Potentiation of aminoglycoside inhibition and reduction of capsular polysaccharide production in Klebsiella pneumoniae by sodium salicylate

This study determined the effects of sodium salicylate combined with several aminoglycoside antibiotics on the growth and capsular polysaccharide (CPS) production of Klebsiella pneumoniae. Salicylate significantly enhanced the inhibitory effect of all aminoglycoside antibiotics against all bacterial strains tested. The production of CPS was decreased by 62–86% when 2.5 mw salicylate was used. Amikacin combined with salicylate reduced CPS only slightly more than salicylate alone. The chelating agents, ethylenediamine tetra-acetic acid and ethylene bis tetraacetic acid, which have similar CPS-reducing properties, did not enhance the inhibitory effect of amikacin. Noncapsular variants of strains of K. pneumoniae were as susceptible to amikacin as the fully encapsulated strains, with or without salicylate present. Therefore, the combination of salicylate and the aminoglycosides acted synergistically to inhibit K. pneumoniae growth, but the increase in antibiotic sensitivity with salicylate was not a result of a reduction in CPS production. The use of salicylate in maximum therapeutic doses may enhance the activity of aminoglycosides sufficiently to allow the dose of aminoglycoside to be reduced when infections due to K. pneumoniae are treated.