Title (eng)
Microbial ecology and infection biology of avian Escherichia coli in chickens and turkeys
Author
Mohamed Kamal Abdelhamid
Assessor
Catherine Logue
Assessor
Joachim Spergser
Degree supervisor
Michael Hess
Degree supervisor
Adel Abbas Shalaby
Degree supervisor
Surya Paudel
Description (eng)
PhD thesis - University of Veterinary Medicine Vienna - 2023 The full text is only available to university members. Please log in!
Abstract (eng)
Avian colibacillosis is a complex and multifaceted disease that can appear in various forms, with the systemic form being particularly common in the field. This disease not only causes significant economic losses in the poultry industry, but also has a largely unresolved pathogenesis and potentially impacts on zoonosis and food safety. In the present thesis, it was aimed to investigate the dynamics of intestinal Escherichia coli (E. coli) within the gastrointestinal tracts of chickens and turkeys across different clinical scenarios. Additionally, the pathogenesis of colibacillosis was deeply explored applying selected in vivo infection models mimicking natural infection and conducting extensive laboratory investigations, including new techniques and novel approaches. In the first experimental trial, interaction of E. coli with Histomonas meleagridis (H. meleagridis), a protozoal parasite that affects the intestinal integrity was investigated in commercial laying chickens. Birds were orally infected with bioluminescent-labelled avian pathogenic Escherichia coli and co-infected with or without a virulent strain of H. meleagridis. Infected birds, along with negative controls, were sequentially necropsied at 7, 10, 14, and 28 days post infection (dpi) and samples for histopathology, bacterial quantification of lux-tagged E. coli, and 16S rRNA gene amplicon sequencing for the caecal and blood microbiota were collected. The results showed that only birds co-infected with Avian pathogenic Escherichia coli (APEC) and H. meleagridis showed gut lesions, pronounced microscopic lesions in systemic organs and reduced body weight. This was accompanied by a substantial impact on the caecal microbial population, which coincided with the severity of caecal pathology. Overall, both bacterial counts and relative abundances of Escherichia coli were higher, and commensal beneficial bacteria such as Lactobacillus were lower in co-infected birds. Furthermore, severe pathology and higher APEC colonization in the co-infected birds were associated with increased E. coli penetration into the caecal wall. Notably, the shared amplicon sequencing variants found in the cecum and blood of co-infected birds predominantly belonged to potential pathogenic bacteria, whereas beneficial bacteria were primarily observed in the negative control birds. In conclusion, the findings suggest that the caecal destruction induced by H. meleagridis enhanced gut colonization of APEC and E. coli penetration into caecal tissues, could potentiate the occurrence of colibacillosis in laying chickens during histomonosis, albeit microbiota in the blood did not confirm this. In the second experimental study, it was aimed to investigate the impact of severe inflammation and necrosis induced by an infection with H. meleagridids on intestinal E. coli colonization and gut wall invasion in turkeys. For this, turkeys were inoculated with attenuated and/or virulent strains of H. meleagridis and were sampled at 7, 14, and 21 dpi. Similar to the observation in laying chickens, a notable shift in caecal microbiota linked to the severity of caecal pathology was seen. The dysbiosis was characterized by an increase in E. coli abundance and a decrease in Lactobacillus spp. relative population. However, unlike in laying chickens, E. coli in the intestine were exclusively localized into the lumen and did not show a tendency to penetrate the caecal wall even in the presence of severe mucosal necrosis. These findings suggest that intestinal E. coli in turkeys, in contrast to chickens, do not tend to cause systemic bacteraemia even when confronted with a compromised gut wall and significant dysbiosis. In the third study, a comprehensive systematic literature review was conducted following PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines, and a random-effects meta-regression model was built to explore the dynamic relationship between the load of intestinal E. coli and the production performance in untreated broiler chickens. Initially, 2108 papers were screened based on a defined search string. Finally, 60 articles were included in the final meta-analysis, and after through standardization process, only records from the ileum and caecum at 21, 35, and 42 days of age were considered for data analysis. The meta-analysis showed that the average E. coli count in the ileum and caecum at 21 days of age was positively associated with the average weight gain, while no statistically significant associations were found at 35 and 42 days of age. The observed positive association between E. coli load and body weight gain in young broilers may be attributed to the prevalence of E. coli, as an early colonizer, within the less diverse gut microbiome characteristic of this particular age group. In the fourth study and manuscript, the sequential progression of pathological and microbial changes in the organs of laying chickens, and E. coli transmission into eggs was investigated in experimentally infected birds. A total of 48 hens were equally allocated into three groups. Birds in groups I, II, and III were inoculated intratracheally with ilux2-E. coli PA14/17480/5-ovary (bioluminescent strain), E. coli PA14/17480/5-ovary, and phosphate buffered saline (PBS), respectively. In addition to the assessment of production parameters, clinical and pathological changes were closely monitored until 16 dpi. Infection with both E. coli strains resulted in clinical symptoms and lesions resembling those seen in field outbreaks. Based on histopathological lesions in the lungs, the progression of colisepticaemia was categorized into newly defined four stages as: stage I (1-3 dpi), stage II (6 dpi), stage III (9 dpi), and stage IV (16 dpi) that were characterized by heterophilic inflammation, mixed cell inflammation, pyogranulomatous inflammation, and convalescence, respectively. With the progression of the disease, bioluminescent signals emitted by the bacteria from the whole-body and various internal organs gradually decreased. This reduction was coupled with a decreasing bacterial colonization, as evidenced by bacteriology and quantitative immunohistochemistry. Furthermore, through the application of double immunofluorescence, immunohistochemistry, and bacteria re-isolation, a novel evidence was provided for the transmission of E. coli into egg contents following colonization of the ovary and oviduct in infected hens. The study reveals new insight into stages of colisepticaemia and the transmission of E. coli into eggs, which have significant implications for poultry health and food safety. In summary, this thesis presents novel insights into the differences in tendency of intestinal E. coli for the colonization and penetration of caecal wall tissues in chickens and turkeys in the presence of H. meleagridis infection. Although the pathological changes, dysbiosis and higher relative abundance of E. coli were similar in both species, caecal wall infiltration by E. coli was only observed in chickens. In broilers, the age dependent dynamic association between the E. coli load and weight gain underscores the importance of carefully assessing commensal E. coli to support bird health during the critical early growth phases, while considering its potential pathogenicity. In laying chickens, the thesis also offers a new perspective on understanding the progression of septicaemic changes during progression of colibacillosis from acute to chronic phase as well as bacterial transmission into eggs. Reproduction of severe clinical signs as well as mortality in layers following intratracheal inoculation route highlights the influence of inoculation route and age of the birds on the severity of disease. Overall, the data in the present thesis will contribute to a better understanding of the microbial ecology and infection biology of avian E. coli, altogether helpful to improve infection control at poultry farms and optimize bird and public health. In addition, the newly established tools such as bacterial bioluminescence in birds and double immunofluorescence are useful tools for future studies.
Description (deu)
PhD Arbeit - Veterinärmedizinische Universität Wien - 2023 Aus rechtlichen Gründen sind nicht alle Teile dieser Arbeit frei zugänglich. Der Zugriff auf den elektronischen Volltext ist auf Angehörige der Veterinärmedizinischen Universität Wien beschränkt. Bitte einloggen!
Type (eng)
Dissertation
Language
[eng]
Persistent identifier
https://phaidra.vetmeduni.ac.at/o:4584
AC number
AC17640218
DOI
10.34876/45rq-va24
Number of pages
150
Date issued
2023
License
All rights reserved