Simple, differential, gram stains
terms, definitions, steps, order
Terms in this set (19)
Why do we use stains?
improve definition; obtain contrast between bacteria and background
What does a negative stain show?
stains the background of bacteria
What does a positive stain show?
stains the bacteria itself
How are positive stains classified?
as simple or differential; simple (1 stain used); differential (2 or more stains used)
What information is provided by a simple stain?
basic information regarding shape and arrangement of bacteria
What information is provided by a differential stain?
information about structure, or a part of the cell (cell wall); whether parts are present (capsule/endospore); distinguishes between parts, identification of bacteria
Who invented Gram staining?
Christian Gram, standard now 1st test done to begin identifying bacteria
How does a gram stain differentiate between bacteria?
It differentiates between bacteria based on the structure of their cell walls.
Gram negative cell wall
thin layer of peptidoglycan; surrounded by an outer membrane composed of phospolipids & lipopolysaccharides
Gram positive cell wall
thick layer of peptidoglycan; no outer membrane
What color do Gram positive cells turn?
What color do Gram negative cells turn?
Why are Gram stains the most important in microbiology?
Because bacteria respond 1 of 2 ways; it quickly identifies two major cell wall tpyes; G+ - thick peptidoglycan, purple; G- thin peptidoglycan, pink
Why do bacteria respond differently to a Gram stain?
it responds differently because of the thickness of peptidoglycan in the cell walls; stains fix differently based on cell wall structure
What is the primary Gram stain?
Crystal violet stains all cells purple regardless of cell wall structure
What is the mordant in Gram stain?
Iodine, which combine with crystal violet to form insoluable crystalline compounds that only stay trapped in thick peptidoglycan. Do not stay trapped in thin layers of peptidoglycan
How do G+ and G- respond to the addition of alcohol?
G- the crystal violet washes away almost completely and destroys the surrounding membrane; G+ the crystal violet compound remains fixed in the thick peptidoglycans due to insoluability
What are the steps in Gram staining?
Crystal Violet, 1-min, wash w/dist. H20
Iodine, 1 min, wash w/dist. H20
95% Alcohol, drop-by-drop, until runs clear
Safranin counterstain, 20 secs, wash w/dist. H20
What happens to G- when Safranin is added?
The red stains gives a pink hue to the cells.
YOU MIGHT ALSO LIKE...
MCAT | Mometrix Comprehensive Guide
Micro Lab Gram staining 🔬
CHAP 4 QUIZ PART 2
OTHER SETS BY THIS CREATOR
Lab Quiz 3 - Microbiology 275
Physiology Exam 2
Module 10 (6/29/18)
THIS SET IS OFTEN IN FOLDERS WITH...
Microbiology: Module 9
Microbiology: Module 4
Ch. 4 Essay
Microbiology: Module 5