Enterobacteriaceae Identification Quiz
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Questions and Answers

Match the following bacteria with their fermentation type:

Escherichia = Lactose Fermenter Shigella = Non-Lactose Fermenter Klebsiella = Lactose Fermenter Salmonella = Non-Lactose Fermenter

Match the following agar types with their characteristics:

EMB Agar = Selective and differential XLD Agar = Detects hydrogen sulfide (H2S) Hektoen Enteric Agar = Targets Salmonella/Shigella SS Agar = Inhibits gram-positive organisms

Match the following non-lactose fermenters with their characteristics:

Salmonella = Produces H2S and black center Shigella = Does not produce H2S Proteus = Non-Lactose Fermenter Yersinia = Non-Lactose Fermenter

Match the following lactose fermenters with their appearance on XLD agar:

<p>Escherichia coli = Yellow colonies Citrobacter = Yellow colonies Serratia = Red colonies with black centers Klebsiella = Yellow colonies</p> Signup and view all the answers

Match the following fermentation results with the media type:

<p>Orange color = Indicates lactose fermentation (HE agar) Blue green color = Indicates Shigella (HE agar) Yellow colonies = Indicates nonpathogens (XLD agar) Colorless colonies = Indicates Shigella (XLD agar)</p> Signup and view all the answers

Match the following carbohydrates found in XLD agar:

<p>Sucrose = In excess to detect fermentation Lactose = In excess to detect fermentation Xylose = Present to detect hydrogen sulfide production Lysine = Used for decarboxylation detection</p> Signup and view all the answers

Match the following colors with their meaning in Hektoen Enteric Agar:

<p>Orange = Low pH from lactose fermentation Blue green = Indicates target pathogen (Shigella) Black center = Indicates H2S production (Salmonella) Yellow = Indicates lactose fermentation</p> Signup and view all the answers

Match the following Enterobacteriaceae species with their classification:

<p>Escherichia coli = Opportunistic pathogen Salmonella spp. = Primary pathogen Klebsiella pneumonia = Opportunistic pathogen Shigella spp. = Primary pathogen</p> Signup and view all the answers

Match the following late lactose fermenters with their initial characteristics:

<p>Serratia = Initially Non-Lactose Fermenter Enterobacter = Initially Non-Lactose Fermenter Citrobacter = Initially Non-Lactose Fermenter (LLF) Proteus = Non-Lactose Fermenter</p> Signup and view all the answers

Match the following characteristics with the correct type of bacteria:

<p>All ferment glucose = Enterobacteriaceae Oxidase negative = Enterobacteriaceae Not very useful in identification = Cellular morphology Facultatively anaerobic = Enterobacteriaceae</p> Signup and view all the answers

Match the following infections with the corresponding Enterobacteriaceae species:

<p>Septicemia = Escherichia coli Urinary tract infections = Klebsiella pneumonia Meningitis = Escherichia coli Gastroenteritis = Salmonella spp.</p> Signup and view all the answers

Match the following media with their use in Enterobacteriaceae identification:

<p>MacConkey Agar = Selective and differential BAP = Macroscopic morphology Crystal violet = Inhibits gram-positive growth Bile salts = Inhibits gram-positive growth</p> Signup and view all the answers

Match the following tests with their characteristics in Enterobacteriaceae:

<p>Nitrate reduction = All reduce nitrate to nitrites Motility test = All motile at body temperature except... Glucose fermentation = All ferment glucose Oxidase test = All are oxidase negative</p> Signup and view all the answers

Match the following terms with their descriptions:

<p>Opportunistic pathogens = Normal flora causing infections in non-normal sites Primary pathogens = Always pathogens Normal flora = Part of the gut microbiome Infections = Result from pathogenic species</p> Signup and view all the answers

Match the following features with the Enterobacteriaceae species:

<p>Mucoid colonies = Klebsiella pneumonia Large gray colonies = Enterobacteriaceae on BAP Pathogenic E. coli = Shigella spp. Non-motility = Klebsiella</p> Signup and view all the answers

Match the following terms with their key characteristics:

<p>Facultatively anaerobic = Can grow with or without oxygen Gram-negative = Identified via Gram staining Coccobacilli = Cellular morphology type Selective plates = Used for pathogenic species identification</p> Signup and view all the answers

Match the following bacterial tests with their primary purpose:

<p>Lactose Utilization Test = Differentiate lactose fermenting from non-lactose fermenting species ONPG Test = Determine if a dLF is a true NLF Glucose Fermentation Test = Test for acid production from glucose O/F Test = Assess aerobic vs anaerobic carbohydrate utilization</p> Signup and view all the answers

Match the bacterial enzymes with their functions:

<p>β-galactoside permease = Transports lactose into the cell β-galactosidase = Breaks down lactose into glucose and galactose Acid production = Indicates glucose fermentation pH indicators = Detects acid presence in media</p> Signup and view all the answers

Match the terms with their definitions:

<p>Lactose = Disaccharide made of glucose and galactose dLF = Bacteria that lack β-galactoside permease NLF = Non-lactose fermenting bacteria Yellow color in ONPG test = Indicates positive result for β-galactosidase activity</p> Signup and view all the answers

Match the test conditions with their results:

<p>Positive ONPG result = Yellow color Negative ONPG result = Clear Lactose Utilization Positive = Lactose fermentation observed Glucose Fermentation = Acids detected by pH indicators</p> Signup and view all the answers

Match the media usage with their testing purpose:

<p>Sterile saline = First step in performing ONPG test Bacterial suspension = Required for ONPG testing High sugar content in OF test = To observe oxidation ability pH indicator media = Used to detect acid from fermentation</p> Signup and view all the answers

Match the products of glucose metabolism pathways:

<p>Glycolysis = Produces pyruvate from glucose Fermentation = Yields strong acids Oxidation = Produces weak acids Anaerobic pathways = Do not require oxygen</p> Signup and view all the answers

Match the characteristics with their respective metabolic pathways:

<p>Oxidation = Aerobic carbohydrate utilization Fermentation = Anaerobic carbohydrate utilization Lactose fermentation = Metabolizes lactose into acids Glucose utilization = Can lead to acid and gas production</p> Signup and view all the answers

Match the enzyme-related features with their corresponding information:

<p>β-galactoside permease = Allows entry of lactose into bacterial cells β-galactosidase = Species that ferment lactose can produce ONPG = Substrate to test for β-galactosidase False-positive potential = Yellow pigment producing bacteria in ONPG test</p> Signup and view all the answers

Match the following compounds with their associated reactions or results:

<p>Butylene glycol = Produces diacetyl Diacetyl + KOH = Red complex formation Citrulline = Converted to putrescine Cadaverine = Product of lysine decarboxylation</p> Signup and view all the answers

Match the following amino acids with their corresponding decarboxylase enzymes:

<p>Lysine = Lysine decarboxylase Ornithine = Ornithine decarboxylase Arginine = Arginine dihydrolase Citrulline = Not applicable in the test</p> Signup and view all the answers

Match the following tests with their specific purposes:

<p>Decarboxylase test = Differentiate Enterobacterales Dihydrolase test = Identify arginine conversion Phenylalanine deaminase test = Oxidatively deaminate phenylalanine Moeller’s broth medium = Detect decarboxylation</p> Signup and view all the answers

Match the following results with their corresponding color changes:

<p>Positive decarboxylation = Purple color Negative decarboxylation = Yellow color Phenylpyruvic acid reaction = Green complex with ferric chloride Un-inoculated media = Yellow color at pH 6.0</p> Signup and view all the answers

Match the following bacteria genera with their ability to produce specific enzymes:

<p>Morganella = Positive for phenylalanine deaminase Proteus = Positive for phenylalanine deaminase Providencia = Positive for phenylalanine deaminase E. coli = Negative for phenylalanine deaminase</p> Signup and view all the answers

Match the following components of Moeller’s broth with their functions:

<p>Glucose = Provides fermentable sugar Peptones = Nutrient source Bromocresol purple = pH indicator Oil overlay = Creates anaerobic environment</p> Signup and view all the answers

Match the following conditions necessary for decarboxylation with their descriptions:

<p>Acid pH = Initial condition for decarboxylation Anaerobic environment = Created by oil overlay Control tube = Used for comparison Alkaline pH shift = Indicates positive result</p> Signup and view all the answers

Match the following products with their respective sources in the deamination test:

<p>Phenylpyruvic acid = From phenylalanine deamination Ammonia = Byproduct of deaminating phenylalanine Putrescine = From ornithine conversion Citrulline = Intermediate in arginine metabolism</p> Signup and view all the answers

Match the following tests with what they detect or indicate:

<p>Methyl red test = Mixed acids from glucose metabolism Voges-Proskauer test = Acetoin production Citrate test = Citrate utilization Indole test = Indole production from tryptophan</p> Signup and view all the answers

Match the carbohydrate fermentation results with their corresponding descriptions:

<p>Glucose only = Acid slant and acid butt on TSI agar Glucose and lactose or sucrose = Ferments multiple carbohydrates Lactose only = Does not ferment glucose Lactose and sucrose = Does not ferment glucose</p> Signup and view all the answers

Match the metabolic products with the tests where they are detected:

<p>Mixed acids = Detected by Methyl red test H2S = Detected in sulfide production test Phenylpyruvate = Found in phenylalanine deaminase test Indole = Produced from tryptophan in Kovac’s reagent</p> Signup and view all the answers

Match the characteristics of indole-positive bacteria:

<p>Produce tryptophanase = Indicates indole production capability Deaminate lysine = Not associated with indole production Decarboxylate tryptophan = Not related to indole Decarboxylate ornithine = Not related to indole</p> Signup and view all the answers

Match the colony colors on various agar media with the organisms they indicate:

<p>Black colonies on XLD = Salmonella Orange colonies on HEK = Shigella Pink colonies on SS agar = E.coli Non-pathogenic Enterobacteriaceae = Indicated by specific agar colors</p> Signup and view all the answers

Match the following tests with their results:

<p>Tryptophan Deaminase Test = Reddish brown positive Citrate Utilization Test = Blue positive Indole Test (Kovac's reagent) = Red positive MIO Agar (Positive Motility) = Clouding of medium</p> Signup and view all the answers

Match the following tests with their purposes:

<p>Tryptophan Deaminase Test = Determine ability to oxidatively deaminate tryptophan Citrate Utilization Test = Determine use of sodium citrate as a carbon source Indole Test = Identify organisms producing tryptophanase MIO Agar = Detect motility and decarboxylase production</p> Signup and view all the answers

Match the following positive results with their corresponding tests:

<p>Citrate Utilization = Blue Indole with Ehrlich's reagent = Red Tryptophan Deaminase Test = Reddish brown MIO Agar Ornithine Decarboxylation = Purple throughout medium</p> Signup and view all the answers

Match the following negative results with their respective tests:

<p>Citrate Utilization = Green Indole Test = Light brown Tryptophan Deaminase Test = Colorless MIO Agar Motility = No clouding of medium</p> Signup and view all the answers

Match the following tests with the correct reagents used:

<p>Indole Test (Spot Method) = DMACA reagent Indole Test (Kovac's reagent) = Kovac's reagent Indole Test (Ehrlich's reagent) = Ehrlich’s reagent MIO Agar = Kovac’s reagent for indole detection</p> Signup and view all the answers

Match the following microorganisms with their positive tests:

<p>E. coli = Tryptophan Deaminase Test positive P. vulgaris = Tryptophan Deaminase Test positive Klebsiella spp. = MIO Agar with positive motility Enterobacter = Differentiated by MIO Agar</p> Signup and view all the answers

Match the following limitations with their respective tests:

<p>Citrate Utilization Test = Some organisms grow without color change Tryptophan Deaminase Test = Light brown can be confusing Indole Test = Result varies with reagent used MIO Agar = Semi-solid medium may complicate reading</p> Signup and view all the answers

Match the following outcomes with their definitions:

<p>Positive result = Indicates the specific enzyme is present Negative result = Indicates the specific enzyme is absent Color change = Reveals chemical activity of organisms No growth = Organisms unable to utilize the substrate</p> Signup and view all the answers

Study Notes

Overview of Enterobacteriaceae Identification Methods

  • Lecture 9 covers identifying Enterobacteriaceae
  • Includes information from Bailey & Scott's (Chapter 12, 19) and Diagnostic Microbiology (Chapter 9, 19)
  • Lecture introduces Enterobacteriaceae, common identification methods, special media and test systems.

Enterobacteriaceae

  • A large family of bacteria, also known as enterics.
  • Common clinical isolates in acute care primarily include Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis.

Bacterial Species and Infections

  • Table 19.3 lists various bacterial species with the diseases they commonly cause.
  • Examples include Escherichia coli linked to bacteriuria, septicemia, and neonatal sepsis.
  • Some are opportunistic pathogens that cause infections in non-normal areas, such as the urinary tract or wounds.

Clinical Significance

  • Two main categories of clinical significance:
    • Opportunistic pathogens (covered in this lecture): These bacteria are part of normal flora but can cause infections in unusual sites.
    • Primary pathogens: These bacteria always cause disease. Examples include Salmonella, Shigella, and Yersinia.

General Characteristics of Enterobacteriaceae

  • All ferment glucose.
  • All reduce nitrates to nitrites.
  • All are oxidase-negative.
  • Most are motile at body temperature, except for Klebsiella, Shigella, and Yersinia.
  • Lack remarkable colony morphologies on typical lab media.

Enterobacteriaceae - Identification

  • Cellular morphology (gram-negative rods/coccobacilli) is not very helpful for identification except to rule out other organisms.
  • Growth conditions are facultatively anaerobic.
  • Molecular methods are modern methods for identification.
  • Macroscopic morphology on BAP is not very helpful for identification, except to rule out other organisms.
  • Larger, moist, gray colonies are sometimes mucoid; selective plates are used for identifying pathogenic species in stool samples.

MacConkey Agar

  • A selective and differential medium for Enterobacteriaceae.
  • Inhibits gram-positive bacteria; lactose fermentation is the key differentiator.
  • Colonies of lactose fermenters appear pink/red (LF); non-lactose fermenters are yellow (NLF). Some may exhibit delayed lactose fermentation (LLF), initially appearing yellow but turning pink/red after 48 hours.

EMB Agar

  • A selective and differential medium often used for Enterobacteriaceae identification.
  • Methylene blue inhibits gram-positive bacteria; lactose and sucrose fermentation differentiate.

Hektoen Enteric Agar (HE)

  • Selective and differential medium specific for Salmonella and Shigella.
  • Bile salts and other inhibitory agents reduce gram-positive growth; lactose and sucrose fermentation aid differentiation.
  • Orange colonies often indicate non-pathogenic organisms.
  • Black colonies with a central black discoloration indicate Salmonella.
  • Blue-green colonies indicate possible target pathogens, like Shigella.

Xylose Lysine Deoxycholate Agar (XLD)

  • Another medium targeted specifically at Salmonella and Shigella identification.
  • Selective for gram-negative bacteria; less than MacConkey or HE.
  • Lactose, sucrose, and xylose fermentation; lysine decarboxylation; and H2S production differentiate.
  • Yellow colonies (non-pathogens)
  • Red colonies with black centers (target pathogens).
  • Colorless/red colonies (Salmonella/Shigella)

Salmonella Shigella Agar (SS)

  • A medium for isolating and differentiating Salmonella and Shigella.
  • Selective for gram-negative bacteria; lactose and neutral red differential.
  • Lactose fermenters (pink); non-lactose fermenters (colorless)
  • This allows identification of non-pathogenic bacteria from possible pathogens.

