Characterization of Silver Resistance and Coexistence of Operon with Antibiotic Resistance Genes Among Gram-Negative Pathogens Isolated from Wound Samples by Using Whole-Genome Sequencing.

Purpose: Due to the extensive consumption of silver-containing compound, silver resistance spreads among gram-negative pathogens and is regarded as a great public problem. In this study, we investigated silver resistance mechanisms and antibiotic resistance genes co-harbored with operon among gram-negative pathogens isolated from wound samples.

Methods: A total of 193 strains of gram-negative pathogens were collected from wound samples between 2018 and 2020 in Xiangya hospital. Silver resistance was obtained by broth microdilution method. The silver resistance mechanisms and the prevalence, genetic environments, and coexistence with antibiotic resistance genes of operon were investigated by polymerase chain reaction (PCR) and whole genome sequencing (WGS).

Results: Among 193 strains, nine strains (4.7%) were resistant to Ag and assigned to the following species: (n = 5) and (n = 4). WGS confirmed that 24 strains carried the entire operon, including the four Ag-resistant and 20 Ag-susceptible strains, while PCR failed to detect some genes, especially , due to sequence variations. In seven strains, Tn7 transposon was identified in the upstream of operon. Spontaneous mutants resistant to Ag were induced in 15 out of 20 Ag-susceptible strains, including strains belonged to high-risk groups (ST11 and ST15). The -positive strains harbored various antibiotic resistance genes, including and . WGS revealed that a single mutation in gene and loss of major porins conferred silver resistance in the five strains.

Conclusion: Our findings emphasize the cryptic silver resistance is prevalent among Enterobacteriaceae with operon or with the combination of operon and major porin loss and increase the understanding of the prevalence of operon with antibiotic resistance genes, especially and .