Exploring ecological modelling to investigate factors governing the colonization success in nosocomial environment of Candida albicans and other pathogenic yeasts

The Bovhyaluronidase Azoximer (Longidaza®) Disrupts Candida albicans and Candida albicans-Bacterial Mixed Biofilms and Increases the Efficacy of Antifungals

Background and Objectives: Candida albicans causes various diseases ranging from superficial mycoses to life-threatening systemic infections often associated with biofilm formation, including mixed fungal−bacterial consortia. The biofilm matrix protects cells, making Candida extremely resistant to treatment. Here, we show that the bovhyaluronidase azoximer (Longidaza®) in vitro destroys the biofilm formed by either C. albicans alone or mixed with bacteria, this way decreasing the concentrations of antimicrobials required for the pathogen’s eradication. Materials and Methods: Bovhyaluronidase azoximer, Longidaza® was obtained from NPO Petrovax Pharm Ltd., Moscow, Russia as lyophilized powder. The antifungal activity was assessed by microdilution assay and CFUs counting. Antibiofilm activity was evaluated via biofilms staining and scanning electron microscopy. Results: Thus, treatment with Longidaza® reduced the biofilm biomass of nine C. albicans clinical isolates by 30−60%, while mixed biofilms of C. albicans with various bacteria were destroyed by 30−40%. Furthermore, the concentration of fluconazole required to achieve a similar reduction of the residual respiratory activity of detached cell clumps of four C. albicans isolates has been reduced four-fold when combined with Longidaza®. While in the biofilm, two of four isolates became significantly more susceptible to fluconazole in combination with Longidaza®. Conclusion: Taken together, our data indicate that Longidaza® is capable of suppression of tissues and artificial surfaces biofouling by C. albicans biofilms, as well as facilitating drug penetration into the cell clumps, this way decreasing the effective MIC of antifungals.

Metabolomic and Proteomic Changes in Candida albicans Biofilm in Response to Zosteric Acid Treatment

Zosteric acid (ZA) is a secondary metabolite of the seagrass Zostera marina, with antibiofilm activity against fungi. Information concerning its mechanisms of action is lacking and this limits the development of more potent derivatives based on the same target and activity structure. The aim of this work was to investigate the ZA mode of action by analyzing the metabolic status of Candida albicans biofilm and its protein expression profile upon ZA treatment. Fourier-Transform Infrared Spectroscopy confirmed that ZA modified the metabolomic response of treated cells, showing changes in the spectral regions, mainly related to the protein compartment. Nano Liquid Chromatography-High-Resolution Mass Spectrometry highlighted that 10 proteins were differentially expressed in the C. albicans proteome upon ZA treatment. Proteins involved in the biogenesis, structure and integrity of cell walls as well as adhesion and stable attachment of hyphae were found downregulated, whereas some proteins involved in the stress response were found overexpressed. Additionally, ZA was involved in the modulation of non-DNA-based epigenetic regulatory mechanisms triggered by reactive oxygen species. These results partially clarified the ZA mechanism of action against fungi and provided insight into the major C. albicans pathways responsible for biofilm formation.

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.

Qualitative and quantitative change of the tolerance to liposomal amphotericin B triggered by biofilm maturation in C. parapsilosis

Candida parapsilosis is an emerging opportunistic pathogen present in both clinical and natural environment, with a strong frequency of biofilm forming strains. While the drugs active against biofilm are rare, liposomal amphotericin B is credited with an antibiofilm activity in some opportunistic species of the genus Candida. Using freshly isolated strains from hospital environment, in this paper we could show the prevalence of biofilm forming vs. nonbiofilm forming strains. The former displayed a large variability in terms of biofilm biomass and metabolic activity. Liposomal amphotericin B minimum inhibitory concentration (MIC) of planktonic cells was below the breakpoint, whereas the sessile cells MIC (SMIC) was 1 or 2 orders of magnitude above the planktonic MIC. When the drug was applied to freshly attached cells, that is, biofilm in formation, the MIC (called SDMIC) was even below the MIC value. All resistance metrics (MIC, SMIC, and SDMIC) were quite variable although no correlation could be detected between them and the metrics used to quantify biofilm activity and biomass production. These findings demonstrate that young biofilm cells are even more susceptible than planktonic cells and that early treatments with this drug can be beneficial in cases of prosthesis implantation or especially when there is the necessity of a CVC reimplantation during a sepsis.

