Human oropharynx as natural reservoir of Streptobacillus hongkongensis

Recently, we reported the isolation of Streptobacillus hongkongensis sp. nov. from patients with quinsy or septic arthritis. In this study, we developed a PCR sequencing test after sulfamethoxazole/trimethoprim and nalidixic acid enrichment for detection of S. hongkongensis. During a three-month study period, among the throat swabs from 132 patients with acute pharyngitis and 264 controls, PCR and DNA sequencing confirmed that S. hongkongensis and S. hongkongensis-like bacteria were detected in 16 patients and 29 control samples, respectively. Among these 45 positive samples, five different sequence variants were detected. Phylogenetic analysis based on the 16S rRNA gene showed that sequence variant 1 was clustered with S. hongkongensis HKU33(T)/HKU34 with high bootstrap support; while the other four sequence variants formed another distinct cluster. When compared with the 16S rRNA gene of S. hongkongensis HKU33(T), the five sequence variants possessed 97.5–100% sequence identities. Among sequence variants 2–5, their sequences showed ≥99.5% nucleotide identities to each other. Forty-two individuals (93.3%) only harbored one sequence variant. We showed that the human oropharynx is a reservoir of S. hongkongensis, but the bacterium is not associated with acute pharyngitis. Another undescribed novel Streptobacillus species is probably also residing in the human oropharynx.