The cytotoxic effect of P. motoro venom, mucus and bacterial culture supernatants on human epithelial cells (HEp-2) was determined by the MTT method which measures the viability of cells in terms of their mitochondrial metabolic rate. Accordingly, PR-171 100 μL of DMEM (Dulbecco’s Modified Eagle’s Medium) containing 106 cells was added to each well of 96 well cell culture plates and incubated for 24 h at 37 °C in a 5% CO2 incubator. After incubation, the medium was discarded and either

100 μL of different concentrations of tissue extract (5 mg, 1 mg, 0.5 mg and 0.1 mg), 100 μL of mucus (v/v) or 100 μL of bacterial culture previously grown for 18 h in DMEM were added to the plates and incubated overnight at 37 °C in a 5% CO2 incubator. After incubation the supernatant was discarded and 20 μL of a 5% solution of MTT in PBS was then added into each well and the plates were incubated for 2 h at 37 °C. One hundred microliters of Triton (1%) was used as positive control. Subsequently, 100 μL/well of methanol (100%) was added to the plate and then incubated for further 10 min. After incubation, the absorbance of each sample was determined at 570 nm in a Spectronic 20 Genesys 1 spectrophotometer. Results were expressed as mean ± SD. Single criterion ANOVA followed

by Bonferroni’s test was used to analyze the data, using SigmaStat 3.0 software. Values with p < 0.05 were considered statistically significant. In order to determine the species of bacteria present in the mucus of P. motoro CH5424802 order rays or environmental water, 89 bacterial strains obtained either from the mucus of P. motoro rays

(n = 24) or from the Alto Paraná river water were isolated and identified. The results showed that only 3.4% of all isolates were Gram positive and they were found only in the mucus. A total of fifteen different species of Gram-negative bacteria were identified, however, Acinetobacter spp., P. aeruginosa, Klebsiella pneumoniae, Klebsiella oxytoca, Serratia spp., Shigella spp. and Enterobacter spp. were encountered only in the mucus whereas Plesiomonas shigelloides and Citrobacter koseri were found only in the water. Six bacterial species, A. hydrophila, Aeromonas sobria, Pseudomonas putida, C. freundii, E. coli and Enterobacter this website cloacae were encountered in both, water and mucus samples ( Table 1). The API 20E and 2API 20NE kits, casein agar and erythrocyte hemolysis assays were utilized to determine the ability of all Gram-negative bacterial isolates to produce gelatinase, caseinase and hemolysin respectively. The results showed that all A. sobria, A. hydrophila and P. aeruginosa strains produced gelatinase. All A. sobria and to a lesser extent, other Gram-negative strains produced hemolysin. Caseinase was produced only by A. sobria, A. hydrophila, P. aeruginosa and C. freundii strains ( Table 2). The antimicrobial profile of each Gram-negative bacterial isolate was determined by the standard disk diffusion method.