Purpose: To identify if any of the previously characterized genes are linked to growth alterations specific to some commonly used food preservatives that may aid in the explanation of their role in stress survival.
Methods: The strains were grown in BHI broth with and without 7% NaCl. Their growth (absorbance at 600 nm) was compared to parallel cultures containing an added GRAS chemical at 37°C. In some cases, growth was assessed via colony counts to verify the phenotypes.
Results: Growth profiles (lag time, doubling time, and maximum growth) in the presence of diacetate, sorbate, deoxycholic acid and nitrite was assessed. The gbuABC mutant showed the greatest growth reduction of all the mutants in the combined NaCl/preservative conditions. In the presence of NaCl and deoxycholic acid, the peak absorbance (maximum growth) for the gbuABC mutant was 0.119 at 43 h vs. the parent strain’s 0.159 at 33 h. The effect on murC (0.139 at 38 h) and lstC (0.141 at 29 h) was less pronounced and ftsK was unaffected. When comparing the time to reach peak absorbance in the other GRAS chemicals, the gbuABC mutant displayed marked delays compared to the parent strain in diacetate (32 h vs. 21 h), sorbate (47 h vs. 28 h) and nitrite (34 h vs. 21 h). These differences were not seen with the other mutants. The effects of these chemicals in absence of added salt stress was not significantly different from the parent strain.
Significance: Analysis of these phenotypes could enhance our understanding of how GRAS preservatives and NaCl affect Listeria and its stress survival genes, improving our understanding of Listeria’s tolerance to environmental stresses. This could lead to improved technology for controlling Listeria in foods.