Corynebacterium striatum Bacteremia Associated with a Catheter-Related Blood Stream Infection

A 49-year-old woman visited our emergency department because of exertional dyspnea due to severe left ventricular functional failure. It progressed to disseminated intravascular coagulation and disturbance of consciousness on day 67 of admission. Gram-positive bacilli were detected from two different blood culture samples on day 67 of admission. An API-Coryne test and sequencing (1~615 bp) of the 16S rRNA gene were performed, and the strain was identified as Corynebacterium striatum. The bacterium was detected from the removed central venous catheter tip too, and the patient was diagnosed with catheter-related bloodstream infection by C. striatum. However, treatment was not effective, and the patient died on day 73 of admission.


Introduction
The Corynebacteria are a group of aerobic, Gram-positive, catalase-positive, nonsporulating, generally nonmotile rods [1]. The Corynebacteria are divided into two groups: Corynebacterium diphtheriae and nondiphtherial Corynebacteria, collectively referred to as diphtheroids. When isolated from clinical specimens, nondiphtherial Corynebacteria, such as Corynebacterium striatum, Corynebacterium amycolatum, Corynebacterium minutissimum, Corynebacterium xerosis, and Corynebacterium freneyi, were originally thought to be contaminants [2], as these strains are commonly considered as part of the normal flora of human skin and mucous membranes. However, in recent years, they have been reported as emerging opportunistic pathogens in immunocompromised patients with end-stage cancer, hematologic malignancy, and critical condition [2]. There are several reports of C. striatum infections including cases of bacteremia, endocarditis, meningitis, pleuropneumonia, osteomyelitis, arthritis, and intrauterine infections [3]. In the present case, we report a catheter-related bloodstream infection caused by C. striatum, in a 49-year-old immunocompetent female patient which has multiple organ failures.

Case Presentation
A 49-year-old woman was brought to our emergency department because of exertional dyspnea due to severe left ventricular functional failure. Her vital signs were unstable; hence, she was immediately admitted to the intensive care unit (ICU). She had two comorbidities: one was diastole cardiomyopathy, and the other was complete atrioventricular block (c-AVB), already treated with a pacemaker implantation (PM).
Although an implantable cardioverter defibrillator (CRT-D, Cardiac Resynchronization Therapy-Defibrillation), with biventricular pacing function, was replaced with PM for severe left ventricular functional decline, on day 12 of admission, an intra-aortic balloon pump (IABP) was also inserted because of multiple organ failure. The IABP was removed on day 16 of admission. Thereafter, there was no obvious fever, signs of infection, so no antibiotics were administered. However, intermittent hemodialysis was continued due to liver failure and renal failure, and an IABP was necessary again after a worsening of cardiac function on day 66. The illness progressed to disseminated intravascular coagulation (DIC) and disturbance of consciousness on day 67 of admission. Therefore, two sets of blood samples for blood culture were collected. Gram-positive bacilli were detected in both blood culture samples; each set included aerobic and anaerobic cultures (Figures 1(b) and 1(c)). A central venous catheter inserted in the patient's right internal jugular vein was removed and the catheter tip was sent for a semiquantitative culture analysis on day 68 of admission. No bacteria species could be identified at this time. Some asynergy in wall motion was detected by echocardiography, but no vegetation was seen. Initially, on day 67 of admission, tazobactam/piperacillin (TAZ/PIPC) (2.25 g every 6 hours) was prescribed. After the results from blood cultures on day 69 of admission, vancomycin (VCM) (1 g every 6 hours) was added to the therapy, while TAZ/PIPC was changed with meropenem (MEPM) (1 g every 6 hours) on day 72. At this time, another two sets of blood samples were collected and blood cultures were negative. However, the patient died on day 73 of admission.
In order to identify the specific strain of infection, the API-Coryne test (BioMèrieux, France) was performed. This method is based on the assessment of biochemical properties. C. striatum/C. amycolatum strain was identified with a probability of 89.7%. The nucleotide sequence (1∼615 bp) of the 16s rRNA gene revealed a 99.7% homology to a specific subtype, that is, C. striatum ATCC 6940 (GenBank: NZ GG667536). The bacterium was detected from the removed central venous catheter tip too. Thus, the patient was diagnosed with a C. striatum catheter-related bloodstream infection. The C. striatum strain was susceptible to VCM, linezolid (LZD), and gentamicin (GM) ( Table 1).

