Questions and Answers
What are the methods used to classify these genera?
biochemical properties, antigenic structure, DNA-DNA hybridization, and 16S rRNA sequencing
What diseases are caused by Enterobacteriaceae?
Human diseases, including one third of all bacteremias, more than 70% of urinary tract infections (UTIs), and many intestinal infections.
Salmonella serotype Typhi, Shigella species, and Yersinia pestis are associated with human disease.
True
Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis are only seen as pathogens.
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What characterizes a third group of Enterobacteriaceae?
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What is the common antigen of Enterobacteriaceae?
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How do Enterobacteriaceae grow?
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What are the nutritional requirements of Enterobacteriaceae?
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Which strains of Enterobacteriaceae are lactose-fermenting?
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What characterizes strains that do not ferment lactose or do so slowly?
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Which genera show resistance to bile salts?
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Which strains of Enterobacteriaceae are known for having capsules?
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What is important for classifying an organism as a member of the Enterobacteriaceae?
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What is significant about the O polysaccharide?
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What role does the lipid A component of LPS play?
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What does the heat-stable lipopolysaccharide (LPS) represent?
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What is the basis of epidemiologic (serologic) classification of the Enterobacteriaceae?
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How are the antigens of Enterobacteriaceae detected?
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How can the interference of K antigens with O antigen detection be fixed?
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Most Enterobacteriaceae are motile.
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What do common fimbriae facilitate?
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What does the sex or conjugative pili facilitate?
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What are some common virulence factors associated with Enterobacteriaceae?
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What initiates many systemic manifestations of gram-negative bacterial infections?
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How are encapsulated Enterobacteriaceae protected from phagocytosis?
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What is phase variation in Enterobacteriaceae?
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What is the function of the type III secretion system?
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Study Notes
Classification of Enterobacteriaceae
- Classified based on biochemical properties, antigenic structure, DNA-DNA hybridization, and 16S rRNA sequencing.
- Distinction made due to diverse pathogenic capabilities.
Human Diseases Caused
- Responsible for approximately one-third of all bacteremias.
- Account for over 70% of urinary tract infections (UTIs).
- Include numerous intestinal infections.
Pathogenic vs. Commensal Organisms
- Salmonella serotype Typhi, Shigella species, and Yersinia pestis are always linked to human disease.
- Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis are normally commensal but can lead to opportunistic infections.
Pathogenicity Acquisition
- Commensal organisms may become pathogenic after acquiring virulence genes via plasmids, bacteriophages, or pathogenicity islands.
Antigens
- Enterobacterial common antigen serves as a common antigen among this family.
- Key to serological classification includes O polysaccharides, K antigens, and H proteins.
Growth and Characteristics
- Enterobacteriaceae can be motile with peritrichous flagella or nonmotile; spores are not formed.
- Aerobically and anaerobically grown on nonselective (e.g., blood agar) and selective media (e.g., MacConkey agar).
- Nutritional requirements are simple; they ferment glucose, reduce nitrate, are catalase-positive, and oxidase-negative.
Lactose Fermentation
- Lactose-fermenting strains include Escherichia, Klebsiella, Enterobacter, Citrobacter, and Serratia, which produce pink-purple colonies on MacConkey agar.
- Non-lactose-fermenting strains like Proteus, Salmonella, Shigella, and Yersinia spp. yield colorless colonies on MacConkey agar.
Resistance and Virulence
- Shigella and Salmonella exhibit resistance to bile salts.
- Klebsiella and some Enterobacter and Escherichia strains possess capsules that protect against phagocytosis.
- Lipid A in LPS is crucial for endotoxic activity and as a virulence factor.
Serologic Classification
- The epidemiologic classification is performed based on antigen types: somatic O polysaccharides, K antigens, and H flagellar proteins.
- Antigen detection is achieved through agglutination with specific antibodies.
Adherence and Genetic Transfer
- Common fimbriae enhance adherence to host cell receptors.
- Sex pili facilitate genetic transfer between bacterial cells.
Common Virulence Factors
- Include endotoxin, capsule, antigenic phase variation, type III secretion systems, growth factor sequestration, serum resistance, and antimicrobial resistance.
Endotoxin Effects
- Systemic manifestations of gram-negative infections feature activation of complement, cytokine release, leukocytosis, thrombocytopenia, and potentially lead to shock and death.
Encapsulation Impact
- Encapsulated strains are shielded from phagocytosis due to hydrophilic capsular antigens that repel phagocytic cells.
Phase Variation
- Offers protection from antibody-mediated cell death, as K, H, and O antigens may vary in expression.
Type III Secretion System
- Serves as a common mechanism for delivering virulence factors into eukaryotic cells, crucial for pathogenicity.
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Test your knowledge on Enterobacteriaceae with these flashcards. Explore their biochemical properties, diseases they cause, and key genera. This quiz is perfect for students studying microbiology or related fields.