Evaluation of Plant Origin Essential Oils as Herbal Biocides for the Protection of Caves Belonging to Natural and Cultural Heritage Sites

Essential Oils as Alternative Green Broad-Spectrum Biocides

Natural compounds from plants represent suitable options to replace synthetic biocides when employed against microorganisms in various applications. Essential oils (EOs) have attracted increased interest due to their biocompatible and rather innocuous nature, and complex biological activity (fungicide, biocide and anti-inflammatory, antioxidant, immunomodulatory action, etc.). EOs are complex mixtures of derived metabolites with high volatility obtained from various vegetal parts and employed to a great extent in different healthcare (natural cures, nutrition, phyto- and aromatherapy, spices) and cosmetics applications (perfumery, personal and beauty care), as well as in cleaning products, agriculture and pest control, food conservation and active packaging, or even for restauration and preservation of cultural artifacts. EOs can act in synergy with other compounds, organic and synthetic as well, when employed in different complex formulations. This review will illustrate the employment of EOs in different applications based on some of the most recent reports in a systematic and comprehensive, though not exhaustive, manner. Some critical assessments will also be included, as well as some perspectives in this regard.

The impact of different acidic conditions and food substrates on Listeria monocytogenes biofilms development and removal using nanoencapsulated carvacrol

Listeria monocytogenes biofilms present a significant challenge in the food industry. This study explores the impact of different acidic conditions of culture media and food matrices on the development and removal of biofilms developed on stainless steel surfaces by wild-type (WT) L. monocytogenes strains as well as in two mutant derivatives, ΔsigB and ΔagrA, that have defects in the general stress response and quorum sensing, respectively. Additionally, the study investigates the efficacy of nanoencapsulated carvacrol as an antimicrobial against L. monocytogenes biofilms developed in Tryptic Soy Broth (TSB) culture media acidified to different pH conditions (3.5, 4.5, 5.5, 6.5), and in food substrates (apple juice, strained yogurt, vegetable soup, semi-skimmed milk) having the same pH levels. No biofilm formation was observed for all L. monocytogenes strains at pH levels of 3.5 and 4.5 in both culture media and food substrates. However, at pH 5.5 and 6.5, increased biofilm levels were observed in both the culture media and food substrates, with the WT strain showing significantly higher biofilm formation (3.04-6.05 log CFU cm-2) than the mutant strains (2.30-5.48 log CFU cm-2). For both applications, the nanoencapsulated carvacrol demonstrated more potent antimicrobial activity against biofilms developed at pH 5.5 with 2.23 to 3.61 log reductions, compared to 1.58-2.95 log reductions at pH 6.5, with mutants being more vulnerable in acidic environments. In food substrates, nanoencapsulated carvacrol induced lower log reductions (1.58-2.90) than the ones in TSB (2.02-3.61). These findings provide valuable insights into the impact of different acidic conditions on the development of L. monocytogenes biofilms on stainless steel surfaces and the potential application of nanoencapsulated carvacrol as a biofilm control agent in food processing environments.

Recolonization dynamics of marble monuments after cleaning treatments: A nine-year follow-up study

The prevention and control of biological patinas on outdoor stone monuments represent a demanding challenge for the conservation of cultural heritage also due to some microorganisms, particularly resistant to treatments, such as black meristematic fungi, an eco-physiological group well known for its tolerance to extreme conditions. Even if several methods and eco-friendly products have been proposed as new alternatives, traditional biocides are still far from being completely replaced. Recolonization is a natural process that occurs sooner or later after cleaning. The time that elapses until its occurrence can vary considerably depending on environmental conditions and the used products; unfortunately, the papers describing the effect of treatments over time are rare. This work aims to shed light on the recolonization process of marble surfaces in the ancient monumental cemetery of Bonaria (Cagliari) after nine years from treatments, evaluating the long-term efficiency of two different cleaning methods, namely dimethyl sulfoxide-based gel (DMSO-based gel) and Biotin T (a didecyldimethylammonium chloride-based product-). In this context, the microflora present before treatments and in the following years was assessed by culture-based methods and identified by molecular techniques, with attention on black meristematic fungi, which were used as reference for the most resistant lithobiontic organisms. Different environmental parameters, such as temperature, exposition, dominant winds, and rainfall, were considered, and infrared thermography, portable light microscopy, and image analysis were used. This research evidenced the influence of water availability and lightning in recolonization processes, the transition from the pioneer fungal community versus more resistant black fungal species after Biotin T treatment, and the long-lasting efficiency of the DMSO-based gel. These findings prove that this low-impact method deserves more attention in the conservation of outdoor marble monuments, emphasizing the importance of long-term studies.

