Antagonistic Interaction of Staphylococcus aureus Toward Candida glabrata During in vitro Biofilm Formation Is Caused by an Apoptotic Mechanism

Candida albicans and Candida glabrata: global priority pathogens

SUMMARYA significant increase in the incidence of Candida-mediated infections has been observed in the last decade, mainly due to rising numbers of susceptible individuals. Recently, the World Health Organization published its first fungal pathogen priority list, with Candida species listed in medium, high, and critical priority categories. This review is a synthesis of information and recent advances in our understanding of two of these species-Candida albicans and Candida glabrata. Of these, C. albicans is the most common cause of candidemia around the world and is categorized as a critical priority pathogen. C. glabrata is considered a high-priority pathogen and has become an increasingly important cause of candidemia in recent years. It is now the second most common causative agent of candidemia in many geographical regions. Despite their differences and phylogenetic divergence, they are successful as pathogens and commensals of humans. Both species can cause a broad variety of infections, ranging from superficial to potentially lethal systemic infections. While they share similarities in certain infection strategies, including tissue adhesion and invasion, they differ significantly in key aspects of their biology, interaction with immune cells, host damage strategies, and metabolic adaptations. Here we provide insights on key aspects of their biology, epidemiology, commensal and pathogenic lifestyles, interactions with the immune system, and antifungal resistance.

Multiphotonic Ablation and Electro-Capacitive Effects Exhibited by Candida albicans Biofilms

This work reports the modification in the homogeneity of ablation effects with the assistance of nonlinear optical phenomena exhibited by C. albicans ATCC 10231, forming a biofilm. Equivalent optical energies with different levels of intensity were irradiated in comparative samples, and significant changes were observed. Nanosecond pulses provided by an Nd:YAG laser system at a 532 nm wavelength in a single-beam experiment were employed to explore the photodamage and the nonlinear optical transmittance. A nonlinear optical absorption coefficient -2 × 10-6 cm/W was measured in the samples studied. It is reported that multiphotonic interactions can promote more symmetric optical damage derived by faster changes in the evolution of fractional photoenergy transference. The electrochemical response of the sample was studied to further investigate the electronic dynamics dependent on electrical frequency, and an electro-capacitive behavior in the sample was identified. Fractional differential calculations were proposed to describe the thermal transport induced by nanosecond pulses in the fungi media. These results highlight the nonlinear optical effects to be considered as a base for developing photothermally activated phototechnology and high-precision photodamage in biological systems.

Biofilm formation by selected microbial strains isolated from wastewater and their consortia: mercury resistance and removal potential

Wastewater often contains an increased amount of mercury and, at the same time, resistant microorganisms. During wastewater treatment, a biofilm of indigenous microorganisms is often unavoidable. Therefore, the objective of this research is to isolate and identify microorganisms from wastewater and investigate their ability to form biofilms for possible application in mercury removal processes. The resistance of planktonic cells and their biofilms to the effects of mercury was investigated using Minimum Biofilm Eradication Concentration-High Throughput Plates. The formation of biofilms and the degree of resistance to mercury were confirmed in polystyrene microtiter plates with 96 wells. Biofilm on AMB Media carriers (Assisting Moving Bad Media) was quantified using the Bradford protein assay. The removal of mercury ions by biofilms formed on AMB Media carriers of selected isolates and their consortia was determined by a removal test in Erlenmeyer flasks simulating MBBR. All isolates in planktonic form showed some degree of resistance to mercury. The most resistant microorganisms (Enterobacter cloacae, Klebsiella oxytoca, Serratia odorifera, and Saccharomyces cerevisiae) were tested for their ability to form biofilms in the presence and absence of mercury, both in polystyrene plates and on ABM carriers. The results showed that among planktonic forms, K. oxytoca was the most resistant. A biofilm of the same microorganisms was more than 10-fold resistant. Most consortia biofilms had MBEC values > 100,000 μg/mL. Among individual biofilms, E. cloacae showed the highest mercury removal efficiency (97.81% for 10 days). Biofilm consortia composed of three species showed the best ability to remove mercury (96.64%-99.03% for 10 days). This study points to the importance of consortia of different types of wastewater microorganisms in the form of biofilms and suggests that they can be used to remove mercury in wastewater treatment bioreactors.

