Partial characterization of bacteriocin AMA-K, produced by Lactobacillus plantarum AMA-K isolated from naturally fermented milk from Zimbabwe

Strain AMA-K, isolated from naturally fermented milk produced in Gwanda, Kafusi area, Zimbabwe, was identified as Lactobacillus plantarum based on sugar fermentation reactions (API 50 CHL) and PCR with species-specific primers. The cell-free supernatant containing bacteriocin AMA-K inhibited the growth of Listeria innocua and Enterococcus faecalis. Based on tricine–SDS–PAGE, bacteriocin AMA-K is 2.9 kDa in size. Activity levels of 12 800 AU/ml was recorded in MRS broth at 30 °C and 37 °C. Complete inactivation or significant reduction in bacteriocin activity was observed after treatment with proteolytic enzymes, but not with catalase and α-amylase. Bacteriocin activity was not destroyed after treatment with SDS, Tween 20, Tween 80, urea, triton X-100 or EDTA. Loss of activity was recorded after treatment with Triton X-114. Bacteriocin AMA-K remained stable after 2 h of incubation at pH 2.0–12.0 and at 100 °C, respectively. The bacteriocin not adheres to the surface of the producer cell and has a bacteriolytic mode of action. Bacteriocin production is stimulated by the presence of Listeria innocua. Lactobacillus plantarum AMA-K grows in milk, but produces only 800 AU bacteriocin per ml after 24 h.