The B. licheniformis CPQBA 571-12 DRM 07 was the only isolate that showed inhibitory features against the pathogen V. alginolyticus BCCM 2068 with inhibition zone of 20 mmin diameter. This could be a probiotic strain in tests in vivo formarine shrimp farming. A common way to
select probiotic candidates is conducting inhibition tests in vitro (Luis-Villaseñor et al., 2011). Gullian et al. (2004) reported that the strain of Bacillus P64 isolated from the hepatopancreas of L. vannamei had a good inhibitory effect against V. harveyi S2 with inhibition zone of 15.3 mm in diameter. Similar results have been shown by Luis-Villaseñor et al. (2011) with Bacillus spp. using the pathogens V. parahaemolyticus (CAIM170) and V. harveyi (CAIM1793)with inhibition zone diameters of 11 and 17.5mm, respectively. The Bacillus inhibitory effects are attributed to the ability of these bacteria to secrete substances, such as toxins, bacteriolytic enzymes, subproduct of primary metabolic pathways, antibiotic substances and bacteriocins that may exert a bacteriostatic or bactericidal effect on a wide range of Grampositives and Gram-negatives, which also explains the inhibitory effect on Vibrio (Schulz et al., 2005).