Effect of pH, temperature and surface contact on the elaboration of fimbriae and flagella by Salmonella serotype Enteritidis

Survival of enteric pathogens exposed to various environmental stresses dep ends upon a number of protective responses, some of which are associated wi th induction of virulence determinants. Flagella and fimbriae are putative virulence determinants of Salmonella spp, and ELISAs specific for the detec tion of flagella and SEF21, SEF14 and SEF17 fimbriae were used to assess th e effect of temperature and pH upon their elaboration by isolates of Salmon ella serotype Enteritidis in planktonic growth and on the surface of two-di mensional gradient agar plates, For three phage type 4 isolates of Enteriti dis of comparative clinical provenance, similar phenotypes for the elaborat ion of these surface antigens were observed. SEF14 fimbriae were elaborated in planktonic growth at 37 degrees C, but not 20 degrees C, at pH 4.77 and above but not at pH 4.04; whereas on agar gradient plates SEF14 fimbriae w ere elaborated poorly but with best yields at pH 4.04, SEF17 fimbriae were elaborated in planktonic growth at 20 degrees C, but not at 37 degrees C, a t pH 6.18 and above but not at pH 5.09 or below; whereas on agar gradient p lates SEF17 fimbriae were elaborated well even at pH 4.65, SEF21 fimbriae w ere expressed very poorly under all conditions tested, Planktonic growth at 37 degrees C induced least flagella whereas growth at 20 degrees C, and pa rticularly surface growth at lower pH values, induced a 'hyper-flagellate' phenotype, Single colonies allowed to form on gradient agar plates were sho wn to generate different colonial morphologies which were dependent on init ial pH. These results demonstrate that the physicochemical environment is a n important determinant of bacterial response, especially the induction of putative virulence factors.