Culture media profoundly affect Candida albicans and Candida tropicalis growth, adhesion and biofilm development

Evaluation of 1,9-Dimethyl-Methylene Blue nanoencapsulation using rhamnolipid nanoparticles to potentiate the Photodynamic Therapy technique in Candida albicans: In vitro study

With the rapid development of nanotechnology, various functional nanomaterials have shown exciting potential in biomedical areas such as drug delivery, antitumor, and antibacterial therapy. These nanomaterials improve the stability and selectivity of loaded drugs, reduce drug-induced side effects, realize controlled and targeted drug release, and increase therapeutic efficacy. The increased resistance to antifungal microbicides in medical practice and their side effects stimulate interest in new therapies, such as Photodynamic Therapy (PDT), which do not generate resistance in microorganisms and effectively control the pathology. The present study aimed to evaluate, in vitro, the efficacy of photodynamic therapy on Candida albicans using 1,9-Dimethyl-Methylene Blue (DMMB) as photosensitizer, red LED (λ630), and nanoencapsulation of DMMB (RL-NPs/DMMB) using rhamnolipids produced by Pseudomonas aeruginosa to evaluate if there is better performance of DMMB + RL particles compared to DMMB alone via the characterization of DMMB + RL and colony forming count. The tests were carried out across six experimental groups (Control, DMMB, RL-NPs, RL-NPs/DMMB, PDT and PDT + RL-NPs/DMMB) using in the groups with nanoparticles, DMMB (750 ng/mL) encapsulated with rhamnolipids in a 1:1 ratio, the light source consisted of a prototype built with a set of red LEDs with an energy density of 20 J/cm2. The results showed that applying PDT combined with encapsulation (RL-NPs/DMMB) was a more practical approach to inhibit Candida albicans (2 log reduction) than conventional applications, with a possible clinical application protocol.

Surfactants' Interplay with Biofilm Development in Staphylococcus and Candida

The capacity of micro-organisms to form biofilms is a pervasive trait in the microbial realm. For pathogens, biofilm formation serves as a virulence factor facilitating successful host colonization. Simultaneously, infections stemming from biofilm-forming micro-organisms pose significant treatment challenges due to their heightened resistance to antimicrobial agents. Hence, the quest for active compounds capable of impeding microbial biofilm development stands as a pivotal pursuit in biomedical research. This study presents findings concerning the impact of three surfactants, namely, polysorbate 20 (T20), polysorbate 80 (T80), and sodium dodecyl sulfate (SDS), on the initial stage of biofilm development in both Staphylococcus aureus and Candida dubliniensis. In contrast to previous investigations, we conducted a comparative assessment of the biofilm development capacity of these two taxonomically distant groups, predicated on their shared ability to reduce TTC. The common metabolic trait shared by S. aureus and C. dubliniensis in reducing TTC to formazan facilitated a simultaneous evaluation of biofilm development under the influence of surfactants across both groups. Our results revealed that surfactants could impede the development of biofilms in both species by disrupting the initial cell attachment step. The observed effect was contingent upon the concentration and type of compound, with a higher inhibition observed in culture media supplemented with SDS. At maximum concentrations (5%), T20 and T80 significantly curtailed the formation and viability of S. aureus and C. dubliniensis biofilms. Specifically, T20 inhibited biofilm development by 75.36% in S. aureus and 71.18% in C. dubliniensis, while T80 exhibited a slightly lower inhibitory effect, with values ranging between 66.68% (C. dubliniensis) and 65.54% (S. aureus) compared to the controls. Incorporating these two non-toxic surfactants into pharmaceutical formulations could potentially enhance the inhibitory efficacy of selected antimicrobial agents, particularly in external topical applications.

Anticandida and antibiofilm activities of extract from Schinopsis brasiliensis Engl. against Candida spp

The pathogenic nature of infections caused by Candida spp. underscores the necessity for novel therapeutic agents. Extracts of Schinopsis brasilienses Engl are \ a promising source of agents with antifungal effects. This study aimed to assess the antifungal potential of the leaf extract of S. brasilienses. The antifungal activity was evaluated by determining the minimum inhibitory concentrations and fungicide concentrations (MIC and MFC). The antibiofilm potential was assessed by counting colony-forming units/mL. The study examined the inhibition kinetics of fungal growth and potential synergism between gallic acid or the extract and nystatin using the Checkerboard method. Cytotoxicity was evaluated through the MTT assay. The extract exhibited antifungal effect against all tested strains, with MIC and MFC ranging from 31.25-250 μg/mL. Gallic acid, the main isolated compound, displayed a MIC of 2000 μg/mL. The extract of S. brasilienses at 31.25 μg/mL inhibited the formation of biofilm by C. albicans and significantly reduced the mass of mature biofilm after 24 and 48 h (p < 0. 05). At a concentration of 125 μg/mL, the extract demonstrated significant inhibition of fungal growth after 6 hours. The combination of gallic acid or extract with nystatin did not exhibit synergistic or antagonistic effect. Furthermore, the extract did not induce cytotoxicity to a human cell line. The extract of S. brasiliensis demonstrates antifungal activity against Candida, generally exhibiting fungicidal action and capacity to inhibit biofilm formation as well as reduce mature biofilms. Additionally, the extract showed low cytotoxicity to human cells.

Antibiofilm Activity of Curcumin and Piperine and Their Synergistic Effects with Antifungals against Candida albicans Clinical Isolates

Background

Candidiasis is the common name for diseases caused by yeast of the genus Candida. Candida albicans is one of the most implicated species in superficial and invasive candidiasis. Antifungals, polyenes, and azoles have been used to treat candidiasis. However, due to the development of antifungal resistance, research of natural substances with potential antifungal effects at low concentrations or combined is also a possibility.

Methods

The broth microdilution method was used to evaluate the antifungal activity. The biofilm formation was assessed using the microtiter plate method. The antibiofilm activities were assessed using micro plaque tetrazolium salt assay (MTT). The combination effect of antifungal with natural substances was made using the checkerboard method.

Results

Among our isolates, clotrimazole was the most resistant, but amphotericin B was the most effective antifungal. The biofilm was formed by all isolates of C. albicans. Curcumin and piperine displayed antibiofilm activity with minimum biofilm inhibitory concentration (MBIC) and minimum eradicating concentration (MBEC) ranging from 64 to 1024 μg/mL and 256 to 2048 μg/mL. In combination, piperine presented double synergistic effects compared to curcumin with all antifungals tested. Curcumin shows more synergistic effect when combined with polyenes than with azoles. However, piperine shows a more synergistic effect when combined with azoles compared to polyenes.

Conclusion

C. albicans was susceptible to curcumin and piperine both on planktonic cells and biofilm. The combination of curcumin and piperine with antifungals has shown synergistic effects against multiresistant clinical isolates of Candida albicans representing an alternative drug research for the treatment of clinical candidiasis.

Poly-Gamma-Glutamic Acid Nanopolymer Effect against Bacterial Biofilms: In Vitro and In Vivo Study

In this study, a biodegradable poly-gamma-glutamic-acid nanopolymer (Ɣ-PGA NP) was investigated for its activity against clinical strains of Gram-positive (Staphylococcus aureus and Streptococcus pyogenes) and Gram-negative (Klebsiella pneumoniae and Escherichia coli), and reference strains of S. aureus ATCC 6538, S. pyogenes ATCC 19615 (Gram-positive), and Gram-negative E. coli ATCC 25922, and K. pneumoniae ATCC 13884 bacterial biofilms. The minimum inhibitory concentration (MIC) effect of Ɣ-PGA NP showed inhibitory effects of 0.2, 0.4, 1.6, and 3.2 μg/mL for S. pyogenes, S. aureus, E. coli, and K. pneumoniae, respectively. Also, MIC values were 1.6, 0.8, 0.2, and 0.2 μg/mL for K. pneumoniae ATCC 13884, E. coli ATCC 25922, S. aureus ATCC 6538, and S. pyogenes ATCC 19615, respectively. Afterwards, MBEC (minimum biofilm eradication concentration) and MBIC (minimum biofilm inhibitory concentration) were investigated to detect Ɣ-PGA NPs efficiency against the biofilms. MBEC and MBIC increased with increasing Ɣ-PGA NPs concentration or time of exposure. Interestingly, MBIC values were at lower concentrations of Ɣ-PGA NPs than those of MBEC. Moreover, MBEC values showed that K. pneumoniae was more resistant to Ɣ-PGA NPs than E. coli, S. aureus, and S. pyogenes, and the same pattern was observed in the reference strains. The most effective results for MBEC were after 48 h, which were 1.6, 0.8, 0.4, and 0.2 µg/mL for K. pneumoniae, E. coli, S. aureus, and S. pyogenes, respectively. Moreover, MBIC results were the most impactful after 24 h but some were the same after 48 h. MBIC values after 48 h were 0.2, 0.2, 0.2, and 0.1 μg/mL for K. pneumoniae, E. coli, S. aureus, and S. pyogenes, respectively. The most effective results for MBEC were after 24 h, which were 1.6, 0.8, 0.4, and 0.4 µg/mL for K. pneumoniae ATCC 13884, E. coli ATCC 25922, S. aureus ATCC 6538, and S. pyogenes ATCC 19615, respectively. Also, MBIC results were the most impactful after an exposure time of 12 h. MBIC values after exposure time of 12 h were 0.4, 0.4, 0.2, and 0.2 μg/mL for K. pneumoniae ATCC 13884, E. coli ATCC 25922, S. aureus ATCC 6538, and S. pyogenes ATCC 19615, respectively. Besides that, results were confirmed using confocal laser scanning microscopy (CLSM), which showed a decrease in the number of living cells to 80% and 60% for MBEC and MBIC, respectively, for all the clinical bacterial strains. Moreover, living bacterial cells decreased to 70% at MBEC while decreasing up to 50% at MBIC with all bacterial refence strains. These data justify the CFU quantification. After that, ImageJ software was used to count the attached cells after incubating with the NPs, which proved the variation in live cell count between the manual counting and image analysis methods. Also, a scanning electron microscope (SEM) was used to detect the biofilm architecture after incubation with the Ɣ-PGA NP. In in vivo wound healing experiments, treated wounds of mice showed faster healing (p < 0.00001) than both the untreated mice and those that were only wounded, as the bacterial count was eradicated. Briefly, the infected mice were treated faster (p < 0.0001) when infected with S. pyogenes > S. aureus > E. coli > K. pneumoniae. The same pattern was observed for mice infected with the reference strains. Wound lengths after 2 h showed slightly healing (p < 0.001) for the clinical strains, while treatment became more obvious after 72 h > 48 h > 24 h (p < 0.0001) as wounds began to heal after 24 h up to 72 h. For reference strains, wound lengths after 2 h started to heal up to 72 h.

