Hiramatsu Yukihiro, Saito Momoko, Otsuka Nao, Suzuki Eri, Watanabe Mineo, Shibayama Keigo, Kamachi Kazunari
Department of Bacteriology II, National Institute of Infectious Diseases, Tokyo, Japan.
Graduate School of Infection Control Sciences, Kitasato University, Tokyo, Japan.
PLoS One. 2016 Jul 22;11(7):e0159999. doi: 10.1371/journal.pone.0159999. eCollection 2016.
Bordetella holmesii causes both invasive and respiratory diseases in humans. Although the number of cases of pertussis-like respiratory illnesses due to B. holmesii infection has increased in the last decade worldwide, little is known about the virulence factors of the organism. Here, we analyzed a B. holmesii isolate that forms large aggregates and precipitates in suspension, and subsequently demonstrated that the autoagglutinating isolate is deficient in Bordetella intermediate protein A (BipA) and that this deletion is caused by a frame-shift mutation in the bipA gene. A BipA-deficient mutant generated by homologous recombination also exhibited the autoagglutination phenotype. Moreover, the BipA mutant adhered poorly to an abiotic surface and failed to form biofilms, as did two other B. holmesii autoagglutinating strains, ATCC 51541 and ATCC 700053, which exhibit transcriptional down-regulation of bipA gene expression, indicating that autoagglutination indirectly inhibits biofilm formation. In a mouse intranasal infection model, the BipA mutant showed significantly lower levels of initial lung colonization than did the parental strain (P < 0.01), suggesting that BipA might be a critical virulence factor in B. holmesii respiratory infection. Together, our findings suggest that BipA production plays an essential role in preventing autoagglutination and indirectly promoting biofilm formation by B. holmesii.
霍氏鲍特菌可引起人类的侵袭性疾病和呼吸道疾病。尽管在过去十年中，全球范围内由霍氏鲍特菌感染引起的百日咳样呼吸道疾病病例数有所增加，但对该菌的毒力因子却知之甚少。在此，我们分析了一株在悬浮液中形成大聚集体并沉淀的霍氏鲍特菌分离株，随后证明该自凝性分离株缺乏鲍特菌中间蛋白A（BipA），且这种缺失是由bipA基因的移码突变引起的。通过同源重组产生的BipA缺陷型突变体也表现出自凝表型。此外，BipA突变体与非生物表面的粘附性较差，且无法形成生物膜，另外两株自凝性霍氏鲍特菌菌株ATCC 51541和ATCC 700053也是如此，它们表现出bipA基因表达的转录下调，这表明自凝间接抑制生物膜形成。在小鼠鼻内感染模型中，BipA突变体的初始肺部定植水平显著低于亲本菌株（P < 0.01），这表明BipA可能是霍氏鲍特菌呼吸道感染中的关键毒力因子。总之，我们的研究结果表明，BipA的产生在防止霍氏鲍特菌自凝以及间接促进其生物膜形成方面起着至关重要的作用。
