Two Synonymous Single-Nucleotide Polymorphisms Promoting Fluoroquinolone Resistance of Escherichia coli in the Environment

Single-nucleotide polymorphism (SNP) is one of the core mechanisms that respond to antibiotic resistance of Escherichia coli (E. coli), which is a major issue in environmental pollution. A specific type of SNPs, synonymous SNPs, have been generally considered as the “silent” SNPs since they do not change the encoded amino acid. However, the impact of synonymous SNPs on mRNA splicing, nucleo-cytoplasmic export, stability, and translation was gradually discovered in the last decades. Figuring out the mechanism of synonymous SNPs in regulating antibiotic resistance is critical to improving antimicrobial therapy strategies in clinics and biological treatment strategies of antibiotic-resistant E. coli-polluted materials. With in silico experimental design with our newly designed algorithm, Multilocus Sequence Type based Identification for Phenotype-single nucleotide polymorphism Analysis (MIPHA), and in vivo validation, we identified 2 important synonymous SNPs 522 G>A and 972 C>T, located at hisD gene, which was previously predicted as a fluoroquinolone resistance-related gene without a detailed mechanism in the E. coli samples with environmental backgrounds. We first discovered that hisD causes gyrA mutation via the upregulation of sbmC and its downstream gene umuD. Moreover, those 2 synonymous SNPs of hisD cause its own translational slowdown and further reduce the expression levels of sbmC and its downstream gene umuD, making the fluoroquinolone resistance determining region of gyrA remains unmutated, ultimately causing the bacteria to lose their ability to resist drugs. This study provided valuable insight into the role of synonymous SNPs in mediating antibiotic resistance of bacteria and a new perspective for the treatment of environmental pollution caused by drug-resistant bacteria. The pollution of food and water by antibiotics and the following appearance of antibiotic-resistant bacteria, especially E. coli has been a huge concern to public health, and the correlations between Synonymous SNP, a part of life evolution, and antibiotic resistance weren’t studied sufficiently. Herein, synonymous SNPs of E. coli samples with environmental backgrounds, which are associated with antibiotic resistance were identified and their detailed contribution to antibiotic resistance was studied. These results indicate that synonymous SNP also plays a key role in antibiotic resistance development and understanding its detailed molecular resistance mechanisms which can help in the prevention and clearance of antimicrobial-resistant bacteria in environments.