Production, partial purification, and characterization of pediocin as a potential sanitizer for stainless steel surfaces contaminated with Listeria monocytogenes (Murray et al.) Pirie

Optimization of the production of pediocin, a bacteriocin produced by Pediococcus acidilactici AA5A, was accomplished as a preliminary step for evaluating its potential as a sanitizing agent for stainless steel surfaces. The influence of fermentation conditions and medium components on pediocin production using batch fermentation was determined. In TGE broth, pediocin production was optimal (6,400 AU/ml) at the 10th hr of cultivation, at 40 deg C, and at an initial pH of 6.0. Maximum activity of 12,800 AU/m) was obtained using a base medium which consisted of 0.5 percent CaCO3, 75 percent crude yeast extract, and supplemented with 1 percent soybean meal, and 2 percent molasses. Good bacteriocin activity (12,800 AU/ml) was achieved using MRS broth with 1 percent yeast extract. The adsorption/desorption method was used to extract and partially purify pediocin. The activities of the semi purified pediocin produced using TGE broth (12,800 AU/ml) and the optimized base medium (3,200 AU/ml) were lower than the activity of the partially purified pediocin (51,200 AU/ml) produced using MRS broth with 1 percent yeast extract. The bacteriocin exhibited heat and pH tolerance at 100 deg C for 60 min and pH 3.0-9.0. Pediocin was able to inhibit the pathogen Listeria monocytogenes LM3. Pediocin concentration and duration of treatment affected the reduction of Listeria monocytogenes LM3 on stainless steel. After an hour, treatment of slides contaminated with the pathogen (allowed to adsorb onto stainless steel for 3 hrs) with pure pediocin (1.0 x 10 sup 5 AU/ml) effectively reduced the number of live cells by 98 percent. Cell counts increased as treatment duration was increased. Treatment of slides with undiluted pediocin for 5 hr resulted in only 56.22 percent reduction. Moreover, 25 percent pediocin (6,400 AU/ml) reduced Listeria monocytegenes populations by only 2.93 percent and viable cell counts in the treated slides increased to approximately the same level as the untreated slides. A negative percent reduction (-7.3 percent) was obtained from slides treated with 50 percent pediocin (800 AU/ml), since Listeria monocytogenes LM3 populations grew to levels higher than the control. Equivalent concentrations of nisin and various concentrations of lactic acid completely inhibited the growth of the pathogen. Microbial reductions of Listeria monocytogenes cells LM3 adsorbed onto stainless steel for 12hr were lower than those obtained in cultures made to adsorb for 3 hrs. Treatment with undiluted pediocin, 50 percent solution, and 25 percent solution resulted in 76.33, 66.00, and 63.33 percent reductions, respectively. Nisin treatment of slides using concentrations equivalent to the pediocin concentrations used resulted in relatively higher reductions (94.5, 91.5, and 92.5 percent) although, 100 percent kill was not achieved. Given the conditions under which treatments were conducted, nisin and lactic acid show greater potential than pediocin as sanitizers for reducing Listeria monocytogenes LM3 populations on stainless steel surfaces.