Proposal of protocols using D-glutamine to optimize the 2,3-bis(2-methoxy-4-nitro-5-sulfophenly)-5-[(phenylamino) carbonyl]-2H-tetrazolium hydroxide (XTT) assay for indirect estimation of microbial loads in biofilms of medical importance

Extract of Sophorae flavescentis radix-Cnidii fructus couplet medicines treats vulvovaginal candidiasis by affecting the vaginal mucosal barrier

Aim: This study investigated the inhibition of extract of Sophorae flavescentis radix-Cnidii fructus couplet medicines (ESCC) on Candida albicans (C. albicans) in vitro and the effect of ESCC on the vaginal mucosal barrier in vivo. Materials & methods: Susceptibility testing was performed with C. albicans SC5314. A vulvovaginal candidiasis mouse model was successfully established. The plate method, Gram staining, hematoxylin and eosin staining and ELISA were used to detect relevant inflammatory indexes: IFN-γ, IL-1 and TNF-α. Quantitative real-time PCR and western blot were used to detect mucosal immune-related factors: MUC1, MUC4, DEFB1 and DEFB2. Results: ESCC was able to inhibit the proliferative activity of C. albicans, and it affected inflammation-related factors and indicators of vaginal mucosal immunity. Conclusion: ESCC showed potential value in the treatment of vulvovaginal candidiasis.

Effect of Antimicrobial Photodynamic Therapy, using Toluidine blue on dual-species biofilms of Candida albicans and Candida krusei

BACKGROUND

Although Candida albicans is the most frequent etiological agent of candidiasis, it has been reported a sizable number of infections related to the non-albicans Candida (NAC) species, Candida krusei. In addition, dual biofilms (biofilms composed by two species) may easily occur in vivo, becoming even more challenging the treatment of an infection. The fungicide effect of Photodynamic Therapy (PDT), using toluidine blue O (TBO) on both C. albicans and C. krusei development has been demonstrated. Thus, the objective of this study was to investigate the effects of PDT on dual-species biofilms of Candida albicans and Candida krusei.

METHODS

The effect of PDT was observed on the metabolic activity of mature dual-species biofilms of Candida albicans and Candida krusei by a metabolic assay based on the reduction of XTT (2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide sodium salt) assay and the identification of Candida albicans and Candida krusei was performed on CHROMagar Candida medium.

RESULTS

it was observed a reduction of ∼30% in the metabolic activity of a mature biofilm treated with PDT, using 0.05mg·mL^-1 TBO and during biofilm formation a predominance of C. albicans on C. krusei was observed. The inhibition observed was related to reduction in the number of Colony Forming Units (CFU) of Candida albicans from 31.33 ± 3.7 to 17.0 ± 1.5. The number of CFU of C. krusei was not significantly modified.

CONCLUSIONS

These results demonstrated the efficiency of PDT in inhibiting the dual-species biofilms of Candida albicans and Candida krusei by reducing C. albicans development.

Addressing artifacts of colorimetric anticancer assays for plant-based drug development

Cancer has become the silent killer in less-developed countries and the most significant cause of morbidity worldwide. The accessible and frequently used treatments include surgery, radiotherapy, chemotherapy, and immunotherapy. Chemotherapeutic drugs traditionally involve using plant-based medications either in the form of isolated compounds or as scaffolds for synthetic drugs. To launch a drug in the market, it has to pass through several intricate steps. The multidrug resistance in cancers calls for novel drug discovery and development. Every year anticancer potential of several plant-based compounds and extracts is reported but only a few advances to clinical trials. The false-positive or negative results impact the progress of the cell-based anticancer assays. There are several cell-based assays but the widely used include MTT, MTS, and XTT. In this article, we have discussed various pitfalls and workable solutions.

The clinical Biofilm Ring Test: a promising tool for the clinical assessment of biofilm-producing Candida species

Candida species are opportunistic pathogens responsible for a variety of diseases, ranging from skin and mucosal lesions to severe systemic, life-threatening infections. Candida albicans accounts for more than 70% of all Candida infections, however, the clinical relevance of other species such as Candida parapsilosis and Candida krusei are being increasingly recognized. Biofilm-producing yeasts cells acquire an increased resistance to antifungal agents, often leading to therapeutic failure and chronic infection. Conventional methods such as crystal violet (CV) and tetrazolium (XTT) reduction assay, developed to evaluate biofilm formation in Candida species are usually time-consuming, present a high intra- and inter-assay variability of the results and are therefore hardly applicable to routine diagnostics. This study describes an in-vitro assay developed for the measurement of biofilm formation in Candida species based on the clinical Biofilm Ring Test® (cBRT). We found a significant concordance between the cBRT and both CV (k = 0.74) and XTT (k = 0.62), respectively. Nevertheless, the cBRT resulted more reliable and reproducible than CV and XTT, requiring a minimal sample manipulation and allowing a high throughput assessment, directly on viable cells. The results indicate that the cBRT may provide a suitable, cost-effective technique for routine biofilm testing in clinical microbiology.

