Fungal persister cells: The basis for recalcitrant infections?

Aspergillus fumigatus escape mechanisms from its harsh survival environments

Aspergillus fumigatus is a ubiquitous pathogenic mold and causes several diseases, including mycotoxicosis, allergic reactions, and systemic diseases (invasive aspergillosis), with high mortality rates. In its ecological niche, the fungus has evolved and mastered many reply strategies to resist and survive against negative threats, including harsh environmental stress and deficiency of essential nutrients from natural environments, immunity responses and drug treatments in host, and competition from symbiotic microorganisms. Hence, treating A. fumigatus infection is a growing challenge. In this review, we summarized A. fumigatus reply strategies and escape mechanisms and clarified the main competitive or symbiotic relationships between A. fumigatus, viruses, bacteria, or fungi in host microecology. Additionally, we discussed the contemporary drug repertoire used to treat A. fumigatus and the latest evidence of potential resistance mechanisms. This review provides valuable knowledge which will stimulate further investigations and clinical applications for treating and preventing A. fumigatus infections. KEY POINTS: • Harsh living environment was a great challenge for A. fumigatus survival. • A. fumigatus has evolved multiple strategies to escape host immune responses. • A. fumigatus withstands antifungal drugs via intrinsic escape mechanisms.

Antibiotics stimulates the development of persistent cells in biofilms of Candida albicans bloodstream isolates

Candida albicans invasive candidiasis is considered a global health problem. In such cases, biofilm formation on implanted devices represents a therapeutic challenge and the presence of metabolically inactive persistent cells (PCs) in these communities increases their tolerance to fungicidal drugs. This study investigated the influence of amoxicillin, AMX; cefepime, CEF; gentamicin, GEN; amikacin, AMK; vancomycin, VAN; and ciprofloxacin, CIP; on the production of PCs in biofilms of C. albicans bloodstream isolates. 48 h-mature biofilms (n = 6) grown in RPMI-1640 supplemented with antibiotics were treated with 100 μg ml-1 amphotericin B and then evaluated for PCs. Biofilms grown in the presence of antibiotics produced more PCs, up to 10×, when exposed to AMX and CIP; 5 × to CEF; and 6 × to GEN and VAN. The results indicate that antibiotics can modulate PC production in C. albicans biofilms. This scenario may have clinical repercussions in immunocompromised patients under broad-spectrum antibiotic therapy.

Drug tolerance and persistence in bacteria, fungi and cancer cells: Role of non-genetic heterogeneity

A common feature of bacterial, fungal and cancer cell populations upon treatment is the presence of tolerant and persistent cells able to survive, and sometimes grow, even in the presence of usually inhibitory or lethal drug concentrations, driven by non-genetic differences among individual cells in a population. Here we review and compare data obtained on drug survival in bacteria, fungi and cancer cells to unravel common characteristics and cellular pathways, and to point their singularities. This comparative work also allows to cross-fertilize ideas across fields. We particularly focus on the role of gene expression variability in the emergence of cell-cell non-genetic heterogeneity because it represents a possible common basic molecular process at the origin of most persistence phenomena and could be monitored and tuned to help improve therapeutic interventions.

The intricate link between iron, mitochondria and azoles in Candida species

Invasive fungal infections are rapidly increasing, and the opportunistic pathogenic Candida species are the fourth most common cause of nosocomial systemic infections. The current antifungal classes, of which azoles are the most widely used, all have shortcomings. Azoles are generally considered fungistatic rather than fungicidal, they do not actively kill fungal cells and therefore resistance against azoles can be rapidly acquired. Combination therapies with azoles provide an interesting therapeutic outlook and agents limiting iron are excellent candidates. We summarize how iron is acquired by the host and transported towards both storage and iron-utilizing organelles. We indicate whether these pathways alter azole susceptibility and/or tolerance, to finally link these transport mechanisms to mitochondrial iron availability. In this review, we highlight putative novel intracellular iron shuffling mechanisms and indicate that mitochondrial iron dynamics in relation to azole treatment and iron limitation is a significant knowledge gap.

Common virulence factors between Histoplasma and Paracoccidioides: Recognition of Hsp60 and Enolase by CR3 and plasmin receptors in host cells

Over the last two decades, the incidence of Invasive Fungal Infections (IFIs) globally has risen, posing a considerable challenge despite available antifungal therapies. Addressing this, the World Health Organization (WHO) prioritized research on specific fungi, notably Histoplasma spp. and Paracoccidioides spp. These dimorphic fungi have a mycelial life cycle in soil and a yeast phase associated with tissues of mammalian hosts. Inhalation of conidia and mycelial fragments initiates the infection, crucially transforming into the yeast form within the host, influenced by factors like temperature, host immunity, and hormonal status. Survival and multiplication within alveolar macrophages are crucial for disease progression, where innate immune responses play a pivotal role in overcoming physical barriers. The transition to pathogenic yeast, triggered by increased temperature, involves yeast phase-specific gene expression, closely linked to infection establishment and pathogenicity. Cell adhesion mechanisms during host-pathogen interactions are intricately linked to fungal virulence, which is critical for tissue colonization and disease development. Yeast replication within macrophages leads to their rupture, aiding pathogen dissemination. Immune cells, especially macrophages, dendritic cells, and neutrophils, are key players during infection control, with macrophages crucial for defense, tissue integrity, and pathogen elimination. Recognition of common virulence molecules such as heat- shock protein-60 (Hsp60) and enolase by pattern recognition receptors (PRRs), mainly via the complement receptor 3 (CR3) and plasmin receptor pathways, respectively, could be pivotal in host-pathogen interactions for Histoplasma spp. and Paracoccidioides spp., influencing adhesion, phagocytosis, and inflammatory regulation. This review provides a comprehensive overview of the dynamic of these two IFIs between host and pathogen. Further research into these fungi's virulence factors promises insights into pathogenic mechanisms, potentially guiding the development of effective treatment strategies.

Synergistic activity of gold nanoparticles with amphotericin B on persister cells of Candida tropicalis biofilms

AIM

The antifungal activity was studied on sessile and persister cells (PCs) of Candida tropicalis biofilms of gold nanoparticles (AuNPs) stabilized with cetyltrimethylammonium bromide (CTAB-AuNPs) and those conjugated with cysteine, in combination with Amphotericin B (AmB).

MATERIALS/METHODS

The PC model was used and synergistic activity was tested by the checkerboard assay. Biofilms were studied by crystal violet and scanning electron microscopy.

RESULTS/CONCLUSIONS

After the combination of both AuNPs and AmB the biofilm biomass was reduced, with significant differences in architecture being observed with a reduced biofilm matrix. In addition, the CTAB-AuNPs-AmB combination significantly reduced PCs. Understanding how these AuNPs aid in the fight against biofilms and the development of new approaches to eradicate PCs has relevance for chronic infection treatment.

Unlocking the enigma of phenotypic drug tolerance: Mechanisms and emerging therapeutic strategies

In the ongoing battle against antimicrobial resistance, phenotypic drug tolerance poses a formidable challenge. This adaptive ability of microorganisms to withstand drug pressure without genetic alterations further complicating global healthcare challenges. Microbial populations employ an array of persistence mechanisms, including dormancy, biofilm formation, adaptation to intracellular environments, and the adoption of L-forms, to develop drug tolerance. Moreover, molecular mechanisms like toxin-antitoxin modules, oxidative stress responses, energy metabolism, and (p)ppGpp signaling contribute to this phenomenon. Understanding these persistence mechanisms is crucial for predicting drug efficacy, developing strategies for chronic bacterial infections, and exploring innovative therapies for refractory infections. In this comprehensive review, we dissect the intricacies of drug tolerance and persister formation, explore their role in acquired drug resistance, and highlight emerging therapeutic approaches to combat phenotypic drug tolerance. Furthermore, we outline the future landscape of interventions for persistent bacterial infections.

