Galleria mellonella as an infection model for Campylobacter jejuni virulence

Characterising phagocytes and measuring phagocytosis from live Galleria mellonella larvae

Over the last 20 years, the larva of the greater waxmoth, Galleria mellonella, has rapidly increased in popularity as an in vivo mammalian replacement model organism for the study of human pathogens. Experimental readouts of response to infection are most often limited to observing the melanization cascade and quantifying larval death and, whilst transcriptomic and proteomic approaches, and methods to determine microbial load are also used, a more comprehensive toolkit of profiling infection over time could transform the applicability of this model. As an invertebrate, Galleria harbour an innate immune system comprised of both humoral components and a repertoire of innate immune cells - termed haemocytes. Although information on subtypes of haemocytes exists, there are conflicting reports on their exact number and function. Flow cytometry has previously been used to assay Galleria haemocytes, but protocols include both centrifugation and fixation - physical methods which have the potential to affect haemocyte morphology prior to analysis. Here, we present a method for live haemocyte analysis by flow cytometry, revealing that Galleria haemocytes constitute only a single resolvable population, based on relative size or internal complexity. Using fluorescent zymosan particles, we extend our method to show that up to 80% of the Galleria haemocyte population display phagocytic capability. Finally, we demonstrate that the developed assay reliably replicates in vitro data, showing that cell wall β-1,3-glucan masking by Candida albicans subverts phagocytic responses. As such, our method provides a new tool with which to rapidly assess phagocytosis and understand live infection dynamics in Galleria.

Galleria mellonella larvae as an alternative model to determine the pathogenicity of avian pathogenic Escherichia coli

RESEARCH HIGHLIGHTS

Galleria mellonella larvae are a viable model for determining APEC pathogenicity.Larval disease score is the main variable for determining APEC pathogenicity.Response variables should be evaluated up to 24 h post-inoculation.

Multidrug resistance among uropathogenic clonal group A E. Coli isolates from Pakistani women with uncomplicated urinary tract infections

OBJECTIVE

Multi-drug resistance (MDR) has notably increased in community acquired uropathogens causing urinary tract infections (UTIs), predominantly Escherichia coli. Uropathogenic E. coli causes 80% of uncomplicated community acquired UTIs, particularly in pre-menopausal women. Considering this high prevalence and the potential to spread antimicrobial resistant genes, the current study was conducted to investigate the presence of clinically important strains of E. coli in Pakistani women having uncomplicated cystitis and pyelonephritis. Women belonging to low-income groups were exclusively included in the study. Seventy-four isolates from urine samples were processed, phylotyped, and screened for the presence of two Single Nucleotide Polymorphisms (SNPs) particularly associated with a clinically important clonal group A of E. coli (CgA) followed by antibiotic susceptibility testing and genome sequence analysis.

RESULTS

Phylogroup B2 was most prevalent in patients and 44% of isolates were positive for the presence of CgA specific SNPs in Fumarate hydratase and DNA gyrase subunit B genes. Antibiotic susceptibility testing showed widespread resistance to trimethoprim-sulfamethoxazole and extended-spectrum beta-lactamase production. The infection analysis revealed the phylogroup B2 to be more pathogenic as compared to the other groups. The genome sequence of E. coli strain U17 revealed genes encoding virulence, multidrug resistance, and host colonization mechanisms.

CONCLUSIONS

Our research findings not only validate the significant occurrence of multidrug-resistant clonal group A E. coli (CgA) in premenopausal Pakistani women suffering from cystitis and pyelonephritis but also reveal the presence of genes associated withvirulence, and drug efflux pumps. The detection of highly pathogenic, antimicrobial-resistant phylogroup B2 and CgA E. coli strains is likely to help in understanding the epidemiology of the pathogen and may ultimately help to reduce the impact of these strains on human health. Furthermore, the findings of this study will particularly help to reduce the prevalence of uncomplicated UTIs and the cost associated with their treatment in women belonging to low-income groups.

Effect of the polysaccharide capsule and its heptose on the resistance of Campylobacter jejuni to innate immune defenses

Campylobacter jejuni is a commensal in many animals but causes diarrhea in humans. Its polysaccharide capsule contributes to host colonization and virulence in a strain- and model-specific manner. We investigated if the capsule and its heptose are important for interactions of strain NCTC 11168 with various hosts and their innate immune defenses. We determined that they support bacterial survival in Drosophila melanogaster and enhance virulence in Galleria mellonella. We showed that the capsule had limited antiphagocytic activity in human and chicken macrophages, decreased adherence to chicken macrophages, and decreased intracellular survival in both macrophages. In contrast, the heptose increased uptake by chicken macrophages and supported adherence to human macrophages and survival within them. While the capsule triggered nitric oxide production in chicken macrophages, the heptose mitigated this and protected against nitrosative assault. Finally, the C. jejuni strain NCTC 11168 elicited strong cytokine production in both macrophages but quenched ROS production independently from capsule and heptose, and while the capsule and heptose did not protect against oxidative assault, they favored growth in biofilms under oxidative stress. This study shows that the wild-type capsule with its heptose is optimized to resist innate defenses in strain NCTC 11168 often via antagonistic effects of the capsule and its heptose.

Genomic characterization of Pseudomonas spp. on food: implications for spoilage, antimicrobial resistance and human infection

BACKGROUND

Pseudomonas species are common on food, but their contribution to the antimicrobial resistance gene (ARG) burden within food or as a source of clinical infection is unknown. Pseudomonas aeruginosa is an opportunistic pathogen responsible for a wide range of infections and is often hard to treat due to intrinsic and acquired ARGs commonly carried by this species. This study aimed to understand the potential role of Pseudomonas on food as a reservoir of ARGs and to assess the presence of potentially clinically significant Pseudomonas aeruginosa strains on food. To achieve this, we assessed the genetic relatedness (using whole genome sequencing) and virulence of food-derived isolates to those collected from humans.

RESULTS

A non-specific culturing approach for Pseudomonas recovered the bacterial genus from 28 of 32 (87.5%) retail food samples, although no P. aeruginosa was identified. The Pseudomonas species recovered were not clinically relevant, contained no ARGs and are likely associated with food spoilage. A specific culture method for P. aeruginosa resulted in the recovery of P. aeruginosa from 14 of 128 (11%) retail food samples; isolates contained between four and seven ARGs each and belonged to 16 sequence types (STs), four of which have been isolated from human infections. Food P. aeruginosa isolates from these STs demonstrated high similarity to human-derived isolates, differing by 41-312 single nucleotide polymorphisms (SNPs). There were diverse P. aeruginosa collected from the same food sample with distinct STs present on some samples and isolates belonging to the same ST differing by 19-67 SNPs. The Galleria mellonella infection model showed that 15 of 16 STs isolated from food displayed virulence between a low-virulence (PAO1) and a high virulence (PA14) control.

CONCLUSION

The most frequent Pseudomonas recovered from food examined in this study carried no ARGs and are more likely to play a role in food spoilage rather than infection. P. aeruginosa isolates likely to be able to cause human infections and with multidrug resistant genotypes are present on a relatively small but still substantial proportions of retail foods examined. Given the frequency of exposure, the potential contribution of food to the burden of P. aeruginosa infections in humans should be evaluated more closely.

Bacteriophage-mediated decolonization of Klebsiella pneumoniae in a novel Galleria mellonella gut colonization model with Enterobacteriaceae

Galleria mellonella larvae have emerged as an invertebrate model for investigating bacterial pathogenesis and potential therapies, addressing ethical concerns related to mammalian models. This model has the advantage of having a simple gut microbiome, which is suitable for gut colonization studies. Intestinal colonization by Enterobacteriaceae significantly contributes to the spread of antibiotic resistance. This study aimed to establish a novel Enterobacteriaceae gut colonization larval model and assess its suitability for evaluating distinct antimicrobial efficacies. Larvae were force-fed sequentially with bacterial doses of K. pneumoniae and E. coli at 0, 24, and 48 h, with survival monitoring at 24 h intervals. Bacterial counts were assessed after 48 h and 120 h of force-feeding. Successfully colonized larvae were subjected to one-time force feeding of a bacteriophage cocktail (107 PFU/larvae) or MIC-based meropenem and ciprofloxacin. The colonized bacterial load was quantified by CFU count. Three doses of 106 CFU/larvae resulted in stable gut colonization, independent of the K. pneumoniae or E. coli strain. Compared with the control, force-feeding of the bacteriophage reduced the colonization of the strain Kp 419614 by 5 log10 CFU/larvae, while antibiotic treatment led to a 3 log10 CFU/larval reduction. This novel G. mellonella model provides a valuable alternative for gut colonization studies, facilitating proof-of-concept investigations and potentially reducing or replacing follow-up experiments in vertebrate models.

