继发性细菌感染是病毒性肺炎（例如流感）重症化的一个非常重要的、也是导致死亡的最重要、最直接的原因之一。包括1918年和2009年的流感大流行。多少年来，人们一直怀疑流感等呼吸道病毒感染重症患者，是始于病毒，死于细菌。但是，一直没有找到证据。最近，有了初步答案。
2017-2018年北京流感流行，重症患者和死亡增多，一度引起社会关注。传染病预防控制国家重点实验室、中国疾病预防控制中心传染病所和协和医院针对这个问题，合作开展了研究。他们发现，一些患者鼻咽部细菌过度增长，占比超过50%，命名为超级优势菌（英文：Super-dominant Pathobiontic Bacteria）。这些超级优势菌可在疾病发展进程中，下行到肺泡造成感染，导致死亡。可以说，许多患者是感染了病毒，因细菌死亡。
为了证实鼻咽部超级优势菌可下行到肺泡的理论，两个团队紧密合作，从患者的咽拭子和肺泡灌洗液分离细菌，进行比较。最后发现，同一患者，从鼻咽部和肺泡分离的菌株的基因组序列完全一致。目前发现具有下行能力的细菌包括，鲍曼不动杆菌、肺炎克雷伯菌、铜绿假单胞菌、纹状体棒状杆菌等。
研究论文“鼻咽部超级优势菌是流感患者继发细菌感染的原因：Super-dominant Pathobiontic Bacteria in the Nasopharyngeal Microbiota as Causative Agents of Secondary Bacterial Infection in Influenza Patients”近日在《Emerging Microbes & Infections》发表。传染病所秦天是第一作者，协和医院李太生主任、传染病所徐建国院士为责任作者。
秦天副研究员认为，许多细菌是“两面菌”，在一定的条件下可转化为致病菌，是医学细菌学研究的新课题。李太生主任认为，这个现象可能具有普遍意义，也许对新型冠状病毒肺炎的治疗有参考意义。
从患者鼻咽部和肺泡灌洗液分离菌株的PFGE图谱及基因组相同
鼻咽部SDPG下行至肺部引起感染
文章信息：
DOI：10.1080/22221751.2020.1737578.
Abstract：The source of secondary lower respiratory tract bacterial infections in influenza patients is not fully understood. A case-control study was conducted during the 2017-2018 influenza epidemic period in Beijing, China. Nasopharyngeal swabs were collected from 52 virologically confirmed influenza patients and 24 healthy medical staff. The nasopharyngeal microbiota taxonomic composition was analysed using high-throughput sequencing of the 16S rRNA gene V3-V4 regions. The super-dominant pathobiontic bacterial genus (SDPG) was defined as that accounting for >50% of sequences in a nasopharyngeal swab. We attempted to isolate bacteria of this genus from both nasopharyngeal swabs and lower-respiratory tract samples and analyse their genetic similarities. We observed a significantly lower taxonomy richness in influenza cases compared with healthy controls. A SDPG was detected in 61% of severe cases but in only 24% of mild cases and 29% of healthy controls. In 10 cases, the species isolated from lower-respiratory tract infection sites were identified as belonging to the nasopharyngeal microbiota SDPG. Genetically identical strains were isolated from both nasopharyngeal swabs and lower-respiratory tract infection sites, including 23 Acinetobacter baumannii strains from six severe cases, six Klebsiella pneumoniae strains from two severe cases, five Pseudomonas aeruginosa strains from one severe and one mild case, and four Corynebacterium striatum strains from two severe cases. The SDPG in the nasopharyngeal microbiota are the likely cause of subsequent infection in influenza patients.
