Galleria mellonella infection models for the study of bacterial diseases and for antimicrobial drug testing

Typical and Atypical Enteroaggregative Escherichia coli Are Both Virulent in the Galleria mellonella Model

Enteroaggregative Escherichia coli (EAEC) is an emerging pathotype responsible for acute and persistent diarrhea. It can be classified as typical and atypical strains, respectively, based on the presence or absence of the AggR regulon, suggesting a higher virulence for typical EAEC. This study aims to evaluate in the Galleria mellonella model if there are differences in the virulence profiles among clinical strains of typical and atypical EAEC, prototype strains EAEC C1096, 042 and its aggR mutant. The clinical EAEC strains (n = 20) were analyzed for the presence of 22 putative virulence factors of EAEC or extraintestinal E. coli by PCR, as well as phenotypic characteristics of virulence (enzymes, siderophore, and biofilm). The survival of the larvae was analyzed after inoculation of 10⁴-10⁷ CFU/larva; the monitoring of bacterial growth in vivo and hemocyte quantification was determined after inoculation of the prototype strains (10⁵ CFU/larva) at different periods after infection. The strains of typical and atypical EAEC presented the same virulence profile for the larva, regardless of the amount or type of genes and phenotypic aspects of virulence analyzed. In addition, the EAEC 042 aggR mutant strain showed a significant reduction in the mortality of the inoculated larvae compared to the wild-type strain. In conclusion, the results obtained herein demonstrate that the virulence of EAEC seems to be related to the AggR regulon, but not exclusively, and atypical EAEC strains may be as virulent as typical ones in vivo in the G. mellonella model.

Staphylococcus aureus-induced sepsis in the lobster cockroach Nauphoeta cinerea

Invertebrates have been instrumental in understanding the mechanisms involved in infectious diseases, considering the idea to replace, reduce and refine the use of mammals as well as to understand the basic principles of immune response in insect. We evaluated the consequences of Staphylococcus aureus-induced sepsis in the last instar nymphs of Nauphoeta cinerea injected with different concentrations of bacteria preserved in two culture media. Infected groups had a decrease in hemolymph metabolites (glucose, amino acids, total proteins, and cholesterol), in contrast to the proteins in the fat body. Higher concentrations of S. aureus caused permanent morphological alterations in adults, decrease in food consumption, increase in isolation, and increase in CFU until death of the cockroaches. Survival and protection of nymphs against a repeated and stronger challenge with the same bacteria varied according to the medium they were conserved. N. cinerea proves to be a suitable and promising model for studies related to bacterial infections.

Host-pathogen interactions upon the first and subsequent infection of Galleria mellonella with Candida albicans

Insects are able to develop enhanced resistance in response to repeated infection. This phenomenon is called immune priming. In this work, so-called "primed" Galleria mellonella larvae were re-infected with a lethal dose of Candida albicans 48 h after injection of a non-lethal dose, while "non-primed" larvae were infected only with a lethal dose. The increased resistance of the primed larvae correlated with a slower rate of body colonisation by the fungus. Changes in the protein profiles were detected in the whole hemolymph of the primed insects. The analysis of low-molecular weight proteins and peptides obtained with the use of three different organic solvents and comparative quantitative HPLC analysis thereof showed that the primed larvae did not have higher amounts of any infection-inducible polypeptides than the non-primed larvae. Moreover, electrophoresis of low-molecular weight polypeptides revealed an even lower level of immune-induced peptides in the primed larvae than in the non-primed ones. Furthermore, the defence activity of larval hemolymph, i.e. the antifungal, antibacterial, and lysozyme-type activity, was up-regulated in the primed larvae at the time of re-infection and, consequently, at the early time points after the infection with the lethal dose. Twenty four hours after the infection, these parameters were equally high in the non-primed and primed larvae. Accordingly, at the time of the injection of the lethal dose, certain immune-inducible genes were up-regulated. However, 24 h after the infection with the lethal dose, their expression in both groups was incomparably higher than at the time of the infection and, in most cases, it was as high in the primed larvae as in the non-primed ones. We found that only anti yeast-like activity was enhanced 24 h after the re-infection. This correlated with results obtained by testing the priming effect in heterologous systems: the primed animals did not exhibit higher resistance to the other pathogens tested.

Prenylated flavonoid-enriched fraction from Maclura tinctoria shows biological activity against Staphylococcus aureus and protects Galleria mellonella larvae from bacterial infection

BACKGROUND

The Atlantic Forest biome extends along the entire Brazilian coast and is home to approximately 20,000 plant species, many of which are endemic; it is considered one of the hotspot regions of the planet. Several of these species are sources of natural products with biological activities that are still unknown. In this study, we evaluated the antimicrobial activity of 90 extracts derived from native Atlantic Forest tree species against Staphylococcus aureus, an important human and veterinary pathogen.

METHODS

Extracts from native Atlantic Forest tree species were evaluated for their antimicrobial activity against S. aureus by in vitro standard methods. Phytochemical fractionation of the extract from Maclura tinctoria was performed by liquid-liquid partitioning. LC-DAD-ESI-MS was used for identification of constituents in the most active fraction. Damage of cells and alterations in the permeability of cell membrane were determined by atomic force microscopy (AFM) and crystal violet uptake assay, respectively. In vivo antimicrobial activity was evaluated using Galleria mellonella larvae infected with S. aureus with survival data collected using the Kaplan-Meier method.

RESULTS

Among the organic or aqueous extracts tested here, 26 showed biological activity. Eight species showed relevant results, with a minimum inhibitory concentration (MIC) below 1 mg/mL. Antibacterial activity was registered for three species for the first time. An organic extract from Maclura tinctoria leaves showed the lowest MIC (0.08 mg/mL). Fractionation of this extract by liquid-liquid partitioning led to obtaining fraction 11FO d with a MIC of 0.04 mg/mL. This fraction showed strong activity against veterinary S. aureus isolates and contributed to the increased survival of Galleria mellonella larvae infected with S. aureus ATCC 29213. The bacterial surface was not altered by the presence of 11FO d, and no cell membrane damage was detected. The LC-DAD-ESI/MS analyses identified prenylated flavonoids as the major constituents responsible for the antibacterial activity of this active extract.

CONCLUSION

A fraction enriched in prenylated isoflavones and flavanones from M. tinctoria showed in vitro and in vivo efficacy as antistaphylococcal agents. These findings justify the need for further research to elucidate the mechanisms of action of these compounds.

The use of chicken and insect infection models to assess the virulence of African Salmonella Typhimurium ST313

Over recent decades, Salmonella infection research has predominantly relied on murine infection models. However, in many cases the infection phenotypes of Salmonella pathovars in mice do not recapitulate human disease. For example, Salmonella Typhimurium ST313 is associated with enhanced invasive infection of immunocompromised people in Africa, but infection of mice and other animal models with ST313 have not consistently reproduced this invasive phenotype. The introduction of alternative infection models could help to improve the quality and reproducibility of pathogenesis research by facilitating larger-scale experiments. To investigate the virulence of S. Typhimurium ST313 in comparison with ST19, a combination of avian and insect disease models were used. We performed experimental infections in five lines of inbred and one line of outbred chickens, as well as in the alternative chick embryo and Galleria mellonella wax moth larvae models. This extensive set of experiments identified broadly similar patterns of disease caused by the African and global pathovariants of Salmonella Typhimurium in the chicken, the chicken embryo and insect models. A comprehensive analysis of all the chicken infection experiments revealed that the African ST313 isolate D23580 had a subtle phenotype of reduced levels of organ colonisation in inbred chickens, relative to ST19 strain 4/74. ST313 isolate D23580 also caused reduced mortality in chicken embryos and insect larvae, when compared with ST19 4/74. We conclude that these three infection models do not reproduce the characteristics of the systemic disease caused by S. Typhimurium ST313 in humans.