CIN Media

  • A medium for isolates that have Yersinia spp. or non-fermenting organisms.
  • Inhibitory agents (cefsulodin, irgasan, novobiocin, bile salts, and crystal violet) reduce growth. Mannitol with phenol red are the differential differentiators.

O/F Basal Media

  • Useful for classifying bacteria as oxidizers or fermenters.
  • Two tubes are used:
    • Aerobic tube
    • Anaerobic tube (covered by mineral oil).

Triple Sugar Iron Agar (TSI)

  • Detects production of acid from fermentation of glucose, lactose, and sucrose, and also hydrogen sulfide.
  • The butt of the tube and the slant are both used for interpretation.
  • Gas may also be noted.
  • Examples of TSI reactions are noted.
  • Several organisms have their own specific reactions and are highlighted.

Glucose Metabolism

  • The Embden-Meyerhof pathway is the essential pathway.
  • Other pathways are mixed acid or butylene glycol pathways, which have their own specific tests.

Methyl Red(MR) test

  • This test determines if mixed acids are produced during glucose metabolism.
  • Positive results are indicated by a red color.

Voges-Proskauer (VP) test

  • Identifies organisms that utilize the butylene glycol pathway.
  • Positive is indicated by the formation of a red complex.

Decarboxylase and Dihydrolase Tests

  • Used to distinguish decarboxylase-producing Enterobacterales from other Gram-negative rods; specific for amino acids (e.g., lysine and ornithine).
  • Moeller's broth is an example of a medium used in these tests, using appropriate pH indicator.
  • A positive result is marked by a color change; a negative result does not change or is a slight change in color.

Phenylalanine Deaminase Test

  • Used to test if bacterial species can deaminate phenylalanine.
  • Positive is indicated by a green color change.

Tryptophan Deaminase Test

  • Identifies organisms that can deaminate tryptophan and produce indole
  • Positive is indicated by a reddish color.

Citrate Utilization Test

  • Tests if an organism can utilize sodium citrate as a carbon source.
  • Positive is indicated by a blue color change.

Indole test

  • A test to detect if indole production occurs from tryptophan.
  • Positive is indicated by a change from colorless to a reddish brown color.

Motility-Indole-Ornithine (MIO) Agar

  • A semi-solid medium useful for differentiating species of Klebsiella, Enterobacter, and Serratia. This is done by testing for motility, ornithine decarboxylase, and indole formation.

Nitrate and Nitrite Reduction

  • This reaction detects the ability of an organism to reduce nitrate.
  • A positive result is marked when a color is not seen or if gas is seen after adding zinc.
  • Negative result turns a reddish brown color.

Urease (Christensen's) Test

  • Determines if an organism can produce urease.
  • Positive result shows a bright pink color.

Multi-test systems

  • Provide comprehensive identification.
  • Can be pure culture or don't require one.
  • pH, enzymatic activity, carbon utilization, visual detection of characters, or molecular methods.
  • API 20E system is an example.

Rapid identification systems

  • Offer quicker results.
  • Several types of rapid methods exist, using different techniques, and include immunochemical methods, mass spectrometry, and molecular biological methods.

Knowledge Checks

  • Answers to relevant knowledge checks.

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BIOL 2010 Lecture 9: Identification Methods for Enterobacteriaceae

Description

Test your knowledge on Enterobacteriaceae bacteria and their fermentation types. This quiz covers various topics including agar characteristics, lactose fermentation, and classification of different species. Match specific terms and features to enhance your understanding of these important microorganisms.

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