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Questions and Answers
Which indicator is used in LIA to detect H2S production?
Which indicator is used in LIA to detect H2S production?
- Phenol red
- Bromocresol purple
- Ferric ammonium citrate and sodium thiosulfate (correct)
- Methyl red
What is the purpose of the slant and butt in LIA?
What is the purpose of the slant and butt in LIA?
- To detect hydrogen sulfide production
- To detect glucose fermentation
- To detect lysine decarboxylation
- To detect aerobic and anaerobic metabolism (correct)
What is the significance of a purple slant and yellow butt on LIA?
What is the significance of a purple slant and yellow butt on LIA?
- Glucose fermentation positive, H2S production positive
- Lysine decarboxylase negative, lysine deaminase positive
- Lysine decarboxylase positive, lysine deaminase negative (correct)
- Glucose fermentation negative, H2S production negative
Which test is used to detect the presence of $eta$-galactosidase activity?
Which test is used to detect the presence of $eta$-galactosidase activity?
Which agar medium is used to simultaneously detect glucose fermentation, lactose fermentation, and hydrogen sulfide production?
Which agar medium is used to simultaneously detect glucose fermentation, lactose fermentation, and hydrogen sulfide production?
What color change is observed on the slant after adding FeCl3 if the result is positive for TRYPTOPHAN deamination?
What color change is observed on the slant after adding FeCl3 if the result is positive for TRYPTOPHAN deamination?
What is the color change observed in the UREASE test for rapid urease producers?
What is the color change observed in the UREASE test for rapid urease producers?
Which of the following microorganisms is a slow/weak urease producer?
Which of the following microorganisms is a slow/weak urease producer?
Which medium is commonly used to determine motility in microorganisms?
Which medium is commonly used to determine motility in microorganisms?
What reaction indicates motility in the SIM (Sulfide Indole Motility) Medium?
What reaction indicates motility in the SIM (Sulfide Indole Motility) Medium?
Which of the following is NOT a member of ENTEROBACTERIACEAE that is motile?
Which of the following is NOT a member of ENTEROBACTERIACEAE that is motile?
What is the purpose of the Oxidation-Fermentation Tests (O/F tests)?
What is the purpose of the Oxidation-Fermentation Tests (O/F tests)?
What happens in the Kligler iron agar tube for a non-oxidizer?
What happens in the Kligler iron agar tube for a non-oxidizer?
What is the purpose of Ortho-nitrophenyl-beta-D-galactopyranoside (ONPG)?
What is the purpose of Ortho-nitrophenyl-beta-D-galactopyranoside (ONPG)?
Which color indicates an alkaline environment in the O/F medium?
Which color indicates an alkaline environment in the O/F medium?
What does an oxidizer produce in the Kligler iron agar open tube?
What does an oxidizer produce in the Kligler iron agar open tube?
What is the pH indicator used in the Oxidation-Fermentation Tests?
What is the pH indicator used in the Oxidation-Fermentation Tests?
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Study Notes
Lysine Iron Agar (LIA)
- LIA is used in conjunction with TSI to screen stool specimens for enteric pathogens
- Composition: aerobic slant, anaerobic butt, lysine, peptones, and a small amount of glucose
- pH Indicator: BROMOCRESOL PURPLE
- H2S Indicator: FERRIC AMMONIUM CITRATE & SODIARY THIOSULFATE
- Manner of Inoculation: STAB-STREAK-STAB
Reactions on LIA
- Lysine Decarboxylation (butt/anaerobic): • K/K (Purple Slant/Purple Butt): LYSINE DECARBOXYLASE (+) LYSINE DEAMINASE (-) • K/A (Purple Slant/Yellow Butt): LYSINE DECARBOXYLASE (-) LYSINE DEAMINASE (-)
- Note: Cadaverine neutralizes organic acids formed by glucose fermentation and reverts to alkaline state
Oxidation-Fermentation Tests
- Purpose: Identification of bacteria based on the oxidation-fermentation pattern
- Medium: Hugh and Leifson O/F basal medium (OFBM)
- pH Indicator: BROMOTHYMOL BLUE
- Uninoculated: GREEN; Acid environment: YELLOW; Alkaline environment: BLUE
- Two tubes: one overlaid with mineral oil (closed – anaerobic) and one without mineral oil (open – aerobic)
- FERMENTER: ACID in BOTH open & closed tube
- OXIDIZER: ACID in OPEN tube; no acid in closed tube
- NON-OXIDIZER: NO ACID in BOTH open & sealed tube
ORTHO-NITROPHENYL-BETA-D-GALACTOPYRANOSIDE (ONPG)
- Determines the presence of Slow/Delayed/Late Lactose Fermenters (LLF)
- ONPG is a colorless molecule structurally similar to LACTOSE
- Can enter cell membrane without lactose permease and is converted into galactose and o-nitrophenyl (yellow chromogen) by Beta-galactosidase
IMViC Reactions
INDOLE TEST
- Used to identify organisms that produce the enzyme TRYPTOPHANASE
- Indicator: 10% FERRIC CHLORIDE (FeCl3) – added after incubation
- Reactions: • (+) GREEN color on slant after adding FeCl3 • (-) Slant remains ORIGINAL COLOR after adding FeCl3
UREASE TEST
- Determines whether a microorganism can hydrolyze urea
- Medium: Christensen’s Urea Agar or Stuart Urea Broth
- pH Indicator: PHENOL RED
- Reactions: • (+) BRIGHT PINK Coloration • (-) No Color Change (YELLOW)
MOTILITY
- Determines whether an organism is motile or non-motile
- Medium: SIM (Sulfide Indole Motility) Medium or any semisolid motility medium
- Streaking: STRAIGHT STAB
- 1% triphenyltetrazolium chloride can be added to aid visualization
- Reactions: • MOTILE (+): SPREAD AWAY from the stab line/HAZY APPEARANCE • NON-MOTILE (-): REMAIN at the stab line
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