Gram + aerobic rods

• Corynebacterium


  Genus of more than 60 species, some pathogenic for humans and animals
• Most important Corynebacterium species

  • Corynebacterium diphtheriae
  • C. ulcerans
  • C. pseudotuber-culosis
  • C. renale group (C. renale, C. pilosum, C. cystitis)
  • C. bovis
• Corynebacterium


  • Gram-positive aerobic pleomorphic rods
  • Cells may be coccoid or club-shaped
  • Organisms from fluid media appear as single cells, pairs, V forms, palisades
  • Most are nonmotile
  • Non-spore forming, non-acid fast
  • Only little tendency to branch
  • Cell wall contains coryne mycolic acid
• C. diphtheriae


  Causes human diphtheria, "bull neck" in children
• C. pseudotuberculosis


  Facultative intracellular parasite, cause of caseous lymphadenitis (CLA) in sheep and goats, ulcerative lymphangitis in horses and abscesses and mastitis in cattle; humans can also be infected
• Corynebacterium renale group


  Commensals of the lower urogenital tract, opportunistic pathogens of the bovine urinary tract, cause cystitis and ascending pyelonephritis
• C. ulcerans


  Best known as a cause of pharyngitis in humans but has also been isolated from cases of bovine mastitis
• C. bovis


  A commensal and (rarely) opportunistic pathogen of the bovine mammary
• Corynebacteria growth


  1. Grow well on blood agar aerobically

  2. Colonies are very small after 24h but enlarge to 1-3 mm after several days of incubation

  3. C. renale has yellowish non hemolytic colonies

  4. C. pseudotuberculosis is β-hemolytic, with white-to-gray, waxy, dry and crumbly colonies

  5. C. pseudotuberculosis inhibits staphylococcal β-hemolysis on blood agar (a reverse CAMP test)

  6. Identification is based mainly on biochemical tests (e.g. API CORYNE)
• Arcanobacterium & Trueperella


  Gram-positive nonmotile coccoid rods, contain several species but Arcanobacterium pyogenes (now: T. pyogenes) and A. heamolyticum are the most important
• Trueperella pyogenes


  Predominant animal pathogen, commonly inhabits mucous membranes of the upper respiratory, gastrointestinal and genital tracts of domestic animals, but is also a common opportunistic pathogen
• Diseases caused by Trueperella pyogenes

  • Cattle: liver abscesses, abscessing mastitis, pneumonia, endometritis, abortion, endocarditis, hoof problems
  • Goat: mastitis
  • Pig: pneumonia, septic arthritis, endocarditis
  • Poultry: Osteomyelitis
  • Sheep: pneumonia, endometritis, abortion
• Diagnosis of T. pyogenes infection


  1. Isolation of the organism from clinical material: blood agar, 48h incubation

  2. Colonies are small, 0.5 mm, surrounded by a zone of β-hemolysis

  3. Most strains are CAMP positive

  4. Catalase negative

  5. Miniaturized commercial kits (e.g. API CORYNE) may also be used for identification
• Rhodococcus


  The only species of veterinary significance is Rhodococcus equi (formerly Corynebacterium equi)
• Rhodococcus equi


  Aerobic, Gram-positive coccobacillus that may be partially acid-fast, causes pyogranulomatous pneumonia in foals and immunosuppressed humans
• Rhodococcus equi


  1. Present in the intestine of many horses and may persist for long periods in manure and soil

  2. Sandy soils in paddocks used for breeding mares are likely sources of infection of foals

  3. Infection manifests as pyogranulomatous bronchopneumonia with cranioventral abscesses and osteomyelitis in long bones and vertebrae (as a result of hematogeneous dissemination)

  4. Foals of 6 weeks of age are typically affected
• Diagnosis of Rhodococcus equi

  1. Clinical samples: lung tissue, tracheal aspirates, bronchoalveolar lavage (BAL) samples

  2. Bacteriologic culture: after 48h incubation colonies are 2-4 mm in diameter, smooth, glistening, often mucoid; most strains produce salmon-pink pigment

  3. Catalase-positive and gives synergistic hemolysis (CAMP reaction) with S. aureus
• Actinomyces


  Gram-positive, non-acid-fast, non-spore-forming rods, some morphological and cultural properties are similar to those of fungi, most species produce a true mycelium that breaks into elements of various size, branching is common, unlike fungi, they do not grow (or grow poorly) on Sabouraud Dextrose Agar, facultatively anaerobic; most species prefer a reduced oxygen environment, commensals in the oropharynx and gastrointestinal tract
• Significant Actinomyces species


