•  A disease causing microorganisms called pathogens (3% 
         of all known microbes)
      •  The others are non pathogenic (97%), the beneficial 
         microbes are 87%
      •  Microbes live on and in our bodies e.g. skin, in the mouth 
         and intestine are known as indigenous microflora (or 
         indigenous microbiota). Some of them cause disease 
         accidentally and known as opportunistic pathogens 
         (10%)
      •  Diseases caused by microbes are called infectious 
         disease
      •  Ubiquitous microbes means that they are virtually found 
         every where  in or on the body and in different 
         environment of the globe
      2                             Dr. Adnan S. Jaran                     29/08/22
      •  Many bacteria and fungi are Saprophytes, which aid in 
         fertilization by returning inorganic nutrients to the soil.
      •  Saprophytes break down dead and dying organic 
         materials (plants and animals) into nitrates, phosphates, 
         carbon dioxide, water and other chemicals necessary for 
         plant growth
      •  Saprophytes also destroy papers, feces and other 
         biodegradable matters, although they cannot break down 
         most plastics or glass
      •  Nitrogen-fixing bacteria, that live in the root nodules of 
         certain plants called legumes are able to return nitrogen 
         from the air to the soil in the form of ammonia for use by 
         other plants
      3                             Dr. Adnan S. Jaran                     29/08/22
                    Introduction to Microbiology
        The spread of certain diseases from one person to 
        another long ago suggested the existence of invisible, 
        transmissible agent of infection.
        Microscopic organisms (microbes) were not seen, 
        however, until Antony Van Leeuwenhock (1632-1723) 
        made microscopes with sufficient magnification, then 
        after, the science of microbiology began. 
     4                       Dr. Adnan S. Jaran            29/08/22
         Leeuwenhock observed motile microorganisms taken 
       from a decayed tooth under the microscope. He 
       observed major morphological classes of bacteria i.e. 
       spheres, rods and spirals as well as large microbes i.e. 
       protozoa, algae and yeast. In 1767 and after the 
       convention of compound microscope, Linnaeus 
       distinguished 6 species of microbes assigned to one 
       class, and 600 types were figured in 1838.
     5                       Dr. Adnan S. Jaran             29/08/22
                   Spontaneous Generation
         Until recent centuries it was widely believed that living 
       organisms can arise spontaneously in decomposing 
       organic matter. For visible organisms, this notion was 
       dispelled in the 17th century. When Redi demonstrated 
       that the appearance of maggots in decomposing meat 
       depended on the deposition of eggs by flies. However, 
       the idea of spontaneous generation persisted for the new 
       world of microbes.
     6                       Dr. Adnan S. Jaran            29/08/22