From a traditional cheese, El-Ma, produced in Algeria, 198 strains of lactic acid bacteria were isolated. Twenty strains among them produced the antimicrobial agent against Listeria monocytogenes ATCC 15313. The strain (No. 1-74) with the highest productivity (60k.eq. μg/ml) was coccus in the form. A high quantity of the agent was produced when it was cultured at 25-35°C, pH 3.2-5.7, in the presence of metal ions (1mM) such as Ca2+, Ni2+ and Ba2+ for 36h, under stationary culture conditions. Heavy metal ions such as Ag+, Cu2+, Co2+, and Zn2+, excess oxygen inhibited the growth and the productivity of the agent.