Effect of phototherapy on the metabolism of Streptococcus mutans biofilm based on a colorimetric tetrazolium assay

The aim of this in vitro study was to determine the effect of violet-blue light on the metabolic activity of early Streptococcus mutans biofilm, reincubated at 0, 2, and 6 h after 5 min of violet-blue light treatment. S. mutans UA159 biofilm cells were cultured for 12 to 16 h in microtiter plates with Tryptic Soy broth (TSB) or TSB with 1% sucrose (TSBS) and irradiated with violet-blue light for 5 min. After irradiation, the plates were reincubated at 37°C for 0, 2, or 6 h in 5% CO₂. Colorimetric tetrazolium salt reduction assay was used to investigate bacterial metabolic activity. Mixed model ANOVA was used to find the difference between the violet-blue light treated and nontreated groups. Bacterial metabolic activity was significantly lower in the violet-blue light group for TSB than in the nontreated group (P < 0.0001) regardless of recovery time. However, the differences between metabolic activity in the treated groups without sucrose decreased over time. For TSBS, metabolic activity was significantly lower with violet-blue light at 0 and 2 h. Violet-blue light inhibited the metabolic activity of S. mutans biofilm cells in the light-treated group. This finding may present a unique treatment method for patients with active caries.

Sodium trimetaphosphate and hexametaphosphate impregnated with silver nanoparticles: characteristics and antimicrobial efficacy

This study aimed to synthesize and characterize materials containing silver nanoparticles (AgNP) with polyphosphates (sodium trimetaphosphate (TMP) or sodium hexametaphosphate (HMP), and evaluate their effect against Candida albicans and Streptococcus mutans. The minimum inhibitory concentration (MIC) was determined, which was followed by the quantification of the biofilm by counting colony-forming units (CFUs), the amount of metabolic activity, and the total biomass. The MICs revealed greater effectiveness of composites containing 10% Ag (TMP + Ag10% (T10) and HMP + Ag10% (H10)) against both microorganisms. It was observed that T10 and H10 reduced the formation of biofilms by 56-76% for C. albicans and by 52-94% for S. mutans for total biomass and metabolic activity. These composites promoted significant log reductions in the number of CFUs, between 0.45-1.43 log₁₀ for C. albicans and 2.88-3.71 log₁₀ for S. mutans (p < .001). These composites demonstrated significant antimicrobial activity, especially against S. mutans, and may be considered a potential alternative for new dental materials.

Protocol for Identifying Natural Agents That Selectively Affect Adhesion, Thickness, Architecture, Cellular Phenotypes, Extracellular Matrix, and Human White Blood Cell Impenetrability of Candida albicans Biofilms

In the screening of natural plant extracts for antifungal activity, assessment of their effects on the growth of cells in suspension or in the wells of microtiter plates is expedient. However, microorganisms, including Candida albicans, grow in nature as biofilms, which are organized cellular communities with a complex architecture capable of conditioning their microenvironment, communicating, and excluding low- and high-molecular-weight molecules and white blood cells. Here, a confocal laser scanning microscopy (CLSM) protocol for testing the effects of large numbers of agents on biofilm development is described. The protocol assessed nine parameters from a single z-stack series of CLSM scans for each individual biofilm analyzed. The parameters included adhesion, thickness, formation of a basal yeast cell polylayer, hypha formation, the vertical orientation of hyphae, the hyphal bend point, pseudohypha formation, calcofluor white staining of the extracellular matrix (ECM), and human white blood cell impenetrability. The protocol was applied first to five plant extracts and derivative compounds and then to a collection of 88 previously untested plant extracts. They were found to cause a variety of phenotypic profiles, as was the case for 64 of the 88 extracts (73%). Half of the 46 extracts that did not affect biofilm thickness affected other biofilm parameters. Correlations between specific effects were revealed. The protocol will be useful not only in the screening of chemical libraries but also in the analysis of compounds with known effects and mutations.

Biofilm formation by Candida albicans and Streptococcus mutans in the presence of farnesol: a quantitative evaluation

The aim of this study was to evaluate the effect of the QS molecule farnesol on single and mixed species biofilms formed by Candida albicans and Streptococcus mutans. The anti-biofilm effect of farnesol was assessed through total biomass quantification, counting of colony forming units (CFUs) and evaluation of metabolic activity. Biofilms were also analyzed by scanning electron microscopy (SEM). It was observed that farnesol reduced the formation of single and mixed biofilms, with significant reductions of 37% to 90% and 64% to 96%, respectively, for total biomass and metabolic activity. Regarding cell viability, farnesol treatment promoted significant log reductions in the number of CFUs, ie 1.3-4.2 log10 and 0.67-5.32 log10, respectively, for single and mixed species biofilms. SEM images confirmed these results, showing decreases in the number of cells in all biofilms. In conclusion, these findings highlight the role of farnesol as an alternative agent with the potential to reduce the formation of pathogenic biofilms.

