Investigation of genomic islands involved in antimicrobial resistance in Proteus mirabilis isolated from swine

Objectives: Proteus mirabilis (P. mirabilis), a Gram-negative, rod-shaped bacterium, is ubiquitously present in natural environments as well as within the intestinal tracts of humans and animals. We isolated P. mirabilis SH-4 from a swine sample and investigated its antibiotic resistance genes (ARGs) along with their genetic structure. Methods: In this study, we have performed antimicrobial susceptibility testing by the broth microdilution method and conducted a comprehensive analysis through whole genome sequencing (WGS) and phylogenomics of P. mirabilis strain SH-4. Results: P. mirabilis SH-4 was found to possess a single chromosome measuring 4 123 479 base pairs in length, with a GC content of 39.06%. Besides, P. mirabilis SH-4 exhibited resistance to eleven antimicrobial agents tested. Through single nucleotide polymorphism (SNP) profiling, we revealed the genetic relationship of SH-4 with other P. mirabilis strains carrying various ARGs. WGS analysis revealed that SH-4 harbored a ΔTn7 transposon and two distinct genomic islands (GIs), designated as PmGRI-9-SH-4 and PmGRI-10-SH-4. ΔTn7 was identified, corresponding to Tn7 with an insertion of IS256 within its sequence. PmGRI-9-SH-4 displayed partial homology to PmGRI1-STP3 and PmGRI1-YN9 (China:Sichuan). Additionally, PmGRI-10-SH-4 contained composite transposons and eleven Type IV secretion system (T4SS) related genes, including traN, traU, traC, and others, with the MDR region situated near the terminus of this GI. Conclusions: In summary, GIs and ISs may serve as crucial facilitators in the acquisition of resistance genes in P. mirabilis. These genetic elements turn P. mirabilis into highly resistant bacteria, culminating in infections that pose significant therapeutic challenges.