Genomic Diversity of the tet(X)-Positive Myroides Species

The rapid spread of <i>tet</i>(X) genes capable of inactivating tigecycline represents a critical challenge to global public health. This study aims to explore the distribution, genetic diversity, and transferability of <i>tet</i>(X) genes in <i>Myroides</i>, a genus of Gram-negative bacteria increasingly implicated in multidrug-resistant (MDR) bacterial infections. From 2021 to 2024, 646 samples of chicken, sheep, soil, and water were randomly collected, yielding nine chicken-derived <i>tet</i>(X)-positive <i>Myroides</i> sp. strains in Shandong, China. All of them were MDR to tetracycline, ceftazidime, gentamicin, amikacin, colistin, ciprofloxacin, gatifloxacin, and trimethoprim-sulfamethoxazole, with elevated minimum inhibitory concentrations (MICs) for tigecycline, florfenicol, and macrolides, but exhibited susceptibility to meropenem (100%), ampicillin-sulbactam (66.7%), and cefotaxime (33.3%). A genomic analysis of the isolates and 86 public <i>tet</i>(X)-positive <i>Myroides</i> genomes revealed the widespread distribution of <i>tet</i>(X) and macrolide-inactivating <i>estT</i> genes across 12 <i>Myroides</i> species, including 7 novel species. Eight <i>tet</i>(X) and eight estT variants were identified, half of which were novel. The phylogenetic analysis highlighted interspecies transmission risks, with IS<i>CR2</i>-mediated transposons of <i>tet</i>(X6) and <i>estT-2</i> across <i>Myroides</i>, <i>Riemerella</i>, <i>Empedobacter</i>, <i>Providencia</i>, <i>Acinetobacter</i>, and <i>Proteus</i> species. These findings illuminate the genomic diversity driving antibiotic resistance in understudied bacterial taxa, with implications for global One Health strategies.