Borg, Antonio
(2025)
Houseflies (Musca domestica) as potential vectors for the spread of ESBL-producing E.coli in humans.
PhD thesis, University of Nottingham.
Abstract
Antimicrobial resistance (AMR) has emerged as a critical global health challenge, with the spread of Extended-Spectrum Beta-Lactamase (ESBL)-producing Escherichia coli being a major concern, particularly in urinary tract infections (UTIs). This research investigates the role of the common housefly (Musca domestica L.) as a vector for transmitting ESBL- producing E. coli from bovine farms and open markets to human environments. The flies collected were not identified to species level, however the housefly (Musca domestica) is considered the most widespread fly species in Malta and is reported to be one of the most abundant and widely distributed in the Maltese Islands. All collected specimens shared similar morphological characteristics and were considered to belong to a single species. Therefore they are referred to in this study as Musca domestica. Through a multidisciplinary approach—integrating field sampling, phenotypic and genotypic analysis, and whole-genome sequencing (WGS), the study explores the prevalence, resistance patterns, and genetic similarity of E. coli strains isolated from flies and UTI patients.
A total of 177 fly traps and 90 fresh manure samples were collected across Malta and Gozo between 2018 and 2021. Simultaneously, 70 UTI-related ESBL-E. coli strains were obtained from clinical samples. Selective culture using TBX agar supplemented with cefotaxime, disc diffusion-based Antimicrobial Susceptibility Testing (AST). The results summarized in Table 4.1, show that a significant number of manure samples harboured CTX-M E. coli isolates. Similarly in Table 4.2, houseflies collected from farms and open markets were analysed for the presence of CTX-M type. PCR screening revealed that 42 % of fly samples carried ESBL-producing E. coli, with 47 % of these harbouring the blaCTX-M resistance gene. Among the UTI isolates, 79 % carried the same gene. WGS identified the blaCTX-M-15 variant as dominant in both environmental and clinical isolates, often carried on IncF-type plasmids and mobilized by the insertion sequence ISEcp1. Crucially, both fly and UTI strains shared virulence genes associated with ExPEC and UPEC lineages, suggesting a strong potential for zoonotic transmission.
The findings underscore the significance of M. domestica as a vector not just for general pathogens but specifically for antimicrobial-resistant, clinically relevant strains of E. coli. The overlap in AMR gene profiles and virulence factors between fly-derived and clinical strains strengthens the hypothesis that flies may serve as a critical link in the environmental-human transmission chain of ESBL-producing E. coli, although they cannot be considered the sole potential carriers. This highlights an urgent need for improved hygiene practices, integrated surveillance across agricultural and healthcare sectors, and further research into environmental pathways of AMR transmission.
| Item Type: |
Thesis (University of Nottingham only)
(PhD)
|
| Supervisors: |
Hobman, Jon
Dodd, Christine
Attard, Everaldo |
| Keywords: |
flies as carriers of disease, house flies, e.coli, Extended-Spectrum Beta-Lactamase (ESBL), Musca domestica, Escherichia coli |
| Subjects: |
Q Science > QL Zoology
Q Science > QR Microbiology |
| Faculties/Schools: |
UK Campuses > Faculty of Science > School of Biosciences |
| Item ID: |
82871 |
| Depositing User: |
Borg, Antonio
|
| Date Deposited: |
12 Dec 2025 04:40 |
| Last Modified: |
12 Dec 2025 04:40 |
| URI: |
https://eprints.nottingham.ac.uk/id/eprint/82871 |
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