Antibacterial Characteristics of N-Alkyl-2-alkylthiopyridinium and N-Alkyl-4-alkylthiopyridinium Salts

N-Alkyl-2-alkylthiopyridinium (2TPX-n : X=I or Br, n=6-18) and N-alkyl-4-alkylthiopyridinium salts (4TPX-n), which have an electron-releasing group on the pyridine ring, were synthesized. Both 2TPBr-12 and 4TPBr-12 showed a wide and potent bactericidal spectrum of activity against Gram-negative bacteria (9 strains) and Gram-positive bacteria (3 strains), compared with N-dodecylpyridinium iodide (P-12) which has no substituents. The activity of these new compounds was not correlated with the hydrophobicity of the bacterial cell surface. This suggests that the bactericidal mechanism of 2TPBr-12 and 4TPBr-12 is different from that of P-12. The bactericidal and bacteriostatic activity of the new compounds against Escherichia coli K12 W3110 was closely influenced by their alkyl chain length. Since they have two hydrophobic alkyl chains in their structure, it seems that hydrophobic association between the molecule of 2TPX-n or 4TPX-n and medium components in the minimum inhibitory concentration measurement system caused the reduction in their apparent concentration. The bactericidal activity of these compounds was dependent on their bacterioclastic activity, and less dependent on their hydrophobicity (RM).