Bautista David E, Whitehead Cassidy R, Mitchell Angela M
Department of Biology, Texas A&M University, College Station, Texas, USA.
bioRxiv. 2025 Jun 25:2025.06.20.660601. doi: 10.1101/2025.06.20.660601.
Antibiotic resistant bacteria have been a rising clinical concern for decades. Beyond acquisition of alleles conferring resistance, bacteria under stress (e.g., from changing environmental conditions or mutations) can have higher intrinsic resistance to antibiotics than unstressed cells. This concern is expanded for gram-negative bacteria which have a protective outer membrane serving as an additional barrier against harmful molecules such as antibiotics. Here, we report a pathway which increases antibiotic resistance (i.e., minimum inhibitory concentration) in response to inactivation of the DNA Mismatch Repair pathway (MMR). This pathway led to increased intrinsic resistance and was independent of secondary mutations. Specifically, deletion of the DNA mismatch repair genes or caused resistance to various antibiotics spanning different classes, molecular sizes, and mechanisms of action in several different K-12 MG1655 strains, and in serovar Typhimurium LT2. This pathway was independent of the SOS response (severe DNA damage response). However, the patterns of resistance correlated with previously reported increases in MMR mutants in rates of homoeologous recombination, homologous recombination between non-identical DNA strands. Mutations expected to lower rates of recombination in MMR mutants also decreased the resistance to most antibiotics. Finally, we found lysis occurs in MMR mutants and may contribute to resistance to other antibiotics. Our results have demonstrated a novel mechanism that increases antibiotic resistance in direct response to loss of MMR genes, and we propose this resistance involves increased rates of homoeologous recombination and cell lysis. The increased antibiotic resistance of MMR mutants provides a path for these cells to survive in antibiotics long enough to develop more specific resistance mutations and so may contribute to the development of new clinical resistance alleles.
几十年来，抗生素耐药细菌一直是日益严重的临床问题。除了获得赋予耐药性的等位基因外，处于应激状态的细菌（例如，由于环境条件变化或突变）比未受应激的细胞对抗生素具有更高的固有耐药性。对于革兰氏阴性菌来说，这种担忧更为突出，因为它们有一层保护性外膜，可作为抵御抗生素等有害分子的额外屏障。在此，我们报告了一条因DNA错配修复途径（MMR）失活而增加抗生素耐药性（即最低抑菌浓度）的途径。该途径导致固有耐药性增加，且与二次突变无关。具体而言，缺失DNA错配修复基因 或 会使几种不同的K-12 MG1655菌株以及鼠伤寒沙门氏菌LT2血清型对不同类别、分子大小和作用机制的多种抗生素产生耐药性。该途径独立于SOS反应（严重DNA损伤反应）。然而，耐药模式与先前报道的MMR突变体中同源重组率的增加相关，同源重组是指非相同DNA链之间的重组。预计会降低MMR突变体中重组率的突变也会降低对大多数抗生素的耐药性。最后，我们发现MMR突变体中会发生裂解，这可能有助于对其他抗生素产生耐药性。我们的结果证明了一种新机制，即直接响应MMR基因缺失而增加抗生素耐药性，并且我们提出这种耐药性涉及同源重组率增加和细胞裂解。MMR突变体抗生素耐药性的增加为这些细胞在抗生素环境中存活足够长的时间以产生更具特异性的耐药突变提供了一条途径，因此可能有助于新的临床耐药等位基因的产生。
