Just A Spoonful of Sugar: Investigating Bacterial-Sugar Adherence to Combat Antibiotic Resistance
By Riya Gandhi
Senior Category (Grades 11-12)
Experiment | Biology, Chemistry
Recently, scientists have attributed antibiotic resistance to “L-form switching,” a process by which bacteria change form to lose their cell wall temporarily. This mechanism allows them to “hide” from antibiotics targeting the cell wall, and to escape specific immune responses that depend on the presence of a cell wall, rendering many modern treatment techniques ineffective.
Researchers have observed that sugar-specific interactions play a pivotal role in bacterial adherence to surface cells. In the case of E. coli and D-mannose specifically, the FimH bacterial adhesion, located at the tip of the type 1 fimbriae, is responsible for regulating E. coli’s attraction to mannose. This project focuses on the interactions between simple sugars (D-mannose, D-glucose and D-fructose) and other pathogenic bacteria found in widely used spaces, to investigate treatment for antibiotic-resistant bacterial infections.
Benedict’s Reagent is a chemical test used to detect reducing sugars. Research has shown that upon interaction, the FimH receptor binding domain on E. coli forms a deep-binding pocket that conceals most of the D-mannose sugar, actively interacting with all of its hydroxyl groups, except for the anomeric one located in the aldehyde group. As only the anomeric oxygen is exposed and not the full aldehyde, the functional group should theoretically be unavailable for detection by Benedict’s Reagent.
Upon interaction with an aldehyde, Cu2+ ions in Benedict’s Reagent form carboxylic acid and a red copper (I) oxide precipitate, which changes the solution colour to varying opacities of blue (once the precipitate is centrifuged, and the supernatant is collected). The “new” opacity qualitatively determines the amount of reducing sugar present. Supposing the bacteria adhere to the sugar using the same mechanisms occurring between D-mannose and E. coli, the presence of both substances combined in Benedict’s Reagent should maintain the natural blue opacity of the solution. This theory was experimentally tested.
There will be a delay in determining each of the bacterial species present in the experiment due to an early school closure. Qualitatively, however, the supernatant of all bacterial-sugar samples appeared clear or were different opacities of Benedict’s Reagent blue. Initially, this method intended to analyze the red wavelengths absorbed by Benedict’s Reagent, though the maximum peak for those wavelengths in all samples containing sugar were lower than that of the Benedict’s Reagent control. This implies that copper (I) oxide particles were still present in each of the samples, and needed to be centrifuged for longer.
Instead, results were calculated using the absorbance for the 240.1 nm wavelength. It is critical to note that each bacteria-Reagent control had the same absorbance in the UV range as the Benedict’s Reagent control, indicating that bacteria do not absorb UV wavelengths. We can conclude that solutions with higher UV absorbance ratios contain more energy-absorbing molecules. Thus, the higher the UV absorbance ratio for each corresponding sample, the more the bacteria successfully inhibited the sugars from reacting with the energy-absorbing chemicals in Benedict’s Reagent. Determining the bacterial species will further support these theories. Still, data demonstrates that in each sample, there was some form of bacterial-sugar attachment to varying extents.
It is important to address that this procedure only tested for bacterial-sugar adherence through the same mechanisms utilized by D-mannose and E. coli. Possible extensions will examine if the sugars used in this experiment are successful in inducing a chemotactic response from each type of bacteria. Using treatment techniques that target bacterial structures other than the cell wall, such as the bacterial fimbriae, is an essential step in addressing antibiotic immunity and developing safe, effective, low-cost, and globally accessible healthcare techniques.