Fermentable and non‐fermentable sugars: A simple experiment of anaerobic metabolism

Abstract

The main objective of this class experiment is to show the time-dependent consumption of a fermentable sugar (glucose) in the presence and absence of a non-fermentable sugar (xylose) by bacteria in anaerobic conditions. The observation of the pH decrease due to acid production and the turbidity increase as a result of cell multiplication, both in function of time, enables an interesting discussion regarding the metabolic pathways and the products of anaerobic fermentation of carbohydrates. Also the time-dependent disappearance of glucose due to its metabolic consumption is compared with the non-disappearance of xylose and permits a discussion of the function of glycolysis and pentose phosphate pathways as metabolic routes.

The effect of carbon source and fluoride concentrations in the streptococcus mutans biofilm formation*

“…Xylose has not promoted the homogeneous occupation of the well, a result that is very similar to the one found when the growth is done without the addition of a carbon source. This reinforces the suggestion of Paulino et al [12], wherein media without the addition of carbohydrate or supplemented only with xylose the growth is insignificant, as well as the acidification of the culture media, possibly due to the small quantity of fermentable sugar, restricted to the intracellular reserves, possibly in the form of polysaccharides, as already described [14]. These reserves would be enough to start the growth, but they would soon be depleted.…”

“…The turbidity of the preinoculate was adjusted to A 600 nm = 0.5, corresponding to ∼10 9 cells/ml (for details see Ref. 12).…”

Use of visible light‐based photodynamic therapy to bacterial photoinactivation

“…Then, 15 μl of the stock was inoculated in “Falcon tubes” (15 ml) containing 4 ml of previously autoclaved TSB medium. The initial number of colony forming units per milliliter (CFU/ml) was estimated by measuring the suspension turbidity with a spectrophotometer and verified by using CFU/ml count on TSA after anaerobic growth at 37 °C for 36 h [2].…”

“…In this class experiment, we describe a methodology adapted to the use of S. mutans , which can be acquired commercially. There is a possibility of isolating a lineage of S. mutans , inoculating a saliva sample in a selective culture medium mitis salivarius bacitracin sucrase [2]. Alternatively, another nonpathogenic microrganism could be used, because the conditions were standardized.…”

“…An example of this unbalance occurs during the development of dental cavity, because the Gram‐positive bacterium Streptococcus mutans is a substantial part of the cell microbiota present in the dental plaque subjected to the development of this disease. These bacteria use the carbohydrates present in the diet as an energy source, in an anaerobic process (mainly lactic fermentation) resulting in the production of organic acids [2]. These acids lower the pH to around 5.0 on the tooth surface [3], inducing its demineralization and causing dental cavity.…”