Protective Effect of Procyanidin-Rich Grape Seed Extract against Gram-Negative Virulence Factors

Biofilm formation and lipopolysaccharide (LPS) are implicated in the pathogenesis of gastrointestinal (GI) diseases caused by Gram-negative bacteria. Grape seeds, wine industry by-products, have antioxidant and antimicrobial activity. In the present study, the protective effect of procyanidin-rich grape seed extract (prGSE), from unfermented pomace of Vitis vinifera L. cv Bellone, on bacterial LPS-induced oxidative stress and epithelial barrier integrity damage has been studied in a model of Caco-2 cells. The prGSE was characterized at the molecular level using HPLC and NMR. The in vitro activity of prGSE against formation of biofilm of Salmonella enterica subsp. enterica serovar Typhimurium and Escherichia coli was investigated. In vivo, prGSE activity using infected Galleria mellonella larvae has been evaluated. The results show that the prGSE, if administered with LPS, can significantly reduce the LPS-induced permeability alteration. Moreover, the ability of the extract to prevent Reactive Oxygen Species (ROS) production induced by the LPS treatment of Caco-2 cells was demonstrated. prGSE inhibited the biofilm formation of E. coli and S. Typhimurium. In terms of in vivo activity, an increase in survival of infected G. mellonella larvae after treatment with prGSE was demonstrated. In conclusion, grape seed extracts could be used to reduce GI damage caused by bacterial endotoxin and biofilms of Gram-negative bacteria.

Comparative pathology of experimental pulmonary tuberculosis in animal models

Research in human tuberculosis (TB) is limited by the availability of human tissues from patients, which is often altered by therapy and treatment. Thus, the use of animal models is a key tool in increasing our understanding of the pathogenesis, disease progression and preclinical evaluation of new therapies and vaccines. The granuloma is the hallmark lesion of pulmonary tuberculosis, regardless of the species or animal model used. Although animal models may not fully replicate all the histopathological characteristics observed in natural, human TB disease, each one brings its own attributes which enable researchers to answer specific questions regarding TB immunopathogenesis. This review delves into the pulmonary pathology induced by Mycobacterium tuberculosis complex (MTBC) bacteria in different animal models (non-human primates, rodents, guinea pigs, rabbits, cattle, goats, and others) and compares how they relate to the pulmonary disease described in humans. Although the described models have demonstrated some histopathological features in common with human pulmonary TB, these data should be considered carefully in the context of this disease. Further research is necessary to establish the most appropriate model for the study of TB, and to carry out a standard characterisation and score of pulmonary lesions.

The Use of Interdisciplinary Approaches to Understand the Biology of Campylobacter jejuni

Campylobacter jejuni is a bacterial pathogen recognised as a major cause of foodborne illness worldwide. While Campylobacter jejuni generally does not grow outside its host, it can survive outside of the host long enough to pose a health concern. This review presents an up-to-date description and evaluation of biological, mathematical, and statistical approaches used to understand the behaviour of this foodborne pathogen and suggests future avenues which can be explored. Specifically, the incorporation of mathematical modelling may aid the understanding of C. jejuni biofilm formation both outside and inside the host. Predictive studies may be improved by the introduction of more standardised protocols for assessments of disinfection methods and by assessment of novel physical disinfection strategies as well as assessment of the efficiency of plant extracts on C. jejuni eradication. A full description of the metabolic pathways of C. jejuni, which is needed for the successful application of metabolic models, is yet to be achieved. Finally, a shift from animal models (except for those that are a source of human campylobacteriosis) to human-specific data may be made possible due to recent technological advancements, and this may lead to more accurate predictions of human infections.

Lepidopteran insects: emerging model organisms to study infection by enteropathogens

The in vivo analysis of a pathogen is a critical step in gaining greater knowledge of pathogen biology and host-pathogen interactions. In the last two decades, there has been a notable rise in the number of studies on developing insects as a model for studying pathogens, which provides various benefits, such as ethical acceptability, relatively short life cycle, and cost-effective care and maintenance relative to routinely used rodent infection models. Furthermore, lepidopteran insects provide many advantages, such as easy handling and tissue extraction due to their large size relative to other invertebrate models, like Caenorhabditis elegans. Additionally, insects have an innate immune system that is highly analogous to vertebrates. In the present review, we discuss the components of the insect's larval immune system, which strengthens its usage as an alternative host, and present an updated overview of the research findings involving lepidopteran insects (Galleria mellonella, Manduca sexta, Bombyx mori, and Helicoverpa armigera) as infection models to study the virulence by enteropathogens due to the homology between insect and vertebrate gut.

Galleria mellonella as a Suitable Model of Bacterial Infection: Past, Present and Future

The increasing interest for Galleria mellonella larvae as an infection model is evidenced by the number of papers reporting its use, which increases exponentially since the early 2010s. This popularity was initially linked to limitation of conventional animal models due to financial, technical and ethical aspects. In comparison, alternative models (e.g. models using Caenorhabditis elegans, Drosophila melanogaster or G. mellonella) were cheap, simple to use and not limited by ethical regulation. Since then, similar results have been established with G. mellonella model comparatively to vertebrates, and it is more and more often used as a robust model per se, not only as an alternative to the murine model. This review attempts to summarize the current knowledge supporting the development of this model, both on immunological and microbiological aspects. For that, we focus on investigation of virulence and new therapies for the most important pathogenic bacteria. We also discuss points out directions for standardization, as well as recent advances and new perspectives for monitoring host-pathogen interactions.

The use of image analysis techniques for the study of muscle melanisation in sand flathead (Platycephalus bassensis)

Muscle melanisation in sand flathead is visible as black spots in the normally white flesh of fish. It is widespread in Tasmania, including at the Tamar Estuary, with increasing frequency of reporting by recreational fishers. The phenomenon is more prevalent in areas impacted by heavy metal pollution and has been linked to heavy metal accumulation. In this study, image processing software ImageJ was employed to study the phenomenon and to establish an objective rating system. A longitudinal profile plot was used to study the greying of the fillet. The degree of melanisation was rated based on the percentage surface area melanised on the surface and in transverse sections of fillets. A muscle melanisation scoring system for sand flathead was established based on visual interpretation using the macroscopic melanisation scoring criteria: melanisation scores 0 = <0.5%, 1 = 0.5-5%, 2 = 5-20%, and 3 = >20% (% = melanised surface area in proportion to the whole fillet). A refined image analysis technique was developed to quantify the percentage of melanised muscle surface area and the muscle melanisation scoring system was statistically validated. Sand flathead fillet with higher melanisation score was shown to be linked to increased intensity of greyness and greater numbers and size of black spots on the surface of fillets and within the flesh. The greying and black spots were primarily concentrated at the anterior region of fillet and around the dorsal vertebrae zone on transverse section of fillets. Overall, findings from this study established the use of image analysis techniques to validate visual inspection and to give a standardised and objective method to determine the degree of melanisation in sand flathead. As muscle melanisation appears to be linked to heavy metal pollution, the standardised scoring system would facilitate future research for environmental pollution and monitoring purposes.

