ETD

• antibiotic resistance
• Bacteriophage
• intracellular bacteria
• mycobacteria
• Mycobacterium abscessus
• Phage therapy

Mycobacterium abscessus is an opportunistic pathogen that poses a major therapeutic challenge due to its broad antibiotic resistance and intracellular persistence characteristics, especially in immunocompromised and cystic fibrosis patients. This thesis evaluated the potential of mycobacteriophages as a promising anti-mycobacterial approach. The first part of the study focused on the characterization of the mycobacteriophage Pisa4 and its genetically engineered strictly lytic derivative. Their host range was initially assessed against a panel of 48 M. abscessus clinical isolates and compared to 7 therapeutic mycobacteriophages by the phage collection of Pittsburgh University. This screening revealed an overall narrow host range, with only 23% of the strains susceptible to at least one phage. The lytic activity of both Pisa4 wild-type and the engineered derivative was then evaluated under planktonic conditions against rough (R) and smooth (S) morphotypes. Both phages displayed bactericidal activity against the R morphotype, whereas no activity was observed against the S morphotype. The activity of the engineered phage against the R strain was then evaluated in THP-1-derived macrophages and A549 lung epithelial cells to assess its intracellular efficacy. However, no bactericidal activity was observed in either cell lines. The second part of the study aimed to expand the collection of mycobacteriophages available for potential therapeutic applications. To this end, the temperate mycobacteriophage Okabe was successfully engineered into a strictly lytic derivative through deletion of the immunity repressor gene, providing a new candidate for future phage therapy against M. abscessus. Overall, this study provides new insights into the opportunities and limitations of phage therapy against M. abscessus.