## 3 Results and Discussion
### Antimicrobial Activity  
Table 12 shows the results of the antimicrobial assay of 6-methyl-2-thiouracil and its complexes.  
The highest antimicrobial activity was exhibited by the CuL1 complex. It was active against all the test-microorganisms. The Pd(II)L1 complex did not inhibit the growth of  
\begin{table}
\begin{tabular}{l c c c} \hline \hline  & \multicolumn{3}{c}{**Complexes**} \\ \cline{2-4}
**Test Microorganisms** & **6-Methyl-2-Thouracil** & **CuL1** & **PdL1** \\ \cline{2-4}  & \multicolumn{3}{c}{**Inhibition Zone, mm**} \\ \hline _Staphylococcus aureus_ ATCC 25923 & - & 8 & - \\ \hline _Escherichia coli_ ATCC 8739 & - & 11 * & 10 * \\ \hline _Eterococcus faecalis_ ATCC 19433 & 11 & 13 & - \\ \hline _Salmonella enterica_ ssp. _ enterica_ ser. & - & 13 & 8 \\ Enetritidis ATCC 13076 & - & 12 & 9 \\ \hline _Pseudomonas aeruginosa_ ATCC 9027 & 9 & 12 & 9 \\ \hline _Proteus vulgaris_ G & 9 * & 11 * & 9 * \\ \hline _Bacillus subtilis_ ATCC 6633 & 9 * & 9 & 10 * \\ \hline _Bacillus cereus_ ATCC 11778 & 9 * & 8 & 9 * \\ \hline _Listeria monocytogenes_ ATCC 8787 & 9 * & 11 & 8 \\ \hline _Klebsiella pneumoniae_ ATCC 13883 & 9 * & 13 * & 11 * \\ \hline _Candidia albicans_ ATCC 10231 & 11 & 11 & 9/10 * \\ \hline _Saccharomyces cerevisiae_ & - & 9 & - \\ \hline \end{tabular}  
Well diameter—7 mm, * Inhibition zone with single cell colonies.  
\end{table}
Table 12: Antimicrobial activity of 6-methyl-2-thiouracil and its complexes.  
S. aureus, E. faecalisis, and S. cerevisiae. 6-methyl-2-thiouracil showed the smallest antimicrobial specter; it was not active against S. aureus, E. coli, S. enterica, and S. cerevisiae. The addition of Cu(II) improved the antimicrobial activity of 6-methyl-2-thiouracil against all of the test microorganisms, except B. cereus. However, there were single cell colonies in the inhibition zones (IZ) against E. coli, P. vulgaris, and K. pneumoniae. This is indicative of different levels of resistance in the microbial population. The addition of Pd(II) on the other hand, led to a loss of activity against E. faecalis and lower activity against L. monocytogenes and C. albicans.  
The inhibition zone diameters for 6-propyl-2-thiouracil are presented in Table 13.  
It showed higher antimicrobial activity against P. vulgaris and both yeasts strains in comparison to the complexes with Cu(II) and Pd(II). The Cu(II) complex inhibited the growth of all test microorganisms to a different degree; the best results were obtained against E. faecalis, S. enterica, and P. aeruginosa. P. vulgaris was resistant to the tested concentration of the Pd(II) complex (unlike against 6-propyl-2-thiouracil), but all other test microorganisms were more sensitive towards its action in comparison to 6-propyl-2-thiouracil. This pattern was also observed in comparison to the Cu(II) complex, except for E. coli, P. vulgaris, and S. cerevisiae. Similar to 6-methyl-2-thiouracil and its complexes, there were single cells in some inhibition zones (e.g., 6-propyl-2-thiouracil against B. cereus, K. pneumoniae, and S. cerevisiae). There were two distinct inhibition zones of the Pd(II) complex against S. aureus and B. cereus: a smaller clear zone and an additional larger zone with single cell colonies within. A more concentrated sample would probably completely inhibit the growth of these microorganisms and significantly increase the antimicrobial activity of the complex.  
Generally, the presence of Cu(II) and Pd(II) ions in the complexes increased the antimicrobial activity of the tested substances, which is in line with the work of other authors [44].