title: How does Listeria monocytogenes combat acid conditions?
abstract: Listeria monocytogenes, a major foodborne pathogen, possesses a number of mechanisms that enable it to combat the challenges posed by acidic environments, such as that of acidic foods and the gastrointestinal tract. One mechanism employed by L. monocytogenes for survival at low pH is the adaptive acid tolerance response (ATR) in which a short adaptive period at a nonlethal pH induces metabolic changes that allow the organism to survive a lethal pH. Overcoming acid conditions by L. monocytogenes involves a variety of regulatory responses, including the LisRK 2-component regulatory system, the SOS response, components of the σ(B) regulon, changes in membrane fluidity, the F0F1-ATPase proton pump, and at least 2 enzymatic systems that regulate internal hydrogen ion concentration (glutamate decarboxylase and arginine deiminase). It is not clear if these mechanisms exert their protective effects separately or in concert, but it is probable that these mechanisms overlap. Studies using mutants indicate that the glutamate decarboxylase system can protect L. monocytogenes when the organism is present in acidic juices, yogurt, salad dressing, mayonnaise, and modified CO2 atmospheres. The glutamate decarboxylase system also has a role in protecting L. monocytogenes against the acidic environment of the stomach. There is a need to study other acid resistance mechanisms of L. monocytogenes to determine their effectiveness in protecting the organism in acidic foods or during transit through the acid stomach.
authors.affiliation: Molecular Characterization of Foodborne Pathogens Research Unit, Eastern Regional Research Center, 600 East Mermaid Lane, Wyndmoor, PA 19038-8598, USA. james.smith@ars.usda.gov
authors.forename: James L
authors.initials: JL
authors.lastname: Smith
authors.forename: Yanhong
authors.initials: Y
authors.lastname: Liu
authors.forename: George C
authors.initials: GC
authors.lastname: Paoli
mesh_terms: D000093:Acetoin / Q000378:metabolism; D000143:Acids / Q000378:metabolism* / Q000494:pharmacology; D000818:Animals; D001426:Bacterial Proteins / Q000502:physiology; D005516:Food Microbiology; D005744:Gastric Acid / Q000378:metabolism; D005968:Glutamate Decarboxylase / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D006867:Hydrolases / Q000378:metabolism; D008089:Listeria monocytogenes / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D008560:Membrane Fluidity; D006180:Proton-Translocating ATPases / Q000378:metabolism; D013014:SOS Response, Genetics / Q000502:physiology; D012808:Sigma Factor / Q000502:physiology
chemical_list: D000143:Acids; D001426:Bacterial Proteins; C079011:SigB protein, Bacteria; D012808:Sigma Factor; D000093:Acetoin; D006867:Hydrolases; C019723:arginine deiminase; D006180:Proton-Translocating ATPases; D005968:Glutamate Decarboxylase