Influence of bacterial presence on biofilm formation of Candida albicans

Interkingdom biofilm of Streptococcus pyogenes and Candida albicans: establishment of an in vitro model and dose-response validation of antimicrobials

Although Streptococcus pyogenes and Candida albicans may colonize tonsillar tissues, the interaction between them in mixed biofilms has been poorly explored. This study established an interkingdom biofilm model of S. pyogenes and C. albicans and verified the dose-response validation of antimicrobials. Biofilms were formed on microplates, in the presence or absence of a conditioning layer of human saliva, using Brain Heart Infusion (BHI) broth or artificial saliva (AS) as a culture medium, and with variations in the microorganism inoculation sequence. Biofilms grown in AS showed higher mass than those grown in BHI broth, and an opposite trend was observed for metabolism. The number of S. pyogenes colonies was lower in AS. Amoxicillin and nystatin showed dose-dependent effects. The inoculation of the two species at the same time, without prior exposure to saliva, and using BHI broth would be the model of choice for future studies assessing the effects of antimicrobials on dual S. pyogenes/C. albicans biofilms.

Engineering Adhesion of the Probiotic Strain Escherichia coli Nissle to the Fungal Pathogen Candida albicans

Engineering live biotherapeutic products against fungal pathogens such as Candida albicans has been suggested as a means to tackle the increasing threat of fungal infections and the development of resistance to classical antifungal treatments. One important challenge in the design of live therapeutics is to control their localization inside the human body. The specific binding capability to target organisms or tissues would greatly increase their effectiveness by increasing the local concentration of effector molecules at the site of infection. In this study, we utilized surface display of carbohydrate binding domains to enable the probiotic E. coli Nissle 1917 to adhere specifically to the pathogenic yeast Candida albicans. Binding was quantified using a newly developed method based on the automated analysis of microscopic images. In addition to a rationally selected chitin binding domain, a synthetic peptide of identical length but distinct sequence also conferred binding. Efficient binding was specific to fungal hyphae, the invasive form of C. albicans, while the yeast form, as well as abiotic cellulose and PET particles, was only weakly recognized.

Exploring the Antimicrobial Potential of Hallachrome, a Defensive Anthraquinone from the Marine Worm Halla parthenopeia (Polychaeta)

Antimicrobial resistance is a critical global health issue, with rising resistance among bacteria and fungi. Marine organisms have emerged as promising, but underexplored, sources of new antimicrobial agents. Among them, marine polychaetes, such as Halla parthenopeia, which possess chemical defenses, could attract significant research interest. This study explores the antimicrobial properties of hallachrome, a unique anthraquinone found in the purple mucus of H. parthenopeia, against Gram-negative bacteria (Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 9027), Gram-positive bacteria (Enterococcus faecalis ATCC 29212, Staphylococcus aureus ATCC 6538, Staphylococcus epidermidis ATCC 12228), and the most common human fungal pathogen Candida albicans ATCC 10231. Antibacterial susceptibility testing revealed that Gram-negative bacteria were not inhibited by hallachrome at concentrations ≤2 mM. However, Gram-positive bacteria showed significant growth inhibition at 0.12-0.25 mM, while C. albicans was inhibited at 0.06 mM. Time-kill studies demonstrated dose-dependent growth inhibition of susceptible strains by hallachrome, which exerted its effect by altering the membrane permeability of C. albicans, E. faecalis, and S. epidermidis after 6 h and S. aureus after 24 h. Additionally, hallachrome significantly reduced biofilm formation and mature biofilm in S. aureus, E. faecalis, and C. albicans. Additionally, it inhibited hyphal growth in C. albicans. These findings highlight hallachrome's potential as a novel antimicrobial agent, deserving further exploration for clinical experimentation.

