MICROBIOLOGY

• As a term, "coryneform ("club-shaped") bacteria" is sometimes used to denote a wide range of Gram-positive rods based on staining characteristics and DNA content (specific G/C ratios).
  
  • Corynebacterium spp. included, but also others (Arcanobacterium, Rothia mucilaginosa).
• Genus with two major human species:
  • Corynebacterium diphtheriae (see separate module)
  • Non-diphtherial species also referred to as "diphtheroids." Classification of this group now based on RNA homology rather than within the previous coryneform group.
    • Many are part of normal human skin flora.
  • A partial listing of most commonly encountered pathogens below, more complete listing (53 pathogens) in Bernard[8]. Organisms remain rare causes of human infection.
  • Zoonoses (usually), rare human pathogen:
    • C. pseudotuberculosis: cause of caseous lymphadenitis in goats and sheep; human infection typically derived from contact with infected animals. Occasional agent of human lymphadenitis or respiratory diphtheria.
    • C. ulcerans: infection from handling infected animals or contact with contaminated milk.
      • An occasional cause of human respiratory diphtherial infection.
      • See the diphtheria module for public health and treatment recommendations.
  • Other occasional human pathogens: often afflicting hospitalized/immunocompromised patients; organisms typically with significant antibiotic-resistance profiles.
    • C. amycolatum: may be under-recognized as frequently misidentified as C. jeikeium or C. urealyticum.
    • C. bovis: bacteremia (rare)
    • C. hemolyticum: now Arcanobacterium hemolyticum.
    • C. jeikeium: originally termed group JK. May cause bacteremia, endocarditis, device/prosthesis infections, wound infections--especially in immunocompromised patients with hematological disorders or vascular catheters.
    • C. kroppenstedtii: implicated as a cause of granulomatous mastitis. See the mastitis module for details.
    • C. striatum: described as an emerging nosocomial pathogen; endocarditis, lung or bone infections, device infections, septic arthritis
    • C.tuberculostearicum:may be misidentified by lab, often multidrug-resistant.
    • C. urealyticum: capable of hydrolyzing urea. Genitourinary infections (encrusted cystitis) >> bacteremia, endocarditis, wound infections.
    • C. xerosis: rare and usually afflicting immunocompromised or cardiac valve patients.
• Species identification recommended for any isolate thought to be causing human infection.
• Gram-positive rods [Fig 1], catalase-positive and non-motile.
  • May be aerobic or facultatively anaerobic.
  • Not acid-fast.
  • Most grow on conventional media, though some require the addition of lipids for growth.