Role of urinary solutes in natural immunity to gonorrhea

Abstract

Natural resistance of the male urethra to gonococci has not been explained by classical immune mechanisms but could result from antibacterial properties of urine. Accordingly, survival of F-62 T2 [colony type] gonococci [Neisseria gonorrhoeae] (107/ml) in midmorning urine was measured by serial dilutions and plate counts. Fifteen killer urines from 8 people all killed >3 logs (average, 5.3) and 13 of 15 were sterilized. Fourteen nonkiller (inhibitor) urines from 7 subjects allowed no growth. Killer urines were more acidic (pH 5.4 vs. 6.4) and more concentrated (861 vs. 717 mosmol[milliosmolar]/kg) than nonkillers. Upon addition of H+, urea and NaCl to urines and broth, pH proved to be the major killing factor, but urea and NaCl were also bactericidal. Susceptibility to urine bactericidal power did not vary with colony type (T2 vs. T4) or strain (F-62 vs. 2 fresh isolates). Killing was rapid (0.5-3 h) and not bacteriolytic. Escherichia coli multiplied 10-fold in urines that inhibited growth of gonococci. The bacteriostatic effect of urine may explain why gonococci do not infect the bladder and kidney during gonorrhea. The bactericidal properties of urine may contribute to resistance against gonococcal urethritis.