Microbiology of Klebsiella and Enterobacter
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Questions and Answers

What is a key virulence factor associated with Klebsiella pneumoniae?

  • Endotoxin
  • Flagella
  • Exotoxin
  • Polysaccharide capsule (correct)

    • Which of the following reactions is positive for Enterobacter species?

  • Urease test
  • Lactose fermentation test
  • Ornithine decarboxylase test (correct)
  • H₂S production

    • Which species of Enterobacter is specifically known to cause osteomyelitis following traumatic wounds?

  • E.cancerogenus (correct)
  • E.hormaechei
  • E.cloacae
  • E.aerogenes

    • Which test yields a positive result for Cronobacter sakazakii?

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

    What characteristic on MacConkey agar differentiates Enterobacter species?

    <p>Pink color with mucoid appearance</p> Signup and view all the answers

    Which of the following is a common isolate of Enterobacter?

    <p>E.cloacae</p> Signup and view all the answers

    Which statement is correct about the differential tests for Klebsiella pneumoniae?

    <p>Positive for the String test</p> Signup and view all the answers

    Which Salmonella serotype is primarily responsible for causing enteric fever?

    <p>Salmonella serotype Typhi</p> Signup and view all the answers

    Which of the following is true regarding the TSIA reaction of Enterobacter?

    <p>A/A, positive gas, negative H₂S</p> Signup and view all the answers

    Which Salmonella serotype does not produce H₂S?

    <p>Salmonella serotype Paratyphi A</p> Signup and view all the answers

    Which of the following is a common source of infection for acute gastroenteritis caused by Salmonella?

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

    How are carriers of Salmonella typically treated to prevent transmission?

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

    Which Salmonella serotype is involved in outbreaks from contaminated food such as peanut butter crackers?

    <p>Salmonella serotype Typhimurium</p> Signup and view all the answers

    What is the typical infective dose required for Salmonella infection?

    <p>$10^{6}$ bacteria</p> Signup and view all the answers

    What biochemical characteristic is negative for all Salmonella species?

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

    Which test result corresponds to Salmonella serotype Typhi in an IMVIC reaction?

    <ul> <li> <ul> <li> <ul> <li> <ul> <li></li> </ul> </li> </ul> </li> </ul> </li> </ul> Signup and view all the answers

    What is the primary pathogenic effect of Salmonella species in humans?

    <p>Causes enteric fever and acute gastroenteritis.</p> Signup and view all the answers

    Which biochemical test shows positive results for Citrobacter koseri?

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

    What is the most common human isolate of Salmonella?

    <p>S.enterica subsp.enterica</p> Signup and view all the answers

    Which of the following statements about Citrobacter koseri is true?

    <p>It can cause outbreaks of neonatal meningitis.</p> Signup and view all the answers

    What is a virulence factor associated with Salmonella enterica?

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

    In the Triple Sugar Iron Agar (TSIA) test, what result indicates Salmonella species?

    <p>K/A with gas and H₂S production</p> Signup and view all the answers

    What characteristic distinguishes Salmonella bongori from other Salmonella species?

    <p>It was isolated from a lizard in Chad.</p> Signup and view all the answers

    What is the typical culture appearance of Salmonella on MacConkey agar?

    <p>Clear and colorless colonies</p> Signup and view all the answers

    What is the most common agent causing enteric fever?

    <p>Salmonella enterica subsp.enterica serotype Typhi</p> Signup and view all the answers

    Which symptoms are commonly associated with enteric fever?

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

    What is a hallmark of infection in enteric fever?

    <p>The presence of 'rose spots'</p> Signup and view all the answers

    What are the common sources of infection for enteric fever?

    <p>Contaminated food and water</p> Signup and view all the answers

    Which specimen is considered the best for detecting the carrier state of Salmonella serotype Typhi?

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

    What is the mode of transmission referred to as the 'Four F's' in relation to Shigella?

    <p>Flies, fingers, food, and fecal matter</p> Signup and view all the answers

    Which of the following agents can cause bacillary dysentery?

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

    What complication is associated with enteric fever affecting the gallbladder?

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

    What is the mode of acquisition for the bacterium described?

