Shape-shifting bacteria: understanding urinary tract infections

Urinary tract infections (UTIs) are the most common bacterial infections worldwide and cost the Australian health care system around $909 million per year. Disease-causing strains of E. coli account for around 70% of cases.

E. coli are normally rod-shaped but change shape when they infect bladder cells. At first, they become rounder and clump together inside the cells, continuing to divide until they fill the cell. As the cell fills up and bursts open, some of the bacteria revert to a rod shape and disperse to infect more cells, while others grow into very long filaments that can’t directly infect cells. The length of these filaments is variable, but they can reach up to 50–100 times the length of a rod before cell division is switched back on and the filaments pinch off to form infectious rods.

So why are the filaments formed? Possibly to evade the immune system: long filaments are hard to engulf. As they emerge from the bursting cell, they could help attach the soon-to-be daughter rod cells to the surface of nearby uninfected bladder cells, ready to infect once cell division generates more rods.

Dr Bill Söderström and his team at the University of Technology Sydney (UTS) work to understand how and why these shape changes happen and how they are controlled. By using a range of super-resolution and fluorescence microscopy techniques at Microscopy Australia’s linked lab at UTS, they showed that when the filament divides into rods the bacteria use the same machinery as normal division, but it is controlled differently. The researchers hope to harness this understanding to develop new therapies for UTIs.

B. Söderström et al., Nature Communications 2022
DOI:10.1038/s41467-022-31378-1

Fluorescence microscopy image showing E. coli filaments (blue) and rods (pink). Rods are 2–4µm long. Imaged by Dr Bill Söderström.