Comparative Analysis of Growth Kinetics of Listeria monocytogenes Lineages I and II in Chopped Red Cabbage

Introduction: In recent years, Listeria monocytogenes has been implicated in human foodborne illness outbreaks associated with fresh produce items. L. monocytogenes outbreaks are attributed to two main lineages (LI and LII). The majority of human Listeriosis is caused by LI strains, yet LII strains are more likely to be recovered from food and food processing environments. There is a lack of information reported on the growth kinetics of these two lineages in produce.

Purpose: To compare the persistence and growth kinetics of two L. monocytogenes lineages on freshly chopped red cabbage using predictive modeling.

Methods: Red cabbage was chopped into 100 g portions and inoculated with ca. 10⁴ CFU/g of a cocktail of either LI (F2365, H7858, R2-503) or LII (LS814, J1-101, J1-067) antibiotic-resistant strains. Samples were stored in deli-style containers at 5°C or 10°C for 14 days, or 25°C for 7 days. At various intervals, samples were stomached and plated onto PCA with appropriate antibiotics. Data were modeled using DMFit from Combase and the USDA Pathogen Modeling Program. A P-value of less than 0.05 was considered significant.

Results: The growth rates ((log CFU/g)/h) of the L. monocytogenes LI cocktail in red cabbage were significantly higher at 5°C (0.006 ± 0.003), 10°C (0.017 ± 0.004), and 25°C (0.051 ± 0.017) than the LII cocktail according to the predictive models. The maximum populations (log CFU/g) attained by LI were also significantly higher at 5°C (3.95 ± 0.035), 10°C (4.23 ± 0.035), and 25°C (4.38 ± 0.049) than LII. Secondary models using the Ratkowsky equation presented r² values of 0.99 and 0.90 for LI and LII, respectively.

Significance: The information obtained from this study will aid in elucidating how L. monocytogenes survives and grows in chopped produce and the reasons why L. monocytogenes LI strains are overrepresented in human foodborne Listeriosis cases.