Disinfectants and pH synergistically inactivate Pseudomonas fluorescens ATCC 13525: insights into cellular redox homeostasis and ultrastructure

Abstract

Peracetic acid (PAA) and hydrogen peroxide (H₂O₂) were more potent at pH 8.2, while linear alkylbenzene sulfonate (LAS) showed higher potency at pH 5.0 against Pseudomonas fluorescens ATCC 13525. The aim was to understand the changes in the cellular redox status, ultrastructure and morphology underlying the synergistic bacterial control effects of selected pH values alone and treatments. The minimum inhibitory concentrations of PAA and H₂O₂ at pH 8.2, and MIC of LAS at pH 5.0 were tested during the stationary growth phase of planktonic cells. pH 8.2 alone mainly elevated the protein carbonyls level and decreased the levels of low molecular weight thiols (LMWT), which could potentiate the effect of H₂O₂ and PAA, while pH 5.0 alone largely decreased the total thiol level that could facilitate LAS action. Free radicals were only detected with LAS and PAA treatments. H₂O₂ and PAA increased the levels of protein carbonyls, while reduced LMWT levels. LAS increased the levels of protein carbonyls, while reduced the total thiol level. H₂O₂, PAA and LAS were also found to increase SOD and decrease catalase specific activities. Each treatment showed distinct alterations and disruption in cytoplasmic structures. We suggest that exposing bacteria to the test oxidants and LAS at the selected pH ranges resulted in high generation of reactive species which activated complex oxidative processes and antioxidant defense pathways causing an imbalance of the cellular redox homeostasis that led to deformity and collapse of ultrastructure at late stage of oxidative damage, and eventual control of bacterial growth.

Keywords:

• Peracetic acid
• hydrogen peroxide
• LAS
• redox
• ultrastructure
• morphology

Acknowledgement

This work was performed at University of Siena and Procter & Gamble Newcastle Innovation Centre (P&G NIC).

Author’s contributions

Osama H. Bekhet conceived and designed the study, performed the laboratory work and statistical analysis and wrote the manuscript.

Availability of data and materials

Data and materials related to this study are available upon reasonable request.

Ethics approval and consent to participate

Not applicable.

Consent for publication

Not applicable.

Disclosure statement

Osama H. Bekhet declares that he has no conflict of interest.

Data availability statement

All data that support the findings reported in this manuscript are available from the author upon reasonable request.

Additional information

Funding

The project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 722871.