In vitro evaluation of adherence of Candida albicans, Candida glabrata, and Streptococcus mutans to an acrylic resin modified by experimental coatings

This study evaluated the effect of experimental coatings, containing zwitterion or hydrophilic monomers, on the adherence of Candida albicans, Candida glabrata, and Streptococcus mutans to an acrylic resin. Acrylic samples (smooth or rough surfaces) were left untreated (control) or coated with one of the following experimental coatings: 3-hydroxypropylmethacrylate (HP) or sulfobetaine methacrylate (S), at concentrations of 25, 30, or 35%. Half of the specimens were coated with saliva. The adhesion test was performed by incubating specimens in C. albicans, C. glabrata, and S. mutans suspensions at 37°C for 90 min. The number of adhered microorganisms was determined by metabolic activity (XTT) and by cell viability (CFU). All coated specimens exhibited lower absorbance and CFU values compared to control specimens. Saliva and roughness did not promote microorganism adherence. An XPS analysis confirmed the modification in the chemical composition of the coatings in the experimental samples. These experimental coatings significantly reduced the adherence of C. albicans, C. glabrata and S. mutans to acrylic resin.

MUNC13-4 protein regulates the oxidative response and is essential for phagosomal maturation and bacterial killing in neutrophils

Neutrophils use diverse mechanisms to kill pathogens including phagocytosis, exocytosis, generation of reactive oxygen species (ROS), and neutrophil extracellular traps. These mechanisms rely on their ability to mobilize intracellular organelles and to deliver granular cargoes to specific cellular compartments or into the extracellular milieu, but the molecular mechanisms regulating vesicular trafficking in neutrophils are not well understood. MUNC13-4 is a RAB27A effector that coordinates exocytosis in hematopoietic cells, and its deficiency is associated with the human immunodeficiency familial hemophagocytic lymphohistiocytosis type 3. In this work, we have established an essential role for MUNC13-4 in selective vesicular trafficking, phagosomal maturation, and intracellular bacterial killing in neutrophils. Using neutrophils from munc13-4 knock-out (KO) mice, we show that MUNC13-4 is necessary for the regulation of p22(phox)-expressing granule trafficking to the plasma membrane and regulates extracellular ROS production. MUNC13-4 was also essential for the regulation of intracellular ROS production induced by Pseudomonas aeruginosa despite normal trafficking of p22(phox)-expressing vesicles toward the phagosome. Importantly, in the absence of MUNC13-4, phagosomal maturation was impaired as observed by the defective delivery of azurophilic granules and multivesicular bodies to the phagosome. Significantly, this mechanism was intact in RAB27A KO neutrophils. Intracellular bacterial killing was markedly impaired in MUNC13-4 KO neutrophils. MUNC13-4-deficient cells showed a significant increase in neutrophil extracellular trap formation but were unable to compensate for the impaired bacterial killing. Altogether, these findings characterize novel functions of MUNC13-4 in the innate immune response of the neutrophil and have direct implications for the understanding of immunodeficiencies in patients with MUNC13-4 deficiency.

Comparative analysis of Candida biofilm quantitation assays

Candida grows on devices producing treatment resistant biofilms. A key tool for the study of biofilms includes an accurate assessment of viable cell growth. This study systematically tested seven techniques, among which the XTT assay provided the most reproducible, accurate, and efficient method for the quantitative estimation of C. albicans biofilms.

Clinical efficacy of a specifically targeted antimicrobial peptide mouth rinse: targeted elimination of Streptococcus mutans and prevention of demineralization

BACKGROUND/AIMS

Streptococcus mutans, the major etiological agent of dental caries, has a measurable impact on domestic and global health care costs. Though persistent in the oral cavity despite conventional oral hygiene, S. mutans can be excluded from intact oral biofilms through competitive exclusion by other microorganisms. This suggests that therapies capable of selectively eliminating S. mutans while limiting the damage to the normal oral flora might be effective long-term interventions to fight cariogenesis. To meet this challenge, we designed C16G2, a novel synthetic specifically targeted antimicrobial peptide with specificity for S. mutans. C16G2 consists of a S. mutans-selective 'targeting region' comprised of a fragment from S. mutans competence stimulation peptide (CSP) conjoined to a 'killing region' consisting of a broad-spectrum antimicrobial peptide (G2). In vitro studies have indicated that C16G2 has robust efficacy and selectivity for S. mutans, and not other oral bacteria, and affects targeted bacteria within seconds of contact.

METHODS

In the present study, we evaluated C16G2 for clinical utility in vitro, followed by a pilot efficacy study to examine the impact of a 0.04% (w/v) C16G2 rinse in an intra-oral remineralization/demineralization model.

RESULTS AND CONCLUSIONS

C16G2 rinse usage was associated with reductions in plaque and salivary S. mutans, lactic acid production, and enamel demineralization. The impact on total plaque bacteria was minimal. These results suggest that C16G2 is effective against S. mutans in vivo and should be evaluated further in the clinic.