Activity of Specialized Biomolecules against Gram-Positive and Gram-Negative Bacteria

Abstract

The increased resistance of bacteria against conventional pharmaceutical solutions, the antibiotics, has raised serious health concerns. This has stimulated interest in the development of bio-based therapeutics with limited resistance, namely, essential oils (EOs) or antimicrobial peptides (AMPs). This study envisaged the evaluation of the antimicrobial efficacy of selected biomolecules, namely LL37, pexiganan, tea tree oil (TTO), cinnamon leaf oil (CLO) and niaouli oil (NO), against four bacteria commonly associated to nosocomial infections: Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli and Pseudomonas aeruginosa. The antibiotic vancomycin and silver nanoparticles (AgNPs) were used as control compounds for comparison purposes. The biomolecules were initially screened for their antibacterial efficacy using the agar-diffusion test, followed by the determination of minimal inhibitory concentrations (MICs), kill-time kinetics and the evaluation of the cell morphology upon 24 h exposure. All agents were effective against the selected bacteria. Interestingly, the AgNPs required a higher concentration (4000–1250 μg/mL) to induce the same effects as the AMPs (500–7.8 μg/mL) or EOs (365.2–19.7 μg/mL). Pexiganan and CLO were the most effective biomolecules, requiring lower concentrations to kill both Gram-positive and Gram-negative bacteria (62.5–7.8 μg/mL and 39.3–19.7 μg/mL, respectively), within a short period of time (averaging 2 h 15 min for all bacteria). Most biomolecules apparently disrupted the bacteria membrane stability due to the observed cell morphology deformation and by effecting on the intracellular space. AMPs were observed to induce morphological deformations and cellular content release, while EOs were seen to split and completely envelope bacteria. Data unraveled more of the potential of these new biomolecules as replacements for the conventional antibiotics and allowed us to take a step forward in the understanding of their mechanisms of action against infection-related bacteria.

Physical, Thermal, and Antibacterial Effects of Active Essential Oils with Potential for Biomedical Applications Loaded onto Cellulose Acetate/Polycaprolactone Wet-Spun Microfibers

“…From the group, the HCO, SAO, and WO did not form any ZoI even though reports have been published on their antibacterial action [27][28][29]. This supports the premise established by Tavares et al that the plant origin and the extraction methods of natural products employed by each company may influence the properties of the final product [5].…”

“…To analyze the EOs capacity to interfere with the cell morphology of Gram-positive and Gram-negative bacteria, visual studies resorting to SEM were conducted. Here, only the most effective EO was selected since the mechanisms of action are very similar among EOs [5]. Bacteria suspensions were prepared at 1 × 10 5 CFUs/mL in MHB and combined at 50% (v/v) with the selected EO (cinnamon leaf oil (CLO)) at MIC value.…”

“…Considering the similarities between the EOs mechanisms of action against bacteria [5], only the most effective, the CLO, was selected to examine the EOs interference in the cell membrane via SEM. Figure 1 shows the morphology of the bacteria before and after contact with CLO at MIC.…”

“…Natural products derived from plants with antimicrobial, anti-inflammatory, antioxidant, and chemo-preventive properties have been used for many generations in traditional medicine [4]. Nowadays, they are gaining new status as an alternative to antibiotics, by preventing and treating infectious diseases with little impact in the environment [5]. Essential oils (EOs) are mixtures of aromatic, volatile, lipophilic biomolecules, extracted from regions of plants (e.g., flowers, leaves, twigs, bark, wood, fruits, etc.)…”

“…Essential oils (EOs) are mixtures of aromatic, volatile, lipophilic biomolecules, extracted from regions of plants (e.g., flowers, leaves, twigs, bark, wood, fruits, etc.) in which they work as secondary metabolites, defending the host from microbial invasion [1,5]. They are formed of complex mixtures of hydrophobic molecules, including thymol, carvacrol, and eugenol (among others), which exhibit a broad spectrum of antimicrobial activity against bacteria, fungi, and viruses.…”