Single Strain High-Depth NGS Reveals High rDNA (ITS-LSU) Variability in the Four Prevalent Pathogenic Species of the Genus Candida

Ribosomal RNA in fungi is encoded by a series of genes and spacers included in a large operon present in 100 tandem repeats, normally in a single locus. The multigene nature of this locus was somehow masked by Sanger sequencing, which produces a single sequence reporting the prevalent nucleotide of each site. The introduction of next generation sequencing led to deeper knowledge of the individual sequences (reads) and therefore of the variants between the same DNA sequences located in different tandem repeats. In this framework, NGS sequencing of the rDNA region was used to elucidate the extent of intra- and inter-genomic variation at both the strain and species level. Specifically, the use of an innovative NGS technique allowed the high-throughput high-depth sequencing of the ITS1-LSU D1/D2 amplicons of 252 strains belonging to four opportunistic yeast species of the genus Candida. Results showed the presence of a large extent of variability among strains and species. These variants were differently distributed throughout the analyzed regions with a higher concentration within the Internally Transcribed Spacer (ITS) region, suggesting that concerted evolution was not able to totally homogenize these sequences. Both the internal variability and the SNPs between strain can be used for a deep typing of the strains and to study their ecology.

Targeting pathogenic fungi, bacteria and fungal-bacterial biofilms by newly synthesized quaternary ammonium derivative of pyridoxine and terbinafine with dual action profile

Many pathogenic bacteria and microscopic fungi form rigid polymicrobial biofilms this way enhancing their resistant to treatment. A series of novel pyridoxine-based quaternary ammonium derivatives of terbinafine characterized by both antifungal and antibacterial activities was designed. The leading compound named KFU-127 exhibits promising antifungal and antibacterial activities against various bacteria and micromycetes in both planktonic and biofilm-embedded forms demonstrating MIC values comparable with those of conventional antifungals and antimicrobials. Similar to other antiseptics like benzalkonium chloride and miramistin, KFU-127 is considerably toxic for eukaryotic cells that limits is application to topical treatment options. On the other hand, KFU-127 reduces the number of viable biofilm-embedded bacteria and C. albicans by 3 orders of magnitude at concentrations 2-4 times lower than those of reference drugs and successfully eradicates S. aureus-C. albicans mixed biofilms. The mechanism of antimicrobial action of KFU-127 is bimodal including both membrane integrity damage and pyridoxal-dependent enzymes targeting. We expect that this bilateral mechanism would result in lower rates of resistance development in both fungal and bacterial pathogens. Taken together, our data suggest KFU-127 as a new promising broad spectrum topical antimicrobial capable of one-shot targeting of bacterial and fungal-bacterial biofilms.

Recognition of Candida albicans and Role of Innate Type 17 Immunity in Oral Candidiasis

Candida albicans is an opportunistic pathogenic fungus considered to be a common member of the human microflora. Similar to some other opportunistic microbes, C. albicans can invade and benefit from its host when the immune status of that host is weakened. Most often this happens to immunocompromised individuals, leading to the infection of oral and vaginal mucosae or the systemic spread of the pathogen throughout the entire body. Oropharyngeal candidiasis (OPC) occurs in up to 90 percent of patients with acquired immunodeficiency syndrome (AIDS), making it the most frequent opportunistic infection for this group. Upon first signs of fungal invasion, a range of host signaling activates in order to eliminate the threat. Epithelial and myeloid type cells detect C. albicans mainly through receptor tyrosine kinases and pattern-recognition receptors. This review provides an overview of downstream signaling resulting in an adequate immune response through the activation of various transcription factors. The study discusses recent advances in research of the interleukin-17 (IL-17) producing innate cells, including natural T helper 17 (nTh17) cells, γδ T cells, invariant natural killer T (iNKT) cells and type 3 innate lymphoid cells (ILC3) that are involved in response to oral C. albicans infections.

