CLS463 Clinical Bacteriology II: Enterobacteriaceae

Questions and Answers

Which characteristic is NOT shared by all Enterobacteriaceae?

They include both opportunistic and primary pathogens.

They can be found in the gut microbiota.

They are primarily rod-shaped bacteria.

They are Gram-positive. (correct)

Which of the following genera are considered opportunistic pathogens within Enterobacteriaceae?

Edwardsiella

Klebsiella (correct)

Salmonella

Shigella

How many genera are classified under the Enterobacteriaceae family?

31 (correct)

Coliform bacteria are a subset of which classification?

All Enterobacteriaceae Signup and view all the answers

Which of the following is NOT a common genus within the Enterobacteriaceae?

Bacillus Signup and view all the answers

What type of bacteria primarily comprise coliforms?

Gram-negative bacilli Signup and view all the answers

Which of the following statements about Enterobacteriaceae is true?

They are commonly part of human gut flora. Signup and view all the answers

Which of the following genera is found in the gut microbiota but can also act as an opportunistic pathogen?

Citrobacter Signup and view all the answers

What color do lactose fermenting enteric bacteria appear on MacConkey Agar?

Pink Signup and view all the answers

What indicator system is used in Hektoen Enteric Agar to show hydrogen sulfide formation?

Ferric iron Signup and view all the answers

What colors are associated with Salmonella species on Xylose Lysine Deoxycholate Agar (XLD)?

Red or pink with black centers Signup and view all the answers

On Eosin Methylene Blue Agar (EMB), what is the appearance of E. coli colonies?

Metallic green sheen colonies Signup and view all the answers

Which of the following best describes Shigella species growth on Hektoen Enteric Agar?

Green colonies Signup and view all the answers

For which type of bacteria is Eosin Methylene Blue Agar (EMB) primarily selective?

Lactose fermenters Signup and view all the answers

What type of media is Xylose Lysine Deoxycholate Agar (XLD)?

Differential and selective Signup and view all the answers

What color do coliforms typically appear on MacConkey Agar?

Yellow to orange Signup and view all the answers

Which statement accurately reflects the purpose of CLED agar?

CLED agar helps identify bacterial species based on their metabolic properties. Signup and view all the answers

What will be the appearance of lactose non-fermenting colonies on CLED agar?

Blue colonies Signup and view all the answers

Which test is used specifically to differentiate between oxidase positive and negative bacteria?

Oxidase Test Signup and view all the answers

What is the principle behind the catalase test?

It assesses the breakdown of hydrogen peroxide. Signup and view all the answers

What indicates a positive result in the nitrate reduction test?

The broth turns red after adding reagents. Signup and view all the answers

Which of the following biochemical tests determines the ability of bacteria to utilize citrate?

Citrate Utilization Test Signup and view all the answers

What indicates the presence of hydrogen sulfide (H2S) in TSI agar?

Black color Signup and view all the answers

What color change indicates acid production during lactose fermentation on CLED agar?

Deep blue to yellow Signup and view all the answers

Which test is NOT typically associated with identifying members of the Enterobacteriaceae family?

Oxidase Test Signup and view all the answers

In the TSI agar test, what condition is indicated by a completely yellow slant and butt?

Both lactose and sucrose are fermented Signup and view all the answers

Which of the following best describes motility in the motility test?

Diffuse growth radiates from the inoculation site Signup and view all the answers

What is the primary use of the API 20E test?

To identify and differentiate members of Enterobacteriaceae Signup and view all the answers

Which two tests are primarily used to assess hydrogen sulfide production?

SIM test and MIU test Signup and view all the answers

In the context of the TSI agar test, what does a red slant with a yellow butt indicate?

Fermentation of glucose only Signup and view all the answers

Which method is NOT mentioned as a technique for detecting bacteria?

Fluorescent antibody tests Signup and view all the answers

What indicates a positive result in the urease test?

The medium turns bright pink Signup and view all the answers

What does the presence of a diffuse zone in semi-solid agar during the motility test imply?

