Lactobacillus species increase the survival of Galleria mellonella infected with Candida albicans and non-albicans Candida clinical isolates

The biocompatibility and antifungal effect of Rosmarinus officinalis against Candida albicans in Galleria mellonella model

This study was performed to evaluate the biocompatibility and antifungal effect of Rosmarinus officinalis against Candida albicans in Galleria mellonella model. Five different concentrations of R. officinalis glycolic extract (50; 25; 12.5 e 6.25 mg/mL) were used to evaluate its biocompatibility in G. mellonella model, in which the nystatin suspension (100; 50; 25; 12.5 e 6.25%) was used as a control group. The antifungal action of R. officinalis glycolic extract was evaluated on C. albicans for 72, 48 and 12 h at two different phases: (1) using the extract as therapeutic agent; and (2) using the extract as prophylactic agent. PBS was used as a negative control group. G. mellonella survival curves were plotted using the Kaplan–Meier method and statistical analysis was performed using the log-rank test (Mantel–Cox) and the significance level was set at (α ≤ 0.05). There was no significant difference among the groups in which all were biocompatible except of a significant death rate of 26.6% with nystatin 100%. In phase 1, it was found that after 7 days, there was no statistically significant difference among the prophylactic treatment groups. In phase 2, the groups of R. officinalis 6.25 mg/mL for 72 h and R. officinalis of 12.5 mg/mL for 24 h promoted the survival rate of the larvae in comparison with the control group with a significant difference (p = 0.017) and (p = 0.032) respectively. Therefore, R. officinalis extract is biocompatible in different concentrations and can be used as a prophylactic agent against fungal infection.

Establishing an invertebrate Galleria mellonella greater wax moth larval model of Neisseria gonorrhoeae infection

Neisseria gonorrhoeae (gonococcus) causes the human sexually transmitted disease gonorrhea. Studying gonococcal pathogenesis and developing new vaccines and therapies to combat the increasing prevalence of multi-antibiotic resistant bacteria has made use of many ex vivo models based on human cells and tissues, and in vivo vertebrate models, for example, rodent, pig and human. The focus of the current study was to examine the utility of the invertebrate greater wax moth Galleria mellonella as an in vivo model of gonococcal infection. We observed that a threshold of ~106 - 107 gonococci/larva was required to kill >50% of larvae (P < 0.05), and increased toxicity correlated with reduced health index scores and pronounced histopathological changes such as increases in the total lesion grade, melanized nodules, hemocyte reaction, and multifocal adipose body degeneration. Larval death was independent of the expression of pilus or Opa protein or LOS sialylation within a single gonococcal species studied, but the model could demonstrate relative toxicity of different isolates. N. meningitidis, N. lacatamica and gonococci all killed larvae equally, but were significantly less toxic (P > 0.05) than Pseudomonas aeruginosa. Larvae primed with nontoxic doses of gonococci were more susceptible to subsequent challenge with homologous and heterologous bacteria, and larval survival was significantly reduced (P < 0.05) in infected larvae after depletion of their hemocytes with clodronate-liposomes. The model was used to test the anti-gonococcal properties of antibiotics and novel antimicrobials. Ceftriaxone (P < 0.05) protected larvae from infection with different gonococcal isolates, but not azithromycin or monocaprin or ligand-coated silver nanoclusters (P > 0.05).

Pre-exposure to Candida glabrata protects Galleria mellonella against subsequent lethal fungal infections

Commensal fungi are an important part of human microbial community, among which Candida albicans and Candida glabrata are two common opportunistic pathogens. Unlike the high pathogenicity of C. albicans, C. glabrata is reported to show low pathogenicity to the host. Here, by using a Galleria mellonella infection model, we were able to confirm the much lower virulence of C. glabrata than C. albicans. Interestingly, pre-exposure to live C. glabrata (LCG) protects the larvae against subsequent various lethal fungal infections, including C. albicans, Candida tropicalis, and Cryptococcus neoformans. Inconsistently, heat-inactivated C. glabrata (HICG) pre-exposure can only protect against C. albicans or C. tropicalis re-infection, but not C. neoformans. Mechanistically, LCG or HICG pre-exposure enhanced the fungicidal activity of hemocytes against C. albicans or C. tropicalis. Meanwhile, LCG pre-exposure enhanced the humoral immunity by modulating the expression of fungal defending proteins in the cell-free hemolymph, which may contribute to the protection against C. neoformans. Together, this study suggests the important role of C. glabrata in enhancing host immunity, and demonstrates the great potential of G. mellonella model in studying the innate immune responses against infections.

