EFFECT OF SALICYLATE ON EXPRESSION OF FLAGELLA BY ESCHERICHIA-COLI AND PROTEUS, PROVIDENCIA, AND PSEUDOMONAS SPP

Osmotic stress, salicylate, and Mar (multiple antibiotic resistance) m utation are known to block the expression of the OmpF porin, Since the se conditions have also been shown to inhibit the expression of P and CFA fimbriae in Escherichia coil, we speculated that they might affect the expression of flagella as well. Hyperosmotic conditions have been shown to block the synthesis of flagellin and expression of flagella in E, call (C, Li, C, J. Louise, W, Shi, and J. Adler, J, Bacteriol, 1 75:2229-2235, 1993), In the current study, sodium salicylate was found to inhibit the motility of E. coli, Proteus mirabilis, Proteus vulgar is, Providencia rettgeri, and Providencia stuartii in a reversible, co ncentration-dependent manner. Swarming did not occur at 20 mM sodium s alicylate. Salicylate also blocked the synthesis of flagellin in E. co il. Phenotypic Mar mutants of E. coli derived from motile strains were amotile. Flagella were markedly reduced as determined by scanning ele ctron microscopy when P. mirabilis was grown in broth containing 20 mM salicylate. Salicylate had no apparent effect, however, on expression of a 40-kDa porin protein in P. mirabilis. This finding suggests that the noted effect of salicylate on Proteus spp. may be mediated throug h a mechanism other than porin production or that the Proteus porin ma y not be analogous to OmpF in E. coli. Salicylate decreased the motili ty of Pseudomonas cepacia but had no effect on Pseudomonas aeruginosa. The exact mechanism by which salicylate exerts its effect is not know n, but it appears to be related to osmoregulation.