Heavy metals contamination is now widespread in the nature. At higher concentration, heavy metals become toxic and disturb the ecosystem including soil microorganisms. To adapt to such constraints, some microorganisms have developed tolerance mechanisms. Indeed, in the environment, the resistance of microorganisms to heavy metal often promotes to antibiotic resistance. This work aims to isolate strains from soil samples collected in Andralanitra landfill, to test their tolerance to heavy metals, to identify tolerant strains and to verify their resistance to antibiotics. According to the dilution method, a total of 48 strains were obtained, 14 were isolated on PDA medium, 10 on Sabouraud agar medium, 10 strains on Mossel agar medium, 7 on AS1 medium, 5 strains on TSA medium and 2 strains with King B medium. Resistance test to heavy metals performed by the wells method showed that out of the 48 isolated strains, 26 were capable to grow in the presence of heavy metals (solution composed of copper, zinc, cadmium, chromium, nickel, lead) at different concentrations. The highest number of tolerant strains was recorded at the concentration of 100mg/L ≤ C ≤ 1000mg/L. Four (4) strains were tolerant to the heavy metals solution at a concentration between 100mg/L and 1500mg/L. The molecular identification of these four most resistant strains by 16S rDNA gene sequencing and ITS gene sequencing allowed to classify them as belonging to the genera Ochrobactrum pseudogrignonense, Arthrobacter nicotianae, Penicillium crustosum and Penicillium commune. The antibiotic sensitivity test using disc diffusion method on Mueller-Hinton agar revealed that Ochrobactrum pseudogrignonense and Penicillium commune were resistant to Trimethoprim, Arthrobacter nicotianae showed resistance to Trimethoprim and Ciprofloxacin, Penicillium crustosum was resistant to all tested antibiotics.

Plants constitute an important source of secondary metabolites in which essential oils are well-known for their use in various domains such as pharmacy, therapeutic, cosmetology and foods. In vitro antimicrobial and antioxidant properties of Ocotea auriculiformis Kost. (Lauraceae) leaves essential oil is demonstrated and its chemical composition is reported in the present study. The essential oil from Ocotea auriculiformis Kost. (Lauraceae) leaves, an endemic plant of Madagascar was extracted by hydrodistillation method. Chemical composition using GC, GC/ MS and NMR 13 C methods showed that the essential oil contained around 47 products in which 93.95% were identified. Known compounds are constituted by 74.7% of hydrocarbons and 19.25% of oxygenated products. The essential oil is rich in sesquiterpene and monoterpene. In vitro antibacterial capacity of the essential oil was assessed by disc method against human and food pathogens. Bacillus cereus and Streptococcus pneumoniae were very sensitive to the essential oil with 11 mm and 25 mm of inhibition zone European Scientific Journal November 2017 edition Vol.13, No.33 ISSN: 1857 -7881 (Print) e -ISSN 1857 365 respectively. The MIC of the essential oil was 1mg/mL for Bacillus cereus and 0.25 mg/mL for Streptococcus pneumoniae. MBC values were 2.5 mg/mL and 0.5 mg/mL, respectively. The ratio MBC/MIC for both strains was inferior to 4 concluding hence that the essential oil has bactericidal effect against the two sensitive strains. In vitro antioxidant capacity of the essential oil was performed according to qualitalive (TLC) and quantitative (measure of DPPH radical scavengening) methods. The essential oil showed antioxidant activity with IC50 value of 0.35 mg/mL

Background: Nowadays, the efficiency of antibiotics is endangered by the development of resistant bacterial strains. Consequently, novel bioactive agents are intensively searched. Marine sponges are well-known for being major sources of bioactive compounds, including unusual sterols. Until now, among sterols, interesting antibacterial activity has been reported exclusively for Δ5 sterols. Objectives: This study aims to describe the steroid composition of the marine sponge Biemna laboutei collected in the North coast of Madagascar, and the antibacterial activity of steroid mixture against human pathogenic strains. Methods: Sponge was extracted in CHCl3/MeOH. Free steroids were separated from other lipids by column chromatography with dichloromethane as specific eluent. Free sterols/steroids and sterol acetates were analyzed by gas chromatography coupled with mass spectrometry. Antibacterial activity (Minimum inhibitory concentration, MIC) of steroid fractions was assessed for eight strains using agar diffusion with cellulose disks. Results: Neutral lipids were the major lipid class (79.1% of total lipids) and the dichloromethane eluted fraction contained only free steroids giving rise to the identification of eleven compounds. These components presented exclusively Δ7 unsaturation, including lathosterol as major one (38.4%) and four 3-oxo-steroids (11.8%). The steroid fraction of B. laboutei has demonstrated efficiency against pathogenic strains but more specifically on the gram(+) Bacillus cereus (MIC of 12.5 µg/mL) and Staphylococcus aureus (MIC of 25 µg/mL). This latter bacterium causes several illnesses, some of those strains being antibiotic-resistant and this becomes a worldwide health problem. Conclusion: This is the first report for an antibacterial activity of a mixture of Δ7 steroids against a resistant strain of S. aureus to many antibiotics.

Background : Silver nanoparticles pose high antibacterial properties against multi drugresistant and non-resistant bacteria. However, bacteria acquire resistance against chemically synthesized silver nanoparticles after repeated exposure. Therefore, there is an inevitable need to understand the mechanistic behavior of silver nanoparticles. Objective: In this study, we have performed a complete proteomic analysis of Escherichia coli after the treatment with silver nanoparticles to find out the mechanism of bactericidal action of silver nanoparticles (AgNPs). Methods: Silver nanoparticles were synthesized using Artemisia annua leaf extract and incubated with Escherichia coli to elucidate the antibacterial assay by determining MIC and the effect on the growth pattern. Further total genome proteins were isolated from control and silver nanoparticles treated bacteria, which were identified by LC MS and Label free quantification analysis technique. Results:: Total identified proteins were 293, out of which 11 proteins were exclusively present in treated bacteria; these are the proteins mainly expressed in stress conditions. Fold change analysis shows that 65 proteins were upregulated where stress proteins are overexpressed while membrane proteins were downregulated. Conclusions: This study reveals that silver nanoparticles inhibit the expression of cellular proteins and cause cell death. Such a study may be helpful in designing drugs against resistant microbes.