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• Non-Spore


  Corynebacterium & Listeria
• Important pathogens in this group

  • Corynebacterium diphtheriae
  • Listeria monocytogenes

  
• General characteristics

  • Gram-positive, pleomorphic, often club-shaped rods
  • Aerobic or facultative anaerobic
  • The individual cells tend to group in V,Y, or palisade arrangements
  • Characterized as "Chinese letters"
  • Have metachromatic granules that give the rod a beaded appearance
  • The granules stain metachromatically

  
• Corynebacterium diphtheriae

  • Infects the nasopharynx or skin
  • Toxigenic strains secrete a potent exotoxin which may cause diphtheria
  • Diphtheria was mainly a disease of small children
  • The symptoms of diphtheria include pharyngitis, fever, swelling of the neck or area surrounding the skin lesion
  • The toxin is distributed to distant organs by the circulatory system
  • Lysogenic bacteriophage encodes for potent exotoxin in virulent strains
  • Invasiveness is under the control of bacterial genes

  
• Typing of diphtheria bacilli

  1. Serotyping

  2. Bacteriophage typing

  3. Bacteriocin typing

  
• Biotypes of C. diphtheriae

  • C. diphtheria gravis, large colonies
  • C. diphtheriae mitis, smaller, small zone of haemolysis
  • C. diphtheriae intermedius, the smallest
  • C. diphtheriae belfanti

  
• Transmission

  • Person to person by inhalation
  • Skin contact
  • Asymptomatic carriage maintains bacteria in population
  • Human are the only natural host
  • Both toxigenic and nontoxigenic organisms reside in the upper respiratory tract and are transmitted by airborne droplets
• Virulence factors

  • Capacity for establishing infection
  • Growing rapidly
  • Elaborating toxin
• Who is at risk?

  • Unvaccinated people
  • Children
  • People in crowded and poor urban area
• Diphtheria toxin


  • It is a heat-labile polypeptide
  • Encoded by tox gene introduced by lysogenic bacteriophage (prophage)
  • Consists of two fragments, A and B
  • The binding (B) fragment mediates binding of the toxin to glycoprotein receptors on the cell membrane
  • The active (A) fragment possesses enzymatic activity (toxic activity) which inhibits polypeptide chain elongation by inactivating the elongation factor EF-2
  • The abrupt arrest of protein synthesis is responsible for the necrotizing and neurotoxic effects of diphtheria toxin
  • All toxigenic C diphtheriae are capable of elaborating the same disease-producing exotoxin
• Mechanism of Action of Diphtheria Toxin

  Inhibition of Protein Synthesis
• Pathogenesis and Pathology


  • Local infection: Infection of the mucosa of tonsils, pharynx, and conjunctiva. The pathogens invade the host through these portals, reproduce, and produce toxin, resulting in local cell damage. The inflammatory reaction leads "diphtherial pseudomembrane".
  • Systemic intoxication: Toxin absorbed and results in distant toxic damage. C. diphtheriae does not actively invade deep tissues and practically never enters the bloodstream.
• Laboratory Diagnosis

  1. Staining method: Alkaline methylene blue (Albert stain), Gram's stain

  2. Cultivation: Tellurite Blood agar plate, Loeffler's serum medium

  3. Toxigenicity tests: Elek test, PCR, Enzyme-linked immunosorbent assay

  4. Diagnostic Schick Skin Test
• Treatment

  • Diphtheria antitoxin (should be given immediately)
  • Penicillin, Erythromycin…. the drug of choice
• Control & Prevention

  Vaccination with diphtheria toxoid, Diphtheria toxoid is included in the DPT vaccine
• Other Coryneform Bacteria

  • Non-lipophilic Corynebacteria
  • Lipophilic Corynebacteria
• Propionibacterium acnes


  • Members of the normal flora of the skin, oral cavity, large intestine
  • Their metabolic products include propionic acid
  • Causes the disease acne vulgaris. It causes acne by producing lipases that split free fatty acids off from skin lipids. These fatty acids can produce tissue inflammation that contributes to acne formation
• Listeria monocytogenes


  • Causes meningitis and sepsis in newborns, pregnant women, and immunosuppressed adults
  • It also causes outbreaks of febrile gastroenteritis
  • It is a major cause of concern for the food industry
  • Short, Gram-positive Pleomorphic rods
  • Motile at room temperature
  • It can survive at refrigerator temperatures (4°C), low pH and high salt condition
  • It has a tumbling end-over-end motility at 22–28 °C but not at 37 °C
  • Facultative anaerobe
  • It produces beta hemolysis
• Listeriosis (Listeria infection)


  • A serious infection caused by eating food contaminated with the bacterium Listeria monocytogen
  • It primarily affects pregnant women, newborns, adults with weakened immune systems, persons with cancer, diabetes, AIDS
• Listeria virulence factors


  • Adherence and invasion
  • Internalin
• Transmission to human

  • Ingestion of unpasteurized milk products
  • Ingestion undercooked meat, and raw vegetables
  • Contact with domestic farm animals and their feces
  • Storage of contaminated food in the refrigerator can increase the risk of gastroenteritis
• Pathogenesis

  • Listeria infections occur primarily in two clinical settings: In the fetus or in a newborn as a result of transmission across the placenta or during delivery; In pregnant women and immunosuppressed adults
  • Pathogenesis is dependent upon the organism ability to invade mononuclear phagocytic cells (intracellular)
  • Immunity to L monocytogenes is primarily cell-mediated
• Laboratory diagnosis

  1. Gram stain: appearance of Gram-positive rods resembling diphtheroids

  2. Cultivation: formation of small colonies with a narrow zone of beta hemolysis

  3. Motility test

  4. Sugar fermentation test