Micro organisms do not grow in air. However, dust and water droplets in air contain micro organisms. Spores produced by micro organisms are light and easily dispersed by air movements away from their sources of production. When these spores land on suitable substrates, they germinate, multiply and produce more spores. Nutrient agar exposed to air, shows the growth of various types of colonies of bacteria and fungi. Common micro organisms found in air are as follows:
• Virus : common cold virus, influenza virus, polio virus, poxvirus, measles Virus
• Bacteria : pneumococci, staphylococci , streptococci, bacillus anthracis (causes anthrax), mycobacterium tuberculosis (causes tuberculosis in humans)
• Fungi : penicillium (blue green mould) , aspergilus, rhizopus nigricans (black or bread mould) , saccromyces (yeast).