Discussion
C. striatum colonizes the skin and mucous membranes of both healthy people and hospitalized patients [4]. The majority of cases of C. striatum infection are hospital-acquired as wound infections and a few reports on systemic infections [5], that is, infection confirmed by isolation of C. striatum from a sterile site, are available. However, most of these cases are represented by patients with implanted indwelling devices or who present an immunosuppression [2,6]. Because her general condition worsened, implanted indwelling devices To our knowledge, this is the second report which found both blood cultures and cultures from a central venous catheter tip positive for the same strain of C. striatum [2]. Since C. striatum may have been isolated from blood sample cultures, it is difficult to distinguish an innocuous contamination from a dangerous infection. Outbreaks caused by multidrug-resistant C. striatum have been reported in patients with prolonged hospitalization, mechanical ventilation, or use of broad-spectrum antibiotics [7,8].
Approximately 0.2 to 0.4% of native valve endocarditis is caused by Corynebacterium spp., while 9% of early and 4% of late prosthetic valve endocarditis are caused by members of the genus [9,10]. Although patients with implanted CRT-D may develop infectious endocarditis, obvious vegetation was never observed on echocardiography in these cases [11].
In addition, there is a report of a patient who underwent hemodialysis and developed sepsis caused by a Corynebacterium sp. [2]. As the same type of bacteria was detected by the catheter tip culture, the cervical catheter was withdrawn during the hemodialysis, as it was presumed to be the port of entry in this case.
The API-Coryne test is a method to distinguish C. striatum from C. amycolatum. Although the biochemical properties of C. amycolatum and C. striatum are similar, only C. striatum contains mycolic acid [12]. However, this compound can only be detected by special analyses, for example, gas chromatography; thus C. striatum identification was confirmed by 16s rRNA gene analysis.
Since most of reports classified C. striatum as susceptible to a wide range of antibiotics [13], it has been suggested that a selective pressure exerted by previous antimicrobial treatment could contribute to its overgrowth. This would eventually lead this strain to become a secondary colonizer in immunocompromised hosts [8].
In general, C. striatum is resistant to penicillin but sensitive to other -lactam antibiotics and to vancomycin. In a previous report, vancomycin was recommended as empirical therapy for serious infections caused by Corynebacterium spp. [14]. Although C. striatum was susceptible to VCM in this case, the patient might have died because administration of VCM was delayed. Therefore, in this case, appropriate antibiotics could not be judged in vivo. However, the optimal antimicrobial therapy for these infections is still controversial. In vitro susceptibility tests showed that linezolid and tigecycline are active against coryneform bacteria, revealing a potential therapeutic value [15,16] of these compounds. Currently, there are no guidelines for the treatment of Corynebacterium spp. infections. Appropriate susceptibility tests and interpretive criteria are critically needed, in light of the growing emergence of multidrug resistance and its involvement in nosocomial infections.
In conclusion, although Corynebacterium could be isolated from a blood culture as a common contaminant, in certain case this observation could conceal a dangerous infection. Patients with a history of exposure to broad-spectrum antibiotics or immunosuppression, as well as critically ill patients with an implanted indwelling device or a central venous catheter, must be considered at high risk of severe infection for this type of bacteria and it is necessary to recognize C. striatum as an emerging nosocomial pathogen. In conclusion, we encountered a case of catheter-related bloodstream infection caused by C. striatum. Unfortunately, we could not successfully treat the patient because of her poor general condition and comorbidity.