Corynebacterium Study Notes

Corynebacterium

General Characteristics

  • Morphology:
    • Pleomorphic, Gram-positive rods that stain irregularly.
    • Occur in angular and palisade arrangements, resembling a fence of stakes.
    • Exhibit club-shaped swellings at one or both ends.
  • Classification:
    • Commonly referred to as club bacterium due to their shape.
    • No spores, non-acid fast, non-motile.
    • Pathogenic species typically are facultative anaerobes.
    • Some species have been reclassified:
    1. Corynebacterium equi - now known as Rhodococcus equi
    2. C. pyogenes - now classified as Actinomyces
    3. C. suis - now recognized as Eubacterium

Notable Species

  • C. diphtheriae:
    • The type species causing human diphtheria.
    • Others called diphtheroid bacilli:
    • Corynebacterium renale (type I)
    • C. pilosum (type II)
    • C. cystitidis (type III)
  • C. renale:
    • Most frequently isolated from bovine mastitis, ureteritis, and pyelonephritis.
    • Predominantly affects female animals.
    • Causes diphtheric inflammation of the bladder, ureters, and kidneys.

Pyelonephritis in Cattle

  • Diseases
    • Refers to bacillary pyelonephritis, infectious pyelonephritis specific to cattle.
  • Morphological Features:
    • Diptheroid bacillus measuring 0.5 x 1.3 to 2.6 micrometers.
    • Exhibits short, stumpy rods thicker at one end than the other.
    • Present in clumps in exudates and cultures.
    • Non-motile, non-spore-forming, non-capsulated.
    • Strongly Gram-positive with characteristic staining patterns using methylene blue (bars and granules).
    • Pili may be present but are fewer in C. renale.

Cultural and Biochemical Characteristics

  • Growth is enhanced by blood or serum.
    1. C. renale:
    • Colonies appear opaque, ivory-colored, dull with uneven margins.
    1. C. pilosum:
    • Cream-colored to pale-yellow, circular, opaque, over 1 mm in diameter.
    1. C. cystitidis:
    • White, entirely circular, semi-translucent, and pinpoint-sized colonies.
  • C. renale in litmus milk:
    • Shows a reduction at the bottom of the tube, leading to soft curd formation that is slowly digested; the medium remains alkaline.
    • Medium separates into a dark red fluid and heavy sediment.
  • Only C. renale produces caseinase, multiplying in bovine urine and generating ammonia from urea.

Antigens and Pathogenesis

  • Each species displays differently structured antigenic pilus proteins.
  • Epizootiology:
    • Highly adapted to the urinary tracts of bovine and ovine species.
    • Transmission occurs via contaminated urine droplets with adherence pilus-mediated mechanisms.
    • Penetration and colonization of the urinary tract facilitated by adherence to aging epithelial cells.
  • C. renale is the most frequently isolated species from pyelonephritis cases; C. pilosum is found in the urine and vagina of healthy cows, occasionally causing cystitis and vaginitis.
  • C. cystitidis:
    • Causes severe hemorrhagic cystitis that may progress to pyelonephritis.
    • Considered a commensal around the prepuce of bulls, involved with urinary bladder infections affecting one or both ureters and kidneys.
  • Ovine posthitis (pizzle rot):
    • Believed to be due to ammonia irritation from C. renale in the prepuce.

Immunity

  • Serum antibody responses occur in cases of pyelonephritis and urethritis but are ineffective in cystitis alone.
  • Protective host responses are generally ineffective; untreated animals rarely recover.

Diagnosis

  1. Characteristic symptoms observed.
  2. Presence of blood clots and necrotic tissue in urine as seen in a Gram stain.

Antimicrobial Susceptibility

  • Sensitive to:
    • Penicillin
    • Streptomycin
    • Kanamycin
    • Erythromycin
    • Polymyxin B
  • Penicillin is the antibiotic of choice, particularly in large doses.

Corynebacterium pseudotuberculosis

General Characteristics

  • Also known as C. ovis or Preisz-Nocard bacillus.
  • Causes caseous lymphadenitis, prevalent in sheep and goats.
  • Occasionally affects horses, camels, mules, rarely found in cattle or humans.
  • Results in suppuration and necrosis of lymph nodes.

Morphology and Staining

  • Pleomorphic rod, sometimes mistaken for a coccus.
  • Rod forms are found in caseous pus from lymph nodes.
  • Non-sporeforming, non-motile, and non-acid fast.