Salmonella Typhimurium ST313 is associated with systemic infection in human populations in sub-Saharan Africa, and contrasts with the related pathovariant ST19 which causes gastrointestinal disease worldwide. Although the systemic pathology associated with ST313 infection in humans has been comprehensively documented in clinical and epidemiological studies, such pathology has been inconsistently reproduced in animal models of infection. Animal models that reliably recapitulate ST313 infection in humans are needed to study the biological mechanisms underpinning the systemic disease caused by ST313. In this study we performed extensive infection experiments, using several defined and alternative animal infection models to look for robust phenotypes that differentiate infection by S. Typhimurium ST313 from ST19. Large sample sizes and multivariate statistical analysis of infection data for inbred chicken lines allowed us to detect small but consistent differences between the strains. Overall, S. Typhimurium ST313 was associated with a reduced infection burden and pathology relative to ST19. This subtle phenotype may reflect the limitation of animal models to accurately represent infection by pathogens that have adapted to specific host phenotypes, for example, immunodeficiency in humans. Our study demonstrates the challenge of using animal models to differentiate closely-related bacterial pathovariants, and shows that inter-pathovar differences detected in animal models of infection often do not reflect clinical differences in humans at the level of disease mechanism.

Wild owls colonized by international clones of extended-spectrum β-lactamase (CTX-M)-producing Escherichia coli and Salmonella Infantis in the Southern Cone of America

Extended-spectrum β-lactamases (ESBLs)-producing Enterobacteriaceae have been classified as critical priority pathogens by the World Health Organization (WHO). We have conducted a microbiological and genomic surveillance study, in order to investigate the occurrence and features of antibiotic-resistant bacteria in wild birds admitted to a wildlife rescue and rehabilitation centre in Chile. This study reports for the first time the occurrence of highly virulent ESBL-producing Escherichia coli and Salmonella enterica serovar Infantis in wild owls inhabiting the Southern Cone of America. Genomic analysis revealed a wide resistome (for antibiotics, heavy metals and disinfectants) among international lineages of E. coli belonging to ST345 and ST2705, and S. Infantis ST32, producing CTX-M-8 or CTX-M-65 ESBLs. On the other hand, wide virulome was associated with a highly virulent behaviour in the Galleria mellonella infection model. Worryingly, all these lineages have been previously reported in humans, supporting that wide resistome and virulome could be contributing to rapid adaptation and dissemination of these clones at the human-animal-environment interface. In summary, wild owls can constitute environmental reservoirs of international clones of ESBL (CTX-M)-producing E. coli and S. Infantis carrying a wide resistome and virulome, in the Southern Cone of America, with potential risks to human, animal and environmental health.

Indomethacin-induced gut damage in a surrogate insect model, Galleria mellonella

Indomethacin is a non-steroidal anti-inflammatory drug that causes gastric ulceration and increased 'leakiness' in rat models, and is used routinely as a toxicology assay to screen novel compounds for repair and restitution properties. We set out to establish conditions for indomethacin-induced gut damage in wax-moth (Galleria mellonella) larvae with a view to reducing the need for rodents in such experimentation. We administered indomethacin (0.5-7.5 µg/larva; 2-30 mg/kg) to G. mellonella via intrahaemocoelic injection and gavage (force-feeding) and monitored survival and development, blood cell (haemocyte) numbers, and changes in gut permeability. Increased levels of gut leakiness were observed within the first 4- to 24 h by tracking fluorescent microspheres in the faeces and haemolymph (blood equivalent). Additionally, we recorded varying levels of tissue damage in histological sections of the insect midgut, including epithelial sloughing and cell necrosis. Degeneration of the midgut was accompanied by significant increases in detoxification-associated activities (superoxide dismutase and glutathione-S-transferase). Herein, we present the first evidence that G. mellonella larvae force-fed indomethacin display broad symptoms of gastric damage similar to their rodent counterparts.

Galleria mellonella Infection Model Identifies Both High and Low Lethality of Clostridium perfringens Toxigenic Strains and Their Response to Antimicrobials

Research progress into mechanisms of the anaerobe Clostridium perfringens and associated diseases has been frustrated by the lack of reliable infection models. Wax moth larvae (Galleria mellonella) have emerged as a viable alternative to other models of infection since they are economic, survive at 37°C and require no specialist equipment. This study aims to establish to what extent G. mellonella larvae can be used to study the virulence of C. perfringens strains and its suitability for studying novel treatment strategies by an improved time-lapse approach to data collection. Mortality and morbidity rates of larvae challenged with 10⁵ CFU of C. perfringens isolates from various sources were observed over 72 h and dose response data obtained. Phenoloxidase enzyme activity was investigated as a marker for immune response and tissue burden assessed by histopathological techniques. Results demonstrate that C. perfringens is pathogenic toward G. mellonella although potency varies dramatically between C. perfringens isolates and the reference strain ATCC 13124 was shown to be avirulent. Infection with C. perfringens strains activated the melanisation pathway resulting in melanin deposition but no increase in enzyme activity was observed. Efficacy of antibiotic therapy (penicillin G, bacitracin, neomycin, and tetracycline) administered parenterally to some extent correlates with that of in vitro analysis. The findings suggest G. mellonella might be a useful in vivo model of infection and convenient as a pre-screening assay for virulence of C. perfringens strains or as a simple, cheap and rapid in vivo assay in the first stage development of novel therapeutics against anaerobes.

HIGHLIGHTS

-Potential novel in vivo model for the study of Clostridium perfringens infection.-Novel time-lapse approach to data collection.-First report of the pathogenicity of C. perfringens toward G. mellonella.-First report of the efficacy of antibiotic therapy in response to C. perfringens infection in G. mellonella.

Bioevaluation of Ranatuerin-2Pb from the Frog Skin Secretion of Rana pipiens and its Truncated Analogues

Antimicrobial peptides (AMPs) are considered as a promising agent to overcome the drug-resistance of bacteria. Large numbers of AMPs have been identified from the skin secretion of Rana pipiens, including brevinins, ranatuerins, temporins and esculentins. In this study, the cDNA precursor of a broad-spectrum antimicrobial peptide, ranatuerin-2Pb, was cloned and identified. Additionally, two truncated analogues, RPa and RPb, were synthesised to investigate the structure-activity relationship of ranatuerin-2Pb. RPa lost antimicrobial activity against Candida albicans, MRSA, Enterococcus faecalis and Pseudomonas aeruginosa, while RPb retained its broad-spectrum antimicrobial activity. Additionally, ranatuerin-2Pb, RPa and RPb demonstrated inhibition and eradication effects against Staphylococcus aureus biofilm. RPb showed a rapid bacterial killing manner via membrane permeabilization without damaging the cell membrane of erythrocytes. Moreover, RPb decreased the mortality of S. aureus infected Galleria mellonella larvae. Collectively, our results suggested that RPb may pave a novel way for natural antimicrobial drug design.

