilms are the preferred mode of life of microorganisms in the target agricultural biotopes. Increasing evidence shows that the spatial organization of microbial communities on crop surfaces may drive important bioprotection mechanisms. The aim of this review is to summarize the evidence of biofilm formation by biocontrol agents on crops and discuss how this surface‐associated mode of life may influence their biology and interactions with other microorganisms and the host and, finally, their overall beneficial activity.

Surface modification strategies for combating catheter-related complications: recent advances and challenges

This review summarizes the progress made in addressing bacterial colonization and other surface-related complications arising from catheter use.

The Correlation Between Biofilm Production and Catheter-Related Bloodstream Infections Sustained by Candida. A Case Control Study

Biofilm forming capacity of yeasts colonizing the intravenous devices is considered a key factor involved in the pathogenesis of Candida catheter-related bloodstream infections (CCRBSI). The biofilm production of strains of Candida spp. isolated both from the CVC and from the blood of patients with CCRBSI was compared to that of strains isolated from patients not having CCRBSI. Results, expressed in terms of Biofilm Index (BI), revealed that biofilm-producing strains were isolated in the CCRBSI group with a frequency significantly higher than in the non-CCRBSI group (χ² = 4.25, p = 0.03). The species more frequently cultured was C. parapsilosis complex (including C. parapsilosis sensu stricto, C. orthopsilosis and C. metapsilosis). When this species was isolated from the CVC tip cultures of the CCRBSI group it showed BIs significantly (p = 0.05) higher than those found in the non-CCRBSI group. All the strains of C. tropicalis isolated from the CCRBSI group produced biofilm. Instead most of the isolates of C. glabrata were non-producers. The cumulative BI of non-albicans Candida strains isolated from CCRBSI patients was significantly higher than that of non-albicans strains cultured from patients non-CCRBSI (χ² = 6.91; p = 0.008). C. albicans was a biofilm producer both in the CCRBSI and in the non-CCRBSI group. When isolated from the blood it showed enhanced biofilm production in the CCRBSI group only, while when colonizing the CVC it displayed high BIs both in the CCRBSI group and in non-CCRBSI group. Our data seem to indicate that the biofilm production capacity should be considered in the clinical management of CCRBSI.

3-Amino-4-aminoximidofurazan derivatives: small molecules possessing antimicrobial and antibiofilm activity against Staphylococcus aureus and Pseudomonas aeruginosa

AIM

The therapeutic treatment of microbial infections involving biofilm becomes quite challenging because of its increasing antibiotic resistance capacities. Towards this direction, in the present study we have evaluated the antibiofilm property of synthesized 3-amino-4-aminoximidofurazan compounds having polyamine skeleton. These derivatives were synthesized by incorporating furazan and biguanide moieties.

METHODS AND RESULTS

Different 3-amino-4-aminoximidofurazan derivatives (PI1-4) were synthesized via protic acid catalysis and subsequently characterized by (1) H NMR and (13) C NMR spectra, recorded at 400 and 100 MHz respectively. We have tested the antimicrobial and antibiofilm activities of these synthetic derivatives (PI1-4) against both Staphylococcus aureus and Pseudomonas aeruginosa. The compounds so tested were also compared with standard antibiotics namely Tobramycin (Ps. aeruginosa) and Azithromycin (Staph. aureus) which were used as a positive control in all experimental sets. All these compounds (PI1-4) exhibited moderate to significant antimicrobial activities against both micro-organisms wherein compound PI3 showed maximum activity. Biofilm inhibition of both micro-organisms was then evaluated by crystal violet and safranin staining, estimation of biofilm total protein and microscopy methods using sub-MIC dose of these compounds. Results showed that all compounds executed anti biofilm activity against both Staph. aureus and Ps. aeruginosa wherein compound PI3 exhibited maximum activity. In relation with microbial biofilm inhibition, we have observed reduction in bacterial motility, proteolytic activity and secreted exo-polysaccharide (EPS) from both Staph. aureus and Ps. aeruginosa when they were grown in presence of these compounds. While addressing the issue of toxicity on host, we have observed that these molecules exhibited minimum level of R.B.C degradation.

CONCLUSION

These findings establish the antibacterial and anti biofilm properties of 3-amino-4-aminoximidofurazan derivatives (PI1-4).

SIGNIFICANCE AND IMPACT OF THE STUDY

Therefore, our current findings demonstrate that 3-amino-4-aminoximidofurazan derivatives (PI1-4) may hold promise to be effective biofilm and microbial inhibitors that may be clinically significant.

A post-planktonic era of in vitro infectious models: issues and changes addressed by a clinically relevant wound like media

Medical science is pitted against an ever-increasing rise in antibiotic tolerant microorganisms. Concurrently, during the past decade, biofilms have garnered much attention within research and clinical practice. Although the significance of clinical biofilms is becoming very apparent, current methods for diagnostics and direction of therapy plans in many hospitals do not reflect this knowledge; with many of the present tools proving to be inadequate for accurately mimicking the biofilm phenomenon. Based on current findings, we address some of the fundamental issues overlooked by clinical labs: the paradigm shifts that need to occur in assessing chronic wounds; better simulation of physiological conditions in vitro; and the importance of incorporating polymicrobial populations into biofilm models. In addition, this review considers using a biofilm relevant in vitro model for cultivating and determining the antibiotic tolerance and susceptibility of microorganisms associated with chronic wounds. This model presents itself as a highly rapid and functional tool that can be utilized by hospitals in an aim to improve bedside treatments.

