Impact of biofilm production by Candida species and antifungal therapy on mortality of patients with candidemia

Anti-Biofilm Activity of Cocultimycin A against Candida albicans

Candida albicans (C. albicans), the most common fungal pathogen, has the ability to form a biofilm, leading to enhanced virulence and antibiotic resistance. Cocultimycin A, a novel antifungal antibiotic isolated from the co-culture of two marine fungi, exhibited a potent inhibitory effect on planktonic C. albicans cells. This study aimed to evaluate the anti-biofilm activity of cocultimycin A against C. albicans and explore its underlying mechanism. Crystal violet staining showed that cocultimycin A remarkably inhibited biofilm formation in a dose-dependent manner and disrupted mature biofilms at higher concentrations. However, the metabolic activity of mature biofilms treated with lower concentrations of cocultimycin A significantly decreased when using the XTT reduction method. Cocultimycin A could inhibit yeast-to-hypha transition and mycelium formation of C. albicans colonies, which was observed through the use of a light microscope. Scanning electron microscopy revealed that biofilms treated with cocultimycin A were disrupted, yeast cells increased, and hypha cells decreased and significantly shortened. The adhesive ability of C. albicans cells treated with cocultimycin A to the medium and HOEC cells significantly decreased. Through the use of a qRT-PCR assay, the expression of multiple genes related to adhesion, hyphal formation and cell membrane changes in relation to biofilm cells treated with cocultimycin A. All these results suggested that cocultimycin A may be considered a potential novel molecule for treating and preventing biofilm-related C. albicans infections.

3-Hydroxy coumarin demonstrates anti-biofilm and anti-hyphal efficacy against Candida albicans via inhibition of cell-adhesion, morphogenesis, and virulent genes regulation

Candida albicans, a common fungus of human flora, can become an opportunistic pathogen and causes invasive candidiasis in immunocompromised individuals. Biofilm formation is the prime cause of antibiotic resistance during C. albicans infections and treating biofilm-forming cells is challenging due to their intractable and persistent nature. The study intends to explore the therapeutic potential of naturally produced compounds by competitive marine bacteria residing in marine biofilms against C. albicans biofilm. To this end, 3-hydroxy coumarin (3HC), a compound identified from the cell-free culture supernatant of the marine bacterium Brevundimonas abyssalis, was found to exhibit anti-biofilm and anti-hyphal activity against both reference and clinical isolates of C. albicans. The compound demonstrated significant inhibitory effects on biofilms and impaired the yeast-to-hyphal transition, wrinkle, and filament morphology at the minimal biofilm inhibitory concentration (MBIC) of 250 µg mL^-1. Intriguingly, quantitative PCR analysis of 3HC-treated C. albicans biofilm revealed significant downregulation of virulence genes (hst7, ume6, efg1, cph1, ras1, als1) associated with adhesion and morphogenesis. Moreover, 3HC displayed non-fungicidal and non-toxic characteristics against human erythrocytes and buccal cells. In conclusion, this study showed that marine biofilms are a hidden source of diverse therapeutic drugs, and 3HC could be a potent drug to treat C. albicans infections.

Novel evidence on sepsis-inducing pathogens: from laboratory to bedside

Sepsis is a life-threatening condition and a significant cause of preventable morbidity and mortality globally. Among the leading causative agents of sepsis are bacterial pathogens Escherichia coli, Klebsiella pneumoniae, Staphylococcus aureus, Pseudomonas aeruginosa, and Streptococcus pyogenes, along with fungal pathogens of the Candida species. Here, we focus on evidence from human studies but also include in vitro and in vivo cellular and molecular evidence, exploring how bacterial and fungal pathogens are associated with bloodstream infection and sepsis. This review presents a narrative update on pathogen epidemiology, virulence factors, host factors of susceptibility, mechanisms of immunomodulation, current therapies, antibiotic resistance, and opportunities for diagnosis, prognosis, and therapeutics, through the perspective of bloodstream infection and sepsis. A list of curated novel host and pathogen factors, diagnostic and prognostic markers, and potential therapeutical targets to tackle sepsis from the research laboratory is presented. Further, we discuss the complex nature of sepsis depending on the sepsis-inducing pathogen and host susceptibility, the more common strains associated with severe pathology and how these aspects may impact in the management of the clinical presentation of sepsis.

