Immunity of the greater wax moth Galleria mellonella

Greater wax moth Galleria mellonella (Lepidoptera: Pyralidae) as a resistant model host for Nosema pyrausta (Microsporidia: Nosematidae)

Galleria mellonella fed 3 million Nosema pyrausta spores per larva showed 0 and 5% infestation rate at 30 °C and 24 °C, respectively. N. pyrausta virulence did not increase after passage through G. mellonella for three generations. When larvae were pretreated with phenylthiourea, Bacillus thuringiensis or combination of both, infection rates were 11%, 15% and 22%, respectively. Injection of untreated and potassium hydroxide-primed spores resulted in approximately 10% and 50% infection, respectively. G. mellonella is resistant to high dosages of N. pyrausta spores, serving as a prospective model of insect resistance to microsporidia, while host immunosuppression and/or spore activation increases success of the pathogen.

Electrochemically Synthesized Silver Nanoparticles Are Active Against Planktonic and Biofilm Cells of Pseudomonas aeruginosa and Other Cystic Fibrosis-Associated Bacterial Pathogens

A novel, electrochemically synthesized, silver nanoparticles (AgNPs) formulation was evaluated in vitro against Pseudomonas aeruginosa, Burkholderia cepacia, Stenotrophomonas maltophilia, and Staphylococcus aureus strains from cystic fibrosis (CF) patients. AgNPs were particularly active against P. aeruginosa and B. cepacia planktonic cells (median MIC: 1.06 and 2.12 μg/ml, respectively) by a rapid, bactericidal and concentration-dependent effect. AgNPs showed to be particularly effective against P. aeruginosa and S. aureus biofilm causing a viability reduction ranging from 50% (1×MIC) to >99.9% (4×MIC). Electron microscopy showed that AgNPs deconstruct extracellular matrix of P. aeruginosa biofilm, and accumulate at the cell surface causing cell death secondary to membrane damage. Compared to Tobramycin, AgNPs showed comparable, or even better, activity against planktonic and biofilm P. aeruginosa cells. AgNPs at concentrations effective against B. cepacia and P. aeruginosa were not toxic to G. mellonella larvae. Our silver-based formulation might be an alternative to antibiotics in CF patients. Further in vitro and in vivo studies are warranted to confirm this therapeutic potential.

Characterisation of the cellular and proteomic response of Galleria mellonella larvae to the development of invasive aspergillosis

Background

Galleria mellonella larvae were infected with conidia of Aspergillus fumigatus and the cellular and humoral immune responses of larvae to the pathogen were characterized as invasive aspergillosis developed.

Results

At 2 h post-infection there was an increase in hemocyte density to 7.43 ± 0.50 × 10⁶/ml from 0.98 ± 0.08 × 10⁶/ml at 0 h. Hemocytes from larvae immune primed for 6 h with heat killed A. fumigatus conidia displayed superior anti-fungal activity. Examination of the spread of the fungus by Cryo-imaging and fluorescent microscopy revealed dissemination of the fungus through the larvae by 6 h and the formation of distinct nodules in tissue. By 24 h a range of nodules were visible at the site of infection and at sites distant from that indicating invasion of tissue. Proteomic analysis of larvae infected with viable conidia for 6 h demonstrated an increase in the abundance of gustatory receptor candidate 25 (37 fold), gloverin-like protein (14 fold), cecropin-A (11 fold). At 24 h post-infection gustatory receptor candidate 25 (126 fold), moricin-like peptide D (33 fold) and muscle protein 20-like protein (12 fold) were increased in abundance. Proteins decreased in abundance included fibrohexamerin (13 fold) and dimeric dihydrodiol dehydrogenase (8 fold).

Conclusion

The results presented here indicate that G. mellonella larvae may be a convenient model for studying the stages in the development of invasive aspergillosis and may offer an insight into this process in mammals.

Electronic supplementary material

The online version of this article (10.1186/s12866-018-1208-6) contains supplementary material, which is available to authorized users.

Galleria mellonella larvae allow the discrimination of toxic and non-toxic chemicals

The acute toxicities of 19 chemicals were assessed using G. mellonella larvae. The results obtained were compared against LD50 values derived from in vitro cytotoxicity tests and against in vivo acute oral LD50 values. In general, cell culture systems overestimated the toxicity of chemicals, especially low toxicity chemicals. In contrast, toxicity testing in G. mellonella larvae was found to be a reliable predictor for low toxicity chemicals. For the 9 chemicals tested which were assigned to Globally Harmonised System (GHS) category 5, the toxicity measured in G. mellonella larvae was consistent with their GHS categorisation but cytotoxicity measured in 3T3 or NHK cells predicted 4 out of 9 chemicals as having low toxicity. A more robust assessment of the likely toxicity of chemicals in mammals could be made by taking into account their toxicities in both cell cultures and in G. mellonella larvae.

