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