Copper toxicity towards Campylobacter jejuni is enhanced by the nickel chelator dimethylglyoxime

The nickel (Ni)-chelator dimethylglyoxime (DMG) was found to be bacteriostatic towards Campylobacter jejuni. Supplementation of nickel to DMG-containing media restored bacterial growth, whereas supplementation of cobalt or zinc had no effect on the growth inhibition. Unexpectedly, the combination of millimolar levels of DMG with micromolar levels of copper (Cu) was bactericidal, an effect not seen in select Gram-negative pathogenic bacteria. Both the cytoplasmic Ni-binding chaperone SlyD and the twin arginine translocation (Tat)-dependent periplasmic copper oxidase CueO were found to play a central role in the Cu-DMG hypersensitivity phenotype. Ni-replete SlyD is needed for Tat-dependent CueO translocation to the periplasm, whereas Ni-depleted (DMG-treated) SlyD is unable to interact with the CueO Tat signal peptide, leading to mislocalization of CueO and increased copper sensitivity. In support of this model, C. jejuni ΔslyD and ΔcueO mutants were more sensitive to copper than the wild-type (WT); CueO was less abundant in the periplasmic fraction of ΔslyD or DMG-grown WT cells, compared to WT cells grown on plain medium; SlyD binds the CueO signal sequence peptide, with DMG inhibiting and nickel enhancing the binding, respectively. Injection of Cu-DMG into Galleria mellonella before C. jejuni inoculation significantly increased the insect survival rate compared to the control group. In chickens, oral administration of DMG or Cu-DMG decreased and even abolished C. jejuni colonization in some cases, compared to both water-only and Cu-only control groups. The latter finding is important, since campylobacteriosis is the leading bacterial foodborne infection, and chicken meat constitutes the major foodborne source.

Interplay between DsbA1, DsbA2 and C8J_1298 Periplasmic Oxidoreductases of Campylobacter jejuni and Their Impact on Bacterial Physiology and Pathogenesis

The bacterial proteins of the Dsb family catalyze the formation of disulfide bridges between cysteine residues that stabilize protein structures and ensure their proper functioning. Here, we report the detailed analysis of the Dsb pathway of Campylobacter jejuni. The oxidizing Dsb system of this pathogen is unique because it consists of two monomeric DsbAs (DsbA1 and DsbA2) and one dimeric bifunctional protein (C8J_1298). Previously, we showed that DsbA1 and C8J_1298 are redundant. Here, we unraveled the interaction between the two monomeric DsbAs by in vitro and in vivo experiments and by solving their structures and found that both monomeric DsbAs are dispensable proteins. Their structures confirmed that they are homologs of EcDsbL. The slight differences seen in the surface charge of the proteins do not affect the interaction with their redox partner. Comparative proteomics showed that several respiratory proteins, as well as periplasmic transport proteins, are targets of the Dsb system. Some of these, both donors and electron acceptors, are essential elements of the C. jejuni respiratory process under oxygen-limiting conditions in the host intestine. The data presented provide detailed information on the function of the C. jejuni Dsb system, identifying it as a potential target for novel antibacterial molecules.

The utilization of Blaptica dubia cockroaches as an in vivo model to test antibiotic efficacy

Insects are now well recognized as biologically relevant alternative hosts for dozens of mammalian pathogens and they are routinely used in microbial pathogenesis studies. Unfortunately, these models have yet to be incorporated into the drug development pipeline. The purpose of this work was to begin to evaluate the utility of orange spotted (Blaptica dubia) cockroaches in early antibiotic characterization. To determine whether these model hosts could exhibit mortality when infected with bacteria that are pathogenic to humans, we subjected B. dubia roaches to a range of infectious doses of Klebsiella pneumoniae, Escherichia coli, Staphylococcus aureus, and Acinetobacter baumannii to identify the medial lethal dose. These results showed that lethal disease did not develop following infection of high doses of S. aureus, and A. baumannii. However, cockroaches infected with E. coli and K. pneumoniae succumbed to infection (LD50s of 5.82 × 10⁶ and 2.58 × 10⁶ respectively) suggesting that this model may have limitations based on pathogen specificity. However, because these cockroaches were susceptible to infection from E. coli and K. pneumoniae, we used these bacterial strains for subsequent antibiotic characterization studies. These studies suggested that β-lactam antibiotic persistence and dose was associated with reduction of hemolymph bacterial burden. Moreover, our data indicated that the reduction of bacterial CFU was directly due to the drug activity. Altogether, this work suggests that the orange-spotted cockroach infection model provides an alternative in vivo setting from which antibiotic efficacy can be evaluated.

Cysteamine Inhibits Glycine Utilisation and Disrupts Virulence in Pseudomonas aeruginosa

Pseudomonas aeruginosa is a major opportunistic human pathogen which employs a myriad of virulence factors. In people with cystic fibrosis (CF) P. aeruginosa frequently colonises the lungs and becomes a chronic infection that evolves to become less virulent over time, but often adapts to favour persistence in the host with alginate-producing mucoid, slow-growing, and antibiotic resistant phenotypes emerging. Cysteamine is an endogenous aminothiol which has been shown to prevent biofilm formation, reduce phenazine production, and potentiate antibiotic activity against P. aeruginosa, and has been investigated in clinical trials as an adjunct therapy for pulmonary exacerbations of CF. Here we demonstrate (for the first time in a prokaryote) that cysteamine prevents glycine utilisation by P. aeruginosa in common with previously reported activity blocking the glycine cleavage system in human cells. Despite the clear inhibition of glycine metabolism, cysteamine also inhibits hydrogen cyanide (HCN) production by P. aeruginosa, suggesting a direct interference in the regulation of virulence factor synthesis. Cysteamine impaired chemotaxis, lowered pyocyanin, pyoverdine and exopolysaccharide production, and reduced the toxicity of P. aeruginosa secreted factors in a Galleria mellonella infection model. Thus, cysteamine has additional potent anti-virulence properties targeting P. aeruginosa, further supporting its therapeutic potential in CF and other infections.

Laser capture microdissection to study Bacillus cereus iron homeostasis gene expression during Galleria mellonella in vivo gut colonization

Bacillus cereus is a Gram-positive opportunistic pathogen closely related to the entomopathogen, Bacillus thuringiensis, both of which are involved in intestinal infections. Iron is an essential micronutrient for full growth and virulence of pathogens during infection. However, little is known about iron homeostasis during gut infection. Therefore, we aimed to assess the expression of B. cereus genes related to bacterial iron homeostasis, virulence and oxidative stress. The hypothesis is that the expression of such genes would vary between early and later stage colonization in correlation to gut cell damage. To perform the study, a germ-free Galleria mellonella model was set up in order to adapt the use of Laser-capture microdissection (LCM), to select precise areas in the gut lumen from frozen whole larval cryo-sections. Analyses were performed from alive larvae and the expression of targeted genes was assessed byspecific pre-amplification of mRNA followed by quantitative PCR. Firstly, the results reinforce the reliability of LCM, despite a low amount of bacterial RNA recovered. Secondly, bacterial genes involved in iron homeostasis are expressed in the lumen at both 3 and 16 hours post force-feeding. Thirdly, iron gene expression is slightly modulated during gut infection, and lastly, the mRNA of G. mellonella encoding for ferritin and transferrin iron storage and transport are recovered too. Therefore, iron homeostasis should play a role in B. cereus gut colonization. Furthermore, we demonstrate for the first time the value of using LCM for specific in situ gene expression analysis of extracellular bacteria in a whole animal.

Virulence assessment of enterohepatic Helicobacter species carried by dogs using the wax moth larvae Galleria mellonella as infection model

BACKGROUND

Enterohepatic species of the genus Helicobacter (EHH) are emerging pathogens that have been associated with gastrointestinal and hepatobiliary diseases in humans. However, studies on their pathogenicity are scarce. Galleria mellonella is a recently proposed model for the study of virulence in different pathogens, such as Campylobacter spp. and Helicobacter pylori. Despite this, its usefulness in EHH has not yet been evaluated. Therefore, we determined the pathogenic potential of different EHH species isolated from dogs in this infection model.

MATERIALS AND METHODS

Four species of EHH (H. bilis, H. canicola, H. canis, and 'H. winghamensis') isolated from fecal samples from domestic dogs were evaluated. Three strains of each species were inoculated in cohorts of G. mellonella at a concentration of 1 × 10⁷  CFU/mL. Survival curves were determined by the Kaplan-Meier method. In addition, the quantification of melanin, bacterial load in hemolymph, and histopathology were evaluated daily post-infection (pi).

