Enterobacteriaceae Flashcards

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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.

False Signup and view all the answers

What characterizes a third group of Enterobacteriaceae?

Those normally commensal organisms that become pathogenic when they acquire virulence genes present on plasmids, bacteriophages, or pathogenicity islands. Signup and view all the answers

What is the common antigen of Enterobacteriaceae?

Enterobacterial common antigen Signup and view all the answers

How do Enterobacteriaceae grow?

Either motile with peritrichous flagella or nonmotile, and do not form spores. They can grow aerobically and anaerobically. Signup and view all the answers

What are the nutritional requirements of Enterobacteriaceae?

Ferment glucose, reduce nitrate, and are catalase positive and oxidase negative. Signup and view all the answers

Which strains of Enterobacteriaceae are lactose-fermenting?

Escherichia, Klebsiella, Enterobacter, Citrobacter, and Serratia; they produce pink-purple colonies on MacConkey agar. Signup and view all the answers

What characterizes strains that do not ferment lactose or do so slowly?

Proteus, Salmonella, Shigella, and Yersinia spp.; they produce colorless colonies on MacConkey agar. Signup and view all the answers

Which genera show resistance to bile salts?

Shigella, Salmonella Signup and view all the answers

Which strains of Enterobacteriaceae are known for having capsules?

Klebsiella, some Enterobacter and Escherichia strains. Signup and view all the answers

What is important for classifying an organism as a member of the Enterobacteriaceae?

The core polysaccharide Signup and view all the answers

What is significant about the O polysaccharide?

It is important for the epidemiologic classification of strains within a species. Signup and view all the answers

What role does the lipid A component of LPS play?

It is responsible for endotoxin activity, an important virulence factor. Signup and view all the answers

What does the heat-stable lipopolysaccharide (LPS) represent?

The major cell wall antigen Signup and view all the answers

What is the basis of epidemiologic (serologic) classification of the Enterobacteriaceae?

Somatic O polysaccharides, K antigens in the capsule, and H proteins in the bacterial flagella. Signup and view all the answers

How are the antigens of Enterobacteriaceae detected?

Agglutination with specific antibodies. Signup and view all the answers

How can the interference of K antigens with O antigen detection be fixed?

Boiling the organism to remove the heat-labile K antigen and expose the heat-stable O antigen. Signup and view all the answers

Most Enterobacteriaceae are motile.

True Signup and view all the answers

What do common fimbriae facilitate?

The ability of bacteria to adhere to specific host cell receptors. Signup and view all the answers

What does the sex or conjugative pili facilitate?

Genetic transfer between bacteria. Signup and view all the answers

What are some common virulence factors associated with Enterobacteriaceae?

Endotoxin, Capsule, Antigenic phase variation, Type III secretion systems, Sequestration of growth factors, Resistance to serum killing, Antimicrobial resistance. Signup and view all the answers

What initiates many systemic manifestations of gram-negative bacterial infections?

Endotoxin—activation of complement, release of cytokines, leukocytosis, thrombocytopenia, disseminated intravascular coagulation, fever, decreased peripheral circulation, shock, and death. Signup and view all the answers

How are encapsulated Enterobacteriaceae protected from phagocytosis?

By the hydrophilic capsular antigens, which repel the hydrophobic phagocytic cell surface. Signup and view all the answers

What is phase variation in Enterobacteriaceae?

A feature that protects the bacteria from antibody-mediated cell death, where K, H, and O antigens may or may not be expressed. Signup and view all the answers

What is the function of the type III secretion system?

A common effector system for delivering their virulence factors into targeted eukaryotic cells. Signup and view all the answers

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.