The avian chorioallantoic membrane in ovo--a useful model for bacterial invasion assays

Bridging the In Vitro to In Vivo gap: Using the Chick Embryo Model to Accelerate Nanoparticle Validation and Qualification for In Vivo studies

We postulate that nanoparticles (NPs) for use in therapeutic applications have largely not realized their clinical potential due to an overall inability to use in vitro results to predict NP performance in vivo. The avian embryo and associated chorioallantoic membrane (CAM) has emerged as an in vivo preclinical model that bridges the gap between in vitro and in vivo, enabling rapid screening of NP behavior under physiologically relevant conditions and providing a rapid, accessible, economical, and more ethical means of qualifying nanoparticles for in vivo use. The CAM is highly vascularized and mimics the diverging/converging vasculature of the liver, spleen, and lungs that serve as nanoparticle traps. Intravital imaging of fluorescently labeled NPs injected into the CAM vasculature enables immediate assessment and quantification of nano-bio interactions at the individual NP scale in any tissue of interest that is perfused with a microvasculature. In this review, we highlight how utilization of the avian embryo and its CAM as a preclinical model can be used to understand NP stability in blood and tissues, extravasation, biocompatibility, and NP distribution over time, thereby serving to identify a subset of NPs with the requisite stability and performance to introduce into rodent models and enabling the development of structure-property relationships and NP optimization without the sacrifice of large populations of mice or other rodents. We then review how the chicken embryo and CAM model systems have been used to accelerate the development of NP delivery and imaging agents by allowing direct visualization of targeted (active) and nontargeted (passive) NP binding, internalization, and cargo delivery to individual cells (of relevance for the treatment of leukemia and metastatic cancer) and cellular ensembles (e.g., cancer xenografts of interest for treatment or imaging of cancer tumors). We conclude by showcasing emerging techniques for the utilization of the CAM in future nano-bio studies.

Proteomic Analysis of Chicken Chorioallantoic Membrane (CAM) during Embryonic Development Provides Functional Insight

In oviparous animals, the egg contains all resources required for embryonic development. The chorioallantoic membrane (CAM) is a placenta-like structure produced by the embryo for acid-base balance, respiration, and calcium solubilization from the eggshell for bone mineralization. The CAM is a valuable in vivo model in cancer research for development of drug delivery systems and has been used to study tissue grafts, tumor metastasis, toxicology, angiogenesis, and assessment of bacterial invasion. However, the protein constituents involved in different CAM functions are poorly understood. Therefore, we have characterized the CAM proteome at two stages of development (ED12 and ED19) and assessed the contribution of the embryonic blood serum (EBS) proteome to identify CAM-unique proteins. LC/MS/MS-based proteomics allowed the identification of 1470, 1445, and 791 proteins in CAM (ED12), CAM (ED19), and EBS, respectively. In total, 1796 unique proteins were identified. Of these, 175 (ED12), 177 (ED19), and 105 (EBS) were specific to these stages/compartments. This study attributed specific CAM protein constituents to functions such as calcium ion transport, gas exchange, vasculature development, and chemical protection against invading pathogens. Defining the complex nature of the CAM proteome provides a crucial basis to expand its biomedical applications for pharmaceutical and cancer research.

Chorioallantoic Membrane Models of Various Avian Species: Differences and Applications

The chorioallantoic membrane model (CAM) of an avian embryo is used as an experimental model in various fields of research, including angiogenesis research and drug testing, xenografting and cancer research, and other scientific and commercial disciplines in microbiology, biochemistry, cosmetics, etc. It is a low-cost, low-maintenance, and well-available in vivo animal model that is non-sentient and can be used as an alternative for other mammal experimental models. It respects the principles of the "3R" rule (Replacement, Reduction, and Refinement)-conditions set out for scientific community providing an essential framework for conducting a more human animal research, which is also in line with constantly raising public awareness of welfare and the ethics related to the use of animal experimental models. In this review, we describe the chorioallantoic membrane of an avian embryo, focusing on its properties and development, its advantages and disadvantages as an experimental model, and the possibilities of its application in various fields of biological research. Since the most common chicken CAM model is already well known and described in many publications, we are particularly focusing on the advantages and application of less known avian species that are used for the CAM model-quail, turkey, and duck.