Activity of novel inhibitors of Staphylococcus aureus biofilms

Staphylococcus aureus is one of the most important pathogens causing chronic biofilm infections. These are becoming more difficult to treat owing to drug resistance, particularly because S. aureus biofilms limit the efficacy of antimicrobial agents, leading to high morbidity and mortality. In the present study, we screened for inhibitors of S. aureus biofilm formation using a natural product library from the Korea Chemical Bank (KCB). Screening by crystal violet-based biomass staining assay identified hit compounds. Further examination of antibiofilm properties of these compounds was conducted and led to the identification of celastrol and telithromycin. In vitro, both celastrol and telithromycin were toxic to planktonic S. aureus and also active against a clinical methicillin-resistant S. aureus (MRSA) isolate. The effect of the compounds on preformed biofilms of clinical MRSA isolates was evaluated by confocal laser scanning microscopy (CLSM), which revealed the absence of typical biofilm architecture. In addition, celastrol and telithromycin inhibited the production of extracellular protein at selected sub-MIC concentrations, which revealed the reduced extracellular polymeric substance (EPS) secretion. Celastrol exhibited greater cytotoxicity than telithromycin. These data suggest that the hit compounds, especially telithromycin, could be considered novel inhibitors of S. aureus biofilm. Although the mechanisms of the effects on S. aureus biofilms are not fully understood, our data suggest that telithromycin could be a useful adjuvant therapeutic agent for S. aureus biofilm-related infections.

A novel targeted/untargeted GC-Orbitrap metabolomics methodology applied to Candida albicans and Staphylococcus aureus biofilms

INTRODUCTION

Combined infections from Candida albicans and Staphylococcus aureus are a leading cause of death in the developed world. Evidence suggests that Candida enhances the virulence of Staphylococcus-hyphae penetrate through tissue barriers, while S. aureus tightly associates with the hyphae to obtain entry to the host organism. Indeed, in a biofilm state, C. albicans enhances the antimicrobial resistance characteristics of S. aureus. The association of these microorganisms is also associated with significantly increased morbidity and mortality. Due to this tight association we hypothesised that metabolic effects were also in evidence.

OBJECTIVES

To explore the interaction, we used a novel GC-Orbitrap-based mass spectrometer, the Q Exactive GC, which combines the high peak capacity and chromatographic resolution of gas chromatography with the sub-ppm mass accuracy of an Orbitrap system. This allows the capability to leverage the widely available electron ionisation libraries for untargeted applications, along with expanding accurate mass libraries and targeted matches based around authentic standards.

METHODS

Optimised C. albicans and S. aureus mono- and co-cultured biofilms were analysed using the new instrument in addition to the fresh and spent bacterial growth media.

RESULTS

The targeted analysis experiment was based around 36 sugars and sugar phosphates, 22 amino acids and five organic acids. Untargeted analysis resulted in the detection of 465 features from fresh and spent medium and 405 from biofilm samples. Three significantly changing compounds that matched to high scoring library fragment patterns were chosen for validation.

CONCLUSION

Evaluation of the results demonstrates that the Q Exactive GC is suitable for metabolomics analysis using a targeted/untargeted methodology. Many of the results were as expected: e.g. rapid consumption of glucose and fructose from the medium regardless of the cell type. Modulation of sugar-phosphate levels also suggest that the pentose phosphate pathway could be enhanced in the cells from co-cultured biofilms. Untargeted metabolomics results suggested significant production of cell-wall biosynthesis components and the consumption of non-proteinaceous amino-acids.

The mycobiome of root canal infections is correlated to the bacteriome

Objectives

Bacterial infection of the root canal system causes apical periodontitis. Less is known about the role of fungi in these infections. This study aimed to assess the fungal prevalence, abundance, and diversity of root canal infections, as well as the relation between fungi and bacteria present in different parts of the root canal.

Materials and methods

Twenty-six teeth with primary apical periodontitis were extracted, split in apical and coronal root segments, and cryo-pulverized. Bacteriome profiles of 23 teeth were analyzed based on the V3-V4 hypervariable region of the 16S ribosomal RNA gene. Mycobiome profiles of six teeth were analyzed based on the internal transcribed spacer (ITS) 1 or ITS2 region. Samples were sequenced on the Illumina MiSeq platform.

Results

A total of 338 bacterial operational taxonomic units (OTUs), 28 ITS1 OTUs, and 24 ITS2 OTUs were identified. Candida and Malassezia were the most frequently identified fungi. No differences could be found between the bacteriome and mycobiome profiles of the apical and coronal root segments. The bacteriome of fungi-positive root segments contained more Actinomyces, Bifidobacterium, four different Lactobacillus OTUs, Propionibacterium, and Streptococcus. A Spearman correlation matrix between bacteriomes and mycobiomes identified no correlations, but separate clusters could be observed.

