Atividade de Antimicrobianos sobre o crescimento de CIanobactérias e produção de Cianotoxinas

Abstract

Contamination of the environment by drugs is a growing concern, especially when it comes to antimicrobials and biocides. These types of substances directly affect the local biota because of its therapeutic nature, and expected stability in organic medium. Among the most heavily used in hospital, household and veterinary means we have ciprofloxacin, a quinolone antimicrobial class, very found in the aquatic environment, and chlorhexidine, biocide of the biguanide class, widely used in hospital and dental environment. Among the micro-organisms most affected by the presence of these harmful substances, cyanobacteria are considered one of the most sensitive, and are the most susceptible because they are distributed throughout the environment, dominating the benthic and planktonic production of various habitats. Cyanobacteria can proliferate in strongly impacted environments and, considering global warming may occur blooms. This phenomenon has become common in surface waters throughout the world, and is worrying due to increased production and release of secondary metabolites by cyanobacteria, among these the cyanotoxins. They can be hepatotoxic, neurotoxic or cytotoxic, and reported several poisoning accidents by animals and even humans, contact with contaminated bodies of water. Objectives: To define the EC50 two cyanobacterial strains of the genus Microcystis under the effect of ciprofloxacin and chlorhexidine. To analyze the production and release of cyanotoxins by four cyanobacterial strains of Microcystis genus, under the influence of certain concentration of ciprofloxacin and chlorhexidine. Methods: Growth inhibition test (OECD 201 protocol), using strains of Microcystis aeruginosa and Microcystis panniformis individually and ciprofloxacin antimicrobial and biocidal chlorhexidine individually. Growth curves were performed and were calculated values of these substance concentration that inhibits 50% of cell growth in culture in the laboratory. Subsequently, four different cyanobacterial strains of Microcystis genus were placed in contact with concentrations of ciprofloxacin and chlorhexidine, near the EC50 set in the previous experiment, and after 96 hours was extracted intracellular and extracellular microcystin, being quantified by enzyme immunoassay. Results: In the first experiment, two of the strains were more sensitive to antimicrobial than the biocidal, also being affected the production of chlorophyll by the cells. In the second experiment, three of the four strains showed higher concentrations of microcystin under effect of ciprofloxacin, and two of the four strains showed higher concentrations of microcystin under effect of chlorhexidine. Conclusions: The results indicate the seriousness of the discharge of effluents containing drug residues in water bodies, providing direct risk to aquatic biota and indirect human population, with the release of harmful secondary metabolites by cyanobacteria.