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Questions and Answers

Which organism is characterized by beta-hemolysis and is a coagulase positive pathogen?

  • Staphylococcus epidermidis
  • Streptococcus pneumoniae
  • Streptococcus pyogenes
  • Staphylococcus aureus (correct)

    • Which of the following statements correctly describes Staphylococcus epidermidis?

  • It is characterized by large, clear zones of hemolysis.
  • It is catalase negative and coagulase positive.
  • It is a novobiocin-sensitive opportunistic pathogen. (correct)
  • It is alpha-hemolytic and typically found in chains.

    • What key biochemical test differentiates Streptococcus pyogenes from Streptococcus pneumoniae?

  • Hemolysis pattern
  • Catalase test
  • Bacitracin sensitivity (correct)
  • Coagulase test

    • Which hemolysis pattern is typical for Streptococcus pneumoniae?

    <p>Alpha-hemolytic with optochin sensitivity (A), Alpha-hemolysis (C)</p> Signup and view all the answers

    How are Staphylococcus species primarily differentiated based on their coagulase test results?

    <p>Staphylococcus aureus is coagulase positive. (D)</p> Signup and view all the answers

    What is the colonial morphology of Staphylococcus aureus?

    <p>Golden, creamy colonies (B)</p> Signup and view all the answers

    Which organism is known to cause strep throat infections and is beta-hemolytic?

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

    Which test can determine if a beta-hemolytic streptococci is a pathogen for conditions like rheumatic fever?

    <p>Bacitracin sensitivity test (C)</p> Signup and view all the answers

    Which characteristic distinguishes Staphylococcus saprophyticus from Staphylococcus epidermidis?

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

    What is the significance of the optochin disk test in identifying Streptococcus pneumoniae?

    <p>Assesses sensitivity to optochin (A)</p> Signup and view all the answers

    Which feature characterizes Bacillus anthracis that differentiates it from Bacillus subtilis?

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

    Which factor indicates that Clostridium perfringens is a beta-hemolytic organism?

    <p>Double zone of hemolysis (D)</p> Signup and view all the answers

    What is a distinct biochemical characteristic of Clostridium difficile?

    <p>Production of toxins causing colitis (C)</p> Signup and view all the answers

    Which combination of traits is accurate for Streptococcus agalactiae?

    <p>Catalase negative, beta-hemolytic (D)</p> Signup and view all the answers

    What differentiates alpha-hemolytic streptococci from beta-hemolytic streptococci on blood agar plates?

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

    Which organism is characterized as a common environmental contaminant with a motile characteristic?

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

    Which organism produces a double-zone hemolysis pattern on blood agar?

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

    What biochemical test result would support the identification of Escherichia coli?

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

    Which characteristic is NOT typical for Staphylococcus aureus?

    <p>Gram-negative bacilli (C)</p> Signup and view all the answers

    For Streptococcus pneumoniae, the following test result is expected:

    <p>Alpha hemolytic (C)</p> Signup and view all the answers

    Which of the following organisms is an H2S producer?

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

    Which test is used to differentiate between lactose fermentation among Enterobacteriaceae?

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

    What feature differentiates Providencia stuartii from Proteus species?

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

    Which of the following organisms is non-motile at 42°C?

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

    Which biochemical reaction would be expected for Klebsiella pneumoniae?

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

    Enterobacter cloacae can be identified by which of the following characteristics?

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

    What distinguishes Citrobacter freundii from other Gram-negative bacilli?

    <p>Produces H2S (A)</p> Signup and view all the answers

    Which organism is associated with gas gangrene?

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

    What is a key characteristic of Shigella sonnei?

    <p>Non-motile (C)</p> Signup and view all the answers

    Flashcards

    Staphylococcus aureus Gram Stain

    Gram-positive cocci in clusters; golden, creamy colonies; beta-hemolytic

    Staphylococcus aureus Catalase

    Positive; key for distinguishing from streptococci

    Staphylococcus aureus Coagulase

    Positive; important factor for identification.

    Staphylococcus epidermidis Gram Stain

    Gram-positive cocci in clusters; white non-hemolytic, small colonies; catalase positive, coagulase negative

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    Streptococcus pyogenes Hemolysis

    Beta-hemolytic; distinct clear zone on blood agar

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    Streptococcus pyogenes Catalase

    Negative; distinguishes it from staphylococci

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    Streptococcus pneumoniae Hemolysis

    Alpha-hemolytic; greenish colonies

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    Bacitracin sensitivity test

    Important for distinguishing streptococcus species, like Streptococcus pyogenes

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    Staphylococcus epidermidis

    Gram-positive cocci (clusters) that are non-hemolytic, small colonies, and part of the normal skin flora.