16S and 18S rDNA Amplicon Sequencing Analysis of Aesthetically Problematic Microbial Mats on the Walls of the Petralona Cave: The Use of Essential Oils as a Cleaning Method

The presence of microbial communities on cave walls and speleothems is an issue that requires attention. Traditional cleaning methods using water, brushes, and steam can spread the infection and cause damage to the cave structures, while chemical agents can lead to the formation of toxic compounds and damage the cave walls. Essential oils (EOs) have shown promising results in disrupting the cell membrane of bacteria and affecting their membrane permeability. In this study, we identified the microorganisms forming unwanted microbial communities on the walls and speleothems of Petralona Cave using 16S and 18S rDNA amplicon sequencing approaches and evaluated the efficacy of EOs in reducing the ATP levels of these ecosystems. The samples exhibited a variety of both prokaryotic and eukaryotic microorganisms, including Proteobacteria, Actinobacteria, Bacteroidetes, Chloroflexi, Firmicutes, the SAR supergroup, Opisthokonta, Excavata, Archaeplastida, and Amoebozoa. These phyla are often found in various habitats, including caves, and contribute to the ecological intricacy of cave ecosystems. In terms of the order and genus taxonomy, the identified biota showed abundances that varied significantly among the samples. Functional predictions were also conducted to estimate the differences in expressed genes among the samples. Oregano EO was found to reduce ATP levels by 87% and 46% for black and green spots, respectively. Consecutive spraying with cinnamon EO further reduced ATP levels, with reductions of 89% for black and 88% for green spots. The application of a mixture solution caused a significant reduction up to 96% in ATP levels of both areas. Our results indicate that EOs could be a promising solution for the treatment of microbial communities on cave walls and speleothems.

Bactericidal Properties of Low-Density Polyethylene (LDPE) Modified with Commercial Additives Used for Food Protection in the Food Industry

This study investigated the influence of commercially available food preservatives: Natamax® (containing natamycin) and Nisaplin® (containing nisin) on the antimicrobial properties of LDPE film, commonly used for food packaging. Studies have shown that the addition of 3% Natamax® or, alternatively, the addition of 5% Nisaplin® provides an LDPE film with effective antimicrobial protection. The applied biocides did not significantly affect the strength and rheological properties of LDPE. However, differences in optical properties were observed. The transparency of the samples decreased slightly with the addition of 3% or 5% Natamax® (by approx. 1% and 3%, respectively). A significant change was observed in the film haze, the addition of 5% Natamax® increased this parameter by approx. 80%, while 5% Nisaplin® increased it by approx. 19%. Both Natamax® and Nisaplin® agents can be successfully used to manufacture food packaging materials with antimicrobial protection. Natamax® showed a stronger bactericidal effect, while Nisaplin® changed other properties less significantly.

Evaluation of Origanum vulgare Essential Oil and Its Active Ingredients as Potential Drugs for the Treatment of Toxoplasmosis

Toxoplasma gondii is a serious hazard to public health and animal husbandry. Due to the current dilemma of treatment of toxoplasmosis, it is urgent to find new anti-T. gondii drugs to treat toxoplasmosis. In this study, the anti-T. gondii activity of Origanum vulgare essential oil (Ov EO) was firstly studied, and then, carvanol (Ca), the main ingredient of Ov EO was evaluated using the MTT assay on human foreskin fibroblast (HFF) cells in vitro. The cytotoxicity was evaluated using the MTT assay on HFF cells. The CC₅₀ of Ov EO and Ca was 134.9 and 43.93 μg/ml, respectively. Both of them exhibited anti-parasitic activity, and inhibited the growth of T. gondii in a dose-dependent manner. For the inhibition effect, Ca was better than Ov EO at the same concentration, the IC₅₀ of Ov EO and Ca was 16.08 and 7.688 μg/ml, respectively. In addition, treatment with Ca, was found to change the morphology of T. gondii tachyzoites and made their shapes curl up. These results showed that Ca was able to inhibit the proliferation of T. gondii by reducing invasion, which may be due to its detrimental effect on the mobility of tachyzoites. Our results indicated that Ca could be a potential new and effective drug for treating toxoplasmosis.