Purpose: The purpose of this study was to compare the production of cellulose, exopolysaccharide fractions, type 1-fimbriae and curli-fimbriae by STEC grown on solid media at 25°C or 37°C.
Methods: A total of 10 and 18 O157 and non-O157 STEC strains were evaluated spectrophotometrically (490 nm) for exopolysaccharide production using the phenol-sulfuric acid method with glucose as a standard. Cells were initially grown on Brain Heart Infusion Agar (BHIA) at 25°C for 48 h (n = 3). Data were expressed in μg/ml and compared using ANOVA (a = 0.05). Production of cellulose, type 1-fimbriae and curli-fimbriae was qualitatively evaluated for strains of same serotype after storage at 25°C for 48 h or 37°C for 24 h (n = 2). A modified Nutrient agar (MNA) base with added Congo Red dye or Calcofluor dye was used to examine curli or cellulose production, based on red color or fluorescence of colonies, respectively. Production of type 1-fimbriae by the same strains was determined with the yeast agglutination test.
Results: Exopolysaccharide (EP) production differed significantly (P < 0.05) among STEC strains, mainly due to one O26 strain, which produced the highest amount of EP. The second highest production was observed by one strain of serogroup O45 and one strain of serogroup O145. Type 1-fimbriae expression was generally higher for both O157:H7 and non-O157 STEC after incubation at 25°C than at 37°C. Specific strains of serotypes O45:H2, O103:H2, O111:H8, O121:H19 and O145:H- exhibited a temperature-independent production of curli-fimbriae or type 1-fimbriae. In addition, phase-switching in production of curli-fimbriae was apparent for specific strains. Cellulose production was not observed for the majority of the strains tested.
Significance: This study shows that adherence of STEC to surfaces is mediated by expression of different polysaccharides and proteins. Non-O157 STEC may have the ability to outperform O157 STEC in attachment mechanisms and levels under different environmental conditions.