BIO 205 Lab Midterm Exam Study Guide
Positive staining
microorganisms appear colored against a clear background
(basic/cationic dyes)
negative staining
microorganisms appear clear against a dark background (1 or
more acidic dyes)
three types of bacterial morphology
1. coccus (sphere)
2. bacillus (rod)
3. coccobacillus (short rod)
what information is obtained from a simple stain?
cell shape, size, and arrangement
How to make smears from broth
transfer 2-3 loopfuls of culture onto glass slide, spread with loop
to create a thin uniform smear, let air dry, heat fix
how to make smear from slant culture
with sterile loop transfer 2-3 loopfuls of water onto glass slide,
sterilize, transfer a pinpoint amount of culture from agar to drop
of water, tap several times with loop to dissolve, spread thin, air
dry, heat fix
purpose of the following when making bacterial slides:
-clean glass slide
,-thin uniform smear
-air drying
-heat fixing
-clean glass slide: to prevent cross contamination
-thin uniform smear: to ensure bacteria is clearly visible with no
clumps
-air drying: to prevent burning of bacteria during heat fixing
-heat fixing: to ensure stains stay on bacteria
state 2 reasons why a negative stain is used
- to visualize outside structures of bacteria
- to stain cells too delicate to be heat fixed
implications of capsules in bacterial diseases
capsules protect bacteria and limit the ability of phagocytes to
engulf bacteria
Can a negative stain show the internal structures of a bacterial
cell?
no
As you rush to be in time for the Microbiology lab, you
accidentally spill coffee on your lab coat and the white fabric
gets stained. Is this a biological stain or simply a compound that
is capable of imparting color to the fabric? Explain your
reasoning.
simply a compound stain capable of imparting color; a
biological stain refers to a compound that changes the color or
, features of a cell such as cell walls or the nucleus of a cell and
helps view them more clearly
principle of differential staining
to see the difference in bacterial cell wall structures
why is differential staining advantageous over simple staining?
using multiple stains can better differentiate between different
microorganisms or structures/ cellular components of a single
organism
various differential staining methods
gram negative
gram positive
acid-fast stain
Gram stain primary stain
crystal violet
All cells take up the purple crystal violet stain - stain for 1 min
(if negative, primary stain is lost during decolorization)
gram stain mordant
Iodine; keeps crystal violet in gram positive cell wall
gram stain decolorizing agent
alcohol; 95% ethanol used to remove crystal violet from gram-
negative cells
gram stain secondary/counterstain
safranin; used to give red color to gram-negative cells
Positive staining
microorganisms appear colored against a clear background
(basic/cationic dyes)
negative staining
microorganisms appear clear against a dark background (1 or
more acidic dyes)
three types of bacterial morphology
1. coccus (sphere)
2. bacillus (rod)
3. coccobacillus (short rod)
what information is obtained from a simple stain?
cell shape, size, and arrangement
How to make smears from broth
transfer 2-3 loopfuls of culture onto glass slide, spread with loop
to create a thin uniform smear, let air dry, heat fix
how to make smear from slant culture
with sterile loop transfer 2-3 loopfuls of water onto glass slide,
sterilize, transfer a pinpoint amount of culture from agar to drop
of water, tap several times with loop to dissolve, spread thin, air
dry, heat fix
purpose of the following when making bacterial slides:
-clean glass slide
,-thin uniform smear
-air drying
-heat fixing
-clean glass slide: to prevent cross contamination
-thin uniform smear: to ensure bacteria is clearly visible with no
clumps
-air drying: to prevent burning of bacteria during heat fixing
-heat fixing: to ensure stains stay on bacteria
state 2 reasons why a negative stain is used
- to visualize outside structures of bacteria
- to stain cells too delicate to be heat fixed
implications of capsules in bacterial diseases
capsules protect bacteria and limit the ability of phagocytes to
engulf bacteria
Can a negative stain show the internal structures of a bacterial
cell?
no
As you rush to be in time for the Microbiology lab, you
accidentally spill coffee on your lab coat and the white fabric
gets stained. Is this a biological stain or simply a compound that
is capable of imparting color to the fabric? Explain your
reasoning.
simply a compound stain capable of imparting color; a
biological stain refers to a compound that changes the color or
, features of a cell such as cell walls or the nucleus of a cell and
helps view them more clearly
principle of differential staining
to see the difference in bacterial cell wall structures
why is differential staining advantageous over simple staining?
using multiple stains can better differentiate between different
microorganisms or structures/ cellular components of a single
organism
various differential staining methods
gram negative
gram positive
acid-fast stain
Gram stain primary stain
crystal violet
All cells take up the purple crystal violet stain - stain for 1 min
(if negative, primary stain is lost during decolorization)
gram stain mordant
Iodine; keeps crystal violet in gram positive cell wall
gram stain decolorizing agent
alcohol; 95% ethanol used to remove crystal violet from gram-
negative cells
gram stain secondary/counterstain
safranin; used to give red color to gram-negative cells