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    Staphylococcus saprophyticus

    Gram-positive cocci (clusters), common UTI pathogen, white non-hemolytic, Catalase +.

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    Streptococcus agalactiae

    Gram-positive cocci (chains), beta-hemolytic, bacitracin-sensitive.

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    Streptococcus pneumoniae

    Gram-positive cocci, alpha-hemolytic, greenish colonies. Optochin-sensitive.

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    Bacillus subtilis

    Gram-positive rods (spore-forming), flat, spreading, rough colonies. Catalase + and motile.

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    Bacillus anthracis

    Gram-positive rods (spore-forming), dry, irregular colonies; non-hemolytic colonies; forms Medusa head colonies. Catalase +, non-motile

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    Clostridium perfringens

    Gram-positive rods (spore-forming), double zone of hemolysis, obligate anaerobe. Causes gas gangrene.

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    Clostridium difficile

    Gram-positive rods (spore-forming), non-hemolytic colonies, anaerobic. Causes pseudomembranous colitis.

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    Escherichia coli (E. coli)

    A gram-negative bacteria commonly found in the human gut, known for beta-hemolysis on blood agar.

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    Klebsiella pneumoniae

    A gram-negative bacterium known for its mucoid colonies and VP positive results.

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    Enterobacter cloacae

    A gram-negative bacterium characterized by yellow XLD colonies and positive ODC.

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    Citrobacter freundii

    Gram-negative bacterium, characterized by yellow or colorless XLD colonies with black centers, positive ONPG and H2S.

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    Serratia marcescens

    A gram-negative bacterium known for pink colonies and the production of red pigment prodigiosin.

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    Proteus mirabilis

    Gram-negative bacterium, characterized by colorless colonies on XLD, urease positive and H2S production.

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    Proteus vulgaris

    Gram-negative bacterium with yellow or colorless XLD colonies, positive TDA and indole.

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    Providencia stuartii

    Gram-negative bacterium characterized by yellow or colorless XLD colonies, positive for indole and citrate.

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    Morganella morganii

    Gram-negative bacterium with yellow or colorless XLD colonies, positive for urease and TDA.

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    Salmonella enteritidis

    Gram-negative bacterium known for red colonies on XLD with black centers, positive for H2S and citrate.

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    Shigella sonnei

    Gram-negative bacterium known for red XLD colonies and characteristically non-motile and indole negative.

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    Yersinia enterocolitica

    Gram-negative bacterium that is motile at a specific temperature, characterized by urease positive and variable indole.

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    Pseudomonas aeruginosa

    Gram-negative bacterium with beta-hemolysis, positive oxidase, known for green/blue colonies and fruity odor.

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    Study Notes

    Gram-Positive Cocci I

    • Staphylococcus aureus: Gram-positive cocci (clusters), golden, creamy colonies, beta-hemolytic, catalase-positive, coagulase-positive. Associated with skin infections, beta-hemolysis is visible on blood agar plates (BAP).
    • Staphylococcus epidermidis: Gram-positive cocci (clusters), white, non-hemolytic, small colonies, catalase-positive, coagulase-negative. Opportunistic pathogen, found on the skin.
    • Streptococcus pyogenes: Gram-positive cocci (chains), large, clear zone of beta-hemolysis, catalase-negative, beta-hemolytic, bacitracin-sensitive. Causes strep throat and pyogenic infections.
    • Streptococcus pneumoniae: Gram-positive cocci (pairs/chains), alpha-hemolysis, greenish colonies, catalase-negative, alpha-hemolytic. Commonly associated with pneumonia and meningitis, optochin sensitivity test is required for confirmation.

    Gram-Positive Cocci II

    • Staphylococcus aureus: Gram-positive cocci (clusters), golden, creamy colonies, beta-hemolytic, catalase-positive, coagulase-positive. Similar to Lab 1, test novobiocin to rule out S. saprophyticus.
    • Staphylococcus epidermidis: Gram-positive cocci (clusters), white, non-hemolytic, small colonies, catalase-positive, coagulase-negative. Part of normal skin flora, distinguished from S. saprophyticus by novobiocin sensitivity.
    • Streptococcus pyogenes: Gram-positive cocci (chains), large, clear zone of beta-hemolysis, catalase-negative, beta-hemolytic..Important to differentiate from S. agalactiae (Group B streptococcus) which is bacitracin-resistant.
    • Streptococcus pneumoniae: Gram-positive cocci (pairs/chains), alpha-hemolysis, greenish colonies, catalase-negative, alpha-hemolytic. Similar to Lab 1.

