Successful Treatment of Disseminated Nocardiosis Caused by Nocardia veterana in a Dog

Yaemsiri, S.; Sykes, J.E.

On day 87, an exploratory laparotomy confirmed the presence of a mid-jejunal mass. Two additional masses were present within the mesentery adjacent to the jejunal mass. Histopathology of the resected jejunal mass revealed severe pyogranulomatous inflammation with intralesional filamentous bacteria. Filamentous bacterial organisms that were suspected to be Nocardia were visualized by light microscopy after staining with gram stain (gram positive), Ziehl-Neelsen (negative), and Kinyoun's acid fast stains (positive). Culture of the jejunal mass for aerobic bacteria, anaerobic bacteria, and fungi yielded very small numbers of Lactobacillus acidophilus, 2 colonies of Candida albicans, and small numbers of Nocardia veterana. The Candida isolate was identified by conventional phenotypic bacterial identification methods as well as matrix-absorption laser desorption ionization-time-of-flight mass spectrometry [MALDI-TOF MS] by comparison with the manufacturer's database. f The Lactobacillus acidophilus and Nocardia veterana isolates were also identified by MALDI-TOF MS. According to the manufacturer, scores <1.7 indicate no reliable identification, scores 1.7 to 1.999 indicate probable genus identification, scores between 2.0 and 2.299 indicate secure genus information and probable species identification, and scores between 2.3 and 3.0 indicate secure genus and species identification. For MALDI-TOF MS, a portion of the colony was spotted onto the manufacturer's stainless steel target plate and allowed to dry. The spot was treated with 70% formic acid in water and allowed to dry before the matrix (a-cyano-4-hydroxycinnamic acid) was applied (extended direct transfer method). The MALDI-TOF MS score values were 2.2, 2.3, and 2.2, for Candida, Lactobacillus, and Nocardia isolates, respectively. Aerobic bacterial culture of the skin biopsies that had been obtained before antimicrobial drug treatment also yielded Nocardia via MALDI-TOF MS (score value 1.6), and the isolate was confirmed to be N. veterana by sequencing of the secA1 gene g (100% homology). 1 Additionally, aerobic bacterial culture of a urine specimen obtained by cystocentesis yielded growth of 100 colony-forming units/mL of N. veterana as identified by MALDI-TOF MS (score value 1.7). Three consecutive blood samples were each obtained for aerobic and anaerobic blood cultures before antimicrobial drug treatment, which yielded growth of N. veterana as identified by MALDI-TOF MS (score value 2.1) in 1 aerobic and 1 anaerobic bottle. Staphylococcus pseudintermedius was grown in another aerobic bottle, identified through both conventional phenotypic identification methods and MALDI-TOF MS (score value 2.0), and was thought to represent a contaminant. Antimicrobial susceptibility testing of Nocardia isolates from the skin biopsy by broth microdilution according to Clinical and Laboratory Standards Institute methodology h revealed susceptibility to TMS [Minimum inhibitory concentration (MIC) ≤0.25/4.75 lg/mL], imipenem (≤2 lg/mL), clarithromycin (≤0.06 lg/mL), and amikacin (≤1 lg/mL).