    <p>Ingestion of undercooked seafood and contaminated water</p> Signup and view all the answers

    Which of the following is a common symptom of the related infection caused by this bacterium?

    <p>Secretory diarrhea and neonatal meningitis</p> Signup and view all the answers

    What characteristic differentiates this bacterium from other members of the Enterobacteriaceae?

    <p>It is oxidase-positive</p> Signup and view all the answers

    What is the significance of the Vibriostatic Test O/129 for this bacterium?

    <p>It shows sensitivity</p> Signup and view all the answers

    Under which condition would you see colonies on Inositol-brilliant green-bile salt agar?

    <p>When tested against Aeromonas species</p> Signup and view all the answers

    What biochemical reaction involves a positive IMVIC reaction for this bacterium?

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

    What type of specimens are typically used for laboratory diagnosis of this bacterium?

    <p>Stool, rectal swab, blood, urine, wound discharge, and CSF</p> Signup and view all the answers

    What role do hemolysins and cytotoxins play in this bacterium’s virulence?

    <p>They contribute to tissue damage and inflammatory response</p> Signup and view all the answers

    Study Notes

    Klebsiella

    • Frequent cause of lower respiratory tract infections in hospitalized patients and immunocompromised individuals.
    • Known for causing ventilator-associated pneumonia due to carbapenemase-producing strains.
    • Produces "currant jelly-like" sputum in infected individuals.
    • Possesses a polysaccharide capsule as a virulence factor.
    • Differentiated by a positive string test, Neufeld-Quellung test, growth on media with potassium cyanide, and an IMVIC reaction of - - + +.
    • TSIA reaction: A/A, (+) gas, (-) H₂S.

    Enterobacter

    • Resembles Klebsiella on MacConkey agar.
    • Can cause bacteremia, nosocomial pneumonia, and urinary tract infections.
    • Colonies exhibit a pink color, sometimes mucoid, on MacConkey agar.
    • Grows on media with potassium cyanide.
    • Positive for ornithine decarboxylase and lysine decarboxylase tests (except "E.cloacae" and "E.gergoviae").
    • "E.aerogenes" and "E.cloacae" are positive for sorbitol fermentation.
    • "E.cloacae" is positive for urease and malonate tests.
    • IMVIC reaction: - - + +.
    • TSIA reaction: A/A, (+) gas, (-) H₂S.
    • Significant species include "E.aerogenes," "E.cloacae subsp.cloacae," "E.cancerogenus," and "E.hormaechei."
    • "E.aerogenes" and "E.cloacae" are the most commonly isolated species.
    • "Enterobacter cancerogenus" (formerly "E.taylorae") has been linked to osteomyelitis following traumatic wounds.

    Cronobacter

    • "Cronobacter sakazakii" (formerly "Enterobacter sakazakii")
    • Found as a contaminant in powdered infant formula.
    • Isolated from individuals with brain abscesses, respiratory, and wound infections.
    • Colonies exhibit a pink color on MacConkey agar and yellow pigmentation with a mucoid appearance on BHIA.
    • IMVIC reaction: - - + +.
    • TSIA reaction: A/A, (+) gas, (-) H₂S.

    Pantoea

    • "Pantoea agglomerans" (formerly "Enterobacter agglomerans")
    • Causes nosocomial outbreaks of septicemia due to contaminated IV fluids.
    • Exhibits a triple decarboxylase negative reaction.
    • Colonies are clear or colorless on MacConkey agar and large with a yellow color on BAP.

    Proteus

    • Produces swarming growth on blood agar.
    • Two clinically relevant species: "P.mirabilis" and "P.vulgaris."
    • "P.mirabilis" is indole-negative and "P.vulgaris" is indole-positive.
    • TSIA reactions:
      • "P.mirabilis:" K/A, (+) gas, (+) H₂S.
      • "P.vulgaris:" K/A, (+/-) gas, (+) H₂S.

