AUTHOR=Fu Yuxin , Mu Dongdong , Qiao Wanjin , Zhu Duolong , Wang Xiangxiang , Liu Fulu , Xu Haijin , Saris Per , Kuipers Oscar P. , Qiao Mingqiang 

TITLE=Co-expression of Nisin Z and Leucocin C as a Basis for Effective Protection Against Listeria monocytogenes in Pasteurized Milk

JOURNAL=Frontiers in Microbiology

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2018.00547

DOI=10.3389/fmicb.2018.00547

ISSN=1664-302X

ABSTRACT=<p>Nisin, an important bacteriocin from <italic>Lactococcus lactis</italic> subsp., is primarily active against various Gram-positive bacteria. Leucocin C, produced by <italic>Leuconostoc carnosum</italic> 4010, is a class IIa bacteriocin used to inhibit the growth of <italic>Listeria monocytogenes.</italic> 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, <italic>L. lactis</italic> N8-r-lecCI (N8 harboring <italic>lecCI</italic> gene) coexpressing nisin–leucocin C was constructed based on the food-grade carrier <italic>L. lactis</italic> N8. Production of both bacteriocins was stably maintained. Antimicrobial measurements showed that the recombinant strain is effectively against <italic>Listeria monocytogenes</italic> and <italic>Staphylococcus aureus</italic> and moderately against <italic>Salmonella enterica</italic> serovar Enteritidis and <italic>Escherichia coli</italic> 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 <italic>L. lactis</italic> 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 <italic>L. monocytogenes</italic> treated with a mixture of EDTA and <italic>L. lactis</italic> N8-r-lecCI supernatant. The practical effect was verified in pasteurized milk through time-kill assay. The <italic>L. lactis</italic> 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.</p>