FP (Phenol Red, EMB, HE, MAC)

• Phenol Red Test selective or differential?

  Differential
• Phenol Red test used for 


  diff members of Enterobacteriaceae from other G(-) rods
• Phenol Red indicates what?

  whether or not fermentation is happening
• When pyruvate is fermented further this leads to


  broth acidification, which turns the broth from red to yellow
• Pyruvate is fermented further to


  variety of acids, alcohols, H2/CO2 (depending)
• What are the components of Phenol Red Broth?


  peptone, fermentable carbohydrate, phenol red
• Phenol red is yellow below


  pH 6.8
• Phenol red is pink above

  pH 7.4
• Phenol Red is red in between

  6.9-7.3
• Durham tube 


  test for gas production (bubble or gas pocket)
• If bacteria cannot ferment they use peptone to grow in broth and this leads to a basic pH. This turns the broth from red to pink
• yellow broth & bubbles in tube: fermentation with acid and gas end products (A/G)
• yellow broth & no bubbles in tube: fermentation with acid end products and no gas being produced (A/-)
• Red broth and no bubbles in tube: no fermentation (-/-)
• Pink broth and no bubbles in tube: use (degradation) of peptone for growth and basic end products (B/-)
• Eosin Methylene Blue (EMB) Agar selective or differential?


  Both
• Components of EMB: peptone, lactose, sucrose, and dyes eosin Y & methylene blue
• EMB selective because

  dyes inhibit growth of G(+) bacteria
• EMB differential because

  for bacteria that have enzymes to allow lactose fermentation
• EMB agar is used for isolation of fecal coliforms
• Coliforms


  members of Enterobacteriaceae that produce acid (and gas) from lactose fermentation
• non coliforms

  members of Enterobacteriaceae that dont ferment lactose
• Strong lactose fermenters dark purple / green metallic color in the medium (EMB)
• An example of a strong lactose fermenter is E. coli (EMB)
• Slower lactose fermenters produce small amounts of acid > results in pink color of growth
• An example of a slow lactose fermenter is Enterobacter aerogenes & Klebsiella (mucoid)
• Nonfermenters are colorless (retain normal color or take coloration of medium) and noncoliform
• An example of a nonfermenter is Shigella
• Poor growth or no growth is an organism inhibited by eosin and methylene blue and is gram-positive (EMB)
• Good growth is not inhibited by dyes and is gram negative (EMB)
• When the growth is pink, the organism ferments lactose with little acid production which means it's a possible coliform. (EMB)
• When the growth is dark (purple to black, with or without green metallic sheen) the organism ferments lactose and/ or sucrose with a lot of acid production. It is a possible coliform. (EMB)
• When the growth is colorless, organism doesnt ferment lactose or sucrose meaning it has no reaction and is a non-coliform. (EMB)
• Hektoen Enteric (HE) Agar selective or differential?


  Both
• HE detects and differentiates between Salmonella and Shigella
• What are the components of HE agar?

  Lactose, sucrose, salicin (fermentable carbohydrates)

  Bromothymol blue and acid fuchsin dyes

  Ferric ammonium citrate and sodium thiosulfate
• (HE) bromothymol blue and acid fuchsin dye are pH indicators that detect acid production from fermentation of sugars (differential).
• Carbohydrates acidify medium turn yellow / orange. Use of peptone by Shigella and Salmonella alkalizes medium turning blue (HE)
• Ferric ammonium citrate (indicator) and sodium thiosulfate (sulfur source) in HE agar enable the detection of hydrogen sulfide production > black centered colonies
• Bile salts in HE inhibit G(+) bacteria (selective)