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A 54-year-old man was admitted to our institute with a diagnosis of infectious endocarditis with vegetation on the mitral valve and severe regurgitation due to Gemella morbillorum infection together with renal dysfunction, which was eventually diagnosed as infection-related pauci-immune necrotizing crescentic glomerulonephritis. Given the refractoriness to antibiotics, the persistent activity of nephritis, and repeated cerebral hemorrhaging, we prioritized steroid therapy over early surgical mitral valve replacement. Following steroid therapy, the glomerulonephritis completely improved. Although the administration of steroid therapy in the active phase of infectious endocarditis remains controversial, it might be indicated if comorbid glomerulonephritis is critical.

We report a case of empyema due to Gemella morbillorum. In this case, an analysis of the aspirate from the pleural effusion revealed empyema and evidence of a Gram-positive coccal bacteria. A biochemical identification system labelled the bacteria as 'unclassified', although we initially suspected the bacterium to belong to the Streptococcus species. 16S ribosomal RNA (16S rRNA) gene sequencing and a phylogenetic tree analysis of the isolated strain confirmed the presence of Gemella morbillorum. To ascertain the true incidence of Gemella species in empyema, 16S rRNA gene sequencing should be used when the standard conventional biochemical methods fail to identify the organism or it identifies it with a low degree of reliability.

Infections caused by Gemella morbillorum are uncommon. This organism is primarily associated with endocarditis and bacteremia and rarely with spondylodiscitis, arthritis, hepatic abscesses and meningitis. Sternal osteomyelitis caused by G. morbillorum has not yet been reported. We herein present a case of sternal osteomyelitis with a mediastinal abscess caused by G. morbillorum that occurred in a 74-year-old diabetic patient following blunt force trauma to the anterior chest wall. The patient was treated successfully with surgical excision and prolonged antibiotic treatment. Early recognition and timely intervention are important for managing life-threatening osteomyelitis of the sternum.

A case of infective endocarditis (IE) caused by a rare pathogen, Gemella morbillorum, is presented. Because of persistent low-grade fever after dental treatment, the patient was given oral antibiotics. Whereas he was diagnosed as having aortic regurgitation by a cardiologist, and IE was not suggested unfortunately. After long-term chemotherapy over five months, he was aware of nocturnal dyspnea and Gemella morbillorum was detected by blood culture. Then, he was treated with intravenous administration of Penicillin-G, and underwent surgical operation for valve replacement. No cases of IE due to this organism have been reported in Japan.