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 .