Bacteria can do a lot of cool stuff. They can break down crude oil and plastic, “eat” metal, shrink tumors, and maybe even control robots. But for all we know about them, there is much that we don’t – what do they sound like, for example? Do they even make any sound at all?
Given their size, you’d be forgiven for thinking bacteria are essentially silent. However, a new study published in Nature Nanotechnology has captured the sound of bacteria for the very first time. The recording reveals the soft thrum of bacterial life, which could be a huge breakthrough in the detection of antibiotic resistance.
Ultrathin graphene drums were used to pick up the subtle sounds of Escherichia coli as they went about their bacterial business.
“What we saw was striking! When a single bacterium adheres to the surface of a graphene drum, it generates random oscillations with amplitudes as low as a few nanometers that we could detect,” Professor Cees Dekker of Delft University and co-author of the paper said in a statement.
“We could hear the sound of a single bacterium!”
To hear these sounds, the team needed an extremely sensitive instrument – with bacteria being so tiny, traditional recording methods wouldn’t suffice. They settled on graphene, which is made up of a single layer of carbon atoms and is good at conducting sound and electricity.
Graphene is "known as the wonder material,” Dr Farbod Alijani, who led the study, said. “It’s very strong with nice electrical and mechanical properties, and it’s also extremely sensitive to external forces.”
Thanks to this sensitivity, the team picked up the minute vibrations of single E. coli. The beats you can hear are believed to be the result of the bacteria's biological processes, particularly the movement of their tails (flagella) that propel them forward. With amplitudes up to 60 nanometers, each beat is pretty small:
“To understand how tiny these flagellar beats on graphene are, it’s worth saying that they are at least 10 billion times smaller than a boxer’s punch when reaching a punch bag,” Alijani explained.
“Yet, these nanoscale beats can be converted to sound tracks and listened to – and how cool is that?”
The authors also investigated how antibiotics might affect this microbe “music”. As you would expect, when bacteria are killed, they no longer make a sound. When E. coli were susceptible to the antibiotic, the tiny cacophony ceased within an hour or two of exposure. However, when bacteria were resistant to the drug, the beats continued as before.
The beats could therefore be used to probe if bacteria are alive – sort of like the pathogenic equivalent of a pulse or heartbeat – and to identify whether they have acquired antibiotic resistance.
“Eventually it can be used as an effective diagnostic toolkit for fast detection of antibiotic resistance in clinical practice,” Alijani hopes.
This is much needed, as resistance continues to be a serious public health concern – there are over 2.8 million antibiotic-resistant infections in the US each year, accountable for 35,000 deaths.
“This would be an invaluable tool in the fight against antibiotic resistance, an ever-increasing threat to human health around the world,” Professor Peter Steeneken concluded.