Comparison of the adhesive and conformational properties of the cell surface biopolymer brush of pathogenic and nonpathogenic species of Listeria

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Abstract
Bacterial strains can be divided into pathogenic and nonpathogenic strains. Distinguishing between the characteristics of these two types will help us understand the mechanisms that bacteria use to cause infections. Thus, the differences in the adhesion to a model hydrophilic silicon nitride surface and in the conformational properties between pathogenic and nonpathogenic Listeria species were probed using atomic force microscopy (AFM). The AFM force-distance approach curves were fitted to two steric models, the steric model and the extended-steric model, which assume the presence of one or two brushes on the bacterial cell surface, respectively. Our results indicated that no significant differences were noticed in the mean adhesion forces measured for pathogenic and nonpathogenic strains using the silicon nitride model surface. However, a larger number of adhesion peaks was found in the AFM retraction curves of the pathogenic strains. Similarly, when the conformational properties, represented by the mean thickness and the mean grafting density of the biopolymer brush, were determined using the steric model, no significant differences were observed between the pathogenic and nonpathogenic strains. However, when the conformational properties, represented by the mean thickness and the mean grafting density of the two brush layers, were quantified using the extended-steric model, it was found that the pathogenic strains had a lower mean grafting density for the first long brush and a higher mean grafting density for the second short brush. Thus, our findings demonstrate that the extended-steric model provides a more detailed view of the conformational properties of Gram-positive Listeria strains and allows for the detection of existing differences.
Funding Information
  • National Institutes of Health (1R03AI077590-01A1 and 5R03AI077590-02)

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