A Mechanism of Unidirectional Transformation, Leading to Antibiotic Resistance, Occurs within Nasopharyngeal Pneumococcal Biofilm Consortia
A Mechanism of Unidirectional Transformation, Leading to Antibiotic Resistance, Occurs within Nasopharyngeal Pneumococcal Biofilm Consortia
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DOI：
10.1128/mbio.00561-18
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发表时间：
2018-05-01
期刊：
影响因子：
6.4
通讯作者：
Vidal, Jorge E.
中科院分区：
文献类型：
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作者：
Lattar, Santiago M.;Wu, Xueqing;Vidal, Jorge E.
肺炎链球菌对链霉素(Str)或甲氧苄氨嘧啶(TMP)等抗生素的耐药基因是通过转化其他肺炎球菌及其近缘种释放的DNA进行重组而获得的。利用自然转化的肺炎球菌，包括D39血清型2(S2)和TIGR4(S4)，我们研究了肺炎球菌鼻咽转化是对称的、不对称的还是单向的。S2(Tet)和S4(Str)在模拟人鼻咽的生物反应器中孵育，产生了Spn(Tet/Str)重组体。双耐药肺炎球菌在接种后4h迅速出现，重组频率为2.5×10(-4)，8h后达到高峰，重组频率为1.1×10(-3)。DNase I处理证实了通过转化获得的抗生素耐药基因。高通量血清分型方法表明，所有双耐药肺炎球菌属于一个血清型谱系(S2(Tet/Str))，因此发生了单向转化。由于每个菌株的密度和两个菌株释放的胞外DNA(EDNA)相似，DNA的异裂和可用于转化的DNA都不是单向转化的因素。无论捐赠者或接受者携带的抗生素耐药基因如何，也无论是否允许能力刺激肽-受体串扰，单向转化都会发生。此外，当两个供体菌株(如S4(ST)r和S19F(TMP))一起培养时，发生了单向转化，导致S19F(Str/TMP)，但Rf低3个数量级(4.9×10(-6))。我们最终证明了导致单向转化的机制是由于接受者抑制了供体的转化。肺炎球菌在人鼻咽中的转化可能导致获得抗生素耐药基因或编码新的衣壳变异体的基因。抗生素和疫苗目前正在对一些菌株施加压力，导致抗生素耐药性增加和血清型替换。这些肺炎球菌菌株也通过转化获得了疫苗类型的毒力特征。在这项研究中，我们总结了带有耐药性标记的菌株的多菌株定植，并选择那些对两种或三种抗生素获得耐药性的菌株，例如将发生在人类鼻咽的菌株。获得双重和三重抗性的菌株来自同一祖代，表明转化是单向的。单向转化是供体菌株转化受到抑制的结果。单向转换对于理解抗性决定因素或包膜转换事件的获取模式具有重要意义。
Streptococcus pneumoniae acquires genes for resistance to antibiotics such as streptomycin (Str) or trimethoprim (Tmp) by recombination via transformation of DNA released by other pneumococci and closely related species. Using naturally transformable pneumococci, including strain D39 serotype 2 (S2) and TIGR4 (S4), we studied whether pneumococcal nasopharyngeal transformation was symmetrical, asymmetrical, or unidirectional. Incubation of S2(Tet) and S4(Str) in a bioreactor simulating the human nasopharynx led to the generation of Spn(Tet/Str) recombinants. Double-resistant pneumococci emerged soon after 4 h postinoculation at a recombination frequency (rF) of 2.5 x 10(-4) while peaking after 8 h at a rF of 1.1 x 10(-3). Acquisition of antibiotic resistance genes by transformation was confirmed by treatment with DNase I. A high-throughput serotyping method demonstrated that all double-resistant pneumococci belonged to one serotype lineage (S2(Tet/Str)) and therefore that unidirectional transformation had occurred. Neither heterolysis nor availability of DNA for transformation was a factor for unidirectional transformation given that the density of each strain and extracellular DNA (eDNA) released from both strains were similar. Unidirectional transformation occurred regardless of the antibiotic-resistant gene carried by donors or acquired by recipients and regardless of whether competence-stimulating peptide-receptor cross talk was allowed. Moreover, unidirectional transformation occurred when two donor strains (e.g., S4(St)r and S19F(Tmp)) were incubated together, leading to S19F(Str/Tmp) but at a rF 3 orders of magnitude lower (4.9 x 10(-6)). We finally demonstrated that the mechanism leading to unidirectional transformation was due to inhibition of transformation of the donor by the recipient.IMPORTANCE Pneumococcal transformation in the human nasopharynx may lead to the acquisition of antibiotic resistance genes or genes encoding new capsular variants. Antibiotics and vaccines are currently putting pressure on a number of strains, leading to an increase in antibiotic resistance and serotype replacement. These pneumococcal strains are also acquiring virulence traits from vaccine types via transformation. In this study, we recapitulated multiple-strain colonization with strains carrying a resistance marker and selected for those acquiring resistance to two or three antibiotics, such as would occur in the human nasopharynx. Strains acquiring dual and triple resistance originated from one progenitor, demonstrating that transformation was unidirectional. Unidirectional transformation was the result of inhibition of transformation of donor strains. Unidirectional transformation has implications for the understanding of acquisition patterns of resistance determinants or capsule-switching events.