Functional textiles impregnated with biogenic silver nanoparticles from Bionectria ochroleuca and its antimicrobial activity

Biogenic silver nanoparticles (AgNPs) were obtained throughout the fungal biosynthesis using extracellular filtrate of the epiphytic fungus B. ochroleuca and were incorporated in cotton and polyester fabrics by common impregnation procedure that was repeated once, twice or four times. Both fabrics were analyzed by scanning electron microscopy (SEM), and the effectiveness of impregnation was determined using inductively coupled plasma optical emission spectrometry (ICP OES). The AgNPs loaded fabrics showed potent antimicrobial activity on Staphylococcus aureus and Escherichia coli as well as on clinically relevant Candida albicans, Candida glabrata, and Candida parapsilosis, indicating that the AgNPs impregnation of cotton and polyester fabrics was efficient. AgNPs effectively inhibited the biofilm formation by Pseudomonas aeruginosa and was not toxic to Galleria mellonella larvae indicating a promising probability of biotechnological application.

Antidotal Action of Some Gold(I) Complexes toward Phosphine Toxicity

Phosphine (PH3) poisoning continues to be a serious problem worldwide, for which there is no antidote currently available. An invertebrate model for examining potential toxicants and their putative antidotes has been used to determine if a strategy of using Au(I) complexes as phosphine-scavenging compounds may be antidotally beneficial. When Galleria mellonella larvae (or wax worms) were subjected to phosphine exposures of 4300 (±700) ppm·min over a 20 min time span, they became immobile (paralyzed) for ∼35 min. The administration of Au(I) complexes auro-sodium bisthiosulfate (AuTS), aurothioglucose (AuTG), and sodium aurothiomalate (AuTM) 5 min prior to phosphine exposure resulted in a drastic reduction in the recovery time (0-4 min). When the putative antidotes were given 10 min after the phosphine exposure, all the antidotes were therapeutic, resulting in mean recovery times of 14, 17, and 19 min for AuTS, AuTG, and AuTM, respectively. Since AuTS proved to be the best therapeutic agent in the G. mellonella model, it was subsequently tested in mice using a behavioral assessment (pole-climbing test). Mice given AuTS (50 mg/kg) 5 min prior to a 3200 (±500) ppm·min phosphine exposure exhibited behavior comparable to mice not exposed to phosphine. However, when mice were given a therapeutic dose of AuTS (50 mg/kg) 1 min after a similar phosphine exposure, only a very modest improvement in performance was observed.

Inactivation of Streptococcus mutans genes lytST and dltAD impairs its pathogenicity in vivo

Background: Streptococcus mutans orchestrates the development of a biofilm that causes dental caries in the presence of dietary sucrose, and, in the bloodstream, S. mutans can cause systemic infections. The development of a cariogenic biofilm is dependent on the formation of an extracellular matrix rich in exopolysaccharides, which contains extracellular DNA (eDNA) and lipoteichoic acids (LTAs). While the exopolysaccharides are virulence markers, the involvement of genes linked to eDNA and LTAs metabolism in the pathogenicity of S. mutans remains unclear. Objective and Design: In this study, a parental strain S. mutans UA159 and derivative strains carrying single gene deletions were used to investigate the role of eDNA (ΔlytS and ΔlytT), LTA (ΔdltA and ΔdltD), and insoluble exopolysaccharides (ΔgtfB) in virulence in a rodent model of dental caries (rats) and a systemic infection model (Galleria mellonella larvae). Results: Fewer carious lesions were observed on smooth and sulcal surfaces of enamel and dentin of the rats infected with ∆lytS, ∆dltD, and ΔgtfB (vs. the parental strain). Moreover, strains carrying gene deletions prevented the killing of larvae (vs. the parental strain). Conclusions: Altogether, these findings indicate that inactivation of lytST and dltAD impaired S. mutans cariogenicity and virulence in vivo.

Utilization of Galleria mellonella larvae to characterize the development of Staphylococcus aureus infection

Staphylococcus aureus is a human opportunistic pathogen that causes a wide range of superficial and systemic infections in susceptible patients. Here we describe how an inoculum of S. aureus activates the cellular and humoral response of Galleria mellonella larvae while growing and disseminating throughout the host, forming nodules and ultimately killing the host. An inoculum of S. aureus (2×10⁶ larva^{- 1} ) decreased larval viability at 24 (80±5.77 %), 48 (55.93±5.55 %) and 72 h (10.23±2.97 %) and was accompanied by significant proliferation and dissemination of S. aureus between 6 and 48 h and the formation of nodules in the host. The hemocyte (immune cell) densities increased between 4 and 24 h and hemocytes isolated from larvae after 24 h exposure to heat-killed S. aureus (2×10⁶ larva^{- 1} ) showed altered killing kinetics as compared to those from control larvae. Alterations in the humoral immune response of larvae 6 and 24 h post-infection were also determined by quantitative shotgun proteomics. The proteome of 6 h-infected larvae was enriched for antimicrobial proteins, proteins of the prophenoloxidase cascade and a range of peptidoglycan recognition proteins. By 24 h there was a significant increase in the abundance of a range of antimicrobial peptides with anti-staphylococcal activity and proteins associated with nodule formation. The results presented here indicate how S. aureus interacts with the larval immune response, induces the expression of a variety of immune-related peptides and also forms nodules which are a hallmark of soft tissue infections during human infection.

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.

[The greater wax moth, Galleria mellonella to study host-pathogen interactions]

The massive use of antibiotics in health and agriculture has led to the emergence of pathogenic microorganisms resistant to frequently used treatments. In 2017, the World Health Organization (WHO) published its first ever list of antibiotic-resistant "priority pathogens", a catalogue of twelve families of bacteria that pose the greatest threat to human health. In this context, a new model for the study of host-pathogen interactions is becoming increasingly popular : the greater wax moth, Galleria mellonella. This butterfly larvae, sometimes considered as a new "laboratory rat", has many practical advantages and is an important host in the study of some steps in the pathogenicity of infectious agents and the identification of new treatments. This review presents this alternative model and describes its possible applications.

In vitro virulence determinants, comparative pathogenicity of Diutina (Candida) mesorugosa clinical isolates and literature review of the D. rugosa complex

Opportunistic mycoses by yeasts have increased considerably in the last three decades. Although Candida albicans is considered one of the most important causes of nosocomial infections, there is a recent shift to non-albicans Candida species as the most frequently isolated yeasts in particular risk groups. Diutina rugosa (formerly Candida rugosa) is a complex that includes four species: D. rugosa sensu stricto, D. neorugosa, D. pseudorugosa, and D. mesorugosa, and they are estimated to represent 0.2% of all Candida clinical isolates. In this study, we analyze nine clinical isolates of D. mesorugosa with focus on the virulence determinants and pathogenicity of the species by means of a Galleria mellonella survival model. Overall, we detected very strong aspartyl-protease and esterase activities. In contrast, both DNase and hemolysin activities were evident in only two of the isolates. None of the isolates was positive for phospholipase activity. All isolates studied were able to form biofilm after 72 h of incubation in a robust manner when compared with the C. albicans strain used as control. Susceptibility testing showed minimum inhibitory concentrations (MICs) ≤1 µg/mL for amphotericin B in all isolates tested. Eight out of nine of the isolates had MICs ≤2 µg/mL for fluconazole. All isolates were resistant to both anidulafungin and caspofungin (MICs ≥1 µg/mL). We found a significant difference (P < 0.0001) amongst the survival curves for the different D. mesorugosa isolates in the Galleria mellonella survival model. Strains HPM309 and H259 produced an acute infection and exhibited the highest virulence, whereas the D. mesorugosa isolates 99-480 and DM17 proved to be the less virulent strains.

