Gram-negative organisms

• Who is the author of the study material on Gram-negative organisms?

  Dr Laura J. Smith
• What is the primary focus of the study material?

  Gram-negative organisms and examples of clinical importance
• What are the learning outcomes of the study material?

  • Describe the basic structure of Gram-negative bacteria with reference to the cell wall.
  • Describe key features of Gram-negative bacteria such as toxin production.
  • Describe examples of Gram-negative bacteria and associated diseases.
• What is the percentage of the peptidoglycan layer in Gram-negative bacteria?


  10%
• What unique structure is primarily found in the cell wall of Gram-negative bacteria?


  The outer membrane, often referred to as the lipopolysaccharide layer (LPS)
• What is contained in the periplasmic space of Gram-negative bacteria?


  It is rich in proteins, including enzymes to break down host cell components
• What are the components of LPS in Gram-negative bacteria?


  Lipid A, core polysaccharide, and O-polysaccharide
• What are endotoxins in Gram-negative bacteria?


  Heat-stable toxins associated with the outer membrane that are released when cells are disrupted
• What symptoms can endotoxins induce?


  Diarrhoea and vomiting
• How do small and large quantities of endotoxins differ in their effects?


  Small quantities cause mild fever, while large quantities can lead to organ failure
• What are the three distinct stages of pathogenesis in Gram-negative infections?


  1. Exposure and adherence to host cells
  2. Invasion, colonisation, and infection
  3. Host damage and disease
• Name some examples of Gram-negative bacteria.

  Salmonella sp., Escherichia coli, Yersinia pestis, Klebsiella sp., Shigella sp.
• What are the key features of Enterobacteriaceae family?


  Rod-shaped, facultative anaerobes, usually motile via flagella, nonsporulating, oxidase negative, and catalase positive
• What diseases can Enterobacteriaceae cause?

  • Septicaemia
  • Urinary tract infections (UTIs)
  • Neonatal meningitis
  • Endocarditis
  • Pneumonia
  • Gastroenteritis
• What is the most prevalent pathogenic strain of E. coli in developed countries?

  Escherichia coli O157:H7
• How can E. coli O157:H7 be transmitted?


  Through ingestion of contaminated food
• What are the symptoms of E. coli O157:H7 infection?


  Severe abdominal pain and bloody diarrhoea
• What virulence mechanisms does E. coli O157:H7 possess?


  Adherence to intestinal epithelial cells via flagella and production of Shiga-like toxin
• What outbreak occurred in 2018 related to E. coli O157:H7?


  A multistate outbreak linked to contaminated romaine lettuce
• What is the significance of E. coli O104:H4 in outbreaks?


  It produces high levels of shiga-toxin and can cause severe illness
• What is the primary host for Yersinia pestis?


  Domestic and wild rodents
• What is the treatment for bubonic plague?


  Streptomycin or gentamicin (injection) and chloramphenicol (IV)
• What is the mortality rate of untreated pneumonic plague cases?


  Up to 90%
• What is the treatment for Neisseria gonorrhoeae infections?


  Penicillin G or amoxicillin
• What is the primary infection caused by Neisseria meningitidis?


  Meningitis
• What is a key characteristic of Pseudomonas aeruginosa?


  It can produce a blue-green pigment called pyocyanin
• What types of infections can Pseudomonas aeruginosa cause?


  Urinary tract infections, surgical wound infections, and bloodstream infections
• What is the significance of Pseudomonas aeruginosa in burn victims?


  It commonly infects the lungs and causes chronic respiratory infections
• What are the key references for further reading on Gram-negative organisms?


  • Brock’s Biology of Microorganisms, 13th Ed, Chapters 3.3, 27.2, 31.2
  • www.gov.uk (P. aeruginosa/E. coli outbreaks)
  • WHO publications on plague