The effect of sodium salicylate on antibiotic susceptibility and synergy in Klebsiella pneumoniae.

Sodium salicylate was combined with the antibiotics amikacin, aztreonam, cefazolin, cefonicid, cefoperazone, ceftizoxime, norfloxacin, doxycycline, clindamycin, imipenem, mezlocillin and trimethoprim-sulphamethoxazole. The activity of the combinations was tested against encapsulated strains of Klebsiella pneumoniae, which differed markedly in their antibiotic susceptibility. The addition of salicylate (from 2 to 350 mg/l) to cultures increased the MIC of most antimicrobial agents from two- to four-fold, with the exception of imipenem and amikacin. Inhibition by imipenem was largely unchanged, and that of amikacin was increased in the presence of salicylate. The synergy of the combination of cefazolin and amikacin was abolished by salicylate, while the synergistic activity of imipenem and amikacin was significantly increased by salicylate. Doxycycline activity was most severely affected by salicylate as antimicrobial activity was significantly diminished at salicylate levels as low as 5 mg/l. In contrast, significant loss of inhibitory activity with other antimicrobials required at least 100 mg/l of salicylate. The clinical implications of salicylate on the sensitivity of K. pneumoniae to antimicrobials are discussed.