Subcutaneous and lymph node granulomas due to Dermatophilus congolensis in a steer.

Abstract

Dermatophilus congolensis infection causes an exudative epidermitis in a wide variety of animals, including man [I]. The organism generally is considered to be unique as a pathogen restricted to the living epidermis [9].Contrary to this opinion, there is evidence for a pathogenic role for this organism in tissues other than skin. Organisms morphologically similar to D. congolensis have been demonstrated microscopically in oral cavity granulomas [4, 8] and lymph nodes of cats [12], tonsillar abscesses in pigs [3], and subcutaneous nodular disease in man [2]. D. congolensis also has been cultured from goats with suppurative lymphadenitis [11], a lymph node abscess in a sheep [I3], a subcutaneous abscess in a lizard [10], and a chronic inflammatory lesion in a lymph node of a cat 17]. This paper records the isolation of D. congolensis from abscesses in a four-year-old crossbred steer. Nineteen steers on feedlot consignment were rejected from slaughter at a metropolitan abattoir because six steers had prominent subcutaneous abscesses at antemortem inspection. Five of the six steers had only a single abscess: on the shoulder, flank (two steers), popliteal groove, and scrotum. These steers were returned to the feedlot and successfully treated with a parenteral penicillin/streptomycin combination. No cause of the lesions in these steers was established. The remaining affected steer was killed and necropsied for disease investigation. This four-year-old crossbred steer had a discharging abscess at the point of each shoulder and a large subcutaneous abscess approximately 250 mm by 200 mm on one flank, in the region of the prefemoral lymph node. At necropsy, the prescapular and superficial inguinal lymph nodes and a single prefemoral lymph node were enlarged and contained thick white granular pus. Smaller abscesses were present in the subcutis over the brisket and rump regions, in the omentum, and on the surface of the diaphragm. Pus samples from a superficial inguinal lymph node, prefemoral lymph node, and the omental lesion were examined bacteriologically. Gram-positive coccoid cells arranged in parallel rows to form thick filaments; some with lateral branches were seen in Gram-stained smears of pus from the lymph nodes but not from the omental lesion. All three samples yielded pure cultures of Gram-positive branched filaments forming hemolytic, yellow, raised, rough, adherent colonies on sheep blood agar after 48 hour aerobic incubation at 37°C. Broth cultures contained motile zoospores. The isolates were identified as D. congolensis by their distinctive morphology and biochemical properties [5]. Tissues for light microscopy were processed by routine histological techniques and 6-llm sections of the superficial inguinal lymph node and brisket lesion were stained with hematoxylin and eosin (HE), Brown and Brenn's modification of Gram's stain (BB), Gomori's methenamine silver stain, Ziehl-Neelsen stain, and periodic acid-Schiff stain. Histologically, the lesions were club-forming granulomas. The centrally located, eosinophilic club formations were surrounded by neutrophils and then by a zone of macrophages, lymphocytes, and Langhans' giant cells which merged with dense fibrous tissue (fig. I). The lesions were histologically very similar to lesions produced by other club-forming organisms, particularly Actinomyces bovis. However, in HE-stained sections, parallel chains of coccoid organisms, resembling D. congolensis, could be seen at the periphery of the club formations