## 3 Discussion
While the distribution of _S. Typhimurium in the inoculated cheese, showed significant differences (_p_ = 0.0005). It was observed that it was similar in the main matrix and the core, meanwhile, the surface showed 1.5 log more than the main matrix. The inhibition of pathogens in ripened cheeses made with raw milk, like Cotija, has also been reported by other authors [23] who have shown the gradual demise of pathogens such as _L. monocytogenes_[24], and the inhibition of other pathogens in fermented cheeses [25; 26]. The absence of inoculated pathogens is associated with the metabolic processes that occurred during cheese maturation and the inhibitory compounds that the other microorganisms have, such as lactic acid bacteria [18; 26; 27]. [PERSON] et al. [25], reported production of bacteriocins from _Enterococcus fiecium_ and _E. faecalis_ recovered from Cotija cheese. This author showed inhibition of _S. aureus_, _Yersini entercoolitia_, _S. Typhimurium and _Pseudomonas aeruginosa_. [PERSON] et al. [18] did not detect pathogenic bacteria like _Salmonella_, _Listeria monocytogenes_, _Brucella_, or _Mycobacterium_ in a metagenomic analysis performed on Cotija cheese. They reported three predominant phyla (_Lactobacillus_, _Leuconostoc_ and _Weissella_) associated with the production of various metabolites with antimicrobial activity. Within the complex microbiota in Cotija cheese, the presence of lactic acid bacteria can inhibit the inoculated pathogens, and the yeast present could have participated in this process [28; 29; 30]. [PERSON] et al. [12] observed that surface of Cotija cheese showed higher counts of yeasts, which is like our study. These microorganisms could contribute to the inactivation of pathogens observed in cheese's surface, in conjunction with physicochemical factors. Also, yeasts can be present in different cheeses [28; 31]. As previously described, the metabolic activity of the microbiota present during the fermentation process generates many compounds ranging from peptides, like bacteriocins, to peroxide and organic acids, among other metabolites that determine the predominance of some microbial groups such as lactic acid bacteria, responsible for the synthesis of these compounds, as well as the typical organoleptic characteristics of Cotija cheese [7; 18; 32]. Even though only the production of lactic acid was quantified in the present investigation, it should be noted that the absence of pathogens coincided with the increase of lactic acid and the consequent drop in pH. Water activity and its decrease also influenced, although to a lesser degree, to the inactivation of the inoculated pathogens. Lactic acid concentration and pH had the highest impact on the decrease of _S. Typhimurium_ and _S. aureus_. Both pathogens showed a gradual decrease associated with increasing acidity and decreasing pH. On the other hand, the inactivation of _L. monocytogenes_ showed no relationship with the parameters determined since it occurred drastically. The present study shows the importance of interaction between microorganisms that constitute the complex microbiota ecosystem of cheese made with no pasteurized milk. The same microbiota present in cheese is used for its production. In Cotija cheese, the robustness of its native ecology is decisive to ensure its quality. Quality control considers the maturity stage, which ensures the absence of pathogens and takes advantage of the characteristics _per se_ of Cotija cheese, including its functional properties provided by its characteristic microbiota [12]. Likewise, the quality of raw material in Cotija cheese is important because it is the one that will determine the type of microorganisms that will carry out the fermentation process and give the desired sensory characteristics. However, the raw material and milk must be free of pathogens like _Brucella_ and _Mycobacterium_[18].