CO ₂ - and Anaerobiosis-Induced Changes in Physiology and Gene Expression of Different Listeria monocytogenes Strains

Abstract

Although carbon dioxide (CO 2 ) is known to inhibit growth of most bacteria, very little is known about the cellular response. The food-borne pathogen Listeria monocytogenes is characterized by its ability to grow in high CO 2 concentrations at refrigeration temperatures. We examined the listerial responses of different strains to growth in air, 100% N 2 , and 100% CO 2 . The CO 2 -induced changes in membrane lipid fatty acid composition and expression of selected genes were strain dependent. The acid-tolerant L. monocytogenes LO28 responded in the same manner to CO 2 as to other anaerobic, slightly acidic environments (100% N 2 , pH 5.7). An increase in the expression of the genes encoding glutamate decarboxylase (essential for survival in strong acid) as well as an increased amount of branched-chain fatty acids in the membrane was observed in both atmospheres. In contrast, the acid-sensitive L. monocytogenes strain EGD responded differently to CO 2 and N 2 at the same pH. In a separate experiment with L. monocytogenes 412, an increased isocitrate dehydrogenase activity level was observed for cells grown in CO 2 -containing atmospheres. Together, our findings demonstrate that the CO 2 -response is a partly strain-dependent complex mechanism. The possible links between the CO 2 -dependent changes in isocitrate dehydrogenase activity, glutamate metabolism and branched fatty acid biosynthesis are discussed.Modified atmosphere packaging (MAP) of foods is used to improve shelf life and safety by inhibition of spoilage organisms and pathogens. The gases used in MAP are most often combinations of oxygen (O 2 ), nitrogen (N 2 ), and carbon dioxide (CO 2 ). In most cases, the bacteriostatic effect is obtained by a combination of decreased O 2 and increased CO 2 concentrations (12). CO 2 is colorless, odorless, noncombustible, and bacteriostatic (21). It is both water and lipid soluble (12), and it does not leave toxic residues on MAP-stored foods (19).In food preservation MAP is frequently used for fresh muscle foods and ready-to-use vegetables stored and displayed at chill temperatures (12). The solubility of CO 2 increases at low temperatures (29), and it has recently been demonstrated that bacterial growth inhibition is proportional to the concentration of CO 2 dissolved in the water phase of a food matrix (8). The solubility of CO 2 is increased at neutral pH, high water activity, high buffer capacity, and high headspace-to-sample ratio (29).Listeria monocytogenes is a food-borne pathogen that can cause the severe human infection listeriosis (2). Cases of listeriosis caused by the consumption of contaminated meat or meat products have been reported since the 1990s (13), and several national prevention programs have been initiated (15). The organism is able to grow in the presence of CO 2 at low temperatures (2). CO 2 concentrations above 70% (N 2 balance gas) are required to inhibit growth of L. monocytogenes (11,17,20,27,43) at chill temperatures (Ͻ7°C), but even at such high CO 2 concentrations, the presence of ju...

Presence of GadD1 Glutamate Decarboxylase in Selected Listeria monocytogenes Strains Is Associated with an Ability To Grow at Low pH

“…In such circumstances, the synthesis of glutamate by, for example, glutamate synthase (lmo1733 and lmo1734) and glutamate dehydrogenase (lmo0560), which have been found to be present in strain EGDe (12), may be significant. Such metabolic flux has also been suggested with respect to the glutamate decarboxylase-mediated response of L. monocytogenes to CO 2 stress (16). While it has not yet been established whether glutamate decarboxylation can be facilitated by glutamate synthesis, it is intriguing that microarray-generated data have demonstrated that overexpression of the E. coli regulator GadE brings about increased expression of genes involved in glutamate-mediated acid resistance and of gltD, involved in glutamate synthesis (13).…”

The Effect of Oxygen on Bile Resistance in Listeria monocytogenes

“…However, information is lacking in regards to the response of L. monocytogenes to bile under physiologically relevant anaerobic and microaerophilic conditions. The expression of genes needed for survival under acidic conditions was found to increase under anaerobic conditions [14,15] and an increase in branch-chain fatty acids in the cell membrane was observed when L. monocytogenes was cultured under elevated carbon dioxide and anaerobic conditions [15]. Additionally, the activity of the bile salt hydrolase has been found to increase under anaerobic conditions [9].…”

Comparison between the Resistance of Benzalkonium Chloride–Adapted and –Nonadapted Biofilms of Listeria monocytogenes to Modified Atmosphere Packaging and Nisin Once Transferred to Mussels

“…It has been demonstrated that CO 2 modifies bacterial membrane permeability by changing the lipid composition (23,27,30,46). Nisin forms pores in the bacterial membrane of its targets by interacting with lipid II, a cell wall precursor (12,14,48).…”