Microbes in the air around us.

1. AEROMICROBIOLOGY
MICROBIOLOGY V
LECTURE 1
DR. M. SONIA ANGELINE
ASSISTANT PROFESSOR
DEPARTMENT OF LIFE SCIENCES
KRISTU JAYANTI COLLEGE

2. INTRODUCTION
◦ Air, mixture of gases comprising the Earth’s atmosphere. The mixture contains a
group of gases of nearly constant concentrations, variable amounts of water
vapor and dust particles.
◦ The air in our atmosphere is composed of molecules of different gases. The most
common gases are nitrogen (78%), oxygen (about 21%), and argon (almost 1%).
Other molecules are present in the atmosphere as well, but in very small
quantities.
◦ The earth's atmosphere is teeming with airborne microorganisms. These
organisms are thought to exhibit correlations with air pollution and weather.
◦ Air is an unfavorable environment for microorganisms, in which they cannot
grow or divide. It is merely a place which they temporarily occupy and use for
movement.
◦ Air lacks nutrients and water required for growth of microorganisms.

3. INTRODUCTION
✓Aeromicrobiology is that zone of biological science which describes the study of air
living microorganisms.
✓These aerial microorganisms are called bioaerosols.
✓These bioaerosols have tremendous capacity to create disease not only in human beings
but also in several other living organisms.
✓The troposphere which is the most nearest aerial layer of earth exhibit the overload of
microorganisms.

4. INTRODUCTION
✓As they travel a long route by air they can cause several diseases and which spread not only in human beings
but also in plants, livestock etc and lead to severe damage.
✓These microbial emissions of air can play a vital role in environmental hygiene.
✓Microbes become suspended in the clouds first, then they transform the chemical composition of clouds by
causing several chemical reactions.
✓Most airborne bacteria originate from natural sources such as the soil, lakes, oceans,
animals, and humans.
✓These aerial microorganisms may spread throughout a long distance after being suspended.
✓Viable airborne microorganisms are not air pollutants, but should be considered as a factor
affecting air quality.

5. DEFINITION
◦ Aerobiology is defined as the study of life present in the air.
◦ Aeromicrobiology relates to the study of environmentally relevant microorganisms.
◦ Microorganisms exist within 300-1000 feet of earth’s surface that have become attached
to fragments of dried leaves, straw or dust particles light enough to be blown by wind.
◦ In dry whether the microbial load of air is high while in wet weather the rain washes the
microorganisms from the air.

6. Air is a poor medium for microbial growth – too dry and no nutrients.
Spore forming and Gram- positive bacteria are resistant to drying.
Dust, water droplets in air carry microbial populations from one place to another
Sneezing, coughing, talking are efficient methods of transferring microbes from one
respiratory tract to another 100 m/sec, 10000 – 100000 bacteria.
Liquid and dust particles settle in the respiratory tract depending on their velocity and size.
Microorganisms colonize specific locations in the respiratory tract.

7. PHYSICAL HABITATS IN AIR
◦ There are two microbial habitats in air-
◦ 1. Atmosphere 2. Clouds
Atmosphere: The layers of atmosphere are differentiated according to intensity of light, variation of temperature
low amount of organic matter and a scarcity of available water making it a non-hospitable environment for
microbes. But these can be deposited by gravity that make them to contact with earth’s surface. By this way the
microbes gradually suspend in the lower part of atmosphere.
◦ There are five layers of atmosphere:
I) Troposphere –> 6-20 km
II) Stratospheres –> 50 km
III)Mesosphere –> 85 km
IV)Thermosphere –> 690 km
V) Exosphere –>10,000 km

8. Structure of the Atmosphere
• Troposphere: This layer is the most important layer of the
atmosphere. Its average height is 13 km. The air we breathe exists
here.
• Stratosphere: It lies above the troposphere which extends up to a
height of 50 km. This layer is almost free from clouds and associated
weather phenomenon. It contains a layer of ozone gas.
• Mesosphere: This is the third layer of the atmosphere. It lies above
the stratosphere. It extends up to the height of 80 km. Meteorites burn
up in this layer on entering from the space.
• Thermosphere: In thermosphere temperature rises very rapidly with
increasing height. Ionosphere is a part of this layer. It extends between
80-400 km. This layer helps in radio transmission.
• Exosphere: The upper most layer of the atmosphere is known as
exosphere. This layer has very thin air. Light gases like helium and
hydrogen float into the space from here

9. PHYSICAL HABITATS IN AIR
Clouds
❖Clouds are another kind of microbial habitat.
❖A visible mass of condensed watery vapor floating in the atmosphere, typically high above the general level of
the ground.
❖Actually clouds acidic environment favours (PH =3-7) the extremophiles growth and suspension.
❖The building blocks of clouds are water and particles—of dust, dirt.
❖They attract water vapor and as they ascend the vapor condenses to form liquid water or ice, which results in
the formation of tiny globules called cloud droplets.
❖Much smaller than raindrops, cloud droplets are extremely light and a mass while they float, mixing with air to
form the fluffy formations we see suspended in the sky.
❖Clouds are alive with tiny bacteria that grab up water vapor in the atmosphere to make cloud droplets,
especially at warmer temperatures.