Integrated post-genomic cell wall analysis reveals floating biofilm formation associated with high expression of flocculins in the pathogen Pichia kudriavzevii

The pathogenic yeast Pichia kudriavzevii, previously known as Candida krusei, is more distantly related to Candida albicans than clinically relevant CTG-clade Candida species. Its cell wall, a dynamic organelle that is the first point of interaction between pathogen and host, is relatively understudied, and its wall proteome remains unidentified to date. Here, we present an integrated study of the cell wall in P. kudriavzevii. Our comparative genomic studies and experimental data indicate that the general structure of the cell wall in P. kudriavzevii is similar to Saccharomyces cerevisiae and C. albicans and is comprised of β-1,3-glucan, β-1,6-glucan, chitin, and mannoproteins. However, some pronounced differences with C. albicans walls were observed, for instance, higher mannan and protein levels and altered protein mannosylation patterns. Further, despite absence of proteins with high sequence similarity to Candida adhesins, protein structure modeling identified eleven proteins related to flocculins/adhesins in S. cerevisiae or C. albicans. To obtain a proteomic comparison of biofilm and planktonic cells, P. kudriavzevii cells were grown to exponential phase and in static 24-h cultures. Interestingly, the 24-h static cultures of P. kudriavzevii yielded formation of floating biofilm (flor) rather than adherence to polystyrene at the bottom. The proteomic analysis of both conditions identified a total of 33 cell wall proteins. In line with a possible role in flor formation, increased abundance of flocculins, in particular Flo110, was observed in the floating biofilm compared to exponential cells. This study is the first to provide a detailed description of the cell wall in P. kudriavzevii including its cell wall proteome, and paves the way for further investigations on the importance of flor formation and flocculins in the pathogenesis of P. kudriavzevii.

Polymicrobial Biofilm Dynamics of Multidrug-Resistant Candida albicans and Ampicillin-Resistant Escherichia coli and Antimicrobial Inhibition by Aqueous Garlic Extract

The polymicrobial biofilm of C. albicans with E. coli exhibits a dynamic interspecies interaction and is refractory to conventional antimicrobials. In this study, a high biofilm-forming multidrug-resistant strain of C. albicans overcomes inhibition by E. coli in a 24 h coculture. However, following treatment with whole Aqueous Garlic Extract (AGE), these individual biofilms of multidrug-resistant C. albicans M-207 and Ampicillin-resistant Escherichia coli ATCC 39936 and their polymicrobial biofilm were prevented, as evidenced by biochemical and structural characterization. This study advances the antimicrobial potential of AGE to inhibit drug-resistant C. albicans and bacterial-associated polymicrobial biofilms, suggesting the potential for effective combinatorial and synergistic antimicrobial designs with minimal side effects.

Update on Candida krusei, a potential multidrug-resistant pathogen

Although Candida albicans remains the main cause of candidiasis, in recent years a significant number of infections has been attributed to non-albicans Candida (NAC) species, including Candida krusei. This epidemiological change can be partly explained by the increased resistance of NAC species to antifungal drugs. C. krusei is a diploid, dimorphic ascomycetous yeast that inhabits the mucosal membrane of healthy individuals. However, this yeast can cause life-threatening infections in immunocompromised patients, with hematologic malignancy patients and those using prolonged azole prophylaxis being at higher risk. Fungal infections are usually treated with five major classes of antifungal agents which include azoles, echinocandins, polyenes, allylamines, and nucleoside analogues. Fluconazole, an azole, is the most commonly used antifungal drug due to its low host toxicity, high water solubility, and high bioavailability. However, C. krusei possesses intrinsic resistance to this drug while also rapidly developing acquired resistance to other antifungal drugs. The mechanisms of antifungal resistance of this yeast involve the alteration and overexpression of drug target, reduction in intracellular drug concentration and development of a bypass pathway. Antifungal resistance menace coupled with the paucity of the antifungal arsenal as well as challenges involved in antifungal drug development, partly due to the eukaryotic nature of both fungi and humans, have left researchers to exploit alternative therapies. Here we briefly review our current knowledge of the biology, pathophysiology and epidemiology of a potential multidrug-resistant fungal pathogen, C. krusei, while also discussing the mechanisms of drug resistance of Candida species and alternative therapeutic approaches.

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.

