Heterologous production of pediocin for the control of Listeria monocytogenes in dairy foods

Pediocin is an antimicrobial peptide naturally produced by Pediococci with the potential to serve as a food-grade preservative for controlling Listeria contamination. The use of Pediococci in dairy products is limited due to their inability to ferment lactose, thus lactic acid bacteria (LAB) have been considered as potential hosts for the heterologous production of pediocin. In this study the four gene operon (papA-D) required for pediocin production was cloned on the nisin-inducible expression vector pMSP3535H3. The resulting vector, pRSNPed2, was electrotransformed into Streptococcus thermophilus, Lactococcus lactis ssp. lactis and Lactobacillus casei. Transformants containing the properly constructed vector were identified by PCR analysis and shown to inhibit the growth of Listeria monocytogenes Scott A. S. thermophilus transformants were all shown to constitutively express pediocin; however, in L. lactis and L. casei both constitutive and inducer-dependent expression was observed. In all cases nisin-induction resulted in optimal pediocin production. Transformants from each LAB host were also shown to inhibit the growth of L. monocytogenes NR30, a nisin-resistant variant of L. monocytogenes Scott A. These results suggest pediocin has the potential to serve as a hurdle component along with nisin for prevention of Listeria contamination of foods.