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

Fixation

Fixation    The stained cells in a microscope should resemble living cells as closely as possible. Fixation is process by which the internal & external structures of cells & microorganisms are preserved & fixed.  It inactivates enzymes that might disrupt cell morphology & toughens cell structures so that they don't change during staining & observation. A microorganism is usually  killed & firmly attached  to microscopic slide during fixation.        There are two fundamentally different types of fixation.  Bacteriologists heat fix bacterial smear by gentle  & an air dried film of bacteria. This adequately overall morphology  but not structures within cells. Chemicals fixation must be used to protect  fine cellular structures & the morphology of larger, more delicate microorganisms. Chemical fixatives penetrate cells & react with cellular  components, usually proteins,lipids to render them inactive, insoluble & immobile.  Common fixatives  
Read more