Introduction
Adherence and invasion are two major mechanisms that bacteria employ in causing pathogenesis in sites of infections. Through the mechanism of adherence, bacteria attach on cellular surface receptors of host cells using adhesins [1, 2]. Usually, bacterial proliferate on the surface of cells and gradually destroy cellular and epithelial membranes, resulting in the invasion of cells and tissues and pathogenesis.
In essence, the ability of bacteria to adhere to and invade cells and tissues determines virulence and pathogenicity [2, 3]. Varied degrees of adhesion and invasion explain the apparent differences in virulence and pathogenicity of Escherichia coli and Salmonella typhimurium. Comparatively, S. typhimurium is more virulent and pathogenic than E. coli due to its ability to invade tissues and cells [1, 2, 3].
Conditions of host surface receptors and the form of adhesive components influence the invasiveness and adherence of bacteria. Therefore, the objective of the study was to determine the invasive and adherence abilities of S. typhimurium relative to E. coli.
In the comparative study of invasiveness and adherence of E. coli and S. typhimurium, the study used INT407 cell line because it resembles intestinal epithelial cells. In their invasiveness and adherence, bacteria have adapted to intestinal epithelial cells because they act as barriers at the site infections [2, 4]. Thus, the selection of INT407 cell line is beneficial to the study because it mimics in vivo environment for S. typhimurium and E. coli [4].
Depending on their mechanisms of pathogenicity, E. coli would stimulate immune response via the MHC class II pathway, while S. typhimurium would elicit through the MHC class I pathway. The MHC class I pathway entails process and presentation of endogenous pathogens whereas the MCH class II encompasses the process and presentation of exogenous pathogens [5]. Even though both bacteria are exogenous pathogens, cross-presentation of antigens from S. typhimurium happens via the MHC class I pathway due to its invasiveness.
Discussion
Comparisons of the results of adherence and invasion demonstrated that E. coli and S. typhimurium have different mechanisms of pathogenesis [1, 2]. According to results, more S. typhimurium with counts of 76 and 20 than E. coli with counts of 50 and 8 adhered to cell lines at dilutions of 10-2 and 10-3 colony forming units per millilitre respectively. Comparison of invasion showed that S. typhimurium was very invasive because the counts were 39 and 7 at 10-1 and 10-2 colony forming units correspondingly, while E. coli did not exhibit invasiveness for no count was observed in cell cells.
Overall, S. typhimurium had a total adherence of 0.076% and invasion of 9.2% relative to E. coli with adherence of 0.05% without invasion. S. typhimurium exhibits both attributes of adherence and invasion for they are integral to the pathogenesis [2, 3]. Mechanism of pathogenesis requires bacteria to proliferate, adhere to cellular surfaces and invade into cells and tissues where they secrete virulent antigens [2, 4]. Thus, invasiveness of S. typhimurium depicted its pathogenic mechanism in intestinal epithelial cells.
The experiment showed that E. coli and S. typhimurium exhibited different mechanisms of pathogenesis. Lack of virulence in E. coli was evident because it has low adherence ability without invasive capacity on intestinal epithelial cells. In contrast, the virulent nature of S. typhimurium emanated from its ability to not only adhere to target cells but also invade them and trigger pathogenesis. Furthermore, the ability of S. typhimurium to invade cells elucidated the stimulation of immune response through the MHC class I pathway following the cross-presentation of antigens.
References
- Kalita A, Hu J, Torres AG. Recent advances in adherence and invasion of pathogenic Escherichia coli. Curr Opin Infect Dis. 2014; 27(5): 459-464.
- Dostal A, Gagnon M, Chassard C, Zimmermann MB, O’Mahony L, Lacroix, C. Salmonella adhesion, invasion, and cellular immune responses are differentially affected by iron concentrations in a combined in vitro gut fermentation-cell model. PLoS ONE. 2014; 9(3): 1-9.
- Ribet D, Cossart P. How bacterial pathogens colonize their hosts and invade deeper tissues. Microb Infect. 2015; 17(3): 173-183.
- Lee HY, Biswas D, Ahn J. In-vitro adhesion and invasion properties of salmonella typhimurium competing with bacteriophage in epithelial cells and chicken macrophages. Rev Bras Cienc Avic. 2015; 17(4): 427-432.
- Rock KL, Reits, E, Neefjes J. Present yourself! By MHC class I and MHC class II molecules. Trends Immunol. 2016; 37(11): 724-737.