Department of Molecular Biosciences, University of Kansas, Lawrence, Kansas, USA.
Department of Microbiology and Molecular Genetics, Oklahoma State University, Stillwater, Oklahoma, USA.
J Bacteriol. 2023 Jun 27;205(6):e0011423. doi: 10.1128/jb.00114-23. Epub 2023 May 16.
The opportunistic bacterium Pseudomonas aeruginosa uses the LasR-I quorum-sensing system to increase resistance to the aminoglycoside antibiotic tobramycin. Paradoxically, -null mutants are commonly isolated from chronic human infections treated with tobramycin, suggesting there may be a mechanism that permits the emergence of -null mutants under tobramycin selection. We hypothesized that some other genetic mutations that emerge in these isolates might modulate the effects of -null mutations on antibiotic resistance. To test this hypothesis, we inactivated in several highly tobramycin-resistant isolates from long-term evolution experiments. In some of these isolates, inactivating further increased resistance, compared with decreasing resistance of the wild-type ancestor. These strain-dependent effects were due to a G61A nucleotide polymorphism in the gene encoding amino acid substitution A21T in the translation elongation factor EF-G1A. The EF-G1A mutational effects required the MexXY efflux pump and the MexXY regulator ArmZ. The mutation also modulated Δ mutant resistance to two other antibiotics, ciprofloxacin and ceftazidime. Our results identify a gene mutation that can reverse the direction of the antibiotic selection of mutants, a phenomenon known as sign epistasis, and provide a possible explanation for the emergence of -null mutants in clinical isolates. One of the most common mutations in Pseudomonas aeruginosa clinical isolates is in the quorum sensing gene. In laboratory strains, disruption decreases resistance to the clinical antibiotic tobramycin. To understand how mutations emerge in tobramycin-treated patients, we mutated in highly tobramycin-resistant laboratory strains and determined the effects on resistance. Disrupting enhanced the resistance of some strains. These strains had a single amino acid substitution in the translation factor EF-G1A. The EF-G1A mutation reversed the selective effects of tobramycin on mutants. These results illustrate how adaptive mutations can lead to the emergence of new traits in a population and are relevant to understanding how genetic diversity contributes to the progression of disease during chronic infections.
机会性病原体铜绿假单胞菌利用 LasR-I 群体感应系统来提高对氨基糖苷类抗生素妥布霉素的耐药性。矛盾的是，-null 突变体通常从接受妥布霉素治疗的慢性人类感染中分离出来，这表明在妥布霉素选择下可能存在一种允许 -null 突变体出现的机制。我们假设，这些分离株中出现的其他一些遗传突变可能会调节 -null 突变对抗生素耐药性的影响。为了验证这一假设，我们在来自长期进化实验的几个高度耐妥布霉素的分离株中失活了。在这些分离株中的一些中，与野生型祖先的耐药性降低相比，失活 进一步增加了耐药性。这些菌株依赖性效应归因于编码翻译延伸因子 EF-G1A 的 基因中的 G61A 核苷酸多态性，导致氨基酸取代 A21T。EF-G1A 突变效应需要 MexXY 外排泵和 MexXY 调节剂 ArmZ。 突变还调节了Δ突变体对另外两种抗生素环丙沙星和头孢他啶的耐药性。我们的结果确定了一种基因突变，它可以逆转 - 突变体抗生素选择的方向，这种现象称为符号上位性，并为临床分离株中 -null 突变体的出现提供了可能的解释。铜绿假单胞菌临床分离株中最常见的突变之一是在群体感应 基因中。在实验室菌株中， 缺失降低了对临床抗生素妥布霉素的耐药性。为了了解在妥布霉素治疗的患者中如何出现 突变，我们在高度耐妥布霉素的实验室菌株中突变了 ，并确定了对耐药性的影响。破坏 增强了一些菌株的耐药性。这些菌株在翻译因子 EF-G1A 中有一个单一的氨基酸取代。EF-G1A 突变逆转了妥布霉素对 突变体的选择性影响。这些结果说明了适应性突变如何导致群体中出现新的特征，这对于理解遗传多样性如何导致慢性感染期间疾病的进展具有重要意义。
