The influence of nutrients on biofilm formation of an ST87 strain of Listeria monocytogenes

Abstract

Biofilm development by pathogenic organisms plays a pivotal role in certain foodborne illnesses. Listeria monocytogenes, specifically the sequence type 87 (ST87), has been widely identified in China. This study aimed to monitor the dynamic process of biofilm formation by a food-isolated L. monocytogenes ST87 strain under diverse nutritional conditions. Results showed that this strain can consistently exhibit high viable cell counts in both nutrient-rich and nutrient-limited conditions. By utilizing cell counting, we discovered the ability of L. monocytogenes ST87 to form biofilms in various nutritional environments, including beef juice and vegetable juice, maintaining levels above 2 Log10 CFU/cm2. Notably, biofilm formation was expedited under nutrient-limited conditions, with cell counts under nutrient-limited vegetable juice presenting significantly higher than that under the nutrient-rich one. The analysis of the composition of extracellular polymeric substances (EPS) showed a consistent pattern between viable cell count and extracellular protein variation within the biofilms. Moreover, an evaluation of nutritional components (protein, fat, total sugar, ash, and pH) in the culture medium unveiled a positive correlation between extracellular substances and pH, but a negative correlation was identified with other nutritional components.