Candida Variety in the Oral Cavity of Mexican Subjects with Type 2 Diabetes Mellitus and TLR2 Gene Expression

BACKGROUND

The aim was to diagnose Candida in the oral cavity of subjects with type 2 diabetes mellitus (T2DM) using a genotyping technique and compare the results with those from conventional diagnosis by Papanicolaou (Pap) staining.

METHODS

Palatal mucosa smears were performed on 18 dental care patients diagnosed with T2DM and grade I, II, and III prosthetic stomatitis who met the inclusion criteria; 18 healthy control subjects were also included in the study. Hemoglobin A1c (HbA1c) levels were determined from total blood. Using exfoliative cytology, the Pap staining technique was used to diagnose candidiasis. Exfoliative cytology was also used for molecular diagnosis; DNA was obtained for Candida genotyping, and RNA was used for gene expression studies.

RESULTS

Clinical patterns indicated that all subjects were positive for Candida; however, Pap analysis revealed only three positive subjects, whereas end-point polymerase chain reaction (PCR) analysis revealed 15 subjects with some type of Candida. The most common Candida species found were Candida guilliermondii (38.8%), Candida krusei (33.3%), Candida tropicalis, and Candida lusitaniae (22.2%). Interestingly, the coexpression of different species of Candida was found in various patients. In all patients, HbA1c levels were increased. Gene expression analysis showed a significant decrease (p ≤ 0.05) in TLR2 expression in positive subjects, whereas TLR4 expression did not differ significantly among patients.

CONCLUSIONS

The end-point PCR technique showed better sensitivity for the diagnosis of Candida when compared with the diagnosis by Pap staining. T2DM subjects showed an increased presence of C. guilliermondii that was correlated with decreased TLR2 expression.

A Preliminary Evaluation on the Antifungal Efficacy of VT-1161 against Persister Candida albicans Cells in Vulvovaginal Candidiasis

Persister cells are a small fraction of the microbial population that survive lethal concentrations of antimicrobial agents. Candida albicans causes vaginal candidiasis, including recurrent vulvovaginal candidiasis, and may survive common antifungal treatments. The triazole VT-1161 is an antifungal agent that specifically targets fungal CYP51, as opposed to the human CYP enzyme. This work illustrates a new role of VT-1161 in eradicating the biofilm created from the persister cells of a primary biofilm of a clinical vaginal isolate of C. albicans. Antifungal activity was determined by the minimum inhibitory concentration (MIC), and the primary biofilm was treated with amphotericin B to obtain persister cells that were able to form a new biofilm. Results obtained using the new azole VT-1161 showed that VT-1161 not only eradicated a secondary biofilm formed from the persister-derived biofilm and counteracted the adhesion of C. albicans in vitro to human cells but also ameliorated C. albicans-induced infection in vivo in Galleria mellonella larvae, suggesting that it could be proposed as an alternative therapeutic strategy for the treatment of recurrent candidiasis.

Nature-Derived Gelatin-Based Antifungal Nanotherapeutics for combatting Candida albicans Biofilms

Infections caused by fungi are emerging global health challenges that are exacerbated by the formation of fungal biofilms. Further challenges arise from environmental contamination with antifungal agents, which promotes environmental acquisition of antifungal resistance. We report the generation of an efficient, sustainable, all-natural antifungal nanotherapeutic based on the integration of an antimicrobial natural essential oil into a gelatin-based nanoemulsion platform. Carvacrol-loaded gelatin nanoemulsions penetrated Candida albicans biofilms, resulting in death of C. albicans cells in biofilms, and displayed selective biofilm elimination without harmful effects on fibroblast cells in a fungal biofilm-mammalian fibroblast co-culture model. Furthermore, the nanoemulsions degraded in the presence of physiologically relevant biomolecules, reducing the potential for environmental pollution and ecotoxicity. Overall, the sustainability, and efficacy of the described gelatin nanoemulsion formulation provides an environmentally friendly strategy for treating biofilm-associated fungal infections, including those caused by drug-resistant fungi.

Candida albicans exhibits heterogeneous and adaptive cytoprotective responses to antifungal compounds

Candida albicans, an opportunistic human pathogen, poses a significant threat to human health and is associated with significant socio-economic burden. Current antifungal treatments fail, at least in part, because C. albicans can initiate a strong drug tolerance response that allows some cells to grow at drug concentrations above their minimal inhibitory concentration. To better characterize this cytoprotective tolerance program at the molecular single-cell level, we used a nanoliter droplet-based transcriptomics platform to profile thousands of individual fungal cells and establish their subpopulation characteristics in the absence and presence of antifungal drugs. Profiles of untreated cells exhibit heterogeneous expression that correlates with cell cycle stage with distinct metabolic and stress responses. At 2 days post-fluconazole exposure (a time when tolerance is measurable), surviving cells bifurcate into two major subpopulations: one characterized by the upregulation of genes encoding ribosomal proteins, rRNA processing machinery, and mitochondrial cellular respiration capacity, termed the Ribo-dominant (Rd) state; and the other enriched for genes encoding stress responses and related processes, termed the Stress-dominant (Sd) state. This bifurcation persists at 3 and 6 days post-treatment. We provide evidence that the ribosome assembly stress response (RASTR) is activated in these subpopulations and may facilitate cell survival.

β-Estradiol and progesterone enhance biofilm development and persister cell formation in monospecies and microcosms biofilms derived from vulvovaginal candidiasis

The present study aimed to: (1) evaluate the influence of the steroid hormones (SH) on biofilm development; (2) investigate the formation of persister cells (PC) in biofilms; and (3) investigate the influence of SH on PC formation. Biofilms were derived from vulvovaginal candidiasis (VVC) samples and evaluated by three models: microcosm biofilms grown in Vaginal Fluid Simulator Medium (MiB-VFSM); monospecies biofilms grown in VFSM (MoB-VFSM) and RPMI media (MoB-RPMI). SH altered cell counting and biomass of biofilms grown in VSFM; MoB-RPMI were negatively affected by SH. SH stimulated the formation of PC in MiB-VFSM but not MoB-VFSM; MoB-RPMI showed a lower number of PC in the presence of SH. The results showed that SH altered the dynamics of biofilm formation and development, depending on the study model. The data suggest the influence of hormones on the physiology of Candida biofilms and reinforce the importance of PC in the pathogenesis of VVC.

Synergistic effect of hydralazine associated with triazoles on Candida spp. in planktonic cells

Objective: To evaluate the antifungal activity of hydralazine hydrochloride alone and in synergy with azoles against Candida spp. and the action mechanism. Methods: We used broth microdilution assays to determine the MIC, checkerboard assays to investigate synergism, and flow cytometry and molecular docking tests to ascertain action mechanism. Results: Hydralazine alone had antifungal activity in the range of 16-128 μg/ml and synergistic effect with itraconazole versus 100% of the fungal isolates, while there was synergy with fluconazole against 11.11% of the isolates. There was molecular interaction with the receptors exo-B(1,3)-glucanase and CYP51, causing reduced cell viability and DNA damage. Conclusion: Hydralazine is synergistic with itraconazole and triggers cell death of Candida spp. at low concentrations, demonstrating antifungal potential.

Eradication of Drug-Tolerant Mycobacterium tuberculosis 2022: Where We Stand

The lungs of tuberculosis (TB) patients contain a spectrum of granulomatous lesions, ranging from solid and well-vascularized cellular granulomas to avascular caseous granulomas. In solid granulomas, current therapy kills actively replicating (AR) intracellular bacilli, while in low-vascularized caseous granulomas the low-oxygen tension stimulates aerobic and microaerophilic AR bacilli to transit into non-replicating (NR), drug-tolerant and extracellular stages. These stages, which do not have genetic mutations and are often referred to as persisters, are difficult to eradicate due to low drug penetration inside the caseum and mycobacterial cell walls. The sputum of TB patients also contains viable bacilli called differentially detectable (DD) cells that, unlike persisters, grow in liquid, but not in solid media. This review provides a comprehensive update on drug combinations killing in vitro AR and drug-tolerant bacilli (persisters and DD cells), and sterilizing Mycobacterium tuberculosis-infected BALB/c and caseum-forming C3HeB/FeJ mice. These observations have been important for testing new drug combinations in noninferiority clinical trials, in order to shorten the duration of current regimens against TB. In 2022, the World Health Organization, following the results of one of these trials, supported the use of a 4-month regimen for the treatment of drug-susceptible TB as a possible alternative to the current 6-month regimen.

