| Summary: | A new series of pyrazolo-benzimidazole hybrid Mannich bases were synthesized, characterized by <sup>1</sup>H-NMR, <sup>13</sup>C-NMR, IR, UV-Vis, MS, and elemental analysis. In vitro cytotoxicity of the new compounds studied on fibroblast cells showed that the newly synthesized pyrazolo-benzimidazole hybrid derivatives were noncytotoxic until the concentration of 1 μM and two compounds presented a high degree of biocompatibility. The antibacterial and antibiofilm activity of the newly synthesized compounds was assayed on Gram-positive <i>Staphylococcus aureus</i> ATCC25923, <i>Enterococcus faecalis</i> ATCC29212, and Gram-negative <i>Pseudomonas aeruginosa</i> ATCC27853, <i>Escherichia coli</i> ATCC25922 strains. All synthesized compounds <b>5a–g</b> are more active against all three tested bacterial strains <i>Staphylococcus aureus</i> ATCC25923, <i>Enterococcus faecalis</i> ATCC29212, and <i>Escherichia coli</i> ATCC25922 than reference drugs (Metronidazole, Nitrofurantoin), with the exception of compounds <b>5d</b> and <b>5g</b>, which are less active compared to Nitrofurantoin, and all synthesized compounds <b>5a–g</b> are more active against <i>Pseudomonas aeruginosa</i> ATCC27853 compared to reference drugs (Metronidazole, Nitrofurantoin). Compound <b>5f</b> showed the best activity against <i>Staphylococcus aureus</i> ATCC 25923, with a MIC of 150 μg/mL and has also inhibited the biofilm formed by all the bacterial strains, having an MBIC of 310 µg/mL compared to the reference drugs (Metronidazole, Nitrofurantoin).
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