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Aspects of antimicrobial resistance in Australian swine-origin Pasteurella multocida

Jones, Suzanna (2020) Aspects of antimicrobial resistance in Australian swine-origin Pasteurella multocida. Honours thesis, Murdoch University.

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Abstract

Pasteurella multocida is a causative agent of many diseases in a broad range of hosts. It is particularly noted in pigs as a cause of pneumonia and atrophic rhinitis. As treatment and control of P. multocida infections has relied heavily on antimicrobials, surveillance of antimicrobial resistance is necessary to ensure that treatment remains effective. The aim of this study was to investigate the antimicrobial resistance (AMR) of P. multocida isolates from Australian pigs, the potential risk of AMR genes spreading from other Gram-negative bacteria and the possibility of using bacteriophages as an alternative treatment to P. multocida infections.

Antimicrobial susceptibility testing was performed on 273 P. multocida isolates collected from pig farms across Australia between 2014 and 2019. Resistance to tetracycline (22.7%), chlortetracycline (22%), florfenicol (0.7%) and ampicillin (0.4%) was identified. Examination of the transferability of AMR genes from ceftriaxone and ampicillin resistant E. coli isolates to P. multocida through plasmidmediated conjugation revealed that AMR genes were not stably transferred from E. coli to P. multocida. Efforts to isolate bacteriophages with lytic activity against P. multocida from environmental samples were not successful, however the addition of mitomycin C to P. multocida strains resulted in lysis of cells and visible clearing of the bacterial culture for 5 of 7 isolates, indicating prophages were induced.

This study demonstrated that P. multocida infections in Australian swine can still be successfully treated with antimicrobials and that the risk of acquiring AMR genes from other highly resistant Gramnegatives is low. Despite low frequency of resistance to tested antimicrobials on-going surveillance and reducing antimicrobial usage should be a priority as P. multocida outbreaks can have significant impact on economic costs and animal welfare. Failure to isolate lytic bacteriophages from environmental sources indicates that phage therapy would be reliant on isolation of phage stocks from sources samples that would carry P. multocida specific phages such as nasopharyngeal wash samples from pigs.

Item Type: Thesis (Honours)
Murdoch Affiliation(s): College of Science, Health, Engineering and Education
Supervisor(s): O'Dea, Mark and Abraham, Sam
URI: http://researchrepository.murdoch.edu.au/id/eprint/61793
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