Isolation, partial identification and evaluation of the beneficial properties of Bacillus strains isolated from Piaractus mesopotamicus

MARCOS G. GUIDOLI; VALERIA I. AMABLE; MARÍA E. CICUTA; SEBASTIÁN SÁNCHEZ; MARÍA E. NADER-MACÍAS

San Miguel de Tucumán

Congreso; VII Congreso Argentino de microbiología general ? SAMIGE del Bicentenario; 2011

SAMIGE

The genus Bacillus constitutes a wide group of rod-shaped Gram-positive bacteria, and is characterized by the ability of producing endospores. Although the genus is not commonly found in marine and fresh water environments, it has been isolated from the guts of several marine and fresh water animals and sediments. Bacteria belonging to this genus have been widely used as probiotics due to the ability to compete for nutrients with other bacteria and to produce antimicrobial substances such as antibiotics and enzymes. In this work the isolation, partial characterization and beneficial properties of eight Bacillus strains from the intestinal tract of Piaractus mesopotamicus, the most frequently cultivated fish species in the north Argentinean region, was evaluated. 70 of the 140 strains isolated from 10 healthy fishes were rod-shaped bacteria, 8 of which were resistant to the temperature treatment indicating its ability to produce endospores. The results of the Shaeffer and Fulton staining, catalase, Voges-Proskauer reaction, NO3- reduction, and growth at 50oC, 65oC and 7% NaCl allowed us to indentify this strains as Bacillus spp. None of the 8 strains were able to produce hydrogen peroxide, and all of them showed an autoagregation index lower than 50% and a hidrophobicity between 0% and 5%. One strain was able to inhibit the growth of Salmonella enteritidis and Klebsiella spp.; another strain inhibited both pathogens and also Stapylococcus aureus and another strain inhibited only the growth of Staphylococcus aureus. All this inhibitions were produced by a metabolite different to organic acids and did not affect the growth of Aeromonas salmonicida, Yersinia rukeri, Streptococcus agalactiae, Streptococcus dysagalactiae, Escherichia coli, Pseudomonas aeruginosa, Listeria monocytogenes and Proteus vulgaris. The inhibition halo was evident only with the in situ growth of the producing strain. The compatibility assays showed that any of the strains inhibited the others. Further studies are being performed to determine the inclusion of these strains in a product to be applied in aquaculture.