Ten strains representative of six species of the Listeria genus were investigated using atomic force microscopy (AFM) to assess heterogeneities in their elasticities. Force- indentation profiles were measured on at least fifteen locations that spread the surface of individual cells (cell level). At least 15 cells, taken from three different cultures were probed (culture/ strain level). For several bacterial species, more than one strain was investigated (species level). Finally, six different Listeria species that varied in their pathogenicity were investigated (genus level). These were the pathogenic L. monocytogenes and L. ivanovii, and the nonpathogenic L. grayi, L. welshimeri, L. seeligeri and L. innocua. The measured indentation profiles were then fit to the Hertz model of contact mechanics to map the Young’s modulus of elasticity. Our data indicated that irrespective of the strain investigated, elasticities were spatially and heterogeneously distributed at cellular, culture/strain, species and genus levels. When averaged at the cellular level, our data indicated that the Young’s moduli for the nonpathogenic cells ranged from 112.7 to 216.6 kPa. In comparison, the Young’s modulus for the pathogenic strain ranged from 82.1 to 153.0 kPa. When heterogeneities in the data were assessed, our preliminary findings indicate that nonpathogenic strains are more heterogeneous than the pathogenic strains in their elasticities at the cellular, culture and species levels. Our findings suggest that each bacteria strain has a unique mechanical identity and results found at any level should not be generalized to other cells, strains or species.

Atomic force microscopy investigations of heterogeneities in the elasticities of pathogenic and non-pathogenic Listeria species

ACS Spring Meeting 2021

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