Synergistic Antibiofilm Effects of Pseudolaric Acid A Combined with Fluconazole against Candida albicans via Inhibition of Adhesion and Yeast-To-Hypha Transition

Candida albicans biofilms are resistant to several clinical antifungal agents. Thus, it is necessary to develop new antibiofilm intervention measures. Pseudolaric acid A (PAA), a diterpenoid mainly derived from the pine bark of Pseudolarix kaempferi, has been reported to have an inhibitory effect on C. albicans. The primary aim of the current study was to investigate the antibiofilm effect of PAA when combined with fluconazole (FLC) and explore the underlying mechanisms. Biofilm activity was assessed by tetrazolium {XTT [2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide salt]} reduction assays. PAA (4 μg/mL) combined with FLC (0.5 μg/mL) significantly inhibited early, developmental, and mature biofilm formation compared with the effect of PAA or FLC alone (P < 0.05). Furthermore, PAA (4 μg/mL) combined with FLC (0.5 μg/mL) produced a 56% reduction in C. albicans biofilm adhesion. The combination of PAA (4 μg/mL) and FLC (0.5 μg/mL) also performed well in inhibiting yeast-to-hypha transition. Transcriptome analysis using RNA sequencing and quantitative reverse transcription PCR indicated that the PAA-FLC combination treatment produced a strong synergistic inhibitory effect on the expression of genes involved in adhesion (ALS1, ALS4, and ALS2) and yeast-to-hypha transition (ECE1, PRA1, and TEC1). Notably, PAA, rather than FLC, may have a primary role in suppressing the expression of ALS1. In conclusion, these findings demonstrate, for the first time, that the combination of PAA and FLC has an improved antibiofilm effect against the formation of C. albicans biofilms by inhibiting adhesion and yeast-to-hypha transition; this may provide a novel therapeutic strategy for treating C. albicans biofilm-associated infection.

IMPORTANCE Biofilms are the primary cause of antibiotic-resistant candida infections associated with medical implants and devices worldwide. Treating biofilm-associated infections is a challenge for clinicians because these infections are intractable and persistent. Candida albicans readily forms extensive biofilms on the surface of medical implants and mucosa. In this study, we demonstrated, for the first time, an inhibitory effect of pseudolaric acid A alone and in combination with fluconazole on C. albicans biofilms. Moreover, pseudolaric acid A in combination with fluconazole exerted an antibiofilm effect through multiple pathways, including inhibition of yeast-to-hypha transition and adhesion. This research not only provides new insights into the synergistic mechanisms of antifungal drug combinations but also brings new possibilities for addressing C. albicans drug resistance.

Anti-Candidal Activity of the Parasitic Plant Orobanche crenata Forssk

Candida albicans (C. albicans) and Candida glabrata (C. glabrata) are part of the human microbiome. However, they possess numerous virulence factors, which confer them the ability to cause both local and systemic infections. Candidiasis can involve multiple organs, including the eye. In the present study, we investigated the anti-candidal activity and the re-epithelizing effect of Orobanche crenata leaf extract (OCLE). By the microdilution method, we demonstrated an inhibitory effect of OCLE on both C. albicans and C. glabrata growth. By crystal violet and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, we showed the ability of OCLE to inhibit the biofilm formation and the viability of yeast cells, respectively. By germ tube and adhesion assays, we proved the capacity of OCLE to affect the morphological transition of C. albicans and the adhesion of both pathogens to human retinal pigment epithelial cells (ARPE-19), respectively. Besides, by MTT and wound healing assay, we evaluated the cytotoxic and re-epithelizing effects of OCLE on ARPE-19. Finally, the Folin-Ciocalteu and the ultra-performance liquid chromatography-tandem mass spectrometry revealed a high content of phenols and the presence of several bioactive molecules in the extract. Our results highlighted new properties of O. crenata, useful in the control of Candida infections.

How does temperature trigger biofilm adhesion and growth in Candida albicans and two non-Candida albicans Candida species?

BACKGROUND

Biofilm formation on biotic and abiotic surfaces is finely regulated by genetic factors but also by oxygen concentration, pH, temperature and other environmental factors, already extensively explored for bacterial biofilms. Much less is known about fungal biofilm, that is considered a virulence factor for Candida pathogenic species among the few fungal species able to grow and survive at high temperatures such as 37°C as well as those induced by fever. The resistance to high temperatures coupled with the ability to form biofilm are threatening factors of these fungal species that could severely impact at an epidemiological level.

OBJECTIVES

In this framework, we decided to study the thermal tolerance of biofilms formed by three medical relevant species such as Candida albicans and two non-Candida albicans Candida species.