Conclusions

A considerable proportion of the root canal infections contain fungi, although fungal diversity is limited. However, when fungi are present, the composition of the bacteriome is clearly different.

Clinical relevance

Interaction between bacteria and fungi in root canal infections may complicate the infection and require alternative treatment strategies.

Electronic supplementary material

The online version of this article (doi:10.1007/s00784-016-1980-3) contains supplementary material, which is available to authorized users.

Modulation of the Substitution Pattern of 5-Aryl-2-Aminoimidazoles Allows Fine-Tuning of Their Antibiofilm Activity Spectrum and Toxicity

We previously synthesized several series of compounds, based on the 5-aryl-2-aminoimidazole scaffold, that showed activity preventing the formation of Salmonella enterica serovar Typhimurium and Pseudomonas aeruginosa biofilms. Here, we further studied the activity spectrum of a number of the most active N1- and 2N-substituted 5-aryl-2-aminoimidazoles against a broad panel of biofilms formed by monospecies and mixed species of bacteria and fungi. An N1-substituted compound showed very strong activity against the biofilms formed by Gram-negative and Gram-positive bacteria and the fungus Candida albicans but was previously shown to be toxic against various eukaryotic cell lines. In contrast, 2N-substituted compounds were nontoxic and active against biofilms formed by Gram-negative bacteria and C. albicans but had reduced activity against biofilms formed by Gram-positive bacteria. In an attempt to develop nontoxic compounds with potent activity against biofilms formed by Gram-positive bacteria for application in antibiofilm coatings for medical implants, we synthesized novel compounds with substituents at both the N1 and 2N positions and tested these compounds for antibiofilm activity and toxicity. Interestingly, most of these N1-,2N-disubstituted 5-aryl-2-aminoimidazoles showed very strong activity against biofilms formed by Gram-positive bacteria and C. albicans in various setups with biofilms formed by monospecies and mixed species but lost activity against biofilms formed by Gram-negative bacteria. In light of application of these compounds as anti-infective coatings on orthopedic implants, toxicity against two bone cell lines and the functionality of these cells were tested. The N1-,2N-disubstituted 5-aryl-2-aminoimidazoles in general did not affect the viability of bone cells and even induced calcium deposition. This indicates that modulating the substitution pattern on positions N1 and 2N of the 5-aryl-2-aminoimidazole scaffold allows fine-tuning of both the antibiofilm activity spectrum and toxicity.

Commensal Protection of Staphylococcus aureus against Antimicrobials by Candida albicans Biofilm Matrix

Biofilm-associated polymicrobial infections, particularly those involving fungi and bacteria, are responsible for significant morbidity and mortality and tend to be challenging to treat. Candida albicans and Staphylococcus aureus specifically are considered leading opportunistic fungal and bacterial pathogens, respectively, mainly due to their ability to form biofilms on catheters and indwelling medical devices. However, the impact of mixed-species biofilm growth on therapy remains largely understudied. In this study, we investigated the influence of C. albicans secreted cell wall polysaccharides on the response of S. aureus to antibacterial agents in biofilm. Results demonstrated significantly enhanced tolerance for S. aureus to drugs in the presence of C. albicans or its secreted cell wall polysaccharide material. Fluorescence confocal time-lapse microscopy revealed impairment of drug diffusion through the mixed biofilm matrix. Using C. albicans mutant strains with modulated cell wall polysaccharide expression, exogenous supplementation, and enzymatic degradation, the C. albicans-secreted β-1,3-glucan cell wall component was identified as the key matrix constituent providing the bacteria with enhanced drug tolerance. Further, antibody labeling demonstrated rapid coating of the bacteria by the C. albicans matrix material. Importantly, via its effect on the fungal biofilm matrix, the antifungal caspofungin sensitized the bacteria to the drugs. Understanding such symbiotic interactions with clinical relevance between microbial species in biofilms will greatly aid in overcoming the limitations of current therapies and in defining potential new targets for treating polymicrobial infections.

The fungus Candida albicans and the bacterium Staphylococcus aureus are important microbial pathogens responsible for the majority of infections in hospitalized patients and are often coisolated from a host. In this study, we demonstrated that when grown together, the fungus provides the bacterium with enhanced tolerance to antimicrobial drugs. This process was mediated by polysaccharides secreted by the fungal cell into the environment. The biofilm matrix formed by these polysaccharides prevented penetration by the drugs and provided the bacteria with protection. Importantly, we show that by inhibiting the production of the fungal polysaccharides, a specific antifungal agent indirectly sensitized the bacteria to antimicrobials. Understanding the therapeutic implications of the interactions between these two diverse microbial species will aid in overcoming the limitations of current therapies and in defining new targets for treating complex polymicrobial infections.

