Models hosts for the study of oral candidiasis

New Applications of Photodynamic Therapy in the Management of Candidiasis

The most important aetiological agent of opportunistic mycoses worldwide is Candida spp. These yeasts can cause severe infections in the host, which may be fatal. Isolates of Candida albicans occur with greater frequency and variable resistance patterns. Photodynamic therapy (PDT) has been recognised as an alternative treatment to kill pathogenic microorganisms. PDT utilises a photosensitizer, which is activated at a specific wavelength and oxygen concentration. Their reaction yields reactive oxygen species that kill the infectious microorganism. A systematic review of new applications of PDT in the management of candidiasis was performed. Of the 222 studies selected for in-depth screening, 84 were included in this study. All the studies reported the antifungal effectiveness, toxicity and dosimetry of treatment with antimicrobial PDT (aPDT) with different photosensitizers against Candida spp. The manuscripts that are discussed reveal the breadth of the new applications of aPDT against Candida spp., which are resistant to common antifungals. aPDT has superior performance compared to conventional antifungal therapies. With further studies, aPDT should prove valuable in daily clinical practice.

Efficacy of different formulations of nystatin in an experimental model of oral candidiasis in sialoadenectomized rats

BACKGROUND/PURPOSE

Oral candidiasis is the most common fungal infection of the oral cavity and has become a focus of attention in recent years because of its association with highly topical immunosuppressive conditions. The aims of this study were to determine the value of microbiological, clinical and histological parameters of Candida albicans colonisation of the dorsal tongue surface as indicators of disease severity, and to evaluate therapeutic response to different formulations of nystatin.

MATERIALS AND METHODS

We used 84 males, 2-month-old Sprague-Dawley sialoadenectomized rats. Different formulations of nystatin were used to evaluate the therapeutic response. The animals were randomized to 2 groups with each of 42 animals and received the experimental treatments from day 17-22.

RESULTS

100% of the rats showed evidence of infection. At 5 and 10 days of starting treatment with nystatin + chitosan, and at 10 days of starting nystatin + orabase, the number of animals with positive dorsal tongue culture decreased significantly (p < 0.05), acting the Nystatin + chitosan more rapidly against Candida. In the control group, the percentage of normal papillae on day 22 and 27 was 83.33% (SD = 1.50) and 79.08% (SD = 2.30), respectively. Significant differences were observed in the mean O'Grady score at 5 and 10 days (p < 0.0001).

CONCLUSION

The model has been shown to be effective in inducing infection, and that the combination of nystatin and chitosan yielded the best therapeutic outcomes at both 5 and 10 days after infection.

Antimicrobial and immunomodulatory responses of photodynamic therapy in Galleria mellonella model

BACKGROUND

New therapeutics are urgently needed for infectious diseases, especially for the fungal infection like Fonsecaea monophora. Photodynamic therapy has been showing antimicrobial activity on some pathogens. The combination of antimicrobial medicines and photodynamic therapy (PDT) might be a practical approach. However, whether the treatment of PDT could do benefits to the host immunity remains poorly documented.

RESULTS

In this study, Galleria mellonella larvae were employed as a model organism to evaluate the activity of PDT, and also to investigate the regulation of humoral immunity by PDT. Photosensitizer 5-aminolevulinic acid (ALA) was applied to the G. mellonella infection model. It was found that ALA-mediated PDT was non-toxic to G. mellonella, and could extend the median survival of infected larvae from 3 days to 5.5 days. We observed that larval hemocytes inhibited the growth of Candida albicans and Staphylococcus aureus, without any contribution by ALA-PDT. Furthermore, the application of ALA-PDT demonstrated the immunomodulation of larval innate immunity as increased hemocyte density counting, cell morphological transformation, and sensitivity to pathogens.

CONCLUSIONS

G. mellonella could be considered as a useful model to study the immunoregulation of PDT. This model revealed that ALA-PDT positively defense against infections through inducing humoral immune responses of larvae.

