Abstract Video:

Methods, Part 1 (Set Up):

(A): The experiment was conducted by setting up five beakers simulating different stomach environments. Each beaker contained one or a combination of the following: [1] different molarities of hydrochloric acid (0.1, 0.5, and 1.0 M) in order to achieve pre-specified pHs, [2] crushed up tums (calcium carbonate to neutralize stomach acid, similar to a PPI), [3] vegetable broth (VB, to mimic food being digested in the stomach), and [4] crushed up probiotic tablets containing lactobacillus bacteria mimicking stomach bacteria. The specific contents of each beaker are described below:

The Beakers:

(D). These beakers then sat for five days in a room temperature environment so that the lactobacillus bacteria could interact with the surrounding environment.

Methods, Part 2 (Bacterial Extraction and Culturing)

Liquid Bacterial Extraction, Plating, and Culturing:

Tube Bacterial Extraction, Plating, and Culturing:

After the two 36-hour periods, bacterial growth in each of the 10 dishes was observed qualitatively.

Results:

Discussion of Results and Significance:

The results yielded a few major findings. First, when comparing growth in different pH growing environments, generally more bacterial growth occurred when the growing environment's pH was higher (i.e., less acidic). This result is evident when comparing the minimal amounts of bacterial growth in the HCl and HCl + Broth petri dishes to the increased growth in the HCl + Tums and the HCl + Broth + Tums petri dishes. The literature supports this result, as multiple studies suggest that lactobacillus grow optimally at more neutral pH's (around 5-7) (3). That is because extreme pH's can [1] disrupt hydrogen bonding in DNA (which contains the instructions needed to produce proteins crucial for growth); [2] slow cellular respiration by disrupting the force responsible for creating a concentration gradient to produce ATP energy (which is necessary for growth); and [3] denature proteins themselves (the workhorses of cells), causing a disruption in cell function that is crucial for growth (3). Notably, Lactobacillus can still grow in acidic conditions, which is why some small amounts of growth even occurred in the HCl tube and the HCl + Broth tube petri dishes, but this growth is significantly less than the growth in the petri dishes with bacteria that grew in higher pH's (3).

FIRST FINDING TAKEAWAY: When applied to the stomach, the first finding suggests that taking antacids, which increase the stomach environment's pH, can increase bacterial growth.

Second, regardless of the growing environment's pH, more bacterial growth occurred on the NG tube than in the liquid around the NG tube. This result was evident when comparing the greater opacity of the bacteria in all of the "tube" petri dishes to the more transparent bacterial colonies in all of the "liquid" petri dishes. This was especially evident when comparing the HCl tube to the HCl liquid, and the broth tube to the broth liquid. The reason for that result is that the NG tube is made from polyurethane, a type of plastic, and bacteria tend to stick to polyurethane because of Van Der Walls forces (attractions and repulsions between atoms and molecules) (10). Polyurethane's chemical structure is polar, meaning that the molecule has a net charge on one side. At the same time, many bacteria, including lactobacillus, contain an outer layer of proteins called an S-layer, and S-layers are polar (10, 11). Polar molecules/regions attract because the partial positive charge will attract the partial negative charge, and therefore the bacteria will be attracted to the polyurethane, forming a biofilm (10, 12). Notably, this attraction is also partly due to the fact that surfaces concentrates nutrients and often contain higher concentrations of necessary nutrients than liquid, so when bacteria, such as lactobacillus, are attached to a surface, they are willing to remain there and benefit (10).

SECOND FINDING TAKEAWAY: The second finding suggests that bacteria tend to grow more on an NG tube than in the surrounding environment.

Third, the presence of broth had somewhat varying and inconclusive effects on bacterial growth. For example, less bacterial growth occurred in the HCl + Broth Tube petri dish than in the HCl Tube petri dish, suggesting that broth somehow harms growth, but more bacterial growth occurred in the HCl + Tums + Broth Tube dish than in the HCl + Tums Tube dish, suggesting that broth somehow helps growth. Based on these results, nothing definitive can be concluded regarding the broth's effect on bacterial growth in the stomach.

THIRD FINDING TAKEAWAY: No definitive conclusion can be made regarding the broth's effect (simulating food) on bacterial growth in the stomach.

Conclusion Video:

Conclusions, Uncertainties and Future Experimentation

In conclusion, the results of this experiment suggest that bacterial growth increases when stomach pH is elevated due to the presence of antacids (simulating PPIs); that bacteria in the stomach tend to stick to the NG tube more than the liquid surrounding the tube, forming a biofilm; and that no conclusive/definitive findings regarding the foo's effect on bacterial growth in the stomach can be made.

Some uncertainties that could have affected results were [1] the sterility of the environment considering that this experiment was completed in a home office, rather than in a lab, and this experiment was premised on the absence of bacteria from the surroundings, [2] the fact that only one trial was completed due to limited materials, so the results might not be as accurate and precise as they would be with more trials, and [3] the fact that growth was evaluated qualitatively and thus the results were necessarily somewhat subjective; next time, a quantitative method would be devised.

Future studies are needed to determine [1] if these results apply in vivo (with the bacteria in the stomach and in a real stomach environment), and [2] if the additional bacterial growth due to a changing stomach environment and the presence of a tube can actually negatively affect the NG tube's functioning, impact feeding or increase infection risk.