Culture media influences Candida parapsilosis growth, susceptibility, and virulence

Introduction

Candida parapsilosis, a pathogenic yeast associated with systemic infections, exhibits metabolic adaptability in response to nutrient availability.

Methods

We investigated the impact of RPMI glucose supplemented (RPMId), TSB, BHI and YPD media on C. parapsilosis growth, morphology, susceptibility (caspofungin and amphotericin B), and in vivo virulence (Galleria mellonella) in planktonic and biofilm states.

Results

High-glucose media favors growth but hinders metabolic activity and filamentation. Media promoting carbohydrate production reduces biofilm susceptibility. Virulence differences between planktonic cells and biofilm suspensions from the same media shows that biofilm-related factors influence infection outcome depending on nutrient availability. Pseudohyphal growth occurred in biofilms under low oxygen and shear stress, but its presence is not exclusively correlated with virulence.

Discussion

This study provides valuable insights into the intricate interplay between nutrient availability and C. parapsilosis pathogenicity. It emphasizes the importance of considering pathogen behavior in diverse conditions when designing research protocols and therapeutic strategies.

Lipid-Like Biofilm from a Clinical Brain Isolate of Aspergillus terreus: Quantification, Structural Characterization and Stages of the Formation Cycle

Invasive infections caused by filamentous fungi have increased considerably due to the alteration of the host's immune response. Aspergillus terreus is considered an emerging pathogen and has shown resistance to amphotericin B treatment, resulting in high mortality. The development of fungal biofilm is a virulence factor, and it has been described in some cases of invasive aspergillosis. In addition, although the general composition of fungal biofilms is known, findings related to biofilms of a lipid nature are rarely reported. In this study, we present the identification of a clinical strain of A. terreus by microbiological and molecular tools, also its in vitro biofilm development capacity: (i) Biofilm formation was quantified by Crystal Violet and reduction of tetrazolium salts assays, and simultaneously the stages of biofilm development were described by Scanning Electron Microscopy in High Resolution (SEM-HR). (ii) Characterization of the organizational structure of the biofilm was performed by SEM-HR. The hyphal networks developed on the surface, the abundant air channels created between the ECM (extracellular matrix) and the hyphae fused in anastomosis were described. Also, the presence of microhyphae is reported. (iii) The chemical composition of the ECM was analyzed by SEM-HR and CLSM (Confocal Laser Scanning Microscopy). Proteins, carbohydrates, nucleic acids and a relevant presence of lipid components were identified. Some structures of apparent waxy appearance were highlighted by SEM-HR and backscatter-electron diffraction, for which CLSM was previously performed. To our knowledge, this work is the first description of a lipid-type biofilm in filamentous fungi, specifically of the species A. terreus from a clinical isolate.

Ceragenin CSA-44 as a Means to Control the Formation of the Biofilm on the Surface of Tooth and Composite Fillings

Recurrent oral infections, as manifested by endodontic and periodontal disease, are often caused by Enterococcus faecalis (E. faecalis) and Candida albicans (C. albicans). Here, we assessed the anti-biofilm activity of ceragenin CSA-44 against these microbes growing as a biofilm in the presence of saliva on the surface of human teeth and dental composite (composite filling) subjected to mechanical stresses. Methods: Biofilm mass analysis was performed using crystal violet (CV) staining. The morphology, viscoelastic properties of the biofilm after CSA-44 treatment, and changes in the surface of the composite in response to biofilm presence were determined by AFM microscopy. Results: CSA-44 prevented biofilm formation and reduced the mass of biofilm formed by tested microorganisms on teeth and dental composite. Conclusion: The ability of CSA-44 to prevent the formation and to reduce the presence of established biofilm on tooth and composite filling suggests that it can serve as an agent in the development of new methods of combating oral pathogens and reduce the severity of oral infections.

A Systematic Survey of Characteristic Features of Yeast Cell Death Triggered by External Factors

Cell death in response to distinct stimuli can manifest different morphological traits. It also depends on various cell death signaling pathways, extensively characterized in higher eukaryotes but less so in microorganisms. The study of cell death in yeast, and specifically Saccharomyces cerevisiae, can potentially be productive for understanding cell death, since numerous killing stimuli have been characterized for this organism. Here, we systematized the literature on external treatments that kill yeast, and which contains at least minimal data on cell death mechanisms. Data from 707 papers from the 7000 obtained using keyword searches were used to create a reference table for filtering types of cell death according to commonly assayed parameters. This table provides a resource for orientation within the literature; however, it also highlights that the common view of similarity between non-necrotic death in yeast and apoptosis in mammals has not provided sufficient progress to create a clear classification of cell death types. Differences in experimental setups also prevent direct comparison between different stimuli. Thus, side-by-side comparisons of various cell death-inducing stimuli under comparable conditions using existing and novel markers that can differentiate between types of cell death seem like a promising direction for future studies.

