Enterobacteriaceae Importance Quiz

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

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!