Increasing Susceptibility of Drug-Resistant Candida albicans to Fluconazole and Terbinafine by 2(5H)-Furanone Derivative

The frequency of mycoses caused by drug-resistant fungal pathogen Candida albicans has increased drastically over the last two decades. The spread of drug-resistant strains, along with the limitations of currently available antifungals, complicates the management of fungal infections, thereby representing great challenges for clinical healthcare. Among various antimicrobial pharmacophores, 2(5H)-furanone derivatives have demonstrated antimicrobial, antifungal, and antibiofilm activities. In this study, we report the antifungal activity of the 2(5H)-furanone derivative F105, consisting of three pharmacophores, namely chlorinated 2(5H)-furanone, sulfonyl group, and l-menthol moiety. Although exhibiting moderate antifungal activity alone with the minimum inhibitory concentration (MIC) values of 32–256 μg/mL, F105 potentiates the activity of fluconazole and terbinafine with fractional inhibitory concentration index (FICI) values of 0.27–0.50. Thus, 16 μg/mL of F105 reduced the MICs of these antifungals against fluconazole-resistant C. albicans isolates four-fold, achieving similar values as for the intermediately susceptible phenotype. Confocal laser scanning microscopy revealed that the fluorescent 2(5H)-furanone derivative F145 was also able to penetrate through biofilms formed by C. albicans. Indeed, in the presence of F105, even sub-MIC concentrations of both fluconazole and terbinafine led to significant reduction of C. albicans CFUs in the mature biofilm. Thus, F105 appears to be a promising candidate for the development of novel antifungal agents as well as enhancers of current antifungal agents, particularly for the treatment of drug-resistant C. albicans infections.

Biofilm Specific Activity: A Measure to Quantify Microbial Biofilm

Microbes growing onto solid surfaces form complex 3-D biofilm structures characterized by the production of extracellular polymeric compounds and an increased resistance to drugs. The quantification of biofilm relays currently on a number of different approaches and techniques, often leading to different evaluations of the ability to form biofilms of the studied microbial strains. Measures of biofilm biomass were carried out with crystal violet (CV) and a direct reading at 405 nm, whereas the activity was assessed with the XTT ((2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide) method. The strains of four pathogenic species of the genus Candida (C. albicans, C. glabrata, C. parapsilosis and C. tropicalis) and of Staphylococcus aureus were employed to determine the effective relatedness among techniques and the specific activity of the biofilm, as a ratio between the XTT and the CV outcomes. Since the ability to form biomass and to be metabolically active are not highly related, their simultaneous use allowed for a categorization of the strains. This classification is putatively amenable of further study by comparing the biofilm type and the medical behavior of the strains.

Biofilms and beyond: expanding echinocandin utility

Echinocandins have been in use for over 15 years, starting with the first approval in 2001. Current trends, such as increasing resistance to fluconazole and shifts toward non-albicans spp. of Candida, suggest a growing role for echinocandins, as reflected by recent (2016) updates to guidelines that recommend echinocandins as first-line treatment for candidaemia. The efficacy, tolerability, and safety of echinocandins and their target site of action (1,3-β-d-glucan synthesis) have prompted research into potential new uses, such as for treatment of biofilm infections, MDR Candida auris and dermatophytes. Moreover, new mycobiome discoveries linking inflammatory bowel disease (IBD; for instance Crohn's disease) to fungi have led to preliminary but encouraging data regarding echinocandin therapy and treatment of IBD. In this article, we will review the available evidence and potential utility of echinocandins and 1,3-β-d-glucan synthesis inhibition in these areas of emerging interest.