10. MICROBIAL COMMUNITIES IN AIR:
Several types of microorganisms such as, bacteria, virus, fungi, yeast and
protozoans form aerosols.
Then these microorganisms have to adapt with the harsh conditions of
atmosphere just for survival. As these can survive the extreme condition some of
them can form endospore.
Bacteria:
Bacillus anthracis, gram positive in nature and it can survive in aerosol. This
bacteria is responsible for anthrax which is associated with dangerous respiratory
diseases of human.
Fungi:
Aspergillus fumigatus is most dangerous aerial fungal pathogen and it is able to
cause human lungs diseases when their conidia are inhaled. There are several
viral pathogens in aerosol in atmosphere which have the capacity to develop
severe diseases in human beings as well as in other animals. The toxins secreted
from airborne microorganisms are highly responsible for severe diseases in
human. A very common type of spores found in air is that of conidia.

11. Virus:
The air is also occupied by viruses. Among those that demonstrate the highest resistance are those with enveloped
nucleocapsids, such as influenza viruses. Among viruses without enveloped nucleocapsids, enteroviruses
demonstrate a relatively high resistance. Viruses are usually more resistant than bacteria.
Lipopolysaccharide (LPS) is one of the most affective airborne toxin that develop from the gram negative
bacteria’s outer membrane. After getting associated with dust in air the LPS may lead to acute respiratory
diseases such as- chest tightness, coughing, fever etc.
What types of dangers are connected to the presence of microorganisms in air?
•Infectious diseases (viral, bacterial, fungal and protozoan),
•Allergic diseases
•Poisoning (exotoxins, endotoxins, mycotoxins).
Bioaerosols may carry microorganisms other than those which evoke respiratory system diseases. The intestinal
microorganisms contained in aerosols may, after settling down, get into the digestive system (e.g. by hands)
causing various intestinal illnesses.

12. Bioaerosols
▪ Bioaerosols are defined as particles of microbial, plant, or animal origin and oftentimes are called “organic dust.”
▪ They can include live or dead bacteria, fungi, viruses, allergens, bacterial endotoxins (components of cell membranes
of Gram-negative bacteria), antigens (molecules that can induce an immune response), toxins (toxins produced by
microorganisms), mycotoxins (toxins produced by fungi), glucans (components of cell walls of many molds), pollen,
and plant fibers.
▪ Microorganisms in air occur in a form of colloidal system or the so-called bioaerosol.
▪ Many of these kinds of bioaerosols are known to cause a variety of human impacts such as infection and sensitivity
over even short periods of time.
▪ Bioaerosols are airborne particles, solid or liquid.
▪ They can be large molecules or volatile compounds.
▪ They contain living organisms.
▪ They will vary in size from a fraction of a micron to around 100 microns.

13. SOURCES OF MICROBES IN AIR
• Although there are lots of microorganisms in air but air is not the natural habitat of all type of
microorganisms because it does not constitute perfect moisture and nutrient for the growth of
microorganisms.
• Infectious dust, droplets, industrial aerial emissions are the major sources of microbes in air today. Actually
big sized aerial droplets get dry on air surfaces.
• The nasal and throat discharges from a patient can be the major source of infectious dust and it is seen
that after getting dried these discharges along with several microorganisms freely float in the air.
• Besides this there is also the presence of droplets in air. The vital sources of droplets are sneezing,
coughing and talking of patients.
• The oral discharges along with mucus of those patients can bear lots of severe infectious microorganisms
which readily spread in the air and play a vital role in the disease development.
• The industrial aerial emissions are full of toxic gases and these gaseous particles are also a major source of
infectious microorganisms in air.
• Atmospheric humidity, temperature are the major controllers of survival of microorganisms in air.

14. Resistance of microorganisms
Humidity:
• The content of water in air is one of the major factors determining the ability to survive.
• At a very low humidity and high temperature cells face dehydration, whereas high humidity may give cells
protection against the solar radiation.
• Microorganisms react differently to humidity variations in air, but nevertheless most of them prefer high
humidity.
• Gram-negative bacteria and enveloped viruses (e.g. influenza virus) deal better with low air humidity which
is contrary to gram-positive bacteria and non-enveloped viruses (e.g. enteroviruses) that have higher survival
rates in high air humidity.
Temperature:
• Temperature can indirectly affect cells by changing the relative-air humidity (the higher the temperature, the
lower the relative humidity) or a direct affect, causing, in some extreme situations, cell dehydration and
protein denaturation (high temperatures) or crystallization of water contained within cells (temperatures
below 0°C).
• Therefore, it can be concluded that low temperatures (but above 0°C) are optimal for the bioaerosol.
According to some researchers the optimal temperatures are above 15°C.

15. Indoor Microflora:
The air found inside the building is referred to as indoor air.
The commonest genera of fungi in indoor air are penicillium, Aspergillus, the
commonest genera of bacteria found in indoor air are Staphylococci, Bacillus and
Clostridium.
Outdoor Microflora:
The air in the atmosphere, which is found outside the buildings, is referred to as
outside air. The dominant microflora of outside air are fungi.
The two common genera of fungi are cladosporium and sporobolomyces, besides
these two the fungi found generally in air are Aspergillus, Alternaria, Phytophthora
and Erysiphe.
The outdoor air also contains besidispores, ascopres of yeast, fragments of
mycelium and canidia of molds.
Among the bacterial genera Bacillus and clostridium, sarcina, mirococcus,
Corynebacterium and Achromobacter are widely found in the outside air, the
number and kind of microorganism may vary from place to place, depending upon
the human population densities.

16. THANK
YOU
https://www.youtube.com/watch?v=vO51sFre6fg-
airborne microorganisms