Production of slime polysaccharides by Shigella dysenteriae type 1

Characterization of Bordetella pertussis growing as biofilm by chemical analysis and FT-IR spectroscopy

Although Bordetella pertussis, the etiologic agent of whooping cough, adheres and grows on the ciliated epithelium of the respiratory tract, it has been extensively studied only in liquid cultures. In this work, the phenotypic expression of B. pertussis in biofilm growth is described as a first approximation of events that may occur in the colonization of the host. The biofilm developed on polypropylene beads was monitored by chemical methods and Fourier transform infrared (FT-IR) spectroscopy. Analysis of cell envelopes revealed minimal differences in outer membrane protein (OMP) pattern and no variation of lipopolysaccharide (LPS) expression in biofilm compared with planktonically grown cells. Sessile cells exhibited a 2.4- to 3.0-fold higher carbohydrate/protein ratio compared with different types of planktonic cells. A 1.8-fold increased polysaccharide content with significantly increased hydrophilic characteristics was observed. FT-IR spectra of the biofilm cells showed higher intensity in the absorption bands assigned to polysaccharides (1,200-900 cm(-1) region) and vibrational modes of carboxylate groups (1,627, 1,405, and 1,373 cm(-1)) compared with the spectra of planktonic cells. In the biofilm matrix, uronic-acid-containing polysaccharides, proteins, and LPS were detected. The production of extracellular carbohydrates during biofilm growth was not associated with changes in the specific growth rate, growth phase, or oxygen limitation. It could represent an additional virulence factor that may help B. pertussis to evade host defenses.

Characterization of Shigella dysenteriae type 1 capsular polysaccharide by immunochemical methods

We have isolated the capsular polysaccharide from the strain of Shigella dysenteriae type 1 8337. The product was purified by ultracentrifugation, treated with enzymes (proteinase K, DNA-RNAase) and analyzed by immunochemical methods. Polyclonal antibodies were obtained from rabbits immunized by whole cell antigens prepared from Shigella by ultrasonic treatment and by purified capsular polysaccharide. Crossed immunoelectrophoresis, PAGE and Western blot analysis showed that this product containing mainly the polysaccharide component also contained glycoprotein and lipopolysaccharide. Double diffusion in agarose gel confirmed that the capsular preparation contained at least three antigens reacting with rabbit polyclonal antiserum.

Surface components of shigellae involved in adhesion and haemagglutination

Strains of Shigella species were studied for their ability to adhere and agglutinate mammalian erythrocytes. Shigella dysenteriae and Sh. flexneri exhibited haemagglutinating (HA) properties when cultured in Casamino Acids-Yeast Extract (CYE) broth in the presence of 1 mmol 1-1 calcium chloride, but other shigellae did not show this property under the same culture conditions. Repeated subcultivation of Sh. boydii, Sh. sonnei and HA negative strains of Sh. dysenteriae and Sh. flexneri in CYE broth medium induced adhesive and haemagglutinating properties that were inhibited by sodium periodate. HA activities of Shigella spp. were also inhibited by N-acetylneuraminic acid, alpha 1-glycoprotein and fetuin, but not by protease. Electron microscopy of Sh. dysenteriae 1, Sh. flexneri 2a, Sh. boydii 12 and Sh. sonnei 1 grown in CYE broth showed the presence of an extracellular slime layer that promoted agglutination of erythrocytes. The slime layer extracted from the cell surface of Shigella spp. showed HA properties, whereas lipopolysaccharide (LPS) obtained from the same strains, except Sh. dysenteriae 1, did not agglutinate erythrocytes. This evidence suggests that the cell surface haemagglutinin is a loosely bound slime layer which is expressed in CYE broth medium.