Sorotipos de Salmonella de efluente de esgoto: níveis de resistência a metais pesados e transferência de marcadores / Salmonella serotypes from effluent sewage waters: levels of resistance to heavy metals, and markers transfer

RESUMO

A total of 278 Salmonella strains resistant to the heavy metals Cu, Hg and Zn were analyzed.The strains included the following four serotypes which were prevalent in isolates from the effluents of two sewage treatment plants in the city of Rio de Janeiro, RJ, from Brazil, 1984 to 1985 S.panama(118), S.typhimurium(58), S.agona(53) and S.oranienburg(49).Confirmation of the resistance patterns using a resistogram indicated in vitro stability for 96.7 por cento of the sample, including the Cu and Hg markers and excluding Zn.Up to 68.7 por cento of the strains were resistant to 200 ug/ml Cu and 77.7 por cento were resistant to 45ug/ml Hg.These frequencies were obtained by submitting the Salmonella strains to increasing concentrations of Cu(100 to 250ug/ml) and Hg(5 to 50 ug/ml)incorporated into nutrient agar. For a total of 268 conjugation experiments, in which the standard Escherichia coli K 12 F-Na1 strain and cultures isolated from sewage water (Citrobacter freundii Tc and Salmonella oranienburg Sm ) were considered to be the recipients, Cu transconjugants were isolated at an overall rate of 19.3 por cento and Hg transcomjugant at a rate of 86.4 por cento.All of the transconjugant analyzed expressed the same level of resistance as the corresponding Salmonella(donor)strain.We discuss the significance of these results in terms of the dissemination of genetic markers in view of the continued discharge of sewage effluent contaning these microorganisms into the Bay of Guanabara