A shell-less hen's egg test as infection model to determine the biocompatibility and antimicrobial efficacy of drugs and drug formulations against Pseudomonas aeruginosa

A shell-less hen's egg based infection test with Pseudomonas aeruginosa was established to investigate the antimicrobial efficacy of drugs and drug formulations close to the in vivo situation. The test system using preincubated fertilized chicken eggs transferred in petri dishes was optimized with respect to the controlled local application of liquid materials and bacteria as well as the bacterial cultivation conditions. The applicability of the ex ovo infection model was confirmed with antimicrobial susceptibility tests using tobramycin, ciprofloxacin and meropenem. The validity of the ex ovo data was demonstrated by correlation with in vitro data of the CellTiter®-Blue and the microplate laser nephelometry assay. Real-time imaging of the progress of infection and the efficacy of the treatment could be realized by the MolecuLight i:X™ technique. Furthermore, in a proof-of-concept efficacy, biocompatibility and even the presence of irritants were determined side-by-side using commercial ophthalmics. In conclusion, this egg based infection model could bridge the gap between in vitro and in vivo models for the evaluation of antimicrobial susceptibility to reduce animal tests according to the 3R concept.

Towards the Development of a Novel Ex Ovo Model of Infection to Pre-Screen Biomaterials Intended for Treating Chronic Wounds

This communication reports preliminary data towards the development of a live ex vivo model of persistent infection that is based on the chick embryo chorioallantoic membrane (CAM), which can be used for pre-screening biomaterials with antimicrobial properties for their antimicrobial and angiogenic potential. Our results showed that it was possible to infect chicken embryos with Staphylococcus aureus, one of the main types of bacteria found in the persistent infection associated with chronic wounds, and maintain the embryos’ survival for up to 48 h. Survival of the embryos varied with the dose of bacteria inoculum and with the use and time of streptomycin application after infection. In infected yet viable embryos, the blood vessels network of the CAM was maintained with minimal disruption. Microbiological tests could confirm embryo infection, but quantification was difficult. By publishing these preliminary results, we hope that not only our group but others within the scientific community further this research towards the establishment of biomimetic and reproducible ex vivo models of persistent infection.

Induction of antiviral responses against avian influenza virus in embryonated chicken eggs with toll-like receptor ligands

Early responses against viruses, such as avian influenza virus (AIV), may be induced by Toll-like receptor (TLR) pathways. In the present study, an in ovo model was employed to study the antiviral activities of TLR ligands. It was hypothesized that administration of TLR ligands in ovo at the appropriate dose and time can reduce AIV titer in embryonated chicken eggs. Moreover, the study aimed to determine the mechanisms involved in the TLR-mediated antiviral responses in the chorioallantoic membrane (CAM). Embryonated eggs (10-14 day old) were treated with TLR2, 4, 7, and 21 ligands using different doses and times pre- and post-AIV infection. The results revealed that treatment of embryonated chicken eggs with TLR ligands reduced AIV replication. Further analysis showed that TLR ligands induced interferon (IFN)-γ and IFN stimulatory genes in the CAM, which may have played a role in the reduction of the AIV titer. The timing and dose of TLR ligands administration had significant impacts on the outcome of the treated eggs. In conclusion, the present study demonstrated that the in ovo route may be employed to determine the antiviral characteristics of TLR ligands against AIV.

Mucormycoses caused by Lichtheimia species

Mucormycoses are life-threatening infections with fungi from the order Mucorales (Mucoromycotina). Although mucormycoses are uncommon compared to other fungal infections, e.g. aspergillosis and candidiasis, the number of cases is increasing especially in immunocompromised patients. Lichtheimia (formerly Absidia) species represent the second to third most common cause of mucormycoses in Europe. This mini review presents current knowledge about taxonomy and clinical relevance of Lichtheimia species. In addition, clinical presentation and risk factors will be discussed. Proper animal infection models are essential for the understanding of the pathogenesis and the identification of virulence factors of fungal pathogens. To date, several animal models have been used to study Lichtheimia infection. A brief overview of the different models and the main conclusions from the infection experiments is summarised in this review.

