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Biogeochemical characterization of sediments under the anthropogenic influence at mouth of Rio de las Minas, Punta Arenas, Chile

Lack of purification of urban wastewaters before its discharge to the natural recipient could represent the epidemiological route for spread of pathogenic bacteria. Currently bacteria resistant to carbapenems has become a worldwide problem (MELETIS, 2016). Three sediment samples were collected during autumn at the mouth of Rio de Minas in Punta Arenas, Chile, South America: two from river flow and one from the Pacific sea. Fine river sediments (sand to silt) were dark brown to black in color, without any smell. X-ray diffraction allowed the identification of mixture of montmorillonite and kaolinite with quartz and albite, while ilmenite was also identified in one sample. Heterotrophic bacteria were found in abundance of 6.2-6.6 log colony-forming unit (CFU)/mL in all three sediment samples. We also found as much as 1.9 and 2.7 log CFU/g of carbapenem-resistant bacteria in river sediments, but they were absent in seawater sediment. The prevalence of carbapenem-resistant bacteria among total heterotrophic bacteria was 29 % and 42 % log CFU. The results are comparable to the prevalence of carbapenem-resistant bacteria (49 % log CFU) reported in landfill leachate (DURN et al., 2014). As confirmed by Bruker MALDI-TOF MS analysis, the carbapenem-resistant bacteria were represented by species of the genus Pseudomonas, which are acquired resistant to carbapenems. Scanning Electron Microscopy confirmed the presence of randomly distributed bacteria (Fig. 1) in the sediment samples. The river sediments under anthropogenic influence of untreated urban and technological wastewaters reveal a significant source of potentially pathogenic carbapenem-resistant bacteria.

bacteria ; clay ; environment

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