Spatial organisation of Listeria monocytogenes and Escherichia coli O157:H7 cultivated in gel matrices

Cédric Saint Martin (1, 2) , Maud Darsonval (1) , Marina Grégoire (1) , Nelly Caccia (2) , Lucas Midoux (1) , Sophie Berland (3) , Sabine Leroy (2) , Florence Dubois-Brissonnet (1) , Mickaël Desvaux (2) , Romain Briandet (1)

1 MICALIS - MICrobiologie de l'ALImentation au Service de la Santé
2 MEDIS - Microbiologie Environnement Digestif Santé
3 SayFood - Paris-Saclay Food and Bioproduct Engineering

The spatial organisation of bacterial pathogens in food matrices remains poorly understood, but is important in improving risk assessment and preventing infection of consumers by contaminated foodstuff. By combining confocal laser scanning microscopy with genetic fluorescent labelling of Listeria monocytogenes and Escherichia coli O157:H7, it was possible to investigate the spatial patterns of colonisation of both foodborne pathogens in gel matrices, alone or in combination, in various environmental conditions. Increasing low melting point agarose (LMPA) concentrations triggers the transition between a motile single-cell lifestyle to a sessile population spatially organised as microcolonies. The size, number and morphology of microcolonies were highly affected by supplementations in NaCl or lactic acid, two compounds frequently used in food products. Strikingly, single-cell motility was partially restored at higher LMPA concentration in the presence of lactic acid for Escherichia coli O157:H7 and in the presence of NaCl for Listeria monocytogenes. Co-culture of both species in the hydrogel affected pathogen colonisation features; Listeria monocytogenes was better able to colonise gel matrices containing lactic acid in the presence of Escherichia coli O157:H7. Altogether, this investigation provides insights into the spatial distribution and structural dynamics of bacterial pathogens in gel matrices. Potential impacts on food safety are discussed.

Mots clés: Listeria monocytogenes; Escherichia coli O157:H7; Matrice alimentaire; Hydrogel; Organisation spatiale; Motilité bactérienne; Microscopie confocale à balayage laser

Domaines: Sciences du Vivant [q-bio]

Cédric Saint Martin, Maud Darsonval, Marina Grégoire, Nelly Caccia, Lucas Midoux, et al.. Spatial organisation of Listeria monocytogenes and Escherichia coli O157:H7 cultivated in gel matrices. Food Microbiology, 2022, 103, pp.103965. ⟨10.1016/j.fm.2021.103965⟩. ⟨hal-03480607⟩