Enemies and brothers in arms: Candida albicans and gram-positive bacteria

Candida albicans is an important human opportunistic fungal pathogen which is frequently found as part of the normal human microbiota. It is well accepted that the fungus interacts with other components of the resident microbiota and that this impacts the commensal or pathogenic outcome of C. albicans colonization. Different types of interactions, including synergism or antagonism, contribute to a complex balance between the multitude of different species. Mixed biofilms of C. albicans and streptococci are a well-studied example of a mutualistic interaction often potentiating the virulence of the individual members. In contrast, other bacteria like lactobacilli are known to antagonize C. albicans, and research has just started elucidating the mechanisms behind these interactions. This scenario is even more complicated by a third player, the host. This review focuses on interactions between C. albicans and gram-positive bacteria whose investigation will without doubt ultimately help understanding C. albicans infections.

Inhibition of mixed fungal and bacterial biofilms on silicone by carboxymethyl chitosan

Mixed biofilms with fungi and bacteria are the leading cause for the failure of medical silicone devices, such as voice prostheses in laryngectomy. In this study, we determined the effect of carboxymethyl chitosan (CM-chitosan) on mixed biofilm formation of fungi and bacteria on silicone which is widely used for construction of medical devices. Mixed biofilm formations were inhibited 72.87% by CM-chitosan. Furthermore, CM-chitosan significantly decreased the metabolic activity of the biofilms using 2, 3-bis (2-methoxy-4-nitro-5-sulfo-phenyl)-2H-tetrazolium-5 carboxanilide (XTT) reduction assay. The examination using confocal laser scanning microscopy and scanning electron microscope confirmed that CM-chitosan inhibited the mixed biofilm and damaged the cells. Effects of CM-chitosan on different stages of biofilms were also evaluated. CM-chitosan inhibited the adhesion of fungi and bacteria with an efficiency of >90%. It prevented biofilm formation at efficiencies of 69.86%, 50.88% and 46.58% when CM-chitosan was added at 90min, 12h and 24h after biofilm initiation, respectively. Moreover, CM-chitosan inhibited Candida yeast-to-hyphal transition. CM-chitosan was not only able to inhibit the metabolic activity of biofilms, but also active upon the establishment and development of biofilm. Therefore, CM-chitosan may serve as a possible antibiofilm agent to limit biofilm formation on voice prostheses.

An Optimized Lock Solution Containing Micafungin, Ethanol and Doxycycline Inhibits Candida albicans and Mixed C. albicans - Staphyloccoccus aureus Biofilms

Candida albicans is a major cause of catheter-related bloodstream infections and is associated with high morbidity and mortality. Due to the propensity of C. albicans to form drug-resistant biofilms, the current standard of care includes catheter removal; however, reinsertion may be technically challenging or risky. Prolonged exposure of an antifungal lock solution within the catheter in conjunction with systemic therapy has been experimentally attempted for catheter salvage. Previously, we demonstrated excellent in vitro activity of micafungin, ethanol, and high-dose doxycycline as single agents for prevention and treatment of C. albicans biofilms. Thus, we sought to investigate optimal combinations of micafungin, ethanol, and/or doxycycline as a lock solution. We performed two- and three-drug checkerboard assays to determine the in vitro activity of pairwise or three agents in combination for prevention or treatment of C. albicans biofilms. Optimal lock solutions were tested for activity against C. albicans clinical isolates, reference strains and polymicrobial C. albicans-S. aureus biofilms. A solution containing 20% (v/v) ethanol, 0.01565 μg/mL micafungin, and 800 μg/mL doxycycline demonstrated a reduction of 98% metabolic activity and no fungal regrowth when used to prevent fungal biofilm formation; however there was no advantage over 20% ethanol alone. This solution was also successful in inhibiting the regrowth of C. albicans from mature polymicrobial biofilms, although it was not fully bactericidal. Solutions containing 5% ethanol with low concentrations of micafungin and doxycycline demonstrated synergistic activity when used to prevent monomicrobial C. albicans biofilm formation. A combined solution of micafungin, ethanol and doxycycline is highly effective for the prevention of C. albicans biofilm formation but did not demonstrate an advantage over 20% ethanol alone in these studies.

Antibiofilm activity of carboxymethyl chitosan on the biofilms of non-Candida albicans Candida species

Although most cases of candidiasis have been attributed to Candida albicans, non-C. albicans Candida species have been isolated in increasing numbers in patients. In this study, we determined the inhibition of carboxymethyl chitosan (CM-chitosan) on single and mixed species biofilm of non-albicans Candida species, including Candida tropicalis, Candida parapsilosis, Candida krusei and Candida glabrata. Biofilm by all tested species in microtiter plates were inhibited nearly 70%. CM-chitosan inhibited mixed species biofilm in microtiter plates and also on medical materials surfaces. To investigate the mechanism, the effect of CM-chitosan on cell viability and biofilm growth was employed. CM-chitosan inhibited Candida planktonic growth as well as adhesion. Further biofilm formation was inhibited with CM-chitosan added at 90min, 12h or 24h after biofilm initiation. CM-chitosan was not only able to inhibit the metabolic activity of Candida cells, but was also active upon the establishment and the development of biofilms.

