Identification and in vitro assessment of potential probiotic characteristics and antibacterial effects of Lactobacillus plantarum subsp. plantarum SKI19, a bacteriocinogenic strain isolated from Thai fermented pork sausage.

A total of 2257 lactic acid bacteria were preliminarily screened for antagonistic activity against Lactobacillus sakei subsp. sakei JCM 1157. Strain SKI19 was selected and identified at the subspecies level as Lactobacillus plantarum subsp. plantarum SKI19, using 16S rRNA gene sequence analysis combined with recA and dnaK genes' amplification. Antibacterial activity of SKI19 was completely lost after treatment of neutralized cell free culture supernatant with proteolytic enzymes, suggesting that SKI19 produced a bacteriocin-like substance that inhibited not only closely related species, but was also effective against Listeria monocytogenes DMST 17303. Viewed under scanning electron microscope, cell membranes of the indicator strain appeared to collapse after exposure to the bacteriocin-like substance. In vitro tests concerning probiotic properties, SKI19 survived under simulated gastrointestinal tract conditions, and adhesion of its cell surface to xylene and chloroform was 90.14 and 89.85%, respectively. Complete inhibition by SKI19 against pathogenic bacteria (Escherichia coli DMST 4212, L. monocytogenes DMST 17303, and Staphylococcus aureus DMST 8840) was observed in co-cultivation under anaerobic conditions. A safety assessment showed that SKI19 was susceptible to several antibiotics and had no haemolytic activity. PCR amplification of virulence factors with the specific primers for ace, asa1, cylLS , efaAfs , hyl, and gelE genes were negative for SKI19. Also, SKI19 did not harbor any hdc, tdc, odc or ldc genes involved in biogenic amine production. The results reveal that SKI19 has probiotic potential and antibacterial activity, and is safe for further application in certain food products.