High-Throughput Rapid and Inexpensive Assay for Quantitative Determination of Low Cell-Density Yeast Cultures

A procedure for microbial cell density determination with a high-throughput densitometric assay was developed to allow a precise quantification of both free and sessile cells, such as those of a biofilm, with a large range from low to high cell densities. Densitometry was chosen because it allows fast, rapid and cost-effective measures; it is non-disruptive; and has an easy learning curve. The method setup, and the further validation, was carried out with strains of Candida albicans, C. tropicalis and C. parapsilosis. Equations were developed at the level of the single strains, of the three species and finally a general one applicable to all three species. In the cross validation, with strains absent from the training set, the method was shown to be robust and flexible. The best results were obtained with species specific equations, although the global equation performed almost as well in terms of correlation between real and estimated density values. In all cases, a correlation around 0.98 between effective and predicted density was obtained with figures ranging from 10² to 10⁸ cells mL⁻¹. The entire analytical part of the procedure can be accomplished with a MS Excel macro provided free of charge.

Echinocandins for management of invasive candidiasis in patients with liver disease and liver transplantation

Candida species remains one of the most important causes of opportunistic infections worldwide. Invasive candidiasis (IC) is associated with considerable morbidity and mortality in liver disease (LD) patients if not treated promptly. Echinocandins are often recommended as a first-line empirical treatment for managing IC and can especially play a critical role in managing IC in LD patients. However, advanced LD patients are often immunocompromised and critically ill. Hence altered pharmacokinetics, drug interactions as well as tolerance issues of antifungal treatments are a concern in these patients. This comprehensive review examines the epidemiology, risk factors and diagnosis of IC in patients with LD and evaluates differences between three available echinocandins for treating this group of patients.

NGS barcode sequencing in taxonomy and diagnostics, an application in "Candida" pathogenic yeasts with a metagenomic perspective

Species identification of yeasts and other Fungi is currently carried out with Sanger sequences of selected molecular markers, mainly from the ribosomal DNA operon, characterized by hundreds of tandem repeats of the 18S, ITS1, 5.8S, ITS2 and LSU loci. The ITS region has been recently proposed as a primary barcode marker making this region the most used one in taxonomy, phylogeny and diagnostics. The introduction of NGS is providing tools of high efficacy and relatively low cost to amplify two or more markers simultaneously with great sequencing depth. However, the presence of intra-genomic variability between the repeats requires specific analytical procedures and pipelines. In this study, 286 strains belonging to 11 pathogenic yeasts species were analysed with NGS of the region spanning from ITS1 to the D1/D2 domain of the LSU encoding ribosomal DNA. Results showed that relatively high heterogeneity can hamper the use of these sequences for the identification of single strains and even more of complex microbial mixtures. These observations point out that the metagenomics studies could be affected by species inflection at levels higher than currently expected.

Yeast Biofilm as a Bridge Between Medical and Environmental Microbiology Across Different Detection Techniques

Medical and environmental microbiology have two distinct, although very short, histories stemming, the first from the pioneering works of Sommelweiss, Pasteur, Lister and Koch, the second mainly from the studies of Bejerink and Winogradsky. These two branches of microbiology evolved and specialized separately producing distinct communities and evolving rather different approaches and techniques. The evidence accumulated in recent decades indicate that indeed most of the medically relevant microorganisms have a short circulation within the nosocomial environment and a larger one involving the external, i.e. non-nosocomial, and the hospital environments. This evidence suggests that the differences between approaches should yield to a convergent approach aimed at solving the increasing problem represented by infectious diseases for the increasingly less resistant human communities. Microbial biofilm is one of the major systems used by these microbes to resist the harsh conditions of the natural and anthropic environment, and the even worse ones related to medical settings. This paper presents a brief outline of the converging interest of both environmental and medical microbiology toward a better understanding of microbial biofilm and of the various innovative techniques that can be employed to characterize, in a timely and quantitative manner, these complex structures. Among these, micro-Raman along with micro-Brillouin offer high hopes of describing biofilms both at the subcellular and supercellular level, with the possibility of characterizing the various landscapes of the different biofilms. The possibility of adding a taxonomic identification of the cells comprising the biofilm is a complex aspect presenting several technical issues that will require further studies in the years to come.

