Microbes frozen in gelatine jail reveal all

[Nipuna]

Looking at how bacteria in gelatin jail talk to their cellmates (Image: J. Connell et al., University of Texas)

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Bacteria held like apple chunks in a fruit jelly could be encouraged to divulge how they spread disease or gain drug resistance. Jason Shear and his colleagues at the University of Texas at Austin have imprisoned colonies of living bacteria in microscopic 3D lattices of gelatin. This lets them control colony structure to investigate how it affects virulence, as well as studying how bacteria communicate.

Understanding bacteria's short-range physical and chemical messaging – known as quorum sensing – helps us fathom how bugs cooperate to cause infection. The way the colony structure affects such capabilities is particularly poorly understood.

Shear's team took bacteria such as Staphylococcus aureus and put them in wells filled with liquid gelatin, growth medium and a chemical that allows gelatin to be set by a laser. The result was a microcolony with a fixed shape.

Building egg boxes
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The gelatin walls stop the bacteria from getting out, but they are porous to very small things, such as molecules and ions. The chemicals that bacteria use to communicate or to attack one another can pass through these walls very easily. "It's a bit like a cloth bag, which is able to hold marbles but will allow water to freely pass through," says Shear. Crucially, the set gelatin is biocompatible and keeps the bacteria alive.

"It's not so much like putting eggs in boxes," Shear adds. "It's more like building an egg box around the egg. By building the box around the randomly distributed objects [the bacteria] we can construct potentially very complex geometries."

"This is exciting stuff," says Bill Keevil, a microbiologist specialising in bacterial dynamics at the University of Southampton in the UK. "Working out how the same microorganisms or different species communicate and respond is very important, as is teasing out the mechanisms behind it."

The technique has already revealed that some distributions of S. aureus and Pseudomonas aeruginosa – which often co-infect wounds – can help S. aureus resist antibiotics.

Journal reference: PNAS, DOI: 10.1073/pnas.1309729110