Application of the chick embryo chorioallantoic membrane in neurosurgery disease

The chick embryo chorioallantoic membrane (CAM) is a highly vascularized extraembryonic membrane. Because of its ease of accessibility, extensive vascularization and immunodeficient environment, the CAM has been broadly used in the oncology, biology, pharmacy, and tissue regeneration research. The present review summarizes the application of the CAM in neurosurgery disease research. We focused on the use of the CAM as an assay for the research of glioma, vascular anomalies, Moyamoya Disease, and the blood-brain barrier.

Embryonated chicken eggs as an alternative model for mixed Clostridium perfringens and Eimeria tenella infection in chickens

The chorioallantoic membrane (CAM) of chicken embryo eggs is a suitable model for viral and bacterial infections. In the present study, a new approach for testing the pathogenesis and virulence of Clostridium perfringens and Eimeria tenella dual infections as a model using the CAM of embryonated chicken eggs was developed. For this purpose, 24 specific pathogen-free (SPF) embryonated chicken eggs were divided into four groups (n = 6) and designated group E, group CP, group CPE, and NC. Sporozoites of E. tenella (20,000 sporozoites) were inoculated into 10-day-old embryonated SPF chicken eggs (groups E and CPE) via allantoic sac route. At 15-day-old, eggs of groups CP and CPE were infected with 10 (4)  cfu C. perfringens via the same route. Assessment of pathogenicity was assessed using gross and histopathological lesions. Embryo mortality reached 17 % after mono-infection with C. perfringens and/or E. tenella and 50 % in the mixed-infected group. Lesions in the CAMs were most numerous and most severe in co-infected eggs (group CPE), reaching the maximum score of 3 in 50 % of the inoculated eggs (P < 0.01). In Eimeria spp.-infected eggs (group E), lesions of score were between 1 and 2. Mono-infection with C. perfringens did not lead to a significant occurrence of lesions. Histopathological investigations of the CAM revealed clusters of Gram-positive bacteria, infiltration with leukocytes, lymphocytes, and developmental stages of E. tenella in the co-infected group. These data suggest that embryonated eggs could be an in ovo model for studying the pathogenesis of mixed infection with Eimeria and C. perfringens.

Embryonated chicken eggs as alternative infection model for pathogenic fungi

Embryonated eggs have been used as infection models for decades in virology and bacteriology. However, they can also be used as an attractive alternative infection model for studying fungal pathogenesis. Here, we discuss some general aspects which need to be considered when working with embryonated eggs as infection models. Furthermore, we provide detailed protocols and technical tips for infection of embryonated eggs with Aspergillus fumigatus and Candida albicans via the chorioallantois membrane, as well as sampling methods for downstream analyses.

Embryonated eggs as an alternative infection model to investigate Aspergillus fumigatus virulence

Infection models are essential tools for studying microbial pathogenesis. Murine models are considered the "gold standard" for studying in vivo infections caused by Aspergillus species, such as A. fumigatus. Recently developed molecular protocols allow rapid construction of high numbers of fungal deletion mutants, and alternative infection models based on cell culture or invertebrates are widely used for screening such mutants to reduce the number of rodents in animal experiments. To bridge the gap between invertebrate models and mice, we have developed an alternative, low-cost, and easy-to-use infection model for Aspergillus species based on embryonated eggs. The outcome of infections in the egg model is dose and age dependent and highly reproducible. We show that the age of the embryos affects the susceptibility to A. fumigatus and that increased resistance coincides with altered chemokine production after infection. The progress of disease in the model can be monitored by using egg survival and histology. Based on pathological analyses, we hypothesize that invasion of embryonic membranes and blood vessels leads to embryonic death. Defined deletion mutant strains previously shown to be fully virulent or partially or strongly attenuated in a mouse model of bronchopulmonary aspergillosis showed comparable degrees of attenuation in the egg model. Addition of nutrients restored the reduced virulence of a mutant lacking a biosynthetic gene, and variations of the infectious route can be used to further analyze the role of distinct genes in our model. Our results suggest that embryonated eggs can be a very useful alternative infection model to study A. fumigatus virulence and pathogenicity.

