Listeria monocytogenes is a Gram-positive food-borne pathogen that is known by its resiliency and ability to cause severe illnesses with a high mortality rate. Although all L. monocytogenes strains have associated virulence genes, not all strains are pathogenic. This implies that the pathogenicity of L. monocytogenes strains is controlled by additional factors besides their genes. Among these factors, we hypothesize that the properties and composition of the bacterial surface biopolymers play important roles in controlling the adherence and the pathogenicity of L. monocytogenes strains. To investigate the role of bacterial surface biopolymers on adherence and pathogenicity of L. monocytogenes to silicon nitride, interaction forces were measured between five L. monocytogenes strains that vary in their serotype and origin. Specifically, we have used atomic force microscopy (AFM) to investigate the interactions between ATCC51776, ATCC19115 (both serovars 4b), EGDe (serovar ½ a), ATCC 19112 (serovar 2) and ATCC15313 (serovar 1) and silicon nitride in water. AFM force measurements on bacteria are the result of both specific forces such as lignad-receptor interactions and non-specific forces such as long-range colloidal forces. To decouple the AFM measured forces to both specific and non-specific forces, an analysis is presented based on the application of Poisson statistics to AFM adhesion data. Prior to applying Poisson model to the adhesion data, the adhesion data was sorted based on AFM force signatures to data collected by pulling on proteins or data collected by stretching carbohydrates. Our results show that for all strains, the predicted force magnitude based on summation of both the specific and non-specific components of forces estimated by applying the Poisson statistics to the adhesion data was very close to the total average measured adhesion force. This was true for both forces measured on proteins or on carbohydrates. Furthermore, Poisson modeling indicated that both specific and non-specific force components were larger for the more virulent strain as compared to those estimated for the avirulent strains. Finally, the total adhesion force measured on bacterial surface carbohydrates was significantly larger than the total adhesion force measured on bacterial surface proteins for all strains tested.