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Unit 2 part 3 - Microbes as a
Component of Air Environment
Aerobiology: study of life in the air
Includes:
-

Aerosolization, aerial transmission and deposition of biological materials

-

Diseases that may be transmitted via respiratory routes

Aeromicrobiology: study of various aspects of intramural (indoor) and extramural (outdoor)
aerobiology in relation to environmentally relevant microorganisms including various bacteria,
fungi, and protozoa
Besides these microbes, other biological materials like pollen, insect debris, animal danders
(chief source of allergic disorders) are also found in air
Air-borne microbes are important pathogens causing diseases in plants, animals, and humans
Viral diseases
Diseases

Pathogens

Influenza

Influenza virus

Chicken pox

Varicella virus

Smallpox

Variola virus

Measles

Rubeola virus

Bacterial diseases
Diseases

Pathogens

Diphtheria

Corynebacterium diphtheriae

Tuberculosis

Mycobacterium tuberculosis

Whooping cough

Neisseria meningitidis

Klebsiella pneumonia

Klebsiella pneumoniae

Scarlet fever

Streptococcus pyogenes

Fungal disease
Diseases

Pathogens

Aspergillosis

Aspergillus fumigatus

Blastomycosis

Blastomyces dermatitidis

Cryptococcosis

Cryptococcus neoformans

Histoplasmosis

Histoplasma neoformans

Allergic Disorders Caused by Air Microflora
A number of allergic disorders are caused by air-borne microflora
The following are present in the air
-

Pollen

-

Fungal spores

-

Insect debris

-

Animal danders

-

Mites

Examples of Allergic Disorders
-

Bronchial asthma

-

Allergic rhinitis

-

Atopic dermatitis

Caused by pollens and fungal spores
Indoor environments: ex
...
3 ug of toxin (death is expected 12 hours after
exposure)
Other examples of air-borne toxins are:
- LPS (Lipopolysaccharides - an endotoxin) produced by gram negative bacteria & cause
respiratory distress syndrome

Bioaerosols

Bioaerosols: microbes associated with air-borne particles (liquid, solid, or both)
They are variable in size
In general the size range from 0
...
1

Accumulation

0
...
0

Coarse

Less than 2
...
High light intensity
2
...
Low amount of organic matter
4
...
g
...
1 km from the earth surface
The boundary layer has three parts
1
...
Turbulent boundary layer
3
...
Launching of bioaerosols into air
2
...
Deposition
Example: Liquid aerosol containing influenza virus into air through cough, sneeze, talking, or
laughing
The virus-containing aerosols are deposited by cough, sneeze, transported through air, inhaled
and deposited in the lungs, and cause new infection

Launching: process in which aerosols become suspended within the earth's atmosphere
-

Launching occurs both from terrestrial and aquatic resources and the atmosphere
become loaded

Mechanisms of Launching:
-

Air Turbulence created by humans, animals and machines and dispersal of waste
material

-

Natural mechanical processes as action of water and wind on contaminated solid
surfaces and release of fungal and bacterial spores

Transport or Dispersion: process by which kinetic energy provided by the movement of air is
transferred to air-borne particles, which results in movement from one point to another

Transport of aerosols can be defined in terms of time and distance
Sub-microscale transport: refers to short time and distance
Ex
...
100m
Common within building & spaces
Microscale transport:
It refers to
Time: 10 min to 1 hour
Distance: 100m to 1 km

Mesoscale transport:
Time: days
Distance: km

Macroscale transport:
Both time and distance still longer

Deposition: air-borne bioaerosols eventually leave the turbulence of the suspended gas and
ultimately deposited on surface by one or combination of mechanisms
These mechanisms include:
a
...
Downward molecular diffusion
c
...
Electrostatic deposition

Atmosphere an Inhospitable Nitch for Microbes
Desiccation OR high temperature
Other Stress Conditions
Do not favor majority of microbes
Microbial adoption under such conditions
Takes place in form of fungal and bacterial spores

Factors which Affect Microbial Survival in the Atmosphere
1
...
Temperature:
-

High temperature promote inactivation

-

Low temperature provide longer survival

3
...
UV-light, x-rays damage DNA

Outdoor Microbiology
Outdoor environments are controlled by two factors
1
...
Presence of air turbulence

Whereas, the following factors control microbial viability
-

Radiation

-

Temperature

-

Relative Humidity (RH)

Air-borne Crop Pathogens
Bioaerosols have direct relevance to agriculture
Air-borne microbes cause a number of plant diseases
Several outbreaks of epidemics of plant diseases have been reported at world level
Examples
Wheat rust - 1978
Gram blight - 1980-83
Cotton leaf curl virus - 1989-93

Role of Bioaerosols in Animal Husbandry
Foot and mouth disease in cattles
Respiratory pathogens
Gastrointestinal pathogens
ex
...
Radiation
b
...
Efficiency of air-filtering system
b
...
Amount of clean air
d

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