A novel α-hemolytic Streptococcus species (Streptococcus azizii sp. nov.) associated with meningoencephalitis in naïve weanling C57BL/6 mice

Abstract

During 1 year, experimentally naïve C57BL/6NCrl weanlings born to timed-pregnant dams from a single vendor demonstrated markedly increased mortality associated with runting, abnormal gait, and decreased activity. Gram-positive, aerobic, α-hemolytic, coccoid bacteria were isolated from the meninges (n = 16), blood (n = 1), and kidneys (n = 1) of clinically affected weanlings (n = 15); from the uterus (n = 1), meninges (n = 1), and oral cavity (n = 2) of 3 dams; and from the meninges and oral cavity of a clinically affected 86-d-old mouse in the same colony. Multifocal, necrosuppurative meningoencephalitis and ventriculitis with intralesional gram-positive coccoid bacteria were present in all but 2 affected animals. The bacterium also was isolated from the oral cavity of an asymptomatic timed-pregnant dam (1 of 23) from the same vendor and from 8 mice at the vendor's facility. All isolates (n = 25) were identified by using 2 semiautomated rapid-identification systems, one of which consistently identified the causative bacterium as Aerococcus viridans 2 (n = 12) or 3 (n = 13), with probabilities of 55.7% to 98.3%. The bacterium did not grow in 6.5% NaCl at 10 °C, thus suggesting a Streptococcus species. Partial 16S rRNA sequencing of 4 isolates suggested S. hyointestinalis (probability, 93.4%) and S. gallinaceus (99.5%). Full 16S rRNA sequences for 3 isolates identified the bacterium as a novel Streptococcus species most closely related to S. acidominimus strain LGM (96.5%) and Streptococcus species strain Smarlab 3301444 (96.3%) and for which we propose the name S. azizii.