RESULTS

G. mellonella larvae are susceptible to EHH infection, exhibiting intra- and inter-species variability. Melanin production became evident from 4 h pi and increased throughout the assay. All species were recovered from the hemolymph after 20 min pi; however, only H. canis could be recovered up to 48 h pi. Histopathology revealed cellular and humoral immune response, evidencing accumulation of hemocytes, nodulation, and melanin deposition in different tissues.

CONCLUSION

EHH species carried by dogs have considerable pathogenic potential, being H. canicola the species with the highest degree of virulence. Thus, G. mellonella is a useful model to assess virulence in these emerging pathogens.

Infected insect gut reveals differentially expressed proteins for cellular redox, metal resistance and secretion system in Yersinia enterocolitica-Helicoverpa armigera pathogenic model

OBJECTIVE

Mouse infection models are frequently used to study the host-pathogen interaction studies. However, due to several constraints, there is an urgent need for a simple, rapid, easy to handle, inexpensive, and ethically acceptable in vivo model system for studying the virulence of enteropathogens. Thus, the present study was performed to develop the larvae of Helicoverpa armigera as a rapid-inexpensive in vivo model system to evaluate the effect of Yersinia enterocolitica strain 8081 on its midgut via a label-free proteomic approach.

RESULTS

Helicoverpa armigera larvae fed with Yersinia enterocolitica strain 8081 manifested significant reduction in body weight and damage in midgut. On performing label-free proteomic study, secretory systems, putative hemolysin, and two-component system emerged as the main pathogenic proteins. Further, proteome comparison between control and Yersinia added diet-fed (YADF) insects revealed altered cytoskeletal proteins in response to increased melanization (via a prophenoloxidase cascade) and free radical generation. In concurrence, FTIR-spectroscopy, and histopathological and biochemical analysis confirmed gut damage in YADF insects. Finally, the proteome data suggests that the mechanism of infection and the host response in Y. enterocolitica-H. armigera system mimics Yersinia-mammalian gut interactions.

CONCLUSIONS

All data from current study collectively suggest that H. armigera larva can be considered as a potential in vivo model system for studying the enteropathogenic infection by Y. enterocolitica strain 8081.

Nutraceutical intervention protects against bacterial and chemical-induced gastrotoxicity in a non-mammalian model, Galleria mellonella

Preparations of the fungus Cordyceps sinensis and bovine colostrum are considered nutraceuticals due to their anti-inflammatory, repair and gut alimentation properties in mammalian models. To reduce the reliance on rodents in routine experimentation, we gauged the capacity of nutraceuticals to alleviate gastric damage in an insect surrogate, Galleria mellonella. Larvae were reared on standard or supplemented diets - 10% (w/w) colostrum, 10% (w/w) C. sinensis, or 5% + 5% each - prior to receiving an oral dose of the NSAID indomethacin (30 mg/kg) or challenged with the bacterial pathogen Campylobacter jejuni (1-3 x10⁶) via two inoculation routes. Insects reared on a cordyceps-supplemented diet proved most resistant to indomethacin-induced gut leakiness, and displayed stable health indices after C. jejuni challenge (~77% survival). Insects reared on a colostrum-supplemented diet also showed recalcitrance in the gut, but were more sensitive to C. jejuni when injected directly into the body cavity (50% survival). The nutraceutical blend yielded improved health outcomes when compared to the standard diet, but was not as effective as either nutraceutical alone. Our findings represent clear evidence that insects were more resistant to known chemical and microbial agitators when reared on nutraceutical-supplemented diets - toxicological endpoints that are shared with vertebrate studies.

Optimization of a Diet for the Greater Wax Moth (Lepidoptera: Pyralidae) Using Full Factorial and Mixture Design

Diet optimization is an important process to increase the efficiency of rearing insects and can be used to develop high-quality insects with specific fitness and life-history traits. Galleria mellonella (L.), the greater wax moth, is widely used in research, microbiology assays, as pet food, and host for biological control agents. Although artificial diets for G. mellonella have been researched and optimized for decades, preliminary tests indicated that the predominantly utilized G. mellonella diet could be improved to yield larger larvae with a short development time. We used a design of experiments (DOE) approach that incorporated multiple full factorial designs and a final mixture design to test the qualitative and quantitative effects of ingredients and their interactions on larval mass and survival. Analysis of 17 ingredient variations in 35 diet formulations yielded an optimized diet that supported high survival and 2.4-fold greater larval body mass than the standard rearing diet. This study demonstrates the importance and efficiency of statistical DOE in guiding the optimization of insect diets to improve traits that represent the quality and fitness of the reared insects.

Overview of rearing and testing conditions and a guide for optimizing Galleria mellonella breeding and use in the laboratory for scientific purposes

The greater wax moth Galleria mellonella is an increasingly popular and consolidated alternative infection model to assess microbial virulence and the effectiveness of antimicrobial compounds. The lack of G. mellonella suppliers aiming at scientific purposes and a lack of well-established protocols for raising and testing these animals may impact results and reproducibility between different laboratories. In this review, we discuss the state of the art of rearing the larvae in situ, providing an overview of breeding and testing conditions commonly used and their influence on larval health and experiments results, from setting up the environment, providing the ideal diet, understanding the effects of pretreatments, choosing the best testing conditions, to exploring the most from the results obtained. Meanwhile, we guide the reader through the most practical ways of dealing with G. mellonella to achieve successful experiments.

Comparison of the Pathogenic Potential of Campylobacter jejuni, C. upsaliensis and C. helveticus and Limitations of Using Larvae of Galleria mellonella as an Infection Model

Campylobacter enteritis in humans is primarily associated with C. jejuni/coli infection. Other species cause campylobacteriosis relatively infrequently; while this could be attributed to bias in diagnostic methods, the pathogenicity of non-jejuni/coli Campylobacter spp. such as C. upsaliensis and C. helveticus (isolated from dogs and cats) is uncertain. Galleria mellonella larvae are suitable models of the mammalian innate immune system and have been applied to C. jejuni studies. This study compared the pathogenicity of C. jejuni, C. upsaliensis, and C. helveticus isolates. Larvae inoculated with either C. upsaliensis or C. helveticus showed significantly higher survival than those inoculated with C. jejuni. All three Campylobacter species induced indistinguishable histopathological changes in the larvae. C. jejuni could be isolated from inoculated larvae up to eight days post-inoculation whereas C. upsaliensis and C. helveticus could only be isolated in the first two days. There was a significant variation in the hazard rate between batches of larvae, in Campylobacter strains, and in biological replicates as random effects, and in species and bacterial dose as fixed effects. The Galleria model is applicable to other Campylobacter spp. as well as C. jejuni, but may be subject to significant variation with all Campylobacter species. While C. upsaliensis and C. helveticus cannot be considered non-pathogenic, they are significantly less pathogenic than C. jejuni.

Novel Clinical Campylobacter jejuni Infection Models Based on Sensitization of Mice to Lipooligosaccharide, a Major Bacterial Factor Triggering Innate Immune Responses in Human Campylobacteriosis

: Human Campylobacter jejuni infections inducing campylobacteriosis including post-infectious sequelae such as Guillain-Barré syndrome and reactive arthritis are rising worldwide and progress into a global burden of high socioeconomic impact. Intestinal immunopathology underlying campylobacteriosis is a classical response of the innate immune system characterized by the accumulation of neutrophils and macrophages which cause tissue destruction, barrier defects and malabsorption leading to bloody diarrhea. Clinical studies revealed that enteritis and post-infectious morbidities of human C. jejuni infections are strongly dependent on the structure of pathogenic lipooligosaccharides (LOS) triggering the innate immune system via Toll-like-receptor (TLR)-4 signaling. Compared to humans, mice display an approximately 10,000 times weaker TLR-4 response and a pronounced colonization resistance (CR) against C. jejuni maintained by the murine gut microbiota. In consequence, investigations of campylobacteriosis have been hampered by the lack of experimental animal models. We here summarize recent progress made in the development of murine C. jejuni infection models that are based on the abolishment of CR by modulating the murine gut microbiota and by sensitization of mice to LOS. These advances support the major role of LOS driven innate immunity in pathogenesis of campylobacteriosis including post-infectious autoimmune diseases and promote the preclinical evaluation of novel pharmaceutical strategies for prophylaxis and treatment.

