Gnb

• How can bacteria be differentiated?

  By testing with the Gram stain

  
• What does the Gram stain attach to in bacteria?

  Peptidoglycan in the cell wall

  
• What color does the Gram stain produce in bacteria?

  Purple

  
• What is the difference in peptidoglycan thickness between Gram positive and Gram negative bacteria?

  Thinner in Gram negative bacteria

  
• What are some medically important Enterobacteriaceae?

  • Escherichia spp.
  • Klebsiella spp.
  • Salmonella spp.
  • Shigella spp.
  • Citrobacter species
  • Enterobacter spp.
  • Morganella spp.
  • Proteus spp.
  • Serratia spp.
  • Yersinia spp.
• What type of bacteria are Enterobacteriaceae classified as?

  Gram negative bacteria (GNB)

  
• What is a common characteristic of Enterobacteriaceae in clinical labs?

  Most common group of GNB cultured
• What type of respiration do Enterobacteriaceae perform?

  Facultative anaerobes
• What do Enterobacteriaceae ferment?

  A wide range of carbohydrates
• On which agar do Enterobacteriaceae grow well?

  MacConkey agar
• What is the catalase test result for Enterobacteriaceae?

  Catalase positive
• What is the oxidase test result for Enterobacteriaceae?

  Oxidase negative
• What are the virulence factors of Enterobacteriaceae?

  • Antigenic structures:
  • >150 heat-stable somatic O (LPS) antigens
  • >100 heat-labile K (capsular) antigens
  • >50 H (flagellar) antigens
  • Toxins & enzymes:
  • Endotoxins (LPS)
  • Exotoxins
  • Colicins
• What diseases are caused by Enterobacteriaceae other than Salmonella and Shigella?

  • Normal intestinal flora (mainly E. coli)
  • Generally do not cause disease
  • Contribute to normal function & nutrition
  • Infections usually caused by E. coli
  • Hospital-acquired infections
  • Community-acquired infections
• When are Enterobacteriaceae considered pathogenic?

  When they reach tissues outside normal flora
• What are frequent sites of infection for Enterobacteriaceae?

  Urinary tract and biliary tract
• What can lead to clinically important infections by Enterobacteriaceae?

  Immunosuppression or indwelling catheters
• What is a common cause of Urinary Tract Infections (UTI)?

  Enterobacteriaceae, especially E. coli
• What are the signs and symptoms of UTI caused by Enterobacteriaceae?

  Suprapubic pain, urinary frequency, dysuria
• What virulence factors are associated with Uropathogenic E. coli in UTIs?

  O antigen types and hemolysin
• What strain of E. coli is associated with pyelonephritis?

  Strain with K antigen and P fimbriae
• What are the common causes of diarrheal diseases associated with E. coli?

  Consumption of contaminated food and water
• What are the pathotypes of diarrhoeagenic E. coli?

  1. ETEC - enterotoxigenic E. coli
  2. EPEC - enteropathogenic E. coli
  3. EHEC - enterohemorrhagic E. coli
  4. EAEC - enteroaggregative E. coli
  5. EIEC - enteroinvasive E. coli
• What is the pathogenesis of ETEC?

  Fimbrial adhesins and heat-stable toxins
• How does EPEC adhere to the mucosal cells?

  Via bundle-forming pilus
• What toxins are produced by EHEC?

  Shiga toxins and intimin
• What is the pathogenesis of EAEC?

  Aggregative adherence via fimbriae
• What is the pathogenesis of EIEC?

  Cellular invasion and intracellular motility
• What is the significance of Enteropathogenic E. coli (EPEC)?

  • Important cause of diarrhoea in infants
  • Adhere to mucosal cells of the small bowel
  • Caused by O antigen and occasionally H antigen types
  • Watery diarrhoea, self-limiting but can be chronic
• What is the significance of Enterotoxigenic E. coli (ETEC)?

  • Causes "traveler's diarrhoea"
  • Adhere to epithelial cells of the small bowel
  • Some strains produce heat-labile exotoxin (LT)
  • LT stimulates production of neutralizing antibodies
  • Strains with both toxins cause more severe diarrhoea
• What is the most common serotype of Shiga toxin-producing E. coli (STEC)?

  O157:H7
• What complications can arise from STEC infections?

  Hemolytic uremic syndrome (HUS)
• What are the common infections caused by Klebsiella pneumoniae?

  • Pneumonia
  • Bloodstream infections
  • Wound or surgical site infections
  • Meningitis
• Who is at risk for Klebsiella pneumoniae infections?

  Patients on ventilators or long antibiotics
• What illnesses are caused by Salmonella spp.?

  • Salmonellosis
  • Typhoid fever
  • Paratyphoid fever
• How do people typically get infected with Salmonella?

  Eating contaminated food or water
• What are the clinical manifestations of Salmonella infections?

  • Diarrhea
  • Fever
  • Stomach cramps
  • Invasion causing severe disease
• What are the species of Shigella?

  • S. flexneri
  • S. boydii
  • S. sonnei
  • S. dysenteriae
• What is the infective dose for Shigella compared to Salmonella?

  Infective dose is 10^3 for Shigella
• What diseases are caused by Shigella?

  • Shigellosis
  • Bacillary dysentery