Expertise

Bioaerosols : Tiny particles, big effect

Marcus Clauß | 01.07.2022

AT Institute of Agricultural Technology

In addition to gaseous emissions livestock also releases airborne microorganisms such as bacteria or molds. These bioaerosols are suspected to affect the health of residents in the immediate vicinity of stables. The evidence is still insufficient, but many questions remain unanswered.

10,000 times magnified bioaerosol particles from a layer house: clearly visible are feather fragments (orange), litter and faeces matter (brown) and bacteria (pink).

While we only inhale a few bacteria with one breath of fresh air, there may be millions of bacteria in a breath full of air in large livestock barns. Airborne bacteria are only a small part of the so-called bioaerosols. These consist of a complex mixture of various biological components, ranging from simple organic molecules with dimensions in the nanometer range of viruses, bacteria and fungal spores to pollen of 0.1 millimeters in diameter, as well as animal and plant residues of different sizes.

This "biological dust" usually forms larger aggregates, to which also odorants or ammonia can be bound. Therefore, we always look at the emissions of bioaerosols "holistically", along with dust, ammonia and odors.

Bioaerosols are found in the vicinity of the stables and in the surrounding environment as they exit via the stable exhaust. Especially in systems with tens of thousands of animals, these emissions into the immediate vicinity of the stables could lead to health problems. However, there is currently no sufficient evidence that residents are at risk, but many questions are still open, to which the Institute of Agricultural Technology will dedicate itself in the future.

Post colorized SEM images

With scanning electron microscopy particle surfaces can be shown with high depth of sharpness. The maximum magnification is up to 100,000-fold. The post-colorizing of the grayscale images allows better discrimination of the different particles.

Bioaerosols at harvest: Upper surface of a leaf fragment

Bioaerosols at harvest: Upper surface of a leaf fragment in detail

Different mold spores collected from the air during harvest of barley.

Different mold spores and hyphae fragments.

Diatom collected from the air at harvest of barley.

Bioaerosols in cattle: Infructescence of a mold of the genus Penicillium.

Nematode collected from the air at harvest of wheat

Small aggregate of mold spores collected from the air at harvest of wheat.

Fragment of a beetle and different mold spores.

Colour code:
brown = filter material; orange = mold spores; yellow = mold hyphae; green = particle of plant origin; red = particle of animal origin; magenta = bacteria; blue = unidentified particle

Transmitted-light microscopy

In transmitted-light microscopy the light goes directly through the probe. This method is especially suitable for the identification of mold spores and pollen. Bacteria appear nearly transparent so they cannot be viewed very well with this method.

Dust particles from 500 mL ambient air sampled on a silicone-coated glass slide. This amount of air is about one breath. Magnification 100x

500 mL air, about one breath, from a chicken house. Compared to fresh ambient air we found about 10,000-fold more particles. Magnification 100x

In assumed fresh forest air many different mold spores are found especially in summer and autum. Magnification 400x

Mold spores are also found in office air. If there is an old color printer sometimes also varicolored toner particles. Magnification 1.000x

Different mold spores are found in the air above fields in summer. Magnification 1.000x

Mold spores appear in the air almost as single spores, sometimes in small aggregates. Magnification 1.000x

Fluorescence microscopy

In fluorescence microscopy different dyes were selectively bound to microorganisms. When irradiated with uv light they shine very bright and we can discriminate them from the background. With this method we investigate the inner structure of the bioaerosol particles.

For this procedure the particles have to stick at the substrate so that they not be washed away by the dye solution. Therefore we collect the particles by means of an impactor directly from the air onto special adhesive silicone surfaces.

With our fluorescence dyes we stain the DNA of the bacteria which shine green to orange when irradiated with uv light. Not only bacteria shine in this way because other particles also contain DNA, however we can recognize them on their characteristic sphere or rod like shape.

Bioaerosol particle from a pig house. No details can be seen with transmitted-light microscopy. The next picture shows the same particle with fluorescence microscopy. Magnification 1.000x

Under the fluorescence microscope the stained bacteria shine very bright, so we can see the inner structure of the particle. Magnification 1.000x

Bioaerosol particles from a chicken house. The next picture shows the same particle with fluorescence microscopy. Magnification 1.000x

The fluorescence light made the composition of the particles visible. At the upper image border a Staphylococci aggregate can be seen. Magnification 1.000x

Bioaerosol probe from an exhibition hall. Presumably this particle was a snot droplet that burst when impacted onto the glass slide and spread the containing bacteria on the surface. Magnification 1.000x

Bioaerosol probe from ambient air. Bacteria are found in aggregates and mold spores as single spores. One exception is the chain of mold spores in the upper third of the picture. Magnification 1.000x

This is a bioaerosol probe from a horse stable. Between many dust particles there is a Staphylococci aggregate in the middle of the picture. Magnification 1.000x

Human skin scale colonized with bacteria. We lose about 10,000 skin scales per minute of which 10 % colonized to average with 1000 bacteria. Magnification 1.000x

Also in indoor air aggregates of bacteria can be found. Here the Staphylococci can be seen even in transmission-light microscopy. Magnification 1.000x

In fluorescence light the Staphylococci appear clearer. The previous picture shows the same particles in transmission-light microscopy. Magnification 1.000x

Bacteria aggregates from different bioaerosol probes. Bacteria are found nearly almost in aggregates. Magnification 1.000x

Mold spores from different bioaerosol probes. In contrast to bacteria mold spores are found in the air almost as single cells or in small aggregates. Magnification 1.000x

Projects

What are the sizes of bio-aerosols?

“What is the size of bio-aerosols?” The answer to this question is not easy to give, because bio-aerosol particles are composed of many different components as viruses, bacteria, moulds, pollen and debris of plants and animals, each with different sizes. It is an important question, too, because the effects of bio-aerosols on human health are depending also on the particle size. For example, large bio-aerosol particles get already stuck in the nose or mouth which may cause a common cold, but small particles can get deep into the lungs and in the worst case may induce pneumonia.

Tracing the flight of bioaerosols

Planned construction of animal housings lead more and more often to resistance in the local population. The reason: Emission of bioaerosols. We develop measuring systems to collect valid data and provide them for health assessment.

How good is the air quality in animal houses?

Poor air quality in stables can harm the respiratory ducts of farm animals; lung function impairment is also a recognised occupational disease of farmers and veterinarians. We investigate the composition of air in animal houses to improve air quality and prevent diseases.

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