Microbiology Enterobacteriaceae Quiz
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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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