GC-MS-Based Metabolomics Study of Single- and Dual-Species Biofilms of Candida albicans and Klebsiella pneumoniae

Candida albicans and Klebsiella pneumoniae frequently co-exist within the human host as a complex biofilm community. These pathogens are of interest because their association is also related to significantly increased morbidity and mortality in hospitalized patients. With the aim of highlighting metabolic shifts occurring in the dual-species biofilm, an untargeted GC-MS-based metabolomics approach was applied to single and mixed biofilms of C. albicans and K. pneumoniae. Metabolomic results showed that among the extracellular metabolites identified, approximately 40 compounds had significantly changed relative abundance, mainly involving central carbon, amino acid, vitamin, and secondary metabolisms, such as serine, leucine, arabitol, phosphate, vitamin B6, cyclo-(Phe-Pro), trehalose, and nicotinic acid. The results were related to the strict interactions between the two species and the different microbial composition in the early and mature biofilms.

Unraveling Pseudomonas aeruginosa and Candida albicans Communication in Coinfection Scenarios: Insights Through Network Analysis

Modern medicine is currently facing huge setbacks concerning infection therapeutics as microorganisms are consistently knocking down every antimicrobial wall set before them. The situation becomes more worrying when taking into account that, in both environmental and disease scenarios, microorganisms present themselves as biofilm communities that are often polymicrobial. This comprises a competitive advantage, with interactions between different species altering host responses, antimicrobial effectiveness, microbial pathogenesis and virulence, usually augmenting the severity of the infection and contributing for the recalcitrance towards conventional therapy. Pseudomonas aeruginosa and Candida albicans are two opportunistic pathogens often co-isolated from infections, mainly from mucosal tissues like the lung. Despite the billions of years of co-existence, this pair of microorganisms is a great example on how little is known about cross-kingdom interactions, particularly within the context of coinfections. Given the described scenario, this study aimed to collect, curate, and analyze all published experimental information on the molecular basis of P. aeruginosa and C. albicans interactions in biofilms, in order to shed light into key mechanisms that may affect infection prognosis, increasing this area of knowledge. Publications were optimally retrieved from PubMed and Web of Science and classified as to their relevance. Data was then systematically and manually curated, analyzed, and further reconstructed as networks. A total of 641 interactions between the two pathogens were annotated, outputting knowledge on important molecular players affecting key virulence mechanisms, such as hyphal growth, and related genes and proteins, constituting potential therapeutic targets for infections related to these bacterial-fungal consortia. Contrasting interactions were also analyzed, and quorum-sensing inhibition approaches were highlighted. All annotated data was made publicly available at www.ceb.uminho.pt/ISCTD, a database already containing similar data for P. aeruginosa and Staphylococcus aureus communication. This will allow researchers to cut on time and effort when studying this particular subject, facilitating the understanding of the basis of the inter-species and inter-kingdom interactions and how it can be modulated to help design alternative and more effective tailored therapies. Finally, data deposition will serve as base for future dataset integration, whose analysis will hopefully give insights into communications in more complex and varied biofilm communities.

Sodium New Houttuyfonate Inhibits Candida albicans Biofilm Formation by Inhibiting the Ras1-cAMP-Efg1 Pathway Revealed by RNA-seq

