Quantitative Assessment of Fungi and bacteria in air inside Bradford Apartment


The experiment was conducted from the week from 10/26/2014 to 11/02/2014 at the Bradford apartments. Different types of agar media were used to estimate and quantitatively assess fungi and bacteria in air within an air-conditioned apartment unit. Fungi are essential to our environment, due to their function of decomposing organic materials. Nevertheless, airborne fungal spores can cause irritations and allergies and can even compromise the human immune system in less maintained buildings. Inappropriate humid control or water damage, as seen in the apartment used for this experiment, can lead to high loads of fungal spores. Thus, this study focuses on the qualitative assessment of Fungi and bacteria in air inside a Bradford Apartment by using different agar media, which were incubated at two different temperatures corresponding to human body temperature (37°C) and room temperature (25°C) . Noticeable is that almost all agars incubated at 25°C show a greater count of colonies than those incubated at 37°C.

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The Apartment of interest is on the top floor and recently experienced some water damage due to a leak in the roof structure. It currently houses an Oceanic 29 gallon Biocube, which evaporates about one gallon of water within a week. The Apartment temperature was set to 25 C while conducting the experiment. The building contains vaulted ceilings and central air conditioning, which creates various microclimates favorable by fungi and bacteria. In addition, the living room and bedroom of the apartment contains carpet. Airborne fungal spores can cause irritations and allergies and can even compromise the human immune system in less maintained buildings (Taylor et al. 2014).

The kingdom Fungi includes funguses or fungi, which represent a large group of eukaryotic organisms. All fungi are heterotrophs, which means they absorb nutrients through their cell walls and cell membranes. They are essential to our environment, because they decompose organic material and therefore, recycle nutrients essential for plant growth. Besides yeast, all fungi consist of elongated filaments, also called hyphae. When the hyphae grows bigger in size, it creates a network called mycelium. Once fruiting, they become mushrooms or molds. Fungi are abundant everywhere, such as dead matter, air, and soil but also in symbiosis with plants, animals and/or with other fungi (Van De Graaff, Kent M. et al, 2009).

Bacteria belong to prokaryotic microorganisms, which lack a true nucleus and bounded organelles. They appear in different shapes such as spiral, spherical or rod-shaped. It is believed that bacteria were the first life form on our planet and are therefore present in soil, water, deep in the earth crust, and extreme conditions such as nuclear reactors. Most bacteria are harmless and can be found on and in the human body like the gastrointestinal tract. They also live in symbiosis with other animals and plants. One of their roles is to break down surrounding organic materials by converting them into absorbable compounds. (Van De Graaff, Kent M. et al, 2009).

The media for this lab includes Rose Bengal Agar (RBA), Potato Dextrose Agar (PDA) and trypticase soy Agar (TSA). In past research experiments PDA and RBA have been used to cultivate fungi. TSA is used for Bacterial growth (Neogen 2011).

Frequent sinus infections were traced back to severe allergic irritations in eyes and sinuses, which compromised the renter’s immune system and caused illness. Therefore, this experiment focuses on bacterial and fungi abundance in air regarding different locations with three different growth media. Due to the structure of the apartment, greater fungal counts should be expected at 25oC than at 37oC.


Experiment was conducted from 10/26/2014 until 11/02/2014. Each agar was prepared with 500 ml deionized water, which was added into three different 1 liter conical flasks. Each dehydrated medium was weighed according to each Agar type: 16 g of Rose Bengal Agar, 39 g of Potato Dextrose Agar, and 40 g of Trypticase Soy Agar. Each dehydrated media was added into its own flask, it was well shaken and mixed. After sealing each flask with aluminum foil and autoclave tape, all three flasks were autoclaved at 15 PSI (120°C) for 20 minutes. Once safe to open the autoclave machine, the flasks were taken out and allowed to cool down.

Meanwhile, 4 petri dishes were labeled for each location, Patio, Bedroom, Living room and bathroom. Each flask was tilted sideways before removing the aluminum foil to prevent contamination through air entering the flask. The solution was then poured into 24 petri dishes. All dishes were left out for about 30 minutes to cool down and solidify.

After sealing each petri dish, there were transported to the location of interest. Two petri dishes of each agar were exposed for 15 minutes at each location besides the patio location, which were exposed for only 5 minutes. Of the two petri dishes from each location, one was incubated at 25°C while the other one was incubated at 37°C.