Fungal quorum-sensing molecules and antiseptics: a promising strategy for biofilm modulation?

New strategies to control fungal biofilms are essential, especially those that interfere in the biofilm organization process and cellular communication, known as quorum sensing. The effect of antiseptics and quorum-sensing molecules (QSMs) have been considered with regard to this; however, little has been elucidated, particularly because studies are often restricted to the action of antiseptics and QSMs against a few fungal genera. In this review, we discuss progress reported in the literature thus far and analyze, through in silico methods, 13 fungal QSMs with regard to their physicochemical, pharmacological, and toxicity properties, including their mutagenicity, tumorigenicity, hepatotoxicity, and nephrotoxicity. From these in silico analyses, we highlight 4-hydroxyphenylacetic acid and tryptophol as having satisfactory properties and, thus, propose that these should be investigated further as antifungal agents. We also recommend future in vitro approaches to determine the association of QSMs with commonly used antiseptics as potential antibiofilm agents.

Biofilm: The invisible culprit in catheter-induced candidemia

Candidemia is the most common form of invasive fungal infection associated with several risk factors, and one of them is the use of medical devices, to which microbial biofilms can attach. Candidemia related to the use of peripheral intravascular and central venous catheters (CVC) is referred to as Candida catheter-related bloodstream infection, with more than 90% being related to CVC usage. The infection is associated with a higher morbidity and mortality rate than nosocomial bacterial infections. Candida spp. can protect themselves from the host immune system and antifungal drugs because of the biofilm structure, which is potentiated by the extracellular matrix (ECM). Candida albicans and Candida parapsilosis are the most pathogenic species often found to form biofilms associated with catheter usage. Biofilm formation of C. albicans includes four mechanisms: attachment, morphogenesis, maturation and dispersion. The biofilms formed between C. albicans and non-albicans spp. differ in ECM structure and composition and are associated with the persistence of colonization to infection for various catheter materials and antifungal resistance. Efforts to combat Candida spp. biofilm formation on catheters are still challenging because not all patients, especially those who are critically ill, can be recommended for catheter removal; also to be considered are the characteristics of the biofilm itself, which readily colonizes the permanent medical devices used. The limited choice and increasing systemic antifungal resistance also make treating it more difficult. Hence, alternative strategies have been developed to manage Candida biofilm. Current options for prevention or therapy in combination with systemic antifungal medications include lock therapy, catheter coating, natural peptide products and photodynamic inactivation.

The Hydrophobic Extract of Sorghum bicolor (L. Moench) Enriched in Apigenin-Protected Rats against Aflatoxin B1-Associated Hepatorenal Derangement

Aflatoxin B1 (AFB1) is a recalcitrant metabolite produced by fungi species, and due to its intoxications in animals and humans, it has been classified as a Group 1 carcinogen in humans. Preserving food products with Sorghum bicolor sheath can minimise the contamination of agricultural products and avert ill health occasioned by exposure to AFB1. The current study investigated the ameliorating effect of Sorghum bicolor sheath hydrophobic extract (SBE-HP) enriched in Apigenin (API) on the hepatorenal tissues of rats exposed to AFB1. The SBE-HP was characterised using TLC and LC-MS and was found to be enriched in Apigenin and its methylated analogues. The study used adult male rats divided into four experimental cohorts co-treated with AFB1 (50 µg/kg) and SBE-HP (5 and 10 mg/kg) for 28 days. Biochemical, enzyme-linked immunosorbent assays (ELISA) and histological staining were used to examine biomarkers of hepatorenal function, oxidative status, inflammation and apoptosis, and hepatorenal tissue histo-architectural alterations. Data were analysed using GraphPad Prism 8.3.0, an independent t-test, and a one-way analysis of variance. Co-treatment with SBE-HP ameliorated an upsurge in the biomarkers of hepatorenal functionality in the sera of rats, reduced the alterations in redox balance, resolved inflammation, inhibited apoptosis, and preserved the histological features of the liver and kidney of rats exposed to AFB1. SBE-HP-containing API is an excellent antioxidant regiment. It can amply prevent the induction of oxidative stress, inflammation, and apoptosis in the hepatorenal system of rats. Therefore, supplementing animal feeds and human foods with SBE-HP enriched in Apigenin may reduce the burden of AFB1 intoxication in developing countries with a shortage of effective antifungal agents.

Aspergillus fumigatus Can Display Persistence to the Fungicidal Drug Voriconazole

Aspergillus fumigatus is a filamentous fungus that can infect the lungs of patients with immunosuppression and/or underlying lung diseases. The mortality associated with chronic and invasive aspergillosis infections remain very high, despite availability of antifungal treatments. In the last decade, there has been a worrisome emergence and spread of resistance to the first-line antifungals, the azoles. The mortality caused by resistant isolates is even higher, and patient management is complicated as the therapeutic options are reduced. Nevertheless, treatment failure is also common in patients infected with azole-susceptible isolates, which can be due to several non-mutually exclusive reasons, such as poor drug absorption. In addition, the phenomena of tolerance or persistence, where susceptible pathogens can survive the action of an antimicrobial for extended periods, have been associated with treatment failure in bacterial infections, and their occurrence in fungal infections already proposed. Here, we demonstrate that some isolates of A. fumigatus display persistence to voriconazole. A subpopulation of the persister isolates can survive for extended periods and even grow at low rates in the presence of supra-MIC of voriconazole and seemingly other azoles. Persistence cannot be eradicated with adjuvant drugs or antifungal combinations and seemed to reduce the efficacy of treatment for certain individuals in a Galleria mellonella model of infection. Furthermore, persistence implies a distinct transcriptional profile, demonstrating that it is an active response. We propose that azole persistence might be a relevant and underestimated factor that could influence the outcome of infection in human aspergillosis. IMPORTANCE The phenomena of antibacterial tolerance and persistence, where pathogenic microbes can survive for extended periods in the presence of cidal drug concentrations, have received significant attention in the last decade. Several mechanisms of action have been elucidated, and their relevance for treatment failure in bacterial infections demonstrated. In contrast, our knowledge of antifungal tolerance and, in particular, persistence is still very limited. In this study, we have characterized the response of the prominent fungal pathogen Aspergillus fumigatus to the first-line therapy antifungal voriconazole. We comprehensively show that some isolates display persistence to this fungicidal antifungal and propose various potential mechanisms of action. In addition, using an alternative model of infection, we provide initial evidence to suggest that persistence may cause treatment failure in some individuals. Therefore, we propose that azole persistence is an important factor to consider and further investigate in A. fumigatus.

Macrophage internalization creates a multidrug-tolerant fungal persister reservoir and facilitates the emergence of drug resistance

Candida glabrata is a major fungal pathogen notable for causing recalcitrant infections, rapid emergence of drug-resistant strains, and its ability to survive and proliferate within macrophages. Resembling bacterial persisters, a subset of genetically drug-susceptible C. glabrata cells can survive lethal exposure to the fungicidal echinocandin drugs. Herein, we show that macrophage internalization induces cidal drug tolerance in C. glabrata, expanding the persister reservoir from which echinocandin-resistant mutants emerge. We show that this drug tolerance is associated with non-proliferation and is triggered by macrophage-induced oxidative stress, and that deletion of genes involved in reactive oxygen species detoxification significantly increases the emergence of echinocandin-resistant mutants. Finally, we show that the fungicidal drug amphotericin B can kill intracellular C. glabrata echinocandin persisters, reducing emergence of resistance. Our study supports the hypothesis that intra-macrophage C. glabrata is a reservoir of recalcitrant/drug-resistant infections, and that drug alternating strategies can be developed to eliminate this reservoir.

