Stains, Properties of Growth Media, Special Culture Requirements

Question 1

gram stain

Answer 1

• 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 -

Question 2

which bugs do not Gram stain well?

Answer 2

• These Microbes May Lack Real Color
  
  • Treponema, Leptospira
  • Mycobacteria
  • Mycoplasma, Ureaplasma
  • Legionella, Rickettsia, Chlamydia, Bartonella, Ehrlichia, Anaplasma

Question 3

why do Treponema and Leptospira not gram stain well?

Answer 3

• too thin to be visualized

Question 4

why do Mycobacteria not gram stain well?

Answer 4

• cell wall has high lipid content

Question 5

why do Mycoplasma and Ureaplasma not gram stain well?

Answer 5

• no cell wall

Question 6

why do Legionella, Rickettsia, Chlamydia, Bartonella, Ehrlichia, and Anaplasma not gram stain well?

Answer 6

• primarily intracellular
• also Chlamydia lack classic peptidoglycan b/c of decrease in muramic acid

Question 7

which bugs do you use Giemsa stain?

Answer 7

• Certain Bugs Really Try my Patience
  
  • Chlamydia
  • Borrelia
  • Rickettsia
  • Trypanosomes
  • Plasmodium

Question 8

what does Periodic Acid Schiff stain?

what is it used to diagnose?

Answer 8

• stains glycogen, mucopolysaccharides
  
  • “PaSs the sugar”
  • used to diagnose Whipple disease
    
    • Tropheryma whipplei

Question 9

which bugs do you use Ziehl Neelsen stain (carbol fusion)?

what is an alternative to this stain?

Answer 9

• 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

Question 10

which bugs do you use India ink stain?

Answer 10

• Cryptococcus neoformans
• mucicarmine can also be used to stain thick polysaccharide capsule red

Question 11

which bugs do you use silver stain?

Answer 11

• Fungi
  
  • Coccidioides
  • Pneuomocystis jirovecii
• Legionella
• Helicobacter pylori

Question 12

which bugs do you use fluorescent antibody stain?

Answer 12

• used to identify many bacteria and viruses
• example is FTA-ABS for confirming syphilis

Question 13

what are the 2 possible properties of growth media?

Answer 13

• selective media
• indivator (differential) media
  
  • same type of media can possess both or neither of these properties

Question 14

explain selective media

Answer 14

• 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

Question 15

explain indicator (differential) media

Answer 15

• 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

Question 16

media used for isolation of H. influenzae

what is the contents of the media?

Answer 16

• media used is chocolate agar
  
  • contains Factors V (NAD+) and X (hematin)

Question 17

media used for isolation of N. gonorrhoeae and N. meningitidis

Answer 17

• Thayer Martin agar

Question 18

how does Thayer Martin agar selectively favor the growth of Neisseria?

Answer 18

• by inhibiting growth of:
  
  • gram + organisms with Vancomycin
  • gram - organisms except Neisseria with Trimethoprim and Colistin
  • fungi with Nystatin
    
    • “Very Typically Cultures Neisseria”

Question 19

media used for isolation of B pertussis

what is the contents of the media?

Answer 19

• Bordet Gengon agar–“Bordet for Bordetella”
  
  • ​contains potato
• Regan Lowe medium
  
  • contains charcoal, blood, and antibiotic

Question 20

media used for isolation of C. diphtheriae

Answer 20

• tellurite agar
• Loffler medium

Question 21

media used for isolation of M. tuberculosis

Answer 21

• Lowenstein Jensen agar

Question 22

media used for isolation of M. pneumoniae

what does that media require?

Answer 22

• Eaton agar
• requires cholesterol

Question 23

media used for isolation of lactose fermenting enterics

what does the fermentation of the bacteria produce?

Answer 23

• MacConkey agar
• fermentation produces acid, causing colonies to turn pink

Question 24

media used for isolation of E. coli

what do the colonies look like in the media?

Answer 24

• Eosin-methylene blue (EMB) agar
• colonies with green metallic sheen

Question 25

media used for isolation of Legionella

Answer 25

• charcoal yeast extract agar buffered with cysteine iron

Question 26

media used for isolation of Fungi

Answer 26

• Sabourand agar
  
  • “Sab’s a fun guy”