BACTERIAL MORPHOLOGY CONTD...

A) STRUCTURE EXTERNAL TO CELL WALL

4)  Cell Wall:  1) Gram Positive Cell Wall : Gram Positive cell wall has greater amount of peptidoglycan (ie around 25 nanometer) & may account for 50% or more of total dry weight of cell. Besides, peptidoglycan gram positive cell wall contains Teichoic acid. It helps to link the peptidoglycan layer & provides negative charge to the cell wall. Though, much gram positive cell wall contains very little lipid but Mycobacteria & Cornyebacterium spp  & other are rich in lipids called Mycolic acid.

                                                      FIG:  B= GRAM NEGATIVE CELL WALL A= GRAM POSITIVE CELL WALL
                                             

             

2).Gram Negative Cell Wall:  Wall of Gram negative bacteria are more complex than those of Gram positive bacteria. It comprises lesser amount of peptidoglycan (2 nm to 3 nm) thick,which  accounts 10% of wall weight. The outer membrane is absent in Gram positive bacteria. The outer membrane is bi-layered structure consisting of phospholipid, proteins,  & lipopolysaccharides(LPS). LPS has toxic property & is also known as Endotoxin.  LPS is absent in gram positive bacteria & comprised of three parts: lipid A, Core Polysaccharide, O Side chain or O Antigen.
                             The protein part contains unique protein called porins which contains to  the passage of small molecules. Periplasmic space lies between outer membrane & cell membrane & it is filled with periplasm that contains digestive enzymes & transfer proteins.


                                          FIG: GRAM NEGATIVE CELL WALL 

Comments

Post a Comment

Popular posts from this blog

Stains/ Dyes

STAINS/ DYES      They are colored organic compounds used for staining microorganisms. Chemically, Stains= Benzene ring+ Chromophore+ Auxochrome According to nature of stain, it can be classified into: 1. Acidic Dyes:   It is dye which has negative charge so they bind to positively charged cell structures like some proteins. Acidic dyes are not very often used in Microbiology lab.except to provide background staining like Capsule staining. Examples: Nigrosine, Picric acid, Eosin, Acid fuschin, India ink etc.  2. Basic Dyes:  This dye have positive charge & bind to negatively charged molecules(nucleic acid, -COOH -OH). Since, surface  of bacterial cells are negatively charged(due to Teichoic acid), basic dyes are most commonly used in bacteriology. Examples: Crystal Violet, Methylene Blue, Safranin , basic fuschin. 3. Neutral Dyes:  They are usually formed from precipitation in which are produced when aqueous acidic & basic stains are combined. Neutral dyes stains nuc
Read more

CLINICAL MICROBIOLOGY

Image
3)   Triple Sugar Iron(TSI) Agar Test:                         The TSI agar test  is used to differentiate among the members of the family Enterobacteriaceae and between Enterobacteriaceae and other intestinal bacteria. The authors have chosen three common bacteria in the family Enterobacteriaceae: Escherichia coli, Proteus vulgaris, and Shigella flexneri .  All three are facultatively anaerobic gram-negative rods. In a TSI tube, E. coli produces an acid butt, an acid or alkaline slant, and no H2S, but does produce gas. P. vulgaris produces an acid butt, an acid or alkaline slant, H2S, and gas. S. flexneri produces an acid butt, an alkaline slant, no H2S, and no gas. For the other intestinal bacteria, the authors have chosen Alcaligenes faecalis and Pseudomonas aeruginosa. Both of these intestinal bacteria are gram-negative aerobic rods. In a TSI tube, A. faecalis produces an alkaline butt, alkaline slant, H2S, and gas; P. aeruginosa, an acid butt, alkaline slant, H2S,
Read more

VIROLOGY

Image
VIRUS IDENTIFICATION:    Identifying viral isolates is not an easy task. For one thing, viruses cannot be seen at all without the use of an electron microscope. Serological methods, such as Western blotting, are the most commonly used means of identification. In these tests, the virus is detected and identified by its reaction with antibodies.  Virologists can identify and characterize viruses by using such modern molecular methods as use of restriction fragment length polymorphisms (RFLPs) and the polymerase chain reaction(PCR).PCR PCR was used to amplify viral RNA to identify the west Nile virus in 1999 in the United States & SARS-associated coronavirus in china in 2002. Viral Multiplication:  The nucleic acid in a virion contains only a few of the genes needed for the synthesis of new viruses. These include genes for the virion structural components, such as the capsid proteins, and genes for a few of the enzymes used in the viral life cycle. These enzymes are
Read more