Candida spp. airway colonization: A potential risk factor for Acinetobacter baumannii ventilator-associated pneumonia

This retrospective study was conducted to identify potential risk factors for Acinetobacter baumannii (A. baumannii) ventilator-associated pneumonia (VAP) and evaluate the association between Candida spp. airway colonization and A. baumannii VAP. Intensive care unit (ICU) patients who were on mechanical ventilation (MV) for ≥48 hours were divided into the following groups: patients with and without Candida spp. airway colonization; colonized patients receiving antifungal treatment or not; patients with A. baumannii VAP and those without VAP. Logistic regression analysis and propensity score matching were used to identify factors independently associated with A. baumannii VAP. Among 618 eligible patients, 264 (43%) had Candida spp. airway colonization and 114 (18%) developed A. baumannii VAP. Along with MV for ≥7 days (adjusted odds ratio [aOR] 8.9, 95% confidence intervals [95% CI] 4.9-15.8) and presence of a central venous catheter (aOR 3.2, 95% CI 1.1-9), Candida spp. airway colonization (aOR 2.6, 95% CI 1.6-4.3) was identified as an independent risk factor for A. baumannii VAP. Patients with Candida spp. airway colonization were more likely to develop A. baumannii VAP than non-colonized patients (23% vs 15%, P=.01 and 34% vs. 15%, P<.001 in propensity score-matched subgroups). Administration of antifungal agents was not associated with A. baumannii VAP (29% vs. 21%, P=.153) but with higher in-hospital mortality (53% vs. 39%, P=.037). Candida spp. airway colonization (43%) and A. baumannii VAP (18%) were common in ICU patients who were on mechanical ventilation for at least 48 hours. Candida spp. airway colonization was an independent risk factor for subsequent A. baumannii VAP.

Defining post-sternotomy mediastinitis for clinical evidence-based studies

Background

Considerable advances have already been made in the treatment of deep thoracic wound infections following a median sternotomy for cardiac surgery. Further improvement in diagnosis, treatment, and outcome will require a targeted approach by multidisciplinary teams. Clear communication and synergy between the various clinical and supportive disciplines would assist in removing the last barriers to standardized evidence-based studies and the development of improved evidence-based guidelines.

Methods

An extensive literature search without language restrictions was carried out on PubMed (Medline), EMBASE, and Web of Science, covering the period 1988 to week 16, 2014, and a manual search of the reference lists was performed regarding all possible definitions and classifications of post-sternotomy mediastinitis. Two hundred and eighteen papers describing post-sternotomy infections in a multitude of terms were identified, and the strengths and weaknesses of the most popular definitions and terms relating specifically to post-sternotomy infections were examined.

Results

This study revealed that clinicians use a multitude of terms to describe post-sternotomy infections without defining the condition under treatment. Occasionally, older epidemiological (surveillance) definitions were used. It also shows that supportive disciplines have their own definitions, or interpretations of existing definitions, to describe these infections.

Conclusion

The outcome of this study is that clinicians have adopted no single definition, which is essential for further improvement for evidence-based studies. We suggest that it is possible to adopt a single term for thoracic infection after a sternotomy (and only sternotomy), and propose a clinical definition for this purpose.

ABM Clinical Protocol #26: Persistent Pain with Breastfeeding

A central goal of The Academy of Breastfeeding Medicine is the development of clinical protocols for managing common medical problems that may impact breastfeeding success. These protocols serve only as guidelines for the care of breastfeeding mothers and infants and do not delineate an exclusive course of treatment or serve as standards of medical care. Variations in treatment may be appropriate according to the needs of an individual patient.

The Comparative Evaluation of the Antimicrobial Effect of Propolis with Chlorhexidine against Oral Pathogens: An In Vitro Study

This study aimed to compare the antimicrobial effectiveness of ethanolic extract of propolis (EEP) to chlorhexidine gluconate (CHX) on planktonic Streptococcus mutans, Streptococcus sobrinus, Lactobacillus acidophilus, Lactobacillus salivarius subsp. salivarius, Aggregatibacter actinomycetemcomitans, Prevotella intermedia, Porphyromonas gingivalis, Staphylococcus aureus, Enterococcus faecalis, Actinomyces israelii, Candida albicans, and their single-species biofilms by agar dilution and broth microdilution test methods. Both agents inhibited the growth of all planktonic species. On the other hand, CHX exhibited lower minimum bactericidal concentrations than EEP against biofilms of A. actinomycetemcomitans, S. aureus, and E. faecalis whereas EEP yielded a better result against Lactobacilli and P. intermedia. The bactericidal and fungicidal concentrations of both agents were found to be equal against biofilms of Streptecocci, P. gingivalis, A. israelii, and C. albicans. The results of this study revealed that propolis was more effective in inhibiting Gram-positive bacteria than the Gram-negative bacteria in their planktonic state and it was suggested that EEP could be as effective as CHX on oral microorganisms in their biofilm state.

