## 4 Biocontrol Methods
### Lactic Acid Bacteria  
Biocontrol, by using LAB to prevent the growth of pathogenic microorganisms, is an increasingly explored strategy in the dairy industry. LAB are effective in inhibiting Gram-positive bacteria, and in the case of artisanal cheeses made with raw milk, they have been used to control foodborne pathogens. LAB produce bioactive metabolites, such as organic acids, antimicrobial peptides, and enzymes, which contribute to the inhibition of pathogens and the extension of the shelf life of products [86]. LAB, a large group of non-sporulating Gram-positive bacteria, such as _Lactococcus_, _Lactobacillus_, _Enterococcus_, _Streptococcus_, and _Leuconostoc_ species, are recognized for their ability to produce lactic acid, antimicrobial peptides, and bacterioxins, having a long history of use in the production of fermented foods and being proven to inhibit or destroy food pathogens, such as _L. monocytogenes_ and _Staphylococcus aureus_[87; 88]. Among them, lactobacilli and lactococci are among the most important LAB species, with beneficial effects on human health. They are generally considered safe (GRAS) and can be used directly in food products. LAB metabolites contribute to the inhibition of the growth of _L. monocytogenes_ through bactericidal and bacteriostatic mechanisms. Advanced metagenomics, proteomics, and metabolomics studies are needed for a better characterization of probiotic bacteria and their role in maintaining intestinal health. Homoferrantative LAB produce lactic acid as their main metabolite, reducing pH and inhibiting the growth of _L. monocytogenes_. Heteroformentative bacteria produce, in addition to lactic acid, ethanol and carbon dioxide, compounds that contribute to the inhibition of bacterial growth by disrupting the cell membrane and denaturing proteins necessary for bacterial survival [89]. Lactic acid and acetic acid are the most important antimicrobial acids, reducing the intracellular pH of pathogenic bacteria and causing the death of microbial cells. Although _L. monocytogenes_ possesses acid tolerance genes, lactic acid at high concentrations can cause their inactivation. For example, a concentration of 0.5% lactic acid reduced the population of _L. monocytogenes_ by 6 log\({}_{10}\) cfu/g in just two hours. LAB also produce antimicrobial compounds such as hydrogen peroxide, which enhances antimicrobial effects by activating the lactoperoxidase system. This system generates hypothiocyanite anionsthat destroy bacterial cellular components. Also, diacetyl, produced by LAB, interferes with the utilization of arginine by bacteria, leading to their death. The consumption of oxygen by LAB creates an anaerobic environment unfavorable for aerobic bacteria [90]. In the case of artisanal cheeses, the use of LAB has been well documented, contributing not only to the control of pathogens but also to the improvement of the nutritional and sensory profile of the products. LAB can degrade harmful compounds such as biogenic amines and cholesterol, contributing to the increase in the concentrations of beneficial substances such as antihypertensive peptides, GABA (aminobutyric acid), and short-chain fatty acids. The latter is essential for metabolic health, and the ability of LAB to produce such compounds makes them a key element in the food industry [86]. Regarding bacterial competition, LAB grow faster than _L. monocytogenes_ and compete effectively for nutrients, negatively affecting the growth of the pathogenic microorganism. Studies show that LAB inhibit _L. monocytogenes_ in various food matrices, especially in meat and ready-to-eat (RTE) dairy products. For example, [PERSON] et al. (2022) [91] isolated several strains of _Lactococcus_ and _Lactobacillus_ from dairy products from Sardinia, observing their anti-listerial activity in fresh cheeses. Three strains significantly reduced _L. monocytogenes_ by 4 log cfu/g, and other strains had a bacteriostatic effect.