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Herein we report the case of a 10-year-old boy with an autosomal mosaic mutation who developed bacteremia. The causative agent was identified as Moraxella osloensis by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and 16S rRNA gene sequencing. In the pediatric population, there have been 13 case reports of infection attributed to M. osloensis and this is the fifth reported case of pediatric bacteremia due to M. osloensis. After Moraxella species infection was confirmed, the patient recovered with appropriate antimicrobial therapy. It is important to consider that M. osloensis can cause serious infections, such as bacteremia, in otherwise healthy children. Keywords: Moraxella osloensis, Bacteremia, MALDI-TOF MS, 16S rRNA gene sequencing

Publisher Summary The glucose-nonfermenting bacteria include organisms in the Neisseriaceae family as well as the genera Flavobacterium, Weeksella, and Agrobacterium, and CDC groups M5, M6, and EF-4. These bacteria either utilize glucose oxidatively or do not utilize glucose oxidatively. Genera that have the greatest pathogenic significance in animals are Moraxella and Acinetobacter. Acinetobacter calcoaceticus is the only species currently listed in the genus Acinetobacter. Species of Acinetobacter are commonly found in soil, water, sewage, food, and milk; they are also a part of the normal flora of humans and animals. In many human and veterinary clinical laboratories, Acinetobacter is the second most common nonfermentative gram-negative bacterium isolated, following Pseudomonas aeruginosa. Acinetobacter grows on most laboratory media—including MacConkey agar—on which colonies are colorless to light pink. Species of the genus Moraxella include Moraxella bovis, Moraxella lacunata, Moraxella phenylpyruvica, Moraxella nonliquefaciens, Moraxella atlantae, Moraxella urethralis, and Moraxella osloensis. The glucose-nonfermenting gram-negative bacteria are differentiated from other oxidative and nonsaccharolytic bacteria—such as pseudomonads—and related bacteria by motility and a flagella stain and by glucose O–F medium. Pseudomonads are motile by polar flagella, whereas most of the nonfermenting bacteria described in this chapter are nonmotile. Agrobacterium is the only motile genus included in the chapter. It is differentiated from other pseudomonads by its peritrichous flagella.