actinomycetes

• How can Listeria monocytogenes be characterized morphologically?


  It is a short, Gram positive, non-spore forming rod.
• What distinguishes Listeria monocytogenes from Corynebacteria?


  Tumbling motility at room temperature but not at 37°C distinguishes it.
• What type of anaerobe is Listeria monocytogenes?


  It is a catalase positive facultative anaerobe.
• What are the two types of listeriosis disease?

  • Perinatal
  • Early onset: intrauterine infection, sepsis, and death before birth
  • Late onset: infected at birth, meningitis, and sepsis within 2-3 weeks
  • Adult
  • In immunocompetent: flu-like symptoms and gastro upset
  • In immunocompromised: meningo-encephalitis and bacteraemia
• What are the main treatments for listeriosis?

  Penicillin and gentamicin are used for treatment.
• What are the sources of infection for Listeria monocytogenes?


  • Infected environment
  • Animals
  • Silage
  • Infected humans
  • Main route: gastrointestinal
  • Associated with dairy products, packaged meat, fruits, and vegetables
• How can infection with Listeria monocytogenes be avoided?


  By pasteurization of dairy foodstuffs and cooking of food.
• What is a notable characteristic of Listeria monocytogenes regarding temperature?


  It is psychrotrophic, meaning it can grow in the fridge.
• What are the characteristics of Actinomycetes?


  • Abundant soil organisms
  • Mycelial structure
  • Generate spores at ends of terminal hyphae
  • Strict aerobes
  • Nutritionally versatile
  • Produce many antibiotics
• What are the characteristics of Corynebacteria?


  • Diverse group of Gram +, aerobic, non-motile club-shaped rods
  • Animal pathogens, plant pathogens, and saprophytes
• What is diphtheria characterized by according to the CDC?


  It is characterized by sore throat, low-grade fever, and an adherent membrane in the respiratory tract.
• How is diphtheria spread?


  It is spread by droplets or by contact.
• What are the effects of the diphtheria toxin?


  • Absorbed onto mucous membrane
  • Causes destruction of epithelium
  • Produces local inflammation
  • Forms a greyish “pseudomembrane”
  • Toxin transported in blood causing lesions in kidney, heart, and nervous system
• What is the mortality rate of diphtheria even with treatment?


  1. 10% mortality rate.
• What are the components of diphtheria toxin?


  • Encoded by lysogenic phage
  • A (catalytic) and B (receptor-binding) domains
  • ADP-ribosylation of elongation factor EF2
  • Prevents protein synthesis
• What is the lethal dose of diphtheria toxin for humans?


  About 0.1 μg/kg.
• What is used as a vaccine for diphtheria?

  • Inactivated toxoid is used as a vaccine.
  • Antitoxin is used for treatment.
  • Toxin is used for the Elek test.
• What are the diagnostic methods for diphtheria?

  • Gram stain or methylene blue shows beaded bugs from swab
  • Aerobic growth on most media, Loeffler's serum media is semi-selective
  • Elek test for toxigenicity
• What is the purpose of the Elek test?


  It tests for the toxigenicity of diphtheria strains.
• What antibiotics are used for treating diphtheria?


  Erythromycin is one of the antibiotics used for treatment.
• What vaccine is used for diphtheria?

  Diphtheria toxoid is used in the DPT vaccine.