Corynebacteria

• Who first described the bacterium causing diphtheria?

  Kleb
• What did Loeffler demonstrate in 1884 regarding the diphtheria bacterium?

  Its etiological significance
• What is the gram stain result for Corynebacterium diphtheriae?

  Gram-positive
• What are the characteristics of Corynebacterium diphtheriae?

  It is non-motile and non-sporing bacilli
• What are the five species of Corynebacteria that can cause disease in humans?

  • C. diphtheriae (Diphtheria)
  • C. haemolyticum (Pharyngitis)
  • C. xerosis (Endocarditis)
  • C. pseudotuberculosis (Tuberculosis-like illness)
  • C. ulcerans (Pharyngitis)
• What is the appearance of Corynebacterium diphtheriae under the microscope?

  It has a "club-shaped" appearance with swollen ends
• What do the granules at the swollen ends of Corynebacterium diphtheriae indicate when stained?

  They give a reddish purple color when stained with Loeffler’s alkaline methylene blue
• What are the other names for the granules found in Corynebacterium diphtheriae?

  Metachromatic granules, Babes Ernst’s granules, and volutin granules
• How does Corynebacterium diphtheriae stain with Albert’s method?

  The granules stain bluish black and the cytoplasm green
• What is the characteristic arrangement of Corynebacterium diphtheriae in smear preparations?

  Adjacent bacteria lie at various angles, resembling Chinese letters
• What is Loeffler’s inspissated serum medium used for?

  It is used to grow Corynebacterium diphtheriae
• How quickly does Corynebacterium diphtheriae grow on Loeffler’s inspissated serum medium?

  In 6-8 hours
• What are the characteristics of colonies of Corynebacterium diphtheriae on Loeffler’s medium?

  They are small, circular, creamy, and glistening
• What is Mcleod’s heated blood tellurite agar medium used for?

  It is the medium of choice to study colony characters of C. diphtheriae
• What is the concentration of potassium tellurite in Mcleod’s medium?

  0.04%
• What are the three colony types (biotypes) of C. diphtheriae?

  • Gravis
  • Intermedius
  • Mitis
• How sensitive is C. diphtheriae to heat?

  It is killed at 60°C in less than 10 minutes
• How does C. diphtheriae respond to dry environments?

  It resists dry environments for months
• What is the primary mode of transmission for C. diphtheriae?

  Spread by droplet infection or hand-to-mouth contact
• What is the average incubation period for C. diphtheriae infection?

  2 to 5 days
• Who are the primary reservoirs for C. diphtheriae?

  Humans, both carriers and cases
• How does effective antibiotic therapy affect C. diphtheriae infectivity?

  It immediately reduces infectivity
• How does passive immunity protect newborns from C. diphtheriae?

  It protects them up to 6 months of age
• What is the most important source of infection for C. diphtheriae?

  Asymptomatic carriers
• What is the major virulence factor associated with C. diphtheriae?

  Diphtheria toxin
• How is diphtheria toxin produced by C. diphtheriae?

  By strains infected with a lysogenic β-phage carrying the tox gene
• What happens to nontoxigenic strains of C. diphtheriae when infected with a β-phage?

  They can be converted to tox+ strains
• What is the composition of diphtheria toxin?

  It is composed of two fragments, A and B
• What is the lethal dose of diphtheria toxin for humans?

  130 ng/kg of body weight
• How does diphtheria toxin affect protein synthesis in eukaryotic cells?

  It blocks protein synthesis
• What is the role of trypsin in the activity of diphtheria toxin?

  It cleaves the toxin into two fragments
• What does fragment A of diphtheria toxin do once inside the cytoplasm?

  It disrupts protein synthesis
• What does ADPR do in the context of diphtheria toxin's action?

  It binds to and inactivates elongation factor 2 (EF-2)
• What environmental conditions affect the production of diphtheria toxin?

  Alkaline pH, oxygen, and iron concentration
• When is diphtheria toxin released in significant amounts?

  When the available iron in the culture medium is exhausted
• What are the two forms of disease caused by C. diphtheriae in humans?

  • Respiratory diphtheria
  • Cutaneous diphtheria
• Where is respiratory diphtheria found, and how common is it in North America and Western Europe?

  It is found worldwide but is uncommon in North America and Western Europe
• How many cases of diphtheria were estimated by the WHO in 2010?

  About 4000 cases
• What does the CDC recommend for international travelers regarding diphtheria?

  They should ensure they are up-to-date on all vaccinations
• What are the initial symptoms of diphtheria?

  Low-grade fever, malaise, and a mild sore throat