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What is Adhesin is useful in- and explain in detail?
Bacterial adhesins 

Specific adhesion to host tissue cells is an essential virulence factor of most bacterial pathogens. 
The fundamental process that determines bacterial attachment to host tissue surfaces is mediated by microbial adhesins.
Most fimbriae of gram-negative bacteria function as adhesins, but in many cases, it is a minor subunit protein at the tip of the fimbriae that is actual adhesin.
In grain-positive bacteria, a protein or polysaccharide surface layer serves as the specific adhesin.