Isolation and Biochemical Characterization of Lactic Acid Bacteria from the Gut of Fresh Food Fishes

Abstract

This study aimed to propose the characterization of lactic acid bacteria (LAB) from the gut of common five marine fishes using morphological, physiological and biochemical characteristics. Fishes Sillago sihama, Rastrelliger kanagurta, Mugil cephalus, Sardinella longiceps and Nemipterus japonicus were collected from Kaasimedu fish market, Chennai, India. Lactic acid producing bacteria were isolated by using MRS broth. From inoculum, the bacterial colonies were observed in MRS agar using streak plate technique and incubated. Different colonies were observed and the colonies were sub-cultured for further study. Five different types of pure cultures were obtained from Sillago sihama, Rastrelliger kanagurta, Mugil cephalus, Sardinella longiceps and Nemipterus japonicus in MRS agar plates and named as LAB 1, LAB 2, LAB 3, LAB 4 and LAB 5, respectively and subjected for gram staining and catalase test to confirm the Lactic acid bacteria by biochemical method. The different small white colonies with smooth, rounded, entire margins were observed LAB 1, LAB 2, LAB 3, LAB 4 and LAB 5 in Sillago sihama, Rastrelliger kanagurta, Mugil cephalus, Sardinella longiceps and Nemipterus japonicus, respectively. The antibiotics and susceptibility test for LAB 2 and LAB 5 showed reasonable activity against Escherichia coli and Staphylococcus aureus. LAB 1 was sensitive to gentamycin, erythromycin and ampicillin drugs. These antibiotics are therefore harmful and destroy this strain of gut flora. However, LAB 1 was resistant to norflaxacin, which is a common antibiotic used to treat stomach disorders like dysentery. This confirmed the action of norfloxacin drug, which restoreed the internal environment of the stomach without destroying gut flora. LAB 5 showed intermediate sensitivity to gentamycin and ampicillin. LAB 4 was also resistant to norfloxacin. It is suggested that the lactic acid bacteria isolated from the fish gut has probiotic properties, especially with reference to being able to inhibit pathogenic strains. Nevertheless, lactic acid bacteria have several beneficial properties and develop novel functional properties for inhibition of microbes by producing growth inhibiting substances and large amounts of lactic acid.