Abstract
This study investigates the effect of citral on growth and on the occurrence of sublethal damage in Listeria innocua Serovar 6a (CECT 910) and Listeria monocytogenes Serovar 4b (CECT 4032) cells that were exposed to citral as a natural antimicrobial agent. Two initial inoculum concentrations were considered in this investigation: 102 and 106 cfu/mL. Citral exhibited antilisterial activity against L. innocua and L. monocytogenes, and the observed effects were dependent on the concentration of citral present in the culture medium (0, 0.150 and 0.250 μL/mL) (p ≤ 0.05). L. innocua had a shorter lag phase than L. monocytogenes, and the two species had nearly identical maximum specific growth rates. These results indicate that L. innocua could be used as surrogate for L. monocytogenes when testing the effects of this antimicrobial. Significant differences in the lag phase and growth rate were observed between the small and large inoculum concentration (p ≤ 0.05). Citral-treated L. innocua and L. monocytogenes that were recovered on selective medium (i.e., TSA-YE-SC) had a shorter lag phase and a higher maximum specific growth rate than cells that were recovered on non-selective medium (i.e., TSA-YE) (p ≤ 0.05). This result suggests that damage occurs at sublethal concentrations of citral.
Highlights
IntroductionListeria monocytogenes can grow under conditions (low temperature) that prevent the survival of other foodborne pathogenic bacteria
Listeria monocytogenes can grow under conditions that prevent the survival of other foodborne pathogenic bacteria
Experimental L. innocua and L. monocytogenes growth curves were obtained using inoculum concentrations of 102 and 106 colony forming units/mL (cfu/mL) in Tryptone Soya Broth (TSB) alone or in TSB supplemented with different concentrations of citral that were below the minimal inhibitory concentration (MIC)
Summary
Listeria monocytogenes can grow under conditions (low temperature) that prevent the survival of other foodborne pathogenic bacteria. This bacterium is an important target organism for elimination from the food supply. As laid down in Commission Regulation (EC) No 2073/2005, L. monocytogenes levels should be lower than 100 colony forming units per gram throughout the shelf life of a food product if the product does not allow growth or if the product is not intended for an at-risk population [1]. Effects of Citral on Listeria innocua and Listeria monocytogenes co-author to contribute to the study design, data collection and analysis, decision to publish, or preparation of the manuscript
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