The Postbiotic Activity of Lactobacillus paracasei 28.4 Against Candida auris

Candida auris has emerged as a medically important pathogen with considerable resistance to antifungal agents. The ability to produce biofilms is an important pathogenicity feature of this species that aids escape of host immune responses and antimicrobial agents. The objective of this study was to verify antifungal action using in vitro and in vivo models of the Lactobacillus paracasei 28.4 probiotic cells and postbiotic activity of crude extract (LPCE) and fraction 1 (LPF1), derived from L. paracasei 28.4 supernatant. Both live cells and cells free supernatant of L. paracasei 28.4 inhibited C. auris suggesting probiotic and postbiotic effects. The minimum inhibitory concentration (MIC) for LPCE was 15 mg/mL and ranges from 3.75 to 7.5 mg/mL for LPF1. Killing kinetics determined that after 24 h treatment with LPCE or LPF1 there was a complete reduction of viable C. auris cells compared to fluconazole, which decreased the initial inoculum by 1-logCFU during the same time period. LPCE and LPF1 significantly reduced the biomass (p = 0.0001) and the metabolic activity (p = 0.0001) of C. auris biofilm. There was also a total reduction (~10⁸ CFU/mL) in viability of persister C. auris cells after treatment with postbiotic elements (p < 0.0001). In an in vivo study, injection of LPCE and LPF1 into G. mellonella larvae infected with C. auris prolonged survival of these insects compared to a control group (p < 0.05) and elicited immune responses by increasing the number of circulating hemocytes and gene expression of antimicrobial peptide galiomicin. We concluded that the L. paracasei 28.4 cells and postbiotic elements (LPCE and LPF1) have antifungal activity against planktonic cells, biofilms, and persister cells of C. auris. Postbiotic supplementation derived from L. paracasei 28.4 protected G. mellonella infected with C. auris and enhanced its immune status indicating a dual function in modulating a host immune response.

Current Aspects in the Biology, Pathogeny, and Treatment of Candida krusei, a Neglected Fungal Pathogen

Fungal infections represent a constant and growing menace to human health, because of the emergence of new species as causative agents of diseases and the increment of antifungal drug resistance. Candidiasis is one of the most common fungal infections in humans and is associated with a high mortality rate when the fungi infect deep-seated organs. Candida krusei belongs to the group of candidiasis etiological agents, and although it is not isolated as frequently as other Candida species, the infections caused by this organism are of special relevance in the clinical setting because of its intrinsic resistance to fluconazole. Here, we offer a thorough revision of the current literature dealing with this organism and the caused disease, focusing on its biological aspects, the host-fungus interaction, the diagnosis, and the infection treatment. Of particular relevance, we provide the most recent genomic information, including the gene prediction of some putative virulence factors, like proteases, adhesins, regulators of biofilm formation and dimorphism. Moreover, C. krusei veterinary aspects and the exploration of natural products with anti-C. krusei activity are also included.

Development of Probiotic Formulations for Oral Candidiasis Prevention: Gellan Gum as a Carrier To Deliver Lactobacillus paracasei 28.4

