| Summary: | Objectives: This study aimed to determine the genetic environment of antimicrobial resistance genes in Proteus mirabilis strain STP3 isolated from a diarrhoeic pig on a swine farm in Sichuan Province, China. Methods: Strain STP3 was subjected to antimicrobial susceptibility testing. Illumina MiSeq (200× coverage) and Nanopore PromethION (100× coverage) platforms were used for genome sequencing. A conjugation experiment was performed to determine the transferability and stability of antimicrobial resistance genes in this strain. Results: The assembled circular genome of P. mirabilis STP3 was 4 115 975 bp with a GC content of 39.58%; no plasmid sequence was detected. A novel genomic resistance island (PmGRI1-STP3) and an SXT/R391 integrative conjugative element (ICE) variant (ICEPmiChnSTP3) were characterised in P. mirabilis STP3. PmGRI1-STP3 of 52.7 kb was located at the 3′ end of tRNA-Sec and shared the greatest identity with PmGRI1-C55 (54% coverage, 99.99% identity). PmGRI1-STP3 carried 16 resistance genes, including the clinically important extended-spectrum β-lactamase (ESBL) gene blaCTX-M-3. ICEPmiChnSTP3 was inserted into the prfC gene. It carried 18 resistance genes, including the rRNA methyltransferase gene cfr and the fluoroquinolone resistance gene aac(6′)-Ib-cr. A class 2 integron (dfrA1–sat2–aadA1) was also identified on transposon Tn7. Mobilisation experiments indicated that ICEPmiChnSTP3 was conjugally mobilised to Escherichia coli. However, PmGRI1-STP3 appeared to lose its mobilisation ability. Conclusion: The identification of two genomic islands (GIs) in this study suggested that genetic elements might be key mediators for resistance gene acquisition in P. mirabilis and that IS26-mediated rearrangements promote the diversity of GIs.
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