Promethazine inhibits efflux, enhances antifungal susceptibility and disrupts biofilm structure and functioning in Trichosporon

Trichosporon spp. are emerging opportunistic fungi associated with invasive infections, especially in patients with haematological malignancies. The present study investigated the in vitro inhibition of efflux pumps by promethazine (PMZ) as a strategy to control T. asahii and T. inkin. Planktonic cells were evaluated for antifungal susceptibility to PMZ, as well as inhibition of efflux. The effect of PMZ was also studied in Trichosporon biofilms. PMZ inhibited T. asahii and T. inkin planktonic cells at concentrations ranging from 32 to 256 μg ml^-1. Subinhibitory concentrations of PMZ inhibited efflux activity in Trichosporon. Biofilms were completely eradicated by PMZ. PMZ potentiated the action of antifungals, affected the morphology, changed the amount of carbohydrates and proteins and reduced the amount of persister cells inside biofilms. The results showed indirect evidences of the occurrence of efflux pumps in Trichosporon and opens a perspective for the use of this target in the control of trichosporonosis.

Antibiotic Tolerance Indicative of Persistence Is Pervasive among Clinical Streptococcus pneumoniae Isolates and Shows Strong Condition Dependence

Streptococcus pneumoniae is an important human pathogen, being one of the most common causes of community-acquired pneumonia and otitis media. Antibiotic resistance in S. pneumoniae is an emerging problem, as it depletes our arsenal of effective drugs. In addition, persistence also contributes to the antibiotic crisis in many other pathogens, yet for S. pneumoniae, little is known about antibiotic-tolerant persisters and robust experimental means are lacking. Persister cells are phenotypic variants that exist as a subpopulation within a clonal culture. Being tolerant to lethal antibiotics, they underly the chronic nature of a variety of infections and even help in acquiring genetic resistance. In this study, we set out to identify and characterize persistence in S. pneumoniae. Specifically, we followed different strategies to overcome the self-limiting nature of S. pneumoniae as a confounding factor in the prolonged monitoring of antibiotic survival needed to study persistence. Under optimized conditions, we identified genuine persisters in various growth phases and for four relevant antibiotics through biphasic survival dynamics and heritability assays. Finally, we detected a high variety in antibiotic survival levels across a diverse collection of S. pneumoniae clinical isolates, which assumes that a high natural diversity in persistence is widely present in S. pneumoniae. Collectively, this proof of concept significantly progresses the understanding of the importance of antibiotic persistence in S. pneumoniae infections, which will set the stage for characterizing its relevance to clinical outcomes and advocates for increased attention to the phenotype in both fundamental and clinical research. IMPORTANCE S. pneumoniae is considered a serious threat by the Centers for Disease Control and Prevention because of rising antibiotic resistance. In addition to resistance, bacteria can also survive lethal antibiotic treatment by developing antibiotic tolerance, more specifically, antibiotic tolerance through persistence. This phenotypic variation seems omnipresent among bacterial life, is linked to therapy failure, and acts as a catalyst for resistance development. This study gives the first proof of the presence of persister cells in S. pneumoniae and shows a high variety in persistence levels among diverse strains, suggesting that persistence is a general trait in S. pneumoniae cultures. Our work advocates for higher interest for persistence in S. pneumoniae as a contributing factor for therapy failure and resistance development.

Cationic Surfactants Based on Arginine-Phenylalanine and Arginine-Tryptophan: Synthesis, Aggregation Behavior, Antimicrobial Activity, and Biodegradation

Cationic surfactants have great potential as drug vehicles and for use in gene therapy (cationic vesicles made from cationic surfactants can encapsulate RNA or DNA for cellular transfer). They can also be used as antimicrobial and antifungal agents to treat human infections. In an era of increasing antimicrobial resistance, the development of new biocompatible surfactants suitable for application as antimicrobial agents is of high interest. In this work, a library of amino acid-based surfactants was synthesized, characterized and tested for antimicrobial activity. The head group architecture (number and type of amino acids, density of cationic charge, ionic character) and the hydrophobic moiety (alkyl chain length and position of the hydrophobic group) were systematically modified, and the effect on the surfactant biological and aggregation behavior was studied. Thus, the pKa values, micellization process, antimicrobial efficiency and biodegradability were evaluated. The critical micelle concentration values of the surfactants depended on their hydrophobic character, but changes in the polar head as well as the position and length of the alkyl chain also significantly affected activity against some of the tested microorganisms. Moreover, biodegradability was closely related to the hydrophobic character of the surfactant and attachment of the alkyl chain to the polar head. The structure-activity relationships established here may open perspectives for the design of effective biodegradable antimicrobial materials that can overcome emerging resistance.

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.

Candida albicans biofilms: antifungal resistance, immune evasion, and emerging therapeutic strategies

Candida albicans is a fungal pathogen that can form biofilms on medical devices and host tissue, resulting in serious, life-threatening infections. These fungal biofilms are inherently resistant to traditional antifungal therapies and the host immune system; therefore, biofilm-associated infections are a huge clinical challenge. This review summarizes the most important insights into C. albicans biofilm-associated antifungal drug resistance mechanisms and immune evasion strategies. In addtion, this review also discusses the strategies for antifungal drug use to combat these processes, providing further evidence for novel drugs research and clinical therapies.

The importance of antimicrobial resistance in medical mycology

Prior to the SARS-CoV-2 pandemic, antibiotic resistance was listed as the major global health care priority. Some analyses, including the O'Neill report, have predicted that deaths due to drug-resistant bacterial infections may eclipse the total number of cancer deaths by 2050. Although fungal infections remain in the shadow of public awareness, total attributable annual deaths are similar to, or exceeds, global mortalities due to malaria, tuberculosis or HIV. The impact of fungal infections has been exacerbated by the steady rise of antifungal drug resistant strains and species which reflects the widespread use of antifungals for prophylaxis and therapy, and in the case of azole resistance in Aspergillus, has been linked to the widespread agricultural use of antifungals. This review, based on a workshop hosted by the Medical Research Council and the University of Exeter, illuminates the problem of antifungal resistance and suggests how this growing threat might be mitigated.

The Anti-Fungal Activity of Nitropropenyl Benzodioxole (NPBD), a Redox-Thiol Oxidant and Tyrosine Phosphatase Inhibitor

Phylogenetically diverse fungal species are an increasing cause of severe disease and mortality. Identification of new targets and development of new fungicidal drugs are required to augment the effectiveness of current chemotherapy and counter increasing resistance in pathogens. Nitroalkenyl benzene derivatives are thiol oxidants and inhibitors of cysteine-based molecules, which show broad biological activity against microorganisms. Nitropropenyl benzodioxole (NPBD), one of the most active antimicrobial derivatives, shows high activity in MIC assays for phylogenetically diverse saprophytic, commensal and parasitic fungi. NPBD was fungicidal to all species except the dermatophytic fungi, with an activity profile comparable to that of Amphotericin B and Miconazole. NPBD showed differing patterns of dynamic kill rates under different growth conditions for Candida albicans and Aspergillus fumigatus and was rapidly fungicidal for non-replicating vegetative forms and microconidia. It did not induce resistant or drug tolerant strains in major pathogens on long term exposure. A literature review highlights the complexity and interactivity of fungal tyrosine phosphate and redox signaling pathways, their differing metabolic effects in fungal species and identifies some targets for inhibition. A comparison of the metabolic activities of Amphotericin B, Miconazole and NPBD highlights the multiple cellular functions of these agents and the complementarity of many mechanisms. The activity profile of NPBD illustrates the functional diversity of fungal tyrosine phosphatases and thiol-based redox active molecules and contributes to the validation of tyrosine phosphatases and redox thiol molecules as related and complementary selective targets for antimicrobial drug development. NPBD is a selective antifungal agent with low oral toxicity which would be suitable for local treatment of skin and mucosal infections.

