Isolation of Bacteria from Air Practical

Isolation of bacteria from air involves various kind of plating techniques in a microbiological laboratory.Today in this practical we are going to cover the all over practical with a general overview.


To plate various type of bacteria present in air on culture media to count colony forming unit(cfu) and isolate those bacterial pure culture for further studies


Isolation of Bacteria from Air Practical

The microbial population (bacteria, algae, fungi, protozoa etc.) in our environment as well as our daily life, as they can gradually modify an ecosystem, causing diseases to plant, animal and human or many, used for the production of antibiotics, enzymes, vaccines . Air often serves as a transport or dispersal medium for many infectious disease. The condition of air differs from one location to another. The outdoor air is predominantly of fungi where as large number of bacteria i.e. Staphylococcus, Bacillus, Clostridium can be found in indoor air. A study of microbial habitats of air is thus essentially important to specify the microbes especially bacteria present in it. However bacteria as a microorganism have beneficial and harmful effect on human beings as well as on other organisms.


  • Nutrient agar
  • Petri plate
  • Conical flask
  • Autoclave
  • Incubator
  • Colony counter
  • Laminar air flow


  1. Nutrient agar media was first prepared in a conical flask, digested and thoroughly sterilized in autoclave along with petri plates at 121 °C at 15 lb/inch square pressure for 15 minutes.
  2. The sterilized media was then poured into petri plates and allowed to solidify for 20 minutes at laminar air flow
  3. The solidified agar plates were then exposed at different location by removing the lid and allowed to remain there for 2 hours. The plates were exposed at microbiology lab, teacher’s room, canteen.
  4. The plates were taken off after exposure and incubated in inverted position at 37 °C for 24 to 48 hours.
  5. After incubation for 24h the growth in every plates were observed for morphological study of various colonies and to count CFU
  6. The counting was carried out by using colony counter whereas morphological features were observed under microscope
  7. Pure culture was done from this colonies by microbiological culture techniques


Different size of bacterial colonies were observed in every plate


Different number and various size of mixed bacterial colonies were observed in each petri plates

PlatesPlates Media (ml)Exposure timeNumber of ColoniesCFU/5min
Microbiology lab2025 min715143
Canteen2025 min25050
Teacher’s Room2025 min18036


Colony forming unit (for air) =(Number of colonies / Exposure time)/ 5 min


From the result we conclude that various kinds of bacterial colonies were observed on each petri plates. The plates were exposed in air at different places for same time interval and various types of bacterial colonies were observed which was present in that location in that particular time.

Read – Isolation of Microorganisms from Soil – Lab Report

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