    Gram-Positive Bacilli

    • Bacillus subtilis: Gram-positive rods (spore-forming), flat, spreading, rough colonies, catalase-positive, spore-former, motile. Environmental contaminant, rarely pathogenic, beta-hemolytic on BAP.
    • Bacillus anthracis: Gram-positive rods (spore-forming), dry, irregular colonies, catalase-positive, non-motile. Associated with anthrax.
    • Clostridium perfringens: Gram-positive rods (spore-forming), double zone of hemolysis, catalase-negative, beta-hemolytic. Obligate anaerobe, spore former, causes gas gangrene.
    • Clostridium difficile: Gram-positive rods (spore-forming), yellow, non-hemolytic colonies, catalase-negative, anaerobic, spore former. Produces toxins causing pseudomembranous colitis.

    Gram-Negative Cocci

    • Neisseria meningitidis: Gram-negative diplococci, gamma-hemolytic, gray, convex colonies on BAP, oxidase-positive; ferments glucose and maltose.
    • Neisseria gonorrhoeae: Gram-negative diplococci, no growth on BAP, small, gray-white, shiny colonies on CHOC, oxidase-positive; ferments glucose only.
    • Moraxella catarrhalis: Gram-negative diplococci, gamma-hemolytic, smooth, opaque gray colonies on BAP. oxidase-positive, asaccharolytic.

    Gram-Negative Coccobacilli

    • Haemophilus influenzae: Gram-negative coccobacilli, large, translucent, moist colonies on CHOC, pungent odor, similar to H. parainfluenzae, which also contains pungent odor. Requires both X and V factors.
    • Haemophilus parainfluenzae: Gram-negative coccobacilli, similar to H. influenzae,requires V factor only, ALA positive.

    Gram-Negative Rods (Enterobacteriaceae)

    • E. coli: Oxidase negative, ONPG positive, indole positive, ferments glucose, lactose, trehalose, xylose, non-H2S producer.
    • Klebsiella pneumoniae: Oxidase negative, VP positive, non-motile, citrate positive, indole negative (variable in some strains).
    • Enterobacter cloacae: Oxidase negative, VP positive, motile, citrate positive, indole negative (variable in some strains).
    • Citrobacter freundii: Oxidase negative, VP positive, citrate positive, indole variable.
    • Serratia marcescens: Oxidase negative, VP positive, motile, produces red pigment.
    • Proteus mirabilis: Oxidase negative, VP positive, motile, TDA positive (deaminase activity), indole negative.
    • Proteus vulgaris: Oxidase negative, VP positive, motile, urease positive, TDA positive, indole positive.
    • Providencia stuartii: Indole positive, citrate positive; urease variable.
    • Morganella morganii: Urease positive, TDA positive, indole positive.
    • Salmonella enteritidis: Indole positive, H2S producer, citrate positive, urease negative.
    • Shigella sonnei: Non-motile, indole negative.
    • Yersinia enterocolitica: Motile at 22°C, urease positive, indole variable.

    Gram-Negative Bacilli - Non-Fermenters

    • Pseudomonas aeruginosa: GNB, beta-hemolytic, metallic blue/green sheen, fruity odor; oxidase-positive, K/K or K/NC.
    • Stenotrophomonas maltophilia: GNB, large, smooth colonies with uneven edges, lavender-green tinge, oxidase-negative.
    • Acinetobacter baumannii: Small GNB or coccobacillus, smaller than Enterobacteriaceae; smooth, opaque, creamy gray-white colonies, oxidase-negative.

    Anaerobes

    • Bacteroides fragilis: Pleomorphic, Gram-negative rod, non-hemolytic, gray colonies with black pigment.
    • Clostridium perfringens: GPB, large rods, double-zone beta hemolysis, translucent colonies; anaerobic; produces toxins, associated with gas gangrene.
    • Clostridium difficile: GPB, large rods, non-hemolytic, yellow colonies, obligate anaerobe. produces toxins (pseudomembranous colitis).

    Candida spp.

    • Candida tropicalis: Large, Gram-positive, ovoid yeast cells, cream-colored, dull, smooth colonies with wrinkled appearance; germ tube negative.
    • Candida albicans: Large, Gram-positive, ovoid yeast cells, creamy, pasty colonies, smooth after 24-48 hours; germ tube positive

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