Controlling Listeria monocytogenes in Cottage cheese through heterologous production of enterocin A by Lactococcus lactis

Aims: Enterocin A is an example of a class IIa bacteriocin with potent anti-listerial activity. This study was initiated with a view to harnessing this activity, through heterologous production by a lactococcal starter strain, to limit levels of Listeria monocytogenes in a food (Cottage cheese). Methods and Results: Plasmid pEnt02 (containing entA, I, T and D genes under the control of a constitutive promoter) was introduced into a Lactococcus lactis strain capable of fermenting lactose. When this bacteriocin-producing starter was used in combination with a non-enterocin A producer, thereby compensating for an associated reduction in acid production, during a Cottage cheese fermentation, a decrease in L. monocytogenes (tagged with lux genes for convenience) levels was evident. Conclusions: Enterocin A, heterologously produced by a food grade lactic acid bacteria (LAB), was therefore shown to have potential for use as a biocontrol agent in food. Significance and Impact of the Study: Many of the most active anti-listerial compounds identified to date are enterocins. However, because of Enterococcus-associated concerns, the use of these antimicrobials in a food setting has been curtailed. Although enterocins have been heterologously produced in LAB to overcome this problem, this study represents the first occasion upon which the benefits of such heterologous production have been demonstrated in a food context.