Determination of mercury concentration by a new spectrophotometric method and evaluation of bacterial diversity in river water samples from Brazil

One of the main micropollutants reported in river water is mercury (Hg), a heavy metal toxic to human and animal organisms that can promote bacterial resistance to antimicrobials used in the clinical practice. Having done this in consideration, monitoring the concentration of Hg in the river is an important indicator of physical-chemical and microbiological quality of water. Thus, in this study the Hg concentration was determined using a new spectrophotometric method in river water samples recovered from Minas Gerais, Brazil. Furthermore, the diversity and antimicrobial resistance of Gram-positive and Gram-negative bacteria isolated from these samples were also reported. A new ultraviolet-visible spectrophotometric method was validated and applied to quantify Hg in water and revealed high concentrations in the samples (0.13–0.35 μg·mL−1), above the limits established by Brazilian standards (0.002 μg·mL−1). Gram-negative bacteria (mainly Escherichia coli) were recovered in greater proportion (88.4%) from water samples with high mercury concentration and showed resistance to tetracycline and ampicillin. Our results highlighted that E. coli resistant to carbapenems, which are latest generation beta-lactams, were detected. In conclusion, the Hg levels are considerably high in river waters in Brazil, and these mercury-rich water sources are important reservoirs of multi-drug resistant bacteria.