Outer membrane: The outer membrane of E. coli is composed of a lipopolysaccharide layer that acts as a physical barrier against stomach acid.
Efflux pumps: E. coli contains efflux pumps which enable it to pump protons (H+) out of the cell, maintaining a neutral pH inside the cytoplasm. The efflux of protons creates an alkaline microenvironment around the bacteria, protecting it from acid damage.
pH homeostasis: E. coli possesses acid-resistance genes that encode proteins involved in maintaining pH homeostasis. These proteins help the bacteria adapt to low pH environments by regulating internal pH and preventing acidification of the cytoplasm. This system regulates the uptake of certain solutes like glutamate and arginine to buffer internal pH.
Biofilm formation: In some cases, E. coli can form biofilms—protective communities of bacteria that grow on surfaces. Biofilms are more resistant to stomach acid compared to individual bacterial cells, as the extracellular matrix produced by the biofilm acts as a barrier against acid penetration.
By employing these mechanisms, E. coli can survive passage through the acidic environment of the stomach and reach the more hospitable conditions of the intestine, where it can multiply and cause infection.
