Discrepant Satellitism for Identification of Granulicatella adiacens Isolates

Granulicatella adiacens is a catalase-negative, oxidase-negative, facultatively anaerobic, Gram-positive coccus [1]. This bacterium is considered nutritionally variant streptococci (NVS) because of its requirement for pyridoxal, L-cysteine, or additional nutrients, such as sulfhydryl compounds, for growth [2]. G. adiacens can grow well on culture medium containing these required nutrients. G. adiacens colonies can grow as satellite colonies around other bacteria, such as Staphylococcus aureus [3]. However, most clinical microbiologists have overlooked the fact that G. adiacens isolates can show discrepant satellite testing results based on the different kinds of nutrients contained in blood agar plates (BAPs) produced by different manufacturers. Here, to the best of our knowledge, we firstly report a discrepant satellite testing result of G. adiacens isolates on BAPs produced by different manufacturers. A 62-yr-old man was admitted to our hospital after 2 days of fever. He had no history of cardiac disease. There was no vegetation on his cardiac valves on the basis of echocardiography results. Blood samples were collected from peripheral veins at two other sites and inoculated into broth media in aerobic and anaerobic blood culture bottles. The BacT/Alert 3D system (BioMérieux Inc, Durham, NC, USA) was used to incubate and monitor bacterial growth. After blood culture tests were performed, the patient received empirical antibiotic treatment with 2 g intravenous cefotaxime every 8 hr. After 3 days of incubation, two sets of aerobic blood culture bottles appeared positive on the basis of visual inspection. Gram staining of the positive smear preparations revealed Gram-positive pleomorphic cocci in pairs and short chains. The cultured blood specimens were inoculated onto BAP, MacConkey agar (MAC), and chocolate agar plates (ASAN Pharmaceutical, Hwaseong, Korea). After 72 hr, pin-point sized, grayish-white colored colonies grew on the BAP and chocolate agar. No colony growth was observed on MAC, and catalase and oxidase tests were negative. We performed a satellite test to identify the organism because the Gram staining and biochemical testing results suggested NVS. A streak of S. aureus ATCC 25923 was made across the BAP surface for satellite testing. These microorganisms exhibited no satellite effect on BAPs. We used the same method to perform a satellite test using another BAP (MICROMEDIA Corp., Busan, Korea), and found that the microorganism exhibited a satellite effect (Fig. 1). The isolate was identified as G. adiacens with 98.7% probability using the VITEK 2 Gram-Positive Identification Card (BioMérieux, Marcy-l’Etoile, France). We performed 16S ribosomal RNA (rRNA) gene sequencing analysis to confirm the identity of the isolate. PCR was used to amplify the first 500 bp of the 5’ end of the 16S rRNA gene using the MicroSeq 500 16S rDNA Bacterial Identification PCR kit