Isolation and Identification of Heavy Metals and Antibiotics Resistant Strains from Antananarivo Dumpsite, Madagascar

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.