Safety assessment and functional properties of four enterococci strains isolated from regional Argentinean cheese

The members of the Enterococcus genus are widely distributed in nature. Its strains have been extensively reported to be present in plant surfaces, soil, water and food. In an attempt to assess their potential application in food industry, four Enterococcus faecium group-strains recently isolated from Argentinean regional cheese products were evaluated using a combination of whole genome analyses and in vivo assays. In order to identify these microorganisms at species level, in silico analyses using their newly reported sequences were conducted. The average nucleotide identity (ANI), in silico DNA-DNA hybridization, and phylogenomic trees constructed using core genome data allowed IQ110, GM70 and GM75 strains to be classified as E. faecium while IQ23 strain was identified as E. durans. Besides their common origin, the strains showed differences in their genetic structure and mobile genetic element content. Furthermore, it was possible to determine the absence or presence of specific features related to growth in milk, cheese ripening, probiotic capability and gut adaptation including sugar, amino acid, and peptides utilization, flavor compound production, bile salt tolerance as well as biogenic amine production. Remarkably, all strains encoded for peptide permeases, maltose utilization, bile salt tolerance, diacetyl and tyramine production genes. On the other hand, some variability was observed regarding citrate and lactose utilization, esterase, and cell wall-associated proteinase. In addition, while strains were predicted to be non-human pathogens by the in silico inspection of pathogenicity and virulence factors, only the GM70 strain proved to be non-virulent in Galleria mellonella model. In conclusion, we propose that, in order to improve the rational selection of strains for industrial applications, a holistic approach involving a comparative genomic analysis of positive and negative features as well as in vivo evaluation of virulence behavior should be performed.

Differences in Virulence Between Legionella pneumophila Isolates From Human and Non-human Sources Determined in Galleria mellonella Infection Model

Legionella pneumophila is a ubiquitous bacterium in freshwater environments and in many man-made water systems capable of inducing pneumonia in humans. Despite its ubiquitous character most studies on L. pneumophila virulence focused on clinical strains and isolates from man-made environments, so little is known about the nature and extent of virulence variation in strains isolated from natural environments. It has been established that clinical isolates are less diverse than man-made and natural environmental strains, suggesting that only a subset of environmental isolates is specially adapted to infect humans. In this work we intended to determine if unrelated L. pneumophila strains, isolated from different environments and with distinct virulence-related genetic backgrounds, displayed differences in virulence, using the Wax Moth Galleria mellonella infection model. We found that all tested strains were pathogenic in G. mellonella, regardless of their origin. Indeed, a panoply of virulence-related phenotypes was observed sustaining the existence of significant differences on the ability of L. pneumophila strains to induce disease. Taken together our results suggest that the occurrence of human infection is not related with the increased capability of some strains to induce disease since we also found a concentration threshold above which L. pneumophila strains are equally able to cause disease. In addition, no link could be established between the sequence-type (ST) and L. pneumophila pathogenicity. We envision that in man-made water distribution systems environmental filtering selection and biotic competition acts structuring L. pneumophila populations by selecting more resilient and adapted strains that can rise to high concentration if no control measures are implemented. Therefore, public health strategies based on the sequence based typing (STB) scheme analysis should take into account that the major disease-associated clones of L. pneumophila were not related with higher virulence in G. mellonella infection model, and that potential variability of virulence-related phenotypes was found within the same ST.

Bacterial and fungal infections induce bursts of dopamine in the haemolymph of the Colorado potato beetle Leptinotarsa decemlineata and greater wax moth Galleria mellonella

Dopamine (DA) is known as a hormone neurotrasnmitter molecule involved in several stress reactions in both vertebrates and invertebrates. Following infections with the fungi Metarhizium robertsii or Beauveria bassiana and the bacterium Bacillus thuringiensis, dopamine the concentration was measured at different time points in the haemolymph of the Colorado potato beetle, Leptinotarsa decemlineata and the larvae of the greater wax moth Galleria mellonella. The infection with M. robertsii increased (4 to 12-fold) DA concentrations in the haemolymph of the potato beetle larvae and the oral infection by B. thuringiensis also lead to a 30 and 45-fold increase. During infection of the greater wax moth larvae with Beauveria bassiana and B. thuringiensis DA increased 4 to 20-fold and about 2 to 2,5-fold respectively, compared to non-infected insects. The relative DA concentrations varied between the two insects and depended on the pathogens and post infection time.