METHODS

Thirty nosocomial strains were investigated for their ability to adhere and grow in proximity and over body temperature (from 31 to 43°C), mimicking different environmental conditions or severe febrile-like reactions.

RESULTS

Candida sessile cells reacted to different temperatures showing a strain-specific response. It was observed that the attachment and growth respond differently to the temperature and that mechanism of adhesion has different outputs at high temperature than the growth.

CONCLUSIONS

This strain-dependent response is probably instrumental to guarantee the best success to cells for the infection, attachment and growth to occur. These observations reinforce the concept of temperature as a major trigger in the evolution of these species especially in this period of increasing environmental temperatures and excessive domestic heating.

Recent progress on anti-Candida natural products

Candida is an intractable life-threatening pathogen. Candida infection is extremely difficult to eradicate, and thus is the major cause of morbidity and mortality in immunocompromised individuals. Morevover, the rapid spread of drug-resistant fungi has led to significant decreases in the therapeutic effects of clinical drugs. New anti-Candida agents are urgently needed to solve the complicated medical problem. Natural products with intricate structures have attracted great attention of researchers who make every endeavor to discover leading compounds for antifungal agents. Their novel mechanisms and diverse modes of action expand the variety of fungistatic agents and reduce the emergence of drug resistance. In recent decades, considerable effort has been devoted to finding unique antifungal agents from nature and revealing their unusual mechanisms, which results in important progress on the development of new antifungals, such as the novel cell wall inhibitors YW3548 and SCY-078 which are being tested in clinical trials. This review will present a brief summary on the landscape of anti-Candida natural products within the last decade. We will also discuss in-depth the research progress on diverse natural fungistatic agents along with their novel mechanisms.

Caspofungin and Polymyxin B Reduce the Cell Viability and Total Biomass of Mixed Biofilms of Carbapenem-Resistant Pseudomonas aeruginosa and Candida spp

Pseudomonas aeruginosa and Candida spp. are biofilm-forming pathogens commonly found colonizing medical devices, being mainly associated with pneumonia and bloodstream infections. The coinfection by these pathogens presents higher mortality rates when compared to those caused by a single microbial species. This study aimed to evaluate the antibiofilm activity of echinocandins and polymyxin B (PMB) against polymicrobial biofilms of carbapenem-resistant (CR) Pseudomonas aeruginosa and Candida spp. (C. albicans, C. parapsilosis, C. tropicalis, and C. glabrata). In addition, we tested the antimicrobial effect on their planktonic and monomicrobial biofilm counterparties. Interestingly, beyond inhibition of planktonic [minimum inhibitory concentration (MIC) = 0.5 μg/ml] and biofilm [minimum biofilm inhibitory concentration (MBIC)₅₀ ≤ 2–8 μg/ml] growth of P. aeruginosa, PMB was also effective against planktonic cells of C. tropicalis (MIC = 2 μg/ml), and polymicrobial biofilms of CR P. aeruginosa with C. tropicalis (MBIC₅₀ ≤ 2 μg/ml), C. parapsilosis (MBIC₅₀ = 4–16 μg/ml), C. glabrata (MBIC₅₀ = 8–16 μg/ml), or C. albicans (MBIC₅₀ = 8–64 μg/ml). On the other hand, while micafungin (MFG) showed highest inhibitory activity against planktonic (MIC ≤ 0.008–0.5 μg/ml) and biofilm (MBIC₅₀ ≤ 2–16 μg/ml) growth of Candida spp.; caspofungin (CAS) displays inhibitory activity against planktonic cells (MIC = 0.03–0.25 μg/ml) and monomicrobial biofilms (MBIC₅₀ ≤ 2–64 μg/ml) of Candida spp., and notably on planktonic and monomicrobial biofilms of CR P. aeruginosa (MIC or MBIC₅₀ ≥ 64 μg/ml). Particularly, for mixed biofilms, while CAS reduced significantly viable cell counts of CR P. aeruginosa and Candida spp. at ≥32 and ≥ 2 μg/ml, respectively; PMB was effective in reducing viable cells of CR P. aeruginosa at ≥2 μg/ml and Candida spp. at ≥8 μg/ml. Similar reduction of viable cells was observed for CAS (32–64 μg/ml) combined with PMB (2 μg/ml). These findings highlight the potential of PMB and CAS for the treatment of polymicrobial infections caused by Candida spp. and critical priority CR P. aeruginosa.