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KLEBSIELLA - ENTEROBACTER - SERRATIA

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  • KLEBSIELLA - ENTEROBACTER - SERRATIA

    KLEBSIELLA - ENTEROBACTER - SERRATIA
    GROUP

    DEFINITION:
    1- Klebsiella: Gram negative rods, non-motile, aerobic and facultatively anaerobic, catalase positive, oxidase negative, attack sugars fermentatively, usually with gas production, KCN positive, VP positive, ornithine decarboxylase negative, urease positive, phenylalanine negative.
    2- Enterobacter: Gram negative rods, motile, aerobic and facultatively anaerobic, catalase positive, oxidase negative, attack sugars fermentatively, gas is produced, VP positive, gluconate positive, gelatin liquefied slowly, ornithine decarboxylase positive.
    3- Serratia: Gram negative rods, motile, aerobic and facultatively anaerobic, catalase positive, oxidase negative, attack sugars fermentatively, often with gas production, VP usually positive, gluconate positive, ornithine decarboxylase positive, deoxyribonuclease positive, produce a red pigment when grown on suitable media.

    DIFFERENCES OF THE GROUP

    Character Klebsiella
    Enterobacter Serratia
    Motility - + +
    Indole + - -
    Red pigment - - +
    Quellung reaction + - -

    SPECIES:
    1. Klebsiella: Medically important species are:
    a) K. pneumoniae (K. aerogenes is now part of K. pneumoniae).
    b) K. rhinoscleromatis.
    c) K. ozaenae.
    2- Enterobacter: Medically important species are:
    a) E. cloacae.
    b) E. aerogenes.
    3. Serratia: Main species of medical importance is S. marcescens.

    PATHOGENSIS:
    All three organisms produce an endotoxin that leads to septic shock.
    K. pneumoniae produces a large capsule that has an antiphagocytic action. Enterobacter and Serratia are opportunistic organisms.
    EPIDEMIOLOGY:
    1- Predisposing factors to Klebsiella infection are: old age, chronic respiratory disease, diabetes, and alcoholism.
    2- Klebsiella carrier rate in the respiratory tract is 10% of normal people.
    3- Enterobacter and Serratia infections occur mainly inside hospitals, usually following intravenous catheterization, respiratory intubation, and urinary tract procedures.
    4- Serratia infection outbreaks occur after using contaminated water in respirators inside intensive care units.
    ¬
    CLINICAL FINDINGS:
    1- Infections produced by members of the group are UTI, pneumonia, bacteraemia, and meningitis.
    2- K. pneumoniae produces a pneumonia with a thick, bloody sputum that progresses to necrosis and abscess formation.
    3- K. ozaenae, causes atrophic rhinitis.
    4- K. rhinoscleromatis, causes a destructive granuloma of nose and pharynx.

    LABORATORY DIAGNOSIS:
    1- Specimens collected: Urine, sputum, pus, infected tissue.
    2- Microscopy: Gram negative rods:
    a) Klebsiella is non-motile, has a big capsule.
    b) Enterobacter and Serratia are motile, and non-capsulated.
    3- Culture: Media are MacConkey, blood agar. Klebsiella produces mucoid colonies, and lactose fermenters. Enterobacter gives similar colonies as Klebsiella, but not so mucoid. Serratia are non-lactose fermenters. Produce red pigment when grown on nutrient agar at room temperature.
    4- Biochemical reactions: Members of the group are similar in most biochemical reactions. They are differentiated by motility, indole, pigment production, and quellung reaction.
    5- Serology: Using pooled antisera to detect monovalent, specific O and K antigens by slide agglutination.
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