Oral streptococci have been associated with systemic diseases, including infective endocarditis and neutropenic bacteremia. We analyzed 58 recent oral streptococcal bloodstream isolates, and we obtained clinical and demographic data for source patients. The sodA gene was found to be a better target than the 16S-23S rRNA internal transcribed spacer for DNA sequence-based species identification. Together, Streptococcus mitis and Streptococcus oralis were significantly more likely than the 12 combined remaining species to be isolated from neutropenic patients. Streptococci are the most abundant inhabitants of the human mouth (6, 24), and they gain frequent access to the bloodstream through periodontal lesions or oral abrasions created by routine activities (32). This can lead to serious illnesses, including infective endocarditis (IE) (28) and neutropenic bacteremia (29). The taxonomy of the oral streptococci has long been a source of confusion (4,9,20,22,31). Sequencing of the 16S rRNA gene has clarified the situation immensely (13); however, this approach lacks the sensitivity required to distinguish certain closely related species, including Streptococcus mitis and Streptococcus oralis (12), or to allow for strain typing or phylogenetic analysis within species. Genes possessing greater variability have therefore been examined, including the 16S-23S rRNA intergenic transcribed spacer (ITS) (2), protein-coding housekeeping genes (1, 5, 7, 10, 12, 14, 15, 19, 23), or both (17, 18). Consensus concerning the gene(s) best suited for these purposes has yet to emerge. Further, although previous studies have identified oral streptococci from clinical blood cultures using definitive sequencing methods (12,23,30), none have reported detailed clinical information about underlying disease. We set out to do both.Bloodstream cultures performed at Virginia Commonwealth University Medical Center Hospital from May 2003 to May 2008 were presumptively identified as containing streptococci by the clinical microbiology laboratory. A computer script was used to exclude nonoral species. To avoid analysis of contaminants, isolation plates were requested only when two or more reports originated from separate cultures of the same patient. One colony from each available isolation plate was grown in broth culture and examined macroscopically and microscopically. If any differences were observed in separate cultures derived from the same patient, both cultures were retained. Otherwise, a single culture from each patient was cryopreserved, and aliquots were removed for PCR amplification.To determine the species identity and phylogenetic relatedness of each isolate, the 16S-23S ITS was amplified using the 6R and 13BF primers described previously (2). When products were not obtained from some isolates, we noted that the final three nucleotides of the 6R primer did not align with 23S rRNA sequences in GenBank from several species of interest. We therefore shortened and simplified the 6R primer, creating 6R-S, and shortened the 13BF primer to ma...
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