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The following points highlight the major effects of adhesion on bacteria. The effects are: 1. Effect on Bacterial Growth 2. Production of Siderophores 3. Structures Involved in Adhesion of Host Cells.
1. Effect on Bacterial Growth:
Growth of uropathogenic strain of E. coli is inhibited after adhesion to uroepithelial cells of human. This effect was adhesion-dependent. It may be demonstrated by separating the uropathogenic cells from bacteria by semi-permeable membrane. Ca++ and cAMP are involved in this process. Inhibition of Ca++ flux abolished the contact-mediated growth inhibition.
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Uro-epithelial cells of UTI (urinary tract infection) patients did not produce adhesion mediated antibacterial effect. But this ability was restored by agents which increased intracellular cAMP levels.
You know that epithelial cells secrete several antibacterial peptides (e.g. cercropins, magainins, etc.). A contact-induced signalling leading to the upregulation of synthesis and secretion of such compounds may have resulted in antibacterial effect.
In contrast, growth of N. gonorrhoeae is enhanced due to adhesion to host’s HeLa cells. Similarly, E. coli cells adhered to epithelial cells derived from intestine or peritoneal cavity grows faster than the non-adhered cells. It may be due to accumulation of waste-products of host cells serving as food base for bacteria.
2. Production of Siderophores:
Siderophores are the low molecular weight, iron-chelating proteins produced by some bacteria. E. coli produces siderophores (aerobactin and enterobactin) which remove iron from host proteins such as lactofferrin.
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Siderophore production is genetically governed by barA gene. Its transcription is induced by attachment of PapG adhesion which is present at the end of P-pilus to its receptor, a Gal containing globoside.
3. Structures Involved in Adhesion of Host Cells:
Sal. typhimurium adhers to epithelial cells and produces several proteins which are important for adherence. This bacterium produces surface appendages called invasomes within 15 minutes of adherence.
Invasomes differ from flagella or pili being three fold thicker than the former. Invasomes mediate the internalisation of the organism by the epithelial cells. A gene present on inv locus governs the entry of Sal. typhimurium into non- phagocytic cells.
Enteropathogenic strains of E. coli attaching to mucosal surface form discrete micro-colonies which is known as ‘localised-adherence’. In vitro investigation has shown that the epithelial cells of bundles of filament (i.e. bundle forming pili) induce the location-adherence.
After adhesion of C. jujeni, epithelial cells are stimulated. Within 60 minutes of adherence, about 14 proteins are synthesised by the bacteria.
