An overview about varieties and detection methods of pathogenic microorganisms in indoor air

Abstract

Various microorganisms of different size ranges present in air are called bioaerosol which mainly includes fungi and bacteria, their metabolites, virus, pollens, etc. Bioaerosols can travel hundreds of meters or even kilometers through air, so that bioaerosols can be transmitted to all corners of public places, greatly increasing the scope of their hazards. Tiny biological particles can directly reach to human lungs through human respiration, resulting in lung diseases and increasing the risk of suffering from lung related disease. Diseases caused by pathogenic species are classified as bacterial diseases, fungal diseases, viral diseases and diseases caused by other pathogenic microorganisms. Everyone spends about 90% of their time indoors. Indoor environments with poor air quality are more likely to cause harm to vulnerable groups such as children, adolescents, the elderly, patients with chronic respiratory diseases and patients with cardiovascular diseases than outdoor pollutions. Bioaerosols may cause human health problems, severely resulting in death. In addition, Candida, Aspergillus fumigatus, Staphylococcus aureus and some other pathogenic microorganisms may cause nosocomial infections. The medical equipment and hospital environment are the main sources of these microorganisms. There are many studies on the types of microorganisms in different indoor environments. However, there are few studies on the sources of microorganisms, especially pathogenic microorganisms, in indoor air. Source-sink analysis shows that the outdoor air is the main source of most indoor microorganisms. In addition, indoor factors (such as occupants, pets, moldy substances, ventilation, etc.) also affect the distribution of indoor microorganisms. Bioaerosol sampling methods are diverse and many methods are still in development. So far, neither a sampling method nor a sampling standard is suitable for collecting various types of airborne microorganisms. Impaction, impingement and filtration are the most common methods for collecting bioaerosols. In addition, the natural sedimentation method, electrostatic precipitation and cyclone are also used to collect bioaerosols. The detection of microorganisms is the second step in bioaerosol monitoring process. Detection methods of microorganisms can be divided into two major categories called culturable approach and nonculturable approach. Culturable approach is a traditional microbiological detection method, which is simple and low cost. The main drawback of the culturable approach is that the proportion of microorganisms that can be cultured and identified in the environment is small (about 10%), so the culturable approach cannot provide information on the total number of microorganisms in the air. With the development of fluorescent dyes, it is possible to quantitate all the microorganisms (including culturable and nonculturable microorganisms) collected in the liquid medium. Advances in genomics and sequencing technologies, as well as advances in nonculturable molecular technologies (such as Genetic Fingerprinting, Metagenomics and Next Generation Sequencing) not only help identify and quantify microbial loads, but also help understand the possible microbial populations changes. In addition, advances in methods such as Chromatography, Immunoassay and PCR are also useful for microorganism identification. Bioaerosol sampling techniques and detection techniques are crucial for assessing bioaerosol levels. Different sampling and detection methods have different advantages and disadvantages, so multiple technologies can be combined to overcome the limitations of each technology. Through comprehensive and systematic understanding of the types and sources of these pathogenic microorganisms, as well as sampling and detection methods, it will help people to understand the influencing factors of indoor microbial communities, reduce the risk of indoor biological aerosols.