Stains, Properties of Growth Media, Special Culture Requirements Flashcards
gram stain
- first line lab test in bacterial identification
- bacteria with thick peptidoglycan layer retain crystal violet dye–gram +
- bacteria with thin peptidoglycan layer turn red or pink with counterstain–gram -
which bugs do not Gram stain well?
-
These Microbes May Lack Real Color
- Treponema, Leptospira
- Mycobacteria
- Mycoplasma, Ureaplasma
- Legionella, Rickettsia, Chlamydia, Bartonella, Ehrlichia, Anaplasma
why do Treponema and Leptospira not gram stain well?
- too thin to be visualized
why do Mycobacteria not gram stain well?
- cell wall has high lipid content
why do Mycoplasma and Ureaplasma not gram stain well?
- no cell wall
why do Legionella, Rickettsia, Chlamydia, Bartonella, Ehrlichia, and Anaplasma not gram stain well?
- primarily intracellular
- also Chlamydia lack classic peptidoglycan b/c of decrease in muramic acid
which bugs do you use Giemsa stain?
-
Certain Bugs Really Try my Patience
- Chlamydia
- Borrelia
- Rickettsia
- Trypanosomes
- Plasmodium
what does Periodic Acid Schiff stain?
what is it used to diagnose?
- stains glycogen, mucopolysaccharides
- “PaSs the sugar”
- used to diagnose Whipple disease
- Tropheryma whipplei
which bugs do you use Ziehl Neelsen stain (carbol fusion)?
what is an alternative to this stain?
- acid fast bacteria
- Mycobacteria–stains mycolic acid in cell wall
- Nocardia
- protozoa
- Cryptosporidium oocysts
- alternative is auramine rhodamine stain for screening
- inexpensive
- more sensitive but less specific
which bugs do you use India ink stain?
- Cryptococcus neoformans
- mucicarmine can also be used to stain thick polysaccharide capsule red
which bugs do you use silver stain?
- Fungi
- Coccidioides
- Pneuomocystis jirovecii
- Legionella
- Helicobacter pylori
which bugs do you use fluorescent antibody stain?
- used to identify many bacteria and viruses
- example is FTA-ABS for confirming syphilis
what are the 2 possible properties of growth media?
- selective media
- indivator (differential) media
- same type of media can possess both or neither of these properties
explain selective media
- favors the growth of particular organism while preventing growth of other organisms
- ie. Thayer Martin agar contains antibiotics that allow the selective growth of Neisseria by inhibiting the growth of other sensitive organisms
explain indicator (differential) media
- yields a color change in response to the metabolism of certain organisms
- ie. MacConkey agar contains a pH indicator
- ie. a lactose fermenter like E. coli will convert lactose to acidic metabolites –> color change
media used for isolation of H. influenzae
what is the contents of the media?
- media used is chocolate agar
- contains Factors V (NAD+) and X (hematin)
media used for isolation of N. gonorrhoeae and N. meningitidis
- Thayer Martin agar
how does Thayer Martin agar selectively favor the growth of Neisseria?
- by inhibiting growth of:
- gram + organisms with Vancomycin
- gram - organisms except Neisseria with Trimethoprim and Colistin
- fungi with Nystatin
- “Very Typically Cultures Neisseria”
media used for isolation of B pertussis
what is the contents of the media?
- Bordet Gengon agar–“Bordet for Bordetella”
- contains potato
- Regan Lowe medium
- contains charcoal, blood, and antibiotic
media used for isolation of C. diphtheriae
- tellurite agar
- Loffler medium
media used for isolation of M. tuberculosis
- Lowenstein Jensen agar
media used for isolation of M. pneumoniae
what does that media require?
- Eaton agar
- requires cholesterol
media used for isolation of lactose fermenting enterics
what does the fermentation of the bacteria produce?
- MacConkey agar
- fermentation produces acid, causing colonies to turn pink
media used for isolation of E. coli
what do the colonies look like in the media?
- Eosin-methylene blue (EMB) agar
- colonies with green metallic sheen
