Answer to March 2014 Photo Quiz

Abstract

Answer: Bacteremia caused by Tsukamurella tyrosinosolvens. The isolate was definitively identified as Tsukamurella tyrosinosolvens via DNA sequence analysis of the 16S rRNA gene. Similar to those of aerobic actinomycetes such as Gordonia spp., Rhodococcus spp., and Nocardia spp., cell walls of Tsukamurella spp. contain mycolic acids and allow for a weakly positive reaction upon modified acid-fast staining (1). The longer bacillary form of Tsukamurella spp. potentiates preliminary differentiation from Gordonia spp. (short coryneform bacilli) and Rhodococcus spp. (some coccoid forms) (1). Additional phenotypic delineation of Tsukamurella spp. can be guided with demonstration of growth in lysozyme (also Nocardia spp.) and specialized characterization of mycolic acid and menaquinone chemistry. However, molecular techniques, particularly those centered on gene sequencing, are necessary for definitive identification of aerobic actinomycetes to both the genus and species levels (1). Tsukamurella spp. have been documented to be etiologies of clinical disease, with reports increasing in recent years. Within a 12-year period at a university hospital, Liu et al. (2) rank ordered isolates of T. tyrosinosolvens, Tsukamurella spumae, and Tsukamurella pulmonis in the context of keratitis or catheter-related bloodstream infection. On rare occasions, Tsukamurella paurometabola has also been implicated in clinical disease (1). Specific to T. tyrosinosolvens, a recent report by Karunakaran et al. (3) typified a common clinical presentation. A catheter-related bloodstream infection in a 51-year-old hematology patient was resolved via catheter removal and an imipenem regimen. T. tyrosinosolvens has also been implicated in cerebellar abscess (4) and presentations of respiratory disease (5, 6). The two preceding citations shared an underlying status of immunosuppression, ranging from antecedent lung transplantation to delivery of chemotherapeutic agents by a central venous catheter. The cerebellar abscess presented in an immunocompetent patient with predisposing chronic otitis media that was refractory to penicillin and cephalosporin agents. Antimicrobial susceptibility testing was not performed on this isolate, due to the inconclusive utility of the Clinical and Laboratory Standards Institute standards for testing aerobic actinomycetes other than Nocardia spp. (7). Liu et al. (2), in a limited data set, suggested that T. pulmonis yielded higher MICs for clindamycin, erythromycin, vancomycin, and tetracycline than other Tsukamurella spp. Antimicrobials with lower MICs across multiple species included gentamicin, levofloxacin, and ciprofloxacin. Similar to data reported by Karunakaran et al. (3), our patient defervesced quickly upon removal of the peripherally inserted central catheter (PICC) line and initiation of antimicrobial therapy. The patient was discharged to home on parenteral vancomycin therapy. (See page 711 in this issue [doi:10.1128/JCM.03462-12] for photo quiz case presentation.)