Table 3.

Glossary of common terms

Term	Definition	Comment
Aerosolization	Converting a liquid or powder into an aerosol; also called atomization and nebulization	Experimental aerobiology depends on equipment and techniques for safe and effective nebulization of the test microbe.
Aerobiology	Study of living organisms and their components in air	This umbrella term includes the study of indoor air quality.
Aerosols	Particles released into the air from a liquid or solid matrix	How long such particles remain suspended depends on the combined influence of the nature of the matrix, air turbulence, light, air temperature, and relative humidity.
Airborne spread	Spread of infections via inhalation of an infectious agent	Such spread requires that respirable particles carrying infectious agents remain suspended in air long enough to be inhaled by a potential host.
Allergens	Materials derived from plants (eg, pollen), fungi (eg, β-[1, 3]-glucan), bacteria or other biologic and nonbiologic sources capable of causing allergic reactions in a host	Whereas there are synthetic chemicals such as plastics capable of inducing allergic reactions, the emphasis here is on biologic materials only.
Biofilm	A slimy, multicellular layer of microbes on moist or submerged surfaces	This often is a mix of several types of microbes, including opportunistic pathogens.
Biological decay	Loss in viability of a given microbe by damage to ≥1 of its biologic functions	Airborne pathogens show different rates of biologic decay depending on their nature, prevailing environmental conditions, and fluid of their origin.
Chembioaction	A negative health outcome from the combined effect of a chemical and biologic agent	This phenomenon is especially relevant in aerobiology because a host is often exposed to potentially harmful biologic, chemical, or physical agents simultaneously or sequentially.
Droplet nuclei	Airborne particles derived from larger droplets after loss of water	Such droplets are crucial for the spread of infectious agents by air as their relatively small size (0.5-5.0 µm) allows for their stability in air while also permitting their retention on inhalation.
Indoor air quality	Quality of the air within buildings and other enclosures, with particular reference to the health and comfort of the occupants	The overall quality of indoor air is dependent on a mix of a variety of factors that may be site and time sensitive.
Infectious agent	A microbe capable of causing an infection	The capacity of a microbe to infect a given host depends not only on its biology but also on the general health status of the host and the portal of entry into the host.
Microbial pathogen	A microbe capable of causing localized or generalized damage to the host	Please see “Infectious agent.”
Microbiome	The totality of microorganisms and their collective genetic material present in or on the human body or in another environment	A certain proportion of the microbes found in a microbiome may not be culturable but detected and identified via their genomes only.
Microbiota	A natural mix of bacteria, fungi, viruses, and protozoa in a host or an environmental niche	This term is now preferred over microflora.
Opportunistic pathogen	A microbial pathogen capable of infecting hosts whose natural defenses are compromised because of advanced age, immunosuppression, or other underlying causes	The number, variety, and health significance of such pathogens is on the rise in conjunction with the rising numbers of those debilitated by acquired or induced immunosuppression.
Pathogen (microbial)	Any microbe capable of causing damage to the host	Even an otherwise innocuous microbe can become pathogenic depending on the general resistance of the host or the microbe's entry into normally sterile areas of the body where it can become an opportunistic pathogen.
Perikairots	Environment-based opportunistic pathogens	Biofilm-based microbes such as legionellae and environmental mycobacteria can infect those debilitated because of age or underlying medical conditions.
Resident microbiota	A mix of microbes normally found in or on the host	Many members of the resident microbiota from skin and mucous surfaces are frequently found in indoor air.
Respirable particles	Particles small enough to access the alveolar space during normal breathing	Such particles may or may not contain viable microbes.
Surrogate microbe	A microbe that resembles ≥1 type of pathogens but is safer and easier to work with in the laboratory; also called a simulant	The use of such microbes is crucial in many aspects of microbiology, in general.
Tidal breathing	The body's automatic inhalation and exhalation process at rest	In addition to coughing and sneezing, tidal breathing can release infectious agents into the air.
Transient microbiota	Microbes temporarily acquired by a host during normal contact with the environment