Abstract
Background: Antimicrobial resistance is a global and rising health concern. Pseudomonas aeruginosa, an opportunistic pathogen, plays an important role in respiratory diseases such as cystic fibrosis (CF). The CF lungs are known to provide bacteria and in particular, P. aeruginosa, with optimal physiological conditions to persist and resist antimicrobial therapies. Iron is essential for all forms of life and plays an essential role at the lung interface between the immune system and P. aeruginosa infections.Objectives: Given the importance of iron as a growth factor for this pathogen, this study aims to investigate new therapeutic combinations using iron starvation. A synthetic iron chelator with high affinity and specificity for iron was introduced and assessed for its antibacterial properties and interaction with a range of marketed antibiotics.
Method: The effect of iron removal by an iron chelator, CP762, was studied using a microdilution assay to determine the minimum inhibitory concentration (MIC) of the chelator and antimicrobials in classic and iron-limited environments. The checkerboard assay was used to screen for synergistic combinations of antibacterial agents (iron chelator and marketed antibiotics) by calculation of fractional inhibitory concentration indexes (FICI). Antibiotics of the tetracyclines, and macrolides groups, and chloramphenicol, were studied in greater detail on clinical isolates of P. aeruginosa using chemically engineered iron-antibiotic complexes or virulence factor expression by RT-qPCR.
Results: The iron chelator CP762 was shown to have an antibacterial activity and was investigated for synergistic interactions with 10 antibiotics from various groups with different modes of action. Synergy was identified for the tetracyclines group, which were previously known to be metal chelators themselves, and CP762 was shown to restore the activity of this group including when pre-bound to iron. CP762 was also synergistic with azithromycin, erythromycin, and chloramphenicol, all of which lack apparent binding sites with iron. Azithromycin, typically used to modulate P. aeruginosa virulence, was selected for further studies assessing the impact of combination with the chelator on the quorum sensing system and expression of virulence traits.
Conclusion: Use of the iron chelator CP762 resulted in significant doxycycline for P. aeruginosa. The impact of azithromycin on biofilm formation and gene expression was not significantly affected by CP762. Overall, this study highlights the beneficial effect of iron scavenging with antibiotics and presents opportunities for CP762 development as a new therapeutic agent.enhancement of antibacterial activity for a number of antibiotics, and reduced the MIC of iron-bond doxycycline for P. aeruginosa. The impact of azithromycin on biofilm formation and gene expression was not significantly affected by CP762. Overall, this study highlights the beneficial effect of iron scavenging with antibiotics and presents opportunities for CP762 development as a new therapeutic agent.
| Date of Award | 1 Sept 2021 |
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| Original language | English |
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| Supervisor | Kenneth Bruce (Supervisor), Vincenzo Abbate (Supervisor) & Bob Hider (Supervisor) |