Sodium bicarbonate enhances the severity of infection in neutropenic mice orally inoculated with Listeria monocytogenes EGD.

Epidemiological studies have suggested an association between antacid therapy and development of listeriosis in humans. In this study we used a neutropenic mouse model to demonstrate that oral administration of sodium bicarbonate shortly before intragastric (i.g.) inoculation with Listeria monocytogenes EGD (serotype 1/2a) significantly increased the severity of the resulting systemic infection. An explanation for this observation is provided by evidence that L. monocytogenes EGD is rapidly inactivated in synthetic gastric fluid at pH below 5. A second strain of L. monocytogenes (CM [serotype 1/2b]) exhibited little ability to cause systemic infection following i.g. inoculation and was not significantly enhanced by administration of sodium bicarbonate. Strain CM was readily inactivated in synthetic gastric fluid even at pH 7. These data suggest that gastric acidity and enzymes provide some innate defense against gastrointestinal listeriosis in neutropenic mice.