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Questions and Answers
What does a K/A result indicate in a Triple Sugar Iron Agar test?
What does a K/A result indicate in a Triple Sugar Iron Agar test?
In Krigler iron agar (KIA), what causes the indicator to change color?
In Krigler iron agar (KIA), what causes the indicator to change color?
What does the formation of a space or crack in the medium during a fermentation test indicate?
What does the formation of a space or crack in the medium during a fermentation test indicate?
Which component is NOT found in Russell Double Sugar Agar (RDS)?
Which component is NOT found in Russell Double Sugar Agar (RDS)?
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What would a blackening of the medium indicate during a sugar fermentation test?
What would a blackening of the medium indicate during a sugar fermentation test?
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Which of the following microorganisms is oxidase positive?
Which of the following microorganisms is oxidase positive?
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What is the indicator used in Christensen's Urea Agar to determine urease activity?
What is the indicator used in Christensen's Urea Agar to determine urease activity?
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Which color change indicates a positive urease test?
Which color change indicates a positive urease test?
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How quickly can Proteus typically hydrolyze urea in a urease test?
How quickly can Proteus typically hydrolyze urea in a urease test?
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What does the decarboxylation test determine about bacterial species?
What does the decarboxylation test determine about bacterial species?
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Study Notes
Gas Production
- Aerogenic: Indicates gas production in media, resulting in bubble formation.
- Nonaerogenic: No gas production observed.
- Cracks in media signify space due to gas formation.
Triple Sugar Iron Agar (TSI) Reactions
- K/A: Fermentation of glucose only.
- A/A: Fermentation of two or more sugars.
- K/K: No sugar fermentation occurs.
- Blackening indicates hydrogen sulfide (H2S) production.
Sugar Fermentation Tests
- Krigler Iron Agar (KIA): Tests for glucose and lactose with ferrous ammonium sulfate, using phenol red as a pH indicator for H2S production.
- Russell Double Sugar Agar (RDS): Contains glucose and lactose without ferrous ammonium sulfate, using Andrade's indicator for pH changes.
Oxidase Testing
- Oxidase Negative: Typical of Enterobacteriaceae.
- Oxidase Positive: Identifies Pseudomonas, Neisseria, Campylobacter, Vibrio.
- Modified Oxidase Test: Differentiates Staphylococcus from Micrococcus.
- Kovac's Oxidase Test: Positive reaction indicated by lavender color within 10-15 seconds.
Urease Test
- Detects ability to hydrolyze urea, resulting in ammonia production which makes media alkaline.
- Positive result: Color change to pink/red; commonly seen with Proteus species.
- Salmon color indicates negative result.
Decarboxylation/Dihydrolase Test
- Assesses capability of amino acid decarboxylation.
- Lysine decarboxylation yields cadaverine and CO₂.
- Ornithine and arginine also undergo decarboxylation producing putrescine and citrulline respectively.
Moeller Decarboxylase Base Medium
- Contains glucose, peptones, and specific amino acids (0.1% concentration).
- Indicators: Bromcresol purple and cresol red.
Amino Acid Utilization
- Bacteria can utilize amino acids as energy and carbon sources.
Nitrate Reduction
- Determines reduction of nitrate to nitrite and beyond (N₂ etc.).
- Presence of nitrite indicated by red color upon adding N,N dimethyl-α-naphthylamine and sulfanilic acid.
- Zinc dust confirms true negative or indicates further reduction.
Sulfide-Indole-Motility Agar (SIM)
- Semisolid medium differentiating gram-negative bacteria in Enterobacteriaceae.
- Cloudiness indicates motility; black precipitate indicates H2S production.
Hippurate Hydrolysis
- Hydrolyzes hippuric acid using hippuricase to produce glycine.
- Glycine detected by ninhydrin reagent resulting in purple color change.
Principles of Identification
- Categories include pH-based, enzyme-based reactions, utilization of carbon sources, and visual detection of growth.
- Metabolic reactions yield binary code; '+' for positive results and '-' for negative.
- Codes compiled generate a profile for organism identification.
Clinical Impact
- Early diagnosis leads to timely and effective patient care.
- Rapid reporting affects treatment choices through accurate antimicrobial selection.
- Rapid diagnostic methods enhance detection speed, utilizing techniques like staining and enzymatic tests for quick results.
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Description
This quiz covers gas production in microbiological media, including aerogenic and nonaerogenic classifications. It also delves into Triple Sugar Iron Agar reactions and various sugar fermentation tests such as Krigler Iron Agar and Russell Double Sugar Agar. Additionally, it addresses oxidase testing and its implications in identifying different bacteria.
