Antimicrobial mechanisms of ortho ‐phthalaldehyde action

Abstract

Biocides generally have multiple biochemical targets. Such a feature easily entangles the analysis of the mechanisms of antimicrobial action. In this study, the action of the dialdehyde biocide ortho-phtalaldehyde (OPA), on bacteria, was investigated using the Gram-negative Pseudomonas fluorescens. The targets of the biocide action were studied using different bacterial physiological indices. The respiratory activity, membrane permeabilization, physico-chemical characterization of the bacterial surfaces, outer membrane proteins (OMP) expression, concomitant influence of pH, contact time and presence of bovine serum albumin (BSA) on respiratory activity, morphological changes and OPA-DNA interactions were assessed for different OPA concentrations. With the process conditions used, the minimum inhibitory concentration was 1500 mg/l, the concentration to promote total loss of bacterial culturability was 65 mg/l and the concentration needed to inactivate respiratory activity was 80 mg/l. These data are evidence that culturability and respiratory activity were markedly affected by the biocide. OPA lead, moreover, to a significant change in cell surface hydrophobicity and induced propidium iodide uptake. Such results suggest cytoplasmic membrane damage, although no release of ATP was detected. At pH 5, the bactericidal action of OPA was stronger, though not influenced by BSA presence. Nevertheless, at pH 9, BSA noticeably (p < 0.05) impaired biocide action. A time-dependent effect in OPA action was evident when contemplating respiratory activity variation, mainly for the lower exposure times. Scanning electron microscopy allowed to detect bacterial morphological changes, translated on cellular elongation, for OPA concentrations higher than 100 mg/l. Interferences at DNA level were, however, restricted to extreme biocide concentrations. The overall bactericidal events occurred without detectable OMP expression changes. In conclusion, the results indicated a sequence of events responsible for the antimicrobial action of OPA: it binds to membrane receptors due to cross-linkage; impairs the membrane functions allowing the biocide to enter through the permeabilized membrane; it interacts with intracellular reactive molecules, such as RNA, compromising the growth cycle of the cells and, at last, with DNA.

Identification of ypqP as a New Bacillus subtilis Biofilm Determinant That Mediates the Protection of Staphylococcus aureus against Antimicrobial Agents in Mixed-Species Communities

“…Biocide molecules can be delayed by the biofilm polymer matrix (52) or diffuse easily into the biofilm but strongly react with organic material, such as the oxidizing agent PAA (53,54). Aldehydes, such as OPA, act as cross-linking agents reacting against proteins, DNA, and RNA (55). Hence, many of the biofilm polymeric substances produced by B. subtilis cells have the potential to hamper biocide reactivity.…”

Antibacterial activity and mode of action of selected glucosinolate hydrolysis products against bacterial pathogens

“…Contact angles were determined automatically using an OCA 15 Plus (DATAPHYSICS, Germany) video-based optical measuring instrument, allowing image acquisition and data analysis. Contact angle measurements were carried out according to Simões et al (2007). Hydrophobicity was evaluated after contact angle measurement, following the van Oss approach (van Oss et al 1987(van Oss et al , 1988(van Oss et al , 1989, where the degree of hydrophobicity of a given surface (s) is expressed as the free energy of interaction between two entities of that surface, when immersed in water (w) -(ΔG sws mJ/ m 2 ).…”

The effects of surface type on the removal of Bacillus cereus and Pseudomonas fluorescens single and dual species biofilms

“…Plus (DATAPHYSICS, Germany) video-based optical measuring instrument, allowing image acquisition and data analysis, and ≥25 contact angle measurements (per liquid and sample) were carried out according to Simões et al (2007b). The surface energy components of bacteria, PMMA and SS were obtained by measuring the contact angles with three pure liquids: water, formamide and -bromonaphthalene (Sigma, Portugal).…”