Experimental aspiration pneumonia induced by human supragingival dental plaque in mice

人类牙菌斑由多种微生物组成，其中一些被认为会引起全身感染，包括吸入性肺炎。为了从实验上证实这一假设，我们检测了小鼠牙菌斑诱导肺炎的能力，菌斑产生的感染位点的微生物特征。等量含1 × 10^7 CFU细菌的龈上牙菌斑悬浮液被送入小鼠气管下部。所有的老鼠在接种后立即表现出疾病的迹象，如皮毛皱褶，呼吸困难，看起来很消瘦。18只小鼠中有12只（66.7%）在接种牙菌斑悬浮液后3天内死亡。检测的3个人类牙菌斑样本均诱发小鼠肺炎。所有死亡小鼠肺中均检出细菌细胞，数量为4.44±0.77 log_<10>CFU/mg。6只存活小鼠中有5只在肺中检出细菌细胞，数量为0.38±0.38 log_<10>CFU/mg。从感染的小鼠肺中检出多种微生物，存活小鼠和接种菌斑后3天内死亡的小鼠均未发现特征性的细菌分布。有代表性的口腔链球菌、中间链球菌和麻疹球菌分别从肺中分离出可诱发肺炎的菌株。这些结果表明，人类龈上牙菌斑是引起肺炎的传染性病原体的来源。

Human dental plaque consists of a wide variety of microorganisms, some of which are believed to cause systemic infections, including aspiration pneumonia. To confirm this hypothesis experimentally, we examined the pneumonia-inducing ability of dental plaque in mice, the microbial features of the infectious locus produced by the plaque. Aliquots of a suspension of supragingival dental plaque containing 1 x 10^7 CFU of bacteria were delivered into the lower part of the trachea of mice. All mice exhibited signs of illness immediately after inoculation such as ruffled fur, labored respiration, and appeared waste. In total, 12 out of 18 mice (66.7%) died within 3 days after inoculation with dental plaque suspension. All the 3 human dental plaque samples tested induced pneumonia in mice. Bacterial cells were recovered from the lungs of all the mice that died, and the number was 4.44 ± 0.77 log_<10>CFU/mg of lung. From 5 out of 6 survived mice, bacterial cells were recovered from the lungs and the number was 0.38±0.38 log_<10>CFU/mg of lung. Various microbial species were recovered from infected lungs examined, and no characteristic bacterial distribution was observed both in the survived mice and the mice that died within 3 days after plaque inoculation. Representative isolates of Streptococcus oralis, Streptococcus intermedius and Gemella morbillorum recovered from lungs showed ability to induce pneumonia, respectively. These results suggest that human supragingival dental plaque is a source of the infectious pathogens that cause pneumonia.