Bacteriology of Air

1. BACTERIOLOGY OF AIR
Name: Jabed Ahmed Choudhury
ID: SH20MLTGNG42
Program: BSc.MLT
Kaziranga University

2. INTRODUCTION
• Air is not a medium for microbial growth but
carrier for particular matter dust and droplet which
may be laid with microorganisms
• Type of microorganisms in air is depend on source
of contamination
• Eg. Coughing, Sneezing

3. Microbial Content Of Air
The microbial content of the air one breathes in is
important, particularly when it contains pathogens. The
microbial, particularly bacterial, content of air depends
on the location, that is, whether it is outdoor air or
indoor air

4. Airborne infection: Transmission of infection
produced by respiratory droplets less than 5 μm in size
Droplet infection: Transmission of infection produced
by respiratory droplets larger than 5 μm in size

6. Essential Conditions For Bacteriological
Examination Of Air
1. Surgical operation theater
2. In hospital wards in which there is an outbreak of
cross-infection
3. Premises where food articles are prepared and packed
4. Premises where pharmaceutical materials are prepared

7. Measurement of Air Contamination
The methods for bacteriological examination of air are of two
types
1. Sedimentation 'settle plate' method
2. Slit sampler

8. Sedimentation 'settle plate' method
Definition: A means of estimating the number of
bacteriapresent in the air by permitting bacteria to
'settle'on open petri dishes (containing culture media)
overa fixed duration. Droplet nuclei require more
time to settle than larger particles.

9. Method: Open plates of culture media are exposed for
specific periods, for example, half to one hour; then
the plates are incubated at 37°C for 24 hours and the
number of colonies counted
❑The method is specially used for testing the air in
surgical theatres and hospital wards

10. Fig.: Bacterial Growth after Incubation

11. Blood Agar Plating Technique For Air Sampling
⮚The sterile Blood agar plates were transported to operation
theatres in sealed plastic bags
⮚The plates were labelled with sample number, site within the
operation theatre, time and date of sample collection and
control plates were kept to monitor any prior contamination of
plates
⮚During air sampling sterile gloves, mouth mask and
protective gown were worn to prevent self-contamination of
the blood agar plate

12. ⮚The index of microbial air contamination was based
on the count of the microbial fallout on to petridishes
left open to the air according to the 1/1/1 scheme
⮚For 1 hour, 1meter above the floor, at least 1m away
from walls or any obstacle
⮚After this exposure, the plates were covered with
their lids and taken to Microbiology laboratory
⮚Incubated in incubator at 37°C for 24 hours
⮚The culture plates that showed discrete macroscopic
colonies were counted using digital colony counter

13. Formula for Conversion of Colony Count (on settle
plate) to Counts / m3
CFU/m3 = a × 1000
p×t× 0.2
a = The number of colonies on Settle plate
p = The surface measurement of plate used
t = Time of exposure of settle plate
★The concentration of airborne bacteria was
expressed as colony forming units per cubic meter
(cfu/m3)

14. Slit Sampler Method
• The Slit sampler was developed by Bourdillon (1941).
• In this a rotating petridish containing suitable nutrient
agar media is placed under a slit through which air is
drawn.

15. • Sampling is done for short time to avoid the
interference of growth of one colony with another. Slit
sampler is one of several sampling methods used for
quantitation of biological aerosols
• In this method, particles from the air are impinged
directly on a rotating agar plate, the plate is incubated,
and the colonies that develop from the bacteria-laden
particles are counted
• Highly efficient device and can collect upto 95% of
the water droplet particles sprayed into air