Origin and species diversity
The air environment contains no nutrients and is unfavorable for the reproduction of microorganisms. For this reason, air microflora is exclusively secondary in nature. Bacteria, fungi, and viruses do not live here permanently, but are merely temporarily transported by wind currents, dust, or liquid droplets. The main sources of atmospheric contamination are soil, open bodies of water, as well as the skin and mucous membranes of humans and animals.
Despite their temporary (transient) status, the morphological diversity of the airborne environment is extremely wide. Practically all forms of the microbial world can be found in air samples. These include various cocci, non-spore-forming rods, bacilli, clostridia, actinomycetes, as well as microscopic fungi and viruses.
Survival factors and geographical distribution
The viability of microbial cells in the open atmosphere is severely restricted. The main physical factor causing mass mortality of microorganisms in the air is direct solar insolation. Natural ultraviolet radiation destroys cellular structures, preventing the global spread of many infections.
The distribution of microbes shows a pronounced geographical dependency.
- Maximum concentration is always registered in large cities, which is associated with high population density, an abundance of dust, and environmental pollution.
- Minimum concentration is observed over ecologically clean zones: forests, mountain ranges, and seas, where the air is naturally purified.
Characteristics of indoor microflora
A specific ecological environment is formed inside buildings. The quantitative and qualitative composition of indoor microflora directly depends on the maintained sanitary regime. The key parameters determining air purity are the frequency of cleaning, ventilation intensity, level of natural light, and, most importantly, human population density. The more people in an enclosed space, the higher the concentration of microorganisms.
Air sanitization and purification methods
To reduce the microbial load in medical, laboratory, and public institutions, a strict set of sanitization methods is applied. The basic and mandatory method is regular wet cleaning, which prevents the lifting and circulation of dust carrying bacteria.
Specialized sanitization methods include:
- UV irradiation: using bactericidal lamps to destroy microorganisms.
- Aerosol disinfection: spraying antiseptic agents.
- Filtered ventilation: creating flows of purified air. This method is of particular importance for rooms with the highest sterility requirements, such as operating suites and microbiological laboratories.
Briefly: answers to topical questions
Which sanitary-indicator bacteria are investigated when assessing the cleanliness of indoor air?
When assessing the cleanliness of indoor air, bacteria that represent the microflora of the upper respiratory tract of humans are investigated. The main sanitary-indicator microorganisms include:
- Staphylococcus aureus (Staphylococcus aureus) — a target microorganism whose presence is strictly regulated (for example, it must be absent in operating rooms).
- Hemolytic streptococci — indicators pointing to a common pathway of shedding alongside airborne pathogens.
Staphylococci in general and pathogenic (coagulase-positive) staphylococci may also be investigated as sanitary-indicator microorganisms.
What methods and devices are used to collect air samples for microbiological testing?
Sedimentation, aspiration, and filtration methods are used to collect air samples for microbiological testing.
- Sedimentation method — free settling of microbes onto open Petri dishes with nutrient medium for 5 minutes; calculation is performed using Omeliansky's formula.
- Aspiration method — forced precipitation of microorganisms via the impact action of an air jet against agar. Krotov's apparatus, the Typhoon-R40M sampler, and Bio Sas Super and Mas 100 devices are used.
- Filtration method — drawing air through a liquid medium using Rechmensky, POV-1, or Dьяkonov devices.
Into which phases is a bacterial aerosol usually divided depending on particle size and settling speed?
Depending on particle size, microbial aerosol is usually divided into three main phases.
- Coarse-droplet liquid phase — consists of droplets with a diameter of more than 0.1 mm (over 100 µm), representing the water-salt envelope of bacteria. Their duration of suspension in the air is several seconds.
- Fine-droplet liquid phase — includes droplets under 0.1 mm in size.
- Bacterial dust — the third phase of bacterial aerosol.
To easily remember places with minimal microbial concentration, think of the ideal vacation route away from people: forests, mountains, and seas.
Class and exam questions
Why is air microflora considered secondary?
Air is not a natural habitat for microbial reproduction. Microbes enter it temporarily from primary environments—soil, water—and are shed from human and animal integuments.
What is the main factor in bacterial death in the atmosphere?
The main damaging factor in the open environment is direct solar insolation, which has a detrimental effect on most microorganisms.
What determines indoor air purity?
It is determined by the established sanitary regime: the regularity of wet cleaning, ventilation frequency, lighting levels, and the density of people in the room.
Which sanitization methods are mandatory for operating rooms?
In operating theaters and microbiological laboratories, continuous ventilation with air filtration and regular UV irradiation with bactericidal lamps are critically important.
What else to study on this topic
- Morphology and resistance of airborne bacteria (cocci, bacilli, clostridia)
- Operating principles of bactericidal UV lamps and their action spectrum
- Design of ventilation and filtration systems for cleanrooms
- Methods of sanitary-microbiological air testing
- Mechanisms of aerosol disinfection of enclosed spaces
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