Triosephosphate Isomerase and Its Product Glyceraldehyde-3-Phosphate Are Involved in the Regulatory Mechanism That Suppresses Exit from the Quiescent State in Yeast Cells

Cells of the budding yeast Saccharomyces cerevisiae form spores or stationary cells upon nutrient starvation. These quiescent cells are known to resume mitotic growth in response to nutrient signals, but the mechanism remains elusive. Here, we report that quiescent yeast cells are equipped with a negative regulatory mechanism which suppresses the commencement of mitotic growth. The regulatory process involves a glycolytic enzyme, triosephosphate isomerase (Tpi1), and its product, glyceraldehyde-3-phosphate (GAP). GAP serves as an inhibitory signaling molecule; indeed, the return to growth of spores or stationary cells is suppressed by the addition of GAP even in nutrient-rich growth media, though mitotic cells are not affected. Reciprocally, dormancy is abolished by heat treatment because of the heat sensitivity of Tpi1. For example, spores commence germination merely upon heat treatment, which indicates that the negative regulatory mechanism is actively required for spores to prevent premature germination. Stationary cells of Candida glabrata are also manipulated by heat and GAP, suggesting that the regulatory process is conserved in the pathogenic yeast. IMPORTANCE Our results suggest that, in quiescent cells, nutrient signals do not merely provoke a positive regulatory process to commence mitotic growth. Exit from the quiescent state in yeast cells is regulated by balancing between the positive and negative signaling pathways. Identifying the negative regulatory pathway would provide new insight into the regulation of the transition from the quiescent to the mitotic state. Clinically, quiescent cells are problematic because they are resistant to environmental stresses and antibiotics. Given that the quiescent state is modulated by manipulation of the negative regulatory mechanism, understanding this process is important not only for its biological interest but also as a potential target for antifungal treatment.

Inhibition of Candida glabrata Biofilm by Combined Effect of Dendritic Compounds and Amphotericin

In the last decade, Candida glabrata has become an important emerging opportunistic pathogen not only because of the increase in nosocomial infections frequency but also because of its ability to form biofilms and its innate resistance to commercial antifungals. These characteristics make this pathogen a major problem in hospital settings, including problems regarding equipment, and in immunosuppressed patients, who are at high risk for candidemia. Therefore, there is an urgent need for the development of and search for new antifungal drugs. In this study, the efficacy of two dendritic wedges with 4-phenyl butyric acid (PBA) at the focal point and cationic charges on the surface ArCO₂G₂(SNMe₃I)₄ (1) and ArCO₂G₃(SNMe₃I)₈ (2) was studied against C. glabrata strain to inhibit the formation of biofilms and eliminate established biofilm. For this, MBIC (minimum biofilm inhibitory concentration), MBDC (minimum biofilm damaging concentrations), as well as MFCB (minimum fungicidal concentration in biofilm) and MBEC (minimum biofilm eradicating concentration) were determined. In addition, different combinations of dendrons and amphotericin B were tested to study possible synergistic effects. On the other hand, cytotoxicity studies were performed. C. glabrata cells and biofilm structure were visualized by confocal microscopy. ArCO₂G₂(SNMe₃I)₄ (1) and ArCO₂G₃(SNMe₃I)₈ (2) dendrons showed both an MBIC of 8 mg/L and a MBDC of 32 mg/L and 64 mg/L, respectively. These dendrons managed to eradicate the entirety of an established biofilm. In combination with the antifungal amphotericin, it was possible to prevent the generation of biofilms and eradicate established biofilms at lower concentrations than those required individually for each compound at these conditions.

Caspofungin at Sub-inhibitory Concentration Promotes the Formation of Candida Albicans Persister Cells

AIMS

Low caspofungin exposure is frequently encountered in patients with invasive candidiasis caused by Candida albicans (C. albicans). This study aimed to investigate the effects of caspofungin on C. albicans at sub-inhibitory concentrations.

METHODS AND RESULTS

First, a comparative transcriptomics analysis was performed on C. albicans receiving caspofungin at sub-minimum inhibitory concentrations (sub-MIC). The results showed that caspofungin significantly changed the mRNA expression profile in DAY185, with DE-mRNAs enriched in the functions of cell wall biosynthesis, metabolism, etc. Subsequently, cellular fitness, cell aggregation, energy metabolism activity, and the proportion of persister cells of C. albicans were quantitatively and/or qualitatively assessed after sub-MIC caspofungin exposure. No significant changes in cell fitness and aggregation formation were observed during treatment of C. albicans with sub-MIC caspofungin. In C. albicans aggregation treated with sub-MIC caspofungin, we observed a decrease in respiratory metabolism and an increase in persister cells; this effect was more pronounced in als1ΔΔ than in DAY185.

CONCLUSIONS

Pre-exposure to sub-MIC caspofungin suppresses C. albicans respiratory metabolism and promotes persister cell development.

SIGNIFICANCE AND IMPACT OF STUDY

Caspofungin should be used with caution in patients with C. albicans infections, as anti-infection therapy may fail due to persister cells.

Phloroglucinol and Its Derivatives: Antimicrobial Properties toward Microbial Pathogens

Phloroglucinol (PG) is a natural product isolated from plants, algae, and microorganisms. Aside from that, the number of PG derivatives has expanded due to the discovery of their potential biological roles. Aside from its diverse biological activities, PG and its derivatives have been widely utilized to treat microbial infections caused by bacteria, fungus, and viruses. The rapid emergence of antimicrobial-resistant microbial infections necessitates the chemical synthesis of numerous PG derivatives in order to meet the growing demand for drugs. This review focuses on the use of PG and its derivatives to control microbial infection and the underlying mechanism of action. Furthermore, as future perspectives, some of the various alternative strategies, such as the use of PG and its derivatives in conjugation, nanoformulation, antibiotic combination, and encapsulation, have been thoroughly discussed. This review will enable the researcher to investigate the possible antibacterial properties of PG and its derivatives, either free or in the form of various formulations.

A Cecropin-4 Derived Peptide C18 Inhibits Candida albicans by Disturbing Mitochondrial Function

Global burden of fungal infections and related health risk has accelerated at an incredible pace, and multidrug resistance emergency aggravates the need for the development of new effective strategies. Candida albicans is clinically the most ubiquitous pathogenic fungus that leads to high incidence and mortality in immunocompromised patients. Antimicrobial peptides (AMPs), in this context, represent promising alternatives having potential to be exploited for improving human health. In our previous studies, a Cecropin-4-derived peptide named C18 was found to possess a broader antibacterial spectrum after modification and exhibit significant antifungal activity against C. albicans. In this study, C18 shows antifungal activity against C. albicans or non-albicans Candida species with a minimum inhibitory concentration (MIC) at 4∼32 μg/ml, and clinical isolates of fluconazole (FLZ)-resistance C. tropicalis were highly susceptible to C18 with MIC value of 8 or 16 μg/ml. Additionally, C18 is superior to FLZ for killing planktonic C. albicans from inhibitory and killing kinetic curves. Moreover, C18 could attenuate the virulence of C. albicans, which includes damaging the cell structure, retarding hyphae transition, and inhibiting biofilm formation. Intriguingly, in the Galleria mellonella model with C. albicans infection, C18 could improve the survival rate of G. mellonella larvae to 70% and reduce C. albicans load from 5.01 × 107 to 5.62 × 104 CFU. For mechanistic action of C18, the level of reactive oxygen species (ROS) generation and cytosolic Ca2 + increased in the presence of C18, which is closely associated with mitochondrial dysfunction. Meanwhile, mitochondrial membrane potential (△Ψm) loss and ATP depletion of C. albicans occurred with the treatment of C18. We hypothesized that C18 might inhibit C. albicans via triggering mitochondrial dysfunction driven by ROS generation and Ca2 + accumulation. Our observation provides a basis for future research to explore the antifungal strategies and presents C18 as an attractive therapeutic candidate to be developed to treat candidiasis.