Covalent immobilization of antimicrobial agents on titanium prevents Staphylococcus aureus and Candida albicans colonization and biofilm formation

OBJECTIVES

Biofilm-associated implant infections represent a serious public health problem. Covalent immobilization of antimicrobial agents on titanium (Ti), thereby inhibiting biofilm formation of microbial pathogens, is a solution to this problem.

METHODS

Vancomycin (VAN) and caspofungin (CAS) were covalently bound on Ti substrates using an improved processing technique adapted to large-scale coating of implants. Resistance of the VAN-coated Ti (VAN-Ti) and CAS-coated Ti (CAS-Ti) substrates against in vitro biofilm formation of the bacterium Staphylococcus aureus and the fungal pathogen Candida albicans was determined by plate counting and visualized by confocal laser scanning microscopy. The efficacy of the coated Ti substrates was also tested in vivo using an adapted biomaterial-associated murine infection model in which control-Ti, VAN-Ti or CAS-Ti substrates were implanted subcutaneously and subsequently challenged with the respective pathogens. The osseointegration potential of VAN-Ti and CAS-Ti was examined in vitro using human bone marrow-derived stromal cells, and for VAN-Ti also in a rat osseointegration model.

RESULTS

In vitro biofilm formation of S. aureus and C. albicans on VAN-Ti and CAS-Ti substrates, respectively, was significantly reduced compared with biofilm formation on control-Ti. In vivo, we observed over 99.9% reduction in biofilm formation of S. aureus on VAN-Ti substrates and 89% reduction in biofilm formation of C. albicans on CAS-Ti substrates, compared with control-Ti substrates. The coated substrates supported osseointegration in vitro and in vivo.

CONCLUSIONS

These data demonstrate the clinical potential of covalently bound VAN and CAS on Ti to reduce microbial biofilm formation without jeopardizing osseointegration.

70th Anniversary Collection for the Microbiology Society: Journal of Medical Microbiology

In the last 70 years, we have seen a radical change in our perception and understanding of the microbial world. During this period, we learned from Woese and Fox there exists a third kingdom called 'Archea' based on the phylogenetic studies of the 16S rRNA that revolutionized microbiology (Woese & Fox, 1977; Woese et al., 1978). Furthermore, we were forced to reckon with the fact that Koch and Pasteur's way of growing cells in test-tubes or flasks planktonically does not necessarily translate to the real-life scenario of bacterial lifestyle, where they prefer to live and function as a closely knit microbial community called biofilm. Thanks are due to Costerton, who led the crusade on the concept of biofilms and expanded its scope of inquiry, which forced scientists and clinicians worldwide to rethink how we evaluate and apply the data. Then progressively, disbelief turned into belief, and now it is universally accepted that the micro-organisms hobnob with the members of their community to communicate and coordinate their behaviour, especially in regard to growth patterns and virulence traits via signalling molecules. Just when we thought that we were losing the battle against bacteria, antimicrobials were discovered. We then witnessed the rise and fall of antibiotics and the development of antibiotic resistance. Due to space and choice limitation, we will focus on the three areas that caused this major paradigm shift (i) antimicrobial resistance (AMR), (ii) biofilm and (iii) quorum sensing (QS), and how the Journal of Medical Microbiology played a major role in advancing the shift.

Searching for new strategies against polymicrobial biofilm infections: guanylated polymethacrylates kill mixed fungal/bacterial biofilms

OBJECTIVES

Biofilm-related human infections have high mortality rates due to drug resistance. Cohabitation of diverse microbes in polymicrobial biofilms is common and these infections present additional challenges for treatment compared with monomicrobial biofilms. Here, we address this therapeutic gap by assessing the potential of a new class of antimicrobial agents, guanylated polymethacrylates, in the treatment of polymicrobial biofilms built by two prominent human pathogens, the fungus Candida albicans and the bacterium Staphylococcus aureus.

METHODS

We used imaging and quantitative methods to test the antibiofilm efficacy of guanylated polymethacrylates, a new class of drugs that structurally mimic antimicrobial peptides. We further compared guanylated polymethacrylates with first-line antistaphylococcal and anti-Candida agents used as combinatorial therapy against polymicrobial biofilms.

RESULTS

Guanylated polymethacrylates were highly effective as a sole agent, killing both C. albicans and S. aureus when applied to established polymicrobial biofilms. Furthermore, they outperformed multiple combinations of current antimicrobial drugs, with one of the tested compounds killing 99.98% of S. aureus and 82.2% of C. albicans at a concentration of 128 mg/L. The extracellular biofilm matrix provided protection, increasing the MIC of the polymethacrylates by 2-4-fold when added to planktonic assays. Using the C. albicans bgl2ΔΔ mutant, we implicate matrix polysaccharide β-1,3 glucan in the mechanism of protection. Data for two structurally distinct polymers suggest that this mechanism could be minimized through chemical optimization of the polymer structure. Finally, we demonstrate that a potential application for these polymers is in antimicrobial lock therapy.

CONCLUSIONS

Guanylated polymethacrylates are a promising lead for the development of an effective monotherapy against C. albicans/S. aureus polymicrobial biofilms.

