Bacteraemia Caused by Kytococcus schroeteri in a Pneumonia Patient

Kytococci are a part of the normal skin microbiota of humans and can cause infections, particularly in patients with prosthetic devices or immunodeficiency. Due to insufficient identification methods and an intrinsic resistance to several β-lactams, infections due to Kytococci are a challenge to clinical microbiologists and clinicians [1]. Here, we report the first Korean case of bacteraemia due to Kytococcus schroeteri in a patient with pneumonia.


Introduction
Kytococci are a part of the normal skin microbiota of humans and can cause infections, particularly in patients with prosthetic devices or immunodeficiency. Due to insufficient identification methods and an intrinsic resistance to several β-lactams, infections due to Kytococci are a challenge to clinical microbiologists and clinicians [1]. Here, we report the first Korean case of bacteraemia due to Kytococcus schroeteri in a patient with pneumonia.

Case Report
A 55-year-old man was admitted to a tertiary-care hospital in Seoul, Korea, for evaluation of fever and dyspnea. The patient had no history of hypertension or diabetes mellitus. The patient had been living in a sanatorium because of quadriplegia resulting from a cerebral infarction diagnosed at age 20 years. Laboratory tests showed a leukocyte count of 12.89 × 10 9 /L (neutrophil 83.6%) and a C-reactive protein level of 156.0 mg/L (normal range, 0.1-6.0 mg/L). A chest X-ray showed a large amount of pleural effusion and marked peribronchovascular markings in the left lung. Percutaneous catheter drainage of the pleural effusion was performed, but the pleural fluid culture did not yield any bacterial growth. The predominant organism of sputum cultures was α-Streptococcus species, which is thought to be part of the normal flora. A blood culture performed the day the patient was admitted showed Gram-positive cocci growth (isolate GNKS01) in an anaerobic blood culture vial, one of six total (three aerobic and three anaerobic).
Subculture of the blood culture fluid yielded small, slightly yellowpigmented, convex, catalase-positive, and non-haemolytic colonies on 5% sheep blood agar after 24 h of incubation in 6% CO 2 at 35°C. Routine Gram staining of the smeared preparation showed Gram-variable cocci in pairs or tetrads ( Figure 1). However, the isolate appeared to be Grampositive after shortening the destaining time from 3-4 sec to 1-2 sec. Morphologic evaluation using scanning electron microscopy (FE SEM S-800, Hitachi, Tokyo, Japan) showed spherical cells (1.0-1.5 μm in diameter) in pairs or tetrads ( Figure 2).
Biochemical features were tested using the GP identification card with Vitek 2 system (bioMérieux, "Marcy-I'Étoile", France). However, the commercial card failed to identify the organism. Analysis using matrix-assisted laser desorption/ionization mass spectrometry (MALDI Biotyper, Bruker Daltonics, Bremen, Germany) also failed to identify the organism. 16S rDNA gene sequencing was performed with a universal bacteria primer set, 27F (5'-AGA GTT TGA TCC TGG CTC AG-3') and 1541R (5'-AAG GAG GTG ATC CAG CCG CA-3'), using an automatic sequencer (ABI 3730xl, AB, Weiterstadt, Germany), and the partial 16s rDNA sequences of the isolate GNKS01 were Antimicrobial susceptibility testing was performed with the disk diffusion method. Minimal inhibitory concentrations (MICs) of antimicrobials were determined with Etest strips (bioMérieux) on Mueller-Hinton agar (Asan Pharmaceutical, Seoul, Korea) following the guidelines of the Clinical and Laboratory Standards Institute [2]. The isolate GNKS01 exhibited similar antimicrobial susceptibility patterns to the type strain DSM 13884 T (Table 1). However, the isolate GNKS01 was susceptible to erythromycin, while the type strain DSM 13884 T was resistant.
The patient was treated with tazobactam and ciprofloxacin. He showed good clinical response, and symptoms and elevated inflammatory markers resolved after 10 days.
K. schroeteri is a Gram-positive coccus; however, the isolate GNKS01 showed Gram-variable results in routine Gram staining. A former case report described a similar phenomenon in which identification was hampered because the microorganism was misidentified as Gramnegative cocci [1]. The authors attributed the cause of the abnormal Gram stain reaction to treatment with β-lactams or the inflamed tissue from which the K. schroeteri was isolated [1]. However, when we performed routine Gram staining for the type strain DSM 13884 T , we also observed Gram-variable results. Thus, we assume that K. schroeteri may have a property that allows it to be easily destained, which could result in its misinterpretation as Gram-negative cocci.
In this case report, K. schroeteri GNKS01 was isolated from a blood specimen of a patient with pneumonia. However, the patient's pleural fluid did not yield any bacterial growth, and the sputum culture did not showed any growth other than α-Streptococcus species. Given that the patient did not have any focal infections other than pneumonia, we consider the possibility that his bacteraemia originated from respiratory infection.
In summary, we report a case of K. schroeteri bacteraemia successfully treated with tazobactam and ciprofloxacin in a patient with pneumonia. We found that Gram-staining results of K. schroeteri can be easily misinterpreted as Gram-negative cocci. Additionally, identification of the Kytococcus spp. isolates using commercially available identification cards and MALDI-TOF MS systems was difficult, indicating the necessity of 16S rDNA gene sequencing.