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Intro to Enterobacteriaceae
- Morphological characteristics
- Classification
- Biochemical properties
- Determinants of pathogenicity
- Mediums used
- Biochemical tests
- Treatments
ENTEROBACTERIACEAE
Gram staining & Morphology |
Gram-negative non-sporing bacilli |
Motile or non-motile |
Flagella |
Peritrichous or Monotrichous |
Well-defined capsule |
Negatively stained |
Attachment |
Fimbrae or Pili |
Complex cell wall |
Outer Membrane and Thick Peptidoglycan |
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Classification
Family |
Enterobacteriaceae |
Genus |
Escherichia, Shigella, Salmonella, Citrobacter, Klebsiella, Enterobacter, Erwinia, Serratia, Hafnia, Edwardsiella, Proteus, Providencia, Morganella, Yersinia |
Determinants of Pathogenicity
ENDOTOXIN |
Lipopolysaccharide |
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- O polysaccharide |
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- Lipid A (toxic) |
EXOTOXIN |
1. ENTEROTOXIN |
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Subunit A induces cAMP formation |
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- Normal contractions -> severe diarrhea |
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Subunit B attaches to plasma membrane of epithelial cells in small intestine |
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2. SHIGA TOXIN |
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Subunit A modifies RNA to inactivate it |
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- Inhibits protein synthesis by inactivation of 60S ribosomes |
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Subunit B binds to globotriaosylceramide (GB3) |
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3. VEROTOXIN (Shiga-like) |
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Biochemical Properties
Facultative Anaerobes |
Ferments Glucose to Acid |
Lactose Fermenters or Non-Lactose Fermenters |
No Cytochrome Oxidase |
Oxidase Test |
Oxidase negative (colorless) |
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tetramethyl-p-phenylenediamine dihydrochloride -> bacterial colonies -> colorless (-) |
| |
positive reaction = formation of purple ring |
Reduces Nitrate to Nitrite |
Red color (+) |
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