Characterization of a Bacteriocin-Like Inhibitory Substance Produced by Lactobacillus plantarum Isolated from Egyptian Home-Made Yogurt

Aly E. Abo-Amer*

ABSTRACT: As demand for reduction of the use of chemical additives in food and for more natural and microbiologically safe food products is increasing, bacteriocins may have considerable potential for food preservation. This work aimed to isolate Lactobacillus strains of potential bioprotective application from Egyptian home-made yogurt. Out of 73 strains of isolated Lactobacillus strains, only four strains of Lactobacillus plantarum (AA110, AA125, AA135 and AA140) demonstrated production of antagonistic activity against foodborne pathogens. The antimicrobial agent excreted by L. plantarum AA135 was the most active against a wide range of Gram-positive and Gram-negative pathogens. Because of the interesting inhibition spectrum of agent AA135, it was selected for further characterization. The activity of the antimicrobial substance produced from L. plantarum AA135 was resistant to heat (121 oC for 30 min), catalase and lysozyme, but was destroyed by papain, trypsin and pepsin. The AA135 compound was produced during growth phase and, when the neutralized and concentrated supernatant was added to a culture of Pseudomonas aeruginosa in logarithmic phase, it produced a rapid decrease in optical density indicative of cell lysis. The AA135 agent could be extracted from the culture supernatant fluids with n-butanol. When 40% ammonium sulphateprecipitated agent was analysed by 10% SDS-PAGE, two peptides with high molecular sizes of ~45 kDa and <45 kDa were seen. L. plantarum AA135 does not contain any plasmid, which indicates that the antagonistic compound’s production is encoded by chromosomal genes. The antibacterial agent was characterized as a bacteriocin-like inhibitory substance and designated as plantaricin AA135. The potential significance for improving the hygiene and safety of the food products is discussed.

KEYWORDS: Lactobacillus plantarum, plantaricin AA135, chromosome, protein patterns.

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Division of Microbiology, Department of Botany, Faculty of Science, Sohag University, Sohag, Egypt

* Corresponding author, E-mail: aaboamer1@sci.sohag.edu.eg

Received 6 Dec 2006, Accepted 1 Mar 2007