Probiotics might provide an alternative approach for the control of oral candidiasis. However, studies on the antifungal activity of probiotics in the oral cavity are based on the consumption of yogurt or other dietary products, and it is necessary to use appropriate biomaterials and specific strains to obtain probiotic formulations targeted for local oral administration. In this study, we impregnated gellan gum, a natural biopolymer used as a food additive, with a probiotic and investigated its antifungal activity against Candida albicans Lactobacillus paracasei 28.4, a strain recently isolated from the oral cavity of a caries-free individual, was incorporated in several concentrations of gellan gum (0.6% to 1% [wt/vol]). All tested concentrations could incorporate L. paracasei cells while maintaining bacterial viability. Probiotic-gellan gum formulations were stable for 7 days when stored at room temperature or 4°C. Long-term storage of bacterium-impregnated gellan gum was achieved when L. paracasei 28.4 was lyophilized. The probiotic-gellan gum formulations provided a release of L. paracasei cells over 24 h that was sufficient to inhibit the growth of C. albicans, with effects dependent on the cell concentrations incorporated into gellan gum. The probiotic-gellan gum formulations also had inhibitory activity against Candida sp. biofilms by reducing the number of Candida sp. cells (P < 0.0001), decreasing the total biomass (P = 0.0003), and impairing hyphae formation (P = 0.0002), compared to the control group which received no treatment. Interestingly, a probiotic formulation of 1% (wt/vol) gellan gum provided an oral colonization of L. paracasei in mice with approximately 6 log CFU/ml after 10 days. This formulation inhibited C. albicans growth (P < 0.0001), prevented the development of candidiasis lesions (P = 0.0013), and suppressed inflammation (P = 0.0006) compared to the mice not treated in the microscopic analysis of the tongue dorsum. These results indicate that gellan gum is a promising biomaterial and can be used as a carrier system to promote oral colonization for probiotics that prevent oral candidiasis.

Extracellular Vesicles from Aspergillus flavus Induce M1 Polarization In Vitro

Immunocompromised patients are susceptible to several fungal infections. The genus Aspergillus can cause increased morbidity and mortality. Developing new therapies is essential to understand the fungal biology mechanisms. Fungal EVs carry important virulence factors, thus playing pivotal roles in fungal pathophysiology. No study to date has reported EV production by Aspergillus flavus, a fungus considered to be the second most common cause of aspergillosis and relevant food contaminator found worldwide. In this study, we produced A. flavus EVs and evaluated the in vitro immunomodulatory effects of EVs on bone marrow-derived macrophages (BMDMs) and in vivo effects in a Galleria mellonella model.

Aspergillus flavus, a ubiquitous and saprophytic fungus, is the second most common cause of aspergillosis worldwide. Several mechanisms contribute to the establishment of the fungal infection. Extracellular vesicles (EVs) have been described as “virulence factor delivery bags” in several fungal species, demonstrating a crucial role during the infection. In this study, we evaluated production of A. flavus EVs and their immunomodulatory functions. We verified that A. flavus EVs induce macrophages to produce inflammatory mediators, such as nitric oxide, tumor necrosis factor alpha (TNF-α), interleukin-6 (IL-6), and IL-1β. Furthermore, the A. flavus EVs enhance phagocytosis and killing by macrophages and induce M1 macrophage polarization in vitro. In addition, a prior inoculation of A. flavus EVs in Galleria mellonella larvae resulted in a protective effect against the fungal infection. Our findings suggest that A. flavus EVs are biologically active and affect the interaction between A. flavus and host immune cells, priming the innate immune system to eliminate the fungal infection. Collectively, our results suggest that A. flavus EVs play a crucial role in aspergillosis.

IMPORTANCE Immunocompromised patients are susceptible to several fungal infections. The genus Aspergillus can cause increased morbidity and mortality. Developing new therapies is essential to understand the fungal biology mechanisms. Fungal EVs carry important virulence factors, thus playing pivotal roles in fungal pathophysiology. No study to date has reported EV production by Aspergillus flavus, a fungus considered to be the second most common cause of aspergillosis and relevant food contaminator found worldwide. In this study, we produced A. flavus EVs and evaluated the in vitro immunomodulatory effects of EVs on bone marrow-derived macrophages (BMDMs) and in vivo effects in a Galleria mellonella model.

Two sporulated Bacillus enhance immunity in Galleria mellonella protecting against Candida albicans

