Streptococcus sinensis was originally described as a causative agent for infective endocarditis in three Chinese patients from Hong Kong in 2002. Subsequently, several cases were reported outside Hong Kong, indicating that it is an emerging pathogen worldwide. We isolated a closely related strain in a young patient diagnosed with infective endocarditis in mainland China. In this paper, we reviewed the course of infection and provided a comprehensive comparison of its clinical characteristics with the reported cases.

Background: Micrococcus yunnanensis (M. yunnanensis) is an endophytic actinomycete that was originally isolated from the roots of Polyspora axillaris in 2009, and no human infections caused by this organism have yet been reported. We report the first case of community-acquired pneumonia caused by M. yunnanensis and propose that M. yunnanensis should be considered as an emerging pathogen in medical practice. A 30-year-old woman was admitted to our hospital with fever, paroxysmal dry cough with sputum, and pharyngalgia. Laboratory tests revealed an increase in several inflammatory indicators, and a computerized tomography scan of the chest showed scattered infection foci in both lungs. Bronchoalveolar lavage fluid was collected via bronchoscopy for microbial culture and pathological examination.Methods: The isolate from bronchoalveolar lavage fluid was identified as M. yunnanensis by 16S rRNA gene sequencing. The patient was diagnosed with community-acquired pneumonia based on the diagnostic criteria.Results: The patient was treated with intravenous amoxicillin/clavulanate potassium, levofloxacin hydrochloride tablets, and compound methoxyphenamine capsules on the day after admission. After 3 days of treatment, the patient's physiological conditions and inflammatory indicators normalized, and 6-month follow-up showed no abnormalities. Conclusion:Although the pathogenicity of M. yunnanensis is unclear, the present case indicates an emerging pathogen in medical practice. MALDI-TOF MS has a limited ability to identify novel or rare pathogenic species, and 16S rRNA gene sequencing is of great value in some circumstance.Abbreviations: AST = antimicrobial susceptibility test, BALF = bronchoalveolar lavage fluid, MALDI-TOF MS = matrix-assisted laser desorption ionization/time of flight mass spectrometry.