Microlab 1 example pictures (part 1)
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What is the shape of this bacteria and what field is it under?
Spirochete: Dark-field light
What staining are these bacteria under?
Negative staining: these are acidic stain and will not penetrate bacterial cell wall. The stains produce either a deposit around bacteria, or a dark background so the bacteria appear unstained with a clear area around them.
What kind of stain are these bacteria in? (Simple or Differential)
Simple staining: the use of a single stain creates contrast between the bacteria and background. It is used to easily discern their shape
What stain is used here and what different shapes can be found?
Gram stain: bacillus and cocci (staphylococci)
List the procedure and result of each procedure in this gram staining.
In this acid fast stain, which letter are the acid-fast bacteria?
What do the unmarked letters in this stain sample represent?
What does this stain sample represent?
Capsule stain: The primary stain is crystal violet. Copper sulfate, a decolorizng agent, removes the primary stain from capsule, leaving it colorless.
Explain the result of each tube.
- A: Red broth indicates no lowering of pH to acid = no fermentation. No gas bubble in durham tube indicates no gas production.
- B: Acid production, no gas.
- C: Acid production and gas production
- D: Alcohol fermentation
What were the results from these fermentation tubes?
- A: No fermentation
- B: Alcohol fermentation (red broth, with bubble)
- C: No fermentation
- D: acid and gas productioini
Interpret the results of these TSI slants:
- A: No fermentation - (control tube) Red slant and butt, indicating alkaline, or no fermentation
- B: Lactose fermentation - Yellow slant and butt, with lifted butt, indicating gas production at the bottom of tube.
- C: H2S production: Red slant, with a dark butt, indicating H2S production
- D: Glucose fermentation - red slant and yellow butt, with a black streak (H2S production). This indicates a nonlactose fermenter.
Which line indicates starch hydrolysis?
- Left line: The complete breakdown of all starch is shown by the clear (white) halo.
- No color change is indicated by the purple to brown color around the streak.
What is the biochemistry of starch hydrolysis? (Substrate, enzymes, and end products)
Starch + alpha-amylase -> glucose subunits
What does the term saccharolytic refer to in the TSI tests?
Describes how microorganisms can break down the glycosidic bonds in carbohydrates
Which side shows Lipid hydrolysis?
Left: clearing of the medium is considered a positive test for lipid hydrolysis
What is the bio chemistry of lipid hydrolysis? (Substrate, enzyme, end product)
- Triglyceride + H2O --Lipase (enzyme)--> Glycerol + Fatty acids
- By adding water, lipase breaks apart the glycerol and fatty acid of triglyceride.
Interpret these H2S SIM tubes. Was there H2S Production, Indole, and/or motility?
H2S: black ppt.
Hydrolysis of tryptophan to indole: red color with Kovac's
Motile: growth not restricted to stab line
- A: No H2S, positive for indole, motile
- B: No H2S, No indole, none motile
- C: H2S, no indole, motile
- D: No H2S, No indole, Motile
- E: H2S, indole, motile
What is the biochemistry rxn of H2S production? (Substrate, enzyme, end products)
Amino acids (Cysteine) + cysteine desulfurase (enzyme) --> H2S (loss of sulfur atom through hydrolysis)
What was the purpose of the IMViC tests? (4 things)
Hint: mediums used were SIM deep tubes, MR-VP broth tubes, Citrate agar slants
- Hydrolysis of tryptophan to indole
- Acid fermentation of glucose
- Glucose fermentation
- Citrate permease
What was the biochemical reaction using the enzyme, tryptophanase? (List its substrate used and the end products)
- Substrate: Tryptophan (amino acid)
- Binds with tryptophanase through hydrolyzation
- Products: INDOLE, pyruvic acid, and ammonia
What is the purpose of Kovacs' reagent? Which tube here shows a positive result using the reagent?
- Purpose is to detect Indole end products
- The right tube shows a positive test with the red colored layer on top
What is Methyl red and what is it used for? What do the tubes on the left and right indicate?
- Methyl red is a pH indicator used to identify how glucose was catabolized by certain bacteria. Some produce a mixed fermentation acids (lowering pH of medium), while others produce acetoin, and fewer organic acids (less lowered pH of medium).
- A lowered pH medium turns the broth red, while a higher pH turns it yellow.
- The tube on the left indicates a positive methyl, while the tube on the right indicates a negative result.
What is the Voges-Proskauer (VP) Test used to detect? What reagents are used and how do they work?
- Its main goal is to look for 2,3-butanediol accumulation in the medium when bacteria ferment glucose.
- It uses KOH and Barritt's reagent to detect ACETOIN, which is a precursor for the synthesis of 2,3-butanediol.
- Once the reagents find acetoin, a cherry-red color develops, indicating a positive VP test.
What is Barritt's reagent used to detect, and which tube here shows its positive result?
- It is used in the Voges-Proskauer (VP) test to detect the presence of acetoin, which means there was glucose fermentation leading to 2,3-butanediol production.
- The tube on the left shows a positive result for the VP test due to the cherry-red color developed.
Which of these citrate tubes shows a positive result?
Tube A: The raised pH from citrate being converted to pyruvic acid turns the slant blue.
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