Application of Microbial Assay for Risk Assessment Biotest in Evaluation of Toxicity of Human and Veterinary Antibiotics

The microbial assay for risk assessment (MARA) is a multispecies, growth inhibition microplate toxicity test with 11 microorganisms individually lyophilized in microplate wells The microbial species representing wide diversity, generated 11 microbial toxic concentration (MTC) values were obtained giving a unique 'toxic fingerprint' profile of the test sample The toxicity of 14 antibiotics was evaluated with the MARA test The fingerprints for each group of antibiotics differ, indicating a particular toxic profile. Tetracyclines were the most toxic antibacterials with the minimum MTC value of 3.6 mu g L(-1). In the group of tetracyclines the order of the three most sensitive microbial strains was the same 2 > 6 > 7 Quinolones affected the most sensitive strain(s) at concentrations of 12-75 mu g L(-1). The MARA bioassay exhibited different spectra of toxic responses to microbial strains for the first and second generation quinolones However, for first generation quinolones strain 6 was substantially more sensitive than the other microorganisms, while second generation quinolones were most toxic to strain 3, followed by 6 then 4. In this instance, the three strains belong to two different phylogenetic groups-strain 3 is gamma-proteotype and strains 4 and 6 are beta-proteotype (C) 2010 Wiley Periodicals, Inc Environ Toxicol 25 487-494, 2010