  • Actinomyces bovis
  • Actinomyces viscosus
  • Actinomyces hordeovulneris
  • Actinomyces (now: Actinobaculum) suis
  • Actinomyces israelii
• Actinomyces bovis


  Oropharynx of cattle, infections are usually initiated by wounds of the oral mucous membrane, affects bony structures and is most commonly seen in the mandible -- "lumpy jaw", as a result of pathologic process, chronic rarefying osteomyelitis develops; bone honeycombed with pus-filled sinuses replaces normal bone, thick, green to yellow pus moves to the surface by way of fistulous tracts (sinus tracts), pus contains macro colonies of Actinomyces bovis up to 5 mm in diameter, often called "sulfur granules"
• Other Actinomycosis


  • Dogs: A. viscosus, A. horde vulneris, rarely A. bovis
  • Swine: Actinomyces suis
  • Humans: Actinomyces israelii
• Actinomyces bovis diagnosis


  1. Actinomycetes can usually be demonstrated in the "sulfur granules" associated with draining lesions

  2. Granules should be washed and crushed on a slide

  3. In Gram preparations, macro colonies appear as a tangled mass of Gram-positive filaments; however, cocci and branched rods may also be observed

  4. Microcolonies are surrounded by ‚clubs' of calcium phosphate ('rosettes')

  5. Bacterial culture: A. bovis prefers an atmosphere containing 10-15% CO2, A. viscosus grows aerobically

  6. Actinomycetes require enriched media, preferably with blood or serum (no hemolysis)

  7. Growth is evident after 48-72 hours of incubation

  8. Colonies are white, rough ("molar tooth") difficult to remove, up to 2 mm in diameter
• Nocardia


  Strictly aerobic, nonmotile, pleomorphic gram-positive organisms, may occur as cocci, rods or diphtheroids; sometimes produce branching filaments and aerial hyphae, partially acid-fast, found in soil, decaying vegetation, water and in animal feces
• Important Nocardia species


  • Nocardia asteroides complex: N. asteroides, N. farcinica, N. nova
  • Nocardia brasiliensis
• Nocardiosis


  Pathogenesis and clinical signs similar to actinomycosis, usually a chronic progressive disease characterized by suppurating and granulomatous lesions, infections are infrequent and non-communicable
• Nocardiosis in animals


  • Cattle: acute or chronic mastitis with granulo-matous lesions and draining fistulous tracts
  • Dogs & cats: localized form of the disease with subcutaneous lesions (mycetomas) and/or lymph node involvement (lymphadenitis)
  • Dogs: thoracic form (suppurative pleuritis and/or peritonitis, abscessation of heart, liver and kidneys); dissemination to the CNS is common
  • Dogs: nocardial stomatitis
  • Humans: subcutaneous or pulmonary forms, often associated with COPD and AIDS
• Nocardia diagnosis


  1. Presumptive diagnosis is based on pathology and laboratory examination

  2. Direct examination (the Gram and acid-fast stain)

  3. Culture (blood agar, Sabouraud agar)

  4. Differentiation is based on phenotypic properties
• Dermatophilus


  Aerobic, gram-positive, branching, filamentous rods, non-acid fast, filaments divide with septa in transverse and horizontal planes → "railroad tracks"
• Dermatophilus congolensis


  An obligate parasite of many species of animals, the causative agent of generalized exudative dermatitis in livestock, infection involving superficial layers of the skin, crusts and scabs up to 2.5 cm thick are formed, lesions may coalesce
• Forms of dermatitis in sheep caused by Dermatophilus congolensis

  • Dermatitis of wool-covered areas -- "lumpy wool"
  • Dermatitis of the face and scrotum
  • Dermatitis of the lower leg and foot -- "strawberry foot rot"
• Diagnosis of Dermatophilus congolensis

  1. Gram-stained smears from clinical materials

  2. Bacterial culture on blood agar or TSA, after 24h of incubation D. congolensis produces tiny, grayish-white round colonies that adhere to the agar, colonies may become orange after 2-5 days, 1-2 mm ø and are often β-hemolytic