Search

In order to investigate the use of semi-synthetic antimicrobial compounds, the objective of this study was to evaluate the 3-(p-chlorophenyl)thio citronellal, a novel compound that is derived from the essential oil of Cymbopogon citratus, against spoilage and pathogenic bacteria in food. This study also evaluated the possible mechanisms of action and cellular targets. Qualitative and quantitative tests and scanning electron microscopy were used to compare 3-(p-chlorophenyl)thio citronellal with citral and (R)-citronellal. It was observed that 3-(p-chlorophenyl)thio citronellal is a potent antimicrobial agent with bactericidal activity against different pathogenic and spoilage bacteria, of which the Gram-positive species were the most sensitive. The minimal inhibitory concentration for 3-(p-chlorophenyl)thio citronellal was approximately 100 times lower than that of citral, and this was corroborated by the kinetic curve of action, demonstrating that cell death was faster when the bacterial cells were treated with 3-(p-chlorophenyl)thio citronellal. This finding showed that the addition of thiol enhances the bioactivity of citral. In vitro testing showed that the compound does not show toxicity. The SEM images showed cell damage with the formation of pores in the cell wall and membrane, which are possibly the cellular targets of the compound.

Streptococcus mutans is the primary bacteria involved in caries. To prevent this disease, fluoride compounds are used; however, these compounds can become toxic at certain concentrations. The purpose of this study was to evaluate the antimicrobial activity of essential oils (Eos) from two eucalyptus species (Eucalyptus globulus and Eucalyptus urograndis) against planktonic and biofilm cells of S. mutans using the agar diffusion assay and by determining the minimum inhibitory concentrations, kinetic of action and ability to inhibit biofilm formation. The synergistic effect of the combined oils was also tested (1:1). Films constructed of biodegradable starch with the EOs were prepared, and their bioactivity was tested using the macrodilution technique. These essential oils were active against S. mutans, and they presented inhibition zones between 14.7 ± 1.2 mm and 35.3 ± 0.34 mm in diameter. It was observed that when the oils were used together, there was an increase in bioactivity. The kinetics of loss of cell viability test showed a reduction of 1 log cycle in the microorganism counts within less than 5 min of contact time. The essential oil from E. globulus gave the best results, requiring only 15 min of contact to cause microbial death; E. urograndis oil required 50 min to induce the same bactericidal effect. These results can be explained by the larger concentration of 1,8-cineole in the EO of E. globulus. Biofilm formation by S. mutans was also inhibited in the presence of the tested oils, which yielded more effective results when compared to 0.1% commercial NaF (sodium fluoride). The increased bioactivity of these oils suggests their technological potential.

This work aimed to evaluate the bioactivity of 3-(p-chlorophenyl)thio citronellal against planktonic and biofilm cells of S. aureus and its use in biodegradable films. 3-(p-chlorophenyl)thio citronellal demonstrated antimicrobial activity against planktonic (MIC = 62.5 ± 0.5 μg.mL−1) and biofilm cells of S. aureus. Regarding barley starch films containing 3-(p-chlorophenyl)thio citronellal, after 4 h of contact there was a difference of 5 log CFU.mL−1 in relation to control film (without additives). The films prepared with 3-(p-chlorophenyl)thio citronellal and citral (its precursor) were more opaque and had lower tensile strength than the control film. However, the addition of the 3-(p-chlorophenyl)thio citronellal in the film had lower effect on the water solubility and tensile strength than the addition of citral. 3-(p-chlorophenyl)thio citronellal have activity against planktonic and biofilm cells of S. aureus and could be applied in biodegradable films as an alternative to inhibit the microbial growth on the surface of food, enhancing food safety.