Influence of interactions between temperature, ferric ammonium citrate and glycine betaine on the growth of Listeria monocytogenes in a defined medium

Aims: To investigate interactions, if any, between temperature, ferric ammonium citrate and glycine betaine on the growth of Listeria monocytogenes in modified Pine's medium ( Pine et al. 1989). Methods and Results: Modified Pine's medium containing 0, 0.044, 0.088 or 0.176 g l(-1) ferric ammonium citrate, and 0 or 1 mM glycine betaine, was inoculated with each of two L. monocytogenes strains and incubated at 4, 25 or 37degreesC. The optical density at 600 nm, and cell numbers, were determined at appropriate time intervals. At 4degreesC, but not other temperatures, increasing ferric ammonium citrate resulted in improved growth in the absence, but not the presence, of glycine betaine. The presence of glycine betaine was inhibitory at 25 and 37degreesC, but not at 4degreesC. Conclusions: Interactions affecting the growth kinetics of L. monocytogenes were apparent between the parameters investigated. Significance and Impact of the Study: Limitations on the use of modified Pine's medium, and the significance of iron metabolism at lower temperatures, were revealed.