Candida albicans increases the pathogenicity of Staphylococcus aureus during polymicrobial infection of Galleria mellonella larvae

This study detailed the responses of Galleria mellonella larvae to disseminated infection caused by co-infection with Candida albicans and Staphylococcus aureus. Doses of C. albicans (1×10⁵ larva^-1) and S. aureus (1×10⁴ larva^-1) were non-lethal in mono-infection but when combined significantly (P<0.05) reduced larval survival at 24, 48 and 72 h relative to larvae receiving S. aureus (2×10⁴ larva^-1) alone. Co-infected larvae displayed a significantly higher density of S. aureus larva^-1 compared to larvae infected solely with S. aureus. Co-infection resulted in dissemination throughout the host and the appearance of large nodules. Co-infection of larvae with C. albicans and S. aureus (2×10⁴ larva^-1) resulted in an increase in the density of circulating haemocytes compared to that in larvae infected with only S. aureus. Proteomic analysis of co-infected larval haemolymph revealed increased abundance of proteins associated with immune responses to bacterial and fungal infection such as cecropin-A (+45.4-fold), recognition proteins [e.g. peptidoglycan-recognition protein LB (+14-fold)] and proteins associated with nodule formation [e.g. Hdd11 (+33.3-fold)]. A range of proteins were also decreased in abundance following co-infection, including apolipophorin (-62.4-fold), alpha-esterase 45 (-7.7-fold) and serine proteinase (-6.2-fold). Co-infection of larvae resulted in enhanced proliferation of S. aureus compared to mono-infection and an immune response showing many similarities to the innate immune response of mammals to infection. The utility of G. mellonella larvae for studying polymicrobial infection is highlighted.

Larva of greater wax moth Galleria mellonella is a suitable alternative host for the fish pathogen Francisella noatunensis subsp. orientalis

Background

Francisella noatunensis subsp. orientalis (Fno) is the etiological agent of francisellosis in cultured warm water fish, such as tilapia. Antibiotics are administered to treat the disease but a better understanding of Fno infection biology will inform improved treatment and prevention measures. However, studies with native hosts are costly and considerable benefits would derive from access to a practical alternative host. Here, larvae of Galleria mellonella were assessed for suitability to study Fno virulence.

Results

Larvae were killed by Fno in a dose-dependent manner but the insects could be rescued from lethal doses of bacteria by antibiotic therapy. Infection progression was assessed by histopathology (haematoxylin and eosin staining, Gram Twort and immunohistochemistry) and enumeration of bacteria recovered from the larval haemolymph on selective agar. Fno was phagocytosed and could survive intracellularly, which is consistent with observations in fish. Virulence of five Fno isolates showed strong agreement between G. mellonella and red Nile tilapia hosts.

Conclusions

This study shows that an alternative host, G. mellonella, can be applied to understand Fno infections, which will assist efforts to identify solutions to piscine francisellosis thus securing the livelihoods of tilapia farmers worldwide and ensuring the production of this important food source.

The Campylobacter jejuni Type VI Secretion System Enhances the Oxidative Stress Response and Host Colonization

The role of the Type VI secretion system (T6SS) in Campylobacter jejuni is poorly understood despite an increasing prevalence of the T6SS in recent C. jejuni isolates in humans and chickens. The T6SS is a contractile secretion machinery capable of delivering effectors that can play a role in host colonization and niche establishment. During host colonization, C. jejuni is exposed to oxidative stress in the host gastrointestinal tract, and in other bacteria the T6SS has been linked with the oxidative stress response. In this study, comparisons of whole genome sequences of a novel human isolate 488 with previously sequenced strains revealed a single highly conserved T6SS cluster shared between strains isolated from humans and chickens. The presence of a functional T6SS in the 488 wild-type strain is indicated by expression of T6SS genes and secretion of the effector TssD. Increased expression of oxidative stress response genes katA, sodB, and ahpC, and increased oxidative stress resistance in 488 wild-type strain suggest T6SS is associated with oxidative stress response. The role of the T6SS in interactions with host cells is explored using in vitro and in vivo models, and the presence of the T6SS is shown to increase C. jejuni cytotoxicity in the Galleria mellonella infection model. In biologically relevant models, the T6SS enhances C. jejuni interactions with and invasion of chicken primary intestinal cells and enhances the ability of C. jejuni to colonize chickens. This study demonstrates that the C. jejuni T6SS provides defense against oxidative stress and enhances host colonization, and highlights the importance of the T6SS during in vivo survival of T6SS-positive C. jejuni strains.

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.

Innate humoral immune defences in mammals and insects: The same, with differences ?

The insect immune response demonstrates many similarities to the innate immune response of mammals and a wide range of insects is now employed to assess the virulence of pathogens and produce results comparable to those obtained using mammals. Many of the humoral responses in insects and mammals are similar (e.g. insect transglutaminases and human clotting factor XIIIa) however a number show distinct differences. For example in mammals, melanization plays a role in protection from solar radiation and in skin and hair pigmentation. In contrast, insect melanization acts as a defence mechanism in which the proPO system is activated upon pathogen invasion. Human and insect antimicrobial peptides share distinct structural and functional similarities, insects produce the majority of their AMPs from the fat body while mammals rely on production locally at the site of infection by epithelial/mucosal cells. Understanding the structure and function of the insect immune system and the similarities with the innate immune response of mammals will increase the attractiveness of using insects as in vivo models for studying host – pathogen interactions.

Bacterial AB5 toxins inhibit the growth of gut bacteria by targeting ganglioside-like glycoconjugates

The AB₅ toxins cholera toxin (CT) from Vibrio cholerae and heat-labile enterotoxin (LT) from enterotoxigenic Escherichia coli are notorious for their roles in diarrheal disease, but their effect on other intestinal bacteria remains unexplored. Another foodborne pathogen, Campylobacter jejuni, can mimic the GM1 ganglioside receptor of CT and LT. Here we demonstrate that the toxin B-subunits (CTB and LTB) inhibit C. jejuni growth by binding to GM1-mimicking lipooligosaccharides and increasing permeability of the cell membrane. Furthermore, incubation of CTB or LTB with a C. jejuni isolate capable of altering its lipooligosaccharide structure selects for variants lacking the GM1 mimic. Examining the chicken GI tract with immunofluorescence microscopy demonstrates that GM1 reactive structures are abundant on epithelial cells and commensal bacteria, further emphasizing the relevance of this mimicry. Exposure of chickens to CTB or LTB causes shifts in the gut microbial composition, providing evidence for new toxin functions in bacterial gut competition.

Bacterial AB₅ toxins, such as cholera toxin, bind to oligosaccharides on the host cell surface and play key roles in the pathogenesis of diarrheal disease. Here, Patry et al. show that these toxins bind also to bacterial oligosaccharides and inhibit the growth of Campylobacter jejuni and gut commensal bacteria.

Proteomic Analysis of the Responses of Candida albicans during Infection of Galleria mellonella Larvae

This study assessed the development of disseminated candidiasis within Galleria mellonella larvae and characterized the proteomic responses of Candida albicans to larval hemolymph. Infection of larvae with an inoculum of 1 × 10⁶ yeast cells reduced larval viability 24 (53.33 ± 3.33%), 48 (33.33 ± 3.33%) and 72 (6.66 ± 3.33%) h post infection. C. albicans infection quickly disseminated from the site of inoculation and the presence of yeast and hyphal forms were found in nodules extracted from infected larvae at 6 and 24 h. A range of proteins secreted during infection of G. mellonella by C. albicans were detected in larval hemolymph and these were enriched for biological processes such as interaction with host and pathogenesis. The candicidal activity of hemolymph after immediate incubation of yeast cells resulted in a decrease in yeast cell viability (0.23 ± 0.03 × 10⁶ yeast cells/mL), p < 0.05) as compared to control (0.99 ± 0.01 × 10⁶ yeast cells/mL). C. albicans responded to incubation in hemolymph ex vivo by the induction of an oxidative stress response, a decrease in proteins associated with protein synthesis and an increase in glycolytic proteins. The results presented here indicate that C. albicans can overcome the fungicidal activity of hemolymph by altering protein synthesis and cellular respiration, and commence invasion and dissemination throughout the host.