Here, we aim to investigate the antifungal effect and mechanism of action of sodium new houttuyfonate (SNH) against Candida albicans. Microdilution analysis results showed that SNH possesses potent inhibitory activity against C. albicans SC5314, with a MIC₈₀ of 256 μg/mL. Furthermore, we found that SNH can effectively inhibit the initial adhesion of C. albicans. Inverted microscopy, crystal violet staining, scanning electron microscopy and confocal laser scanning microscopy results showed that morphological changes during the transition from yeast to hypha and the biofilm formation of C. albicans are repressed by SNH treatment. We also found that SNH can effectively inhibit the biofilm formation of clinical C. albicans strains (Z103, Z3044, Z1402, and Z1407) and SNH in combination with fluconazole, berberine chloride, caspofungin and itraconazole antifungal agents can synergistically inhibit the biofilm formation of C. albicans. Eukaryotic transcriptome sequencing and qRT-PCR results showed that SNH treatment resulted in significantly down-regulated expression in several biofilm formation related genes in the Ras1-cAMP-Efg1 pathway (ALS1, ALA1, ALS3, EAP1, RAS1, EFG1, HWP1, and TEC1) and significantly up-regulated expression in yeast form-associated genes (YWP1 and RHD1). We also found that SNH can effectively reduce the production of key messenger cAMP in the Ras1-cAMP-Efg1 pathway. Furthermore, using Galleria mellonella as an in vivo model we found that SNH can effectively treat C. albicans infection in vivo. Our presented results suggest that SNH exhibits potential antibiofilm effects related to inhibiting the Ras1-cAMP-Efg1 pathway in the biofilm formation of C. albicans.

Proposal for a microcosm biofilm model for the study of vulvovaginal candidiasis

This study proposes a microcosm biofilm (MiB) model for the study of vulvovaginal candidiasis (VVC). Different conditions that mimic the vaginal environment were tested for MiB formation. The best growth conditions were obtained with samples incubated in vaginal fluid simulator medium pH 4.5 at 35 °C under a microaerophilic atmosphere. MiBs were evaluated for growth kinetics, fluconazole susceptibility and morphology. Samples containing high numbers of bacteria were analyzed for metagenomics. At 48 h, MiBs presented a higher cell density (CFU ml^-1), a higher biomass and tolerance to fluconazole than their corresponding monospecies biofilms. Morphological analysis of MiBs revealed blastoconidia preferentially adhered to epithelial cells. Abundant Lactobacillus spp. were detected in two clinical samples; their MiBs showed a lower biomass and a higher fluconazole susceptibility. The proposed model proved to be a useful tool for the study of the complex microbial relationship in the vaginal environment, and may help to find new strategies for VVC control.

Application of Antibiotics/Antimicrobial Agents on Dental Caries

Dental caries is the most common oral disease. The bacteriological aetiology of dental caries promotes the use of antibiotics or antimicrobial agents to prevent this type of oral infectious disease. Antibiotics have been developed for more than 80 years since Fleming discovered penicillin in 1928, and systemic antibiotics have been used to treat dental caries for a long time. However, new types of antimicrobial agents have been developed to fight against dental caries. The purpose of this review is to focus on the application of systemic antibiotics and other antimicrobial agents with respect to their clinical use to date, including the history of their development, and their side effects, uses, structure types, and molecular mechanisms to promote a better understanding of the importance of microbial interactions in dental plaque and combinational treatments.

Microbiota in vaginal health and pathogenesis of recurrent vulvovaginal infections: a critical review

Recurrent vulvovaginal infections (RVVI) has not only become an epidemiological and clinical problem but also include large social and psychological consequences. Understanding the mechanisms of both commensalism and pathogenesis are necessary for the development of efficient diagnosis and treatment strategies for these enigmatic vaginal infections. Through this review, an attempt has been made to analyze vaginal microbiota (VMB) from scratch and to provide an update on its current understanding in relation to health and common RVVI i.e. bacterial vaginosis, vulvovaginal candidiaisis and Trichomoniasis, making the present review first of its kind. For this, potentially relevant studies were retrieved from data sources and critical analysis of the literature was made. Though, culture-independent methods have greatly unfolded the mystery regarding vaginal bacterial microbiome, there are only a few studies regarding the composition and diversity of vaginal mycobiome and different Trichomonas vaginalis strains. This scenario suggests a need of further studies based on comparative genomics of RVVI pathogens to improve our perceptive of RVVI pathogenesis that is still not clear (Fig. 5). Besides this, the review details the rationale for Lactobacilli dominance and changes that occur in healthy VMB throughout a women's life. Moreover, the list of possible agents continues to expand and new species recognised in both health and VVI are updated in this review. The review concludes with the controversies challenging the widely accepted dogma i.e. "VMB dominated with Lactobacilli is healthier than a diverse VMB". These controversies, over the past decade, have complicated the definition of vaginal health and vaginal infections with no definite conclusion. Thus, further studies on newly recognised microbial agents may reveal answers to these controversies. Conversely, VMB of women could be an answer but it is not enough to just look at the microbiology. We have to look at the woman itself, as VMB which is fine for one woman may be troublesome for others. These differences in women's response to the same VMB may be determined by a permutation of behavioural, cultural, genetic and various other anonymous factors, exploration of which may lead to proper definition of vaginal health and disease.

