Antibacterial activity of 65 2-acetylpyridine thiosemicarbazones and related compounds was determined by using clinical isolates of nine bacterial genera. Minimal inhibitory concentrations (MICs) of 0.002 to 0.062 ,ug/ml were obtained with 23% of the compounds for Neisseria gonorrhoeae and 0.016 to 0.062 ug/Iml with 17% of the compounds for N. meningitidis. Staphylococcus aureus was inhibited in the MIC range of 0.125 to 0.5 /Lg/ml by 18% of the thiosemicarbazones, whereas 26% inhibited group D enterococcus with an MIC of 0.25 to 2.0 Itg/ml.Poor antibacterial activity was shown toward the gram-negative bacilli, i.e., Pseudomonas, Klebsiella-Enterobacter, Shigella, Escherichia coli, and Proteus.

We have investigated the in vitro antibacterial activity of 13 2-acetylpyridine-1-oxide thiosemicarbazones and 5 thiosemicarbazides against 80 clinically significant bacterial cultures, including 13 isolates with known antibiotic resistance. Of the thiosemicarbazones tested, 5 had minimal inhibitory concentrations (MICs) of 0.25 μg/ml for Neisseria gonorrhoeae isolates; 1 of these had an MIC range of 0.25–0.5 μg/ml for the Neisseria meningitidis cultures, and 2 had MICs of 2 and 2–4 μg/ml for Staphylococcus aureus and Streptococcus faecalis isolates, respectively. Two of the thiosemicarbazides had MICs of 0.25 μg/ml for N. gonorrhoeae, whereas 2 others had MICs of 2–4 and 4–8 μg/ml for S. aureus and S. faecalis isolates, respectively. The test compounds were ineffective against the gram-negative enteric cultures and the Pseudomonas isolates.