Lesson 7 Flashcards
• Are the common dyes used in bacteriology.
• Are cationic or have positively charged groups
(pentavalent nitrogen) that bind to negatively
charged molecules like nucleic acids and
proteins.
• Examples: methylene blue, basic fuchsin, crystal
violet, safranin and malachite green
Basic Dyes
• Are anionic or possess anionic charged groups
(carboxyls and phenolic) that bind to positively
charged cell structures.
• Examples: Eosin, Rose Bengal and acid fuchsin
Acid Dyes
■ A single stain is used.
■ It is directed towards coloring the forms and shapes present.
■ Inoculum size for staining: 105 CFU/mL
■ Examples: Malachite Green, Methylene Blue, Crystal Violet,
Carbolfuchsin, Safranin
Simple Stain
■ It divides bacteria into separate groups
■ It is directed towards coloring components of
those elements present.
■ Inoculum size for staining: 105 CFU/mL
Differential Staining
Enumerate the steps in doing differential staining
A.
Application of primary stain
B. Application of mordant
C. Application of decolorizing
agent
D. Application of secondary
stain or counterstain
■ Directed specifically at identification of an
organism
■ Identifies:
– Chlamydia trachomatis
– Bordetella pertussis
– Legionella pneumophila
– Herpes Simplex virus
– Varicella-Zoster virus
– Cytomegalovirus
– Adenoviruses and Respiratory viruses
DNA-Probe Mediated Staining
■ Demonstrate presence of capsule
■ Study bacterial gas vacuoles and viral morphology
■ Study cells sensitive to heat fixing
■ Result: Bacteria appear as light-colored bodies
against a dark background – the cell surface
repels the acidic stain since the bacterial cells are
negatively charged
■ Example: India ink or Nigrosin dye (acidic stain)
Negative Staining
Is the most used differential stain in the clinical microbiology laboratory
Gram Stain
Bacteria with thick cell walls containing teichoic acid retain the crystal violet-iodine complex
dye after decolorization and appear purple, thus they are?
Gram-Positive
Other bacteria with thinner cell walls containing lipopolysaccharides do not retain the dye
complex and appear deep pink, and they are?
Gram-negative
All cocci are Gram-positive except?
Neisseria, Veillonella and Branhamella
All bacilli are Gram-negative except ?
Actinomyces, Arcanobacterium, Atopobium, Bacillus,
Bifidobacterium, Clostridium, Corynebacterium, Cutibacterium, Erysipelothrix, Gardnerella,
Kurthia, Lactobacillus, Listeria, Mycobacterium, Nocardia, Rhodococcus, Tsukamurella
What are the exceptions in Gram staining?
■ Organisms that exist almost exclusively within host cells (Chlamydia).
■ Organisms that lack cell walls (Mycoplasma and Ureaplasma).
■ Organisms with insufficient dimension to be resolved by light microscopy (Spirochetes).
It is used to stain bacteria that have high lipid content in
their cell walls
Acid-fast Staining
Ideal for cryptosporidia and cyclospora parasites in stools specimens
Modified Kinyoun Method