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.

CapC, a Novel Autotransporter and Virulence Factor of Campylobacter jejuni

Campylobacter jejuni is recognized as an important causative agent of bacterial gastroenteritis in the developed world. Despite the identification of several factors contributing to infection, characterization of the virulence strategies employed by C. jejuni remains a significant challenge. Bacterial autotransporter proteins are a major class of secretory proteins in Gram-negative bacteria, and notably, many autotransporter proteins contribute to bacterial virulence. The aim of this study was to characterize the C. jejuni 81116 C8J_1278 gene (capC), predicted to encode an autotransporter protein, and examine the contribution of this factor to virulence of C. jejuni The predicted CapC protein has a number of features that are consistent with autotransporters, including the N-terminal signal sequence and the C-terminal β-barrel domain and was determined to localize to the outer membrane. Inactivation of the capC gene in C. jejuni 81116 and C. jejuni M1 resulted in reduced insecticidal activity in Galleria mellonella larvae. Furthermore, C. jejuni capC mutants displayed significantly reduced adherence to and invasion of nonpolarized, partially differentiated Caco-2 and T84 intestinal epithelial cells. Gentamicin treatment showed that the reduced invasion of the capC mutant is primarily caused by reduced adherence to intestinal epithelial cells, not by reduced invasion capability. C. jejuni capC mutants caused reduced interleukin 8 (IL-8) secretion from intestinal epithelial cells and elicited a significantly diminished immune reaction in Galleria larvae, indicating that CapC functions as an immunogen. In conclusion, CapC is a new virulence determinant of C. jejuni that contributes to the integral infection process of adhesion to human intestinal epithelial cells.IMPORTANCECampylobacter jejuni is a major causative agent of human gastroenteritis, making this zoonotic pathogen of significant importance to human and veterinary public health worldwide. The mechanisms by which C. jejuni interacts with intestinal epithelial cells and causes disease are still poorly understood due, in part, to the heterogeneity of C. jejuni infection biology. Given the importance of C. jejuni to public health, the need to characterize novel and existing virulence mechanisms is apparent. The significance of our research is in demonstrating the role of CapC, a novel virulence factor in C. jejuni that contributes to adhesion and invasion of the intestinal epithelium, thereby in part, addressing the dearth of knowledge concerning the factors involved in Campylobacter pathogenesis and the variation observed in the severity of human infection.

Identification of temperature regulated factors of Campylobacter jejuni and their potential roles in virulence

Campylobacter jejuni is the major cause of bacterial gastroenteritis in man, while it is generally regarded as a commensal of the avian gut. Consumption and handling of contaminated poultry meat products are major risk factors for human infection. The body temperature in man (37 °C) and chickens (42 °C) differ markedly, and differential gene regulation and protein expression at different temperatures may in part explain the behaviour in the two hosts. We performed proteomics analyses with C. jejuni cells grown at 37 °C and 42 °C. Time-of-flight mass spectrometry (Q-Tof) analysis was carried out after samples were digested with the Filter-Aided Sample Preparation (FASP) method and peptides were fractionated by strong anion exchanges. Differentially regulated proteins were identified by Mascot and Scaffold analyses. Triple quadrupole (QQQ) mass spectrometer analysis confirmed that a total of 33 proteins were differentially regulated between 37 °C and 42 °C. Several upregulated proteins were selected for their corresponding gene knock-out mutants to be tested for their virulence in the Galleria mellonella model. To correlate with other tissue/animal models, the GADH mutant was selected for its reduced ability to colonize chickens. At 37 °C, the mutants of outer membrane protein Omp50 and Chaperone GroEL significantly increased virulence; while at 42 °C, the mutants of YceI, Omp50, and GADH reduced virulence against Galleria mellonella compared with the wild type strains. The results of current and previous studies indicate that GADH is a virulent factor in G. mellonella and a colonization factor in chickens. The workflow of this study may prove a new way to identify stress related virulent factors. The implications of these findings are discussed for pathogenesis in the model and other hosts.

Galleria mellonella is low cost and suitable surrogate host for studying virulence of human pathogenic Vibrio cholerae

Vibrio cholerae causes a severe diarrheal disease affecting millions of people worldwide, particularly in low income countries. V. cholerae successfully persist in aquatic environment and its pathogenic strains results in sever enteric disease in humans. This dual life style contributes towards its better survival and persistence inside host gut and in the environment. Alternative animal replacement models are of great value in studying host-pathogen interaction and for quick screening of various pathogenic strains. One such model is Galleria mellonella, a wax moth which has a complex innate immune system and here we investigate its suitability as a model for clinical human isolates of O1 El TOR, Ogawa serotype belonging to two genetically distinct subclades found in Pakistan (PSC-1 and PSC-2). We demonstrate that the PSC-2 strain D59 frequently isolated from inland areas, was more virulent than PSC-1 strain K7 mainly isolated from coastal areas (p=0.0001). In addition, we compared the relative biofilm capability of the representative strains as indicators of their survival and persistence in the environment and K7 showed enhanced biofilm forming capabilities (p=0.004). Finally we present the annotated genomes of the strains D59 and K7, and compared them with the reference strain N16961.

The Galleria mellonella larvae as an in vivo model for evaluation of Shigella virulence

Shigella spp. causing bacterial diarrhea and dysentery are human enteroinvasive bacterial pathogens that are orally transmitted through contaminated food and water and cause bacillary dysentery. Although natural Shigella infections are restricted to humans and primates, several smaller animal models are used to analyze individual steps in pathogenesis. No animal model fully duplicates the human response and sustaining the models requires expensive animals, costly maintenance of animal facilities, veterinary services and approved animal protocols. This study proposes the development of the caterpillar larvae of Galleria mellonella as a simple, inexpensive, informative, and rapid in-vivo model for evaluating virulence and the interaction of Shigella with cells of the insect innate immunity. Virulent Shigella injected through the forelegs causes larvae death. The mortality rates were dependent on the Shigella strain, the infectious dose, and the presence of the virulence plasmid. Wild-type S. flexneri 2a, persisted and replicated within the larvae, resulting in haemocyte cell death, whereas plasmid-cured mutants were rapidly cleared. Histology of the infected larvae in conjunction with fluorescence, immunofluorescence, and transmission electron microscopy indicate that S. flexneri reside within a vacuole of the insect haemocytes that ultrastructurally resembles vacuoles described in studies with mouse and human macrophage cell lines. Some of these bacteria-laden vacuoles had double-membranes characteristic of autophagosomes. These results suggest that G. mellonella larvae can be used as an easy-to-use animal model to understand Shigella pathogenesis that requires none of the time and labor-consuming procedures typical of other systems.

Using Galleria mellonella as an Infection Model for Campylobacter jejuni Pathogenesis

Nonmammalian model systems of infection have been employed recently to study bacterial virulence. For instance, Galleria mellonella (the greater wax moth) has been shown to be susceptible to infection by many bacterial pathogens including the enteric pathogen Campylobacter jejuni. In contrast to the traditional animal models for C. jejuni such as the chick colonization model and ferret diarrheal model, the Galleria mellonella infection model has the advantages of lower cost, ease of use and no animal breeding is required. However, injecting the larvae with bacteria requires care to avoid killing of larvae, which could lead to misleading results. Here, we describe the infection of G. mellonella larvae by C. jejuni and how to record/interpret results.

