Bacterial Count Analysis

Since its discovery back in the 17th century, bacteria have always been associated with disease and health issues. However, bacteria are also responsible for several natural and helpful processes that help our body stay healthy and safe. Moreover, bacteria is a naturally occurring creature and in many cases having an environment that is bacteria-free does not imply that it is harmless to human bodies. In fact, having a certain level of bacteria might implicate in a healthier condition than if no bacteria are found, especially when considering the presence of toxic chemicals or undesired environmental conditions. Thus, the detection of bacterial count in your indoor air can give you a much better insight into the quality of your indoor air and may present the answer to several different questions.

What is bacterial count?

Bacterial count can be described as simply the count of bacteria in a determined sample. However, up to 40 million different bacteria cells can be found in a gram of soil and over a million can be found in a millimeter of freshwater. In fact, bacteria are biological cells that are only a few micrometers big and can be seen in several different shapes (rods, spheres, and spirals).

Being one of the first forms of life present on earth, bacteria are found in almost every environment imaginable and are responsible for key processes that ensure photosynthesis and healthy growth of several species. By being the only organism that produces B12, the presence of bacteria in nature is fundamental for the existence of life altogether. For humans, bacteria are not only part of their food chain, but they have also played a key role in our digestion being present in our mouths and intestine. Other natural processes also use bacteria in the human body to ensure the healthy biological functioning of the organism. Finally, as technology developed, humankind has found applications for bacteria while producing fermented food, in molecular biology, genetics, and biochemistry.

Due to its small size, bacteria are estimated through the colony-forming unit (CFU) which is the number of viable bacteria cells in a sample. However, when analyzing CFU it is important to keep in mind that several different species of bacteria interact differently with the human body and to understand the effects of higher or lower amounts of bacteria it is important to determine the species and what is their interaction with the human body. In sum, not all bacteria are bad for your health, although sometimes a small concentration of a single species can be life-threatening.

How can I control the level of bacteria in my indoor environment?

Bacteria are easily transported from outdoor to indoor environments through airflow, attached to body and clothes or through air vents in buildings. Their small size also allows them to be carried within our body and be transmitted from one individual to the next by sneezing, coughing and other fluid exchange. Meanwhile, not all bacteria are harmful and their presence is unavoidable in the environment. What is important in these cases is to avoid the propagation of certain harmful bacteria that, in most cases, have dissemination routes that are well defined. Therefore, it is important to have a proactive attitude towards the prevention of the spreading of these bacteria with several prophylaxis measures. Overall, bacteria levels can be reduced by:

  • Constantly renewing the indoor air, avoiding the accumulation of bacteria concentration to harmful levels
  • Careful cleaning of indoor areas, avoiding accumulation of moisture, dirt and other surfaces that can concentrate bacteria
  • Increase sunlight incidence indoors as the UV light help control bacteria propagation

What are the health effects of bacteria in indoor environments?

First, it is important to understand that even small samples present numerous types of bacteria simultaneously and it is not possible to assign CFU as a parameter by itself as an indication of health hazard. In fact, when analyzing the limit threshold presented by several different entities worldwide, a huge discrepancy in CFU units considered as a health hazards is seen. Table 1 presents the analyzing of hazard concentration of CFU in indoor air according to 6 different environmental agencies worldwide.

Canada Public WorksWHOOSHAACGIHHong KongCommission of European CommitteesSingapore
Indoor CFU count should be lower than outside.
There is contamination if indoor quantity is >500 CFU/m3 compared to outdoors.
500 CFU/m3Contamination indicators: >1000 CFU/m3<100 CFU/m3 considered of no concern
200 CFU/m3 recommended as a guideline for bioaerosols
500/1000 CFU/m3Houses (CFU/m3):
>10.000 very high
<10.000 high
< 1000 intermediate
<200 low
<50 very low
  Non-industrial indoor (CFU/m3):
>2000 very high
<2000 high
<500 intermediate
<100 low
<25 very low
<500 CFU/m

Note here that all these entities present significant variation to what is considered their acceptable limit for the indoor level of the bacterial count. This is mainly due to large variations in species found worldwide or even within different areas of the same city. Therefore, presenting the major health effects of high bacterial count in the household can be at sometimes challenging.

However, four major types of bacteria are found most frequently indoors and can be considered when estimating the general health effects of bacteria indoors. Micrococcus is one of the most common bacteria found indoor and can be found in the skin, soil, water, and meats. It normally causes spoilage of raw food and in case of ingestion can cause diarrhea and other irritations of the intestine walls. Micrococcus is also associated with bad smells from human sweat. Staphylococcus is well known due to the MRSA, a drug-resistant strain of the bacteria that is commonly found in hospitals. Contact with these bacteria can cause skin infection and toxic shock syndrome.

How can I monitor the bacterial count indoor?

Indoor bacterial count is quite a simple process but, to carry out the analysis, it is recommended that a specialized team be assigned for the task as there is risk of being exposed to larger amounts of toxic bacteria and hazardous compounds that might risk the health of those handling the samples.

Overall, the bacterial count is carried out by fixating a sample of bacteria on an agar substrate and left to grow for a determined period of time. Depending on species, concentration and environmental conditions, bacteria might require different temperatures, times of growth or lighting conditions to allow for detection and counting. Therefore, this standard procedure has a couple of variations that can be referred to as:

  • The pour plate method
  • The spread plate method
  • The membrane filter
  • The Miles and Misra method

Clearly, even to determine the best conditions to consider for the CFU counting, an extensive background on microbiology and the overall species that are frequent in the given conditions is necessary to allow for proper assessment.

After the species has been grown on the agar plate, software such as the Open CFU can be used to help count the number of colonies and further estimate the species found. Some electronic systems develop an estimation of the CFU to help quantify these units such as the Most Probable Number (MPN), which are useful when considering low concentration of cells.

How can IAQ help?

Clearly, CFU estimations are a valuable tool to determine the severity of an indoor bacteria infestation. However, the information alone does not determine if the individuals are at risk or not just based on the number of bacteria found. A proper speciation is required to determine the type of bacteria found and what is their relationship with human health.

In this case, IAQ relies on a specialized team that is capable of collecting samples of your indoor air, dust, dirt and other surfaces that might present the growth of bacteria colonies and properly carry out CFU assessments. Furthermore, IAQ is the only company in Singapore that provides speciation analysis and is capable of pointing out the specific species present in your indoor environment. With this in-depth analysis, IAQ is able to determine if your specific concentration of CFU/m3 is in fact harmful and what are the measures to be implemented to address the problem.

By speciation, IAQ is able to determine if your CFU level is associated with outdoor species, natural occurring bacteria or even mold. This information is extremely important when assessing the overall indoor air quality of your environment and proposing solutions to lower these levels. Thus, IAQ provides a highly qualified service that will help you determine the level of contamination and species of bacteria contaminating your indoor air meanwhile also pointing out the problematic areas in your environment assisting with the development of economic, fast and effective solutions to ensure the quality of your indoor air.


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