Test Bank For Microbiology A Systems Approach, 7th Edition By Marjorie Kelly Cowan and Heidi Smith Chapter 1-25 [Questions with Answers

Test Bank For Microbiology A Systems Approach, 7th Edition By Marjorie Kelly Cowan and Heidi Smith Chapter 1-25 [Questions with Answers Gram Negative Bacteria - correct answers-Gram Negative Bacteria have a very thin peptidoglycan layer, so CV iodine is easily washed away ( decolorized by ethanol wash). Therefore gram negative bacteria is counter stained by Safranin and appear red. Real Image - correct answers-Light is concentrated by the condenser through the specimen and then through the objective lens where it is them refracted and the image is them enlarged. Levels of magnification? - correct answers-Final magnification is calculated by multiplying power of the objective by power of the ocular. (Ocular is always 10) What is magnification? - correct answers-The increase in size of a visible object What is Resolution? - correct answers-Resolution is the ability to distinguish between two separate objects. Shorter wavelengths produce higher resolution. What is immersion oil used for? - correct answers-Immersion oil is a technique used to increase the resolution of a microscope. What is contrast used for? - correct answers-Contrast is a sample (light vs. dark)is achieved by altering the refractive index. Easiest way to contrast is by staining. What is Wet Mount? - correct answers-Wet Mount is used to observe microorganisms in their natural state. Heat Fixation - correct answers-A loopful of cells are smeared onto the surface of a slide and allowed to air dry. The slide is briefly passed over the flame to fix the cells to the slide by denaturing the lipids and proteins which acts like glue. Specimen must be dry before heat fixation to prevent the cells from boiling. What are positive stains? - correct answers-Positive stains are positively charges dyes which adhere directly to negatively charged cell surfaces. How many types of stains? - correct answers-Positive and negative stains What are negative stains? - correct answers-Acidic dyes are negatively charged. They stain the background of the slide and leave the specimen unstained. Smear is not heat fixed prior to negative staining. What is a simple stain? - correct answers-A simple stain is where only one type of dye is used. It is used to see basic morphology, size and arrangement of cells. What is a differential stain? - correct answers-More than one dye is used to contrast different types of cells or cell structures. Gram stain (most important) Spore stain Acid-Fast Stain Gram Stain - correct answers-A staining method that distinguishes between two different kinds of bacterial cell walls. Cells either stain purple (Gram +) or red (gram -) 4 Steps for Gram Staining - correct answers-1. Primary Stain (Crystal Violet) Purple 2. Iodine Treatment ( to form complex with Crystal Violet) called a mordant 3. Decolorization (with ethyl alcohol) 4. Counterstain (safranin) Red What is a Mordant? - correct answers-Anything that is added to the primary step eg. heat or iodine. Gram positive bacteria - correct answers-Gram positive bacteria retain the primary stain (crystal violet) because thick peptidoglycan layer traps CV-iodine complex and resist decolorization Acid-Fast Stain - correct answers-Used primarily to stain members of the Genus Mycobacterium which causes Tuberfulosis and Leprosy. Mycobacteria have a very thick, waxy cell wall rich in mycolic acids (long fatty acids) Acid-Fast Staining Procedure - correct answers-1. Smear is prepared 2. Primary stain (carbol fuchsin) Red Dye 3. Carbol Fuchsin contains Phenol and is heated (mordant) so it penetrates cell wall . 4. Decolorization (acid-Alcohol) HCL ETDH 5. Counterstain with Methylene Blue 6. Acid Fast cells remain red and others are blue.