Decreased lipopolysaccharide content and enhanced susceptibility of leptospiras to serum leptospiricidal action and phagocytosis after treatment with diphenylamine.

Growth of leptospiras in the presence of diphenylamine (DPA) caused a decrease in the content of leptospiral lipopolysaccharide (LPS). In association with this decrease of LPS, leptospiras became susceptible to anti-leptospiral action of normal rabbit serum (NRS), leptospiricidal action of antibody and complement, and killing by phagocytes. DPA-treated leptospiras were eliminated rapidly from the blood of infected mice and could not grow in the animals.