The inhibitory effect of photodynamic therapy on dual-species biofilms of Candida albicans and Candida krusei can be determined by Candida albicans/Candida krusei ratio

Candida krusei and Candida albicans present the ability to form communities of microorganisms called biofilms. Biofilms can be composed of a single species or more and are an important virulence factor. The inhibition of C. albicans and C. krusei as well as of their dual-species biofilms by antimicrobial Photodynamic Therapy (aPDT) has been demonstrated. This study aimed to investigate the effect of aPDT, with TBO, on dual-species biofilms of C. albicans and C. krusei using different culture mediums, RPMI-1640 and Sabouraud-dextrose broth (SDB) to produce biofilms presenting different C. albicans/C. krusei ratio. Biofilms formed using RPMI-1640 presented a higher C. albicans/C. krusei ratio, however, biofilms formed using SDB presented a predominance of C. krusei. The metabolic activity of biofilms produced using RPMI-1640 was inhibited by aP (∼40%), while biofilms produced using SDB were not affected by aPDT. In addition, biofilm biomass was reduced in biofilms produced using RPMI-1640 and treated with aPDT (∼20%). The results demonstrated that aPDT reduces C. albicans development in dual-species biofilms with C. krusei. However, no effect could be observed on C. krusei, demonstrating that C. krusei, when present in the structure of dual-species biofilms can be resistant to aPDT.

Synthesis, characterisation, and solution behaviour of Ag(I) bis(phenanthroline-oxazine) complexes and the evaluation of their biological activity against the pathogenic yeast Candida albicans

Three Ag(I) bis(phenanthroline-oxazine) complexes with varying lipophilicity were synthesised and characterised. The solution stoichiometry of 1:2 Ag(I):ligand was determined for each complex by the continuous variation Job's plot method using NMR spectroscopy. NMR studies were also carried out to investigate the fluxional behaviour of the Ag(I) complexes in solution. The biological activity of the silver(I) complexes and the corresponding ligands towards a clinical strain of Candida albicans MEN was studied using broth microdilution assays. Testing showed the choice of media and the duration of incubation were key determinants of the inhibitory behaviour towards Candida albicans, however, the difference between freshly prepared and pre-prepared solutions was insignificant in minimal media. The activity of the metal-free ligands correlated with the length of the alkyl chain. In minimal media, the methyl ester phenanthroline-oxazine ligand was effective only at 60 μM, limiting growth to 67% of the control, while a 60 μM dose of the propyl ester analogue limited fungal growth at < 20% of the control. MIC50 and MIC80 values for the propyl and hexyl ester analogues were calculated to be 45 and 59 µM (propyl), and 18 and 45 µM (hexyl). Moreover, in a study of activity as a function of time it was observed that the hexyl ester ligand maintained its activity for longer than the methyl and propyl analogues; after 48 h a 60 μM dose held fungal growth at 24% of that of the control. Complexation to Ag(I) was much more effective in enhancing biological activity of the ligands than was increasing the ester chain length. Significantly no difference in activity between the three silver(I) complexes was observed under the experimental conditions. All three complexes were substantially more active than their parent ligands against Candida albicans and AgClO4 and the three silver(I) bis(phen-oxazine) complexes have MIC80 values of < 15 μM. The ability of the silver(I) complexes to hold fungal growth at about 20% of the control even after 48 h incubation at low dosages (15 μM) showcases their superiority over the simple silver(I) perchlorate salt, which ceased to be effective at dosages below 60 μM at the extended time point.

Multi-Omics Profiling of Candida albicans Grown on Solid Versus Liquid Media

Candida albicans is a common pathogenic fungus that presents a challenge to healthcare facilities. It can switch between a yeast cell form that diffuses through the bloodstream to colonize internal organs and a filamentous form that penetrates host mucosa. Understanding the pathogen's strategies for environmental adaptation and, ultimately, survival, is crucial. As a complementary study, herein, a multi-omics analysis was performed using high-resolution timsTOF MS to compare the proteomes and metabolomes of Wild Type (WT) Candida albicans (strain DK318) grown on agar plates versus liquid media. Proteomic analysis revealed a total of 1793 proteins and 15,013 peptides. Out of the 1403 identified proteins, 313 proteins were significantly differentially abundant with a p-value < 0.05. Of these, 156 and 157 proteins were significantly increased in liquid and solid media, respectively. Metabolomics analysis identified 192 metabolites in total. The majority (42/48) of the significantly altered metabolites (p-value 0.05 FDR, FC 1.5), mainly amino acids, were significantly higher in solid media, while only 2 metabolites were significantly higher in liquid media. The combined multi-omics analysis provides insight into adaptative morphological changes supporting Candida albicans' life cycle and identifies crucial virulence factors during biofilm formation and bloodstream infection.

The influence of negative pressure wound therapy on bacterial and fungal growth

BACKGROUND

The use of negative pressure wound therapy (NPWT) in superinfected wounds is controversial. The mechanism of action is unclear, but recent studies have shown lower atmospheric oxygen levels within the dressing. Therefore, different oxygen-favoring bacteria and fungi might benefit or face impaired thriving conditions. The aim of this in vitro study is to investigate the influence of NPWT on bacterial and fungal growth.

METHODS

Salmonella enterica subsp. enterica serovar Typhimurium, Pseudomonas aeruginosa and Candida albicans strains were cultured on concentrated agars and attached to a standard NPWT-device. After 48 hours, colonies were separately harvested from the agar and foam. Optical density (OD) was obtained in order to estimate bacterial loads.

RESULTS

For all tested microorganisms, no overall significant differences were found compared to controls. Subanalysis showed lower OD levels from the agar beneath the foam in the NPWT-group.

CONCLUSION

NPWT removed bacteria and fungi from the wound surface but accumulation is found within the foam. The use of NPWT showed no influence on bacterial or fungal growth selection. With superinfected wounds, the use of NPWT should thoroughly be evaluated as toxins and virulence factors may not fully be evacuated.

Anti-adherent activity of nano-coatings deposited by thermionic vacuum arc plasma on C. albicans biofilm formation

BACKGROUND

The purpose of this study was to analyze the anti-adherent activity of nano-coatings deposited by Thermionic Vacuum Arc plasma on C. albicans ATCC 10231 biofilm.

MATERIALS AND METHODS

A total of 80 disc-shaped (2 × 10 mm) polymethymethacrylate samples were prepared and divided into four groups with 10 samples in each group (Control, ZnO, SnO2, Ag) (n = 10). Using thermionic vacuum arc plasma, they were coated with ZnO, SnO2, and Ag. 3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and Crystal Viole (CV) assays were conducted for biofilm quantification. Scanning electron microscopy (SEM) was used to observe biofilm images of C. albicans biofilm.

RESULTS

MTT and CV mean values differ statistically significantly between all groups (p ⩽ 0.05). The SnO2 group had the lowest mean value, whereas the control group received the highest value.

CONCLUSION

SnO2 coating shown greater anti-adherent activity than either metal oxides. C. albicans biofilm formation on denture base surfaces is reduced following Thermionic Vacuum Arc plasma coating with SnO2.

Could Helium Plasma Treatment be a Novel Approach to Prevent the Biofilm Formation of Candida albicans?

There is no definitive method to prevent Candida albicans (C. albicans) biofilm formation on polymethyl methacrylate (PMMA) surfaces. The objective of this study was to evaluate the effect of Helium plasma treatment (before the application of removable dentures to the patient) to prevent or reduce C. albicans ATCC 10,231 the anti-adherent activity, viability, and biofilm formation on PMMA surfaces. One hundred disc-shaped PMMA samples (2 mm × 10 mm) were prepared. The samples were randomly divided into 5 surface groups and treated with different concentrations of Helium plasma: G I: Control group (untreated), G II: 80% Helium plasma-treated group, G III: 85% Helium plasma-treated group, G IV: 90% Helium plasma-treated group, G V: 100% Helium plasma-treated group. C. albicans viability and biofilm formations were evaluated using 2 methods: MTT (3-(4,5-dimethyl thiazolyl-2)-2, 5-diphenyltetrazolium bromide) assays and Crystal Violet (CV) staining. The surface morphology and C. albicans biofilm images were observed with scanning electron microscopy. The Helium plasma-treated PMMA groups (G II, G III, G IV, G V) observed a significant reduction in C. albicans cell viability and biofilm formation compared with the control group. Treating PMMA surfaces with different concentrations of Helium plasma prevents C. albicans viability and biofilm formation. This study suggests that Helium plasma treatment might be an effective strategy in modifying PMMA surfaces to prevent denture stomatitis formation.

