Lab 2 Flashcards
(42 cards)
Whats the purpose of gram stain
Helps determine the type of antibiotic treatment required for a bacterial infection
Whats a capsule stain
Its used to detect cells that can produce a capsule (an extracellular structure composed of polysaccharides)
What is contained in acid fast bacteria
Mycolic acid
Whats the acid fast stain used for in hwhich genus
Used to identify the bacteria in the genus mycobacterium
What are some ways motility of bacteria is determined
By hanging drop and motility test
Motility is an important differential characteristic of the family
Enterobacteriaceae
Bacillus subtilus: gram stain, cell morphology, cell arrangement, motility, capsule, spore stain
gram positive
rod
single and short chains
+/- (slow)
no capsule
forms endospore
Micrococcus
roseus (red
colonies) or
Micrococcus
luteus (yellow
colonies): gram stain, cell morphology, cell arrangement, motility, capsule, spore stain
Gram postive,
coccus,
pairs/tetrads (cuboidal organization),
not motile
no capsules
no spore stain
E. coli: gram stain, cell morphology, cell arrangement, motility, capsule, spore stain
Gram negative
small rod (coccobacillus)
Single
Motile
no capsule
No spore
Staphylococcus epidermidis: gram stain, cell morphology, cell arrangement, motility, capsule, spore stain
Gram positie
coccus
usually clusters/some single/pairs/tetrads
Non motile
No capsule
No spore
Latococcus lactis: gram stain, cell morphology, cell arrangement, motility, capsule, spore stain
Gram positive
Avoid coccus, apprearing stretched in a direction
Usually cahins/pairs
not motile
has capsule
does not form spore
Which bacteria forms capsule
Lactococcus lactis
How does gram stain work
Primary stain: basic crystal violet -> dissociate into CV+ and CV-
CV+ binds to negative cell well -> stains everything purple.
A mordant (Gram’s iodine) is applied. Iodine interacts with the CV+, forming larger complexes
Gram positive bacteria, with a thicker polypeptoidolgycan layer retains the crystal violet better.
95% ethanol is used to decolorize the sample. The large crystsal violet-iodine complex cannot be removed from the tigthened peptidoglycan layer -> it is trapped in gram positve.
Gram negative color is lost.
After decolrixation, counter stain is applied and taken up by gram negative cells
Whats the primary and secondary stain
Safranin
When can gram variability occur?
- Cultures are older than 24 hours -> gram positive wall begins to lose its integrity and has difficulty maintaining the primary dye
- Bacterial semars are too thick, the stains/decolorizing agent has difficulty penetrating through to all the cells
- Bacteria are endospore formers -> have difficulty taking up the primary dye. The area containing endoposre in bacillus remains unstained
- Bacillus spp. can hae reduced thickness of peptidoglycan during grwoth -> appear gram negative (pink(
Gram positive is (color)
Purple
Gram negative is (color)
red
Steps of gram stain
Heat fix, air dried
- Crystal violet
- Iodine
- decolorize
- Safranin
Which happens if smear is too thick
See gram variable cells (pink and purple cells0
What happens if you over decolirze
false negatives
What happens if you under decolorize
flase postive
If you forget to add grams iodine
false negative since gram positive -> lose the primay stain
Older cultures can result in
Gram variability.
Since gram positive begins to lose its integrity, has difficulty maintaining the dye
Which bacteria causes tooth decay
Streptococcus mutans
