Microbiology Enterobacteriaceae Quiz
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Questions and Answers

Which of the following genera is NOT listed as a new genus in the family Enterobacteriaceae?

  • Cedecea
  • Budivicia
  • Obesumbacteri
  • Klebsiella (correct)

What type of infections can E. coli cause in susceptible patients?

  • Opportunistic infections (correct)
  • Primarily skin infections
  • Only gastrointestinal infections
  • Only respiratory infections

What is the role of colicins in bacteria?

  • They are bactericidal proteins that attack closely related strains (correct)
  • They assist in forming biofilms
  • They enhance bacterial reproduction
  • They act as enzymes to digest food

How do infections from Enterobacteriaceae typically originate?

<p>From animal reservoirs, human carriers, or endogenous spread (C)</p> Signup and view all the answers

What function do plasmids have in colicin-producing strains?

<p>They encode the bacteriocins and control their production (A)</p> Signup and view all the answers

Which of these is an example of a genera that is associated with disease in humans?

<p>Salmonella (A)</p> Signup and view all the answers

What is colicin typing used for?

<p>As an epidemiologic tool for typing organisms (A)</p> Signup and view all the answers

What percentage of urinary tract infections (UTIs) is caused by Enterobacteriaceae?

<p>More than 70% (B)</p> Signup and view all the answers

What is the size range of the described Gram (-) bacilli?

<p>0.3 to 1.0 µm x 1.0-6.0 µm (C)</p> Signup and view all the answers

Which of the following is a characteristic of fimbriae?

<p>Assist in attachment through adhesins (C)</p> Signup and view all the answers

What indicates fermentation in selective media?

<p>Color change in the medium (A)</p> Signup and view all the answers

Which organism is considered a rapid lactose fermenter?

<p>Escherichia coli (B)</p> Signup and view all the answers

What differentiates non-lactose fermenters from lactose fermenters?

<p>The color of the colonies (A)</p> Signup and view all the answers

Which of the following bacteria is known to resist bile salts?

<p>Shigella (B)</p> Signup and view all the answers

What is a characteristic of Klebsiella compared to other species in the family?

<p>It has a prominent capsule (A)</p> Signup and view all the answers

Which of the following is NOT a characteristic of the mentioned Gram (-) bacilli?

<p>Ability to form spores (B)</p> Signup and view all the answers

What role does the Lipid A component of LPS play in gram-negative bacterial infections?

<p>It is responsible for systemic manifestations. (C)</p> Signup and view all the answers

Why are encapsulated Enterobacteriaceae resistant to phagocytosis?

<p>Capsules interfere with antibody binding. (B)</p> Signup and view all the answers

What is antigenic phase variation in Enterobacteriaceae?

<p>Certain antigens can be alternately expressed or not expressed. (A)</p> Signup and view all the answers

Which of the following is a common virulence factor among Enterobacteriaceae?

<p>Endotoxin activity. (C)</p> Signup and view all the answers

How do K antigens interact with other bacterial types?

<p>Some cross-react with polysaccharides of other bacteria. (C)</p> Signup and view all the answers

In what way do encapsulated Enterobacteriaceae act as nutritional scavengers?

<p>They absorb nutrients from their host. (D)</p> Signup and view all the answers

What is the significance of antibody development against capsular antigens?

<p>It diminishes the protective role of the capsule. (B)</p> Signup and view all the answers

Which type of antibody primarily interacts with H antigens?

<p>IgG. (C)</p> Signup and view all the answers

What is the purpose of heavily inoculating Selenite F or Gram Negative Broth?

<p>To enrich a small portion of the specimen (C)</p> Signup and view all the answers

How soon must you subculture from Selenite Broth for salmonella isolation?

<p>Within 8-12 hours (C)</p> Signup and view all the answers

What color do lactose nonfermenters produce on MacConkey Agar?

<p>Colorless colonies (A)</p> Signup and view all the answers

Which of the following properties is true for E.coli on EMB agar?

<p>It exhibits a greenish metallic sheen (B)</p> Signup and view all the answers

Which medium is selective for isolating Salmonella spp. and Shigella spp.?

<p>Hektoen Enteric Agar (C)</p> Signup and view all the answers

What indicates an E.coli colony on XLD agar?

<p>Changed to color at the upper part (C)</p> Signup and view all the answers

Which of the following statements about Gram Negative Broth is correct?

<p>It enhances recovery of Salmonella in small numbers (D)</p> Signup and view all the answers

Who developed MacConkey Agar?

<p>Alfred Theodore MacConkey (D)</p> Signup and view all the answers

What indicates a positive reaction in the phenylalanine deaminase test?