Microbial Warfare on Three Fronts: Mixed Biofilm of Aspergillus fumigatus and Staphylococcus aureus on Primary Cultures of Human Limbo-Corneal Fibroblasts

Background

Coinfections with fungi and bacteria in ocular pathologies are increasing at an alarming rate. Two of the main etiologic agents of infections on the corneal surface, such as Aspergillus fumigatus and Staphylococcus aureus, can form a biofilm. However, mixed fungal–bacterial biofilms are rarely reported in ocular infections. The implementation of cell cultures as a study model related to biofilm microbial keratitis will allow understanding the pathogenesis in the cornea. The cornea maintains a pathogen-free ocular surface in which human limbo-corneal fibroblast cells are part of its cell regeneration process. There are no reports of biofilm formation assays on limbo-corneal fibroblasts, as well as their behavior with a polymicrobial infection.

Objective

To determine the capacity of biofilm formation during this fungal–bacterial interaction on primary limbo-corneal fibroblast monolayers.

Results

The biofilm on the limbo-corneal fibroblast culture was analyzed by assessing biomass production and determining metabolic activity. Furthermore, the mixed biofilm effect on this cell culture was observed with several microscopy techniques. The single and mixed biofilm was higher on the limbo-corneal fibroblast monolayer than on abiotic surfaces. The A. fumigatus biofilm on the human limbo-corneal fibroblast culture showed a considerable decrease compared to the S. aureus biofilm on the limbo-corneal fibroblast monolayer. Moreover, the mixed biofilm had a lower density than that of the single biofilm. Antibiosis between A. fumigatus and S. aureus persisted during the challenge to limbo-corneal fibroblasts, but it seems that the fungus was more effectively inhibited.

Conclusion

This is the first report of mixed fungal–bacterial biofilm production and morphological characterization on the limbo-corneal fibroblast monolayer. Three antibiosis behaviors were observed between fungi, bacteria, and limbo-corneal fibroblasts. The mycophagy effect over A. fumigatus by S. aureus was exacerbated on the limbo-corneal fibroblast monolayer. During fungal–bacterial interactions, it appears that limbo-corneal fibroblasts showed some phagocytic activity, demonstrating tripartite relationships during coinfection.

In situ functionalizing calcium phosphate biomaterials with curcumin for the prevention of bacterial biofilm infections

This study developed a novel bioactive bone substitute (hydroxyapatite, HA) with improved anti-biofilm activity by functionalizing with curcumin (anti-biofilm compound) which provide sufficient flux of curcumin concentration for 14 days. The released curcumin acts to inhibit biofilm formation and control the number of viable planktonic cells simultaneously. To prepare curcumin-functionalized HA, different concentrations of curcumin (up to 3% w/v) were added simultaneously during the precipitation process of HA. The highest loading (50 mg/g HA) of curcumin onto HA was achieved with 2% w/v of curcumin. Physicochemical characterizations of curcumin-functionalized HA composites revealed that curcumin was successfully incorporated onto HA. Curcumin was sustainably released over 14 days, while higher curcumin release was observed in acidic condition (pH 4.4) compared to physiological (pH 7.4). The cytotoxicity assays revealed that no significant difference on bone cells growth on curcumin-functionalized HA and non-functionalized HA. Curcumin-functionalized HA was effective to inhibit bacterial cell attachment and subsequent biofilm maturation stages. The anti-biofilm effect was stronger against Staphylococcus aureus compared to Pseudomonas aeruginosa. The curcumin-functionalized HA composite significantly delayed the maturation of S. aureus compared to non-functionalized HA in which microcolonies of cells only begin to appear at 96 h. Up to 3.0 log reduction in colony forming unit (CFU)/mL of planktonic cells was noted at 24 h of incubation for both microorganisms. Thus, in this study we have suggested that curcumin loaded HA could be an alternative antimicrobial agent to control the risk of infections in post-surgical implants.

