Air is the simplest one It occurs in á single phase - gas. In addition to various gases, dust and condensed vapour may also be found in air. In addition to gases, dust particles and water vapour, air also contains microorganisms. There are vegetative cells and spores of bacteria, fungi and algae, viruses and protozoan cysts. Air is often exposed to sunlight, it has a higher temperature and less moisture. So, if not protected from desiccation, most of these microbial forms will die. Air is mainly a transport or dispersal medium for microorganisms They occur in relatively small numbers in air when compared with soil or water. Microflora of air Air can be studied under two headings Outdoor microflora and Indoor microflora

2. Composition of air
• Air is the simplest one
• It occurs in á single
phase - gas.
• In addition to various
gases, dust and
condensed vapour may
also be found in air.
Nitrogen,
78%
Oxygen, 21%
Argon,
0.90%
Carbon
dioxide, 0.03 %
Hydrogen,
0.01%
Other gases -
Trace
amounts, 0
-20%
0%
20%
40%
60%
80%
100%
0 1 2 3 4 5 6 7
Relative Quantities of Various Gases in
Air

3. • T0 varies near the
earth’s surface
• Steady decrease of
10C / 150m until
top of the
trophosphere
• Above that the T0
starts to increase.

4. • Temperate region –
trophosphere
extends up to –
11km.
• Tropical region – up
to 16km.
• This layer contains
heavy load of
microorganisms.

5. Distribution
• In addition to gases, dust particles and water vapour, air also
contains microorganisms.
• There are vegetative cells and spores of bacteria, fungi and
algae, viruses and protozoan cysts.
• Air is often exposed to sunlight, it has a higher temperature and
less moisture. So, if not protected from desiccation, most of these
microbial forms will die.
• Air is mainly a transport or dispersal medium for microorganisms
• They occur in relatively small numbers in air when compared with
soil or water.

6. Microflora of air
• Air can be studied under two headings
Outdoor
Microflora
Indoor
Microflora

7. i) Outdoor Microflora
• The air in the atmosphere, which is found outside the building is
referred to as outside air.
• It is larger in volume than the indoor air
• The dominant flora of outside air is fungi.
• The two common fungi are
o Deuteromycete - Cladosporium and
o Basidiomycete - yeast Sporobolomyces.
• Basidiospores, ascospores of yeasts, fragment of mycelium and
conidia of molds are also common.

8. Bacteria
• Spores of Bacillus and Clostridium
• Resistant non-spore formers such as Sarcina lutea and
Micrococcu luteus.
• Non-pathogenic species of Corynebacterium and
• Few Gram negative rods such as coliforms and
Achromobacteriaceae are the widely occurring ones.

9. Air flora over the sea
• The air flora over the sea is
quite different from that of
landscapes
• Includes the following
genera,
Genera
•Achromobacter
•Bacillus,
•Corynebacterium,
•Flavobacterium,
•Micrococcus,
•Sarcina and
•Staphylococcus.

10. Air flora at very high altitudes
4 km from the
earth's surface
• Dark spored fungi such as Cladosporium and Alternaria
• Bacteria like Bacillus and Micrococcus
• Concentration - about 2 to 500 per m3
30 km from the
earth's surface
• Spores have been detected
• But in very low concentration
• At this altitudes the microorganisms are subjected to severe conditions
like desiccation, ultraviolet radiation and low temperature.

11. Number of microorganisms may vary from place to place.
• For example, mainly due to the difference in human population
densities.
 In countries - several hundreds of bacteria are found per cubic
meters.
 In cities - several thousands of bacteria are seen per cubic meters.
• During summer – over agricultural lands - fungal spores are found in
ten thousand per cubic meter.
• The relative abundance of fungal spores in air is due to the air acts as a
means of transport for the fungal spores.

12. Air over the sea
has less Microbes
Air over the terrestrial
surface has more
Microbes

13. Spore density
• Varies on an annual (caused by climatic changes – T 0) and daily basis.
 In temperate countries - winter temperature is less favourable, during
rainy season rain washes out the spores present in air, thus causing a
reduction in spore density.
 In tropical countries - high temperature causes desiccation leading to a
reduction in spore density.
• Spore discharge depends on the diurnal fluctuation.
 Colorless basidiospores - released during night.
 Sporangia of Phytopthora - released max level during day
 Spore formation in Erysiphe - controlled by light and they mature only
during midday.

14. ii) Indoor Microflora
• The air found inside the building is referred to as indoor air.
• The air inside the room will not be still
o Cold air blowing through the windows and doors
o Turbulence created by moving people.
• The dominant genera
o Common saprophytic fungi are
• Penicillium
• Aspergillus.

15. o Bacteria
• Usually the bacterial flora of indoor air reflects that of human skin and
respiratory tract.
• The frequent bacterial species are Staphylococci, Bacillus and Clostridium
perfringens.
• number may vary depending upon various factors like ventilation, number
of occupants in the room (being infected, other pathogenic bacteria and/or
viruses of the respective diseases may also be present), etc.
• ventilated rooms - several hundred bacteria per m3 will be present.