T The dense fog that rolls over San Francisco's Golden Gate Bridge is synonymous with the Bay Area. More than an emblem for the coastal city, however, the fog could also be a huge highway for genes that produce dangerous, antibiotic-resistant "superbugs", scientists warn in a study published in Environmental Science and Technology . The rise of superbacteria in the overreach and misuse of antibiotics is tough enough to control, but now it looks like they might rise from the air.
The alarming spread of infections caused by supergonorrhea and Staphylococcus aureus shows how strong the antibiotic resistance bacterial problem has become. In January, the World Health Organization found that 500,000 people in 22 countries had antibiotic-resistant infections that were almost untreatable. The reason these superbugs are so dangerous is because they carry certain antibiotic resistance genes (ARGs) that protect them from most of the drugs.
Usually ARGs spread when a lucky superbug survives after a dose of antibiotics has killed most of his comrades, allowing this superbug to breed and create its own colony of minions that share its superior genetic material. But the team behind the new study found that these ARGs can spread in other ways: they can become in the air and migrate from bacteria to bacteria around the world ̵
"ARGs may be released into remote regions or other places where antibiotics are being used less," said author Maosheng Yao Ph.D. University of Environmental Sciences Beijing University reports Inverse. "Ordinary bacteria could become resistant to antibiotics when they ingest these ARGs."
Airborne ARGs make Yao and his team nervous because they are the second, more difficult-to-manage gene accumulation method. Unlike animals who have to wait to pass their genetic material on to the next generation, bacteria can inject each other with genetic material, including ARGs. The effects are permanent because the genes are encoded in the DNA of the recipient bacteria.
This process, called Horizontal Transfer makes air resistance such a threat. Air currents that circulate in urban environments swirl around millions of people every day, raising the likelihood that a typical resistant bacterium may encounter an antibiotic-resistant bacterium.
The shocking observation raised two questions for Yao. Which cities around the world are ARG tourism hotspots and how do they even get blown up?
To investigate, the team studied the levels of airborne bacteria in 19 cities including San Francisco, Beijing, and Paris with a particularly ingenious method. They randomly picked cars from each city and took samples of particles that had accumulated on the inside of the AC filters, which were shown to faithfully reproduce particles in outdoor pollutants. By scraping the filters themselves, the team had many samples to screen for their ARGs.
Their screening revealed 30 different types of ARGs that make bacteria resistant to seven types of antibiotics.
Beijing, China and Brisbane, Australia cited as the cities with the largest diversity in the air of ARGs, but the types of ARGs in the air were from the city to city very different. For example, Melbourne's air contained high levels of airborne genes that confer resistance to drugs such as penicillin and low levels of resistance to ciproflaxin, an antibiotic used to treat typhoid fever.
Apart from this analysis, a city led the list of highest concentrations of ARGs in their air: San Francisco. Although the city as a whole had less air pollution than particle-packed cities like Beijing, Yao was surprised to discover that the Bay Area had more in-between ARGs than Paris, Beijing and Singapore and more than 100 times more ARGs than the relatively small town of Bandung, Indonesia.
"For some cities with good air quality, we have discovered higher abundances of ARGs, even including ARGs designed to withstand the strongest antibiotics," explains Yao. Where did they come from?
Yao suggests that these genes have their origins in treatment plants, hospitals or animal feeders. In particular, wastewater is often treated with antibiotics that, if they are unable to kill all bacteria, could cause the survivors to develop a variety of resistance genes. Previous research has also shown that wastewater is likely to be aerosolized – meaning that the particles in the water can escape into the air.
Whatever drives the spread of antibiotic resistance, it's time to double it, researchers at the University of Exeter Medical School wrote in one Industry-funded mBio study on Tuesday. "So far, there has been much research to address this problem and reduce hospitals and reduce clinical prescribing, but we now know that the environment will play a role in the development and spread of resistance to antibiotics," said lead author William Gaze , Ph.D. "We all need to think holistically about the environmental management of waste, including how we handle our wastewater."
Even though the genes of these wastewater-borne bacteria do not become airborne globetrotters in cities around the world, it's better to keep our sewers under better control, says Yao. In the meantime, do a favor to the citizens of San Francisco and stop flushing antibiotics in the bathroom.