1. AERO-MICROBIOLOGY Lecture #02 Amjad Khan Afridi Lecturer,
Department of Health & Biological Science

2. What is Aero-microbiology..?
Aero microbiology is the study of living microbes which are suspended in the air, and are referred to as bio aerosols.
Less atmospheric microorganisms as compared to oceans and soil
Chance to travel long distances with the help of wind
Small particles stay suspended longer and so they travel farther.
Ecologically significant
associated with disease in humans, animals and plants.

3. Physical/Microbial Habitats in air
There are two microbial habitats in air
1. Atmosphere
2. Clouds

4. 1. Atmosphere: The atmosphere as a habitat is characterized by; high light intensities, extreme temperature variations, low amount of organic matter and a lack of available water making it a non-hospitable environment for microorganisms and generally unsuitable habitat for their growth.
the major layers are the troposphere, stratosphere, mesosphere, thermosphere and exosphere. 

5. 2. Clouds:
A visible mass of condensed watery vapor floating in the atmosphere, typically high above the general level of the ground.
Clouds are also an acidic environment, with a pH ranging from 3 to 7.

6. Sources of micro-organisms in air
Air is not a favorable environment for the microbial growth
Quite a number of sources -introduction of microbes in the air
The most common source is soil
Plant pathogens can spread more rapidly as compared to animal pathogens
The main source of the introduction of microbes in the air is human beings

7. Bio aerosols…
Bioaerosols are airborne particles, solid or liquid which contain living organisms or biological material . 
Bio aerosols are classified on the bases of their sizes and they mostly range in um in diameter.

8. Transmission of microbes in Air
The microbes released in the air are in three forms depending upon on the size and moisture content. These three forms are
Droplets,
(2) Droplets Nuclei,
(3) Infectious dust.
Currently, the term droplet is often taken to refer to droplets >5 μm in diameter that fall rapidly to the ground under gravity, and therefore are transmitted only over a limited distance (e.g.
Millions of Droplets are released when we sneeze, and mucus is expelled at about 200 miles away.
≤1 m). 

9. Droplets:
These droplets are water droplets that carry micro-organisms if a diseased person released them.
Droplet is often taken to refer to droplets >5 μm in diameter that fall rapidly to the ground under gravity, and therefore are transmitted only over a limited distance (e.g. ≤1 m). 
These droplets contain saliva and mucus.
The microorganisms they carry are mostly of respiratory tract.
The size of droplet determines for how long micro-organisms stay on the droplets and droplets of large size settle in the air rapidly.
These droplets carrying microorganism are source of infectious disease.

10. Cont… (2) Droplets Nuclei:
Particles of liquid, 1-5 um in diameter released during sneezing and coughing.
Droplet nuclei are considered to be the raw material for the respiratory disorders.
It contains saliva and mucus on its surface.
Due to their small size they suspend in the air for a longer period of time.
Droplet nuclei are considered to be the constant source of bacterial infections if the bacteria present on its surface remains viable.
The viability of bacteria depends on the physical factored i.e. humidity, sunlight, moisture and the size of droplets as well.
Airborne droplet nuclei
Airborne droplet nuclei develop when the fluid of pathogenic droplets (1-5 µm in size; micrometre = one-thousandth of a millimetre) evaporates. They are so small and light they may remain suspended in the air for several hours. Thus, they may also infect persons entering a room which has been left by a patient long ago. Also, airborne droplet nuclei can be widely dispersed by air currents. Tuberculosis, chickenpox, measles and possibly also influenza may be transmitted this way.

11. (3) Infected dust particles:
These dust particles introduced in the air by bed making, handling a handkerchief, dealing with a patient having dried secretion, digging and ploughing.
Microorganisms stick to the surface of these droplets and get suspended in the air.

12. 26th September, 2022

13. Factors affecting Microbial Survival in air
Factors affecting on the microbial survival in air are
1. Temperature
2. Humidity
3. Nutrient content
4. Acidity and pH
5. Radiations

14. Cont…
Temperature is the major factor in controlling the growth of microbes in the air, as high temperature inhibits the growth of microbes and sometimes denatures the structural conformation of microbes.
Humidity has its own role in maintaining the growth of microbes in air.
In general, it has been reported that most gram-negative bacteria associated with aerosols tend to survive for longer periods at low to mid levels of relative humidities.
The opposite tends to be true for gram-positive bacteria, which tend to remain viable longer in association with high relative humidities. Thus, the ability of a microorganism to remain viable in a bioaerosol is related to the organism’ s surface biochemistry.

