Prospecção de bactérias intestinais em beijupirá cultivado

Abstract

Bacterial diseases restrict the expansion of intensive sea cage cobia (Rachycentron canadum) farming. They are usually treated with antibiotics, which in excess may lead to bacterial drug-resistance. Antibiotic residue can also reach the wild fish or other animals, fish farmers and fish consumers. In this study it was aimed to identify, by biochemical and molecular tests, potentially pathogenic Gram-negative bacteria multi-resistant to antibiotics and potentially probiotic Gram-positive bacteria isolated from farmed cobia intestine in different periods of the year. Ten fingerlings and 30 juveniles were collected, of which 82.5% showed evidence of bacterial infection and 47.5% of nephrocalcinosis. Biochemical and molecular identification results agreed in 86.11% of the 72 Gram-negative strains isolated. There were identified 18 species, 12 genera and five families, Aeromonaceae, Neisseriaceae, Pseudomonadaceae, Vibrionaceae and Enterobacteriaceae, the last one being more significant (63.88 %). The most frequent species were Enterobacter cloacae (27.78%) and Photobacterium damselae subsp. damselae (25%), greater pathogen to cobia. Antibiogram showed that 95.83% of the strains were penicillin resistant (6,25 μg), 62.50% ampicillin resistant (10 ug) and 15.28% enrofloxacin resistant (5 ug). Antibiotic multi-resistance was detected in 69.44% of the strains tested and E. cloacae achieved the highest MAR rate (0.8571). Regarding Gram-positive bacteria, 53 strains were obtained and classified in 13 species of the families Enterococcaceae, Paenibacillaceae, Staphylococcaceae, Streptococcaceae e Bacillaceae. Bacillus cereus was the most frequent species (39.62%) and Bacillaceae the most representative family. Antibacterial activity was observed in 16.98% of the strains, which produced inhibition zones ranged from 9.33 ± 0.58 to 28.77 ± 0.25 mm against Vibrio vulnificus, V. parahaemolyticus and V. alginolyticus. Species presenting antibacterial activity were Staphylococcus piscifermentans, S. lugdunensis, Bacillus spp., Enterococcus spp., E. faecium and Lactococcus lactis subsp. lactis. Of these, E. faecium was the most significant species (33.33%) producing the largest inhibition zones especially against V. vulnificus. Period of year was not significant (P ≥ 0.05) for cobia’s intestinal bacterial diversity, multidrug resistance of Gram-negative, or to the quantity of Gram-positive with antimicrobial properties. Intestine from R. canadum contains Gram-negative bacteria multi-drug resistant and potentially pathogenic to aquatic animals and humans, and Gram-positive bacteria with antimicrobial activity against vibrios, which must be considered as a prophylactic and/or therapeutic alternative against vibriosis in cobia farming.