Merging FT-IR and NGS for simultaneous phenotypic and genotypic identification of pathogenic Candida species

The rapid and accurate identification of pathogen yeast species is crucial for clinical diagnosis due to the high level of mortality and morbidity induced, even after antifungal therapy. For this purpose, new rapid, high-throughput and reliable identification methods are required. In this work we described a combined approach based on two high-throughput techniques in order to improve the identification of pathogenic yeast strains. Next Generation Sequencing (NGS) of ITS and D1/D2 LSU marker regions together with FTIR spectroscopy were applied to identify 256 strains belonging to Candida genus isolated in nosocomial environments. Multivariate data analysis (MVA) was carried out on NGS and FT-IR data-sets, separately. Strains of Candida albicans, C. parapsilosis, C. glabrata and C. tropicalis, were identified with high-throughput NGS sequencing of ITS and LSU markers and then with FTIR. Inter- and intra-species variability was investigated by consensus principal component analysis (CPCA) which combines high-dimensional data of the two complementary analytical approaches in concatenated PCA blocks normalized to the same weight. The total percentage of correct identification reached around 97.4% for C. albicans and 74% for C. parapsilosis while the other two species showed lower identification rates. Results suggested that the identification success increases with the increasing number of strains actually used in the PLS analysis. The absence of reliable FT-IR libraries in the current scenario is the major limitation in FTIR-based identification of strains, although this metabolomics fingerprint represents a valid and affordable aid to rapid and high-throughput to clinical diagnosis. According to our data, FT-IR libraries should include some tens of certified strains per species, possibly over 50, deriving from diverse sources and collected over an extensive time period. This implies a multidisciplinary effort of specialists working in strain isolation and maintenance, molecular taxonomy, FT-IR technique and chemo-metrics, data management and data basing.

The role of biofilm forming on mortality in patients with candidemia: a study derived from real world data

BACKGROUND

Evaluation of the role on patient mortality exerted by biofilm forming (BF) Candida strains, by using predictive clinical data.

METHODS

Eighty-nine strains isolated from Candida bloodstream infection, occurring in two Italian University Hospitals, were employed in this study. A random forest (RF) model was built with a procedure of iterative selection of the risk factors potentially able to predict the probability of death. The similarity between patient conditions and Bayesian clustering was calculated in order to evaluate the role of predictors in the stratification of the death risk.

RESULTS

Three different groups of patients with different probability of death were obtained with a RF approach: Group 1 (mortality in 33.3% of cases), Group 2 (death in 50% of cases), and Group 3 (mortality in 76.9% of cases). The comparison between these three groups showed that BF correlated well with increased mortality in patients, admitted for medical diagnosis, with high APACHE II score and treated with azoles. Early treatment within 24 h between candidemia diagnosis and the beginning of antifungal therapy was associated with the lowest of BF rate and mortality.

CONCLUSIONS

BF by Candida spp. seems to be clinically associated with increased mortality especially in medical patients with higher Apache II score or treated with azoles.

High-contrast Brillouin and Raman micro-spectroscopy for simultaneous mechanical and chemical investigation of microbial biofilms

Mechanical mapping with chemical specificity of biological samples is now made possible by joint micro-Brillouin and micro-Raman measurements. In this work, thanks to the unprecedented contrast of a new tandem Fabry-Perot interferometer, we demonstrate simultaneous detection of Brillouin and Raman spectra from different Candida biofilms. Our proof-of-concept study reveals the potential of this label-free joint micro-spectroscopy technique in challenging microbiological issues. In particular, heterogeneous chemo-mechanical maps of Candida biofilms are obtained, without the need for staining or touching the sample. The correlative Raman and Brillouin investigation evidences the role of both extracellular polymeric substances and of hydration water in inducing a marked local softening of the biofilm.