    Citrobacter

    • "Citrobacter koseri" (formerly "C.diversus")
    • Causes outbreaks of neonatal meningitis and brain abscesses in nursery units.
    • Citrobacter species are differentiated by various biochemical tests.
    • "C.freundii" is indole-negative, H₂S-positive, grows in KCN, and has an IMVIC reaction of +-+ .
    • "C.koseri" is indole-positive, H₂S-negative, does not grow in KCN, and has an IMVIC reaction of +++.
    • TSIA reactions:
      • "C.freundii": A/A, (+) gas, (+) H₂S, or K/A, (+) gas, (+) H₂S.
      • "C.koseri": K/A, (+) gas, (-) H₂S.

    Salmonella

    • Highly pathogenic enterobacteria causing enteric fever (typhoid fever) and acute gastroenteritis (food poisoning).
    • Not part of the human intestinal flora but commensals of the gastrointestinal tract in animals.
    • Transmissible through human carriers.
    • Acquired through ingestion of contaminated animal food products, improperly cooked poultry, milk, eggs, and dairy, and direct human contact.
    • Two species:
      • "S.enterica" (type species) and "S.bongori."
    • Subspecies of "S.enterica":
      • "S.enterica subsp.enterica (I)," "S.enterica subsp.salamae (II)," "S.enterica subsp.arizonae (IIIa)," "S.enterica subsp.diarizonae (IIIb)," "S.enterica subsp.houtenae (IV)," and "S.enterica subsp.indica (VI)."
    • Most common human isolate: "S.enterica subsp.enterica (I)."
    • "S.enterica" possesses fimbriae and enterotoxin as virulence factors.
    • Colonies are clear and colorless on MacConkey agar and colorless with black centers on SSA.
    • Possesses somatic O and flagellar H antigens for serological grouping.
    • "Salmonella serotype Typhi" has a Vi antigen, which is antiphagocytic and may interfere with intracellular killing.
    • "S.bongori" was isolated from a host lizard in Bongor, Chad, Africa, and can also be isolated from other cold-blooded animals.
    • All former species of Salmonella are now designated as serotypes under "S.enterica subsp.enterica" (e.g., "S.enterica subsp.enterica serotype Typhi").
    • Thousands of Salmonella serotypes exist.
    • Examples of Salmonella serotypes include: "Salmonella serotype Typhi," "Salmonella serotype Paratyphi A, B, and C," "Salmonella serotype Choleraesuis," and "Salmonella serotype Typhimurium."
    • "Salmonella serotype Typhi" is the main causative agent of enteric fever.
    • "Salmonella serotype Paratyphi A, B, and C," and "Salmonella serotype Choleraesuis" are etiologic agents of paratyphoid fever.
    • All Salmonella species are motile except "Salmonella serotype Pullorum" and "Salmonella serotype Gallinarum."
    • All species produce gas except "Salmonella serotype Gallinarum" and "Salmonella serotype Typhi."
    • All species produce H₂S except "Salmonella serotype Paratyphi A."
    • LDC: Positive (except "Salmonella serotype Paratyphi A").
    • Urease: Negative.
    • Growth on media with KCN: Negative.
    • IMVIC reaction: - + - -.
              • (Salmonella serotype Typhi).
    • TSIA reaction:
      • K/A, (+) gas, (+) H₂S.
      • K/A, (-) gas, (+) H₂S (Salmonella serotype Typhi).

    General Categories of Salmonella Infection

    • Salmonellae are found in various animals, acting as reservoirs and sources of infections, except "Salmonella serotype Typhi" and "Salmonella serotype Paratyphi."
    • Carriers of Salmonella excrete organisms in their feces, potentially contaminating food if hygiene is compromised or there are issues with water sanitation.
    • Carriers can be treated with antimicrobial therapy if gallbladder infection is not evident.
    • Isolation of Salmonellae on culture plates is diagnostic for typhoid fever.
    • Cholecystectomy may be recommended for chronic enteric carriers.

    1: Acute Gastroenteritis

    • One of the most common forms of food poisoning.
    • Commonly caused by "S.enterica subsp.enterica," originating from animals.
    • "Salmonella serotype Typhimurium" has been linked to outbreaks from contaminated foods like peanut butter crackers and cereals.
    • Sources include poultry products, milk, and pet handling.
    • Dissemination occurs through contaminated kitchen utensils.
    • Infective dose is approximately 10⁶ bacteria.
    • Symptoms: Nausea, vomiting, fever, chills, watery diarrhea, and abdominal pain.