Heterodimeric Rifampicin-Tobramycin conjugates break intrinsic resistance of Pseudomonas aeruginosa to doxycycline and chloramphenicol in vitro and in a Galleria mellonella in vivo model

Intrinsic resistance in Pseudomonas aeruginosa, defined by chromosomally encoded low outer membrane permeability and constitutively over-expressed efflux pumps, is a major reason why the pathogen is refractory to many antibiotics. Herein, we report that heterodimeric rifampicin-tobramycin conjugates break this intrinsic resistance and sensitize multidrug and extensively drug-resistant P. aeruginosa to doxycycline and chloramphenicol in vitro and in vivo. Tetracyclines and chloramphenicol are model compounds for bacteriostatic effects, but when combined with rifampicin-tobramycin adjuvants, their effects became bactericidal at sub MIC levels. Potentiation of tetracyclines correlates with the SAR of this class of drugs and is consistent with outer membrane permeabilization and efflux pump inhibition. Overall, this strategy finds new uses for old drugs and presents an avenue to expand the therapeutic utility of legacy antibiotics to recalcitrant pathogens such as P. aeruginosa.

Sea snake cathelicidin (Hc-cath) exerts a protective effect in mouse models of lung inflammation and infection

We investigated the anti-inflammatory and antibacterial activities of Hc-cath, a cathelicidin peptide derived from the venom of the sea snake, Hydrophis cyanocyntus, using in vivo models of inflammation and infection. Hc-cath function was evaluated in in vitro, in vivo in the wax moth, Galleria mellonella, and in mouse models of intraperitoneal and respiratory Pseudomonas aeruginosa infection. Hc-Cath downregulated LPS-induced pro-inflammatory responses in macrophages and significantly improved the survival of P. aeruginosa infected G. mellonella over a 5-day period. We also demonstrated, for the first time, that Hc-cath can modulate inflammation in a mouse model of LPS-induced lung inflammation by significantly reducing the release of the pro-inflammatory cytokine and neutrophil chemoattractant, KC, resulting in reduced cellular infiltration into the lungs. Moreover, Hc-cath treatment significantly reduced the bacterial load and inflammation in mouse models of P. aeruginosa intraperitoneal and respiratory infection. The effect of Hc-cath in our studies highlights the potential to develop this peptide as a candidate for therapeutic development.

Efficacy of bacteriophage treatment against carbapenem-resistant Acinetobacter baumannii in Galleria mellonella larvae and a mouse model of acute pneumonia

Background

Acinetobacter baumannii is an opportunistic pathogen that causes serious nosocomial infection in intensive care units. In particular, carbapenem-resistant A. baumannii (CRAB) strains have been increasing in the past decade, and they have caused major medical problems worldwide. In this study, a novel A. baumannii lytic phage, the YMC 13/03/R2096 ABA BP (phage Βϕ-R2096), which specifically causes the lysis of CRAB strains, was characterized in detail in vitro and in silico, and the in vivo effectiveness of phage therapy was evaluated using Galleria mellonella and a mouse model of acute pneumonia.

Results

The A. baumannii phage Βϕ-R2096 was isolated from sewage water using CRAB clinical strains selected from patients at a university hospital in South Korea. The complete genome of the phage Βϕ-R2096, which belongs to the Myoviridae family, was analyzed. Phage Βϕ-R2096 inhibited bacterial growth in a dose-dependent manner and exhibited high bacteriolytic activity at MOI = 10. In the evaluation of its therapeutic potential against CRAB clinical isolates using two in vivo models, phage Βϕ-R2096 increased the survival rates of both G. mellonella larvae (from 0 to 50% at 24 h) and mice (from 30% with MOI = 0.1 to 100% with MOI = 10 for 12 days) in post-infection of CRAB. In particular, phage Βϕ-R2096 strongly ameliorated histologic damage to infected lungs, with bacterial clearance in the lungs observed on day 3 postinfection in the mouse acute pneumonia model. Moreover, in vivo studies revealed no mortality or serious side effects in phage-treated groups.

Conclusion

The results of this study strongly suggest that phage Βϕ-R2096, a novel A. baumannii lytic phage, could be an alternative antibacterial agent to control CRAB infections. This study is the first report to compare in vivo evaluations (G. mellonella larvae and a mouse acute pneumonia model) of the therapeutic efficacy of a phage against CRAB infections.

Electronic supplementary material

The online version of this article (10.1186/s12866-019-1443-5) contains supplementary material, which is available to authorized users.

Pathogenicity patterns of mucormycosis: epidemiology, interaction with immune cells and virulence factors

Fungi of the basal lineage order Mucorales are able to cause infections in animals and humans. Mucormycosis is a well-known, life-threatening disease especially in patients with a compromised immune system. The rate of mortality and morbidity caused by mucormycosis has increased rapidly during the last decades, especially in developing countries. The systematic, phylogenetic, and epidemiological distributions of mucoralean fungi are addressed in relation to infection in immunocompromised patients. The review highlights the current achievements in (i) diagnostics and management of mucormycosis, (ii) the study of the interaction of Mucorales with cells of the innate immune system, (iii) the assessment of the virulence of Mucorales in vertebrate and invertebrate infection models, and (iv) the determination of virulence factors that are key players in the infection process, for example, high-affinity iron permease (FTR1), spore coat protein (CotH), alkaline Rhizopus protease enzyme (ARP), ADP-ribosylation factor (ARF), dihydrolipoyl dehydrogenase, calcineurin (CaN), serine and aspartate proteases (SAPs). The present mini-review attempts to increase the awareness of these difficult-to-manage fungal infections and to encourage research in the detection of ligands and receptors as potential diagnostic parameters and drug targets.

Assessing the Pathogenicity of Two Bacteria Isolated from the Entomopathogenic Nematode Heterorhabditis indica against Galleria mellonella and Some Pest Insects

The entomopathogenic nematodes Heterorhabditis are parasites of insects and are associated with mutualist symbiosis enterobacteria of the genus Photorhabdus; these bacteria are lethal to their host insects. Heterorhabditis indica MOR03 was isolated from sugarcane soil in Morelos state, Mexico. The molecular identification of the nematode was confirmed using sequences of the ITS1-5.8S-ITS2 region and the D2/D3 expansion segment of the 28S rRNA gene. In addition, two bacteria HIM3 and NA04 strains were isolated from the entomopathogenic nematode. The genomes of both bacteria were sequenced and assembled de novo. Phylogenetic analysis was confirmed by concatenated gene sequence datasets as Photorhabdus luminescens HIM3 (16S rRNA, 23S rRNA, dnaN, gyrA, and gyrB genes) and Pseudomonas aeruginosa NA04 (16S rRNA, 23S rRNA and gyrB genes). H. indica MOR03 infects Galleria mellonella, Tenebrio molitor, Heliothis subflexa, and Diatraea magnifactella larvae with LC50 values of 1.4, 23.5, 13.7, and 21.7 IJs/cm², respectively, at 48 h. These bacteria are pathogenic to various insects and have high injectable insecticide activity at 24 h.

