Occurrence of Listeria spp. in Soft Cheese and Ice Cream: Effect of Probiotic Bifidobacterium spp. on Survival of Listeria monocytogenes in Soft Cheese

Abstract

<i>Listeria monocytogenes</i> is one of the most important emerging foodborne pathogens. The objectives of this work were to investigate the incidence of <i>Listeria</i> spp. and <i>L. monocytogenes</i> in soft cheese and ice cream in Assiut city, Egypt, and to examine the effect of some probiotic <i>Bifidobacterium</i> spp. (<i>Bifidobacterium breve</i>, <i>Bifidobacterium animalis</i>, or a mixture of the two) on the viability of <i>L. monocytogenes</i> in soft cheese. The existence of <i>Listeria</i> spp. and <i>L. monocytogenes</i> was examined in 30 samples of soft cheese and 30 samples of ice cream. Bacteriological analyses and molecular identification (using 16S rRNA gene and <i>hlyA</i> gene for <i>Listeria</i> spp. and <i>L. monocytogenes</i>, respectively) were performed on those samples. Additionally, <i>Bifidobacterium</i> spp. were incorporated in the making of soft cheese to study their inhibitory impacts on <i>L. monocytogenes</i>. Out of 60 samples of soft cheese and ice cream, 25 samples showed <i>Listeria</i> spp., while <i>L. monocytogenes</i> was found in only 2 soft cheese samples. Approximately 37% of soft cheese samples (11 out of 30) had <i>Listeria</i> spp. with about 18.0% (2 out of 11) exhibiting <i>L. monocytogenes</i>. In ice cream samples, <i>Listeria</i> spp. was presented by 47% (14 out of 30), while <i>L. monocytogenes</i> was not exhibited. Moreover, the addition of <i>B. animalis</i> to soft cheese in a concentration of 5% or combined with <i>B. breve</i> with a concentration of 2.5% for each resulted in decreasing <i>L. monocytogenes</i> efficiently during the ripening of soft cheese for 28 d. <i>Listeria</i> spp. is widely found in milk products. Probiotic bacteria, such as <i>Bifidobacterium</i> spp., can be utilized as a natural antimicrobial to preserve food and dairy products.