17 Questions
What color change indicates a positive result in the Methyl Red test?
Pink
In the Voges Proskauer test, what compound reacts with guanidine compounds to give a red colored compound?
Acetoine
Which medium is used for the Voges Proskauer test?
MR-VP medium
At what temperature is incubation done in the procedures described?
35°C
What does a red slant and a retained yellow butt in a TSI tube indicate?
Alkaline over acid reaction
What does a yellow color indicate in the Methyl Red test?
Negative result
Which organisms are capable of producing hydrogen sulfide gas in TSI reactions?
Citrobacter, Arizona Salmonella, Proteus, Arizona
What is the purpose of Lysine Iron Agar (LIA) medium?
To detect urease production
In a TSI tube showing an alkaline over alkaline (K/K) reaction, what does this signify?
No sugar fermentation
Which group of organisms show the H2S K/A TSI reaction?
Citrobacter, Arizona Salmonella, Proteus, Arizona
What is indicated by a TSI tube showing acid over alkaline (A/A) reaction?
Fermentation of sugars with acid production
On TSI agar, what does a yellow color indicate?
Fermentation of sugars with acid production
What is the purpose of Triple Sugar Iron (TSI) agar?
To test for fermentation ability
Which indicator is used in TSI agar to detect acidic or alkaline conditions?
pH indicator - phenol red
What happens to the TSI agar when all sugars are fermented by the microorganisms?
It remains yellow
Which condition leads to the reaction called acid over acid (A/A) fermenting 2 or all sugars on TSI agar?
Limited glucose utilization followed by lactose utilization
Which aspect of growth conditions does TSI agar primarily assess?
Sugar fermentation patterns
Study Notes
Methyl Red (MR) Test
- Inoculate MR-VP medium and incubate at 35°C, observing for color change at 15, 30, and 60 minutes up to 4 hours
- Result: + (pink or red) indicates pH 4.5 or lower, - (no color change) indicates pH above 4.5
- Principle: Measures acidity produced by microorganisms from dextrose fermentation
Voges-Proskauer (VP) Test
- Uses MR-VP medium, 5% alpha-naphthol, 40% KOH, and 0.5% creatine
- Principle: Detects acetoine production by microorganisms, which reacts with guanidine compounds to form a red-colored compound
- Result: + (red color) indicates acetoine production, - (no color change) indicates no acetoine production
Triple Sugar Iron Agar (TSI) Test
- Uses TSI medium containing glucose, lactose, and sucrose, with phenol red as pH indicator and ferrous ammonium sulfate as H2S indicator
- Principle: Measures glucose utilization, acid production, and H2S production by microorganisms
- Result: Various reactions possible, including A/A, K/A, K/K, depending on glucose fermentation and H2S production
TSI Reactions
- A/A: Acid over acid, indicates fermentation of all sugars
- K/A: Alkaline over acid, indicates glucose fermentation only
- K/K: Alkaline over alkaline, indicates no sugar fermentation
- Combinations of these reactions can distinguish between different microorganisms, such as Serratia, Escherichia, Enterobacter, Klebsiella, Citrobacter, Arizona, Salmonella, Proteus, Shigella, Providencia, and Yersinia
Lysine Iron Agar (LIA) Test
- Uses LIA medium containing lysine, peptones, glucose, ferric ammonium citrate, and sodium thiosulfate
- Principle: Detects decarboxylation or deamination of lysine and H2S production by microorganisms
- Result: + (alkaline or acid reaction) indicates lysine decarboxylation or deamination, - (no reaction) indicates no lysine metabolism
Extended Spectrum Beta-lactamases (ESBLs)
- Cause plasmid-mediated antibiotic resistance to cephalosporins and carbapenems
- Found in microorganisms such as E. coli, Klebsiella, and Serratia
- Examples of ESBLs include carbapenemase, cephalosporinase, and metallo-β-lactamase
Learn about the procedure for conducting the Methyl Red test, including the incubation conditions and observation points for color change. Understand how to interpret a positive result as pink or red, indicating a low pH value. Explore the principle behind the test based on acid production from dextrose by different organisms.
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