Interactions between oral commensal Candida and oral bacterial communities in immunocompromised and healthy children

Candida species are usually found as commensal microorganisms in the oral cavity of healthy people. During chemotherapy, cytostatic drugs lead to depletion of the oral flora with the emergence of a dominant bacterial species. The transition from commensal to pathogenic state, further associated with yeast colonization and oral mucositis implies a replacement of the dominant microorganism by Candida albicans. This process goes plausibly through cooperation between C. albicans and bacteria. This study focused on the first step of cooperation between microorganisms isolated from the same oral flora either of leukemic or healthy children. C. albicans isolated from 8/20 children were cultured to display their noninvasive blastosporic yeast form and mixed with their dominant bacteria to study the capacity of planktonic aggregation and the early state of biofilm formation. None of the dominant bacteria opposed the presence of yeast, on the contrary, an interesting cooperation was observed. This behavior is apparently different from that observed when mixing the type strains. In fact, three mutated C. albicans strains display, by their spontaneous ability to form filament, enhanced risks of virulence for leukemic ill carriers. Despite such risks, neither oral nor systemic pathology were observed in ill patients probably because the study was conducted during the first course of chemotherapy and Candida colonization is related to the number of chemotherapeutic cycles. The presence of C. albicans during the initial cycle represents, by its ability to interact with oral bacteria, an actual threat for further cures.

Evaluation of combined growth media for in vitro cultivation of oropharyngeal biofilms on prosthetic silicone

In the upper aerodigestive tract, biofilm deposits by oropharyngeal microbes can cause failure of medical polymer devices like voice prostheses. Previous studies on testing of inhibitive strategies still lack of comparability due to varying study protocols concerning growth media, microbial species and growth conditions. Goal of the study was therefore to test cultivation of a mixed biofilm of isolated oropharyngeal microbes under in vitro growth conditions using mixtures of common growth media. Mixtures of yeast peptone dextrose medium (YPD), fetal bovine serum (FBS), RPMI 1640, Yeast nitrogen base medium (YNB) and brain heart infusion (BHI) were tested to grow mixed biofilm deposits of Candida albicans, Candida tropicalis, Staphylococcus aureus, Streptococcus epidermidis, Rothia dentocariosa and Lactobacillus gasseri on medical grade silicone. Periodic assessment of living biofilm was performed over 22 days by a digital microscope and the cultivated biofilm structures were analyzed by scanning electron microscopy after completion of the study. Mixtures of BHI, YPD and FBS improved microscopic growth of multispecies biofilm deposits over time, while addition of RPMI and YNB resulted in reduction of visible biofilm deposit sizes. A mixtures of FBS 30% + YPD 70% and BHI 30% + YPD 70% showed enhanced support of permanent surface growth on silicone. Growth kinetics of in vitro multispecies biofilms can be manipulated by using mixtures of common growth media. Using mixtures of growth media can improve growth of longterm multispecies oropharyngeal biofilm models used for in vitro testing of antibiofilm materials or coatings for voice prostheses.

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.

