Purpose: The aim of the current study was to isolate and characterize a lactic acid bacterium exhibiting antimicrobial activity against gram-negative bacteria.
Methods: Sixty-eight lactic acid bacteria (LAB) isolates from commercial yogurt and cheese were initially screened for antimicrobial activities against three standard indicator organisms: Staphylococcus aureus, Listeria monocytogenes and Escherichia coli (O157:H7).
Results: Although most of the LAB isolates (93%) exhibited antimicrobial activity against the indicator organisms, only one representative isolate was selected for further characterization. This isolate was identified to be Lactobacillus parafarraginis by 16S rRNA, accession number KU495926. It was of interest to note that the isolate inhibited fourteen multidrug resistant (MDR) and extended spectrum beta-lactamase (ESBL) bacteria from clinical sources by spot and well diffusion assays. The minimum inhibitory concentration (MIC) of the lyophilized crude extract was ~20 mg/ml. The 14 isolates were Escherichia coli (5), Pseudomonas aeruginosa (2), Acinetobacter baumannii/haemolyticus (3), Enterobacter aerogenes (1), Proteus mirabilis (2) and Klebsiella pneumoniae (1). Further analyses of the crude extract by SDS-PAGE, fast perfusion liquid chromatography (FPLC) and PCR suggested that the inhibitory agent is a bacteriocin. The antimicrobial activity was associated with a protein band of ~ 75 kDa while the polymerase chain reaction (PCR) detected the gene (sakT-β) for sakacinT-β chain in the bacterial chromosome, but not the gene (sakT-α) for sakacinT-α chain.
Significance: The results of this study suggest that the bacteriocin produced by Lactobacillus parafarraginis KU495926 may have potential application in the preservation of fermented dairy products.