The bacteria are motile Signup and view all the answers

In the indole test, what does a red color near the top after adding Kovac’s reagent signify?

Tryptophan is hydrolyzed Signup and view all the answers

What is the purpose of the Voges-Proskauer test?

To identify glucose conversion to acetoin Signup and view all the answers

What color indicates a positive citrate utilization test?

Intense blue Signup and view all the answers

What do the letters in the acronym IMViC stand for?

Indole, Methyl, Voges, Citrate Signup and view all the answers

What is indicated by a yellow-brown color in the Voges-Proskauer test?

Negative result for acetoin production Signup and view all the answers

What is the main action of the urease enzyme in the urease test?

Hydrolyzing urea to release ammonia and carbon dioxide Signup and view all the answers

What three possible end products can result from the hydrolysis of tryptophan?

Indole, pyruvic acid, ammonia Signup and view all the answers

Study Notes

Enterobacteriaceae Overview

Enterobacteriaceae is a family of Gram-negative bacilli, comprising 31 genera and over 100 species.
Many members are part of normal gut flora in humans and animals, referred to as enterobacteria or "enteric bacteria."
Other members exist in water, soil, or as parasites in various organisms.

Classification

Enterobacteriaceae is classified as Gram-negative rods, in contrast to Gram-positive bacteria.
Coliform bacteria, such as E. coli and Klebsiella pneumoniae, are always present in the digestive tracts of animals and humans.

Pathogenicity

Enterobacteriaceae are categorized into opportunistic pathogens which can cause infections outside the intestine (e.g., Escherichia, Enterobacter, Citrobacter).

Isolation Media

MacConkey Agar (Mac):
- Lactose fermenters produce pink colonies; non-lactose fermenters appear yellow.
Xylose Lysine Deoxycholate Agar (XLD):
- Isolates Salmonella and Shigella; Salmonella appears as red/pink with black centers, Shigella as red, and coliforms as yellow/orange.
Hektoen Enteric Agar (HE):
- Differentiates Salmonella (blue-green/black colonies) from Shigella (green colonies) and coliforms (yellow/salmon color).
Eosin Methylene Blue Agar (EMB):
- E. coli shows a metallic green sheen; lactose fermenters are brown/pink, while non-fermenters remain the color of the medium.
Cystine Lactose Electrolyte Deficient Agar (CLED):
- Used for urinary isolates; lactose fermenters form yellow colonies, non-fermenters appear blue.

Biochemical Tests for Identification

Indole Test: Indicates ability to decompose tryptophan into indole, detected with Kovac’s reagent.
Methyl Red (MR) Test: Assesses acid production from glucose fermentation.
Voges–Proskauer (VP) Test: Detects acetoin production; a cherry red color indicates a positive result.
Citrate Utilization Test: Assesses the ability to use citrate as a carbon source; bromothymol blue indicates a color change.
Triple Sugar Iron (TSI) Agar Test: Tests for glucose, lactose fermentation, gas production, and H2S formation; black indicates H2S production.
Motility Test: Determines motility based on growth patterns in semi-solid media; motile organisms spread, non-motile remain localized.
Urease Test: Identifies organisms that hydrolyze urea, turning the medium pink if positive.

Additional Tests

Nitrate Reduction Test: Evaluates the ability to reduce nitrate to nitrite.
SIM/MIU Tests: Assess H2S production, indole formation, and motility.

Analytical Techniques

API 20 E System: A microtube strip for rapid identification and differentiation of Enterobacteriaceae members.
Automation Methods: Include VITEK-2 and MALDI-TOF MS for more efficient testing.
Molecular Methods: Techniques such as PCR and real-time PCR offer precise detection of bacteria.

IMViC Tests

IMViC stands for Indole, Methyl Red, Voges-Proskauer, Citrate tests, crucial for the identification of Enterobacteriaceae.

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Description

This quiz covers the key concepts of Enterobacteriaceae from the CLS463 Clinical Bacteriology II lecture by Dr. Ohoud Alhumaidan. Learn about their importance, classification, and identification tests. This is essential for understanding their role in microbiology and medicine.