Mixed biofilms of pathogenic Candida-bacteria: regulation mechanisms and treatment strategies

Mixed-species biofilm is one of the most frequently recorded clinical problems. Mixed biofilms develop as a result of interactions between microorganisms of a single or multiple species (e.g. bacteria and fungi). Candida spp., particularly Candida albicans, are known to associate with various bacterial species to form a multi-species biofilm. Mixed biofilms of Candida spp. have been previously detected in vivo and on the surfaces of many biomedical instruments. Treating infectious diseases caused by mixed biofilms of Candida and bacterial species has been challenging due to their increased resistance to antimicrobial drugs. Here, we review and discuss the clinical significance of mixed Candida-bacteria biofilms as well as the signalling mechanisms involved in Candida-bacteria interactions. We also describe possible approaches for combating infections associated with mixed biofilms, such as the use of natural or synthetic drugs and combination therapy. The review presented here is expected to contribute to the advances in the biomedical field on the understanding of underlying interaction mechanisms of pathogens in mixed biofilm, and alternative approaches to treating the related infections.

Mechanism of Candida pathogenesis: revisiting the vital drivers

Candida is the most implicated fungal pathogen in the clinical setting. Several factors play important roles in the pathogenesis of Candida spp. Multiple transcriptional circuits, morphological and phenotypic switching, biofilm formation, tissue damaging extracellular hydrolytic enzymes, metabolic flexibility, genome plasticity, adaptation to environmental pH fluctuation, robust nutrient acquisition system, adherence and invasions (mediated by adhesins and invasins), heat shock proteins (HSPs), cytolytic proteins, escape from phagocytosis, evasion from host immune system, synergistic coaggregation with resident microbiota, resistance to antifungal agents, and the ability to efficiently respond to multiple stresses are some of the major pathogenic determinants of Candida species. The existence of multiple connections, in addition to the interactions and associations among all of these factors, are distinctive features that play important roles in the establishment of Candida infections. This review describes all the underlying factors and mechanisms involved in Candida pathogenesis by evaluating pathogenic determinants of Candida species. It reinforces the already available pool of data on the pathogenesis of Candida species by providing a clear and simplified understanding of the most important factors implicated in the pathogenesis of Candida species. The Candida pathogenesis network, an illustration linking all the major determinants of Candida pathogenesis, is also presented. Taken together, they will further improve our current understanding of how these factors modulate virulence and consequent infection(s). Development of new antifungal drugs and better therapeutic approaches to candidiasis can be achieved in the near future with continuing progress in the understanding of the mechanisms of Candida pathogenesis.

Medically important interactions of staphylococci with pathogenic fungi

Staphylococci are common inhabitants at several human body sites and are also implicated in infections either as primary or opportunistic pathogens. These bacteria can thus both contribute to the host defense being a part of the commensalistic microbiota or synergize with the other microbes during the infection process. Among fungi, staphylococci interact synergistically with Candida spp. and Aspergillus fumigatus, and antagonistically with Cryptococcus neoformans and Trichosporon asahii. These interactions are highly dynamic and are orchestrated by a multitude of microbial and host factors. During such cross-talks, staphylococci can modulate the virulence, immune response or drug resistance of the coexisting microbe(s), thereby influencing the infection course, disease severity, treatment strategy and the clinical outcome.

Candida spp./Bacteria Mixed Biofilms

The ability to form biofilms is a common feature of microorganisms, such as bacteria or fungi. These consortiums can colonize a variety of surfaces, such as host tissues, dentures, and catheters, resulting in infections highly resistant to drugs, when compared with their planktonic counterparts. This refractory effect is particularly critical in polymicrobial biofilms involving both fungi and bacteria. This review emphasizes Candida spp.-bacteria biofilms, the epidemiology of this community, the challenges in the eradication of such biofilms, and the most relevant treatments.

