In vitro assessment of probiotic properties and gamma-aminobutyric acid production of selected lactic acid bacteria strains

This study aimed to perform an in vitro assessment of probiotic properties and to select lactic acid bacteria (LAB) strains that can produce the bioactive compound, gammaaminobutyric acid (GABA). A total of seven LAB strains of various species were examined for probiotic properties. These strains produced antimicrobial substances to inhibit the growth of target pathogenic bacteria. All selected LAB strains could withstand GI tract conditions. The strains showed bile salt hydrolase (BSH) activities. An antibiotic susceptibility test revealed that all examined strains were susceptible to ampicillin, chloramphenicol, erythromycin, gentamycin, penicillin and tetracycline, whereas they were resistant to kanamycin, norfloxacin, streptomycin and vancomycin. All strains of LAB in the current study gave high adhesion to Caco-2 cells ranging from 23.32-75.48%. Moreover, all tested LAB cells could inhibit Salmonella enterica serovar Enteritidis invasion of Caco-2 cells. Additionally, the tested LAB cells and cell-free supernatants (CFS) showed low cytotoxicity to inhibit the proliferation of Caco-2 cells. Moreover, three LAB strains, L. curvatus FJNP12, L. plantarum SKKL1 and W. cibaria SFM5, clearly showed GABA production based on the TLC results. Additionally, these strains also yielded high amounts of GABA according to an HPLC method, 15.66, 11.76 and 5.62 g/L, respectively. The open reading frame (ORF) of the gadB gene of L. plantarum SKKL1 revealed that it was 1,407 bp in length, encoding a polypeptide of 469 amino acids, with a molecular weight of 53.56 kDa and an isoelectric point (pI) of 5.58 predicted using the ExPASy program. These strains could be used in starter cultures for value-added agricultural products.