Antimicrobial potential of natural deep eutectic solvents.

Natural deep eutectic solvents (NADES) are a new class of green solvents, which can solubilize natural and synthetic chemicals of low water solubility. NADES are mixtures of two or three compounds of hydrogen bond acceptors and hydrogen bond donors. Many NADES' components are of natural origin and therefore, NADES are presumed to be nontoxic and often exhibit antimicrobial activity. This work aimed to investigate the potential antimicrobial effect of menthol, capric acid and Solutol™, and their associated eutectic system on two Gram-positive bacteria (Staphylococcus aureus ATCC 6538 and Bacillus subtilis ATCC 6633), two Gram-negative bacteria (Escherichia coli ATCC 8739 and Pseudomonas aeruginosa ATCC 9027) and one fungus (the yeast Candida albicans ATCC 10231). The results obtained showed a stronger antimicrobial effect for the NADES when compared to their individual components and that they exhibit a promising antimicrobial activity against S. aureus and C. albicans and good activity against P. aeruginosa. NADES exhibited no observable antimicrobial activity against spore-forming B. subtilis.

A review of the antimicrobial activity of thermodynamically stable microemulsions.

Microemulsions are thermodynamically stable, transparent, isotropic mixtures of oil, water and surfactant (and sometimes a co-surfactant), which have shown potential for widespread application in disinfection and self-preservation. This is thought to be due to an innate antimicrobial effect. It is suggested that the antimicrobial nature of microemulsions is the result of a combination of their inherent kinetic energy and their containing surfactants, which are known to aid the disruption of bacterial membranes. This review examines the contemporary evidence in support of this theory.

The effect of subminimal inhibitory concentrations of antibiotics on virulence factors expressed by Staphylococcus aureus biofilms.

AIMS: The effect of subminimal inhibitory concentrations (sub-MICs) of cefalexin, ciprofloxacin and roxithromycin was investigated on some virulence factors [e.g. coagulase, Toxic Shock Syndrome Toxin 1 (TSST-1) and biofilm formation] expressed by Staphylococcus aureus biofilms. METHODS AND RESULTS: Biofilms were grown with and without the presence of 1/16 MIC of antibiotics on Sorbarod filters. Eluate supernatants were collected, and coagulase and TSST-1 production were evaluated. Coagulase production was reduced in eluates exposed to roxithromycin when compared to control, while TSST-1 production was reduced in biofilms exposed to cefalexin and to a lesser extent, ciprofloxacin. In addition, the ability of Staph. aureus to produce biofilm in microtitre plates in the presence of sub-MIC antibiotics indicated that cefalexin induced biofilm formation at a wide range of sub-MICs. TSST-1 produced from the challenged and control biofilms was purified, and its proliferative activity was studied on single cell suspension of mouse splenocytes using MTS/PMS assay. No significant difference in the activity between the treated toxin and the control has been observed. CONCLUSIONS: Antibiotics at sub-MIC levels interfere with bacterial biofilm virulence expression depending on the type and concentration of antibiotic used. SIGNIFICANCE AND IMPACT OF THE STUDY: The establishment of sub-MICs of antibiotics in clinical situations may result in altered virulence states in pathogenic bacteria.

Microemulsions are highly effective anti-biofilm agents.

AIMS: The demonstration of the antibiofilm effects of pharmaceutical microemulsions. METHODS AND RESULTS: Microemulsions were prepared as physically stable oil/water systems. Previous work by this group has shown that microemulsions are highly effective antimembrane agents that result in rapid losses of viability in planktonic populations of Pseudomonas aeruginosa and Staphylococcus aureus. In this experiment a microemulsion preparation was used upon established biofilm cultures of Ps. aeruginosa PA01 for a period of 4 h. The planktonic MIC of sodium pyrithione and the planktonic and biofilm MICs of cetrimide were used as positive controls and a biofilm was exposed to a volume of normal sterile saline as a treatment (negative) control. Results indicate three log-cycle reductions in viability within the microemulsion treated biofilm, as compared to those observed in control treatments of similar biofilms (one log-cycle reduction in viabilities). CONCLUSIONS: The results indicate that the microemulsions are highly effective antibiofilm agents. SIGNIFICANCE AND IMPACT OF THE STUDY: This study suggests that microemulsions may have a role in the treatment of industrial and environmental biofilms.

Antimicrobial susceptibility changes and T-OMP shifts in pyrithione-passaged planktonic cultures of Pseudomonas aeruginosa PAO1.

AIMS: The aim of this study was to determine whether passaging Pseudomonas aeruginosa PAO1 with sub-MICs of the pyrithione biocides results in both the induction of decreased susceptibility towards these antimicrobials and associated outer membrane profile changes. METHODS AND RESULTS: Previous work by this group has shown that it is possible to induce susceptibility changes towards the isothiazolone biocides in Ps. aeruginosa PAO1 by successive passages in the presence of increasing sub-MICs of biocide. This procedure was accompanied by the loss of a 35 kDa outer membrane protein, T-OMP. In this experiment, this process was repeated with the biocides sodium pyrithione (NaPT), zinc pyrithione (ZnPT) and cetrimide. The pattern of susceptibility was similar to that observed with the isothiazolone biocides. Upon removal of biocide, the observed MIC did not return to the original pre-exposure value. The onset and development of resistance was accompanied by the loss of T-OMP from outer membrane profiles, which suggests that this is a non-specific membrane channel whose production within the cell is sensitive to biocide presence. The T-OMP reappeared when the cells were passaged in the absence of pyrithione. Cross-resistance studies indicated that induced resistance to one biocide yields partial resistance towards other members of the group and the positive control. CONCLUSIONS: These results indicate that the pyrithione biocides have similar susceptibility profiles in Ps. aeruginosa to those exhibited by the isothiazolones, but that the acquired changes in susceptibility to the pyrithiones is largely irreversible. SIGNIFICANCE AND IMPACT OF THE STUDY: This study indicates that acquired susceptibility changes towards sub-MICs of selected biocides are multifactorial in nature.