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

Yaemsiri, S.; Sykes, J.E.

This is a detailed description of the use of MALDI-TOF for identification of Nocardia veterana in a dog in North America. It also describes successful treatment of Nocardia veterana bacteremia in a dog with antimicrobial drugs and discontinuation of immunosuppressive drug treatment. Nocardia are filamentous branching gram-positive bacteria found in soil and plant matter. Disseminated nocardiosis is a relatively uncommon disease in dogs and cats and is most often reported in immunocompromised animals or in individuals on immunosuppressive medications such as cyclosporine. 2, 3 With the more widespread application of gene sequencing and MALDI-TOF MS for bacterial identification, novel species of Nocardia have been identified, including N. veterana, which was first discovered in 2001 in human bronchoalveolar lavage fluid. 4 Initially, the role of N. veterana in clinical disease was poorly understood, but it was subsequently isolated from a mycetoma in a woman with systemic lupus erythematous (SLE). 5 Phylogenetically, N. veterana is closely related to N. nova, N. africana, and N. vaccinii and until recently had been indistinguishable from these species based on antimicrobial susceptibility testing and restriction fragment length polymorphism (RFLP) analysis. 6, 7 Historically, 16S rRNA gene sequencing has been used most commonly for identification as the 16S rRNA gene is highly conserved among Nocardia species. 8 However, in the case of a newer Nocardia spp., N. kruczakiae, and N. veterana, 16S rRNA gene sequencing could not differentiate between these 2 distinct species. 9 New techniques using secA1 gene were able to discriminate between different Nocardia spp. better than 16S rRNA gene and therefore may be more clinically useful for Nocardia spp. identification. 1 These techniques, however, are not readily available at most clinical laboratories, and with results taking up to several days to return, implementation of appropriate treatment can be delayed. MALDI-TOF MS has recently emerged as a rapid and reliable method of species identification. 10 Within minutes, MALDI-TOF MS analyzes the protein composition of a bacterial or fungal isolate and compares it to a library of mass spectrometry profiles, which is unique for each species. The ability of this technology to rapidly determine the identity of a bacterial isolate makes this technology particularly useful for identification of slow-growing, fastidious organisms such as Nocardia. 11 Some of the isolates made from the dog reported here had low identity score values. Recently, it has been shown that repeat extraction, duplicate spotting on the target plate, and addition of other libraries can increase genus-level and specieslevel identification significantly. 12 Since it was first isolated, fewer than 20 cases of N. veterana infection have been reported in the human literature. 5, 7, [13] [14] [15] [16] [17] [18] Inhalation is thought to be the most common route of transmission, and in the few reported cases of human N. veterana infections, pulmonary manifestations predominate. 6, 7, 13 However, a wide variety of other clinical manifestations of N. veterana infection have been reported in humans including urinary tract infections, brain and bowel abscesses, endogenous endophthalmitis, nodular lymphangitis, mycetomas, and bacteremia. 5, [14] [15] [16] [17] [18] [19] In veterinary medicine, reports of N. veterana infection have been limited to bovine mastitis resulting from direct inocul