Purpose: To compare the growth characteristics of the most important L. monocytogenes serotypes from different origins submitted to stress conditions and different temperatures.
Methods: Twenty-two L. monocytogenes isolates−12 from clinical cases (eight serotype 4b and four serotype 1/2a) and 10 isolates from food (six serotype 4b and four serotype 1/2a) and one L. monocytogenes Scott A strain and one Listeria innocua−were analyzed for the ability to grow in brain heart infusion (BHI) broth with 11% NaCl at 4 °C, 10 °C and 25 °C for 73, 42 and 15 days, respectively.
Results: The majority of L. monocytogenes strains, regardless of their origin, showed ability to remain viable or even grow at 4 °C and in high osmotic conditions usually applied to control pathogens in the food industry. At 10 °C most strains could adapt and grow, however there was no statistical difference (P > 0.05) for parameters such as lag phase duration, maximum growth rate and maximum cell density. At 25 °C all strains were able to grow and increase their population up to 5 log CFU/ml. Statistical analysis for this condition showed significant differences (P <0.05), with clinical strains showing longer lag phase and lower maximum cell density compared to food strains.
Significance: The global tendency in decreasing NaCl concentration in processed foods, for health reasons, may facilitate L. monocytogenes survival and growth in these products. Therefore, food companies will have to look for additional growth barriers to assure product safety.