Abstract
Nisin, an important bacteriocin from Lactococcus lactis subsp., is primarily active against various Gram-positive bacteria. Leucocin C, produced by Leuconostoc carnosum 4010, is a class IIa bacteriocin used to inhibit the growth of Listeria monocytogenes. Because two bacteriocins have different modes of action, the combined use of them could be a potential strategy for effective inhibition of foodborne pathogens. In this study, L. lactis N8-r-lecCI (N8 harboring lecCI gene) coexpressing nisin–leucocin C was constructed based on the food-grade carrier L. lactis N8. Production of both bacteriocins was stably maintained. Antimicrobial measurements showed that the recombinant strain is effectively against Listeria monocytogenes and Staphylococcus aureus and moderately against Salmonella enterica serovar Enteritidis and Escherichia coli because of its stronger antibacterial activity than the parental strain, this result first demonstrated that the co-expression of nisin and leucocin C results in highly efficient antimicrobial activity. The checkerboard assay showed that the antibacterial activity of L. lactis N8-r-lecCI supernatant was enhanced in the presence of low concentration of EDTA. Analysis of the scanning electron microscope image showed the biggest cellular morphology change in L. monocytogenes treated with a mixture of EDTA and L. lactis N8-r-lecCI supernatant. The practical effect was verified in pasteurized milk through time-kill assay. The L. lactis N8-r-lecCI strain expressing both nisin and leucocin C has a promising application prospect in pasteurized milk processing and preservation because of its strong antibacterial activity.
Highlights
Pathogen control is a significant issue in the food industry
The inhibitory effect of N8-r-bacteriocin leucocin C and its immunity gene (lecCI) was more distinct than the plasmid expression strains N8-p-lecCI and NZ9000-p-lecCI, indicating the superior antibacterial activity of N8-r-lecCI
The proteins from the culture supernatants were concentrated and analyzed with SDS-PAGE to confirm whether or not leucocin C inhibits the growth of L. monocytogenes
Summary
Foodborne diseases can spread further and more rapidly than before because of the increasing transnational trade, travel, and migration (Kaferstein et al, 1997). Various measures have been implemented to decrease infections caused by foodborne pathogens (Gandhi and Chikindas, 2007), foodborne disease outbreaks from. The foodborne pathogen Listeria, the causative agent of listeriosis (Yousef and Lou, 1999), can grow at refrigeration temperatures and adapt to low pH and high salt concentration (Cole et al, 1990). As such, this pathogen can overcome various bacteriostatic measures, increasing the difficulty of anti-listeria treatments
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