Antimicrobial activity of new 2-thioxo-benzo[g]quinazolin-4(3H)-one derivatives

Background: The antimicrobial activity of a synthesized series of 28 2-thioxo-benzo[g]quinazolin-4(3H)-one derivatives was evaluated in vitro against five Gram-positive bacteria, including Bacillus subtilis, Enterococcus faecalis, Staphylococcus aureus, Staphylococcus epidermidis and Streptococcus pyogenes. The antibacterial activity was extended to include five Gram-negative bacteria: Pseudomonas aeruginosa, Escherichia coli, Proteus mirabilis, Klebsiella oxytoca and Enterobacter cloacae. Furthermore, the antifungal activity was evaluated against 10 fungal strains, including Aspergillus fumigatus, Syncephalastrum racemosum, Geotricum candidum, Candida albicans, Aspergillus niger, Cryptococcus neoformans, Candida tropicalis, Penicillium expansum, Microsporum canis and Trichophyton mentagrophytes. Methods: The agar well diffusion method was adopted against Gram-positive and Gram-negative bacteria and fungi, using ampicillin, gentamicin and amphotericin B as reference drugs, respectively. Results: The findings of the antibacterial studies revealed that most of the tested compounds possess strong activity against both bacterial species. Compounds 8 and 23 were the most active on Gram-positive bacteria, while several compounds demonstrated significant antibacterial activity on Gram-negative bacteria, especially Escherichia coli. Furthermore, several compounds showed strong antifungal activity against many of the investigated fungi. The obtained results were reinforced by determination of the minimum inhibitory concentration for the active compounds against Gram-positive and Gram-negative bacteria, as well as fungi, compared to the reference drugs. Conclusion: Many of the investigated compounds showed potent activity against all tested microbial species. The discovery has provided a foundation for the synthesized compounds to serve as a platform for further design and development of more potent antimicrobial agents.