Crawlies Up My In­ner Tubes

by Elio

I get some­what squea­mish when think­ing of bugs crawl­ing up my uri­nary tract. Per­haps you do too. The story of E. coli as­cend­ing the uri­nary tract, how­ever, turns out to be fas­ci­nat­ing, which as­suages my dainty feel­ings.

Hu­man uri­nary tract. Source

Que pasa ? Mob­ley and col­leagues re­port that E. coli 's trek up the uri­nary track in­volves fla­gel­lar motil­ity – not sur­pris­ing in it­self. But it turns out that this motil­ity is re­quired for the climb from blad­der to kid­ney, not for mak­ing it into the blad­der. The main find­ing in this pa­per is that ex­pres­sion of fla­gel­lar genes co­in­cides with the organism's as­cent into the ureters en route to col­o­niz­ing the kid­neys.

This find­ing was not easy to come by. It re­quired the use of a fancy imag­ing tech­nique, biophoton­ic imag­ing by name. The au­thors in­tro­duced lux re­porter genes into a fla­gel­lar gene, fliC ; the bac­teria lu­mi­nesced when this gene was ex­pressed. They then in­jected these or­gan­isms into the ure­thra of mice and fol­lowed light emis­sion on the whole an­i­mal in real time. Five hours is all it takes for the bac­te­ria to ex­press fliC and start mov­ing up the ureters. Mu­tants de­fec­tive in fliC could co­lonize the blad­der, but could not as­cend to the kid­neys.

The in­set panel shows an ep­ithe­lial cell peel­ing off from the sur­face of the blad­der dur­ing a uri­nary tract infec­t­ion. The main panel shows a cell from the blad­der wall, which is com­pletely ob­scured by ad­hering E. coli CFT­073. Credit: H. Mob­ley, Univ. of Michi­gan Med­ical School.

Ureters are long (~25–30 cm in adults) and thin (~3 mm in di­am­e­ter), so turn­ing on fla­gella may be nec­es­sary to make this awe­some jour­ney, trav­el­ing in one di­rec­tion through such a long and nar­row pipe. And they flip the switch in a few hours!