Diversity of Mercury Resistant Escherichia coli Strains Isolated from Aquatic Systems in Rio de Janeiro, Brazil

Escherichia coli may harbor genetic mercury resistance markers which makes this bacterial species a promising alternative for bioremediation processes. The objective of this study was to investigate phenotypic and genetic characteristics related to diversity and mercury resistance among 178 Escherichia coli strains isolated from residential, industrial, agricultural, and hospital wastewaters and recreational waters at Rio de Janeiro city. Genetic and conventional methods were carried out in order to determine mercury resistance. Random amplification of polymorphic DNA (RAPD-PCR) and denaturing gradient gel electrophoresis (DGGE) were used to investigate genetic variability. RAPD data revealed a high degree of polymorphism among E. coli mercury resistant strains and showed reproducibility and good discriminative results. DGGE typing detected diversity within the merA gene fragment. Our findings represent an improvement in epidemiological studies of HgR E. coli and support the evidence of nonclonal nature of mercury resistant E. coli strains circulating in rural and urban aquatic systems in Rio de Janeiro city.