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.
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.
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!