Corynebacterium ulcerans, an emerging human pathogen

While formerly known infections of Corynebacterium ulcerans are rare and mainly associated with contact to infected cattle, C. ulcerans has become an emerging pathogen today. In Western Europe, cases of respiratory diphtheria caused by C. ulcerans have been reported more often than infections by Corynebacterium diphtheria, while systemic infections are also increasingly reported. Little is known about factors that contribute to host colonization and virulence of this zoonotic pathogen. Research in this field has received new impetus by the publication of several C. ulcerans genome sequences in the past years. This review gives a comprehensive overview of the basic knowledge of C. ulcerans, as well as the recent advances made in the analysis of putative virulence factors.

Insights into Campylobacter jejuni colonization and enteritis using a novel infant rabbit model

A lack of relevant disease models for Campylobacter jejuni has long been an obstacle to research into this common enteric pathogen. Here we used an infant rabbit to study C. jejuni infection, which enables us to define several previously unknown but key features of the organism. C. jejuni is capable of systemic invasion in the rabbit, and developed a diarrhea symptom that mimicked that observed in many human campylobacteriosis. The large intestine was the most consistently colonized site and produced intestinal inflammation, where specific cytokines were induced. Genes preferentially expressed during C. jejuni infection were screened, and acs, cj1385, cj0259 seem to be responsible for C. jejuni invasion. Our results demonstrates that the infant rabbit can be used as an alternative experimental model for the study of diarrheagenic Campylobacter species and will be useful in exploring the pathogenesis of other related pathogens.

All Yersinia enterocolitica are pathogenic: virulence of phylogroup 1 Y. enterocolitica in a Galleria mellonella infection model

Yersinia enterocolitica is a zoonotic pathogen and a common cause of gastroenteritis in humans. The species is composed of six diverse phylogroups, of which strains of phylogroup 1 are considered non-pathogenic to mammals due to the lack of the major virulence plasmid pYV, and their lack of virulence in a mouse infection model. In the present report we present data examining the pathogenicity of strains of Y. enterocolitica across all six phylogroups in a Galleria mellonellla model. We have demonstrated that in this model strains of phylogroup 1 exhibit severe pathogenesis with a lethal dose of as low as 10 c.f.u., that this virulence is an active process and that flagella play a major role in the virulence phenotype. We have also demonstrated that the complete lack of virulence in Galleria of the mammalian pathogenic phylogroups is not due to carriage of the pYV virulence plasmid. Our data suggest that all Y. enterocolitica can be pathogenic, which may be a reflection of the true natural habitat of the species, and that we may need to reconsider the eco-evo perspective of this important bacterial species.

Role of Indole Production on Virulence of Vibrio cholerae Using Galleria mellonella Larvae Model

Cell to cell communication facilitated by chemical signals plays crucial roles in regulating various cellular functions in bacteria. Indole, one such signaling molecule has been demonstrated to control various bacterial phenotypes such as biofilm formation and virulence in diverse bacteria including Vibrio cholerae. The present study explores some key factors involved in indole production and the subsequent pathogenesis of V. cholerae. Indole production was higher at 37 °C than at 30 °C, although the growth at 37 °C was slightly higher. A positive correlation was observed between indole production and biofilm formation in V. cholerae. Maximum indole production was detected at pH 7. There was no significant difference in indole production between clinical and environmental V. cholerae isolates, although indole production in one environmental isolate was significantly different. Both growth and indole production showed relevant changes with differences in salinity. An indole negative mutant strain was constructed using transposon mutagenesis and the direct effect of indole on the virulence of V. cholerae was evaluated using Galleria mellonella larvae model. Comparison to the wild type strain, the mutant significantly reduced the mortality of G. mellonella larvae which regained its virulence after complementation with exogenous indole. A gene involved in indole production and the virulence of V. cholerae was identified.

Virulence Characterisation of Salmonella enterica Isolates of Differing Antimicrobial Resistance Recovered from UK Livestock and Imported Meat Samples

Salmonella enterica is a foodborne zoonotic pathogen of significant public health concern. We have characterized the virulence and antimicrobial resistance gene content of 95 Salmonella isolates from 11 serovars by DNA microarray recovered from UK livestock or imported meat. Genes encoding resistance to sulphonamides (sul1, sul2), tetracycline [tet(A), tet(B)], streptomycin (strA, strB), aminoglycoside (aadA1, aadA2), beta-lactam (bla TEM), and trimethoprim (dfrA17) were common. Virulence gene content differed between serovars; S. Typhimurium formed two subclades based on virulence plasmid presence. Thirteen isolates were selected by their virulence profile for pathotyping using the Galleria mellonella pathogenesis model. Infection with a chicken invasive S. Enteritidis or S. Gallinarum isolate, a multidrug resistant S. Kentucky, or a S. Typhimurium DT104 isolate resulted in high mortality of the larvae; notably presence of the virulence plasmid in S. Typhimurium was not associated with increased larvae mortality. Histopathological examination showed that infection caused severe damage to the Galleria gut structure. Enumeration of intracellular bacteria in the larvae 24 h post-infection showed increases of up to 7 log above the initial inoculum and transmission electron microscopy (TEM) showed bacterial replication in the haemolymph. TEM also revealed the presence of vacuoles containing bacteria in the haemocytes, similar to Salmonella containing vacuoles observed in mammalian macrophages; although there was no evidence from our work of bacterial replication within vacuoles. This work shows that microarrays can be used for rapid virulence genotyping of S. enterica and that the Galleria animal model replicates some aspects of Salmonella infection in mammals. These procedures can be used to help inform on the pathogenicity of isolates that may be antibiotic resistant and have scope to aid the assessment of their potential public and animal health risk.

Utility of Greater Wax Moth Larva (Galleria mellonella) for Evaluating the Toxicity and Efficacy of New Antimicrobial Agents

There is an urgent need for new antimicrobial agents to combat infections caused by drug-resistant pathogens. Once a compound is shown to be effective in vitro, it is necessary to evaluate its efficacy in an animal infection model. Typically, this is achieved using a mammalian model, but such experiments are costly, time consuming, and require full ethical consideration. Hence, cheaper and ethically more acceptable invertebrate models of infection have been introduced, including the larvae of the greater wax moth Galleria mellonella. Invertebrates have an immune system that is functionally similar to the innate immune system of mammals, and often identical virulence and pathogenicity factors are used by human pathogenic microbes to infect wax moth larvae and mammals. Moreover, the virulence of many human pathogens is comparable in wax moth larvae and mammals. Using key examples from the literature, this chapter highlights the benefits of using the wax moth larva model to provide a rapid, inexpensive, and reliable evaluation of the toxicity and efficacy of new antimicrobial agents in vivo and prior to the use of more expensive mammalian models. This simple insect model can bridge the gap between in vitro studies and mammalian experimentation by screening out compounds with a low likelihood of success, while providing greater justification for further studies in mammalian systems. Thus, broader implementation of the wax moth larva model into anti-infective drug discovery and development programs could reduce the use of mammals during preclinical assessments and the overall cost of drug development.

Epidemiology of Campylobacter jejuni infections in Sweden, November 2011-October 2012: is the severity of infection associated with C. jejuni sequence type?

BACKGROUND

Campylobacter jejuni is among the most frequent causes of bacterial gastroenteritis in Europe. Over 8,000 C. jejuni multilocus sequence typing sequence types (STs) have been described; ST-21 and ST-45 have been identified as the most frequent types in all human studies so far. In contrast to other STs, ST-22 has been associated with the Guillain-Barré syndrome and ST-677 was recently linked to severe systemic infections in Finland. We investigated risk factors associated with hospitalisation in individuals with C. jejuni infections acquired in Sweden.

METHODS

A total of 1,075 individuals with domestically acquired C. jejuni infection diagnosed between November 2011 and October 2012 in Sweden were included in this retrospective cohort study. Typing data for the isolates as well as clinical data including hospitalisation dates and diagnosis codes for individuals with C. jejuni infection were obtained. Factors associated with hospitalisation and length of hospitalisation were investigated by multivariable analysis.

RESULTS

A total of 289 individuals were hospitalised due to C. jejuni infection (26.8%); those with co-morbidities were over 14 times more likely to become hospitalised than those without (odds ratio [OR]: 14.39, 95% confidence interval [CI]: 6.84-30.26). Those with underlying co-morbidities were also hospitalised longer than those without (4.22 days vs. 2.86 days), although this was not statistically significant. C. jejuni ST-257 (OR: 2.38; CI: 1.08-5.23), but not ST-22 or ST-677, was significantly associated with hospitalisation.

