Corynebacterium kutscheri Infection: Pseudotuberculosis
Corynebacterium kutscheri is a diphtheroid bacillus that causes a syndrome in mice and rats termed “pseudotuberculosis.” This was one of the first infectious disease syndromes to be recognized in laboratory mice and rats in 1894 by D.
Kutscher. Once quite common in these species, it is now rare. However, it remains a significant pathogen that occasionally infects colonies of mice and rats.Epizootiology and Pathogenesis
Infection is usually subclinical, with sporadic hematogenous dissemination following entry through oral or enteric mucosa, from which the organisms spread to regional lymph nodes and to other internal organs. The organism may persist as a subclinical infection for long periods with no detectable circulating antibodies. The usual sites for the colonization of C. kutscheri in mice are the oral cavity, cecum, and colon. Clinical manifestations of the disease usually occur in conjunction with predisposing factors that compromise the immune response. Variation in susceptibility to C. kutscheri among strains of mice has been attributed to mononuclear phagocyte function. BALB/c-nude, A/J, CBA/N, MPS, and BALB/cCr mice were found to be most susceptible, C3H/He mice intermediate, and C57BL/6Cr, B10. BR/SgSn, ddY, and ICR mice resistant to colonization and disease induction. Male mice appear to harbor higher numbers of bacteria and a higher carrier rate.
Pathology
Infection is most often subclinical, but disease may arise as outbreaks or intermittent morbidity in enzootically infected colonies. Cervical and mesenteric lymph nodes of carrier animals may be enlarged (reactive) but without abscessation. Raised, gray-white nodules up to 1 cm in diameter may be present in liver, kidney, and lungs and, to a lesser extent, in other tissues, including subcutis. Suppurative and erosive arthritis may also be present, particularly in the carpal/metacarpal or tarsal/metatarsal joints, with marked swelling and erythema. Conjunctivitis has also been described.
Microscopically, lesions feature coagulation to caseation necrosis, with peripheral aggregations of leukocytes, dominated by neutrophils. Suppurative thrombosis and embolization involving the pulmonary or mesenteric and portal vessels may be evident. Prominent colonies of Gram-positive bacilli are evident, particularly in the junctional areas between necrotic centers and peripheral reactive zones (see Rat Chapter 2, "Corynebacterium kutscheri Infection”).Diagnosis
Characteristic bacterial colonies, with "Chinese letter configurations” among less dense colonies, are readily evident within suppurative lesions and are best visualized in tissue sections stained with Gram stains. The distribution and nature of the lesions consistent with pseudotuberculosis require culture and identification of C. kutscheri. Differential diagnoses include other disseminated chronic bacterial infections that induce abscesses, including Staphylococcus and Streptococcus, and arthritis associated with Mycoplasma or Streptobacillus. Culture of oropharyngeal washes, cervical lymph nodes, mesenteric lymph nodes, and cecum is useful for detecting carrier animals, and culture of feces has been shown to be a useful noninvasive screening method.
Other Corynebacterium spp.-Associated Disease
Keratoconjunctivitis with ulcerative keratitis has been reported in aged B6 mice infected with Corynebacterium spp. Older mice inoculated in the conjunctival sac with the organism developed the typical lesions, but younger mice were resistant to the disease. Corynebacterium hoff- mani can be a frequent isolate from BALB/c mice with conjunctivitis. It is likely that ocular infection is predisposed by microophthalmia (B6) or entropion (BALB/c) in these strains. Corynebacterium mastitidis has been associated with suppurative preputial gland adenitis.