## 3 Results and Discussion
### Antimicrobial Activity
This, in turn, can curtail escalating healthcare expenditures and bolster overall productivity. On the other hand, regarding the stem, previous studies by [PERSON] and [PERSON], 2014 [28] and [PERSON] et al., 2017 [29] have demonstrated the inhibitory effect of this by-product on bacterial growth. This effect is attributed to the accumulation of phenolic compounds, such as caffe acid and p-coumaric acid, which contain hydroxyl (OH) groups in their structure. These compounds interact with the bacterial cell membrane, destabilizing its structure, leading to lysis and the release of cellular components [28; 29]. The hydroxyl (OH) groups promote electron shifts with proton exchange, disrupting the cytoplasmic membrane gradient in bacterial cells, ultimately depleting ATP levels and potentially leading to cell death [28]. Furthermore, it is evident that stem extracts exhibit greater effectiveness in inhibiting the growth of gram-positive isolates compared to gram-negative ones. This disparity can be attributed to the lipopolysaccharide-saccharide layer present on the outer membrane of gram-negative bacteria, acting as a physical barrier that impedes the penetration of phenolic compounds [30]. In comparison to other by-products, a study by [PERSON] et al., 2010 [31] focused on evaluating the antimicrobial activity of extracts from Riesling grape skins, specifically targeting bacterial isolates of _E. coli_ and _S. aureus_, employing a distinct methodology. The results of their study revealed inhibition halos ranging from 1 to 6 mm for the _S. aureus_ bacteria. It is notable that these values, compared to the results presented in Table 6 of our research, were comparatively lower. For the _E. coli_ bacterial isolate, [PERSON] et al. 's study [31] showed no inhibition of bacterial growth, mirroring the outcome of our investigation. However, the findings from [PERSON] et al., 2010 [32] stand in contrast to [PERSON] et al., 2010 [31]. [PERSON] et al. 's study demonstrated inhibition halos for the _E. coli_ bacterial isolate with extracts from skins and seeds of the Shiraz (Syrah) grape variety, indicating inhibition values of 4 \(\pm\) 0.06 mm (excluding the 6 mm disc diameter used in the study) for the film extract and 7 \(\pm\) 0.12 mm (excluding the 6 mm disc diameter used in the \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Antibiotic** & \multicolumn{6}{c}{**CN 10 \(\mu\)g**} \\ \hline
**Bacterial Strains** & **ALF PF** & **BM PF** & **Jaen PF** & **ALF S** & **BM S** & **Jaen S** \\ \hline _Escherichia coli_ ATCC & 0 & 0 & 0 & 0 & 0 & 0 \\ _Acintelobacter humantii_ & 0 & 0 & 0 & 0 & 0 & 0 \\ MJMC 525 & & & & & & \\ _Acintelobacter humantii_ & 0 & 0 & 0 & 0 & 0 & 0 \\ MJMC 561 & & & & & & \\ _Pseudomonas aeruginosa_ & & - & - & - & - & 0 & 0 \\ MJMC 526 & & & & & & \\ _Pseudomonas aeruginosa_ & & 44 & 40 & 48 & 40 & 0 & 0 \\ _Pseudomonas aeruginosa_ & & & & & & \\ _MJMC 559_ & & & & & & \\ _Staphylococcus aureus_ ATCC & 57 & 48 & 57 & 48 & 33 & 43 \\ MRSA MJMC 534-B & 52 & 43 & 52 & 30 & 0 & 48 \\ MRSA MJMC 583 & 100 & 77 & 92 & - & 0 & 69 \\ \hline \hline \end{tabular} CN, gentamicin; ALF, Affocheiro; BM, Borrado das Moscas; PF, Pruning Firewood; S, Stems; MRSA, Methhicillin-resistant Staphylococcus aureus; ATCC, American Type Culture Collection; -, not performed.  
\end{table} 
Table 7: Percentage of inhibition zone diameter (%RIZD) in relation to the tested antibiotic. study) for the seed extract. In contrast, for the bacterium _S. aureus_, [PERSON] et al. 's study yielded inhibition halos of 11 \(\pm\) 0.23 and 12 \(\pm\) 0.10 mm (excluding the 6 mm disc diameter used in the study), which were higher than the values obtained in our study, considering other extracts of by-products and the varieties under investigation. These findings highlight the variability in antimicrobial activity observed across different studies, emphasizing the influence of the extraction method, grape variety, and specific bacterial isolates being tested. While [PERSON] et al. 's results showed modest inhibition, [PERSON] et al.