Polyphasic study of plant- and clinic-associated Pantoea agglomerans strains reveals indistinguishable virulence potential

Pantoea species are ubiquitous in nature and occasionally associated with infections caused by contaminated clinical material. Hence, Pantoea agglomerans is considered as an opportunistic pathogen of humans. Since species of the genus Pantoea and closely related species of other Enterobacteriaceae genera are phenotypically very similar, many clinical isolates are misassigned into P. agglomerans based on the use of quick commercial-offered biochemical tests. Our objective was to find markers enabling discrimination between clinical and plant isolates and to assess their virulence potential. We characterized 27 Pantoea strains, including 8 P. agglomerans isolates of clinical, and 11 of plant origin by biochemical tests and genotyping, including analysis of 16S rDNA and gapA gene sequences, and pattern polymorphisms of ITS- and ERIC/REP-DNA. All data showed that no discrete evolution occurred between plant-associated and clinical P. agglomerans isolates. Based on the typing results, five clinical- and five plant-associated P. agglomerans strains representing the majority of clades were tested on a model plant and in embryonated eggs. On soybean plants P. agglomerans strains independent of their origin could develop stable epiphytic populations. Surprisingly, in the embryonated egg model there was no difference of virulence between clinical and vegetable P. agglomerans isolates. However, these strains were significantly less virulent than a phytopathogenic P. ananatis isolate. We suggest that, independent of their origin, all P. agglomerans strains might possess indistinguishable virulence potential.

Annexins as cell-type-specific markers in the developing chicken chorionallantoic membrane

Between day E8 and E12 of embryonic development, the chicken chorioallantoic membrane (CAM) undergoes massive structural rearrangement enabling calcium-uptake from the eggshell to supply the growing embryo. However, the contribution of the various cell types of the chorionic epithelium including the capillary covering (CC) cells, villus cavity (VC) cells, endothelial-like cells, and basal cells to this developmental program is largely unknown. In order to obtain markers for the different cell types in the chorionic epithelium, we determined the expression patterns of various calcium-binding annexins in the developing chicken CAM. By reverse transcription/polymerase chain reaction with primers deduced from nucleotide sequences available in various databases, the presence of annexin (anx)-1, anx-2, anx-5, and anx-6 was demonstrated at days E8 and E12. Quantitative immunoblotting with novel antibodies raised against the recombinant proteins revealed that anx-1 and anx-5 were significantly up-regulated at day E12, whereas anx-2 and anx-6 expression remained almost unchanged in comparison to levels at day E8. Immunohistochemistry of paraffin-embedded sections of E12 CAM revealed anx-1 in CC cells and VC cells. Anx-2 was localized in capillaries in the chorionic epithelium and in basal cells of the allantoic epithelium, whereas anx-6 was detected in basal cells or endothelial-like cells of the chorionic epithelium and in the media of larger vessels in the mesenchyme. A 2-day exposure of the CAM to a tumor cell spheroid resulted in strong proliferation of anx-1-expressing CC cells suggesting that these cells participate in the embryonic response to experimental intervention. Thus, annexins exhibit complementary expression patterns and represent appropriate cell markers for the further characterization of CAM development and the interpretation of results obtained when using CAM as an experimental model.

Detection and localization of avian alphaherpesviruses in embryonic tissues following in ovo exposure

We investigated whether chicken embryonic tissues are susceptible to infection with virulent Marek's disease virus (MDV). Groups of embryonic day (ED) 17 chicken embryos and 1-day-old chicks were compared for tissue sites of viral persistence of MDV and herpesvirus of turkeys (HVT) in lungs, thymuses, bursae of Fabricius and spleens. MDV DNA was detectable in the lungs and thymuses of embryos at 3 days post-inoculation (DPI) by in situ hybridization, while HVT DNA was only present in embryonic lungs. The target cells in lungs and thymuses appeared non-lymphoid and lymphoid, respectively. By 5 days post-inoculation, both viruses were detectable in all organs examined and persisted after hatch. Although MDV DNA was present in the embryo, there was little evidence of viral replication. These findings demonstrate the differences in pathogenesis of embryonic infection with MDV and HVT and provide evidence that the chicken embryo is susceptible to infection with a virulent avian herpesvirus.