## 2 Results
### Antimicrobial Effects of CAR1 and THY5 during a Challenge Test of Beef Minced Meat  
The antimicrobial effects of CAR1 and THY5 EOs against _L. monocytogenes_ OH and \(S\). Typhimurium LT2 was also evaluated in a complex food matrix of beef minced meat during storage at 4 \({}^{\circ}\)C for 7 days. The 0.5% concentration was used in order to reproduce the conditions of maximum antimicrobial concentration as in the direct contact test. The presence of CAR1 EOs caused a reduction of the bacterial population of both _L. monocytogenes_ OH and \(S\). Typhimurium LT2 by about 1 log CFU/g one day after contamination, remaining essentially unchanged until the third day (Figure 3A,B). In both sets of experiments, there was an increase in microbial load after seven days of storage both in the presence and absence of the EOs, suggesting an onset of recontamination of the minced meat. In parallel, the absence of _L. monocytogenes_ OH and \(S\). Typhimurium LT2 in the food matrix in the artificially uncontaminated sample was assessed.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Pathogen Indicator**} & \multicolumn{5}{c}{**Inhibition Halo Radius (mm)**} \\ \cline{2-6}  & **CAR1** & **CAR2** & **CAR3** & **THY3** & **THY5** \\ \hline _Listeria monocytogenes_ OH & +++ & +++ & +++ & +++ & +++ \\ \hline _Listeria monocytogenes_ SA & + & + & + & +++ & +++ \\ \hline _Listeria monocytogenes_ CAL & +++ & +++ & +++ & +++ & +++ \\ \hline _Listeria immocua_ 1770 & ++ & ++ & ++ & +++ & +++ \\ \hline _Salmonella enterica_ Typhimurium LT2 & +++ & ++ & +++ & +++ & +++ \\ \hline _Salmonella enterica_ Give & +++ & +++ & +++ & +++ & +++ \\ \hline _Salmonella enterica_ Derby & +++ & +++ & +++ & +++ & +++ \\ \hline Enterotoxigenic _E. coli_ (ETEC) K88 & +++ & +++ & +++ & +++ & ++ \\ \hline _Pseudomonas putida_ WSC358 & +++ & ++ & +++ & +++ & ++ \\ \hline _Pseudomonas putida_ KT2240 & +++ & ++ & ++ & ++ & ++ \\ \hline _Pseudomonas fluorescens_ B13 & + & + & + & ++ & ++ \\ \hline \hline \end{tabular} Antimicrobial activity was considered high (+++) when the value of the inhibition halo radius (hr) was greater than 7.5 mm (hr \(>\) 7.5 mm), medium (++) when between 5 and 7.5 mm (5 mm \(\leq\) hr \(\leq\) 7.5 mm) and low (+) when less than 5 mm (hr \(<\) 5 mm).  
\end{table}
Table 3: Antimicrobial activity of oregano EOs against indicator pathogens (spot test).  
Regarding the antimicrobial activity of 0.5% THY5, a different effect was observed against the two pathogens tested. The microbial load of _L. monocytogenes_ OH remained essentially unchanged after 1 and 2 days in the contaminated samples in the presence of EO, whereas a reduction of approximately 1 and 2 logs in the microbial load was observed at 3 and 7 days, respectively (Figure 3C). The minced meat in the absence of THY5 had a similar microbial titer of about 1 \(\times\) 10\({}^{5}\) CFU/g during all storage timepoints.  
The results of the challenge test set up with \(S\). Typhimurium LT2 indicated that the antimicrobial effect of THY5 EO was already appreciable at the first day with a reduction of approximately 1.5 log CFU/g and a further decrease of 1 log CFU/g was observed at the following timepoints (2, 3 days). On day 7, an increase of about 0.6 log CFU/g suggested the start of recontamination of the minced meat (Figure 3D). Surprisingly, from the second day of storage at 4 \({}^{\circ}\)C, a reduction in the microbial titer was observed in the absence of EO.