Rihab Ben Slama

Chemical Composition and Cytotoxic and Antioxidant Activities of Satureja montana L. Essential Oil and Its Antibacterial Potential against Salmonella Spp. Strains

The present study describes chemical composition as well as cytotoxic, antioxidant, and antimicrobial activities of winter savory Satureja montana L. essential oil (EO). The plant was collected from south France mountain, and its EO was extracted by hydrodistillation (HD) and analysed by gas chromatography/mass spectrometry (GC/MS). Thirty-two compounds were identified accounting for 99.85% of the total oil, where oxygenated monoterpenes constituted the main chemical class (59.11%). The oil was dominated by carvacrol (53.35%), -terpinene (13.54%), and the monoterpenic hydrocarbons p-cymene (13.03%). Moreover, S. montana L. EO exhibited high antibacterial activities with strong effectiveness against several pathogenic food isolated Salmonella spp. including S. enteritidis with a diameter of inhibition zones growth ranging from 21 to 51 mm and MIC and MBC values ranging from 0.39–1.56 mg/mL to 0.39–3.12 mg/mL, respectively. Furthermore, the S. montana L. EO was investigated for its cytotoxic and antioxidant activities. The results revealed a significant cytotoxic effect of S. montana L. EO against A549 cell line and an important antioxidant activity. These findings suggest that S. montana L. EO may be considered as an interesting source of components used as potent agents in food preservation and for therapeutic or nutraceutical industries.

Adhesive ability and biofilm metabolic activity of Listeria monocytogenes strains before and after cold stress

Listeria monocytogenes is an important pathogen responsible for major outbreaks associated with food products. Adhesion to surfaces leads to significant modifications in cell physiology. In this work, the ability of L. monocytogenes to produce biofilm and its ability to adhere to abiotic surfaces under cold stress were evaluated. Metabolic activity of biofilm formed by L. monocytogenes before and after cold stress was measured in vitro using the colorimetric method based on the reduction of the tetrazolium salt 2,3-bis(2methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT). The ability to adhere to abiotic surfaces was determined by the ability of the cells to metabolically reduce bromure de 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium (MTT) to a formazan dye. Our results show that L. monocytogenes strains were able to adhere to abiotic materials with different degrees. In fact, cold stressed strains (-20°C) were more adhesive to polyethylene, glass, polyvinyl chloride and stainless style surfaces than non-stressed cells. Our observations show that the hydrophily varied with cold stress period. At freezing temperature, L. monocytogenes was strongly hydrophobic. Genetic studies of adhesive genes of L. monocytogenes will be required to fully understand the importance of this observation. Keywords: Listeria monocytogenes , slime production, cold stress, abiotic-surfaces, biofilm formation

Antibiofilm formation and anti-adhesive property of three mediterranean essential oils against a foodborne pathogen Salmonella strain

Plant extracts, and their essential oils (EOs) are rich in a wide variety of secondary metabolites with antimicrobial properties. Our aim was to determine the bioactive compound in three mediterranean essential oils belonging to Lamiaceae family, Satureja montana L., Thymus vulgaris L. and Rosmarinus officinalis L., and to assess their antimicrobial, antibiofilm and anti-adhesive potentials against a foodborne pathogen Salmonella strain. The antibacterial activity of EOs and its biofilm inhibition potencies were investigated on 2 reference strains Salmonella typhimurium and 12 Salmonella spp. isolated from food. Biofilm inhibition were assessed using the 2, 3-bis [2-methyloxy-4-nitro-5-sulfophenyl]-2H-tetrazolium-5-carboxanilide (XTT) reduction assay. The analytical data indicated that various monoterpene hydrocarbons and phenolic monoterpenes constitute the major components of the oils, but their concentrations varied greatly among the oils examined. Our results showed that S. montana L. and T. vulgaris L. essential oils possess remarkable anti biofilm, anti-adhesive and bactericidal properties, compared to R. officinalis EO. There is an indication that Rosmary EO might inhibit biofilm formation at higher concentrations. Therefore, the witer savory and thyme EOs represent a source of natural compounds that exhibit potentials for use in food systems to prevent the growth of foodborne bacteria and extend the shelf life of the processed food.

Antifouling processes and toxicity effects of antifouling paints on marine environment. A review

The production infrastructure in aquaculture invariably is a complex assortment of submerged components with cages, nets, floats and ropes. Cages are generally made from polyamide or high density polyethylene (PEHD). All of these structures serve as surfaces for biofouling. However, cage nets and supporting infrastructure offer fouling organisms thousands of square meters of multifilament netting. Thats why, before immersing them in seawater, they should be coated with an antifouling agent. It helps to prevent net occlusion and to increase its lifespan. Biofouling in marine aquaculture is a specific problem and has three main negative effects. It causes net occlusion and so restricts water and oxygen exchange. Besides, the low dissolved oxygen levels from poor water exchange increases the stress levels of fish, lowers immunity and increases vulnerability to disease. Also, the extra weight imposed by fouling causes cage deformation and structural fatigue. The maintenance and loss of equipment cause the increase of production costs for the industry. Biocides are chemical substances that can prohibit or kill microorganisms responsible for biofouling. The expansion of the aquaculture industry requires the use of more drugs, disinfectants and antifoulant compounds (biocides) to eliminate the microorganisms in the aquaculture facilities. Unfortunately, the use of biocides in the aquatic environment has proved to be harmful as it has toxic effects on the marine environment. The most commonly used biocides in antifouling paints are Tributyltin (TBT), Chlorothalonil, Dichlofluanid, Sea-Nine 211, Diuron, Irgarol 1051 and Zinc Pyrithione. Restrictions were imposed on the use of TBT, thats why organic booster biocides were recently introduced. The replacement products are generally based on copper metal oxides and organic biocides. This paper provides an overview of the effects of antifouling biocides on aquatic organisms. It will focus on the eight booster biocides in common use, despite little data are available for some of them. Toxicity values and effects of these antifoulants will also be mentioned for different species of fish, crustaceans, invertebrates and algae.