Galleria mellonella as a consolidated in vivo model hosts: New developments in antibacterial strategies and novel drug testing

A greater ethical conscience, new global rules and a modified perception of ethical consciousness entail a more rigorous control on utilizations of vertebrates for in vivo studies. To cope with this new scenario, numerous alternatives to rodents have been proposed. Among these, the greater wax moth Galleria mellonella had a preponderant role, especially in the microbiological field, as demonstrated by the growing number of recent scientific publications. The reasons for its success must be sought in its peculiar characteristics such as the innate immune response mechanisms and the ability to grow at a temperature of 37°C. This review aims to describe the most relevant features of G. mellonella in microbiology, highlighting the most recent and relevant research on antibacterial strategies, novel drug tests and toxicological studies. Although solutions for some limitations are required, G. mellonella has all the necessary host features to be a consolidated in vivo model host.

Current Status and Trends in Alternative Models to Study Fungal Pathogens

Fungal infections affect over a billion people, with mortality rates estimated at 1⁻2 million per year [...].

From moths to caterpillars: Ideal conditions for Galleria mellonella rearing for in vivo microbiological studies

Galleria mellonella is a well-accepted insect model for the study of pathogen-host interactions and antimicrobial compounds. The main advantages of this model include the low cost of maintenance, the fast life cycle, the possibility of using a large number of caterpillars and the innate immune system, which is evolutionarily conserved relative to mammals. Because of these advantages, different research groups have been working to implement the rearing of G. mellonella in laboratory conditions. This protocol describes our experience in the rearing of G. mellonella caterpillars for experimental infection models and the influence of different artificial diets on developmental and physiological parameters. Here, we suggest a diet composition that benefits the life cycle of G. mellonella by accelerating the larval phase length and increasing the caterpillar weight. This diet also stimulated the immune system of G. mellonella by increasing the hemolymph volume and hemocyte concentration. In addition, our rearing protocol generated caterpillars that are more resistant to infection by Staphylococcus aureus, Escherichia coli and Candida albicans. A standard G. mellonella rearing protocol is fundamental to minimize external influences on the results, and this simple and easy protocol can support researchers starting to rear G. mellonella.

Galleria mellonella as a model invertebrate host for the study of muriform cells of dematiaceous fungi

AIM

To study the pathogenesis of chromoblastomycosis using the alternative model host Galleria mellonella.

METHODOLOGY

We analyzed the virulence of different dematiaceous fungal strains and the host immune responses (hemocytes density and morphological changes) to Fonsecaea monophora by the alternative infection model. Then detected the development of the pathogenic muriform cells within larvae under microscope.

RESULTS

Increasing inocula resulted in greater larval mortality and Cladophialophora carrionii was the most virulent. Low inocula activated the humoral immune response significantly. Moreover, the conidia underwent morphological transition to muriform cells within larvae.

CONCLUSION

We developed an invertebrate host model that can be used to evaluate the virulence of dematiaceous fungi, which may provide further insights into overcoming current limitations in studying chromoblastomycosis in vivo.

Combination of Estrogen and Immunosuppressive Agents to Establish a Mouse Model of Candidiasis with Concurrent Oral and Vaginal Mucosal Infection

Mouse model is an appropriate tool for pathogenic determination and study of host defenses during the fungal infection. Here, we established a mouse model of candidiasis with concurrent oral and vaginal mucosal infection. Two C. albicans strains sourced from clinical candidemia (SC5314) and mucosal infection (ATCC62342) were tested in ICR mice. The different combinational panels covering estrogen and immunosuppressive agents, cortisone, prednisolone and cyclophosphamide were used for concurrent oral and vaginal candidiasis establishment. Prednisolone in combination with estrogen proved an optimal mode for concurrent mucosal infection establishment. The model maintained for 1 week with fungal burden reached at least 10(5) cfu/g of tissue. This mouse model was evaluated by in vivo pharmacodynamics of fluconazole and host mucosal immunity of IL-17 and IL-23. Mice infected by SC5314 were cured by fluconazole. An increase in IL-23 in both oral and vaginal homogenates was observed after infection, while IL-17 only had a prominent elevation in oral tissue. This model could properly mimic complicated clinical conditions and provides a valuable means for antifungal assay in vivo and may also provide a useful method for the evaluation of host-fungal interactions.

