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</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</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</p> Signup and view all the answers

    What is colicin typing used for?

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

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

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

    Which of the following is a characteristic of fimbriae?

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

    What indicates fermentation in selective media?

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

    Which organism is considered a rapid lactose fermenter?

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

    What differentiates non-lactose fermenters from lactose fermenters?

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

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

    <p>Shigella</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</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</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.</p> Signup and view all the answers

    Why are encapsulated Enterobacteriaceae resistant to phagocytosis?

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

    What is antigenic phase variation in Enterobacteriaceae?

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

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

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

    In what way do encapsulated Enterobacteriaceae act as nutritional scavengers?

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

    Which type of antibody primarily interacts with H antigens?

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

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

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

    What color do lactose nonfermenters produce on MacConkey Agar?

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

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

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

    What indicates an E.coli colony on XLD agar?

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

    Who developed MacConkey Agar?

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

    Which characteristic of litmus milk indicates acid production?

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

    Which component is crucial for indole production in MIO medium?

    <p>Tryptophan</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</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.</p> Signup and view all the answers

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

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

    Which organism is expected to grow in KCN Broth Base?

    <p>Citrobacter freundii</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.</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</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.</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.</p> Signup and view all the answers

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

    <p>Shigella</p> Signup and view all the answers

    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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    Enterobacteriaceae: Introduction and Classification PDF

    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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