Microorganisms in Air

Topics: Bacteria, Microorganism, Water Pages: 5 (1269 words) Published: August 30, 2013
To compare the number and the types of viable airborne microorganisms present in different intramural and extramural environments through sedimentation method using gravity plates and impingement technique

Microorganisms live in numerous habitats making them ubiquitous in nature. They can be found on land, in fresh or salt water environment, in our body and even in the most hostile environments. They are spread in nature either by active (e.g. motility) or passive dispersal (e.g. air, water or by means of vectors) (Stolp, 1988). In this exercise, microorganisms present in air were examined in the different intramural and extramural environments.

The microbial flora of air is transient and variable. Air, unlike water and land, is not a medium for growth of microorganisms. Nevertheless, it acts as a carrier of particulate matter, dust, droplets which can be laden by microorganisms (Aneja, 2005). These microorganisms in air are derived from the terrestrial environment, thus they too indicate the flora of the adjacent soil from where they originated.

To quantify and determine the kinds of microorganisms that contaminate the air in the aforementioned environments, samples from the air were collected using sedimentation method. This method was demonstrated using gravity plate method and impingement technique. The results were gathered and tabulated in Tables 3.1-3.3. In addition to the counts obtained in Tables 3.2 and 3.3, the corresponding CFU/cubic ft of air in each site was also calculated.

Table 3.1 Comparison of the number of microorganisms among the different plates exposed to the different areas using gravity plate method. SITE| PCA| PDA| NA|
Street| 30, 43| 37| 0, 0| 40, 65| 53|
Rooftop| 47, 34| 41| 0, 0| 96, 55| 76|
Laboratory room| 50, 40| 45| 0, 0| 52, 68| 60|

Table 3.2. Counts and number of colony forming units (CFU) of bacteria on PCA plates using impingement technique. SITE| COUNTS| CFU/mL| CFU/ft3 of air|
| 100| 101| | |
Street| 6, 3| 10, 5| <2.5x101 ESPC| <2.3x102 ESPC| Rooftop| 1, 2| 1, 6| <2.5x101 ESPC| <2.3x102 ESPC| Laboratory room| 2, 0| 1, 8| <2.5x101 ESPC| <2.3x102 ESPC|

Table 3.3. Counts and number of colony forming units (CFU) of fungi on PDA plates using impingement technique. SITE| COUNTS| CFU/mL| CFU/ft3 of air|
| 100| 101| | |
Street| 0, 0| 0, 0| <1.0 ESPC| <9.3 ESPC|
Rooftop| 36, 159| 0, 6| 3.6x102| 3.4x103|
Laboratory room| 0, 3| 0, 0| <2.5x101 ESPC| <2.3x102 ESPC|

In gravity plate method, microorganisms in air are collected, as the name suggests, through the influence of gravity on an agar medium. In contrary, in impingement technique, it employs a liquid medium placed in an air sampling apparatus which is then attached to a vacuum source for particle collection. The sampled air is drawn by this vacuum source through a narrow inlet tube into the air sampling apparatus containing the collection medium. Suspended particles in air become impinged once the air strikes the surface of the liquid (Raid Methods Ltd., 2001-2013). Marble beads were also added to the liquid medium to minimize the abrupt changes in the direction of the air when it hits the liquid surface. Thus, microbial cells suspended in air are prevented from being damaged. Aliquots of the liquid medium are then diluted and plated to determine microbial counts.

In this exercise, three different media were used. Potato Dextrose Agar (PDA) medium was used to enumerate fungi (yeasts and molds) in the air. To ensure that this medium will selectively grow fungal cells, streptomycin was added to inhibit the growth of bacteria and other contaminating organisms. On the other hand, Plate Count Agar (PCA) with nystatin was used to determine the plate counts of bacteria. The same principle goes with the addition of...

References: Aneja, K. R. (2005). Experiments in Microbiology, Plant Pathology and Biothechnology. 4th ed. New Delhi:
New Age International.
Stolp, H. (1988). Microbial Ecology: Organisms, Habitats, Activities. New York: Cambridge University
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