Potential Risk of Spreading Resistance Genes within Extracellular-DNA-Dependent Biofilms of Streptococcus mutans in Response to Cell Envelope Stress Induced by Sub-MICs of Bacitracin
Potential Risk of Spreading Resistance Genes within Extracellular-DNA-Dependent Biofilms of Streptococcus mutans in Response to Cell Envelope Stress Induced by Sub-MICs of Bacitracin
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DOI：
10.1128/aem.00770-20
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发表时间：
2020-08-01
影响因子：
4.4
通讯作者：
Senpuku, Hidenobu
中科院分区：
文献类型：
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作者：
Nagasawa, Ryo;Sato, Tsutomu;Senpuku, Hidenobu
抗生素用于治疗或预防某些类型的细菌感染。抗生素的不适当使用不必要地促进抗生素耐药性并增加耐药细菌，并且控制这些细菌是困难的。虽然耐药细菌的出现是一个严重的问题，但耐药细菌的行为尚未完全了解。在这项研究中，我们研究了变形链球菌的行为，变形链球菌是龋齿的主要病原体，对杆菌肽具有耐药性，杆菌肽是一种细胞壁靶向抗生素，并专注于在杆菌肽存在下的生物膜形成。S.在1/8x MIC的杆菌肽存在下，变形杆菌UA 159最强烈地诱导细胞外DNA（eDNA）依赖性生物膜形成。缺乏杆菌肽抗性的Δ mbrC和Δ mbrD突变株在1/2x MIC的杆菌肽存在下也形成生物膜。野生型和突变体之间的这种差异是由在对数中期诱导atIA表达引起的。我们还发现，某些rgp基因参与合成的鼠李糖-葡萄糖多糖相关的细胞壁合成下调杆菌肽。此外，葡萄糖基转移酶-I也参与了依赖于eDNA的生物膜形成。生物膜导致转化效率提高，并促进水平基因转移。生物膜也诱导氨苄青霉素和万古霉素，抗生素靶向细胞壁的合成，表明细胞包膜应力触发生物膜的形成。因此，atIA和rgp基因的表达受S.变形杆菌，其形成eDNA依赖性生物膜，促进水平基因转移以响应由抗生素的亚MIC诱导的细胞包膜应激。重要性已经报道抗生素在亚抑制浓度下诱导许多细菌中的生物膜形成。因此，可以想象，针对药物敏感性细菌的MIC可以促进耐药细菌的生物膜形成。由于耐药细菌已经扩散，因此了解耐药细菌的行为非常重要。变形链球菌对杆菌肽具有耐药性，并且杆菌肽（一种细胞壁靶向抗生素）的1/8x MIC可诱导eDNA依赖性生物膜形成。Delta mbrC和Delta mbrD菌株对杆菌肽不耐药，在1 /2 X MIC的杆菌肽存在下也形成生物膜，野生型和突变体的生物膜均促进水平基因转移。另一种细胞壁靶向抗生素万古霉素对生物膜和基因转移的影响与杆菌肽相似。因此，用细胞壁靶向抗生素治疗可能会促进生物膜中耐药基因的传播。因此，在使用抗生素时，应研究亚MIC抗生素存在下耐药菌的行为。
Antibiotics are used to treat or prevent some types of bacterial infection. The inappropriate use of antibiotics unnecessarily promotes antibiotic resistance and increases resistant bacteria, and controlling these bacteria is difficult. While the emergence of drug-resistant bacteria is a serious problem, the behavior of drug-resistant bacteria is not fully understood. In this study, we investigated the behavior of Streptococcus mutans, a major etiological agent of dental caries that is resistant to bacitracin, which is a cell wall-targeting antibiotic, and focused on biofilm formation in the presence of bacitracin. S. mutans UA159 most strongly induced extracellular DNA (eDNA)-dependent biofilm formation in the presence of bacitracin at 1/8x MIC. The Delta mbrC and Delta mbrD mutant strains, which lack bacitracin resistance, also formed biofilms in the presence of bacitracin at 1/2x MIC. This difference between the wild type and the mutants was caused by the induction of atIA expression in the mid-log phase. We also revealed that certain rgp genes involved in the synthesis of rhamnose-glucose polysaccharide related to cell wall synthesis were downregulated by bacitracin. In addition, glucosyltransferase-I was also involved in eDNA-dependent biofilm formation. The biofilm led to increased transformation efficiencies and promoted horizontal gene transfer. Biofilms were also induced by ampicillin and vancomycin, antibiotics targeting cell wall synthesis, suggesting that cell envelope stress triggers biofilm formation. Therefore, the expression of the atIA and rgp genes is regulated by S. mutans, which forms eDNA-dependent biofilms, promoting horizontal gene transfer in response to cell envelope stress induced by sub-MICs of antibiotics.IMPORTANCE Antibiotics have been reported to induce biofilm formation in many bacteria at subinhibitory concentrations. Accordingly, it is conceivable that the MIC against drug-sensitive bacteria may promote biofilm formation of resistant bacteria. Since drug-resistant bacteria have spread, it is important to understand the behavior of resistant bacteria. Streptococcus mutans is bacitracin resistant, and the 1/8x MIC of bacitracin, which is a cell wall-targeted antibiotic, induced eDNA-dependent biofilm formation. The Delta mbrC and Delta mbrD strains, which are not resistant to bacitracin, also formed biofilms in the presence of bacitracin at 1 /2 X MIC, and biofilms of both the wild type and mutants promoted horizontal gene transfer. Another cell walltargeted antibiotic, vancomycin, showed effects on biofilms and gene transfer similar to those of bacitracin. Thus, treatment with cell wall-targeted antibiotics may promote the spread of drug-resistant genes in biofilms. Therefore, the behavior of resistant bacteria in the presence of antibiotics at sub-MICs should be investigated when using antibiotics.