Ans : The atmosphere as a habitat is characterised by high light intensities, extreme temperature variations, low amount of organic matter and a scarcity of available water making it a non – hospitable environment for micro organisms and generally unsuitable habitat for their growth. Nevertheless, substantial number of microbes are Sound in the lower regions of the atmosphere.
No microbes arc indigenous to the atmosphere, rather they represent all ochthonous populations transported from aquatic and terrestrial habitats into the atmosphere. Microbes of air within 300-1,000 or more feet of the earth’s surface are the organisms of soil that have become attached to fragments of dried leaves, straw or dust particles, being blown away by the wind. Species vary greatly in their sensitivity to a given value of relative humidity, temperature and radiation exposures . More microbes are found in air over land masses than far at sea. Spores of fungi, especially Altemaria, Cladosporium , Penicillium and Aspergillus are more numerous than other forms over sea within about 400 miles of land in both polar and tropical air masses at all altitudes up to about 10,000 feet.
Microbes found in air over populated land areas, below altitude of 500 feet in clear weather include spores of Bacillus and clostridium, ascos pores of yeasts, fragments of myceilium and spores of molds and strepto mycetaceae, pollen, protozoan cysts, algae , Micrococcus, Cornyebacterium etc. In the dust and air of schools and hospital wards or the rooms of persons suffering from infectious diseases, microbes such as tubercle bacilli streptococci, pneumococci and staphylococci have been demonstrated.
These respiratory bacteria arc dispersed in air in ( he droplets of saliva and mucus produced by coughing, snee / ing, talking and laughing. Viruses ol respiratory tract and some enteric tract are also transmitted by dust and air.
Pathogens in dust are primarily derived from the objects contaminated with infectious secretions that after drying become infectious dust. Droplets are usually formed by snee / ing, coughing and talking . Lach droplet consists of saliva and mucus and each may contain thousands of microbes. It has been estimated that the number of bacteria in a single sneeze may be between 10,00 and 100,000. Small droplets in a warm, dry atmosphere arc dry before they reach the floor and thus quickly become droplet nuclei.
Many plant pathogens are also transported from one field to another through air and the spread of many fungal diseases ol plants can be predicted by measuring the concentration of airborne lungal spores. Human bacterial pathogens which cause important airborne diseases such as diphtheria, meningitis, pneumonia, tuberculosis and whooping cough are described. in the chapter ” Bacterial Diseases of Man “.
Allergic disorders by air microflora : Microflora of air is responsible for several allergic disorders. A range of airborne particles, such as pollen, fungal spores, insect debris, animal danders, mites etc. are recognised allergens. They bring about such allergic disorders as bronchial asthma, allergic rhinitis and atopic dermatitis. In most countries pollen has been implicated and studied in relation to these allergic disorders.
However, it has now been established that fungal spores are also equally important allergic agents. Fungal aerosols are present in much higher densities than pollen in some environments under some climatic conditions. A thorough screening of diurnal, seasonal and annual variations in both indoor as well as outdoor environments is necessary for diagnosis and therapeutic management of these disorders. In indoor environment, such as home and occupational surroundings, persons are exposed to fungal allergens.
Fungal aeroallergens in the outdoor environments originate from such sources as cereal crops, decaying vegetable matter and organic debris. In indoor environment damp walls, dustbins, mattresses, window frames, humidifiers etc. are chief source of fungal allergens. Since first report of a fungus implicated in asthma in 1726 by J. Floyer, spores of a range of fungal taxa have been shown of clinical interest and being studied world over for their implications in respiratory allergic reactions. Aeromycology has now become an established field of research, involving scientists of basic sciences as well as professional areas.
Several molds (species of Aspergillus, Penicillium, Mucor, Rhizopus). yeasts and rust and smut spores are shown to be implicated in occupational allergy. On the basis of prik and intradermal skin tests, several fungi have been identified as agents of Type I hypersensitivity disorders. These include species of Alternaria, Axpergillus, Candida, Cladosporium, Curvularia, Drc chslera, Epicoccum, Fusarium, Mucor , Nigrospora, Penicillium, Rhizopus and Trichoderma.
Besides skin test , fungal allergy is diagnosed by the use of inhalation challenge , RAST , ELISA , immunodor and immunoblot techniques . These immunological techniques have proved to be useful in the diagnosis and treatment of pollen and fungal allergic disorders.
India is not only a sub – continent of rich biodiversity but also has various geo – climatic ones. In a given zone there are experienced marked seasonai fluctuations in temperature and relative humidity. Consequently the sources and nature of aeroallergens differ in different areas and in different seasons of a given area . For instance, pollen becomes important inhalant allergens chiefly in two seasons – (i) months of September- November, dominated by pollens of weeds and grasses, and (ii) months of March – May, dominated by pollens of trees .
Q. 1. Describe in detail the constitution of air with respect to microorganisms.
Q. 2. Add a note on allergic disorders by air microflora