Screening of lactic acid bacteria from gastrointestinal tracts of marine fish for their potential use as probiotics

One hundred and sixty isolates of lactic acid bacteria (LAB) with inhibitory activity against pathogenic Escherichia coli were isolated from gastrointestinal tracts of fish, shrimp and shellfish. One hundred and sixteen isolates were obtained from fish, twenty isolates from shrimp and twenty-four isolates from shellfish. Three strains were selected based on their bile and acid tolerances. All acid-tolerant strains showed inhibitory activity against human pathogens, including Staphylococcus aureus, Listeria monocytogenes, Salmonella sp. and Escherichia coli. However, the antibacterial activities were lost when the culture supernatants were neutralized to pH 6.5-7.0 and treated with catalase, indicating that the inhibition may be contributed by acid and hydrogen-peroxide production of the strains. Nucleotide sequences of their 16s rDNA showed 98% (655/668 bp), 97% (691/712 bp) and 98% (492/501 bp) homology to Pediococcus pentosaceus LM2, Pediococcus pentosaceus SL4 and Enterococcus faecium SF, respectively.