Enhancing effect of chitosan on methylene blue-mediated photodynamic therapy against C. albicans: a study in planktonic growth, biofilms, and persister cells

Chitosan (CS) is a natural polymer extracted from the exoskeleton of crustaceans. Due to its cationic structure, CS has been studied as a possible enhancer of antimicrobial photodynamic therapy (aPDT). The objective was to evaluate the association of CS with methylene blue (MB)-mediated aPDT on Candida albicans, investigating its effects on planktonic growth, biofilms, and cells persistent to fluconazole. The ability of CS to interfere with MB absorption by Candida cells was also evaluated. For the assays, planktonic cells of C. albicans were cultivated for 24 h, and the biofilms were formed for 48 h. For the induction of persister cells, C. albicans was cultivated with high concentration of fluconazole for 48 h. Treatments were performed with MB, CS or MB+CS, followed by irradiation with LED (660 nm). As results, aPDT with MB (300 µm) reduced the planktonic cells by 1.6 log10 CFU, while the MB+CS association led to a reduction of 4.8 log10 CFU. For aPDT in biofilms, there was a microbial reduction of 2.9 log10 CFU for the treatment with MB (600 µm) and 5.3 log10 CFU for MB+CS. In relation to persister cells, the fungal reductions were 0.4 log10 CFU for MB and 1.5 log10 CFU for MB+CS. In the absorption assays, the penetration of MB into Candida cells was increased in the presence of CS. It was concluded that CS enhanced the antimicrobial activity of aPDT in planktonic growth, biofilms, and persister cells of C. albicans, probably by facilitating the penetration of MB into fungal cells.

Two-in-One Surfactant Disinfectant Potential of Xylitol Dicaprylate and Dilaurate Esters Synthesized by Talaromyces thermophilus galactolipase for Cleaning Industries

Talaromyces thermophilus galactolipase (TTL) was found to produce alcohol sugar fatty acid diesters. The modulation of the solvent composition was used for the esterification reaction screening of diesters from xylitol and various fatty acids using the immobilized Talaromyces thermophilus galactolipase. The reactions were assessed by LC-MS analysis. The antimicrobial activity assay showed that both xylitol dicaprylate and xylitol dilaurate esters had more ability to inhibit the growth of several bacteria involved in surface contamination in the food industry. The xylitol dilaurate ester has the highest activity against Gram-positive strains with the lowest MIC values of 0.0016 and 0.005 mg mL^-1 against Bacillus licheniformis and Staphylococcus aureus, respectively. Xylitol dicaprylate ester is more active against Gram-negative ones with significantly low MIC values of 0.25 and 0.4 mg mL^-1 against Escherichia coli and Pseudomonas aeruginosa, respectively. The highest antifungal activity of the xylitol dicaprylate ester has been also proven, with a MIC value of 0.02 mg mL^-1 against Penicillium occitanis and Fusarium solani. A better reduction in critical micelle concentrations and air-water surface tension were observed with these diesters compared to their corresponding monoesters in addition to their efficient emulsifying properties. The stability of these diesters in a liquid detergent formula after one year of storage was tested by a positive oil spreading assay and a retained antimicrobial activity. They exhibit a typical surfactant behavior with a two-in-one effect that can act as a detergent and a disinfectant with potential use in different cleaning processes.

Repurposing pantoprazole and haloperidol as efflux pump inhibitors in azole resistant clinical Candida albicans and non-albicans isolates

Candida species have a major role in nosocomial infections leading to high morbidity and mortality. Increased resistance to various antifungals, especially azoles is a significant problem. One of the main mechanisms for azole resistance is the up-regulation of efflux pump genes including CDR1 and MDR1. In the current study, clinical Candida isolates were identified to the species level and the antifungal susceptibility (AFS) of different Candida species was determined by disk diffusion method. Furthermore, the main mechanisms of azole resistance were investigated. Finally, haloperidol and pantoprazole were tested for their potential synergistic effect against fluconazole-resistant isolates. One hundred and twenty-two Candida clinical isolates were used in this study. 70 isolates were Candida albicans (57.4%), the non-albicans Candida species include: C. krusei (20.5%), C. tropicalis (6.6%), C. parapsilosis (5.7%), C. dubliniensis (4.9%) and C. glabrata (4.9%). The AFS testing showed that resistance to fluconazole and voriconazole were 13.1% (n = 16) and 9.8% (n = 12), respectively. Among the 16 resistant isolates, eight isolates (50%) were strong biofilm producers, seven (43.8 %) formed intermediate biofilm and one had no biofilm. All resistant strains overexpressed efflux pumps. Using RT-PCR, the efflux genes CDR1, MDR1 and ABC2 were over-expressed in azole resistant isolates. Haloperidol-fluconazole and pantoprazole-fluconazole combinations reduced the MIC of fluconazole in resistant isolates. The current study showed an increase in azole resistance of Candida species. The majority of resistant isolates form biofilm, and overexpress efflux pumps. Pantoprazole and Haloperidol showed a noteworthy effect as efflux pump inhibitors which oppose the fluconazole resistance in different Candida species.

Caffeic acid protects against DNA damage, oxidative and inflammatory mediated toxicities, and upregulated caspases activation in the hepatorenal system of rats treated with aflatoxin B1

Aflatoxicosis can induce largescale toxicities in predisposed populations. Food fortification with adequate antioxidant sources may reduce the toxic burden from aflatoxicosis. We examined the individual and combined effect of Caffeic acid (CA) on the aflatoxin B₁ (AFB₁)-induced hepatic and renal injury in male rats. Five experimental rat cohort (n = 6) consisting of the control (2 mL/kg corn oil), AFB₁ alone (50 μg/kg), CA alone (40 mg/kg), AFB₁+CA₁ (50 μg/kg + 20 mg/kg) and AFB₁+CA₂ (50 μg/kg + 40 mg/kg) were so treated for 28 consecutive days. Upon sacrifices, diagnostic markers of hepatorenal functions, oxidative stress, inflammation, oxidative deoxyribonucleic acid -DNA-damage and apoptosis were analysed. Our results showed that CA reduced AFB₁-induced toxicities in rats' liver and kidneys by significantly increasing (p < 0.05) endogenous antioxidant and the anti-inflammatory IL-10 level. Caffeic acid simultaneously reduced hepatic and renal dysfunction biomarkers in the serum, oxidative stress, and lipid peroxidation levels. Besides, CA diminished reactive oxygen and nitrogen species, inflammatory nitric oxide levels, interleukin-1 β and the activities of xanthine oxidase and myeloperoxidase. Additionally, CA reduced DNA damage and caspase-mediated apoptotic responses and preserved the cytoarchitecture of rats' liver and kidneys treated with AFB₁. These data suggest that CA can be used as a food additive to mitigate AFB₁-induced toxicity in the examined organs.

Activity of Free and Liposome-Encapsulated Essential Oil from Lavandula angustifolia against Persister-Derived Biofilm of Candida auris

The high virulence of Candida auris, a pathogen fungus considered as a global threat for public health, is due to its peculiar traits such as its intrinsic resistance to conventional antifungals. Its biofilm lifestyle certainly promotes the prolonged survival of C. auris after disinfection or antifungal treatments. In this work, for the first time, we detected persister cells in a biofilm of C. auris in a microwell plate model, following caspofungin treatment. Furthermore, we showed how persisters can progressively develop a new biofilm in situ, mimicking the re-colonization of a surface which may be responsible for recalcitrant infections. Plant-derived compounds, such as essential oils, may represent a valid alternative to combat fungal infections. Here, Lavandula angustifolia essential oil, as free or encapsulated in liposomes, was used to eradicate primary and persister-derived biofilms of C. auris, confirming the great potential of alternative compounds against emergent fungal pathogens. As in other Candida species, the action of essential oils against C. auris involves ROS production and affects the expression of some biofilm-related genes.