Methods and Challenges of Using the Greater Wax Moth (Galleria mellonella) as a Model Organism in Antimicrobial Compound Discovery

Among non-mammalian infection model organisms, the larvae of the greater wax moth Galleria mellonella have seen increasing popularity in recent years. Unlike other invertebrate models, these larvae can be incubated at 37 °C and can be dosed relatively precisely. Despite the increasing number of publications describing the use of this model organism, there is a high variability with regard to how the model is produced in different laboratories, with respect to larva size, age, origin, storage, and rest periods, as well as dosing for infection and treatment. Here, we provide suggestions regarding how some of these factors can be approached, to facilitate the comparability of studies between different laboratories. We introduce a linear regression curve correlating the total larva weight to the liquid volume in order to estimate the in vivo concentration of pathogens and the administered drug concentration. Finally, we discuss several other aspects, including in vivo antibiotic stability in larvae, the infection doses for different pathogens and suggest guidelines for larvae selection.

A powerful in vivo alternative model in scientific research: Galleria mellonella

Murine models are suggested as the gold standard for scientific research, but they have many limitations of ethical and logistical concern. Then, the alternative host models have been developed to use in many aspects especially in invertebrate animals. These models are selected for many areas of research including genetics, physiology, biochemistry, evolution, disease, neurobiology, and behavior. During the past decade, Galleria mellonella has been used for several medical and scientific researches focusing on human pathogens. This model commonly used their larvae stage due to their easy to use, non-essential special tools or special technique, inexpensive, short life span, and no specific ethical requirement. Moreover, their innate immune response close similarly to mammals, which correlate with murine immunity. In this review, not only the current knowledge of characteristics and immune response of G. mellonella, and the practical use of these larvae in medical mycology research have been presented, but also the better understanding of their limitations has been provided.

Klebsiella pneumoniae infection biology: living to counteract host defences

Klebsiella species cause a wide range of diseases including pneumonia, urinary tract infections (UTIs), bloodstream infections and sepsis. These infections are particularly a problem among neonates, elderly and immunocompromised individuals. Klebsiella is also responsible for a significant number of community-acquired infections. A defining feature of these infections is their morbidity and mortality, and the Klebsiella strains associated with them are considered hypervirulent. The increasing isolation of multidrug-resistant strains has significantly narrowed, or in some settings completely removed, the therapeutic options for the treatment of Klebsiella infections. Not surprisingly, this pathogen has then been singled out as an 'urgent threat to human health' by several organisations. This review summarises the tremendous progress that has been made to uncover the sophisticated immune evasion strategies of K. pneumoniae. The co-evolution of Klebsiella in response to the challenge of an activated immune has made Klebsiella a formidable pathogen exploiting stealth strategies and actively suppressing innate immune defences to overcome host responses to survive in the tissues. A better understanding of Klebsiella immune evasion strategies in the context of the host-pathogen interactions is pivotal to develop new therapeutics, which can be based on antagonising the anti-immune strategies of this pathogen.

Voriconazole inhibits cross-kingdom interactions between Candida albicans and Actinomyces viscosus through the ergosterol pathway

Candida albicans and Actinomyces viscosus are prominent microbes associated with dental root caries. The aim of this study was to investigate the effect of C. albicans on A. viscosus biofilms and to identify the mechanisms associated with this interaction. A. viscosus and C. albicans strains (wide-type and mutants) were used to form biofilms in vitro and in vivo, which were subsequently analysed by crystal violet assay and scanning electron microscopy (SEM) to investigate the effect of C. albicans on A. viscosus growth. A viable plate count and survival curve for C. albicans mutants and A. viscosus combinations were used to identify which C. albicans pathway was crucial for cross-kingdom interactions. Voriconazole was used to block their interactions both in vitro and in vivo. SEM, fluorescence in situ hybridisation (FISH), quantitative PCR and survival curve analyses were performed to evaluate the activity of voriconazole on C. albicans and A. viscosus interactions. The biomass and virulence of mixed-species biofilms were significantly enhanced compared with the A. viscosus biofilm alone. However, this was not observed in the mixed-species biofilms with the C. albicans mutant erg11Δ/Δ in vitro and in vivo, indicating that azoles may work on the mixed-species biofilms. As expected, voriconazole can effectively reduce the biomass of mixed-species biofilms. A high concentration of voriconazole (1 µg/mL) reduced the abundance of C. albicans, whilst a low voriconazole concentration (0.25 µg/mL) blocked their interactions similar to the effect of the erg11Δ/Δ mutant. Voriconazole may be a candidate strategy to combat root caries pathogens.

Investigation of Novel pmrB and eptA Mutations in Isogenic Acinetobacter baumannii Isolates Associated with Colistin Resistance and Increased Virulence In Vivo

Colistin resistance in Acinetobacter baumannii is of great concern and is a threat to human health. In this study, we investigate the mechanisms of colistin resistance in four isogenic pairs of A. baumannii isolates displaying an increase in colistin MICs. A mutation in pmrB was detected in each colistin-resistant isolate, three of which were novel (A28V, I232T, and ΔL9-G12). Increased expression of pmrC was shown by semi-quantitative reverse transcription-PCR (qRT-PCR) for three colistin-resistant isolates, and the addition of phosphoethanolamine (PEtN) to lipid A by PmrC was revealed by mass spectrometry. Interestingly, PEtN addition was also observed in some colistin-susceptible isolates, indicating that this resistance mechanism might be strain specific and that other factors could contribute to colistin resistance. Furthermore, the introduction of pmrAB carrying the short amino acid deletion ΔL9-G12 into a pmrAB knockout strain resulted in increased pmrC expression and lipid A modification, but colistin MICs remained unchanged, further supporting the strain specificity of this colistin resistance mechanism. Of note, a mutation in the pmrC homologue eptA and a point mutation in ISAba1 upstream of eptA were associated with colistin resistance and increased eptA expression, which is a hitherto undescribed resistance mechanism. Moreover, no cost of fitness was observed for colistin-resistant isolates, while the virulence of these isolates was increased in a Galleria mellonella infection model. Although the mutations in pmrB were associated with colistin resistance, PEtN addition appears not to be the sole factor leading to colistin resistance, indicating that the mechanism of colistin resistance is far more complex than previously suspected and is potentially strain specific.

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.

Linezolid in Combination With Azoles Induced Synergistic Effects Against Candida albicans and Protected Galleria mellonella Against Experimental Candidiasis

The incidence of resistant Candida isolates has increased continuously in recent decades, especially Candida albicans. To overcome this resistance, research on antifungal sensitizers has attracted considerable attention. Linezolid was found to inhibit the growth of Pythium insidiosum and synergize with amphotericin B against Cryptococcus neoformans. The objective of this study was to determine the interactions of linezolid and azoles against C. albicans in vitro and in vivo. In vitro, linezolid combined with azoles induced synergistic effects not only against some susceptible C. albicans isolates, but also against all tested resistant C. albicans isolates. For all resistant isolates, exposure to the combination of linezolid with azoles induced a significant decrease in the minimum inhibitory concentrations (MIC) of azoles, from >512 to 0.5–1 μg/mL for fluconazole, from >16 to 0.25–1 μg/mL for itraconazole, and from >16 to 0.03–0.25 μg/mL for voriconazole. Additionally, linezolid synergized with fluconazole against biofilms that were preformed for ≤ 12 h from both susceptible and resistant C. albicans, and the sessile MIC of fluconazole decreased from >1024 to 1–4 μg/mL. In vivo, linezolid plus azoles prolonged the survival rate of infected Galleria mellonella larvae twofold compared with the azole monotherapy group, significantly decreased the fungal burden of the infected larvae, and reduced the damage of resistant C. albicans to the larval tissue. These findings will contribute to antifungal agent discovery and new approaches for the treatment of candidiasis caused by C. albicans.

