CLINICAL MICROBIOLOGY

4) Oxidative/Fermentative Test: 
                     During the process of metabolism ie breakdown of complex organic molecules, certain amount of energy is released . Most mos have the capability of catabolizing carbohydrates . Both the extracellular & intracellular enzymes are necessary for the degradation of carbohydrates . Extracellular enzymes degrade complex carbohydrate into simpler carbohydrate which can pass to the cell. The intracellular enzymes catabolize these simpler molecules to generate energy. The end product of this degradation is used in glycolysis for the generation of energy.
  Glycolysis is one of the metabolic pathway in which simple sugar is converted in a form of energy as ATP. If the glucose after entering a cell is catabolized aerobically the process is called oxidative metabolism where oxygen serves as final electron acceptor. If glucose is catabolized anaerobically, the fermentative metabolism takes place where organic molecules serve as final electron acceptor. The end products of carbohydrate fermentation can be either be the organic acids like lactic, formic or acetic or organic gases like hydrogen or carbon dioxide. 

 Whether an organism is oxidative or fermentative can be determined by using Hugh & Leifson's Media(O/F Medium). In this method two tubes are used, one open to air & the other sealed with paraffin to create anaerobic condition. By utilizing glucose results in production of acid which changes the color of medium to yellow. Change in color of medium to yellow in both tubes suggests fermentation  while only in open tube suggests oxidation. Certain mos do not use glucose  but instead utilizes nitrogen source, here tryptone. In such case, the medium changes to blue color due to the production of alkaline end products. 

 Please visit these links for references:
www.microbelibrary.org/...test/3151-oxidative-fermentative-test-protocol
en.wikipedia.org/wiki/Oxidative/fermentation_glucose_test‎
antranik.org › Science › Biology › Microbiology‎
https://www.inkling.com/read/...atlas...7/oxidationfermentation-test‎
pictures.life.ku.dk/atlas/microatlas/veterinary/pheno_tests/OF_Test_1
www.youtube.com/watch?v=JxdEElHUXqs‎












Cited BY Kamal Singh Khadka 
Assistant Professor in PU, RE-COST, PNC, LA, NA
POKHARA.

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