    2. Enteric fever (Typhoid fever)

    • Febrile disease developing from consuming contaminated food prepared by infected individuals or carriers.
    • Transmission can occur through fomites.
    • The gallbladder is the site of long-term carriage.
    • "Salmonella enterica subsp.enterica serotype Typhi" is the most common agent causing enteric fever.
    • Other agents causing enteric fever (paratyphoid fever) include "Salmonella serotype Paratyphi A, B, and C," and "Salmonella serotype Choleraesuis."
    • Sources of infection: Human carriers, food handlers, contaminated food, and water.
    • Outbreaks often occur due to improper sewage disposal, poor sanitation, and lack of clean water supply.
    • Symptoms: Malaise, anorexia, myalgia, and a severe frontal headache.
    • Complications: Necrosis in the gallbladder (necrotizing cholecystitis) and Peyer's patches (lymphoid issues of the bowel).
    • Hallmark of infection: Appearance of "rose spots" during the second week of fever.

    3: Bacteremia

    • Occurs with and without extraintestinal infection caused by non-typhoidal Salmonella species.
    • Characterized by prolonged fever and intermittent bacteremia.
    • Causative agents include "Salmonella serotype Typhimurium," "Salmonella serotype Paratyphi," and "Salmonella serotype Choleraesuis."
    • Optimal specimens for Salmonella identification:
      • Blood: First week of infection.
      • Stool: Second to third week of infection.
      • Urine: Third week of infection.
      • Bone marrow: The best specimen for detecting the carrier state of "Salmonella serotype Typhi."

    Shigella

    • Closely related to Escherichia.
    • Members are not part of human microflora or animal commensals.
    • Non-motile, intracellular pathogens that multiply within intestinal epithelial cells (enterocytes).
    • Most species cause bacillary dysentery.
    • Transmission occurs through the "four F's" (flies, fingers, food, fecal), contaminated food and water from infected persons, and the fecal-oral route.
    • Found in fresh and estuarine water and has been isolated from warm- and cold-blooded animals.
    • "Shigella sonnei" often cross-agglutinates with Shigella.
    • It's the only oxidase-positive member of the Enterobacteriaceae.
    • It is motile by monotrichous or lophotrichous flagella.
    • Isolated from HIV-positive individuals with inflammatory bowel disease.
    • Considered an occupational hazard for veterinarians, fish handlers, and those involved in aquatic sports.
    • Acquired via ingestion of undercooked seafood (oysters and shrimp) and contaminated water; entry can occur through skin cuts.
    • Virulence factors: Hemolysins, cytotoxins, and production of exoenzymes.
    • Microscopy: Straight bacilli occurring singly, in pairs, short chains, or filamentous forms.
    • Sensitive to vibriostatic test O/129.
    • Related infections: Secretory diarrhea, neonatal meningitis, and septicemia.

    Cultural Characteristics

    • Colonies appear shiny, opaque, and non-hemolytic on BAP.
    • Colonies are clear and colorless on MAC, with some strains failing to grow.
    • Colonies exhibit white or green to pink color on inositol-brilliant green-bile salt agar, differentiating from colorless Aeromonas species.
    • Growth occurs on HEA but not on TCBS (TCBS supports growth of Vibrio spp., especially "V.cholerae").
    • Colonies do not grow on media containing NaCl.

    Biochemical and Serological Characteristics

    • Ferments glucose, maltose, and trehalose.
    • Oxidase test: Positive.
    • Positive for trio decarboxylase test, arginine, ornithine, and lysine decarboxylase.
    • Inositol fermentation: Positive.
    • IMVIC reaction: ++--.
    • TSIA reaction: K/A, (-) gas, (-) H₂S.
    • Antigenic determinants: Somatic O and flagellar H.

    Laboratory Diagnosis of Enterobacteriaceae

    • Specimens: Stool, rectal swab, blood, urine, wound discharge, and CSF.
    • Stool specimens are commonly used to isolate Enterobacteriaceae, but not for routine testing unless there are concerns about true intestinal pathogens.
    • Routine stool testing should include culture or toxin detection to identify EHEC.

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