The ability of farnesol to prevent adhesion and disrupt Fusarium keratoplasticum biofilm

A biofilm is represented by a community of microorganisms capable of adhering to a surface and producing substances that envelop the cells, forming an extracellular matrix. The extracellular matrix is responsible for protecting microorganisms against environmental stress, hosts the immune system and confers resistance to antimicrobials. Fusarium keratoplasticum is a common species of FSSC (Fusarium solani species complex) associated with human infections, being the most prevalent species related to biofilm formation in hospital water systems and internal pipelines. With this in mind, this study aimed to characterise the biofilm formed by the fungus F. keratoplasticum and to evaluate the effects of farnesol, a fungal quorum sensing (QS) molecule, on the preformed biofilm and also during its formation at different times (adhesion and 24, 48 and 72 h). F. keratoplasticum is able to adhere to an abiotic surface and form a dense biofilm in 72 h, with increased total biomass and matrix modulation with the presence of extracellular DNA, RNA, polysaccharides and proteins. Farnesol exhibited important anti-biofilm activity, causing the destruction of hyphae and the extracellular matrix in preformed biofilm and preventing the adhesion of conidia, filamentation and the formation of biofilm. Few studies have characterised the formation of biofilm by filamentous fungi. Our findings suggest that farnesol acts efficiently on F. keratoplasticum biofilm since this molecule is capable of breaking the extracellular matrix, thereby disarranging the biofilm.

Antagonistic Interaction of Staphylococcus aureus and Staphylococcus epidermidis with Rhizopus arrhizus Mediated by Phenol Soluble Modulins and Organic Acids

Rhizopus arrhizus (R. arrhizus) is a common causative agent of mucormycosis that usually enters the human body through the respiratory tract and skin. Both these sites harbor staphylococci as a part of the normal microflora, indicating the possibility of interspecies interactions. We aimed to elucidate this interaction and identify the molecular mechanisms involved. Both Staphylococcus aureus (S. aureus) and Staphylococcus epidermidis (S. epidermidis) substantially hindered R. arrhizus radial growth, spore germination, and liquid culture biomass. Secreted components in the stationary-phase supernatant were responsible for this activity. The active components, based on molecular weight-based fractionation, mass spectrometry, and ion exclusion chromatography, were identified as a truncated version of phenol soluble modulin α2 (Δ1Δ2PSMα2) and PSMα3 in S. aureus, PSMδ in S. epidermidis, and organic acids in both the species. Exposure to the phenol soluble modulins (PSMs) extensively damaged the fungal spores and pre-existing hyphae, leading to bleb formation, shriveling, hyphal shrinkage, and cell distortion.

Pathogenetic Impact of Bacterial-Fungal Interactions

Polymicrobial infections are of paramount importance because of the potential severity of clinical manifestations, often associated with increased resistance to antimicrobial treatment. The intricate interplay with the host and the immune system, and the impact on microbiome imbalance, are of importance in this context. The equilibrium of microbiota in the human host is critical for preventing potential dysbiosis and the ensuing development of disease. Bacteria and fungi can communicate via signaling molecules, and produce metabolites and toxins capable of modulating the immune response or altering the efficacy of treatment. Most of the bacterial–fungal interactions described to date focus on the human fungal pathogen Candida albicans and different bacteria. In this review, we discuss more than twenty different bacterial–fungal interactions involving several clinically important human pathogens. The interactions, which can be synergistic or antagonistic, both in vitro and in vivo, are addressed with a focus on the quorum-sensing molecules produced, the response of the immune system, and the impact on clinical outcome.

Oral microbial biofilms: an update

Human oral cavity (mouth) hosts a complex microbiome consisting of bacteria, archaea, protozoa, fungi and viruses. These bacteria are responsible for two common diseases of the human mouth including periodontal (gum) and dental caries (tooth decay). Dental caries is caused by plaques, which are a community of microorganisms in biofilm format. Genetic and peripheral factors lead to variations in the oral microbiome. It has known that, in commensalism and coexistence between microorganisms and the host, homeostasis in the oral microbiome is preserved. Nonetheless, under some conditions, a parasitic relationship dominates the existing situation and the rise of cariogenic microorganisms results in dental caries. Utilizing advanced molecular biology techniques, new cariogenic microorganisms species have been discovered. The oral microbiome of each person is quite distinct. Consequently, commonly taken measures for disease prevention cannot be exactly the same for other individuals. The chance for developing tooth decay in individuals is dependent on factors such as immune system and oral microbiome which itself is affected by the environmental and genetic determinants. Early detection of dental caries, assessment of risk factors and designing personalized measure let dentists control the disease and obtain desired results. It is necessary for a dentist to consider dental caries as a result of a biological process to be targeted than treating the consequences of decay cavities. In this research, we critically review the literature and discuss the role of microbial biofilms in dental caries.