Interplay of surface factors in colonization by a diarrhea pathogen

What is it about?

Enteroaggregative Escherichia coli (EAEC) are exceptional colonizers of the human intestine and can cause diarrhea. EAEC attach via multiple proteins and structures including long appendages, produced by assembling molecules of AafA, and a short surface protein called Hra1. EAEC also secrete an anti-adherence protein (Aap, also known as dispersin), which remains loosely attached to the cell surface. This study shows that dispersin covers Hra1, such that adhesive properties of EAEC seen in the laboratory are largely produced by AafA structures. When the bacteria colonize, dispersin is sloughed off, or otherwise removed, so that Hra1-mediated adherence occurs. All three factors are required for optimal colonization, as well as to produce the signature stacked-brick adherence pattern of EAEC.

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Why is it important?

This study reveals that the EAEC antiaggregation protein functions to prevent premature adherence by outer surface proteins and not pili as previously presumed. This also illustrates that investigating colonization factors one at a time may not reveal the true picture or complexity of multifactorial phenotypes like bacterial adherence or biofilm formation. Optimal colonization requires the AAF fimbriae, at least one outer surface adhesin and an antiaggregative protein. It is probable that co-evolved colonization factors dictate colonization mechanisms and outcomes among other bacterial colonizers as well.

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