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.
"The species L. monocytogenes is widely studied in the developed world and is known as an enteroinvasive gastrointestinal pathogen (Barbuddhe and Chakraborty, 2009). There are no strains of L. monocytogenes with unique properties that lead to persistence (Carpentier and Cerf, 2011) and there are mechanisms that can protect the organism when present in acidic juices, yogurt, salad dressings, mayonnaise, and modified CO 2 atmospheres (Smith et al., 2013). Humans can become infected when contaminated food is ingested because the acidic stomach environment and its surface proteins (Bierne and Cossart, 2007) can help the organism to attach to the gut and multiply in the host's cell-cytosol (Pizarro-Cerdá and Cossart, 2009). "
[Show abstract][Hide abstract] ABSTRACT: Despite the world-wide reports of outbreaks of food-borne listeriosis, the occurrence of
Listeria is still not widely reported in Nigeria. This is possibly due to lack of a large cold
storage food chain and the absence of a comprehensive surveillance system for food-borne
pathogens. Searches carried out on major databases revealed that Listeria has been reported in
humans, animals, environment and food in Nigeria. In Nigeria, the organism has been reported
in pregnant women and neonates while ruminants dominate reports of occurrence in animals.
In food especially fish, L. monocytogenes is reported more than any other Listeria species.
The organism has been isolated from water bodies and soils from different environments in
Nigeria. However, all reports on the occurrence of Listeria spp. were based on classical
serotyping, biochemical tests and dark colouration of media due to hydrolysis of aesculin with
no emerging pattern of infection or dominant molecular serotype. There is an opportunity
to utilize the current polymerase chain reaction based molecular techniques to characterize
Listeria spp. so that accurate information on existing Listeria strains and sources of infection
can be established in all regions in Nigeria.
International Food Research Journal 04/2015; 22(2):455-464.
"Interestingly all elements of the GAD system are transcriptionally upregulated in Listeria during colonization of the GI tract (Archambaud et al., 2012). L. monocytogenes strains also possess an arginine deiminase (ADI) pathway and an agmantine (AgDI) deiminase system that contribute to pH homeostasis (Ryan et al., 2008; Smith et al., 2013). The ADI system is not present in the nonpathogenic species L. innocua. "
[Show abstract][Hide abstract] ABSTRACT: The foodborne pathogen Listeria monocytogenes has the capacity to survive and grow in a diverse range of natural environments. The transition from a food environment to the gastrointestinal tract begins a process of adaptation that may culminate in invasive systemic disease. Here we describe recent advances in our understanding of how L. monocytogenes adapts to the gastrointestinal environment prior to initiating systemic infection. We will discuss mechanisms used by the pathogen to survive encounters with acidic environments (which include the glutamate decarboxylase and arginine deiminase systems), and those which enable the organism to cope with bile acids (including bile salt hydrolase) and competition with the resident microbiota. An increased understanding of how the pathogen survives in this environment is likely to inform the future design of novel prophylactic approaches that exploit specific pharmabiotics; including probiotics, prebiotics, or phages.
Frontiers in Cellular and Infection Microbiology 02/2014; 4:9. DOI:10.3389/fcimb.2014.00009 · 3.72 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Enteric bacteria such as Escherichia coli have acquired a wide array of acid stress response systems to counteract the extreme acidity encountered when invading the host's digestive or urinary tracts. These acid stress response systems are both enzyme and chaperone based. The 3 main enzyme-based acid resistance pathways are glutamate-, arginine-, and lysine-decarboxylase pathways. They are under a complex regulatory network allowing the bacteria to fine tune its response to the external environment. HdeA and HdeB are the main chaperones involved in acid stress response. The decarboxylase systems are also found in Vibrio cholera, Vibrio vulnifus, Shigella flexneri, and Salmonella typhimurium, although some differences exist in their functional mechanism and regulation.
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