Design, Synthesis, and Nanostructure-Dependent Antibacterial Activity of Cationic Peptide Amphiphiles

The development of bacterial resistant strains is a global health concern. Designing antibiotics that limit the rise of pathogenic resistance is essential to efficiently treat pathogenic infections. Self-assembling amphiphilic molecules are an intriguing platform for the treatment of pathogens because of their ability to disrupt bacterial membranes and function as drug nanocarriers. We have designed cationic peptide amphiphiles (PAs) that can form micelles, nanofibers, and twisted ribbons with the aim of understanding antimicrobial activity at the supramolecular level. We have found that micelle-forming PAs possess excellent antimicrobial activity against various Gram-positive and Gram-negative pathogens, such as methicillin-resistant Staphylococcus aureus (MRSA) and multidrug-resistant Klebsiella pneumoniae with minimal inhibitory concentrations (MICs) ranging between 1 and 8 μg/mL, when compared to nanofibers with MICs >32 μg/mL. The data suggest that the antimicrobial activity of the PAs depends on their morphology, amino acid sequence, the length of the alkyl tail, and the overall hydrophobicity of the PA. Scanning electron microscopy, confocal microscopy, and flow cytometry studies using MRSA and Escherichia coli K12 strains showed that PAs increase cell membrane permeability and disrupt the integrity of pathogen's membrane, leading to cell lysis and death. PAs are a promising platform to develop new antimicrobials that could work as nanocarriers to develop synergistic antibacterial therapies.

Relationship Between Different Resistance Mechanisms and Virulence in Acinetobacter baumannii

Aim: This study analyzed the virulence of several Acinetobacter baumannii strains expressing different resistance mechanisms using the Caenorhabditis elegans infection model. Results: Strains susceptible/resistant to carbapenems (presenting class D (OXA-23, OXA-24), class B metallo-β-lactamase (MBL) (NDM-1), penicillin binding protein (PBP) altered and decreased expression of Omp 33-36 kDa) and isogenic A. baumannii strains susceptible/resistant to colistin (presenting loss of lipopolysaccharide (LPS) and pmrA mutations) were included to evaluate the virulence using the C. elegans infection model. The nematode killing assay, bacterial ingestion in worms, and bacterial lawn avoidance assay were performed with the Fer-15 mutant line. A. baumannii strains generally presented low virulence, showing no difference between carbapenem-resistant strains (expressing class D, MBLs, or altered PBP) and their isogenic susceptible strains. In contrast, the absence of the Omp 33-36 kDa protein in the knockout was associated with a decrease of virulence, and a significant difference was observed between colistin-resistant mutants and their susceptible counterpart when the mechanism of resistance was associated with the loss of LPS but not with its modification. Conclusions: Resistance to carbapenems in A. baumannii associated with the production of OXA-type or NDM-type enzymes does not seem to affect their virulence in the C. elegans infection model. In contrast, the presence of Omp 33-36 kDa, and high level resistance to colistin related with the loss of LPS, might contribute with the virulence profile in A. baumannii.

Resistance to Nano-Based Antifungals Is Mediated by Biomolecule Coronas

Fungal infections are a growing global health and agricultural threat, and current chemical antifungals may induce various side-effects. Thus, nanoparticles are investigated as potential novel antifungals. We report that nanoparticles' antifungal activity strongly depends on their binding to fungal spores, focusing on the clinically important fungal pathogen Aspergillus fumigatus as well as common plant pathogens, such as Botrytis cinerea. We show that nanoparticle-spore complex formation was enhanced by the small nanoparticle size rather than the material, shape or charge, and could not be prevented by steric surface modifications. Fungal resistance to metal-based nanoparticles, such as ZnO-, Ag-, or CuO-nanoparticles as well as dissolution-resistant quantum dots, was mediated by biomolecule coronas acquired in pathophysiological and ecological environments, including the lung surfactant, plasma or complex organic matters. Mechanistically, dose-dependent corona-mediated resistance occurred via reducing physical adsorption of nanoparticles to fungal spores. The inhibitory effect of biomolecules on the antifungal activity of Ag-nanoparticles was further verified in vivo, using the invertebrate Galleria mellonella as an A. fumigatus infection model. Our results explain why current nanoantifungals often show low activity in realistic application environments, and will guide nanomaterial designs that maximize functionality and safe translatability as potent antifungals for human health, biotechnology, and agriculture.

A new class of prophylactic metallo-antibiotic possessing potent anti-cancer and anti-microbial properties

A family of metallo-antibiotics of general formula [Cu(N,N)(CipA)Cl] where N,N is a phenanthrene ligand and CipA is a derivative of the clinically used fluoroquinolone antibiotic ciprofloxacin – targeting immunocompromised cancer patients undergoing chemotherapy.

The Galleria mellonella Infection Model for Investigating the Molecular Mechanisms of Legionella Virulence

Legionella species evolved virulence factors to exploit protozoa as replicative niches in the environment. Cell culture infection models demonstrated that many of these factors also enable the bacteria to thrive in human macrophages; however, these models do not recapitulate the complex interactions between macrophages, lung epithelial, and additional immune cells, which are crucial to control bacterial infections. Thus, suitable infection models are required to understand which bacterial factors are important to trigger disease. Guinea pigs and, most frequently, mice have been successfully used as mammalian model hosts; however, ethical and economic considerations impede their use in high-throughput screening studies of Legionella isolates or small molecule inhibitors.Here, we describe the larvae of the lepidopteran Galleria mellonella as insect model of Legionella pathogenesis. Larvae can be obtained from commercial suppliers in large numbers, maintained without the need of specialized equipment, and infected by injection. Although lacking the complexity of a mammalian immune system, the larvae mount humoral and cellular immune responses to infection. L. pneumophila strain 130b and other prototype isolates withstand these responses and use the Defective in organelle trafficking/Intracellular multiplication (Dot/Icm) type IV secretion system (T4SS ) to inject effectors enabling survival and replication in hemocytes, insect phagocytes, ultimately leading to the death of the larvae. Differences in virulence between L. pneumophila isolates or gene deletion mutants can be analyzed using indicators of larval health and immune induction, such as pigmentation, mobility, histopathology, and survival. Bacterial replication can be measured by plating hemolymph or by immunofluorescence microscopy of isolated circulating hemocytes from infected larvae. Combined, these straightforward experimental readouts make G. mellonella larvae a versatile model host to rapidly assess the virulence of different Legionella isolates and investigate the role of specific virulence factors in overcoming innate host defense mechanisms.

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.

