Researchers have discovered that black carbon makes certain bacteria more resistant to antibiotics, revealing a new mechanism of how air pollution harms our health. Their findings also shed new light on the dangers megacities and their high levels of air pollution pose to humans around the world, as Elke Bunge reports.
Lung diseases, heart attacks, even changes to the human brain are caused by minuscule suspended particulates that enter the human body when we breathe them in, allowing them into our bodies so they can unleash their damaging effects.
Outdoor air pollution alone is thought to be responsible for at least 3.3 million deaths per year. This means that five out of every 100,000 people die prematurely each year from the insidious smog.
But as a team of researchers from the University of Leicester how now discovered, these already shocking figures do not take into consideration infections of the respiratory tract that are triggered solely by air pollution – and their new resistance to conventional antibiotics.
Black carbon changes how bacteria behave
For their research, Dr Julie Morrissey and her colleagues took cell cultures from mice and examined how pollution affects two types of bacteria, Staphylococcus aureus and Streptococcus pneumoniae.
Both bacteria are known to accumulate in the nose and throat area, but they can remain in what are called biofilms without causing any problems to the carrier. When a person is weakened, however, these biofilms migrate deeper into the body and are responsible for severe respiratory infections.
Particulate matter such as black carbon is one of the main components of air pollution. And black carbon is the smallest particle made of pure carbon with a particular property: it has a high surface-area-to-volume ratio. When it comes in contact with mucous, it is capable of entering the biofilm together with the bacteria.
The scientists suspected that the black carbon-coated biofilms become resistant to drugs. To prove this hypothesis, they artificially produced biofilms and chose a black carbon load that resembles long-term exposure in the respiratory track.
Spreading from nose to lungs
With their experiment, the scientists succeeding in proving that the black carbon-exposed biofilms were thicker and more complex around the bacteria, thus shielding the bacteria from drugs. The bacteria were especially resistant to common antibiotics.
“Black carbon alters the antibiotic tolerance of Staphylococcus aureus communities and importantly increases the resistance of communities of Streptococcus pneumoniae to penicillin, the front line treatment of bacterial pneumonia,” wrote the scientists.
In a further experiment, the scientists discovered that the black carbon even caused the bacteria to spread more quickly into the lungs.
A test with mice showed that when the animals were exposed to a mixture of black carbon and Streptococcus pneumoniae in the nose, the bacteria was present in the lungs just seven days later.
But when the mice were only exposed to the bacteria, it remained restricted to the upper respiratory tract and did not spread.
Said Morrissey: “The bacteria which cause respiratory infections are affected by air pollution.”
Urbanisation, megacities pose new risks
Knowing how particulate matter and black carbon affect our health as well as the way in which they alter the behaviour of bacteria has important implications for the treatment of infectious diseases.
“Our research could initiate an entirely new understanding of how air pollution affects human health. It will lead to enhancement of research to understand how air pollution leads to severe respiratory problems and perturbs the environmental cycles essential for life,” said Morrissey.
Their findings are all the more important given how urbanisation in megacities is linked with extreme levels of air pollution.
The researchers plan to collaborate further with biologists, chemists, social scientists and urban planners to investigate how increasing urbanisation promotes infectious diseases.