The aim of this study was to evaluate the effects of Bacillus subtilis and Bacillus atrophaeus on Galleria mellonella immunity challenged by Candida albicans. Firstly, we analyzed the susceptibility of G. mellonella to bacilli (vegetative and sporulating forms). It was found that both vegetative and sporulating forms were not pathogenic to G. mellonella at a concentration of 1 × 10⁴ cells/larva. Next, larvae were pretreated with two species of Bacillus, in the vegetative and sporulating forms, and then challenged with C. albicans. In addition, the gene expression of antimicrobial peptides (AMPs) such as Gallerimycin, Gloverin, Cecropin-D and Galiomicin was investigated. Survival rates increased in the Bacillus treated larvae compared with control larvae inoculated with C. albicans only. Cells and spores of Bacillus spp. upregulated Gloverin, Galiomicin and Gallerimycin genes in relation to the control group (PBS + PBS). When these larvae were infected with C. albicans, the group pretreated with spores of B. atrophaeus and B. subtilis showed a greater increase in expression of Galiomycin (49.08-fold and 13.50-fold) and Gallerimycin (27.88-fold and 68.15-fold), respectively, compared to the group infected with C. albicans only (p = 0.0001). After that, we investigated the effects of B. subtilis and B. atrophaeus on immune system of G. mellonella evaluating the number of hemocytes, quantification of melanization, cocoon formation and colony forming units (CFU) count. Hemocyte count increased in response to stimulation by Bacillus, and a higher increase was achieved when larvae were inoculated with B. subtilis spores (p = 0.0011). In the melanization assay, all groups tested demonstrated lower production of melanin compared to that in the phosphate-buffered saline (PBS) group. In addition, full cocoon formation was observed in all groups analyzed, which corresponded to a healthier wax worm. Hemolymph culture revealed higher growth of B. atrophaeus and B. subtilis in the groups inoculated with spores. We concluded that spores and cells of B. atrophaeus and B. subtilis stimulated the immune system of G. mellonella larvae and protected them of C. albicans infection.

Optimization and Characterization of a Galleria mellonella Larval Infection Model for Virulence Studies and the Evaluation of Therapeutics Against Streptococcus pneumoniae

Streptococcus pneumoniae is the leading cause of bacterial pneumonia. Infection is linked to high morbidity and mortality rates and antibiotic resistance within this pathogen is on the rise. Therefore, there is a need for novel antimicrobial therapies. To lower the time and costs of the drug discovery process, alternative in vivo models should be considered. As such, Galleria mellonella larvae can be of great value. The larval immunity consisting of several types of haemocytes is remarkably similar to the human innate immune system. Furthermore, these larvae don’t require specific housing, are cheap and are easy to handle. In this study, the use of a G. mellonella infection model to study early pneumococcal infections and treatment is proposed. Firstly, the fitness of this model to study pneumococcal virulence factors is confirmed using streptococcal strains TIGR4, ATCC^®49619, D39 and its capsule-deficient counterpart R6 at different inoculum sizes. The streptococcal polysaccharide capsule is considered the most important virulence factor without which streptococci are unable to sustain an in vivo infection. Kaplan–Meier survival curves showed indeed a higher larval survival after infection with streptococcal strain R6 compared to strain D39. Then, the infection was characterized by determining the number of haemocytes, production of oxygen free radicals and bacterial burden at several time points during the course of infection. Lastly, treatment of infected larvae with the standard antibiotics amoxicillin and moxifloxacin was evaluated. Treatment has proven to have a positive outcome on the course of infection, depending on the administered dosage. These data imply that G. mellonella larvae can be used to evaluate antimicrobial therapies against S. pneumoniae, apart from using the larval model to study streptococcal properties. The in-depth knowledge acquired regarding this model, makes it more suitable for use in future research.

Immune Response of Galleria mellonella against Human Fungal Pathogens

In many aspects, the immune response against pathogens in insects is similar to the innate immunity in mammals. This has caused a strong interest in the scientific community for the use of this model in research of host⁻pathogen interactions. In recent years, the use of Galleria mellonella larvae, an insect belonging to the Lepidoptera order, has emerged as an excellent model to study the virulence of human pathogens. It is a model that offers many advantages; for example, it is easy to handle and establish in every laboratory, the larvae have a low cost, and they tolerate a wide range of temperatures, including human temperature 37 °C. The immune response of G. mellonella is innate and is divided into a cellular component (hemocytes) and humoral component (antimicrobial peptides, lytic enzymes, and peptides and melanin) that work together against different intruders. It has been shown that the immune response of this insect has a great specificity and has the ability to distinguish between different classes of microorganisms. In this review, we delve into the different components of the innate immune response of Galleria mellonella, and how these components manifest in the infection of fungal pathogens including Candida albicans, Aspergillus fumigatus, Cryptococcus neoformans, and Histoplasma capsulatum.