Isolamento e seleção de bactérias candidatas a probiótico para utilização em cultivo do camarão marinho (Litopenaeus vannamei, Boone, 1931)

Abstract

Shrimp farming is an activity susceptible to diseases that can lead to reduced productivity and increase mortality, generating significant economic losses for the sector. Probiotics supplements have been used as an alternative to solve this problem and the use of probiotic strains isolated from shrimp farming or natural environment has been evaluated to shrimp farming disease control. The aim of this study was to isolate microorganisms from the intestinal tract of natural marine environment shrimps, characterize, select and test possible probiotic bacteria that can be used in the prevention of infectious diseases and improving the growth performance of white shrimp (Litopenaeus vannamei). From bowel samples of wild shrimp (Penaeus schimitti), collected in Santo Amaro da Purificação-Bahia, were isolated eighteen strains of lactic acid bacteria, which eleven was Gram-positive, catalase negative and coccos-rod shaped cell morphology. All cultures were tested in vitro for acidity and bile salts resistence, and four selected strains (PURS2, PURS8, PURS17 and PURS20), subjected to in vivo tests to evaluate growth performance of juvenile Litopenaeus vannamei and challenged against the Vibrio harveyi. These strains were identified by molecular biology and species confirmed by carbohydrate fermentation profile as Enterococcus faecium (PURS17) and Enterococcus gallinarum (PURS2, and PURS8 PURS20). The performance parameters evaluated: survival rate, final weight, weight gain and final biomass did not differ (P>0,05) between probiotics strains. After challenge with Vibrio harveyi, levels of lactic acid bacteria in shrimp was not reduced (p>0,05) in any treatment and heterotrophic bacteria was significantly reduced (p <0.05) only for the positive control. For Vibrios spp. were detected significant reductions (p <0.05) in all treatments, except for the PURS8 (E. gallinarun). These results indicate a positive response of the probiotic cultures PURS2, PURS20 (E. gallinarun) and PURS17 (E. faecium) in inhibition of Vibrio harveyi. After challenge the survival rate of shrimp fed with E. faecium and E. gallinarum supplemented diet and the negative control was statistically superior (p <0.05) compared to positive control. The reduced population of vibrios and higher survival rate in shrimp fed probiotic strains may be linked, possibly as a result of the intestine and hepatopancreas colonization by this microorganisms, by competitive exclusion or by action of bacteriocins.