Most of us think of the air as empty space, a transparent medium carrying oxygen and other molecules. Yet for Dr. Sofya Pozdniakova of the Barcelona Institute for Global Health, air is anything but inert. In her work, presented at the PREPARE-TID consortium webinar, she demonstrated that aerosols, microscopic particles suspended in the atmosphere, host complex microbial communities and, critically, carry antimicrobial resistance (AMR) genes. These airborne microorganisms and genetic elements can disperse across neighborhoods, regions, and even continents, redefining how we understand environmental reservoirs and pathways of AMR transmission.
Air, reimagined
Aerosols, the tiny solid or liquid particles suspended in air, are born of both natural and human activity: sea spray, Saharan dust, volcanic eruptions, but also fossil fuel combustion and agriculture. Air quality monitoring stations across Europe track them diligently, reporting particulate matter (PM) concentrations that define “good” or “bad” air days.
But what if those filters, the same ones used to measure pollution, were also capturing the DNA of living organisms? Plants, insects, fungi, bacteria, even viruses. With next-generation sequencing (NGS), the familiar PM filter becomes something more: a biological ledger of the world around us, revealing the diversity of life aloft.
Life in the air
When one-eighth of a single filter from Barcelona was placed on agar plates, colonies of bacteria and fungi bloomed. Yet these visible colonies represented barely 1% of the organisms detectable in the air sample. The rest required metagenomic sequencing to uncover.
Dr. Pozdniakova and collegues has shown that air is “alive”. At 3,000 meters altitude, air sampled during flight campaigns over Japan carried microbial communities strikingly similar to those at ground level. Seasonal shifts reflected long-range transport: air masses traveling over 2,000 km brought microbial signatures from distant regions, detached from local sources.
“The atmosphere itself”, she argued, “functions as a global microbial conveyor belt, moving organisms, and their resistance genes, across continents”.
Breathing AMR
Culturing airborne bacteria provided a sobering glimpse into resistance profiles. Genera such as Bacillus, Micrococcus, and Lactobacillus dominated the plates. Among them, Micrococcus luteus stood out for its multidrug resistance, though the precise mechanisms remain unknown. If plasmid-mediated, it could act as a donor to other bacteria.
Metagenomics widened the analysis:
- Genes conferring resistance to macrolides, lincosamides, streptogramins, tetracyclines, and β-lactams were all detected.
- By antibiotic class, aminoglycoside resistance genes were most abundant, followed by tetracycline resistance.
- These signatures mirror human activity, especially heavy use of these drugs in medicine and livestock production.
In short, the air is not only a microbial habitat but a reservoir of resistance determinants.
The urban aerobiome
Barcelona served as a testbed for how air’s microbial communities differ across landscapes. Over a year, samples were collected from five sites: transit hubs, urban background districts, and a greenbelt. The results revealed that each site had its own stable microbial “fingerprint.”
- Urban cores were dominated by genera such as Deinococcus and Paracoccus, markers of dense anthropogenic environments.
- The greenbelt harbored unique taxa, including Rubrobacter and Mycolatopsis, absent from the city center.
- Beaches, paradoxically open and ventilated, emerged as ARG hotspots, particularly for genes conferring resistance to vancomycin and disinfectants.
The stability of these signatures was surprising. Air, it turns out, is not homogenous: it reflects the neighborhoods it passes through, carrying the microbial imprints of human and environmental activity.
Indoors: hospitals and care homes
Dr. Pozdniakova’s team extended their work to a hospital and an elderly care center.
The results?
Shared species linked the two environments, but each also had distinct profiles. The care center’s air was dominated by fungi associated with trees (Teletopsis ashingtonis), mirroring the greenery surrounding the facility. The hospital’s air, by contrast, carried clinically relevant pathogens, including Staphylococcus and Clostridioides difficile.
Resistance genes amplified the concern. Hospital samples contained a higher proportion of target-alteration genes, underscoring the risk of airborne AMR in clinical environments. Culturing revealed viable Staphylococcus and Bacillus strains not seen in sequencing data, some displaying divergent resistance profiles even when isolated from the same room.
This dual approach, combining culturomics with metagenomics, highlighted an essential truth: each method “sees” what the other misses. Spores may evade DNA extraction but flourish on plates; fragile cells may leave DNA traces but refuse to grow.
Only by layering both do we glimpse the full picture.
Methodological hurdles
Air, as a biological sample, is uniquely challenging. Compared to soil or seawater, it is an ultra-low biomass matrix. Microbial DNA concentrations can be six orders of magnitude lower than in other environments. This scarcity raises risks of contamination, false positives, and amplification bias.
Dr. Pozdniakova emphasized several best practices:
- Negative controls and mock communities at low biomass levels to detect amplification artifacts.
- Rigorous decontamination of sampling equipment, including bleaching steps.
- Development of specialized DNA extraction protocols: her team created an in-house phenol–chloroform method with enzymatic treatment, outperforming commercial kits for stubborn filters.
Even with these measures, challenges remain. Nanopore sequencing, while powerful for long reads, demands sufficient input DNA, often hard to achieve with air samples. Collaborations with kit developers are ongoing to refine approaches for ultra-low biomass environments.
Why this matters
Airborne resistance may feel abstract, until one considers the populations most exposed. Hospitals, elderly care centers, urban transit hubs: these are places where vulnerable individuals spend time, where infections can spread quickly, and where AMR is already a crisis.
The implication of Dr. Pozdniakova’s work is clear: airborne AMR surveillance should be integrated into One Health frameworks. The air is not sterile; it is a reservoir and a transport system. Resistance genes move with dust storms, with urban breezes, with the recirculated air of hospital wards. Ignoring this pathway leaves a critical blind spot.
A new dimension of One Health
Where Olga Makarova’s work highlights resistance in the dogs at our side, Dr. Pozdniakova’s research exposes it in the very air we breathe. Both stories converge on the same message: AMR is not confined to hospitals or farms. It is woven through daily life, transmitted through intimate contacts and invisible atmospheres alike.
In the quiet hum of an air filter or the panting breath of a Labrador lies the reminder that resistance is everywhere. To track it, we must look not only at bloodstream infections or food chains, but at parks, living rooms, transit stations, and skies.
This shift in perspective, from seeing air as empty to recognizing it as biologically charged, could redefine AMR surveillance. In the end, every breath may carry more than oxygen. It may carry the next chapter in the story of resistance.
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