Cytotoxicity, Antibacterial, Antioxidant, and Antibiofilm Properties of Tunisian Juglans regia Bark Extract

Tunisian Juglans regia bark ethanol extract (JREE) was examined for antibacterial, antibiofilm, and antioxidant activity. Its anti-proliferative effect was evaluated on normal (MRC-5) and cancer (HT29 and HEp-2) cell lines. The data revealed that JREE inhibited the growth of pathogenic bacteria (MICs value ranged from 32 to 128 μg.mL-1) and induced a strong antibiofilm effect (BIC50 was 23, 30, and 43 μg.mL-1 for Micrococcus luteus, Staphylococcus epidermidis, and Staphylococcus aureus, respectively). The JREE showed high scavenging property against 2,2-diphenyl-l-1-picrylhydrazil (DPPH) radical (IC50 = 3.5 μg.mL-1) and exhibited anti-proliferative effects with IC50 values ranging from 6.6 to 25.5 μg.mL-1.

Modulation of drug resistance and biofilm formation of Staphylococcus aureus isolated from the oral cavity of Tunisian children.

OBJECTIVES This study aims to investigate the antimicrobial and the anti-biofilm activities of Lactobacillus plantarum extract (LPE) against a panel of oral Staphylococcus aureus (n=9) and S. aureus ATCC 25923. The in vitro ability of LPE to modulate bacterial resistance to tetracycline, benzalchonium chloride, and chlorhexidine were tested also. METHODS The minimum inhibitory concentrations (MICs) and the minimal bactericidal concentrations of Lactobacillus plantarum extract, tetracycline, benzalchonium chloride and clohrhexidine were determined in absence and in presence of a sub-MIC doses of LPE (1/2 MIC). In addition, the LPE potential to inhibit biofilm formation was assessed by microtiter plate and atomic force microscopy assays. Statistical analysis was performed on SPSS v. 17.0 software using Friedman test and Wilcoxon signed ranks test. These tests were used to assess inter-group difference (p<0.05). RESULTS Our results revealed that LPE exhibited a significant antimicrobial and anti-biofilm activities against the tested strains. A synergistic effect of LPEs and drug susceptibility was observed with a 2-8-fold reduction. CONCLUSION LPE may be considered to have resistance-modifying activity. A more detailed investigation is necessary to determine the active compound responsible for therapeutic and disinfectant modulation.

Molecular analysis of the role of osmolyte transporters opuCA and betL in Listeria monocytogenes after cold and freezing stress

Listeria monocytogenes is a food-borne pathogen of humans and other animals. The striking ability to survive several stresses usually used for food preservation makes L. monocytogenes one of the biggest concerns to the food industry. This ubiquity can be partly explained by the ability of the organism to grow and persist at very low temperatures, a consequence of its ability to accumulate cryoprotective compound called osmolytes. A quantitative RT-PCR assay was used to measure mRNA transcript accumulation for the stress response genes opuCA and betL (encoding carnitine and betaine transporters, respectively) and the housekeeping gene 16S rRNA. Assays were conducted on mid-exponential phase L. monocytogenes cells exposed to conditions reflecting cold and freezing stress, conditions usually used to preserve foods. We showed that expression of the two cold-adapted genes encoded the transporters of the cryoprotectants carnitine and betaine in ATCC 19115 and the food-isolated L. monocytogenes S1 is induced after cold and freezing stress exposure. Furthermore, transcriptional analysis of the genes encoding opuCA and betL revealed that each transporter is induced to different degrees upon cold shock of L. monocytogenes ATCC 19115 and S1. Our results confirm an increase in carnitine uptake at low temperatures more than in betaine after cold-shocked temperature compared to the non-stress control treatment. It was concluded the use of carnitine and betaine as cryoprotectants is essential for rapid induction of the tested stress response under conditions typically encountered during food preservation.

Change in physiological cellular state of halophilic Bacillus sp. under long marine stress starvation conditions

The aim of this study is to give insight about the effect of long marine stress starvation conditions in the physiological responses of three potential halophilic probiotic Bacillus isolates isolated from Artemia culture. Bacteria were cultured in sterilized seawater and incubated at ambient temperature for one year. The obtained results showed that the isolates viability was maintained during the studied period. Compared to normal cells, starved cells increased their adhesive ability and cell surface hydrophobicity. Our data demonstrated that the tested isolates maintained their enzymatic profile in non-starvation conditions and under stress conditions they expressed enzymes like esterase lipase (C8), amylase, lipase, and caseinase. The present finding suggests that the tested strains have developed strategies that allow them to overcome stressful conditions in the absence of nutrients and makes them as a potential candidate probiotics.