Aqueous spice extracts as alternative antimycotics to control highly drug resistant extensive biofilm forming clinical isolates of Candida albicans

Candida albicans form biofilm by associating with biotic and abiotic surfaces. Biofilm formation by C. albicans is relevant and significant as the organisms residing within, gain resistance to conventional antimycotics and are therefore difficult to treat. This study targeted the potential of spice-based antimycotics to control C. albicans biofilms. Ten clinical isolates of C. albicans along with a standard culture MTCC-3017 (ATCC-90028) were screened for their biofilm-forming ability. C. albicans M-207 and C. albicans S-470 were identified as high biofilm formers by point inoculation on Trypticase Soy Agar (TSA) medium as they formed a lawn within 16 h and exhibited resistance to fluconazole and caspofungin at 25 mcg and 8 mcg respectively. Aqueous and organic spice extracts were screened for their antimycotic activity against C. albicans M-207 and S-470 by agar and disc diffusion and a Zone of Inhibition was observed. Minimal Inhibitory Concentration was determined based on growth absorbance and cell viability measurements. The whole aqueous extract of garlic inhibited biofilms of C. albicans M-207, whereas whole aqueous extracts of garlic, clove, and Indian gooseberry were effective in controlling C. albicans S-470 biofilm within 12 h of incubation. The presence of allicin, ellagic acid, and gallic acid as dominant compounds in the aqueous extracts of garlic, clove, and Indian gooseberry respectively was determined by High-Performance Thin Layer Chromatography and Liquid Chromatography-Mass Spectrometry. The morphology of C. albicans biofilm at different growth periods was also determined through bright field microscopy, phase contrast microscopy, and fluorescence microscopy. The results of this study indicated that the alternate approach in controlling high biofilm-forming, multi-drug resistant clinical isolates of C. albicans M-207 and S-470 using whole aqueous extracts of garlic, clove, and Indian gooseberry is a safe, potential, and cost-effective one that can benefit the health care needs with additional effective therapeutics to treat biofilm infections.

Cell wall composition in Cryptococcus neoformans is media dependent and alters host response, inducing protective immunity

Introduction

Cryptococcus neoformans is a basidiomycete fungus that can cause meningoencephalitis, especially in immunocompromised patients. Cryptococcus grows in many different media, although little attention has been paid to the role of growth conditions on the cryptococcal cell wall or on virulence.

Objective

The purpose of this study was to determine how different media influenced the amount of chitin and chitosan in the cell wall, which in turn impacted the cell wall architecture and host response.

Methods

Yeast extract, peptone, and dextrose (YPD) and yeast nitrogen base (YNB) are two commonly used media for growing Cryptococcus before use in in vitro or in vivo experiments. As a result, C. neoformans was grown in either YPD or YNB, which were either left unbuffered or buffered to pH 7 with MOPS. These cells were then labeled with cell wall-specific fluorescent probes to determine the amounts of various cell wall components. In addition, these cells were employed in animal virulence studies using the murine inhalation model of infection.

Results

We observed that the growth of wild-type C. neoformans KN99 significantly changes the pH of unbuffered media during growth. It raises the pH to 8.0 when grown in unbuffered YPD but lowers the pH to 2.0 when grown in unbuffered YNB (YNB-U). Importantly, the composition of the cell wall was substantially impacted by growth in different media. Cells grown in YNB-U exhibited a 90% reduction in chitosan, the deacetylated form of chitin, compared with cells grown in YPD. The decrease in pH and chitosan in the YNB-U-grown cells was associated with a significant increase in some pathogen-associated molecular patterns on the surface of cells compared with cells grown in YPD or YNB, pH 7. This altered cell wall architecture resulted in a significant reduction in virulence when tested using a murine model of infection. Furthermore, when heat-killed cells were used as the inoculum, KN99 cells grown in YNB-U caused an aberrant hyper-inflammatory response in the lungs, resulting in rapid animal death. In contrast, heat-killed KN99 cells grown in YNB, pH 7, caused little to no inflammatory response in the host lung, but, when used as a vaccine, they conferred a robust protective response against a subsequent challenge infection with the virulent KN99 cells.

Conclusion

These findings emphasize the importance of culture media and pH during growth in shaping the content and organization of the C. neoformans cell wall, as well as their impact on fungal virulence and the host response.

Rosemary essential oil and its components 1,8-cineole and α-pinene induce ROS-dependent lethality and ROS-independent virulence inhibition in Candida albicans

The essential oil from Rosmarinus officinalis L., a composite mixture of plant-derived secondary metabolites, exhibits antifungal activity against virulent candidal species. Here we report the impact of rosemary oil and two of its components, the monoterpene α-pinene and the monoterpenoid 1,8-cineole, against Candida albicans, which induce ROS-dependent cell death at high concentrations and inhibit hyphal morphogenesis and biofilm formation at lower concentrations. The minimum inhibitory concentrations (100% inhibition) for both rosemary oil and 1,8-cineole were 4500 μg/ml and 3125 μg/ml for α-pinene, with the two components exhibiting partial synergy (FICI = 0.55 ± 0.07). At MIC and 1/2 MIC, rosemary oil and its components induced a generalized cell wall stress response, causing damage to cellular and organelle membranes, along with elevated chitin production and increased cell surface adhesion and elasticity, leading to complete vacuolar segregation, mitochondrial depolarization, elevated reactive oxygen species, microtubule dysfunction, and cell cycle arrest mainly at the G1/S phase, consequently triggering cell death. Interestingly, the same oils at lower fractional MIC (1/8-1/4) inhibited virulence traits, including reduction of mycelium (up to 2-fold) and biofilm (up to 4-fold) formation, through a ROS-independent mechanism.

Biofilm formation and antibiotic resistance among Coagulase Negative Staphylococcus species isolated from central venous catheters of intensive care unit patients

PURPOSE

This study was conducted to determine the biofilm formation of coagulase negative Staphylococcus species (CoNS) isolated from patients with catheter related blood stream infection (CRBSI) and colonized central venous catheters (CVC) and their antibiotic susceptibility patterns and in situ biofilm formation of CVC tips.

METHODS

Eighty-two CoNS isolated from intensive care unit (ICU) patients with CRBSI (n ​= ​8) or colonized CVC (n ​= ​74) were included. Species identification and antibiotic susceptibility test were done. All isolates were screened for biofilm formation using crystal violet and 3-(4,5-dimethylthiazole-2-yl)-2-5-diphenyl-2H-tetrazolium bromide (MTT) assays and categorized as strong or moderate biofilm formers. CVC tips were subjected to crystal violet stain and scanning electron microscopy (SEM) to detect in-situ biofilm formation.

RESULTS

Staphylococcus haemolyticus (n ​= ​34; 41%) was the commonest to cause both CRBSI and CVC colonization. All 82 CoNS produced biofilms. Among them 77 (93.90%) were strong biofilm formers including all from CRBSI patients and 05 (6.10%) were moderate biofilm formers as detected by both methods. SEM showed bacteria adhered to surfaces of CVC tips with microbial-aggregates embedded in extracellular matrix. Mean crystal violet absorbance of CVC from CRBSI patients (0.6628) was significantly higher than colonized CVC (mean value 0.5592) (p ​= ​0.030). S. haemolyticus showed higher resistance to cloxacillin compared to other CoNS (p ​= ​0.039).

CONCLUSION

Majority of CoNS isolated were strong biofilm formers. In-situ biofilm formation on CVC tips were significantly evident in CRBSI patients compared to CVC colonized patients. S. haemolyticus is the commonest to cause both CRBSI and CVC colonization and shows significantly higher cloxacillin resistance rate.

Optotracing for live selective fluorescence-based detection of Candida albicans biofilms

Candida albicans is the most common fungal pathogen in humans, implicated in hospital-acquired infections, secondary infections in human immunodeficiency virus (HIV) patients, and is a significant contributor to the global antimicrobial resistance (AMR) burden. Early detection of this pathogen is needed to guide preventative strategies and the selection and development of therapeutic treatments. Fungal biofilms are a unique heterogeneous mix of cell types, extracellular carbohydrates and amyloid aggregates. Perhaps due to the dominance of carbohydrates in fungi, to date, few specific methods are available for the detection of fungal biofilms. Here we present a new optotracing-based method for the detection and analysis of yeast and biofilms based on C. albicans SC5314 as a model. Using commercial extracts of cell wall carbohydrates, we showed the capability of the optotracer EbbaBiolight 680 for detecting chitin and β-glucans. The sensitivity of this tracer to these carbohydrates in their native environment within fungal cells enabled the visualization of both yeast and hyphal forms of the microbe. Analysis of optotracer fluorescence by confocal laser scanning microscopy revealed extensive staining of fungi cell walls as well as the presence of intracellular amyloid aggregates within a subpopulation of cells within the biofilm. Further analysis of the photophysical properties of bound tracers by spectroscopy and spectral imaging revealed polymorphisms between amyloid aggregates within yeast and hyphal cells and enabled their differentiation. With exceptional spatial and temporal resolution, this assay adds a new technique that facilitates future understanding of fungal biofilms and their formation, and enables direct, unbiased diagnostics of these medically relevant biofilms, as well as the development of antifungal strategies.