<p>Appearance of a light to deep-green color (A)</p> Signup and view all the answers

What happens to the litmus milk when an alkaline pH is achieved?

<p>It changes to a purplish-blue color (C)</p> Signup and view all the answers

What differentiates motile organisms from non-motile organisms in the MIO medium?

<p>Cloudiness or turbidity throughout the medium (D)</p> Signup and view all the answers

Which characteristic of litmus milk indicates acid production?

<p>Pink to red color change (B)</p> Signup and view all the answers

What is a limitation of using litmus milk as a medium?

<p>It can yield unreliable and diverse results (A)</p> Signup and view all the answers

What does the appearance of bubbles in coagulated milk during the litmus milk test signify?

<p>Gas production during fermentation (B)</p> Signup and view all the answers

Which component is crucial for indole production in MIO medium?

<p>Tryptophan (A)</p> Signup and view all the answers

How can the media help in the identification of microbial species?

<p>Through differentiation of gram-negative bacilli and enterics (C)</p> Signup and view all the answers

What is the principle of KCN Broth Base in differentiating enteric bacilli?

<p>It facilitates the recognition of slow fermentative bacilli. (A)</p> Signup and view all the answers

Which of the following provides essential growth nutrients in KCN Broth Base?

<p>Proteose peptone (C)</p> Signup and view all the answers

Which organism is expected to grow in KCN Broth Base?

<p>Citrobacter freundii (D)</p> Signup and view all the answers

What characteristic is true for Salmonella in the context of KCN broth?

<p>It does not produce enzymes resistant to KCN. (A)</p> Signup and view all the answers

What is the appropriate temperature and duration for incubating KCN Broth Base?

<p>37°C for 24-48 hours (D)</p> Signup and view all the answers

What is a critical consideration when inoculating KCN Broth Base?

<p>Ensuring the inoculum is light to avoid misinterpretation. (C)</p> Signup and view all the answers

Which of the following statements is true regarding the storage of prepared KCN Broth Base?

<p>It should be stored at 2 - 25°C shielded from light. (B)</p> Signup and view all the answers

Which organism is NOT expected to grow in KCN Broth Base?

<p>Shigella (D)</p> Signup and view all the answers

Flashcards

Enterobacteriaceae Family

A family of bacteria that includes many disease-causing species.

Citrobacter

A genus within the Enterobacteriaceae family.

Septicemia

Blood poisoning caused by bacteria.

UTI

Urinary Tract Infection.

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Opportunistic Infections

Infections that happen when a normal part of your body's flora harms you.

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Colicins

Bactericidal substances produced by certain bacteria.

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Bacteriocins

Bactericidal substances produced by bacteria.

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Colicin Typing

Using colicins to identify different strains of bacteria.

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Endogenous Transmission

Spread of an infection from a patient's own bacteria within their body.

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Nosocomial Infection

Infection acquired in a hospital setting.

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Enterobacteriaceae Family

A family of bacteria, often associated with the intestinal tract of animals

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Gram-negative bacilli

Rod-shaped bacteria that do not retain the crystal violet stain in the Gram stain method.

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Facultative anaerobe

An organism that can survive with or without oxygen.

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Fimbriae

Short, bristle-like fibers on bacterial surfaces, aiding attachment to surfaces or other bacteria.

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Lactose fermenters

Bacteria capable of breaking down lactose, a sugar.

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Colonial Characteristics

Identifying bacteria based on their colony appearance on different growth mediums.

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Hektoen Enteric Agar (HE)

Selective medium used in bacterial identification, specifically for the Enterobacteriaceae family.

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Xylose Lysine Desoxycholate (XLD)

A selective medium used to differentiate bacteria by observing colony characteristics.

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Bile salt resistance

Ability of some bacteria to withstand bile, a substance in the digestive system.

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Capsule

A protective layer surrounding some bacteria.

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Antigenic variation in flagella

The ability of a bacteria to change the type of its flagella, thus preventing the host's immune system from recognizing it.

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H Antigen

A type of flagellar antigen in bacteria capable of causing agglutination with Anti-H antibody (mainly IgG).

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Endotoxin

A virulence factor found in Gram-negative bacteria. Its activity depends on the Lipid A component of LPS (lipopolysaccharide), released during cell lysis.

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Capsule (bacteria)

A protective layer surrounding some bacteria, preventing phagocytosis by interfering with antibody binding and complement activation.

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Antigenic Phase Variation

A bacterial mechanism that alters the expression of capsular (K) and flagellar (H) antigens, providing protection from antibody-mediated lysis.

