The secret of cholera’s sneaky virulence

It started, as game-changing discoveries often do, with a simple observation. Back in 2012, a student in Associate Professor Diane McDougald’s Sydney lab, Parisa Noorian, noticed something weird: when she fed the bacteria Vibrio cholerae to protozoa – shape-shifting single-cell organisms that live in water and soil – they didn’t just eat lunch. Instead, the protozoa spat the bacteria out, undigested, as packages.

Why? Did they suspect the bacteria would make them sick? Or had the bacteria found a way to avoid being digested? What was going on?

In answering the question, McDougald and her team uncovered an important new story about the way virulence evolves in microbes, many of which present a significant risk to humans and their activities. The work has attracted the attention of microbiologists around the world and earned the small, nimble group of researchers from UTS the prestigious 2021 Australian Museum UNSW Eureka Prize for Scientific Research.

Over a painstaking decade, McDougald, colleague Dr Gustavo Espinoza-Vergara and their team at the UTS iThree Institute found that the cholera bacteria expelled by the protozoan host had, in fact, been turbocharged in the process. Protected inside the packages, known as expelled food vacuoles or EFVs for short, the bacteria were stronger, ten times more infective than they had been, impervious to antibiotics and to most attempts to kill them. The unexpected discovery has powerful implications for detecting dangerous bacteria, combatting microbial resistance to antibiotics, safeguarding drinking water, for farming and aquaculture sustainability and for predicting emerging diseases.

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