Evaluation of the biofilm life cycle between Candida albicans and Candida tropicalis

Candida tropicalis is an emergent pathogen with a high rate of mortality associated with its biofilm formation. Biofilm formation has important repercussions on the public health system. However, little is still known about its biofilm life cycle. The present study analyzed the biofilm life cycle of Candida albicans and C. tropicalis during various timepoints (24, 48, 72, and 96 h) through biomass assays, colony-forming unit (CFU) counting, and epifluorescence and scanning electron microscopies. Our results showed a significant difference between C. albicans and C. tropicalis biofilms in each biomass and viability assay. All-time samples in the biomass and viability assays confirmed statistical differences between the Candida species through pairwise Wilcoxon tests (p < 0.05). C. albicans demonstrated a lower biomass growth but reached nearly the same level of C. tropicalis biomass at 96 h, while the CFU counting assays exhibited a superior number of viable cells within the C. tropicalis biofilm. Statistical differences were also found between C. albicans and C. tropicalis biofilms from 48- and 72-h microscopies, demonstrating C. tropicalis with a higher number of total cells within biofilms and C. albicans cells with a superior cell area and higher matrix production. Therefore, the present study proved the higher biofilm production of C. tropicalis.

Antibiofilm Activity of Essential Fatty Acids Against Candida albicans from Vulvovaginal Candidiasis and Bloodstream Infections

Purpose

Methods

Results

Conclusion

Lactobacilli displacement and Candida albicans inhibition on initial adhesion assays: a probiotic analysis

Objective

This study evaluates the probiotic activity of three vaginal Lactobacillus gasseri (H59.2, IMAUFB014, and JCM1131) and one non-vaginal L. plantarum ATCC14917 against three Candida albicans (ATCC10231, candidiasis, and healthy vaginal microbiota). Displacement of lactobacilli and adhesion inhibition of C. albicans were evaluated on an abiotic surface through adhesion assays with different experimental settings (ES) through low (1.0E + 03 CFU/ml) and high (1.00E + 09 CFU/ml) levels of colonization. ES simulated dysbiosis (ES1 and ES4), candidiasis (ES2), and healthy vaginal microbiota (ES3).

Results

At ES2 and ES3, L. gasseri H59.2 showed discrepant inhibition values among C. albicans isolates (ES2: P = 0.008, ES3: P = 0.030; two‐way ANOVA). L. plantarum was only displaced by 23%, 31%, 54%, and 94% against low and high levels of C. albicans ATCC10231. L. plantarum was less displaced, when compared to L. gasseri strains (ES1: 61–84%, ES2: 82–96%, ES3: 83–95%, and ES4: 73–97%), showing multiple statistical differences (ES1: P =  < 0.001, ES2: P = 0.003, and ES3: P =  < 0.001; two‐way ANOVA). L. plantarum also showed a superior inhibition of C. albicans ATCC10231 in ES1 (81%) and ES2 (58%) when compared to L. gasseri strains (ES1: 27–73%, P < 0.001; and ES2:1–49%, P < 0.001; two‐way ANOVA).

Supplementary Information

The online version contains supplementary material available at 10.1186/s13104-022-06114-z.

Biofilm formation of Candida isolates from xerostomic post-radiotherapy head and neck cancer patients

Oral candidiasis is a common problem in post-radiation head and neck cancer (HNC) patients. While biofilm formation is a crucial virulence factor for Candida colonization, existing information on biofilm formation capability of Candida in cancer patients is scarce.

OBJECTIVE

To evaluate biofilm formation capability of Candida spp. colonized in xerostomic post-radiotherapy HNC patients.

DESIGN

Candida albicans and non-albicans Candida species were previously isolated from xerostomic post-radiation cancer patients and healthy individuals. Biofilm mass and biofilm metabolic activity were investigated by crystal violet and MTT assays, respectively. Their relationship with clinical parameters was analyzed using Mann-Whitney U and Chi-square tests.

RESULTS

A total of 109 and 45 Candida isolates from 64 cancer patients and 34 controls, respectively, were evaluated. Both biofilm mass and metabolic activity of Candida isolates from cancer patients were higher than those from controls. The between-group differences were statistically significant in C. albicans (p < 0.001) for biofilm mass, and in C. tropicalis (p = 0.01) for biofilm metabolic activity. Overall, C. tropicalis was the best biofilm producers in both groups. Additionally, we found that higher biofilm formation among C. albicans was associated with low saliva buffering capacity.

CONCLUSIONS

C. albicans and C. tropicalis isolated from xerostomic post-radiation cancer patients had higher biofilm formation capability than those from healthy individuals. Our findings suggest that, in addition to compromised host factors, higher biofilm formation capability may also contribute to the pathogenesis of oral candidiasis in HNC patients. This novel information potentially adds to proper management for these patients.

Characterization of Candida albicans and Staphylococcus aureus polymicrobial biofilm on different surfaces

BACKGROUND

Staphylococcus aureus and Candida albicans have been co-isolated from biofilm-associated diseases such as denture stomatitis, periodontitis, and burn wound infections, as well as from medical devices. However, the polymicrobial biofilm of both microorganisms has not been fully characterized.

AIMS

To characterize the polymicrobial biofilm of C. albicans and S. aureus in terms of microbial density, synergy, composition, structure, and stability against antimicrobials and chemical agents.

METHODS

Crystal violet assay was used to measure the biofilm formation. Scanning electron microscopy and confocal microscopy were used to analyze the structure and chemical composition of the biofilms, respectively.

RESULTS

Supplemented media with fetal bovine serum (FBS) decreased the biofilm formation of S. aureus and the polymicrobial biofilm. For C. albicans, depending on the culture media, the addition of glucose or FBS had a positive effect in biofilm formation. FBS decreased the adhesion to polystyrene wells for both microorganisms. Supplementing the media with glucose and FBS enhanced the growth of C. albicans and S. aureus, respectively. It seems that C. albicans contributes the most to the adhesion process and to the general structure of the biofilms on all the surfaces tested, including a catheter model. Interestingly, S. aureus showed a great adhesion capacity to the surface of C. albicans in the biofilms. Proteins and β-1,6-linked polysaccharides seem to be the most important molecules in the polymicrobial biofilm.

CONCLUSIONS

The polymicrobial biofilm had a complex structure, with C. albicans serving as a scaffold where S. aureus adheres, preferentially to the hyphal form of the fungus. Detection of polymicrobial infections and characterization of biofilms will be necessary in the future to provide a better treatment.

Molecular investigations on Candida glabrata clinical isolates for pharmacological targeting

Prevalence of drug resistant C. glabrata strains in hospitalized immune-compromised patients with invasive fungal infections has increased at an unexpected pace. This has greatly pushed researchers in identification of mutations/variations in clinical isolates for better assessment of the prevailing drug resistance trends and also for updating of antifungal therapy regime. In the present investigation, the clinical isolates of C. glabrata were comprehensively characterized at a molecular level using metabolic profiling and transcriptional expression analysis approaches in combination with biochemical, morphological and chemical profiling methods. Biochemically, significant variations in azole susceptibility, surface hydrophobicity, and oxidative stress generation were observed among the isolates as compared to wild-type. The ¹H NMR profiling identified 18 differential metabolites in clinical strains compared to wild-type and were classified into five categories, that include: sugars (7), amino acids and their derivatives (7), nitrogen bases (3) and coenzymes (1). Transcriptional analysis of selective metabolic and regulatory enzymes established that the major differences were found in cell membrane stress, carbohydrate metabolism, amino acid biosynthesis, ergosterol pathway and turnover of nitrogen bases. This detailed molecular level/metabolic fingerprint study is a useful approach for differentiating pathogenic/clinical isolates to that of wild-type. This study comprehensively delineated the differential cellular pathways at a molecular level that have been re-wired by the pathogenic clinical isolates for enhanced pathogenicity and virulence traits.

The clinical isolates of Candida glabrata were characterized and found to be different in terms of metabolic pathways that could be targeted for drug development.

Metabolic profile of Candida albicans and Candida parapsilosis interactions within dual-species biofilms

Within the oral cavity, the ability of Candida species to adhere and form biofilms is well recognized, especially when C. albicans is considered. Lately, a knowledge gap has been identified regarding dual-species communication of Candida isolates, as a way to increase virulence, with evidences being collected to support the existence of interactions between C. albicans and C. parapsilosis. The present work evaluated the synergistic effect of the two Candida species, and explored chemical interactions between cells, evaluating secreted extracellular alcohols and their relation with yeasts´ growth and matrix composition. Four clinical strains of C. albicans and C. parapsilosis species, isolated from single infections of different patients or from co-infections of a same patient, were tested. It was found that dual-species biofilms negatively impacted the growth of C. parapsilosis and their biofilm matrix, in comparison with mono-species biofilms, and had minor effects on the biofilm biomass. Alcohol secretion revealed to be species- and strain-dependent. However, some dual-species cultures produced much higher amounts of some alcohols (E-nerolidol and E, E-Farnesol) than the respective single cultures, which proves the existence of a synergy between species. These results show evidence that interactions between Candida species affect the biofilm matrix, which is a key element of oral biofilms.

