Acid effects on listeria

Acid conditions restrict the growth of listeria. Used in kitchens and food production, these include acid-based disinfectants and preservatives. The first human defence is the acid in the stomach.

To enhance and extend the use of acid conditions against this pathogen, the MONOGAD (Elucidating novel roles and mechanisms of the GAD system in stress resistance and virulence of listeria monocytogenes) project has investigated one of its potent acid resistance systems, glutamate decarboxylase (GAD).

The GAD system consumes the acid-inducing protons and adds them to glutamate to produce γ-aminobutyric acid. Previous work by the scientists in MONOGAD had researched an internal GAD, GADi, system in listeria and how it works with an external GAD network of biochemical events, GADe.

MONOGAD research overturned the previously held theory that GAD protects the bacteria through its buffering capacity. Results suggest that the acid condition protection system works as a result of consumption of protons.

The EGD listeria strain is acid resistant and MONOGAD focused on its biochemistry to find out what conditions favour or work against its resistance. Firstly, EGD uses GADi and not GADe and various decarboxylases could add to the acid resistance of GADi in some strains.

Moreover, when added in a defined medium in the early stationary growth phase, the GAD system was activated by good overall sources of amino acids, but not through increased GAD activity. These included casaminoacids, tryptone soy broth, trypticase or proteose peptone. However, individual amino acids were unable to activate the GAD system, but a low level of activation was observed with L-cysteine, L-tryptophane and sodium chloride.

MONOGAD research has uncovered fine details of the biochemistry of acid-resistant strains in listeria that could be used in control of the pathogen. Its impact is not limited to gastroenteritis and flu symptoms, and an infection can lead to meningitis. In pregnancy, listeriosis can cause premature delivery or stillbirth and serious problems for the newborn.