Multivalency effects on Pseudomonas aeruginosa biofilm inhibition and dispersal by glycopeptide dendrimers targeting lectin LecA

The galactose specific lectin LecA partly mediates the formation of antibiotic resistant biofilms by Pseudomonas aeruginosa, an opportunistic pathogen causing lethal airways infections in immunocompromised and cystic fibrosis patients, suggesting that preventing LecA binding to natural saccharides might provide new opportunities for treatment. Here 8-fold (G3) and 16-fold (G4) galactosylated analogs of GalAG2, a tetravalent G2 glycopeptide dendrimer LecA ligand and P. aeruginosa biofilm inhibitor, were obtained by convergent chloroacetyl thioether (ClAc) ligation between 4-fold or 8-fold chloroacetylated dendrimer cores and digalactosylated dendritic arms. Hemagglutination inhibition, isothermal titration calorimetry and biofilm inhibition assays showed that G3 dendrimers bind LecA slightly better than their parent G2 dendrimers and induce complete biofilm inhibition and dispersal of P. aeruginosa biofilms, while G4 dendrimers show reduced binding and no biofilm inhibition. A binding model accounting for the observed saturation of glycopeptide dendrimer galactosyl groups and LecA binding sites is proposed based on the crystal structure of a G3 dendrimer LecA complex.

Candida Biofilms: Development, Architecture, and Resistance

Intravascular device-related infections are often associated with biofilms (microbial communities encased within a polysaccharide-rich extracellular matrix) formed by pathogens on the surfaces of these devices. Candida species are the most common fungi isolated from catheter-, denture-, and voice prosthesis-associated infections and also are commonly isolated from contact lens-related infections (e.g., fungal keratitis). These biofilms exhibit decreased susceptibility to most antimicrobial agents, which contributes to the persistence of infection. Recent technological advances have facilitated the development of novel approaches to investigate the formation of biofilms and identify specific markers for biofilms. These studies have provided extensive knowledge of the effect of different variables, including growth time, nutrients, and physiological conditions, on biofilm formation, morphology, and architecture. In this article, we will focus on fungal biofilms (mainly Candida biofilms) and provide an update on the development, architecture, and resistance mechanisms of biofilms.

Synergistic interactions in mixed-species biofilms of pathogenic bacteria from the respiratory tract

INTRODUCTION

Mixed-species biofilms are involved in a wide variety of infections. We studied the synergistic interactions during dual-species biofilm formation among isolates of Pseudomonas aeruginosa, Acinetobacter baumannii, and Stenotrophomonas maltophilia.

METHODS

Isolates were cultured as single-species and all possible combinations of dual-species biofilms.

RESULTS

The 61 A. baumannii biofilms increased by 26-fold when cultured with S. maltophilia isolates; 62 A. baumannii biofilms increased by 20-fold when cultured with S. maltophilia isolates; and 31 P. aeruginosa biofilms increased by 102-fold when cultured with S. maltophilia 106.

CONCLUSIONS

Synergy was observed between two isolates, including those that inherently lacked biofilm formation ability.

Pathogens protection against the action of disinfectants in multispecies biofilms

Biofilms constitute the prevalent way of life for microorganisms in both natural and man-made environments. Biofilm-dwelling cells display greater tolerance to antimicrobial agents than those that are free-living, and the mechanisms by which this occurs have been investigated extensively using single-strain axenic models. However, there is growing evidence that interspecies interactions may profoundly alter the response of the community to such toxic exposure. In this paper, we propose an overview of the studies dealing with multispecies biofilms resistance to biocides, with particular reference to the protection of pathogenic species by resident surface flora when subjected to disinfectants treatments. The mechanisms involved in such protection include interspecies signaling, interference between biocides molecules and public goods in the matrix, or the physiology and genetic plasticity associated with a structural spatial arrangement. After describing these different mechanisms, we will discuss the experimental methods available for their analysis in the context of complex multispecies biofilms.

Cellular Components Mediating Coadherence of Candida albicans and Fusobacterium nucleatum

Candida albicans is an opportunistic fungal pathogen found as part of the normal oral flora. It can be coisolated with Fusobacterium nucleatum, an opportunistic bacterial pathogen, from oral disease sites, such as those involved in refractory periodontitis and pulp necrosis. The physical coadherence between these 2 clinically important microbes has been well documented and suggested to play a role in facilitating their oral colonization and colocalization and contributing to polymicrobial pathogenesis. Previous studies indicated that the physical interaction between C. albicans and F. nucleatum was mediated by the carbohydrate components on the surface of C. albicans and the protein components on the Fusobaterium cell surface. However, the identities of the components involved still remain elusive. This study was aimed at identifying the genetic determinants involved in coaggregation between the 2 species. By screening a C. albicans SN152 mutant library and a panel of F. nucleatum 23726 outer membrane protein mutants, we identified FLO9, which encodes a putative adhesin-like cell wall mannoprotein of C. albicans and radD, an arginine-inhibitable adhesin-encoding gene in F. nucleatum that is involved in interspecies coadherence. Consistent with these findings, we demonstrated that the strong coaggregation between wild-type F. nucleatum 23726 and C. albicans SN152 in an in vitro assay could be greatly inhibited by arginine and mannose. Our study also suggested a complex multifaceted mechanism underlying physical interaction between C. albicans and F. nucleatum and for the first time revealed the identity of major genetic components involved in mediating the coaggregation. These observations provide useful knowledge for developing new targeted treatments for disrupting interactions between these 2 clinically relevant pathogens.