Development of an Anti-Biofilm Screening Technique Leads to the Discovery of a Peptoid with Efficacy against Candida albicans

Bacteria and fungi can secrete and reside within a complex polysaccharide matrix, forming a biofilm that protects these pathogens from the immune response and conventional antibiotics. Because many microbial pathogens grow within biofilms in clinical settings, there is a need for antimicrobial agents effective against biofilm-protected infections. We report the adaptation of a phenotypic high-throughput assay for discovering antimicrobial peptoids toward the screening of combinatorial libraries against established biofilms. This method, termed the Inverted Peptoid Library Agar Diffusion (iPLAD) assay, required optimization of growth media, reducing reagent, and fungal viability reporter. Once optimized, iPLAD was used to screen a combinatorial peptoid library against Candida albicans, a biofilm-forming fungal pathogen responsible for most hospital-acquired infections. This screening resulted in a lipopeptoid termed RMG9-11 with excellent activity against several species of Candida, including drug-resistant strains of C. albicans and the emerging and dangerous C. auris. Additionally, the cytotoxicity of RMG9-11 against several mammalian cell lines was minimal. This work provides a new method for the identification of compounds effective against biofilm-protected pathogens and demonstrates its utility by identifying a promising anti-Candida peptoid.

Biofilm-formation capability depends on environmental oxygen concentrations in Candida species

BACKGROUND

Although oxygen concentrations inside of the human body vary depending on organs or tissues, few reports describe the relationships between biofilm formation of Candida species and oxygen concentrations. In this study, we investigated the biofilm-forming capabilities of Candida species under various oxygen conditions.

METHODS

We evaluated the adhesion and biofilm formation of Candida albicans and C. tropicalis under aerobic, microaerobic (oxygen concentration 5%), or anaerobic conditions. We also examined how oxygen concentration affects adhesion/maturation by changing adhesion/maturation phase conditions. We used crystal violet assay to estimate the approximate biofilm size, performed microscopic observation of biofilm morphology, and evaluated adhesion-associated gene expression.

RESULTS

The adhered amount was relatively small except for a clinical strain of C. tropicalis. Our biofilm-formation analysis showed that C. albicans formed a higher-size biofilm under aerobic conditions, while C. tropicalis favored microaerobic conditions to form mature biofilms. Our microscopic observations were consistent with these biofilm-formation analysis results. In particular, C. tropicalis exhibited more hyphal formation under microaerobic conditions. By changing the adhesion/maturation phase conditions, we represented that C. albicans had favorable biofilm-formation capability under aerobic conditions, while C. tropicalis showed enhanced biofilm formation under microaerobic adhesion conditions. In good agreement with these results, the C. tropicalis adhesion-associated gene expression tended to be higher under microaerobic or anaerobic conditions.

CONCLUSIONS

C. albicans favored aerobic conditions to form biofilms, whereas C. tropicalis showed higher biofilm-formation ability and promoted hyphal growth under microaerobic conditions. These results indicate that favorable oxygen conditions significantly differ for each Candida species.

Efficacy of true cinnamon (Cinnamomum verum) leaf essential oil as a therapeutic alternative for Candida biofilm infections

Objective(s):

The essential oil (EO) extracted from Cinnamomum verum leaves has been used as an antimicrobial agent for centuries. But its antifungal and antibiofilm efficacy is still not clearly studied. The objective of this research was to evaluate the in vitro antifungal and antibiofilm efficacy of C. verum leaf EO against C. albicans, C. tropicalis, and C. dubliniensis and the toxicity of EO using an in vitro model.

Materials and Methods:

The effect of EO vapor was evaluated using a microatmosphere technique. CLSI microdilution assay was employed in determining the Minimum Inhibitory (MIC) and Fungicidal Concentrations (MFC). Killing time was determined using a standard protocol. The effect of EO on established biofilms was quantified and visualized using XTT and Scanning Electron Microscopy (SEM), respectively. Post-exposure intracellular changes were visualized using Transmission Electron Microscopy (TEM). The toxicological assessment was carried out with the Human Keratinocyte cell line. The chemical composition of EO was evaluated using Gas Chromatography-Mass Spectrometry (GC-MS).

Results:

All test strains were susceptible to cinnamon oil vapor. EO exhibited MIC value 1.0 mg/ml and MFC value 2.0 mg/ml against test strains. The killing time of cinnamon oil was 6 hr. Minimum Biofilm Inhibitory Concentration (MBIC₅₀) for established biofilms was <0.2 mg/ml for all test strains. SEM images exhibited cell wall damages, cellular shrinkages, and decreased hyphal formation of Candida. TEM indicated intracellular vacuolation, granulation, and cell wall damages. Cinnamon leaf oil caused no inhibition of HaCaT cells at any concentration tested. Eugenol was the abundant compound in cinnamon oil.

Conclusion:

C. verum EO is a potential alternative anti-Candida agent with minimal toxicity on the human host.

Antifungal Activity and Potential Mechanism of 6,7, 4'-O-Triacetylscutellarein Combined With Fluconazole Against Drug-Resistant C. albicans

The increased resistance of Candida albicans to conventional antifungal drugs poses a huge challenge to the clinical treatment of this infection. In recent years, combination therapy, a potential treatment method to overcome C. albicans resistance, has gained traction. This study assessed the effect of 6,7,4′-O-triacetylscutellarein (TA) combined with fluconazole (FLC) on C. albicans in vitro and in vivo. TA combined with FLC showed good synergistic antifungal activity against drug-resistant C. albicans in vitro, with a partial inhibitory concentration index (FICI) of 0.0188–0.1800. In addition, the time-kill curve confirmed the synergistic effect of TA and FLC. TA combined with FLC showed a strong synergistic inhibitory effect on the biofilm formation of resistant C. albicans. The combined antifungal efficacy of TA and FLC was evaluated in vivo in a mouse systemic fungal infection model. TA combined with FLC prolonged the survival rate of mice infected with drug-resistant C. albicans and reduced tissue invasion. TA combined with FLC also significantly inhibited the yeast-hypha conversion of C. albicans and significantly reduced the expression of RAS-cAMP-PKA signaling pathway-related genes (RAS1 and EFG1) and hyphal-related genes (HWP1 and ECE1). Furthermore, the mycelium growth on TA combined with the FLC group recovered after adding exogenous db-cAMP. Collectively, these results show that TA combined with FLC inhibits the formation of hyphae and biofilms through the RAS-cAMP-PKA signaling pathway, resulting in reduced infectivity and resistance of C. albicans. Therefore, this study provides a basis for the treatment of drug-resistant C. albicans infections.

Streptococcus salivarius K12 inhibits Candida albicans aggregation, biofilm formation and dimorphism

Candida albicans causes candidiasis, particularly in immunocompromised patients. Streptococcus salivarius K12 (K12) is a probiotic isolated from a healthy oral cavity. The study aimed to determine the effect of K12 on C. albicans aggregation, biofilm formation and dimorphism. C. albicans ATCC MYA-4901, acquired immunodeficiency syndrome (AIDS) isolate (ALC2), and oral cancer isolate (ALC3) and K12 were used in the study. All C. albicans strains and K12 were grown in yeast peptone dextrose agar and brain heart infusion agar, respectively, prior to aggregation, biofilm and dimorphism assays. Auto-aggregation of C. albicans MYA-4901 and ALC2 was categorised as high, while the co-aggregation of the strains was low in the presence of K12. C. albicans total cell count decreased significantly when co-cultured with K12 compared with monocultured C. albicans biofilm (p < 0.05). Inhibition of yeast-to-hyphae transition was also observed when co-cultured with K12. In conclusion, K12 inhibits C. albicans aggregation, biofilm formation and dimorphism.

High-Throughput Computational Analysis of Biofilm Formation from Time-Lapse Microscopy

Candida albicans biofilm formation in the presence of drugs can be examined through time-lapse microscopy. In many cases, the images are used qualitatively, which limits their utility for hypothesis testing. We employed a machine-learning algorithm implemented in the Orbit Image Analysis program to detect the percent area covered by cells from each image. This is combined with custom R scripts to determine the growth rate, growth asymptote, and time to reach the asymptote as quantitative proxies for biofilm formation. We describe step-by-step protocols that go from sample preparation for time-lapse microscopy through image analysis parameterization and visualization of the model fit. © 2021 Wiley Periodicals LLC. Basic Protocol 1: Sample preparation Basic Protocol 2: Time-lapse microscopy: Evos protocol Basic Protocol 3: Batch file renaming Basic Protocol 4: Machine learning analysis of Evos images with Orbit Basic Protocol 5: Parametrization of Orbit output in R Basic Protocol 6: Visualization of logistic fits in R.

Influence of Nutrient Media Compared to Human Synovial Fluid on the Antibiotic Susceptibility and Biofilm Gene Expression of Coagulase-Negative Staphylococci In Vitro

Bacterial antibiotic resistance and biofilm formation are mechanisms usually involved in the pathogeny of implant-related infections. Worldwide, antibiotic susceptibility tests are usually carried out using nutrient-rich media. Clinical routine laboratories and even research centers use for example EUCAST or CLSI for guidelines. In this study, we investigated the effect of different nutrient media on the antibiotic susceptibility and icaADBC gene expression of bacteria in biofilm. As media, Müller-Hinton Bouillon (MHB), Tryptic Soy Broth (TSB) and human synovial fluid (SF) diluted 1:4 in phosphate buffered saline (PBS), each also supplemented with 1% glucose, were used. The influence of different nutrient media on the antibiotic susceptibility of coagulase-negative staphylococci (CoNS) was evaluated by counting of colony-forming units (CFU) and by checking the metabolic activity of the bacteria. We used reverse transcriptase and real-time qPCR to investigate the influence of nutrient media on the biofilm gene expression. We used two-way analysis of variance (ANOVA). p < 0.05 was considered to be statistically significant. Significant differences in growth and antibiotic susceptibility were detected in all strains tested among the different media used. The nutrient media showed influence on the cell viability of all bacteria after antibiotic treatment. IcaADBC gene expression was significantly influenced by glucose and all nutrient media. The results highlight the influence of glucose on the antibiotic susceptibility, growth and gene expression of all strains tested. For all strains, a significant difference in bacterial recovery, viability and gene expression were found when compared to biofilm grown in SF.