Cultural and Biochemical Features

  • Growth is slow on all ordinary media; colonies reach maximum size in several days.
    • Fully developed colonies:
    • Papilliform centers surrounded by concentric rings parallel to an irregular margin.
    • Colonies appear grayish or yellowish with a dry surface.
  • High lipid content in the cell wall.
  • Mild hemolysis occurs on blood agar.

Antigens and Toxins

  • Two serotypes:
    • Serotype I:
    • Predominantly found in sheep and goats; infrequent in cattle.
    • Serotype II:
    • Found in buffalo and cattle.
  • Exotoxin:
    • Comprises phospholipase D, which causes intravascular hemolysis, necrosis, pulmonary edema, and shock.
    • Acts synergistically with phospholipase C of Rhodococcus equi.

Epizootiology and Pathogenesis

  • Caseous lymphadenitis typically spreads directly from open abscesses and enters through skin abrasions.
  • Causes ulcerative lymphangitis on fetlocks of horses and pectoral abscesses (pigeon fever).
  • Known as a facultative intracellular parasite.
  • Pathogenicity attributed to:
    1. Phospholipase D:
    • Increases vascular permeability.
    1. Heat-stable pyogenic factor:
    • Attracts leukocytes.
    1. Large amounts of surface lipids:
    • Toxic for phagocytes.
  • Disease primarily starts as a wound infection, resulting in local inflammation where entry occurred.
    • Progresses to regional lymph nodes, causing enlargement and pus-filled formation resembling concentric onion-like layers.
  • Causes ulcerative lymphangitis in horses, analogous to cutaneous glanders (farcy).
    • Nodules appear on the legs, breaking down to form ulcers exuding thick green pus, usually mixed with blood.
  • Pigeon fever:
    • Characterized by large painful abscesses in the pectoral, abdominal, and inguinal regions.
    • Lesions in adult horses develop slowly and can recur even after drainage.
    • Generalized infection can lead to death.
  • Rarely isolated from cattle.

Immunity

  • Antibodies are detected through multiple tests:
    • Agglutination test, toxin neutralization in mice and rabbits, antihemolysin inhibition test, hemolysin inhibition test, double immunodiffusion technique, and ELISA.
  • There is no proven vaccination providing high levels of protection.

Diagnosis

  1. Identification of lesions.
  2. Observation of dry, scaly colonies producing hemolysis on BAP.

Antimicrobial Susceptibility

  • Sensitive to:
    • Penicillin
    • Ampicillin
    • Chloramphenicol
    • Erythromycin
    • Gentamycin
    • Tetracycline
  • In vivo responses to treatment are generally poor.

Diseases in Humans

  • Present localized adenopathy, hepatomegaly, often accompanied by fatigue and myalgia.

Corynebacterium bovis

General Characteristics

  • Found in the milk of healthy udders, reproductive tracts of cows and bulls; can act as a primary pathogen in mastitis outbreaks.

Genus Eubacterium

Notable Species

  • C. suis:
    • Associated with cystitis and pyelonephritis in sows.

Morphology and Staining

  • Pleomorphic, slim, Gram-positive rods.
  • Non-spore forming, non-motile.
  • Exhibits branching and Chinese letter patterns in staining.

Cultural and Biochemical Features

  • Optimally grows under anaerobic conditions at 37ºC.
  • Colonies on blood agar plate are gray, tiny, and shiny after 24 hours, becoming flattened with a gray matte appearance as they mature.
  • No hemolysis occurs on blood agar; enrichment with tryptic soy and urea enhances growth.

Epizootiology and Pathogenesis

  • Most male pigs in enzootic areas carry this organism in their prepuce, seldom found in females.
  • Colonization of the bladder can lead to cystitis, with urine containing blood clots and purulent materials.
  • Bladder infections can ascend to kidneys, resulting in ureteritis and pyelonephritis.

Diagnosis

  1. Blood and pus found in the urine of breeding sows.
  2. Microscopic examination of urine sediment and pus revealing Gram-positive, slender coryneform organisms.
  3. Aerobic and anaerobic urine cultures on BAP and CNA agar demonstrate a Gram-positive anaerobic coryneform.

Antimicrobial Susceptibility

  • Sensitive to Penicillin.