All petri storage units were sterilized before exposed petri dishes were placed upside-down inside of it. The first storage united only contained petri dishes incubated of 25oC, where as the second unit contained only dishes incubated for 37°C. Each united was labeled accordantly and placed in its according incubation set to 25°C or 37°C. After a week, plates were examined and number of colonies were noted. Only fungi colonies were recorded on Rose Bengal and Potato Dextrose agar, while Trypticase Soy Agar only noted Bacteria colonies.


Note that high numbers of 35 and 26 fungi colonies have been counted on RBA and PDA which were exposed outside for 5 minutes and incubated at 25°C. In contrast, TSA only showed 7 bacterial colonies at the same conditions. TSA shows great numbers of 19 bacterial colonies at 25°C in the bathroom, while Rose bengal only counts fungi colony for the same location. On the other hand, Potato Dextrose counts 4 fungal colonies. Noticeable is that almost all agars incubated at 25°C show a greater count of colonies than those incubated at 37°C, except PDA for the bathroom (Table 1).


Fungi are present everywhere in great numbers and play an important role in decomposing organic matter. Our subtropical climate outside contains heat and moisture, which can affect the building structure. Furthermore, the apartment houses a 29 gallon Oceanic Biocube, which evaporates approximately one gallon within a week. The greatest amount of colonial growth was noted outside on my patio in PDA and RBA. PDA is composed of Potato Starch and Dextrose that encourages fungal growth, because dextrose and starch are a sugar unit called glucose. It functions as an energy source for fungal sporulation. This explains why 26 fungi colonies have been noted on PDA. The final pH of PDA is 5.6 +/- 0.2 which inhibits most bacterial growth but provides a good base for fungi. Some of the components in Rose Bengal Agar are soy pentose and dextrose. These substances provide nitrogen, vitamins, and energy encouraging fungal growth. Rose Bengal is a major ingredient in the Agar to avoid rapidly growing molds and inhibits bacterial growth. Another ingredient is Magnesium Sulfate, providing trace elements essential for good fungal growth. All the ingredients provide a perfect base for fungal growth, explaining the 35 colonies counted. On the other hand, the air inside the apartment is filtered, dried, cooled down, and distributed by the air conditioner. Nevertheless, the water vapor from the aquarium causes high humidity within the apartment and changes the air conditions within the rooms.

Some fungi and bacteria live in symbiosis within the human gastrointestinal tract. This explains why the greatest number of bacterial colonies were present in the bathroom. One ingredient in TSA is Pancreatic Digestion of casein, which provides nitrogen, vitamins and carbons for good bacterial growth. A majority of bacteria and fungi are known to survive very harsh conditions known to humans. Therefore, even though the bathroom is frequently cleaned, some bacteria and fungi are able to survive. As a result, 19 colonies in the bathroom were collected and incubated. Bacteria and fungi grow in many environments with different temperatures, from the cold arctic to hot springs. Therefore, the optimum growth temperatures vary. Bacteria can be psychrophilic, mesophilic, or thermophilic, with wide ranges of temperatures. Bacteria living within the human digestive system are exposed to a temperature of 37°C, explaining the colonial count at 37°C (Eddleman 1998).

Fungi can live in different ranges of temperatures just as Bacteria, but the ranges differ. Most fungi are mesophilic, which lay between 18°C-22°C. Some fungi are tolerant to temperature changes, meaning they can survive or even grow in higher or lower temperatures varying from their optimum temperature. On the one hand, if the temperatures rise below the optimum temperature range, it can slow down or even inhibit chemical reactions, which can slow down growth. On the other hand, higher temperatures lead to denaturation of enzymes causing death of the cell. Therefore, the petri dishes incubated at 25°C have a greater number of colonies than the ones incubated at 37°C (Neogen 2008).


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Neogen. “POTATO DEXTROSE AGAR.” Acumedia. 4 April, 2011. Web. 19 September, 2013. 1-2.

Neogen. “ROSE BENGAL CHLORAMPHENICOL AGAR.” Acumedia. 2 January, 2012. Web. 19 September, 2013. 1-2.

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Number of colony forming unites (CFU)
Rose Bengal Agar Potato Dextrose Agar Trypticase Soy Agar
Sites: Temp. 25 C 37 C 25 C 37 C 25 C 37 C
Patio 35 4 26 4 7 1
Living Room 2 0 3 0 14 1
Bedroom 4 0 3 0 6 2
Bathroom 1 2 6 14 19 15