The sensitivity of Staphylococcus aureus 79 and 80, and Escherichia coli 95 to sodium salicylate, nicotinaldehyde singly, and in combination with nicotinic acid or nicotinamide.

Minimum bactericidal concentrations of salicylate, nicotinaldehyde singly, and in combination with nicotinic acid, or nicotinamide were determined for Staphylococcus aureus 79 and 80, and Escherichia coli 95, at inocula of 10(7)--10(2). The bactericidal dose of salicylate was affected markedly by the inoculum size. The bactericidal dose of nicotinic acid, or nicotinamide was affected only slightly by the size of the inoculum. Escherichia coli 95 was least affected by the inoculum size. Nicotinaldehyde is a far more bactericidal agent than is nicotinic acid, or nicotinamide; its bactericidal dose was approximately a tenth that of nicotinic acid, or nicotinamide. S. aureus 79 and 80 were affected synergistically by the combinations of nicotinic acid, or nicotinamide with salicylate. Nicotinaldehyde reduced the effectiveness of nicotinic acid, at all inoculum sizes, of S. aureus 79, while the reduction of effectiveness of nicotinamide was only found with inocula of 10(7)--10(5). At low inocula, 10(4)--10(2), an additive effect was demonstrated. S. aureus 80 was antagonistically affected, at all inoculum sizes, by the combination of nicotinaldehyde with nicotinamide, while with nicotinic acid a slight synergy was noted. In contrast, Escherichia coli 95 was antagonistically affected, at all inoculum sizes, by combinations of nicotinic acid, nicotinamide with salicylate, or nicotinaldehyde.