## 2 Results
### Microbiological Parameters in Uninoculated Samples  
Milk, Curd, and Whey Analysis  
Before the beginning of the cheese production, the natural presence of _Staphylococcus aureus_, _Salmonella_ spp., _Listeria monocytogenes_ and staphylococcal toxin was analyzed, as well as lactic acid bacteria (LAB), aerobic mesophilic bacteria (AMB), coliform organisms (CO), molds and yeasts (M/Y) indicators in milk, uninoculated curd and whey. Only _S. aureus_ and _Listeria_ were recovered in milk, curd, and whey (Table 1), and two species were identified, _L. monocytogenes_ and _L. Ivanovii_. Enterotoxin (<1 ng/mL) and _Salmonella_ were not detected in any non-inoculated samples.  
_Staphylococcus aureus_. Once the cheese was molded, it was left in the ripening chamber for 24 h, and then the native _S. aureus_ was enumerated, finding values of 7.4 log MPN/g in the non-inoculated cheese. Table 1 shows the behavior of _S. aureus_ in the different sections and sampling times of the non-inoculated cheese.  
The statistical analysis of the non-inoculated cheese did not show a significant difference in the distribution of _S. aureus_ regarding the analyzed sampled area up to 45 days (\(p\) = 0.343), the last sample obtained in which the bacteria was recovered. In addition, during the ripening process, no traces of staphylococcal enterotoxin were detected (<1 ng/mL).  
_Listeria monocytogenes_. In cheese made with non-inoculated milk, native _L. monocytogenes_ counts increased at 24 h, reaching a population of 7.2 log MPN/g and then drastically decreased on day 15, when samples from the core had 2.9 log MPN/g, and later, no _L. monocytogenes_ was detected. On the other hand, the main matrix and surface samples allowed  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{3}{c}{_Staphylococcus aureus_} & \multicolumn{3}{c}{_Listeria monocytogenes_} \\ \hline  & \multicolumn{3}{c}{**(Log MPN/mL or g)**} & \multicolumn{3}{c}{**(Log MPN/mL or g)**} \\ \hline  & **Milk** & **Curd** & **Whey** & **Milk** & **Curd** & **Whey** \\ \hline
0 * & 5.9 & 6.4 & 5.9 & 5.9 & 7.5 & 7 \\ \hline Cheese & Surface & Main matrix & Core & Surface & Main matrix & Core \\ \hline
24 h & & 7.4 & & & 7.2 & \\
7 d & 6.5 \({}^{\rm a}\) & 6.1 \({}^{\rm b}\) & 4.9 \({}^{\rm b}\) & 3.4 \({}^{\rm A}\) & 4.3 \({}^{\rm B}\) & 4.1 \({}^{\rm B}\) \\
15 d & 6.7 \({}^{\rm a}\) & 6.5 \({}^{\rm b}\) & 5.6 \({}^{\rm b}\) & 3.1 \({}^{\rm A}\) & 2.7 \({}^{\rm B}\) & 2.9 \({}^{\rm B}\) \\
30 d & 4.5 \({}^{\rm a}\) & 3.9 \({}^{\rm b}\) & ND & 1 \({}^{\rm A}\) & 0.3 \({}^{\rm B}\) & ND \\
45 d & 1.1 \({}^{\rm a}\) & ND & ND & ND & ND & ND \\
60 d & ND & ND & ND & ND & ND & ND \\
75 d & ND & ND & ND & ND & ND & ND \\
90 d & ND & ND & ND & ND & ND & ND \\ \hline \hline \end{tabular} d = days of maturation; ND = not detected; * _Salmonella_ and staphylococci enterotoxin were not detected. Values with different superscripts (\({}^{\rm a,b}\) or \({}^{\rm A,B}\)) in the rows, are significantly different between adjacent columns of the same pathogen (\(p\) < 0.05).  
\end{table}
Table 1: Behavior of pathogens in Cotija cheese made with uninoculated milk.  
Figure 1: Revaluated sections of Cotija cheese (From [PERSON] et al., 2016 [12]).  
the pathogen to survive until day 30, with a recovery of 0.3 and 1 log MPN/g, respectively (Table 1).