Novel approach to study gastropod-mediated innate immune reactions against metastrongyloid parasites

The anthropozoonotic metastrongyloid nematodes Angiostrongylus cantonensis and Angiostrongylus costaricensis, as well as Angiostrongylus vasorum, Crenosoma vulpis, Aelurostrongylus abstrusus and Troglostrongylus brevior are currently considered as emerging gastropod-borne parasites and have gained growing scientific attention in the last years. However, the knowledge on invertebrate immune responses and on how metastrongyloid larvae are attacked by gastropod immune cells is still limited. This work aims to describe an in vitro system to investigate haemocyte-derived innate immune responses of terrestrial gastropods induced by vital axenic metastrongyloid larvae. We also provide protocols on slug/snail management and breeding under standardized climate conditions (circadian cycle, temperature and humidity) for the generation of parasite-free F0 stages which are essential for immune-related investigations. Adult slug species (Arion lusitanicus, Limax maximus) and giant snails (Achatina fulica) were maintained in fully automated climate chambers until mating and production of fertilized eggs. Newly hatched F0 juvenile specimens were kept under parasite-free conditions before experimental use. An improved protocol for gastropod haemolymph collection and haemocyte isolation was established. Giemsa-stained haemolymph preparations showed adequate haemocyte isolation in all three gastropod species. Additionally, a protocol for the production of axenic first and third stage larvae (L1, L3) was established. Haemocyte functionality was tested in haemocyte-nematode-co-cultures. Scanning electron microscopy (SEM) and light microscopy analyses revealed that gastropod-derived haemocytes formed clusters as well as DNA-rich extracellular aggregates catching larvae and decreasing their motility. These data confirm the usefulness of the presented methods to study haemocyte-mediated gastropod immune responses to better understand the complex biology of gastropod-borne diseases.

Studies on localization and protein ligands of Galleria mellonella apolipophorin III during immune response against different pathogens

A lipid-binding protein apolipophorin III (apoLp-III), an exchangeable component of lipophorin particles, is involved in lipid transport and immune response in insects. In Galleria mellonella, apoLp-III binding to high-density lipophorins and formation of low-density lipophorin complexes upon immune challenge was reported. However, an unanswered question remains whether apoLp-III could form different complexes in a pathogen-dependent manner. Here we report on pathogen- and time-dependent alterations in the level of apoLp-III free and lipophorin-bound form that occur in the hemolymph and hemocytes shortly after immunization of G. mellonella larvae with different pathogens, i.e. Gram-negative bacterium Escherichia coli, Gram-positive bacterium Micrococcus luteus, yeast-like fungus Candida albicans, and filamentous fungus Fusarium oxysporum. These changes were accompanied by differently persistent re-localization of apoLp-III in the hemocytes. The apoLp-III-interacting proteins were recovered from immune hemolymph by affinity chromatography on a Sepharose bed with immobilized anti-apoLp-III antibodies. ApoLp-I, apoLp-II, hexamerin, and arylphorin were identified as main components that bound to apoLp-III; the N-terminal amino acid sequences of G. mellonella apoLp-I and apoLp-II were determined for the first time. In the recovered complexes, the pathogen-dependent differences in the content of individual apolipophorins were detected. Apolipophorins may thus be postulated as signaling molecules responding in an immunogen-dependent manner in early steps of G. mellonella immune response.

The O-specific polysaccharide lyase from the phage LKA1 tailspike reduces Pseudomonas virulence

Pseudomonas phage LKA1 of the subfamily Autographivirinae encodes a tailspike protein (LKA1gp49) which binds and cleaves B-band LPS (O-specific antigen, OSA) of Pseudomonas aeruginosa PAO1. The crystal structure of LKA1gp49 catalytic domain consists of a beta-helix, an insertion domain and a C-terminal discoidin-like domain. The putative substrate binding and processing site is located on the face of the beta-helix whereas the C-terminal domain is likely involved in carbohydrates binding. NMR spectroscopy and mass spectrometry analyses of degraded LPS (OSA) fragments show an O5 serotype-specific polysaccharide lyase specificity. LKA1gp49 reduces virulence in an in vivo Galleria mellonella infection model and sensitizes P. aeruginosa to serum complement activity. This enzyme causes biofilm degradation and does not affect the activity of ciprofloxacin and gentamicin. This is the first comprehensive report on LPS-degrading lyase derived from a Pseudomonas phage. Biological properties reveal a potential towards its applications in antimicrobial design and as a microbiological or biotechnological tool.