Competitive Interactions between C. albicans, C. glabrata and C. krusei during Biofilm Formation and Development of Experimental Candidiasis

In this study, we evaluated the interactions between Candida albicans, Candida krusei and Candida glabrata in mixed infections. Initially, these interactions were studied in biofilms formed in vitro. CFU/mL values of C. albicans were lower in mixed biofilms when compared to the single biofilms, verifying 77% and 89% of C. albicans reduction when this species was associated with C. glabrata and C. krusei, respectively. After that, we expanded this study for in vivo host models of experimental candidiasis. G. mellonella larvae were inoculated with monotypic and heterotypic Candida suspensions for analysis of survival rate and quantification of fungal cells in the haemolymph. In the groups with single infections, 100% of the larvae died within 18 h after infection with C. albicans. However, interaction groups achieved 100% mortality after 72 h of infection by C. albicans-C. glabrata and 96 h of infection by C. albicans-C. krusei. C. albicans CFU/mL values from larvae hemolymph were lower in the interacting groups compared with the monoespecies group after 12 h of infection. In addition, immunosuppressed mice were also inoculated with monotypic and heterotypic microbial suspensions to induce oral candidiasis. C. albicans CFU/mL values recovered from oral cavity of mice were higher in the group with single infection by C. albicans than the groups with mixed infections by C. albicans-C. glabrata and C. albicans-C. krusei. Moreover, the group with single infection by C. albicans had a higher degree of hyphae and epithelial changes in the tongue dorsum than the groups with mixed infections. We concluded that single infections by C. albicans were more harmful for animal models than mixed infections with non-albicans species, suggesting that C. albicans establish competitive interactions with C. krusei and C. glabrata during biofilm formation and development of experimental candidiasis.

Recent mouse and rat methods for the study of experimental oral candidiasis

The Candida genus expresses virulence factors that, when combined with immunosuppression and other risk factors, can cause different manifestations of oral candidiasis. The treatment of mucosal infections caused by Candida and the elucidation of the disease process have proven challenging. Therefore, the study of experimentally induced oral candidiasis in rats and mice is useful to clarify the etiopathology of this condition, improve diagnosis, and search for new therapeutic options because the disease process in these animals is similar to that of human candidiasis lesions. Here, we describe and discuss new studies involving rat and mouse models of oral candidiasis with respect to methods for inducing experimental infection, methods for evaluating the development of experimental candidiasis, and new treatment strategies for oral candidiasis.

Role of bacterial lipopolysaccharide in enhancing host immune response to Candida albicans

Human infections involving yeast of the genus Candida often occur in the presence of bacteria, and, as such, it is important to understand how these bacteria influence innate host immunity towards Candida. Dectin-1 is a cell receptor of macrophages for Candida albicans recognition. The aim of this study was to examine dectin-1 expression by monocytes after stimulation with bacterial lipopolysaccharide (LPS), followed by heat-killed C. albicans (HKC). Freshly isolated human peripheral blood monocytes (PBMCs) and human monocytes cell line (THP-1) cells expressed low levels of dectin-1. Stimulation with LPS and GM-CSF/IL-4 was found to increase dectin-1 expression in both CD14⁺ human PBMC and THP-1 cells. Enhanced dectin-1 expression resulted in increased phagocytosis of Candida. When THP-1 cells were challenged only with HKC, detectable levels of IL-23 were not evident. However, challenge by LPS followed by varying concentrations of HKC resulted in increased IL-23 expression by THP-1 cells in HKC dose-dependent manner. Increased expression of IL-17 by PBMC also occurred after stimulation with Candida and LPS. In conclusion, bacterial LPS induces an enhanced immune response to Candida by immune cells, and this occurs through increasing dectin-1 expression.

Utility of insects for studying human pathogens and evaluating new antimicrobial agents

Insect models, such as Galleria mellonella and Drosophila melanogaster have significant ethical, logistical, and economic advantages over mammalian models for the studies of infectious diseases. Using these models, various pathogenic microbes have been studied and many novel virulence genes have been identified. Notably, because insects are susceptible to a wide variety of human pathogens and have immune responses similar to those of mammals, they offer the opportunity to understand innate immune responses against human pathogens better. It is important to note that insect pathosystems have also offered a simple strategy to evaluate the efficacy and toxicity of many antimicrobial agents. Overall, insect models provide a rapid, inexpensive, and reliable way as complementary hosts to conventional vertebrate animal models to study pathogenesis and antimicrobial agents.