Candida krusei isolated from fruit juices ultrafiltration membranes promotes colonization of Escherichia coli O157:H7 and Salmonella enterica on stainless steel surfaces

To clarify the interactions between a common food spoilage yeast and two pathogenic bacteria involved in outbreaks associated with fruit juices, the present paper studies the effect of the interplay of Candida krusei, collected from UF membranes, with Escherichia coli O157:H7 and Salmonella enterica in the overall process of adhesion and colonization of abiotic surfaces. Two different cases were tested: a) co-adhesion by pathogenic bacteria and yeasts, and b) incorporation of bacteria to pre-adhered C. krusei cells. Cultures were made on stainless steel at 25°C using apple juice as culture medium. After 24 h of co-adhesion with C. krusei, both E. coli O157:H7 and S. enterica increased their counts 1.05 and 1.11 log CFU cm², respectively. Similar increases were obtained when incorporating bacteria to pre-adhered cells of Candida. Nevertheless C. krusei counts decreased in both experimental conditions, in a) 0.40 log CFU cm² and 0.55 log CFU cm² when exposed to E. coli O157:H7 and S. enterica and in b) 0.18 and 0.68 log CFU cm², respectively. This suggests that C. krusei, E. coli O157:H7, and S. enterica have a complex relationship involving physical and chemical interactions on food contact surfaces. This study supports the possibility that pathogen interactions with members of spoilage microbiota, such as C. krusei, might play an important role for the survival and dissemination of E. coli O157:H7 and Salmonella enterica in food-processing environments. Based on the data obtained from the present study, much more attention should be given to prevent the contamination of these pathogens in acidic drinks.

The vaginal mycobiome: A contemporary perspective on fungi in women's health and diseases

Most of what is known about fungi in the human vagina has come from culture-based studies and phenotypic characterization of single organisms. Though valuable, these approaches have masked the complexity of fungal communities within the vagina. The vaginal mycobiome has become an emerging field of study as genomics tools are increasingly employed and we begin to appreciate the role these fungal communities play in human health and disease. Though vastly outnumbered by its bacterial counterparts, fungi are important constituents of the vaginal ecosystem in many healthy women. Candida albicans, an opportunistic fungal pathogen, colonizes 20% of women without causing any overt symptoms, yet it is one of the leading causes of infectious vaginitis. Understanding its mechanisms of commensalism and patho-genesis are both essential to developing more effective therapies. Describing the interactions between Candida, bacteria (such as Lactobacillus spp.) and other fungi in the vagina is funda-mental to our characterization of the vaginal mycobiome.

Influence of Candida krusei and Candida glabrata on Candida albicans gene expression in in vitro biofilms

OBJECTIVE

The present study aimed to evaluate the interactions between the species Candida albicans, Candida krusei and Candida glabrata in monotypic and mixed biofilm models formed in vitro as well as the relative expression of the ALS1, ALS3, HWP1, BCR1, EFG1, TEC1, SAP5, PLB2 and LIP9 genes.

MATERIAL AND METHODS

Mixed (C. albicans/C. krusei and C. albicans/C. glabrata) and monotypic biofilms were cultured for 0, 12 and 24h. Gene expression was analyzed in the same biofilm model in which the number of CFU/mL was counted.

RESULTS

The C. albicans CFU/mL values were lower at the 12 and 24h time points in the mixed biofilms compared with the monotypic biofilms, and decreases of 56.23% and 64.4% in C. albicans were observed when this species was associated with C. glabrata and C. krusei, respectively. In the presence of C. krusei, the expression of the ALS3, HWP1, BCR1, EFG1 and TEC1 genes of C. albicans was completely inhibited, indicating both transcriptome and the phenotypic antagonism between these two species, but genes related to the secretion of enzymes were stimulated. In the presence of C. glabrata, C. albicans showed a similar gene expression profile to that obtained in association with C. krusei, though it was altered to a lesser degree.

CONCLUSION

We conclude that C. krusei and C. glabrata may alter or inhibit the mechanisms involved in the in vitro adherence and formation of C. albicans biofilms, influencing the pathogenicity of this species and suggesting a competitive interaction with C. krusei and C. glabrata in biofilm formation.

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.