Antifungal activity of Syzygium samarangense leaf extracts against Candida

Candida species are opportunistic human fungal pathogens that cause acute and chronic infections against which only few antifungal agents are available. Here we have elucidated the antifungal effect of Syzygium samarangense leaf extracts (SSLE). Antifungal activity of SSLE was studied against Candida albicans, C. krusei, C. parapsilosis, C. glabrata, C. auris and C. tropicalis. Following experiments were performed: minimum fungicidal concentration (MFC) determination, agar well disc diffusion assays, fungal morphology analysis using scanning electron microscope (SEM), ex vivo fungal survival assays on porcine tongue and skin and in vivo fungal survival assays using Drosophila melanogaster fly model. Results demonstrated MFC of SSLE ranges between 100 and 125 mg ml^-1 . SEM images showed cell wall degradation of C. albicans when treated with SSLE. Around 75% decrease in C. albicans viability was observed when infected porcine tongue and skin were treated using SSLE. The C. albicans infected D. melanogaster when fed with SSLE showed significant decrease (around 80%) of fungal count than the infected control. Furthermore, agar plate disc diffusion assays demonstrated that the antifungal activity of SSLE could be due to chalcone, which is one of the active constituents in SSLE. Our study demonstrated that SSLE could be used for the topical treatment of Candida infections.

The Impact of Cultivation Media on the In Vitro Biofilm Biomass Production of Candida spp

The yeasts of the genus Candida are among the most clinically significant fungal pathogenic agents. One of the unique features of the Candida species' pathogenicity is their ability to form biofilms. Generally, infections caused by biofilm-forming microorganisms tend to have chronic course and are difficult to treat. This fact highlights the need to search for drugs with anti-biofilm activities. At present, there are variety of protocols for performing antifungal anti-biofilm activity testing in which fundamental differences, especially in the choice of cultivation media for biofilm formation, can be noted. In our study, we focused on the effect of four different culture media on biofilm biomass formation in ten Candida spp. strains. With emphasis placed on clinical significance, strains of the C. albicans species were predominantly included in this study. Based on our results, we can conclude that the availability of other components in the culture media, such as amino acids or proteins, and not just the commonly mentioned glucose availability, helps promote the transition of Candida yeasts into a sessile form and leads to in vitro robust biofilm formation. We revealed that biofilm formation in C. albicans strains was enhanced, especially in media supplemented with fetal bovine serum (FBS). The nutritionally balanced cultivation medium with 10 g/L glucose and 10% (v/v) FBS evidently showed the most significant benefit for in vitro biofilm production in C. albicans strains.

Antibiotics as a Stressing Factor Triggering the Harboring of Helicobacter pylori J99 within Candida albicans ATCC10231

First-line treatment for Helicobacter pylori includes amoxicillin and clarithromycin or metronidazole plus a proton pump inhibitor. Treatment failure is associated with antibiotic resistance and possibly also with internalization of H. pylori into eukaryotic cells, such as yeasts. Factors triggering the entry of H. pylori into yeast are poorly understood. Therefore, the aim of this study was to evaluate whether clarithromycin or amoxicillin trigger the entry of H. pylori into C. albicans cells.

METHODS

H. pylori J99 and C. albicans ATCC 10231 were co-cultured in the presence of subinhibitory concentrations of amoxicillin and clarithromycin as stressors. Bacterial-bearing yeasts were observed by fresh examination. The viability of bacteria within yeasts was evaluated, confirming the entry of bacteria into Candida, amplifying, by PCR, the H. pylori16S rRNA gene in total yeast DNA.

RESULTS

Amoxicillin significantly increased the entry of H. pylori into C. albicans compared to the control.

CONCLUSION

the internalization of H. pylori into C. albicans in the presence of antibiotics is dependent on the type of antibiotic used, and it suggests that a therapy including amoxicillin may stimulate the entry of the bacterium into Candida, thus negatively affecting the success of the treatment.

Polymeric micelles with anti-virulence activity against Candida albicans in a single- and dual-species biofilm

Infections caused by fungal biofilms with rapidly evolving resistance against the available antifungal agents are difficult to manage. These difficulties demand new strategies for effective eradication of biofilms from both biological and inert surfaces. In this study, polymeric micelles comprised of di-block polymer, poly-(ethylene glycol) methyl ether methacrylate and poly 2-(N,N-diethylamino) ethyl methacrylate polymer, P(PEGMA-b-DEAEMA), were observed to exhibit remarkable inhibitory effects on hyphal growth of Candida albicans (C. albicans) and C. tropicalis, thus preventing biofilm formation and removing existing biofilms. P(PEGMA-b-DEAEMA) micelles showed biofilm removal efficacy of > 40% and a 1.4-log reduction in cell viability of C. albicans in its single-species biofilms. In addition, micelles alone promoted high removal percentage in a mixed biofilm of C. albicans and C. tropicalis (~ 70%) and remarkably reduced cell viability of both strains. Co-delivery of fluconazole (Flu) and amphotericin B (AmB) with micelles showed synergistic effects on C. albicans biofilms (3-log reduction for AmB and 2.2-log reduction for Flu). Similar effects were noted on C. albicans planktonic cells when treated with the micellar system combined with AmB but not with Flu. Moreover, micelle-drug combinations showed an enhancement in the antibiofilm activity of Flu and AmB against dual-species biofilms. Furthermore, in vivo studies using Caenorhabditis elegans nematodes revealed no obvious toxicity of the micelles. Targeting morphologic transitions provides a new strategy for defeating fungal biofilms of polymorphic resistance strains and can be potentially used in counteracting Candida virulence.

In-vitro Antibacterial and Antibiofilm Activity of Cinnamomum verum Leaf Oil against Pseudomonas aeruginosa, Staphylococcus aureus and Klebsiella pneumoniae

Phytomedicines are becoming more popular in treatment of infectious diseases worldwide. Cinnamomum verum essential oil (EO) has been used as a therapeutic alternative for various diseases. This study aimed to evaluate the antibacterial and antibiofilm activity of the C. verum leaf EO against Pseudomonas aeruginosa, Staphylococcus aureus and Klebsiella pneumoniae. Effect of EO vapor on planktonic cells was determined using microatmosphere technique. CLSI M7-A10 method was employed in Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) experiments. Effect of EO on established biofilms was quantified and visualized using XTT and Scanning Electron Microscope (SEM). In-vitro toxicity was evaluated using Human Keratinocytes (HaCaT). Chemical analysis of EO was done using Gas Chromatography- Mass Spectrometry (GC-MS). All tested strains were sensitive to cinnamon oil vapor. EO exhibited 0.5 and 1.0 mg/mL MIC and MBC against all test strains. Minimum Biofilm Inhibitory and Biofilm Eradication Concentrations (MBIC50 and MBEC) were 1.0 and 4.0 mg/mL. SEM indicated cellular shrinkages, cell wall damages, and decreased biofilm densities. Cinnamon oil didn't show any toxicity on HaCaT cell at any concentration tested. Eugenol was the most abundant compound in C. verum oil. C. verum EO shows an antibacterial and antibiofilm activity with minimal toxicity on host.

Interkingdom interaction between C. albicans and S. salivarius on titanium surfaces

BACKGROUND

In oral candidiasis models, Candida albicans and Streptococcus salivarius sp. biofilms have an antagonistic relationship. Due to this, S. salivarius have been used experimentally as probiotic. However, the interaction between these microorganisms in the peri-implantitis-like microenvironment remains unknown. This study aimed to evaluate the interaction between C. albicans and S. salivarius biofilms developed on titanium surfaces, under reduced oxygen levels.

METHODS

Titanium specimens were pre-conditioned with artificial saliva (1 h, 37 °C). Single-species biofilms of C. albicans (ATCC 90028) and co-culture biofilms of C. albicans and S. salivarius (ATCC 7073) was developed for 24 and 72 h on titanium specimens. Subsequently, the effect of these intervals of biofilm formation and the interactions among the cells were evaluated. Biofilms from cultures were collected and analyzed for cell viability (CFU/mL), biofilm biomass, and total protein dosage. Data were analyzed using Mann-Whitney test (α = 5%). In addition, co-culture biofilms were analyzed using fluorescence microscopy.

RESULTS

C. albicans growth did not change due to the presence of S. salivarius. Besides, co-culture biofilms showed a significant difference in the number of viable cells between 24 and 72 h of biofilm development (p < 0.05). The highest biofilm biomass and protein dosage were observed in co-cultures at 72 h of biofilm development. Fluorescence microscopy showed that co-cultures biofilms at 24 h have limited number of pseudo-hyphal and hyphae cells of C. albicans. At 72 h, these types of cells have increased. S. salivarius in both stages of development was present in some clusters surrounded by C. albicans.

CONCLUSIONS

Co-cultivation of C. albicans with S. salivarius in biofilms developed on titanium surfaces, under lower oxygen levels, did not affect fungus growth. In addition, S. salivarius did not hind C. albicans virulence. These findings suggest that the use of S. salivarius as a probiotic would be ineffective in peri-implant disease treatment.

