Leptotrichia hongkongensis sp. nov., a novel Leptotrichia species with the oral cavity as its natural reservoir

A straight, non-sporulating, Gram-variable bacillus (HKU24^T) was recovered from the blood culture of a patient with metastatic breast carcinoma. After repeated subculturing in BACTEC Plus Anaerobic/F blood culture broth, HKU24^T grew on brucella agar as non-hemolytic, pinpoint colonies after 96 h of incubation at 37 °C in an anaerobic environment and aerobic environment with 5% CO₂. Growth was enhanced with a streak of Staphylococcus aureus. HKU24^T was non-motile and catalase-negative, but positive for alkaline phosphatase, ß-glucosidase, and α-glucosidase. It hydrolyzed phenylphosphonate and reduced resazurin. 16S rRNA, groEL, gyrB, recA, and rpoB sequencing showed that HKU24^T occupies a distinct phylogenetic position among the Leptotrichia species, being most closely related to Leptotrichia trevisanii. Using HKU24^T groEL, gyrB, recA, and rpoB gene-specific primers, fragments of these genes were amplified from one of 20 oral specimens. Based on phenotypic and genotypic characteristics, we propose a new species, Leptotrichia hongkongensis sp. nov., to describe this bacterium.