Candida survival strategies

Only few Candida species, e.g., Candida albicans, Candida glabrata, Candida dubliniensis, and Candida parapsilosis, are successful colonizers of a human host. Under certain circumstances these species can cause infections ranging from superficial to life-threatening disseminated candidiasis. The success of C. albicans, the most prevalent and best studied Candida species, as both commensal and human pathogen depends on its genetic, biochemical, and morphological flexibility which facilitates adaptation to a wide range of host niches. In addition, formation of biofilms provides additional protection from adverse environmental conditions. Furthermore, in many host niches Candida cells coexist with members of the human microbiome. The resulting fungal-bacterial interactions have a major influence on the success of C. albicans as commensal and also influence disease development and outcome. In this chapter, we review the current knowledge of important survival strategies of Candida spp., focusing on fundamental fitness and virulence traits of C. albicans.

Virulence and pathogenicity of Candida albicans is enhanced in biofilms containing oral bacteria

This study examined the influence of bacteria on the virulence and pathogenicity of candidal biofilms. Mature biofilms (Candida albicans-only, bacteria-only, C. albicans with bacteria) were generated on acrylic and either analysed directly, or used to infect a reconstituted human oral epithelium (RHOE). Analyses included Candida hyphae enumeration and assessment of Candida virulence gene expression. Lactate dehydrogenase (LDH) activity and Candida tissue invasion following biofilm infection of the RHOE were also measured. Candida hyphae were more prevalent (p < 0.05) in acrylic biofilms also containing bacteria, with genes encoding secreted aspartyl-proteinases (SAP4/SAP6) and hyphal-wall protein (HWP1) up-regulated (p < 0.05). Candida adhesin genes (ALS3/EPA1), SAP6 and HWP1 were up-regulated in mixed-species biofilm infections of RHOE. Multi-species infections exhibited higher hyphal proportions (p < 0.05), up-regulation of IL-18, higher LDH activity and tissue invasion. As the presence of bacteria in acrylic biofilms promoted Candida virulence, consideration should be given to the bacterial component when managing denture biofilm associated candidoses.

Differential gene expression profiling of Actinobacillus pleuropneumoniae during induction of primary alveolar macrophage apoptosis in piglets

Actinobacillus pleuropneumoniae (A. pleuropneumoniae) is the causative agent of porcine pleuropneumonia, a disease that causes serious problems for the swine industry. Successful infection by this bacterium requires breaking the first line of defence in the lungs, the primary alveolar macrophages (PAMs). Therefore, exploring A. pleuropneumoniae-PAM interactions will provide vital groundwork for the scientific control of this infectious disease, which has been little studied up to now. In this work, PAMs were isolated from piglets and co-incubated with A. pleuropneumoniae serovar 5b strain L20 in vitro, and their interaction, PAM cell death, and differential gene expression of A. pleuropneumoniae in response to PAM cell death were observed and analysed using confocal microscopy, electron microscopy, RT-PCR, Western blot, flow cytometry and the use of a gene expression profile chip. A. pleuropneumoniae quickly adhered to and invaded PAMs, inducing apoptosis, which was confirmed using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The highest percentage of apoptosis in cells was confirmed using flow cytometry when the cells were infected at a multiplicity of infection (MOI) of 10 and incubated for 5 h, with higher expression of activated caspase-3 as measured by Western blot. Using microarray gene chips with 2868 probes containing nearly all of the genomic sequence of A. pleuropneumoniae serotype 5b strain L20, a total of 185 bacterial genes were found to be differentially expressed (including 92 up-regulated and 93 down-regulated genes) and involved in the process of apoptosis, as compared with the expression of control bacteria cultured without PAMs in BHI medium (mean expression ratios >1.5-fold, p < 0.05). The up-regulated genes are involved in energy metabolism, gene transcription and translation, virulence related gene such as LPS, Trimeric Autotransporter Adhesin, RTX and similar genes. The down-regulated genes are involved in amino acid, cofactor, and vitamin metabolism, and also include ABC transporters. These data demonstrate that A. pleuropneumoniae induces apoptosis of PAMs and undergoes complex changes in gene transcription, including expression changes in known and potential virulence factors. Some potentially novel virulence targets have been identified, suggesting new strategies for the development of vaccines and medicines for both preventive and clinical use.