Cell lysis induced by nisin in sensitive strains of Lactococcus lactis: In vitro and in situ studies

Nisin is a bacteriocin that produces pores in the cell wall, and releases the intracellular material. The present work aimed to evaluate the cell lysis of Lactococcus lactis subsp. lactis, by either adding nisin directly in the medium or by adding a nisin-producing bacteria, developed in two studies. The in vitro study assessed 19 strains of L. lactis for their ability to metabolise citrate and diacetyl, and their sensitivity to nisin and NaCl. In the in situ study, the effect of nisin on the cellular lysis of L. lactis during the ripening of Chihuahua cheese was analysed. Three different types of cheese were manufactured and monitored for 90 days: a control cheese made with a commercial dairy starter culture, a cheese made with a nisin-producing bacteria and nisin, and a cheese without nisin but made with nisin-producing bacteria. The in vitro study showed that ten out of 19 strains tested were resistant to the action of nisin, and nine were sensitive. It also revealed that different concentrations of NaCl influenced the lytic effect of nisin in L. lactis. The in situ study showed that cell lysis remained constant during the ripening of all cheeses.