Combination Therapy to Treat Fungal Biofilm-Based Infections

An increasing number of people is affected by fungal biofilm-based infections, which are resistant to the majority of currently-used antifungal drugs. Such infections are often caused by species from the genera Candida, Aspergillus or Cryptococcus. Only a few antifungal drugs, including echinocandins and liposomal formulations of amphotericin B, are available to treat such biofilm-based fungal infections. This review discusses combination therapy as a novel antibiofilm strategy. More specifically, in vitro methods to discover new antibiofilm combinations will be discussed. Furthermore, an overview of the main modes of action of promising antibiofilm combination treatments will be provided as this knowledge may facilitate the optimization of existing antibiofilm combinations or the development of new ones with a similar mode of action.

Automated quantification of Candida albicans biofilm-related phenotypes reveals additive contributions to biofilm production

Biofilms are organized communities of microbial cells that promote persistence among bacterial and fungal species. Biofilm formation by host-associated Candida species of fungi occurs on both tissue surfaces and implanted devices, contributing to host colonization and disease. In C. albicans, biofilms are built sequentially by adherence of yeast to a surface, invasion into the substrate, the formation of aerial hyphal projections, and the secretion of extracellular matrix. Measurement of these biofilm-related phenotypes remains highly qualitative and often subjective. Here, we designed an informatics pipeline for quantifying filamentation, adhesion, and invasion of Candida species on solid agar media and utilized this approach to determine the importance of these component phenotypes to C. albicans biofilm production. Characterization of 23 C. albicans clinical isolates across three media and two temperatures revealed a wide range of phenotypic responses among isolates in any single condition. Media profoundly altered all biofilm-related phenotypes among these isolates, whereas temperature minimally impacted these traits. Importantly, the extent of biofilm formation correlated significantly with the additive score for its component phenotypes under some conditions, experimentally linking the strength of each component to biofilm mass. In addition, the response of the genome reference strain, SC5314, across these conditions was an extreme outlier compared to all other strains, suggesting it may not be representative of the species. Taken together, development of a high-throughput, unbiased approach to quantifying Candida biofilm-related phenotypes linked variability in these phenotypes to biofilm production and can facilitate genetic dissection of these critical processes to pathogenesis in the host.

Adhesion of Candida tropicalis to polystyrene and epithelial cell lines: Insights of correlation of the extent of adherent yeast cells among distinct surfaces

Candida tropicalis is an emerging fungal pathogen associated with high mortality. We aimed to compare adherence capability of C. tropicalis to polystyrene and epithelial cell lines (HeLa and Vero), and determine whether adherent blastoconidia is cell-type specific. Blastoconidia adhesion to epithelial cells and polystyrene were determined by crystal violet assay. The percentage of epithelial cells with adhered blastoconidia and the number of adhered blastoconidia per cell line were determined by light microscopy. The correlation between adhesion surfaces was assessed by Pearson's correlation coefficient. The adhesiveness of C. tropicalis to polystyrene was greater than that observed for ephitelial cells. High correlation values (r² 0.9999222, p 0.007941) were found for the adhesion capability between biotic and polystyrene surface for isolates 100.10 (obtained from blood) and 335.07 (obtained from tracheal secretion). The number of adherent blastoconidia per HeLa cell was greater in comparison to that observed for Vero cells (P<0.05). Further, high correlation (r² 1, p 0.0001) was found for the adhesion ability between HeLa cells and Vero cells. The results suggest a correlation of C. tropicalis adhesion capability among different surfaces, and that the adhesion to epithelial cells is specific to the cell type.

Lipo-chitooligosaccharides as regulatory signals of fungal growth and development

Lipo-chitooligosaccharides (LCOs) are signaling molecules produced by rhizobial bacteria that trigger the nodulation process in legumes, and by some fungi that also establish symbiotic relationships with plants, notably the arbuscular and ecto mycorrhizal fungi. Here, we show that many other fungi also produce LCOs. We tested 59 species representing most fungal phyla, and found that 53 species produce LCOs that can be detected by functional assays and/or by mass spectroscopy. LCO treatment affects spore germination, branching of hyphae, pseudohyphal growth, and transcription in non-symbiotic fungi from the Ascomycete and Basidiomycete phyla. Our findings suggest that LCO production is common among fungi, and LCOs may function as signals regulating fungal growth and development.

Candida tropicalis RON1 is required for hyphal formation, biofilm development, and virulence but is dispensable for N-acetylglucosamine catabolism

NDT80-like family genes are highly conserved across a large group of fungi, but the functions of each Ndt80 protein are diverse and have evolved differently among yeasts and pathogens. The unique NDT80 gene in budding yeast is required for sexual reproduction, whereas three NDT80-like genes, namely, NDT80, REP1, and RON1, found in Candida albicans exhibit distinct functions. Notably, it was suggested that REP1, rather than RON1, is required for N-acetylglucosamine (GlcNAc) catabolism. Although Candida tropicalis, a widely dispersed fungal pathogen in tropical and subtropical areas, is closely related to Candida albicans, its phenotypic, pathogenic and environmental adaptation characteristics are remarkably divergent. In this study, we focused on the Ron1 transcription factor in C. tropicalis. Protein alignment showed that C. tropicalis Ron1 (CtRon1) shares 39.7% identity with C. albicans Ron1 (CaRon1). Compared to the wild-type strain, the C. tropicalis ron1Δ strains exhibited normal growth in different carbon sources and had similar expression levels of several GlcNAc catabolic genes during GlcNAc treatment. In contrast, C. tropicalis REP1 is responsible for GlcNAc catabolism and is involved in GlcNAc catabolic gene expressions, similar to C. albicans Rep1. However, REP1 deletion strains in C. tropicalis promote hyphal development in GlcNAc with low glucose content. Interestingly, CtRON1, but not CaRON1, deletion mutants exhibited significantly impaired hyphal growth and biofilm formation. As expected, CtRON1 was required for full virulence. Together, the results of this study showed divergent functions of CtRon1 compared to CaRon1; CtRon1 plays a key role in yeast-hyphal dimorphism, biofilm formation and virulence.

LAY ABSTRACT

In this study, we identified the role of RON1, an NDT80-like gene, in Candida tropicalis. Unlike the gene in Candida albicans, our studies showed that RON1 is a key regulator of hyphal formation, biofilm development and virulence but is dispensable for N-acetylglucosamine catabolism in C. tropicalis.

Small noncoding RNA sRNA0426 is involved in regulating biofilm formation in Streptococcus mutans

Evidence suggests that small noncoding RNAs (sRNAs) are involved in the complex regulatory networks governing biofilm formation. Few studies have investigated the role of sRNAs in Streptococcus mutans (S. mutans). In the present study, the association between sRNA and biofilm formation in S. mutans was explored. sRNAs that are differentially expressed in the biofilm and planktonic states of this bacterium were identified by quantitative real‐time PCR (qRT‐PCR). Confocal laser scanning microscopy was used to investigate the characteristics of biofilm formation in a standard strain of S. mutans (UA159, ATCC 700610) and ten clinical strains. Bioinformatics analyses were employed to predict and examine potential sRNA regulatory pathways. The results showed that sRNA0426 has a strong positive relationship with dynamic biofilm formation. Moreover, sRNA0426 expression was positively correlated with exopolysaccharide (EPS) production. Bioinformatics analyses showed that sRNA0426 is involved in biofilm formation such as metabolic pathways, especially carbon metabolism. Five target mRNAs (GtfB, GtfC, GtfD, ComE, and CcpA) involved in the synthesis of EPS were selected for further evaluation; the expression levels of three of these mRNAs (GtfB, GtfC, and CcpA) were positively correlated with sRNA0426 expression levels, and the expression level of one (ComE) was negatively correlated. In conclusion, the results suggested that sRNA0426 may play an important and positive role in the biofilm formation of S. mutans and provide novel insight into the S. mutans biofilm regulatory network.

In vitro Interaction of Pseudomonas aeruginosa Biofilms With Human Peripheral Blood Mononuclear Cells

The human immune cell response against bacterial biofilms is a crucial, but still poorly investigated area of research. Herein, we aim to establish an in vitro host cell-biofilm interaction model suitable to investigate the peripheral blood mononuclear cell (PBMC) response to Pseudomonas aeruginosa biofilms. P. aeruginosa biofilms were obtained by incubating bacteria in complete RPMI 1640 medium with 10% human plasma for 24 h. PBMC obtained from healthy donors were added to preformed P. aeruginosa biofilms. Following a further 24 h incubation, we assessed (i) PBMC viability and activation; (ii) cytokine profiles in the supernatants; and (iii) CFU counts of biofilm forming bacteria. Cell-death was <10% upon 24 h incubation of PBMC with P. aeruginosa biofilms. PBMC incubated for 24 h with preformed P. aeruginosa biofilms were significantly more activated compared to PBMC incubated alone. Interestingly, a marked activation of CD56⁺CD3⁻ natural killer (NK) cells was observed that reached 60% of NK cells as an average of different donors. In the culture supernatants of PBMC co-cultured with P. aeruginosa biofilms, not only pro-inflammatory (IL-1β, IFN-γ, IL-6, and TNF-α) but also anti-inflammatory (IL-10) cytokines were significantly increased as compared to PBMC incubated alone. Furthermore, incubation of biofilms with PBMC, caused a statistically significant increase in the CFU number of P. aeruginosa, as compared to biofilms incubated without PBMC. In order to assess whether PBMC products could stimulate the growth of P. aeruginosa biofilms, we incubated preformed P. aeruginosa biofilms with or without supernatants obtained from the co-cultures of PBMC with biofilms. In the presence of the supernatants, the CFU count of biofilm-derived P. aeruginosa, was two to seven times higher than those of biofilms incubated without supernatants (P < 0.01). Overall, the results obtained shed light on the reciprocal interaction between human PBMC and P. aeruginosa biofilms. P. aeruginosa biofilms induced PBMC activation and cytokine secretion but, in turn, the presence of PBMC and/or PBMC-derived components enhanced the number of P. aeruginosa biofilm associated bacteria. This may indicate a successful bacterial defensive/persistence strategy against immune response.