DC-SIGN targets amphotericin B-loaded liposomes to diverse pathogenic fungi

BACKGROUND

Life-threatening invasive fungal infections are treated with antifungal drugs such as Amphotericin B (AmB) loaded liposomes. Our goal herein was to show that targeting liposomal AmB to fungal cells with the C-type lectin pathogen recognition receptor DC-SIGN improves antifungal activity. DC-SIGN binds variously crosslinked mannose-rich and fucosylated glycans and lipomannans that are expressed by helminth, protist, fungal, bacterial and viral pathogens including three of the most life-threatening fungi, Aspergillus fumigatus, Candida albicans and Cryptococcus neoformans. Ligand recognition by human DC-SIGN is provided by a carbohydrate recognition domain (CRD) linked to the membrane transit and signaling sequences. Different combinations of the eight neck repeats (NR1 to NR8) expressed in different protein isoforms may alter the orientation of the CRD to enhance its binding to different glycans.

RESULTS

We prepared two recombinant isoforms combining the CRD with NR1 and NR2 in isoform DCS12 and with NR7 and NR8 in isoform DCS78 and coupled them to a lipid carrier. These constructs were inserted into the membrane of pegylated AmB loaded liposomes AmB-LLs to produce DCS12-AmB-LLs and DCS78-AmB-LLs. Relative to AmB-LLs and Bovine Serum Albumin coated BSA-AmB-LLs, DCS12-AmB-LLs and DCS78-AmB-LLs bound more efficiently to the exopolysaccharide matrices produced by A. fumigatus, C. albicans and C. neoformans in vitro, with DCS12-AmB-LLs performing better than DCS78-AmB-LLs. DCS12-AmB-LLs inhibited and/or killed all three species in vitro significantly better than AmB-LLs or BSA-AmB-LLs. In mouse models of invasive candidiasis and pulmonary aspergillosis, one low dose of DCS12-AmB-LLs significantly reduced the fungal burden in the kidneys and lungs, respectively, several-fold relative to AmB-LLs.

CONCLUSIONS

DC-SIGN's CRD specifically targeted antifungal liposomes to three highly evolutionarily diverse pathogenic fungi and enhanced the antifungal efficacy of liposomal AmB both in vitro and in vivo. Targeting significantly reduced the effective dose of antifungal drug, which may reduce drug toxicity, be effective in overcoming dose dependent drug resistance, and more effectively kill persister cells. In addition to fungi, DC-SIGN targeting of liposomal packaged anti-infectives have the potential to alter treatment paradigms for a wide variety of pathogens from different kingdoms including protozoans, helminths, bacteria, and viruses which express its cognate ligands.

Spatially structured yeast communities: Understanding structure formation and regulation with omics tools

Single-celled yeasts form spatially structured populations - colonies and biofilms, either alone (single-species biofilms) or in cooperation with other microorganisms (mixed-species biofilms). Within populations, yeast cells develop in a coordinated manner, interact with each other and differentiate into specialized cell subpopulations that can better adapt to changing conditions (e.g. by reprogramming metabolism during nutrient deficiency) or protect the overall population from external influences (e.g. via extracellular matrix). Various omics tools together with specialized techniques for separating differentiated cells and in situ microscopy have revealed important processes and cell interactions in these structures, which are summarized here. Nevertheless, current knowledge is still only a small part of the mosaic of complexity and diversity of the multicellular structures that yeasts form in different environments. Future challenges include the use of integrated multi-omics approaches and a greater emphasis on the analysis of differentiated cell subpopulations with specific functions.

Transcription Factors of CAT1, EFG1, and BCR1 Are Effective in Persister Cells of Candida albicans-Associated HIV-Positive and Chemotherapy Patients

Background

Biofilm is an accumulation of cells, which are formed on mucosal surfaces of the host as well as on medical devices. The inherent resistance of Candida strains producing biofilms to antimicrobial agents is an important and key feature for biofilm growth, which can lead to treatment failure. This resistance is due to the regulatory increase of the output pumps, the presence of extracellular matrix, and the existence of persister cells. Persister cells are phenotypic variants that have MICs similar to antibiotic-sensitive populations and are able to tolerate high doses of antibiotics. The current study investigated the possible role of EFG1, BCR1, and CAT1 in the establishment or maintenance of persister cells in Candida albicans strains that produce biofilms.

Methods

After identifying Candida isolates by molecular methods, C. albicans isolates were confirmed by sequencing. Isolation of persister cells and determination of their MIC were performed by microdilution method. Then, RNA extraction and cDNA synthesis were performed from 60 C. albicans isolates under promoting and inducing conditions. Afterward, the mean expression of BCR1, EFG1, and CAT1 genes in both persister and non-persister groups was calculated using real-time qPCR. Phylogeny tree of persister and non-persister group isolates was drawn using ITS fragment.

Results

A total of 77 persister isolates were taken from the oral cavity of HIV patients as well as from patients undergoing chemotherapy. Biofilm intensity in persister isolates separated from HIV-infected patients was different from the non-persister group. The mean fold change of BCR1 (10.73), CAT1 (15.34), and EFG1 (2.41) genes in persister isolates was significantly higher than these genes in isolates without persister.

Conclusion

It can be concluded that the most important factor in the production of persister cells is biofilm binding and production, not biofilm development or mature biofilm production, which was found in the expression of BCR1 gene without change in the expression of EFG1 gene in the persister group. Also, catalase plays an essential role in the production of persister in C. albicans biofilm producers with ROS detoxification.

Fluorescent toys 'n' tools lighting the way in fungal research

Although largely overlooked compared to bacterial infections, fungal infections pose a significant threat to the health of humans and other organisms. Many pathogenic fungi, especially Candida species, are extremely versatile and flexible in adapting to various host niches and stressful situations. This leads to high pathogenicity and increasing resistance to existing drugs. Due to the high level of conservation between fungi and mammalian cells, it is hard to find fungus-specific drug targets for novel therapy development. In this respect, it is vital to understand how these fungi function on a molecular, cellular as well as organismal level. Fluorescence imaging allows for detailed analysis of molecular mechanisms, cellular structures and interactions on different levels. In this manuscript, we provide researchers with an elaborate and contemporary overview of fluorescence techniques that can be used to study fungal pathogens. We focus on the available fluorescent labelling techniques and guide our readers through the different relevant applications of fluorescent imaging, from subcellular events to multispecies interactions and diagnostics. As well as cautioning researchers for potential challenges and obstacles, we offer hands-on tips and tricks for efficient experimentation and share our expert-view on future developments and possible improvements.

Paeonol assists fluconazole and amphotericin B to inhibit virulence factors and pathogenicity of Candida albicans

This study aimed to evaluate the mono- and dual- antifungal activities of paeonol (PAE) and fluconazole (FLZ)/amphotericin B (AmB). To this end, the effects of PAE and FLZ/AmB on cell surface hydrophobicity, hydrolase activity, morphological transition were investigated in vitro and in a Galleria mellonella infection model. The results showed a relatively high minimum inhibitory concentration (MIC) and sessile MIC (SMIC) of PAE alone. However, compared with the single drug, the combined use of PAE and FLZ/AmB had a potent synergistic potential to inhibit the virulence factors for Candida. The concomitant use of two drugs was consistently more effective than either drug alone for increasing survival rate, decreasing the fungal burden, and alleviating the pathological features of G. mellonella infected by the fungus. Taken together, these findings demonstrate the anti-Candida effects of PAE plus FLZ/AmB and their potential to increase the sensitivity of C. albicans to FLZ/AmB of PAE.