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Sequestration of Growth Factors

Bacteria's ability to acquire nutrients in the body (in-vivo) to grow, distinct from the nutrients in enriched culture media.

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Overlapping antigenic structures

Similar antigens exist between Enterobacteriaceae and other bacteria, including shared antigens between different bacterial species.

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GN Enrichment Broth

A broth used to enrich samples for Salmonella and Shigella, inhibiting the growth of other bacteria.

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Selenite F

A selective medium used to isolate Salmonella from specimens with high amounts of mixed bacteria, inhibiting E. coli and other coliforms.

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McConkey Agar

A selective and differential medium used to isolate Gram-negative bacteria, differentiating between lactose fermenters and non-fermenters.

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MacConkey Agar - Lactose Fermenters

Bacteria that ferment lactose on McConkey Agar produce red colonies.

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MacConkey Agar - Lactose Non-Fermenters

Bacteria that don't ferment lactose on McConkey Agar produce colorless colonies.

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Hektoen Enteric Agar (XLD)

A selective medium for isolating Salmonella and Shigella, differentiating between them based on colony characteristics.

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XLD Agar - Salmonella Colonies

Salmonella colonies on XLD agar appear pink with a black center.

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XLD Agar - E.Coli Colonies

E. coli colonies on XLD agar show a color change in the upper part of the plate.

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Incubation of plates

Plates are incubated at 35 degrees celsius between 24-48 hours to allow growth of bacteria.

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KCN Broth

A lab medium used to differentiate enteric bacteria, like Citrobacter freundii, based on their response to cyanide (KCN).

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Litmus Milk Test

A microbiological test used to differentiate bacteria, mainly Enterobacteriaceae, Clostridium, and lactic acid bacteria, based on their reactions with litmus milk.

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Salmonella sensitivity

Salmonella bacteria typically do not grow in KCN broth.

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Acid pH in Litmus Milk

Litmus milk turns pink to red when the pH is acidic.

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Alkaline pH in Litmus Milk

Litmus milk turns purplish-blue when the pH is alkaline.

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Enteric bacilli

A broad group of bacteria found in the intestines of warm-blooded animals.

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Reduction in Litmus Milk

A white color change in litmus milk indicates reduction.

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KCN Test Result – Growth

The presence of growth in KCN broth usually indicates the presence of Enterobacter, Klebsiella, Proteus, Citrobacter, Providencia, or Hafnia.

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Acid Curd

A hard curd with a clear liquid supernatant (whey) in litmus milk indicates acid formation.

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KCN Test Result – No Growth

The absence of growth, in the KCN broth, would suggest Escherichia, Arizona, Salmonella, or Shigella bacteria, typically showing sensitivity to KCN.

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Citrobacter freundii

A particular type of enteric bacillus with enzymes that tolerate cyanide making it grow in KCN Broth

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Digestion (Litmus milk)

The dissolution of a clot, yielding a clear, grayish, watery fluid, and a shrunken, insoluble pink clot in litmus milk.

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Rennet Curd

Litmus milk forms a soft curd that later peptonizes (becomes alkaline, with brown supernatant).

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Salmonella arizonae group

A group of bacteria similar to Salmonella that are also typically sensitive to KCN in lab mediums.

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Escherichia

Bacteria of the Escherichia genus known to be affected by KCN and not grow in KCN broth.

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Gas Production (Litmus milk)

Bubbles forming in the coagulated milk, indicating gas production.

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Clinical lab use of KCN Test

Not commonly used in clinical labs because of KCN's hazardous nature.

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Phenylalanine Deaminase Test

A test to determine if bacteria can produce the enzyme phenylalanine deaminase, resulting in a green color.

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MIO Medium

A medium used for motility, indole production, and ornithine decarboxylation tests on bacteria.

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Bacterial Motility

The ability of bacteria to move on their own using flagella.

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Study Notes

Enterobacteriaceae

  • Family of medically important Gram-negative bacilli
  • Largest and most heterogeneous group of bacteria
  • 63 genera defined, 20-25 are clinically significant
  • Classified based on DNA homology, biochemical properties, and antigenic structures
  • Susceptibility to genus and species-specific bacteriophages, nucleic acid hybridization, and sequencing, and antibiotic susceptibility patters
  • Gram-negative bacilli, rounded ends, 0.3-1.0 µm x 1.0-6.0 µm (sometimes coccobacilli)
  • Facultatively anaerobic, non-spore-forming
  • Some with polar flagella, catalase-positive, oxidase-negative, reduce nitrate to nitrite, acid production from glucose fermentation
  • Simple nutritional requirements
  • Worldwide in soil, water, and vegetation—part of normal intestinal flora of most animals, including humans

