Rearrangement of the oxidative stress response of Pseudomonas aeruginosa under combined osmotic and fluoroquinolone stress: Enzymatic and proteomic alterations

Articles in Press

Document Type : Original Article- Persian

Authors

1 Department of Biology, Zanjan Branch, Islamic Azad University, Zanjan, Iran

2 Department of Biology, Zanjan Branch, Islamic Azad University, Zanjan, Iran.

Abstract

Pseudomonas aeruginosa is an opportunistic pathogen with a remarkable capacity to adapt to environmental stresses and antibiotic exposure. The combined effects of osmotic stress and fluoroquinolones on the reorganization of oxidative stress responses, particularly in multidrug resistant strains, remain incompletely understood. The present study aimed to investigate phenotypic, enzymatic, protein-level alterations in the antioxidant defense system of P. aeruginosa under combined osmotic and fluoroquinolone stress conditions.

Three clinical MDR strains and one reference strain were exposed to ciprofloxacin, norfloxacin, and ofloxacin. Fluoroquinolones were applied at sub-inhibitory concentrations corresponding to one-quarter and one-half of the minimum inhibitory concentration , while osmotic stress was induced using 0.3 M and 0.5 M sodium chloride. Changes in MIC, phenotypic antibiotic susceptibility, bacterial growth, antioxidant enzyme activities including superoxide dismutase , catalase and glutathione peroxidase as well as the expression levels of OxyR, KatA, and SodB proteins, were evaluated.

The results demonstrated that the combination of osmotic stress and sub-inhibitory concentrations of fluoroquinolones led to increased minimum inhibitory concentrations, reduced phenotypic susceptibility, and the induction of responses associated with adaptive antibiotic tolerance in multidrug-resistant strains.These conditions were accompanied by a relative reduction in bacterial growth and significant increases in antioxidant enzyme activities and the levels of the investigated proteins. The most pronounced changes were observed in MDR strains exposed to 0.5 M osmotic stress, whereas the reference strain exhibited more limited responses.

The findings indicate that osmotic stress enhances antibiotic tolerance in P. aeruginosa through the upregulation of OxyR-associated oxidative defense components and the strengthening of the cellular antioxidant system. These findings are more appropriately interpreted within the framework of stress adaptive tolerance and do not provide direct evidence for the development of stable genetic antibiotic resistance. Such adaptive responses may contribute to the survival, persistence, and ecological fitness of multidrug-resistant strains in clinical environments

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Journal of Microbial Biology

Articles in Press, Accepted Manuscript
Available Online from 14 July 2026

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