CONCLUSION

ST-677 was not associated with increased hospitalisation or a longer hospital stay in our study whilst ST-257 was. However, individuals with C. jejuni infections were generally more frequently hospitalised than previously demonstrated; this requires further consideration including possible targeted interventions.

The Two-Component System CpxRA Negatively Regulates the Locus of Enterocyte Effacement of Enterohemorrhagic Escherichia coli Involving σ(32) and Lon protease

Enterohemorrhagic Escherichia coli (EHEC) is a significant cause of serious human gastrointestinal disease worldwide. EHEC strains contain a pathogenicity island called the locus of enterocyte effacement (LEE), which encodes virulence factors responsible for damaging the gut mucosa. The Cpx envelope stress response of E. coli is controlled by a two-component system (TCS) consisting of a sensor histidine kinase (CpxA) and a cytoplasmic response regulator (CpxR). In this study, we investigated the role of CpxRA in the expression of LEE-encoded virulence factors of EHEC. We found that a mutation in cpxA significantly affected adherence of EHEC to human epithelial cells. Analysis of this mutant revealed the presence of high levels of CpxR which repressed transcription of grlA and ler, the main positive virulence regulators of the LEE, and influenced negatively the production of the type 3 secretion system–associated EspABD translocator proteins. It is known that CpxR activates rpoH (Sigma factor 32), which in turns activates transcription of the lon protease gene. We found that transcription levels of ler and grlA were significantly increased in the lon and cpxA lon mutants suggesting that lon is involved in down-regulating LEE genes. In addition, the Galleria mellonella model of infection was used to analyze the effect of the loss of the cpx and lon genes in EHEC's ability to kill the larvae. We found that the cpxA mutant was significantly deficient at killing the larvae however, the cpxA lon mutant which overexpresses LEE genes in vitro, was unable to kill the larvae, suggesting that virulence in the G. mellonella model is T3SS independent and that CpxA modulates virulence through a yet unknown EHEC-specific factor. Our data provides new insights and broadens our scope into the complex regulatory network of the LEE in which the CpxA sensor kinase plays an important role in a cascade involving both global and virulence regulators.

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

Galleria mellonella (greater wax moth or honeycomb moth) has been introduced as an alternative model to study microbial infections. G. mellonella larvae can be easily and inexpensively obtained in large numbers and are simple to use as they don't require special lab equipment. There are no ethical constraints and their short life cycle makes them ideal for large-scale studies. Although insects lack an adaptive immune response, their innate immune response shows remarkable similarities with the immune response in vertebrates. This review gives a current update of what is known about the immune system of G. mellonella and provides an extensive overview of how G. mellonella is used to study the virulence of Gram-positive and Gram-negative bacteria. In addition, the use of G. mellonella to evaluate the efficacy of antimicrobial agents and experimental phage therapy are also discussed. The review concludes with a critical assessment of the current limitatons of G. mellonella infection models.

Genetic import and phenotype specific alleles associated with hyper-invasion in Campylobacter jejuni

BACKGROUND

Campylobacter jejuni is a major zoonotic pathogen, causing gastroenteritis in humans. Invasion is an important pathogenesis trait by which C. jejuni causes disease. Here we report the genomic analysis of 134 strains to identify traits unique to hyperinvasive isolates.

METHODS

A total of 134 C. jejuni genomes were used to create a phylogenetic tree to position the hyperinvasive strains. Comparative genomics lead to the identification of mosaic capsule regions. A pan genome approach led to the discovery of unique loci, or loci with unique alleles, to the hyperinvasive strains.

RESULTS

Phylogenetic analysis showed that the hyper-invasive phenotype is a generalist trait. Despite the fact that hyperinvasive strains are only distantly related based on the whole genome phylogeny, they all possess genes within the capsule region with high identity to capsule genes from C. jejuni subsp. doylei and C. lari. In addition there were genes unique to the hyper-invasive strains with identity to non-C. jejuni genes, as well as allelic variants of mainly pathogenesis related genes already known in the other C. jejuni. In particular, the sequence of flagella genes, flgD-E and flgL were highly conserved amongst the hyper-invasive strains and divergent from sequences in other C. jejuni. A novel cytolethal distending toxin (cdt) operon was also identified as present in all hyper-invasive strains in addition to the classic cdt operon present in other C. jejuni.

CONCLUSIONS

Overall, the hyper-invasive phenotype is strongly linked to the presence of orthologous genes from other Campylobacter species in their genomes, notably within the capsule region, in addition to the observed association with unique allelic variants in flagellar genes and the secondary cdt operon which is unlikely under random sharing of accessory alleles in separate lineages.

Heterogeneity in the Infection Biology of Campylobacter jejuni Isolates in Three Infection Models Reveals an Invasive and Virulent Phenotype in a ST21 Isolate from Poultry

Although Campylobacter is the leading cause of bacterial foodborne gastroenteritis in the world and the importance of poultry as a source of infection is well understood we know relatively little about its infection biology in the broiler chicken. Much of what we know about the biology of Campylobacter jejuni is based on infection of inbred or SPF laboratory lines of chickens with a small number of isolates used in most laboratory studies. Recently we have shown that both the host response and microbial ecology of C. jejuni in the broiler chicken varies with both the host-type and significantly between C. jejuni isolates. Here we describe heterogeneity in infection within a panel of C. jejuni isolates in two broiler chicken breeds, human intestinal epithelial cells and the Galleria insect model of virulence. All C. jejuni isolates colonised the chicken caeca, though colonisation of other parts of the gastrointestinal tract varied between isolates. Extra-intestinal spread to the liver varied between isolates and bird breed but a poultry isolate 13126 (sequence type 21) showed the greatest levels of extra-intestinal spread to the liver in both broiler breeds with over 70% of birds of the fast growing breed and 50% of the slower growing breed having C. jejuni in their livers. Crucially 13126 is significantly more invasive than other isolates in human intestinal epithelial cells and gave the highest mortality in the Galleria infection model. Taken together our findings suggest that not only is there considerable heterogeneity in the infection biology of C. jejuni in avian, mammalian and alternative models, but that some isolates have an invasive and virulent phenotype. Isolates with an invasive phenotype would pose a significant risk and increased difficulty in control in chicken production and coupled with the virulent phenotype seen in 13126 could be an increased risk to public health.

PerR controls oxidative stress defence and aerotolerance but not motility-associated phenotypes of Campylobacter jejuni

The foodborne bacterial pathogen Campylobacter jejuni is an obligate microaerophile that is exposed to atmospheric oxygen during transmission through the food chain. Survival under aerobic conditions requires the concerted control of oxidative stress systems, which in C. jejuni are intimately connected with iron metabolism via the PerR and Fur regulatory proteins. Here, we have characterized the roles of C. jejuni PerR in oxidative stress and motility phenotypes, and its regulon at the level of transcription, protein expression and promoter interactions. Insertional inactivation of perR in the C. jejuni reference strains NCTC 11168, 81-176 and 81116 did not result in any growth deficiencies, but strongly increased survival in atmospheric oxygen conditions, and allowed growth around filter discs infused with up to 30 % H2O2 (8.8 M). Expression of catalase, alkyl hydroperoxide reductase, thioredoxin reductase and the Rrc desulforubrerythrin was increased in the perR mutant, and this was mediated at the transcriptional level as shown by electrophoretic mobility shift assays of the katA, ahpC and trxB promoters using purified PerR. Differential RNA-sequencing analysis of a fur perR mutant allowed the identification of eight previously unknown transcription start sites of genes controlled by Fur and/or PerR. Finally, inactivation of perR in C. jejuni did not result in reduced motility, and did not reduce killing of Galleria melonella wax moth larvae. In conclusion, PerR plays an important role in controlling oxidative stress resistance and aerobic survival of C. jejuni, but this role does not extend into control of motility and associated phenotypes.