Clinical Significance

  • Frequently encountered in clinical labs
  • Associated with infections in various parts of the human body
  • Some are strict pathogens, while others are opportunistic pathogens
  • Enterobacter named for its location in the intestines of animals
  • Includes Salmonella, Escherichia coli, Yersinia pestis, Klebsiella, Shigella
  • Can cause eye, skin, meningitis, bacteremia, pneumonia, and urinary tract infections

Human Infections

  • Infections from lapses in personal hygiene, poor sanitation, or colonization of skin/respiratory tract of hospitalized patients
  • Ingestion of contaminated food, water
  • Nosocomial transmission from contact with patients, contaminated medical instruments
  • Endogenous infections from normal flora

Additional Features

  • Four major features: ferment glucose (often with gas formation), reduce nitrates to nitrites (except Erwinia and Pantoea), are cytochrome oxidase negative (except Plesiomonas), and are motile (except Klebsiella, Shigella, and Yersinia)
  • Oxidase reaction important to distinguish Enterobacteriaceae from gram-negative, non-fermenters
  • Harbor chromosomal elements encoding colicins/bacteriocins, high molecular weight bactericidal proteins active against strains of the same species; production controlled by plasmids

Antigenic Structures

  • Complex antigenic structure

  • Classified by heat-stable somatic antigens (>150), heat-labile capsular antigens (>100), and flagellar antigens (>50).

  • Kauffman-White Classification used to classify Salmonella based on O and H antigens (exceeds 2000 serovars).

  • Somatic (O Ag) antigen, a key LPS component on gram-negative bacteria, is variable, along with core polysaccharide. Lipid A is present in all enterics.

    • O antigens linked to specific human diseases (e.g., E. coli O antigen in diarrhea and UTI).

  • Capsular (K Ag) antigen—heat labile protein or polysaccharide; often associated with increased virulence; inhibits agglutination with specific O antisera. This must be boiled for 30 minutes to detect O antigen.

  • Flagellar (H Ag) antigen—protein; heat-labile

Virulence Factors

  • Endotoxin (LPS): A virulence factor shared by all aerobic and some anaerobic Gram-negative bacilli; its Lipid A component initiates many systemic manifestations of Gram-negative bacterial infections such as complement activation, DIC, thrombocytopenia, shock, and death (released during cell lysis)
  • Capsule: Protects encapsulated enterics from phagocytosis by repelling hydrophobic phagocytic cells. Protects from antibody mediated lysis.
  • Antigenic phase variation: The expression of the capsular K and flagellar H antigens is genetically controlled and can be alternately expressed. Prevents from antibody mediated lysis.
  • Sequestration of growth factors: Bacteria can be nutritional scavengers in vivo; obtains iron by binding to heme proteins (such as hemoglobin )or iron-chelating proteins.

Resistance to Serum Killing

  • Capsule can protect the organisms from serum killing. Other unidentified components prevent complement binding.
  • Antimicrobial Resistance: Many enterics have developed resistance, particularly to, beta-lactam antibiotics (resulting in high cost and limited treatments), ESBLs and ABLs

Enterotoxins

  • Bacterial substances causing diarrhea by influencing the small intestine

Laboratory Diagnosis

  • Specimen Collection and Transport: Use appropriate media for isolation of both opportunistic and fastidious pathogens; stool cultures are commonly used.
  • Direct microscopic examination: Gram-stained smears of fecal specimens; helps clinicians to diagnose infections for targeted treatment.
  • Culture: Use non-selective media (BAP/Chocolate Agar), selective/differential media (MacConkey, EMB, HE, XLD), and enrichment broths (Selenite, GN)
  • Biochemical tests: Indole, Methyl Red, Voges-Proskauer, Citrate, Urease, Motility, Malonate, Phenylalanine Deaminase, ONPG, KCN
  • Selective media examples: MacConkey, Eosin Methylene Blue (EMB), Desoxycholate Citrate Agar (DCA), Endo Agar.
  • Highly selective media examples: Hektoen Enteric Agar (HE), Brilliant Green Agar, Bismuth Sulfite Agar (BS), XLD

Other Important Information

  • Classification of Enterobacteriaceae based on lactose fermentation is useful
  • Phage typing is possible for identification of Salmonella variants

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Description

Test your knowledge on the Enterobacteriaceae family, including various genera, their roles in infections, and specific characteristics of E. coli. This quiz covers the diverse aspects of pathogenic bacteria and their implications in human health, including colicin production and urinary tract infections.

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