Investigating the interactions of foodborne bacteria in mixed cultures, as affected by the fat content in viscoelastic 3D models

Recent research has shown that food products have a diverse, natural microbiome and, consequently, understanding bacterial interactions and their communication within complex microenvironments, is of importance for product quality and safety. In this study, we systematically studied the growth dynamics and potential antagonism of food related bacteria in mixed cultures, as affected by changes in the fat concentration of 3D viscoelastic in vitro models. Listeria monocytogenes was co-cultured with either Escherichia coli , Pseudomonas aeruginosa or Lactococcus lactis on fat rich 3D models and the bacterial kinetics and spatial organisation were monitored and compared over time. We observed interesting differences in macroscopic growth patterns that were bacterial strain dependent. Most bacteria showed a reduction of their growth in co-culture as compared to single cultures, especially in the late-exponential growth phase. L. monocytogenes was the dominant bacterium with the highest antagonistic activity and stress adaptability. At microscopic level, especially in co-cultures of L. monocytogenes and E . coli , we observed an overproduction of extracellular polymeric substances and the formation of elongated cells. However, there was no apparent influence of the fat concentration of the viscoelastic models on the co-culture growth. Our work contributes to a better understanding of bacterial interactions in 3D systems. • Co-cultures in 3D models disturbed the bacterial growth, in late exponential but not in stationary phase • Listeria monocytogenes was the most virulent bacterium with the highest antagonistic activity and also the highest stress adaptability • Microbial growth in mixed cultures was not affected by the fat content of the 3D models.