Obligate aerobic, gram-positive, weak acid-fast, nonmotile bacilli, Tsukamurella tyrosinosolvens: Minireview of a rare opportunistic pathogen

Abstract

Tsukamurella species are obligate aerobic, gram-positive, weak acid-fast, nonmotile bacilli. They are found in various environments, such as soil, water, sludge, and petroleum reservoir wastewater, and belong to the order Actinomycetales. In 2016, there was a reclassification of species within the genus Tsukamurella, merging the species Tsukamurella tyrosinosolvens (T. tyrosinosolvens) and Tsukamurella carboxydivorans. Tsukamurella species are clinically considered to be a rare opportunistic pathogen, because most reported cases have been related to bacteremia and intravascular prosthetic devices and immunosuppression. To date, it has been isolated only from human specimens, and has always been associated with clinical disease; human infections are very rare. Reported infections have included pneumonia, brain abscesses, catheter-related bloodstream infections, ocular infections, bacteremia, and sepsis presenting with septic pulmonary emboli in patients who are immunocompromised. To date, there is no commercially available test for identification. On the other hand, sequence-based identification, including matrix-assisted laser desorption ionization time-of-flight mass spectrometry, is an alternative method for identifying clinical isolates that are either slow growers or difficult to identify through biochemical profiling. The golden standards for diagnosis and optimal management still remain to be determined. However, newer molecular biological techniques can provide accurate identification, and contribute to the appropriate selection of definitive therapy for infections caused by this organism. Combinations of several antimicrobial agents have been proposed for treatment, though the length of treatment for infections has yet to be determined, and should be individualized according to clinical response. Immunocompromised patients often experience severe cases due to infection, and life-threatening T. tyrosinosolvens events associated with dissemination and/or failure of source control have occurred. Favorable prognoses can be achieved through earlier identification of the cause of infection, as well as successful management, including appropriate antibiotic therapy together with source control. Further analyses of similar cases are required to establish the most adequate diagnostic methods and treatment regimens for infections.

Keywords: Combination antibiotic therapy; Gram-positive bacilli; Matrix-assisted laser desorption ionization time-of-flight mass spectrometry; Opportunistic infection; Sequence-based identification; Tsukamurella tyrosinosolvens.

Figure 1

Gram staining of Tsukamurella tyrosinosolvens from aerobic bottles, blood cultures (× 1000 magnification). Blood sample from a catheter-related blood stream infection patient, at our institution. Numerous rod-shaped bacteria are confirmed.

Figure 2

Tsukamurella tyrosinosolvens on a blood agar plate. The blood sample was taken at our institution, from a patient with a catheter-related blood stream infection. A: The development of flat, huge, dry, and white- to light-cream-colored bacterial mass is confirmed; B: A close-up image. The development of flat, huge, dry, and white- to light-cream-colored colonies, in addition to crow's feet in the overlapping portion, is confirmed.