Introduction to Microbiology Microbiology is the study of microorganisms, a large and diverse group of microscopic organisms which must be viewed with a microscope that exist as single cells or cell clusters; it also includes viruses, which are microscopic but not cellular . Importance of microbiology The importance of microbiology includes: used in biomedical research, creation of medicines, environmental applications and new research tools. Bacteria are important for fixing N2 in a usable form for plants. Bacteria and some fungi are important in decomposition and recycling of materials. Industry applications of microbiology: waste management, food industry, mining, medicine, research and biotechnology. Anatomy of bacteria The bacterial cell is a prokaryote cell which is simpler, and therefore smaller, than a eukaryote cell, lacking a nucleus and most of the other organelles of eukaryotes. Nuclear material of prokaryotic cell consist of a single chromosome which is in direct contact with cytoplasm. Here the undefined nuclear region in the cytoplasm is called nucleoid. A prokaryotic cell has two architectural regions: • On the outside, flagelig and pilli project from the cell’s surface. These are structures (not present in all prokaryotes) made of proteins that facilitate movement and communication between cells; • Enclosing the cell is the cell envelope — generally consisting of a cell wall covering a plasma membrane though some bacteria also have a further covering layer called a capsule. The envelope gives rigidity to the cell and separates the interior of the cell from its environment, serving as a protective filter. Though most prokaryotes have a cell wall, there are exceptions such as Mycoplasma (bacteria) and Thermoplasma (archaea). The cell wall consists of peptidoglycan in.bacteria, and acts as an additional barrier against exterior forces. It also prevents the cell from expanding and finally bursting (cytolysis) from osmotic pressure against a hypotonic environment. Extra cellular structures *Capsule The cell capsule is a very large structure this a gelatinous structure is present in some bacteria outside the cell wall. It is considered a virulence factor because it enhances the ability of bacteria to cause disease . The capsule may be polysaccharide as in pneumococci , meningococci or polypeptide as Bacillus anthracis or hyaluronic acid as in streptococci . The capsule is antigenic. The capsule has antiphagocytic function so it determines the virulence of many bacteria. It also plays a role in attachment of the organism to mucous membranes Demonstration of Capsule 1. India ink staining: the capsule appears as a clear halo around the bacterium as the ink can't penetrate the capusule. 2. Serological methods: Capsular material is antigenic and can be demonstrated by mixing it with a specific anticapsular serum. When examined under the microscope, the capsule appears 'swollen' due to an increase in its refractivity. This phenomenon is called as capsule swelling reaction or Quellung phenomenon. 3. Special capsule staining: These techniques employ copper salts as mordants for staining the capsule . For Vaccination capsular material is effective against some organisms (e.g., H. influenzae type b and S. pneumoniae). *Flagella Flagella are the organelles of cellular motility. They arise from cytoplasm and extrude through the cell wall. They are long and thick thread-like appendages, protein in nature called flagellin. Three types of arrangement are known: monotrichous (single polar flagellum), lophotrichous (multiple polar flagella), and peritrichous (flagella distributed over the entire cell). staining with basic fuchsin makes the flagella visible in the light microscope *Fimbriae (pill) They are short and thin hair like filaments, formed of protein called pilin (antigenic). Fimbriae are responsible for attachment of bacteria to specific receptors of human cell (adherence). There are special types of pili called (sex pili) involved in conjunction. *Cilia Cilia are especially notable on the single-celled protozoans. They are composed of extensions of the cell membrane that contain microtubules, they move materials like these present in respiratory system that consists of mucus-secreting cells lining the trachea and bronchi, and ciliated epithelial cells that move the mucus ever-upward .