title: Antimycobacterial and cytotoxicity activity of microcystins.
abstract: BACKGROUND
  The present work aimed to evaluate the antimycobacterial activity and cytotoxicity of Microcystis aeruginosa toxins, the MC-LR variant and purified extract of [D-Leu(1)] microcystin-LR.
  
  
  METHODS
  The antimicrobial activity of M. aeruginosa extract and microcystin was evaluated by resazurin microtiter assay against Mycobacterium tuberculosis, M. terrae, M. chelonae and M. kansasii. The cytotoxicity assay was performed by trypan blue exclusion against the HTC cell line.
  
  
  RESULTS
  Antimicrobial activity was observed in the hexanic extract of M. aeruginosa (RST 9501 strain) against M. tuberculosis, including sensitive and resistant strains with minimal inhibitory concentrations (MIC) between 1.93 μM and 0.06 μM. The high activity of M. aeruginosa hexanic extract could be attributed to the major presence of the toxins MC-LR and [D-Leu(1)] MC-LR that showed activity at MIC between 53 and 0.42 μM against tested mycobacterial strains. Even at the highest concentration tested, no toxicity of M. aeruginosa extracts was identified against HTC cells.
  
  
  CONCLUSIONS
  These preliminary results suggest that [D-Leu(1)] MC-LR is a promising candidate for the development of a new antimycobacterial agent.
authors: Research Center in Medical Microbiology, Federal University of Rio Grande (FURG), Rio Grande, Rio Grande do Sul State Brazil.
authors: Daniela Fernandes
authors: DF
authors: Ramos
authors: Brazilian Corporation of Agricultural Research (Embrapa), Concórdia, Santa Catarina State Brazil.
authors: Alexandre
authors: A
authors: Matthiensen
authors: School of Chemistry and Food, Federal University of Rio Grande (FURG), Rio Grande, Rio Grande do Sul State Brazil.
authors: Wilson
authors: W
authors: Colvara
authors: Graduation Program in Physiological Sciences, Institute of Biological Sciences, Federal University of Rio Grande (FURG), Rio Grande, Rio Grande do Sul State Brazil.
authors: Ana Paula Souza
authors: AP
authors: de Votto
authors: Graduation Program in Physiological Sciences, Institute of Biological Sciences, Federal University of Rio Grande (FURG), Rio Grande, Rio Grande do Sul State Brazil.
authors: Gilma Santos
authors: GS
authors: Trindade
authors: Research Center in Medical Microbiology, Federal University of Rio Grande (FURG), Rio Grande, Rio Grande do Sul State Brazil.
authors: Pedro Eduardo Almeida
authors: PE
authors: da Silva
authors: Laboratory of Cyanobacteria and Phycotoxins, Institute of Oceanography, Federal University of Rio Grande (FURG), Rio Grande, Rio Grande do Sul State Brazil.
authors: João Sarkis
authors: JS
authors: Yunes
keywords: Antimycobacterial agents; Cytotoxic activity; Microcystins; Mycobacteria