Observing Microorganisms PDF

Observing Microorganisms  If a microbe measures 10 μm in length, how long is it in nanometers? Compound Light Microscopy  Light  Shorter wavelengths of light provide greater resolution  Compound Light Microscopy  The refractive index is a measure of the light-bending ability of a medium ...

Observing Microorganisms  If a microbe measures 10 μm in length, how long is it in nanometers? Compound Light Microscopy  Light  Shorter wavelengths of light provide greater resolution  Compound Light Microscopy  The refractive index is a measure of the light-bending ability of a medium  The light may bend in air so much that it misses the high-magnification lens  Immersion oil is used to keep light from bending Light Microscopy Simple Stains  Simple stain: Use of a single basic dye  A mordant may be used to hold the stain or coat the specimen to enlarge it (acts like a sealant) Differential Stains  Gram Stain  Classifies bacteria into gram-positive or gram-negative  Gram-positive bacteria tend to be killed by penicillin and detergents  Gram-negative bacteria are more resistant to antibiotics Micrograph of Gram-Stained Bacteria Acid-Fast Stain  Stained waxy cell wall (mycolic acids) is not decolorized by acid-alcohol (color “holds fast” in acid)  Mycobacterium (M. Tuberculosis, M. leprae) Color of Color of Acid-fast Non–Acid-fast Primary stain: Red Red Carbolfuchsin Decolorizing Red Colorless agent: Acid-alcohol Counterstain: Red Blue Methylene blue Acid-Fast Bacteria