The Co-Isolation of Lactic Acid Bacteria (LAB) and A Related Pathogenic Strain from Pangasius Nasutus

Abstract

Catfish species Pangasius nasutus, or locally known as Patin Buah is one of a popular aquaculture product in Malaysia. Probiotic strain is an attractive alternative to conventional antibiotics in managing aquaculture diseases. Pangasius can be a source of bacterial strain in developing suitable probiotic useful in Pangasius rearing. This study highlights on the isolation of LAB strains from the selected tissues from P. nasutus which are the heart, stomach, and intestines. These strains were subjected to morphological, biochemical, and genotypic characterisations. Three different strains were isolated from fish tissues, H-Hn from heart; S-Hn from stomach; and I-Sk from intestine. Biochemical characterisation were consistent with ribosomal rRNA sequencing, in which strain H-Hn (acc. No. MW504962) is highly similar (100%) to Lactococcus lactis, and both I-Sk (MW504964) and S-Hn (MW504963) are similar (99%) to Lactococcus garvieae. All strains appeared to be non-spore forming, non-motile, Gram-positive coccus, catalase and citrate negative, and fermenting sugar. Unlike H-Hn, both H-Sk and I-Sk strains were able to grow at 6.5% NaCl and at higher temperature (45°C). The antimicrobial properties were assessed using agar disk diffusion assay against several indicator organisms (Escherichia coli, Pseudomonas aeruginosa, Salmonella typhimurium, Staphylococcus aureus and Vibrio parahaemolyticus). These strains exhibited varying degree of inhibitory properties against the indicator organisms. Strain H-Hn inhibited E. coli and V. parahaemolyticus. Meanwhile, strains I-Sk and S-Hn showed a rather broad-spectrum inhibition. From P. nasutus, other L. lactis strain, a pathogenic species from L. garvieae could also be found especially in their gut tissues. The presence of L. garvieae in commercial P. nasutus should raise some concern to those who like to consume this fish. Meanwhile, the LAB strains isolated has probiotics potential that can be commercially used in the managing fish diseases in aquaculture.