In the current case, CRBSI caused by T. tyrosinosolvens, which is very rare in children, was identified using a modified secA1 sequence. The patient was successfully treated with VCM monotherapy and CVC removal. Improper CVC management during the overnight stay outside of the hospital may have caused the infection.

T. tyrosinosolvens and related species are sometimes misdiagnosed for contaminant microorganisms or other species because they are difficult to identify with standard laboratory tests. Delays in accurate diagnosis and misdiagnoses can lead to suboptimal antibiotic selection, delayed treatment, which in turn may lead to systemic infection and poor prognosis [3, 5, 9,10,11,12]. A method for identifying uncommon pathogens is MALDI TOF-MS, which provides reasonably rapid genus-level identification, and, therefore, better patient care [13]. However, MALDI TOF-MS is not able to identify Tsukamurella species as there are few genetic differences between them [5, 10,11,12]. Species-level identification is important as it can contribute to the correct epidemiological characterization of unusual pathogens. Several tests have been successful for species identification, including 16 S rRNA gene sequencing and sequencing of several target genes [14, 15]. However, previous studies have shown that the majority of Tsukamurella species have highly similar 16 S rRNA gene sequences, and as a result, it has been found to be insufficiently discriminative in identifying Tsukamurella species [3, 5, 9, 11, 14]. By contrast, the secA1 sequence has been shown to be suitable for the discrimination of clinically important Tsukamurella spp [16]. In this case, modified secA1 sequencing was necessary for species identification.

Most reported cases of T. tyrosinosolvens infection have been related to bacteremia due to intravascular prosthetic devices, immunosuppression following hematological malignancy or post chemotherapy, and graft-versus-host disease after bone marrow transplant [3, 17, 18]. The optimal management of Tsukamurella infections has yet to be determined. To date, the CLSI document M24 provides criteria for susceptibility testing of Tsukamurella species by the broth microdilution method [19]. If there is doubt about the results of the broth microdilution method, CLSI recommends the disk diffusion test to be performed. In most case reports, susceptibility to amikacin, clarithromycin, imipenem, ciprofloxacin, and trimethoprim-sulfamethoxazole and resistance to penicillin, cefoxitin, and expanded-spectrum cephalosporins have been reported in Tsukamurella isolates [3, 9]. Based on the treatment principles for nocardiosis and atypical mycobacterial infections, a number of antimicrobial agent combinations have been proposed as potential treatments for Tsukamurella infections [3, 6]. Our isolate was susceptible to VCM and quinolones, in line with the results of previous reports. The patient in this case wastreated with VCM monotherapy for 14 days and CVC removal with good outcome.

A previous study identified multiple inappropriate infection control practices, with the most likely cause being improper management of CVC lines [20]. In the current case, the patient had stayed outside of the hospital for 3 days prior to onset and we suspect that the infection was caused by improper CVC management during this time.

In conclusion, in addition to rapid genus identification by MALDI TOF-MS, secA1 sequencing may be a useful diagnostic tool in the confirmation of Tsukamurella spp. Rapid identification facilitates faster treatment, and may lead to a good prognosis. Providing proper management of CVCs is essential for prevention of infection.