15. Nutrient contents or availability is less in the atmosphere, so it does not support the microbial growth.
pH: Every microorganisms have their own specific pH requirement so change in pH may affect their growth as well as survival in the environment.
Radiation damages microorganisms genomes.
i.e. shorter UV wavelengths and ionizing radiation such as X-rays

16. Particles suspended in air are called aerosols.
These pose a threat to human health mainly through respiratory intake and deposition in nasal and bronchial airways.
Smaller aerosols travel further into the respiratory system and generally cause more health problems than larger particles.
For this reason the U.S. Environmental Protection Agency (EPA) has divided airborne particulates into two size categories:
PM10 , which refers to particles with diameters less than or equal to 10 m (10,000 nm), and
PM 2.5 , which are particles less than or equal to 2.5 m (2500 nm) in diameter.
Where does PM10 come from? PM10 is any particulate matter in the air with a diameter of 10 micrometers or less, including smoke, dust, soot, salts, acids, and metals. Particulate matter can also be formed indirectly when gases emitted from motor vehicles and industries undergo chemical reactions in the atmosphere.29-Jun-2022

17. Aeromicrobiological pathway
The aero-microbiological pathway describes:
The launching of bioaerosols into the air;
(2) The subsequent transport via diffusion and dispersion of these particles; and finally
(3) their deposition
An example of this pathway is that of liquid aerosols containing the influenza virus launched into the air through a cough, sneeze, or even through talking. These virus-associated aerosols are dispersed by a cough or sneeze, transported through the air, inhaled, and deposited in the lungs of a nearby person, where they may begin a new infection
5.6.1 Launching The process whereby particles become suspended within Earth ’ s atmosphere is termed launching. Because bioaerosols must be launched into the atmosphere to be transported, it is important to understand this process. The launching of bioaerosols is mainly from terrestrial and aquatic sources, with greater airborne concentrations or atmospheric loading being associated with terrestrial sources than with aquatic sources. Some researchers speculate that there may even be atmospheric sources of bioaerosols in addition to terrestrial and aquatic ones. This phenomenon is related to the limited potential for microorganisms to reproduce while airborne. This, however, is an area of aeromicrobiology for which there is little available information. Launching into the surface boundary layers can include, but is certainly not limited to, diverse mechanisms such as the following: air turbulence created by the movement of humans, animals, and machines; the generation, storage, treatment, and disposal of waste material; natural mechanical processes such as the action of water and wind on contaminated solid or liquid surfaces; and the release of fungal spores as a result of natural fungal life cycles.
5.6.2 Transport Transport or dispersion is the process by which kinetic energy provided by the movement of air is transferred to airborne particles, with resultant movement from one point to another. This “ energy of motion ” gained by airborne particles is considerable and can result in dissemination of airborne microorganisms over long distances. Transport of bioaerosols can be defined in terms of time and distance.
As bioaerosols travel through time and space, different forces act on them such as diffusion, inactivation, and ultimately deposition. Diffusion is the scattering and/or dissipation of bioaerosols in response to a concentration gradient as well as gravity, and is generally aided by airflow and atmospheric turbulence.
5.6.3 Deposition The last step in the AMB pathway is deposition. An airborne bioaerosol will eventually leave the turbulence of the suspending gas and will ultimately be deposited on a surface by one or a combination of interrelated mechanisms. T

19. Mechanism to control Bio aerosol pathogenicity
Hospitals and Microbiology laboratories are two such indoor environments that come under the category of Aero-microbiology with possibly the highest potential for the aero-solization of pathogenic microbes.

20. Biocidal Agents and Physical Isolation.
The control of bio aerosols can be managed in a variety of ways and at each point of their spread whether it be launching, transport or deposition. The mechanisms used to control bio aerosols include;
Ventilation,
Filtration,
UV Treatment,
Thermal Treatment,
Biocidal Agents and Physical Isolation.
Prevention tips include good ventilation to swap indoor and outdoor air.
Ventilation methods, such as opening a window or using fans, help to exchange dirty air.
Wearing a hospital mask in public, and covering sneezes and coughs with an elbow or tissue, 

21. End
Date: 3rd October, 2022