Questions and Answers
Which of these groups of organisms are included in the Enterobacteriaceae family?
Why are the Enterobacteriaceae important?
They are ubiquitous organisms found in soil, vegetation, and water; they cause over 70% of UTIs and intestinal issues, and some are opportunistic pathogens.
What does CRE stand for?
Carbapenem-resistant Enterobacteriaceae
Which of the following are common medically important Enterobacteriaceae?
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All Enterobacteriaceae are gram-positive.
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Most Enterobacteriaceae are ____ with several exceptions.
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What structure is primarily responsible for the virulence of many Enterobacteriaceae?
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What unique feature characterizes the cell wall of Enterobacteriaceae?
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What are the growth characteristics of Enterobacteriaceae?
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Match the following biochemical tests with their purpose in identifying Enterobacteriaceae:
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What is MacConkey agar used for?
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What is a key virulence factor of Enterobacteriaceae?
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Capsules are not found in Enterobacteriaceae.
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Study Notes
Importance of Enterobacteriaceae
- Ubiquitous in soil, vegetation, and water worldwide
- Responsible for over 70% of urinary tract infections (UTIs) and intestinal diseases
- Some species, like E. coli, Klebsiella, and Proteus mirabilis, are normal flora that can become opportunistic pathogens
Carbapenem-Resistant Enterobacteriaceae (CRE)
- Multidrug-resistant, particularly carbapenem-resistant strains
- Emerging as a significant global health threat
Common Medically Important Enterobacteriaceae
- Includes:
- Citrobacter freundii
- Citrobacter koseri
- Enterobacter aerogenes
- Enterobacter cloacae
- Escherichia coli
- Klebsiella pneumoniae
- Morganella morganii
- Proteus mirabilis
- Salmonella enterica (including Typhi, Paratyphi, Typhimurium)
Structural Features of Enterobacteriaceae
- All are Gram-negative rods, non-spore forming
- Lipopolysaccharides (LPS) constitute major cell wall antigen
- Identified by somatic O polysaccharides, capsular K antigens, and flagellar H proteins
Motility of Enterobacteriaceae
- Majority are motile, except for Klebsiella, Shigella, and Yersinia
- Motile species typically possess peritrichous flagella
- Some exhibit swarming behavior
Presence of Fimbriae
- Possess fimbriae (pili), essential for adhesion to host cell receptors
- Common pili are chromosomally encoded; sex pili are plasmid-encoded
Unique Cell Wall Characteristics
- Gram-negative structure with LPS as an endotoxin
- Features a small amount of peptidoglycan, partly resistant to lysozyme
- Increased resistance to antibiotics, particularly penicillin and other beta-lactams, due to outer membrane and porins
Growth Characteristics
- All are facultative anaerobes, utilizing carbohydrates
- Most ferment glucose; some lactose fermenters produce pink colonies on MacConkey agar
- Many enteric pathogens show resistance to bile salts
Biochemical Tests for Identification
- Tests include:
- Indole test
- Voges-Proskauer
- Citrate utilization
- KIA (Kligler's Iron Agar)
- SIM (Sulfide Indole Motility) media
- IMVIC tests
- All are oxidase negative, catalase positive, and reduce nitrate
Fermentation Capabilities
- All Enterobacteriaceae ferment glucose, but not all Gram-negative bacteria do
- Lactose fermentation is seen in specific genera, including Klebsiella, E. coli, Enterobacter, and slow fermenters like Citrobacter
MacConkey Agar
- Contains bile salts and crystal violet to inhibit Gram-positive bacteria
- Lactose fermentation leads to acid production, turning crystal violet pink
- E. coli is a strong lactose fermenter; Salmonella and Shigella do not ferment lactose
EMB (Eosin Methylene Blue) Media
- Inhibits Gram-positive growth; lactose fermentation produces a purple coloration or green sheen in cases of high lactose fermentation
Endotoxin as a Virulence Factor
- Lipid A part of LPS responsible for biological activity of endotoxin
- Released during cell lysis, triggering immune responses that can lead to fever, shock, and potentially death
Capsule as a Virulence Factor
- Capsules are notable in Klebsiella, Enterobacter, and E. coli; some possess a loose, diffusible slime layer
- Capsule impedes phagocytosis and binding of antibodies, having implications for immune evasion
Antigenic Phase Variation
- Expression of O antigens, K antigens, and H antigens is genetically regulated
- Allows bacteria to evade antibody-mediated destruction by altering surface antigens
Antigenic Variation as a Defense Mechanism
- Involves variations in O, K, H antigens, and pili antigens
- Protects against immune system responses, crucial for survival in the fluctuating environment of the human body
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Description
Test your knowledge about the Enterobacteriaceae family, which plays a crucial role in human health and disease. This quiz covers the significance of these organisms, their role in UTIs, and the emerging threat of multidrug-resistant bacteria. Get ready to explore this essential topic in microbiology!
