Isolation and Identification of Potential Probiotics Bacteria from the Gut of Oreochromis niloticus and Clarias gariepinus in Uganda

Abstract

Bacterial infections remain a hindrance to aquaculture expansion globally. Increased fish mortality and poor performance resulting from ill health has forced farmers to resort to the use of antibiotics globally. However, prolonged use of these drugs in aquaculture is becoming restrained as pathogens develop resistance to drugs and unpredicted long term effect on public health. Alternative approaches to control disease are proposed of which probiotics have come forward. Therefore, the purpose of this study was to identify potential probiotic bacteria in the guts of fish from different sampling sites around Kampala. Fish were obtained from selected cages, ponds, tanks and hatcheries around Kampala, including different parts of Lake Victoria. The fish were gutted and the guts aseptically swabbed with subsequent culture on both general purpose and selective media. The identification of various isolates was based on gram staining and biochemical tests. Probiotic screening was done using the agar spot method. Results revealed complete growth across all samples. The total microbial load was highest in the samples from the lake (1204.8±12.7 × 10 5 cfu/g). Out of the three probiotic genera isolated, only Lactobacillus spp (LB) and Lactococcus spp (LC) showed antibacterial activity against selected pathogenic bacteria. The activity of LB was significantly (p< 0.0001) higher against Streptococcus spp (17.0±0.2 mm) as compared to Proteus at 9±0.02 mm and Pseudomonas (7.5±0.2 mm). Lactobacillus spp did not show any antimicrobial activity against Staphylococcus aureus . For Lactococcus spp , probiotic activity was only detected against Proteus spp (5.5±0.2 mm). Although our study shows that Lactobacillus spp and Lactococcus spp possess probiotic activity against a number of pathogenic bacteria, characterization of these isolates is paramount before further manipulation.