טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentNiderman-Meyer Orly
SubjectAdherence Mechanism of the Bacterium Vibrio cholerae to
Starch Granules
DepartmentDepartment of Biotechnology and Food Engineering
Supervisors Dr. Eyal Shimoni
Professor Yechezkel Kashi
Full Thesis textFull thesis text - English Version


Abstract

Cholera is a severe diarrheal disease caused by Vibrio cholerae (V. cholerae) that is pathogenic to humans. Cholera can become epidemic and deadly without adequate medical care. Cholera patient death is caused by the loss of fluids and salts; therefore, appropriate rehydration therapy can reduce the mortality rate from as much as 50% to less than 1%. In order to further reduce the symptoms associated with cholera, improvement of the Oral Rehydration Solution (ORS) by starch granule incorporation was suggested. Here we report for the first time that V. cholerae adheres to starch granules incorporated in ORS. Adhesion of 98% of the cells was observed within two minutes of incubation when corn starch granules were used. Other starches showed varied adhesion rates, indicating that starch source may play a role in the adhesion. Comparing V. cholerae adhesion with the adhesion of other pathogens suggests the involvement of starch degradation capabilities. The present work explores the mechanisms involved in this adhesion and the possibility of its occurrence in-vivo. Our findings suggest that both specific and nonspecific interactions are involved in the adhesion. Nonspecific hydrophobic interactions may play a role, since both V. cholerae and corn starch granules exhibited hydrophobic properties when tested in a xylene-water system. In addition, the presence of bile acids reduced the adhesion. The adhesion also involves some specific carbohydrate-binding moieties on the cell surface, as reflected by reduced adhesion following pretreatment of the bacteria with proteinase K and sodium-m-periodate. Further investigations strengthened these observations, showing a significant inhibitory effect of low-molecular-weight carbohydrate-containing media. Moreover, we attempted to identify and characterized the starch binding proteins present on V. cholerae surface. Binding cell lysate to starch and removing the adhered proteins using either glucose or bile acids led to the identification of several candidates V. cholerae outer membrane-associated starch-binding proteins (SBP). Different sets of candidate SBPs were isolated by removal with glucose solution or bile acids. Simulating the upper gastrointestinal tract conditions in-vitro, both bile salts and amylolytic activity of the pancreatic juices were found to have an inhibitory effect on V. cholerae adherence to starch. However, during acute diarrhea, this inhibitory effect may be significantly reduced due to dilution, suggesting that adhesion does occur in vivo. Such adhesion may contribute to the beneficial effects found following administration of granular starch-based oral rehydration solution to cholera patients and can be further used to improve the current ORT.