Could Histoplasma capsulatum Be Related to Healthcare-Associated Infections?

Healthcare-associated infections (HAI) are described in diverse settings. The main etiologic agents of HAI are bacteria (85%) and fungi (13%). Some factors increase the risk for HAI, particularly the use of medical devices; patients with severe cuts, wounds, and burns; stays in the intensive care unit, surgery, and hospital reconstruction works. Several fungal HAI are caused by Candida spp., usually from an endogenous source; however, cross-transmission via the hands of healthcare workers or contaminated devices can occur. Although other medically important fungi, such as Blastomyces dermatitidis, Paracoccidioides brasiliensis, and Histoplasma capsulatum, have never been considered nosocomial pathogens, there are some factors that point out the pros and cons for this possibility. Among these fungi, H. capsulatum infection has been linked to different medical devices and surgery implants. The filamentous form of H. capsulatum may be present in hospital settings, as this fungus adapts to different types of climates and has great dispersion ability. Although conventional pathogen identification techniques have never identified H. capsulatum in the hospital environment, molecular biology procedures could be useful in this setting. More research on H. capsulatum as a HAI etiologic agent is needed, since it causes a severe and often fatal disease in immunocompromised patients.

Ethanol and Isopropyl Alcohol Exposure Increases Biofilm Formation in Staphylococcus aureus and Staphylococcus epidermidis

Introduction

Alcohols, including ethanol and isopropyl alcohol, are used in clinical practice for disinfection and infection prevention. Recent studies, however, demonstrate that alcohols may enhance biofilm production in Staphylococci.

Methods

We quantified biofilm formation in the presence of ethanol and isopropyl alcohol in six different, well-characterized strains of Staphylococcus epidermidis and Staphylococcus aureus. After 24 h of biofilm development, each strain was exposed to normal saline (NS), ethanol, or isopropyl alcohol (40%, 60%, 80% and 95%) for additional 24 h incubation. Adherent biofilms were stained and optical density was determined. Viability of strains was also determined after alcohol exposure.

Results

Ethanol increased biofilm formation in all six strains compared to normal saline (p < 0.05). There was increased biofilm formation with increasing ethanol concentration. Isopropyl alcohol also increased biofilm formation with increasing alcohol concentration in all six strains (p < 0.01 vs NS). The slime-negative, chemical mutant strain of S. epidermidis increased biofilm formation after exposure to both alcohols, likely reverting back its primary phenotype through modulation of the intercellular adhesin repressor. All strains demonstrated viability after exposure to each alcohol concentration, though viability was decreased.

Conclusion

Ethanol and isopropyl alcohol exposure increases biofilm formation of S. aureus and S. epidermidis at concentrations used in clinical settings. Ethanol and isopropyl alcohol did not eradicate viable Staphylococci from formed biofilm.

Electronic supplementary material

The online version of this article (doi:10.1007/s40121-015-0065-y) contains supplementary material, which is available to authorized users.

Fungal β-1,3-glucan increases ofloxacin tolerance of Escherichia coli in a polymicrobial E. coli/Candida albicans biofilm

In the past, biofilm-related research has focused mainly on axenic biofilms. However, in nature, biofilms are often composed of multiple species, and the resulting polymicrobial interactions influence industrially and clinically relevant outcomes such as performance and drug resistance. In this study, we show that Escherichia coli does not affect Candida albicans tolerance to amphotericin or caspofungin in an E. coli/C. albicans biofilm. In contrast, ofloxacin tolerance of E. coli is significantly increased in a polymicrobial E. coli/C. albicans biofilm compared to its tolerance in an axenic E. coli biofilm. The increased ofloxacin tolerance of E. coli is mainly biofilm specific, as ofloxacin tolerance of E. coli is less pronounced in polymicrobial E. coli/C. albicans planktonic cultures. Moreover, we found that ofloxacin tolerance of E. coli decreased significantly when E. coli/C. albicans biofilms were treated with matrix-degrading enzymes such as the β-1,3-glucan-degrading enzyme lyticase. In line with a role for β-1,3-glucan in mediating ofloxacin tolerance of E. coli in a biofilm, we found that ofloxacin tolerance of E. coli increased even more in E. coli/C. albicans biofilms consisting of a high-β-1,3-glucan-producing C. albicans mutant. In addition, exogenous addition of laminarin, a polysaccharide composed mainly of poly-β-1,3-glucan, to an E. coli biofilm also resulted in increased ofloxacin tolerance. All these data indicate that β-1,3-glucan from C. albicans increases ofloxacin tolerance of E. coli in an E. coli/C. albicans biofilm.