Isolation and Characterization of a Novel Alpha-Hemolytic spp. from the Oral Cavity and Blood of Septicemic Periparturient Immunodeficient Mice.

MISTRG is an immunodeficient mouse strain that expresses multiple human cytokines that support hematopoietic stem cell maintenance and myelopoiesis. While establishing a breeding colony of MISTRG mice in a dedicated barrier room, 6 cases of death or disease occurred in pregnant or postpartum mice. Clinically, this manifested as hunched posture, dyspnea, and 1 case of emaciation with ataxia. Pathologic analysis of 7 mice revealed multisystemic necrosuppurative inflammation variably affecting the uterus and placenta, joints, meninges, inner and middle ears, kidneys, and small intestine. Bacteria cultured from the blood of septic mice were identified with 89% probability by the Vitek 2 identification system as with atypical biochemical parameters; the API 20E/NE system fully differentiated the isolates as a novel species. MALDI Biotyper-based mass spectrometry also indicated that the phenotype represented a novel spp. Sequencing revealed that the full-length 16S rRNA gene identity was below 97% with known species, including the 2 closest species and . We propose the name spp. nov to our novel isolates. All male mice in this colony remained healthy despite their association with diseased female mice. Overall, 19% of the colony carried the novel in their oral cavity, but it could not be detected in feces. The organism was sensitive to amoxicillin, which was administered via drinking water throughout pregnancy and weaning to establish a colony of pathogen-negative future breeders. The colony remained disease-free and culture-negative for spp. nov after treatment with amoxicillin. We suspect that oral colonization of MISTRG mice with the novel species and its associated unique pathology in periparturient mice is potentially the principal cause of loss of this strain at several institutions. Therefore, screening the oral cavity for α-hemolytic streptococci followed by targeted antibiotic treatment may be necessary when establishing MISTRG and allied immunodeficient mouse strains.