The rapid rise and spread of multi-resistant microbial pathogens have forced the consideration of alternative methods of combating infection. Biological control of infectious diseases, a new emerging biological tool, offers a powerful alternative to conventional synthetic chemicals either in human and animal health management as well as agricultural and food biotechnology. However, microbes produce an extraordinary array of microbial defense systems. These include broad-spectrum classical antibiotics, metabolic by-products (organic acids), lytic agents (lysozymes), numerous types of proteinaceous exotoxins, and bacteriocins. In the microbial world, the antimicrobial peptides are an important part of the defense system of bacteria and they are referred to as bacteriocins. Traditional antibiotics are also produced by some bacteria but the conventional antibiotics and bacteriocins should be considered as different antimicrobial compounds (Abriouel, Franz, Omar, & Gálvez, 2011).

Bacteriocins are ribosomally synthesized antimicrobial compounds that are produced by bacteria and which usually inhibit closely related species or species within the same ecological niches. The specificity of their action and their proteinaceous nature distinguish them from other classical antibiotics (Vaca, Ortiz, & Sansinenea, 2022). Four major classes of bacteriocins were described: (i) lantibiotics that contain unusual amino acids such as lanthionines and b-methyllanthionines; (ii) nonlantibiotic, small, heat-stable bacteriocins including Listeria-active peptides (cystibiotics), thiol-activated peptides (thiolbiotics) and complexes of two peptides bacteriocins; (iii) large heatlabile bacteriocins; and (iv) complex bacteriocins associated with other chemical moieties (H.-J. Lee & Kim, 2011). There has been a recent explosion in the interest of bacteriocins as natural preservatives and they have been extensively studied, because of their potential application as food additive in dairy systems and as therapeutic agents against Gram-positive bacteria. Although Gram-positive Bacillus species are often considered to be promising biocontrol agents that are as effective as Gram-negative bacteria, they have received much less attention and studied for their production of compounds with potential uses in many fields. Above all, those produced by Gram-positive bacteria have attracted much more interest particularly for their promising agricultural potential, as they can open new opportunities for the alleviation of various undesirable pathogenic concerns. In particular, Bacillus strains are generally known to be thermotolerant and spore-forming species that show rapid growth in liquid culture and are widely distributed in soils and some food sources. Different Bacillus species produce bacteriocins. These include BLIS produced by Bacillus cereus ATCC 4579, coagulin produced by Bacillus coagulans, and bacthuricin F4, entomocin 110 thuricin 17 (T17) produced by Bacillus thuringiensis. However, and despite their promising properties as potential antibacterial agents, only a few bacteriocins from the genus Bacillus have been fully characterized (Mouloud, Daoud, Bassem, Laribi Atef, & Hani, 2013).

L. monocytogenes is a widespread foodborne pathogen that causes listeriosis, a disease with a 20–30% mortality rate in susceptible people. Due to its extreme resilience, the existence of L. monocytogenes on food contact surfaces is particularly worrying. Listeriosis is a serious infection usually caused by the consumption of food contaminated with L. monocytogenes. This lowincidence disease has the highest mortality rate among foodborne zoonoses, resulting in a significant medical, social, and economic burden. Outbreaks of Listeria spp. infections in the 1990s were primarily linked to deli meats and hot dogs. Now, Listeria outbreaks are often linked to dairy products and produce. Investigators have traced recent outbreaks to soft cheeses, celery, sprouts, cantaloupe, frozen vegetables and ice cream (Lu et al., 2021).

The aim of this study is purify the bacteriocins production by Bacillus spp. isolate from dairy sludge and characterizes their properties. Also, the effect of purified bacteriocin against L. monocytogenes will be evaluated.