Microbiology

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 .
*Cell Wall
The bacterial cell wall is strength layer composed of a substance variously referred to as murein, mucopeptide, or peptidoglycan (all are synonyms). In addition to giving osmotic protection, the cell wall plays an essential role in cell division as well as serving as a primer for its own biosynthesis. Various layers of the wall are the sites of major antigenic determinants of the cell surface, and one component—the lipopolysaccharide of gram-negative cell walls—is responsible for the nonspecific endotoxin activity of gram-negative bacteria.
The Peptidoglycan Layer
Peptidoglycan is a complex polymer consisting of three parts: a backbone, composed of alternating N-acetylglucosamine and N-acetylmuramic acid; a set of identical tetrapeptide side chains attached to N-acetylmuramic acid; and a set of identical peptide cross-bridges .
The tetrapeptide side chains of all species, however, have certain important features in common. Most have L-alanine at position 1 (attached to N-acetylmuramic acid), D-glutamate or substituted D-glutamate at position 2, and D-alanine at position 4. Position 3 is the most variable one: Most gram-negative bacteria have diaminopimelic acid at this position, to which is linked the lipoprotein cell wall component. Gram-positive bacteria usually have L-lysine at position 3; however, some may have diaminopimelic acid or another amino acid at this position.
Diaminopimelic acid is a unique element of bacterial cell walls. It is never found in the cell walls of Archaea or eukaryotes. Diaminopimelic acid is the immediate precursor of lysine in the bacterial biosynthesis of that amino acid The fact that all peptidoglycan chains are cross-linked means that each peptidoglycan layer is a single giant molecule. In gram-positive bacteria, there are as many as 40 sheets of peptidoglycan, comprising up to 50% of the cell wall material; in gram-negative bacteria, there appears to be only one or two sheets, comprising 5–10% of the wall material.