Evolution of Burkholderia pseudomallei in Recurrent Melioidosis

Burkholderia pseudomallei, the etiologic agent of human melioidosis, is capable of causing severe acute infection with overwhelming septicemia leading to death. A high rate of recurrent disease occurs in adult patients, most often due to recrudescence of the initial infecting strain. Pathogen persistence and evolution during such relapsing infections are not well understood. Bacterial cells present in the primary inoculum and in late infections may differ greatly, as has been observed in chronic disease, or they may be genetically similar. To test these alternative models, we conducted whole-genome comparisons of clonal primary and relapse B. pseudomallei isolates recovered six months to six years apart from four adult Thai patients. We found differences within each of the four pairs, and some, including a 330 Kb deletion, affected substantial portions of the genome. Many of the changes were associated with increased antibiotic resistance. We also found evidence of positive selection for deleterious mutations in a TetR family transcriptional regulator from a set of 107 additional B. pseudomallei strains. As part of the study, we sequenced to base-pair accuracy the genome of B. pseudomallei strain 1026b, the model used for genetic studies of B. pseudomallei pathogenesis and antibiotic resistance. Our findings provide new insights into pathogen evolution during long-term infections and have important implications for the development of intervention strategies to combat recurrent melioidosis.类鼻疽伯克霍尔德菌（Burkholderia pseudomallei）是人类类鼻疽病的致病原，可引发重症急性感染，伴随致死性脓毒症并导致患者死亡。成人患者的疾病复发率居高不下，多数情况为初始感染菌株再度激活所致。目前对于此类复发性感染过程中病原体的持续存活与演化机制仍缺乏充分了解。正如慢性感染中所观察到的那样，原发接种物与晚期感染中的细菌细胞可能存在显著遗传差异，也可能在基因层面高度相似。为验证这两种对立假说，本研究对4名泰国成人患者间隔6个月至6年分离得到的克隆性原发与复发类鼻疽伯克霍尔德菌分离株开展全基因组比对分析。我们在4组菌株对中均检测到遗传差异，其中部分变异（包括一段330千碱基对的缺失）累及基因组的大片区域。多数变异与抗生素耐药性增强相关。此外，我们在107株额外的类鼻疽伯克霍尔德菌菌株中，发现TetR家族转录调节因子存在有害突变的正向选择证据。作为本研究的一部分，我们以碱基对级精度完成了类鼻疽伯克霍尔德菌1026b菌株的基因组测序——该菌株是类鼻疽伯克霍尔德菌致病机制与抗生素耐药性遗传研究的经典模式菌株。本研究结果为长期感染过程中的病原体演化提供了全新视角，同时对开发对抗复发性类鼻疽病的干预策略具有重要指导意义。