Antimicrobial photodynamic therapy with phenothiazinium photosensitizers in non-vertebrate model Galleria mellonella infected with Fusarium keratoplasticum and Fusarium moniliforme

Fusarium keratoplasticum and Fusarium moniliforme are filamentous fungi common in the environment and cause mycosis in both animals and plants. Human infections include mycetoma, keratitis and onychomycosis, while deeper mycosis occurs in immunocompromised patients. Most of the Fusarium spp. are frequently resistant to treatment with currently used antifungals. The frequent occurrence of antifungal resistance has motivated the study of antimicrobial photodynamic therapy as an alternative treatment for fungal infections. Many studies have investigated the in vitro use of antimicrobial photodynamic therapy to kill fungi, but rarely in animal models of infection. Thus, here we employed the invertebrate wax moth Galleria mellonella to study the in vivo effects of antimicrobial photodynamic therapy with three different phenothiazinium photosensitizers, methylene blue, new methylene blue N and the pentacyclic S137 against infection with microconidia of Fusarium keratoplasticum and Fusarium moniliforme. The effect of antimicrobial photodynamic therapy using these photosensitizers and light-emitting diodes with an emission peak at 635 nm and an integrated irradiance from 570 to 670 nm of 9.8 mW cm^-2 was investigated regarding the toxicity, fungal burden, larval survival and cellular immune response. The results from this model indicate that antimicrobial photodynamic therapy with methylene blue, new methylene blue N and S137 is efficient for the treatment of infection with F. keratoplasticum and F. moniliforme. The efficiency can be attributed to the fungal cell damage caused by antimicrobial photodynamic therapy which facilitates the action of the host immune response.

Recent Advances in the Use of Galleria mellonella Model to Study Immune Responses against Human Pathogens

The use of invertebrates for in vivo studies in microbiology is well established in the scientific community. Larvae of Galleria mellonella are a widely used model for studying pathogenesis, the efficacy of new antimicrobial compounds, and immune responses. The immune system of G. mellonella larvae is structurally and functionally similar to the innate immune response of mammals, which makes this model suitable for such studies. In this review, cellular responses (hemocytes activity: phagocytosis, nodulation, and encapsulation) and humoral responses (reactions or soluble molecules released in the hemolymph as antimicrobial peptides, melanization, clotting, free radical production, and primary immunization) are discussed, highlighting the use of G. mellonella as a model of immune response to different human pathogenic microorganisms.

Pseudomonas aeruginosa mutants defective in glucose uptake have pleiotropic phenotype and altered virulence in non-mammal infection models

Pseudomonas spp. are endowed with a complex pathway for glucose uptake that relies on multiple transporters. In this work we report the construction and characterization of Pseudomonas aeruginosa single and multiple mutants with unmarked deletions of genes encoding outer membrane (OM) and inner membrane (IM) proteins involved in glucose uptake. We found that a triple ΔgltKGF ΔgntP ΔkguT mutant lacking all known IM transporters (named GUN for Glucose Uptake Null) is unable to grow on glucose as unique carbon source. More than 500 genes controlling both metabolic functions and virulence traits show differential expression in GUN relative to the parental strain. Consistent with transcriptomic data, the GUN mutant displays a pleiotropic phenotype. Notably, the genome-wide transcriptional profile and most phenotypic traits differ between the GUN mutant and the wild type strain irrespective of the presence of glucose, suggesting that the investigated genes may have additional roles besides glucose transport. Finally, mutants carrying single or multiple deletions in the glucose uptake genes showed attenuated virulence relative to the wild type strain in Galleria mellonella, but not in Caenorhabditis elegans infection model, supporting the notion that metabolic functions may deeply impact P. aeruginosa adaptation to specific environments found inside the host.

Total Synthesis of Xanthoangelol B and Its Various Fragments: Toward Inhibition of Virulence Factor Production of Staphylococcus aureus

As an alternative strategy to fight antibiotic resistance, two-component systems (TCSs) have emerged as novel targets. Among TCSs, master virulence regulators that control the expression of multiple virulence factors are considered as excellent antivirulence targets. In Staphylococcus aureus, virulence factor expression is tightly regulated by a few master regulators, including the SaeRS TCS. In this study, we used a SaeRS GFP-reporter system to screen natural compound inhibitors of SaeRS, and identified xanthoangelol B 1, a prenylated chalcone from Angelica keiskei as a hit. We have synthesized 1 and its derivative PM-56 and shown that 1 and PM-56 both had excellent inhibitory potency against the SaeRS TCS, as demonstrated by various in vitro and in vivo experiments. As a mode of action, 1 and PM-56 were shown to bind directly to SaeS and inhibit its histidine kinase activity, which suggests a possibility of a broad spectrum inhibitor of histidine kinases.

Imidacloprid induced alterations in oxidative stress, biochemical, genotoxic, and immunotoxic biomarkers in non-mammalian model organism Galleria mellonella L. (Lepidoptera: Pyralidae)

Imidacloprid (IMI), a neonicotinoid insecticide, is widely used to control pests in agriculture. We investigated the changes in antioxidant enzyme activities, lipid peroxidation levels, biochemical effects, genotoxic effect, and immunotoxic effect of sublethal doses (0.25, 0.50, 0.75, and 1.00 µg) of IMI at different time periods (24, 48, 72, and 96 h) on a model organism, Galleria mellonella L. The results indicated that there were dose-dependent increases in both antioxidant enzyme activities (SOD and CAT) and MDA levels. Protein content was not affected by IMI at 24th and 48th, whereas it was decreased by the highest dose of IMI (1.00 µg) at 72nd and 96th h. Lipid and carbohydrate contents were reduced with increasing doses of IMI. Micronucleus frequency significantly increased in all IMI doses. All IMI doses caused a significant decrease in THC at 24th, 48th, and 72nd h. Our results can help to illustrate the effects of IMI in target organisms and indirectly may aid to discover potential risk of it on nontarget organisms. Future studies, at molecular levels, will be helpful in understanding the mechanism of action of IMI on these biomarkers.

The insect, Galleria mellonella, is a compatible model for evaluating the toxicology of okadaic acid

The polyether toxin, okadaic acid, causes diarrhetic shellfish poisoning in humans. Despite extensive research into its cellular targets using rodent models, we know little about its putative effect(s) on innate immunity. We inoculated larvae of the greater wax moth, Galleria mellonella, with physiologically relevant doses of okadaic acid by direct injection into the haemocoel (body cavity) and/or gavage (force-feeding). We monitored larval survival and employed a range of cellular and biochemical assays to assess the potential harmful effects of okadaic acid. Okadaic acid at concentrations ≥ 75 ng/larva (≥ 242 μg/kg) led to significant reductions in larval survival (> 65%) and circulating haemocyte (blood cell) numbers (> 50%) within 24 h post-inoculation. In the haemolymph, okadaic acid reduced haemocyte viability and increased phenoloxidase activities. In the midgut, okadaic acid induced oxidative damage as determined by increases in superoxide dismutase activity and levels of malondialdehyde (i.e. lipid peroxidation). Our observations of insect larvae correspond broadly to data published using rodent models of shellfish-poisoning toxidrome, including complementary LD₅₀ values: 206–242 μg/kg in mice, ~ 239 μg/kg in G. mellonella. These data support the use of this insect as a surrogate model for the investigation of marine toxins, which offers distinct ethical and financial incentives.

Galleria mellonella - a novel infection model for the Mycobacterium tuberculosis complex

Animal models have long been used in tuberculosis research to understand disease pathogenesis and to evaluate novel vaccine candidates and anti-mycobacterial drugs. However, all have limitations and there is no single animal model which mimics all the aspects of mycobacterial pathogenesis seen in humans. Importantly mice, the most commonly used model, do not normally form granulomas, the hallmark of tuberculosis infection. Thus there is an urgent need for the development of new alternative in vivo models. The insect larvae, Galleria mellonella has been increasingly used as a successful, simple, widely available and cost-effective model to study microbial infections. Here we report for the first time that G. mellonella can be used as an infection model for members of the Mycobacterium tuberculosis complex. We demonstrate a dose-response for G. mellonella survival infected with different inocula of bioluminescent Mycobacterium bovis BCG lux, and demonstrate suppression of mycobacterial luminesence over 14 days. Histopathology staining and transmission electron microscopy of infected G. mellonella phagocytic haemocytes show internalization and aggregation of M. bovis BCG lux in granuloma-like structures, and increasing accumulation of lipid bodies within M. bovis BCG lux over time, characteristic of latent tuberculosis infection. Our results demonstrate that G. mellonella can act as a surrogate host to study the pathogenesis of mycobacterial infection and shed light on host-mycobacteria interactions, including latent tuberculosis infection.