Fungal Biofilms as a Valuable Target for the Discovery of Natural Products That Cope with the Resistance of Medically Important Fungi-Latest Findings

The development of new antifungal agents that target biofilms is an urgent need. Natural products, mainly from the plant kingdom, represent an invaluable source of these entities. The present review provides an update (2017-May 2021) on the available information on essential oils, propolis, extracts from plants, algae, lichens and microorganisms, compounds from different natural sources and nanosystems containing natural products with the capacity to in vitro or in vivo modulate fungal biofilms. The search yielded 42 articles; seven involved essential oils, two Brazilian propolis, six plant extracts and one of each, extracts from lichens and algae/cyanobacteria. Twenty articles deal with the antibiofilm effect of pure natural compounds, with 10 of them including studies of the mechanism of action and five dealing with natural compounds included in nanosystems. Thirty-seven manuscripts evaluated Candida spp. biofilms and two tested Fusarium and Cryptococcus spp. Only one manuscript involved Aspergillus fumigatus. From the data presented here, it is clear that the search of natural products with activity against fungal biofilms has been a highly active area of research in recent years. However, it also reveals the necessity of deepening the studies by (i) evaluating the effect of natural products on biofilms formed by the newly emerged and worrisome health-care associated fungi, C. auris, as well as on other non-albicans Candida spp., Cryptococcus sp. and filamentous fungi; (ii) elucidating the mechanisms of action of the most active natural products; (iii) increasing the in vivo testing.

Biofilm formation in clinically relevant filamentous fungi: a therapeutic challenge

Biofilms are highly-organized microbial communities attached to a biotic or an abiotic surface, surrounded by an extracellular matrix secreted by the biofilm-forming cells. The majority of fungal pathogens contribute to biofilm formation within tissues or biomedical devices, leading to serious and persistent infections. The clinical significance of biofilms relies on the increased resistance to conventional antifungal therapies and suppression of the host immune system, which leads to invasive and recurrent fungal infections. While different features of yeast biofilms are well-described in the literature, the structural and molecular basis of biofilm formation of clinically related filamentous fungi has not been fully addressed. This review aimed to address biofilm formation in clinically relevant filamentous fungi.

Endurance of extremely prolonged nutrient prevention across kingdoms of life

Numerous observations demonstrate that microorganisms can survive very long periods of nutrient deprivation and starvation. Moreover, it is evident that prolonged periods of starvation are a feature of many habitats, and many cells in all kingdoms of life are found in prolonged starvation conditions. Bacteria exhibit a range of responses to long-term starvation. These include genetic adaptations such as the long-term stationary phase and the growth advantage in stationary phase phenotypes characterized by mutations in stress-signaling genes and elevated mutation rates. Here, we suggest using the term "endurance of prolonged nutrient prevention" (EPNP phase), to describe this phase, which was also recently described in eukaryotes. Here, we review this literature and describe the current knowledge about the adaptations to very long-term starvation conditions in bacteria and eukaryotes, its conceptual and structural conservation across all kingdoms of life, and point out possible directions that merit further research.

Aprepitant, an antiemetic agent, interferes with metal ion homeostasis of Candida auris and displays potent synergistic interactions with azole drugs

With the rapid increase in the frequency of azole-resistant species, combination therapy appears to be a promising tool to augment the antifungal activity of azole drugs against resistant Candida species. Here, we report the effect of aprepitant, an antiemetic agent, on the antifungal activities of azole drugs against the multidrug-resistant Candida auris. Aprepitant reduced the minimum inhibitory concentration (MIC) of itraconazole in vitro, by up to eight-folds. Additionally, the aprepitant/itraconazole combination interfered significantly with the biofilm-forming ability of C. auris by 95 ± 0.13%, and significantly disrupted mature biofilms by 52 ± 0.83%, relative to the untreated control. In a Caenorhabditis elegans infection model, the aprepitant/itraconazole combination significantly prolonged the survival of infected nematodes by ~90% (five days post-infection) and reduced the fungal burden by ~92% relative to the untreated control. Further, this novel drug combination displayed broad-spectrum synergistic interactions against other medically important Candida species such as C. albicans, C. krusei, C. tropicalis, and C. parapsilosis (ƩFICI ranged from 0.08 to 0.31). Comparative transcriptomic profiling and mechanistic studies indicated aprepitant/itraconazole interferes significantly with metal ion homeostasis and compromises the ROS detoxification ability of C. auris. This study presents aprepitant as a novel, potent, and broad-spectrum azole chemosensitizing agent that warrants further investigation.

Eradication of Candida albicans Biofilm Viability: In Vitro Combination Therapy of Cationic Carbosilane Dendrons Derived from 4-Phenylbutyric Acid with AgNO3 and EDTA

Candida albicans is a human pathogen of significant clinical relevance. This pathogen is resistant to different drugs, and most clinical antifungals are not effective against the prevention and treatment of C. albicans infections. As with other microorganisms, it can produce biofilms that serve as a barrier against antifungal agents and other substances, contributing to infection in humans and environmental tolerance of this microorganism. Thus, resistances and biofilm formation make treatment difficult. In addition, the complete eradication of biofilms in implants, catheters and other medical devices, is challenging and necessary to prevent relapses of candidemia. Therefore, it is a priority to find new molecules or combinations of compounds with anti-Candida biofilm activity. Due to the difficulty of treating and removing biofilms, the aim of this study was to evaluate the in vitro ability of different generation of cationic carbosilane dendrons derived from 4-phenylbutyric acid, ArCO₂G_n(SNMe₃I)_m, to eradicate C. albicans biofilms. Here, we assessed the antifungal activity of the second generation dendron ArCO2G₂(SNMe₃I)₄ against C. albicans cells and established biofilms since it managed to seriously damage the membrane. In addition, the combinations of the second generation dendron with AgNO₃ or EDTA eradicated the viability of biofilm cells. Alterations were observed by scanning electron microscopy and cytotoxicity was assessed on HeLa cells. Our data suggest that the dendritic compound ArCO₂G₂(SNMe₃I)₄ could represent an alternative to control the infections caused by this pathogen.

Candidemia and Invasive Candidiasis

Invasive candidiasis (IC) is a collective term that refers to a group of infectious syndromes caused by a variety of species of Candida, 6 of which cause most cases globally. Candidemia is probably the most commonly recognized syndrome associated with IC; however, Candida can cause invasive infection of any organ, especially visceral organs, vasculature, bones and joints, the eyes and central nervous system. Targeted prevention and empirical therapy are important interventions for patients at high risk for IC, and the current approach should be based on a combination of clinical risk factors and non-culture-based diagnostics, when available.

The Influence of Cellulose-Type Formulants on Anti-Candida Activity of the Tyrocidines

Candida species are highly adaptable to environmental changes with their phenotypic flexibility allowing for the evasion of most host defence mechanisms. Moreover, increasing resistance of human pathogenic Candida strains has been reported against all four classes of available antifungal drugs, which highlights the need for combinational therapies. Tyrocidines are cyclic antimicrobial peptides that have shown synergistic activity with antifungal drugs such as caspofungin and amphotericin B. However, these cyclodecapeptides have haemolytic activity and cytotoxicity, but they have been used for decades in the clinic for topical applications. The tyrocidines tend to form higher-order structures in aqueous solutions and excessive aggregation can result in variable or diminished activity. Previous studies have shown that the tyrocidines prefer ordered association to celluloses. Therefore, a formulation with soluble cellulose was used to control the oligomer stability and size, thereby increasing the activity against Candida spp. Of the formulants tested, it was found that commercial hydroxy-propyl-methyl cellulose, E10M, yielded the best results with increased stability, increased anti-Candida activity, and improved selectivity. This formulation holds promise in topical applications against Candida spp. infections.