Virulence Characteristics of mecA-Positive Multidrug-Resistant Clinical Coagulase-Negative Staphylococci

Coagulase-negative staphylococci (CoNS) are an important group of opportunistic pathogenic microorganisms that cause infections in hospital settings and are generally resistant to many antimicrobial agents. We report on phenotypic and genotypic virulence characteristics of a select group of clinical, mecA-positive (encoding penicillin-binding protein 2a) CoNS isolates. All CoNS were resistant to two or more antimicrobials with S. epidermidis strain 214EP, showing resistance to fifteen of the sixteen antimicrobial agents tested. Aminoglycoside-resistance genes were the ones most commonly detected. The presence of megaplasmids containing both horizontal gene transfer and antimicrobial resistance genetic determinants indicates that CoNS may disseminate antibiotic resistance to other bacteria. Staphylococcus sciuri species produced six virulence enzymes, including a DNase, gelatinase, lipase, phosphatase, and protease that are suspected to degrade tissues into nutrients for bacterial growth and contribute to the pathogenicity of CoNS. The PCR assay for the detection of biofilm-associated genes found the eno (encoding laminin-binding protein) gene in all isolates. Measurement of their biofilm-forming ability and Spearman’s rank correlation coefficient analyses revealed that the results of crystal violet (CV) and extracellular polymeric substances (EPS) assays were significantly correlated (ρ = 0.9153, P = 3.612e-12). The presence of virulence factors, biofilm-formation capability, extracellular enzymes, multidrug resistance, and gene transfer markers in mecA-positive CoNS clinical strains used in this study makes them powerful opportunistic pathogens. The study also warrants a careful evaluation of nosocomial infections caused by CoNS and may be useful in studying the mechanism of virulence and factors associated with their pathogenicity in vivo and developing effective strategies for mitigation.

Evaluation of Biofilm Formation in Candida tropicalis Using a Silicone-Based Platform with Synthetic Urine Medium

Molecular mechanisms of biofilm formation in Candida tropicalis and current methods for biofilm analyses in this fungal pathogen are limited. (2) Methods: Biofilm biomass and crystal violet staining of the wild-type and each gene mutant strain of C. tropicalis were evaluated on silicone under synthetic urine culture conditions. (3) Results: Seven media were tested to compare the effects on biofilm growth with or without silicone. Results showed that biofilm cells of C. tropicalis were unable to form firm biofilms on the bottom of 12-well polystyrene plates. However, on a silicone-based platform, Roswell Park Memorial Institute 1640 (RPMI 1640), yeast nitrogen base (YNB) + 1% glucose, and synthetic urine media were able to induce strong biofilm growth. In particular, replacement of Spider medium with synthetic urine in the adherence step and the developmental stage is necessary to gain remarkably increased biofilms. Interestingly, unlike Candida albicans, the C. tropicalisROB1 deletion strain but not the other five biofilm-associated mutants did not cause a significant reduction in biofilm formation, suggesting that the biofilm regulatory circuits of the two species are divergent. (4) Conclusions: This system for C. tropicalis biofilm analyses will become a useful tool to unveil the biofilm regulatory network in C. tropicalis.

Optimum Inhibition of Amphotericin-B-Resistant Candida albicans Strain in Single- and Mixed-Species Biofilms by Candida and Non-Candida Terpenoids

Candida albicans is one of the most common human fungal pathogens and represents the most important cause of opportunistic mycoses worldwide. Surgical devices including catheters are easily contaminated with C. albicans via its formation of drug-resistant biofilms. In this study, amphotericin-B-resistant C. albicans strains were isolated from surgical devices at an intensive care center. The objective of this study was to develop optimized effective inhibitory treatment of resistant C. albicans by terpenoids, known to be produced naturally as protective signals. Endogenously produced farnesol by C. albicans yeast and plant terpenoids, carvacrol, and cuminaldehyde were tested separately or in combination on amphotericin-B-resistant C. albicans in either single- or mixed-infections. The results showed that farnesol did not inhibit hyphae formation when associated with bacteria. Carvacrol and cuminaldehyde showed variable inhibitory effects on C. albicans yeast compared to hyphae formation. A combination of farnesol with carvacrol showed synergistic inhibitory activities not only on C. albicans yeast and hyphae, but also on biofilms formed from single- and mixed-species and at reduced doses. The combined terpenoids also showed biofilm-penetration capability. The aforementioned terpenoid combination will not only be useful in the treatment of different resistant Candida forms, but also in the safe prevention of biofilm formation.

Colonization of Wild Saccharomyces cerevisiae Strains in a New Winery

The aim of this work was to study the fungal colonization of a new winery over time, specifically for Saccharomyces cerevisiae. Therefore, we analyzed the flora present before the arrival of the first harvest on the floor, the walls and the equipment of this new winery by Illumina MiSeq. The genus Saccharomyces (≤0.3%) was detected on floor and equipment but the presence of S. cerevisiae species was not reported. Wild S. cerevisiae strains were isolated from a ‘Pied de Cuve’ used during the first vintage to ensure the alcoholic fermentation (AF). Among 25 isolates belonging to this species, 17 different strains were identified highlighting a great intraspecific diversity. S. cerevisiae strains were also isolated from different vats throughout the spontaneous fermentations during the first vintage. The following year, some of these strains were isolated again during AF. Some of them (four) were found in the winery equipment before the arrival of the third harvest suggesting a potential colonization by these strains. To better understand what promotes the yeast colonization of the winery’s environment, the ability to form a biofilm on solid surfaces for eight colonizing or non-colonizing strains was studied. This capacity, different according to the strains, could partly explain the colonization observed for certain strains.

Antifungal susceptibility profiles of rare ascomycetous yeasts

Objectives

To generate antifungal susceptibility patterns for Trichomonascus ciferrii (Candida ciferrii), Candida inconspicua (Torulopsis inconspicua) and Diutina rugosa species complex (Candida rugosa species complex), and to provide key parameters such as MIC50, MIC90 and tentative epidemiological cut-off values (TECOFFs).

Methods

Our strain set included isolates of clinical origin: C. inconspicua (n = 168), D. rugosa species complex (n = 90) [Candida pararugosa (n = 60), D. rugosa (n = 26) and Candida mesorugosa (n = 4)], Pichia norvegensis (Candida norvegensis) (n = 15) and T. ciferrii (n = 8). Identification was performed by MALDI-TOF MS or internal transcribed spacer sequencing. Antifungal susceptibility patterns were generated for azoles, echinocandins and amphotericin B using commercial Etest and the EUCAST broth microdilution method v7.3.1. Essential agreement (EA) was calculated for Etest and EUCAST.

Results

C. inconspicua, C. pararugosa and P. norvegensis showed elevated azole MICs (MIC50 ≥0.06 mg/L), and D. rugosa and C. pararugosa elevated echinocandin MICs (MIC50 ≥0.06 mg/L). EA between methods was generally low (<90%); EA averaged 77.45%. TECOFFs were suggested for C. inconspicua and D. rugosa species complex.

Conclusions

Rare yeast species tested shared high fluconazole MICs. D. rugosa species complex displayed high echinocandin MICs, while C. inconspicua and P. norvegensis were found to have high azole MICs. Overall, the agreement between EUCAST and Etest was poor and therefore MIC values generated with Etest cannot be directly compared with EUCAST results.

Filamentous Non-albicans Candida Species Adhere to Candida albicans and Benefit From Dual Biofilm Growth

Non-albicans Candida species (NACS) are often isolated along with Candida albicans in cases of oropharyngeal candidiasis. C. albicans readily forms biofilms in conjunction with other oral microbiota including both bacteria and yeast. Adhesion between species is important to the establishment of these mixed biofilms, but interactions between C. albicans and many NACS are not well-characterized. We adapted a real-time flow biofilm model to study adhesion interactions and biofilm establishment in C. albicans and NACS in mono- and co-culture. Out of five NACS studied, only the filamenting species C. tropicalis and C. dubliniensis were capable of adhesion with C. albicans, while C. parapsilosis, C. lusitaniae, and C. krusei were not. Over the early phase (0-4 h) of biofilm development, both mono- and co-culture followed similar kinetics of attachment and detachment events, indicating that initial biofilm formation is not influenced by inter-species interactions. However, the NACS showed a preference for inter-species cell-cell interactions with C. albicans, and at later time points (5-11 h) we found that dual-species interactions impacted biofilm surface coverage. Dual-species biofilms of C. tropicalis and C. albicans grew more slowly than C. albicans alone, but achieved higher surface coverage than C. tropicalis alone. Biofilms of C. dubliniensis with C. albicans increased surface coverage more rapidly than either species alone. We conclude that dual culture biofilm of C. albicans with C. tropicalis or C. dubliniensis offers a growth advantage for both NACS. Furthermore, the growth and maintenance, but not initial establishment, of dual-species biofilms is likely facilitated by interspecies cell-cell adherence.