Diamine derivative anti-Trichomonas vaginalis and anti-Tritrichomonas foetus activities by effect on polyamine metabolism

Human and bovine trichomoniasis are sexually transmitted diseases (STD) caused by Trichomonas vaginalis and Tritrichomonas foetus, respectively. Human trichomoniasis is the most common non-viral STD in the world and bovine trichomoniasis causes significant economic losses to breeders. Considering the significant impact of the infections caused by these protozoa and the treatment failures, the search for new therapeutic alternatives becomes crucial. In this study the effect of diamines and amino alcohols in the in vitro viability of trichomonads was evaluated. Screening demonstrated the high activity of diamine 4 against these protozoa. Although cytotoxicity against HMVII cell line and slight hemolysis were observed in vitro, the compound showed no toxic effect on the Galleria mellonella in vivo model. Importantly, diamine 4 was active against both trichomonads species at 6h and 24h of incubation, and these effects was reverted by putrescine, a polyamine, suggesting competition for the same metabolic pathway. These findings indicate that the mechanism of action of diamine 4 is through the polyamine metabolism, a pathway distinct from that presented by metronidazole, the drug usually used to treat trichomoniasis and to which resistance is widely reported. These data demonstrate the importance of diamines as potential novel candidates as anti-T. vaginalis and anti-T. foetus agents.

Evolution and Function of Thioester-Containing Proteins and the Complement System in the Innate Immune Response

The innate immune response is evolutionary conserved among organisms. The complement system forms an important and efficient immune defense mechanism. It consists of plasma proteins that participate in microbial detection, which ultimately results in the production of various molecules with antimicrobial activity. Thioester-containing proteins (TEPs) are a superfamily of secreted effector proteins. In vertebrates, certain TEPs act in the innate immune response by promoting recruitment of immune cells, phagocytosis, and direct lysis of microbial invaders. Insects are excellent models for dissecting the molecular basis of innate immune recognition and response to a wide range of microbial infections. Impressive progress in recent years has generated crucial information on the role of TEPs in the antibacterial and antiparasite response of the tractable model insect Drosophila melanogaster and the mosquito malaria vector Anopheles gambiae. This knowledge is critical for better understanding the evolution of TEPs and their involvement in the regulation of the host innate immune system.

A Novel Restraint Device for Injection of Galleria mellonella Larvae that Minimizes the Risk of Accidental Operator Needle Stick Injury

Larvae of the insect Galleria mellonella are increasingly being used for studying pathogenic microbes and their virulence mechanisms, and as a rapid model for screening novel antimicrobial agents. The larvae (waxworms) are most frequently infected by injection of pathogenic organisms into the haemocoel through the insect's prolegs. The mostly widely used method for restraining the waxworms for injection is by grasping them between the operator's fingers, which puts the operator at risk of needle stick injury, an important consideration when working with highly pathogenic and/or drug-resistant microorganisms. While use of a stab proof glove can reduce this risk of injury, it does so at the loss of manual dexterity and speed, resulting in a more labor-intensive, and cumbersome assay. We describe a simple cost effective device (the so-called “Galleria Grabber”) for restraining waxworms for injection that keeps the operator's fingers clear of the needle thus reducing the risk of injury.

Insect Immunity to Entomopathogenic Nematodes and Their Mutualistic Bacteria

Entomopathogenic nematodes are important organisms for the biological control of insect pests and excellent models for dissecting the molecular basis of the insect immune response against both the nematode parasites and their mutualistic bacteria. Previous research involving the use of various insects has found distinct differences in the number and nature of immune mechanisms that are activated in response to entomopathogenic nematode parasites containing or lacking their associated bacteria. Recent studies using model insects have started to reveal the identity of certain molecules with potential anti-nematode or antibacterial activity as well as the molecular components that nematodes and their bacteria employ to evade or defeat the insect immune system. Identification and characterization of the genes that regulate the insect immune response to nematode-bacteria complexes will contribute significantly to the development of improved practices to control insects of agricultural and medical importance, and potentially nematode parasites that infect mammals, perhaps even humans.