Gram-positive bacteria use their adhesive pili to attach to host cells during

early stages of a bacterial infection. These extracellular hair-like appendages

experience mechanical stresses of hundreds of picoNewtons; however, the presence

of an internal isopeptide bond prevents the pilus protein from unfolding. Here,

we describe a method to interfere with nascent pili proteins through a peptide

that mimics one of the β-strands of the molecule. By using AFM-based force

spectroscopy, we study the isopeptide bond formation and the effect of the

peptide in the elasticity of the pilus protein. This method could be used to

afford a new strategy for mechanically targeted antibiotics by simply blocking

the folding of the bacterial pilus protein.