Isolation, characterization and in vivo efficacy of Escherichia phage myPSH1131

Phage therapy is the use of lytic bacteriophages to cure infections caused by bacteria. The aim of this study is to isolate and to characterize the bacteriophages against Escherichia coli isolated from clinical samples. For isolation of bacteriophages, water samples were collected from the Ganges River, and phage enrichment method was followed for phage isolation. Microbiological, genomic and lyophilization experiments were carried out to characterize the bacteriophage. Galleria mellonella was used to study the potential of phages against E. coli infection. Escherichia phage myPSH1131 belonging to Podoviridae family and found to have broad host range infectivity (n = 31) to infect Enterohemorrhagic E. coli (n = 9), Enteropathogenic E. coli (n = 6), Enterotoxigenic E. coli (n = 3), Enteroaggregative E. coli (n = 3), Uropathogenic E. coli (n = 9) and one unknown E. coli. The genome size is 76,163 base pairs (97 coding regions) and their genes show high similarity to SU10 phage. Lyophilization studies showed that the use of 1M sucrose, 2% gelatin and the combination of both 0.5M sucrose plus 1% gelatin could restore phage viability up to 20 months at 4°C. For in vivo studies, it was observed that a single phage dose can reduce the E. coli infection but to achieve 100% survival rate the infected larvae should be treated with three phage doses (20 μL, 10³ PFU/mL) at 6 hours interval. The characterized Escherichia phage myPSH1131 was found to have broad host range activity against E. coli pathogens and in vivo studies showed that multiple doses are required for effective treatment.

Applications of Invertebrate Animal Models to Dimorphic Fungal Infections

Dimorphic fungi can be found in the yeast form during infection and as hyphae in the environment and are responsible for a large number of infections worldwide. Invertebrate animals have been shown to be convenient models in the study of fungal infections. These models have the advantages of being low cost, have no ethical issues, and an ease of experimentation, time-efficiency, and the possibility of using a large number of animals per experiment compared to mammalian models. Invertebrate animal models such as Galleria mellonella, Caenorhabditis elegans, and Acanthamoebacastellanii have been used to study dimorphic fungal infections in the context of virulence, innate immune response, and the efficacy and toxicity of antifungal agents. In this review, we first summarize the features of these models. In this aspect, the growth temperature, genome sequence, availability of different strains, and body characteristics should be considered in the model choice. Finally, we discuss the contribution and advances of these models, with respect to dimorphic fungi Paracoccidioides spp., Histoplasma capsulatum, Blastomyces dermatitidis, Sporothrix spp., and Talaromyces marneffei (Penicillium marneffei).

Novel small molecules affecting cell membrane as potential therapeutics for avian pathogenic Escherichia coli

Avian pathogenic Escherichia coli (APEC), a most common bacterial pathogen of poultry, causes multiple extra-intestinal diseases in poultry which results in significant economic losses to the poultry industry worldwide. In addition, APEC are a subgroup of extra-intestinal pathogenic E. coli (ExPEC), and APEC contaminated poultry products are a potential source of foodborne ExPEC infections to humans and transfer of antimicrobial resistant genes. The emergence of multi-drug resistant APEC strains and the limited efficacy of vaccines necessitate novel APEC control approaches. Here, we screened a small molecule (SM) library and identified 11 SMs bactericidal to APEC. The identified SMs were effective against multiple APEC serotypes, biofilm embedded APEC, antimicrobials resistant APECs, and other pathogenic E. coli strains. Microscopy revealed that these SMs affect the APEC cell membrane. Exposure of SMs to APEC revealed no resistance. Most SMs showed low toxicity towards chicken and human cells and reduced the intracellular APEC load. Treatment with most SMs extended the wax moth larval survival and reduced the intra-larval APEC load. Our studies could facilitate the development of antimicrobial therapeutics for the effective management of APEC infections in poultry as well as other E. coli related foodborne zoonosis, including APEC related ExPEC infections in humans.

Thinking Outside the Box-Novel Antibacterials To Tackle the Resistance Crisis

The public view on antibiotics as reliable medicines changed when reports about "resistant superbugs" appeared in the news. While reasons for this resistance development are easily spotted, solutions for re-establishing effective antibiotics are still in their infancy. This Review encompasses several aspects of the antibiotic development pipeline from very early strategies to mature drugs. An interdisciplinary overview is given of methods suitable for mining novel antibiotics and strategies discussed to unravel their modes of action. Select examples of antibiotics recently identified by using these platforms not only illustrate the efficiency of these measures, but also highlight promising clinical candidates with therapeutic potential. Furthermore, the concept of molecules that disarm pathogens by addressing gatekeepers of virulence will be covered. The Review concludes with an evaluation of antibacterials currently in clinical development. Overall, this Review aims to connect select innovative antimicrobial approaches to stimulate interdisciplinary partnerships between chemists from academia and industry.

Peptide dendrimers as "lead compounds" for the treatment of chronic lung infections by Pseudomonas aeruginosa in cystic fibrosis patients: in vitro and in vivo studies

Aim

In the present work, the potential of the D-enantiomeric dendrimers dG3KL and dTNS18 was evaluated in relation to tobramycin (Tob), for the development of novel antibacterials to treat Pseudomonas aeruginosa chronic lung infections in patients with cystic fibrosis.

Results

The activity of dendrimers against planktonic P. aeruginosa cells was less than Tob against three of the four strains tested (median minimum inhibitory concentration [MIC] 8 vs 1 µg/mL, respectively), but 32-fold higher against the PaPh32 strain isolated at posttransplantation stage. Results from comparative minimum bactericidal concentration/MIC evaluation and time-kill assay suggested a bactericidal mechanism for all test agents. Subinhibitory concentrations of both dendrimers and Tob significantly affected biofilm formation by all strains in a dose-dependent manner, although the PaPh26 strain, isolated during the chronic stage of infection, was particularly susceptible to dendrimers. The activity of dendrimers against preformed P. aeruginosa biofilm was generally comparable to Tob, considering both dispersion and viability of biofilm. Particularly, exposure to the test agent at 10 × MIC caused significant biofilm death (>90%, even to eradication), though with strain-specific differences. Single administration of dendrimers or Tob at 10 × MIC was not toxic in Galleria mellonella wax-moth larvae over 96 hours. However, contrarily to Tob, dendrimers were not protective against systemic infection caused by P. aeruginosa in G. mellonella. Kinetics of P. aeruginosa growth in hemolymph showed that bacterial load increased over time in the presence of dendrimers.

Conclusion

Overall, our findings indicated that dG3KL and dTNS18 peptide dendrimers show in vitro activity comparable to Tob against both P. aeruginosa planktonic and biofilm cells at concentrations not toxic in vivo. Further studies are warranted to explore different dosages and to increase the bioavailability of the peptides to solve the lack of protective effect observed in G. mellonella larvae.