Salicylate or bismuth salts enhance opsonophagocytosis of Klebsiella pneumoniae.

After treatment of encapsulated Klebsiella pneumoniae with salicylate or bismuth compounds, phagocytic uptake by human peripheral white blood cells or rat alveolar macrophages was assessed. Without salicylate pretreatment of bacteria, a 30-60% net increase in viable bacteria resulted in phagocytic assays after a 1 hour incubation. With salicylate pretreatment, dose-related decreases in bacterial counts were seen, achieving a maximal reduction of 60% with 240 microM salicylate pretreatment. Bacterial variants producing less capsule were more serum sensitive and more readily phagocytosed. Micrographs of Giemsa-stained cells revealed phagocytic uptake of multiple bacteria after salicylate pretreatment, but virtually no uptake of untreated bacteria. Opsonization with polyclonal antiserum decreased bacterial cell counts by 20% without and by 90% with salicylate pretreatment of bacteria. Pretreatment of bacteria with bismuth salts also enhanced opsonophagocytosis of encapsulated bacteria. Thus, agents known to reduce capsule expression in K. pneumoniae also enhance phagocytic uptake of bacteria.