Characterisation of novel Tn 7-derivatives and Tn 7-like transposon found in Proteus mirabilis of food-producing animal origin in China

Objectives: This study aimed to clarify the characteristics of Tn 7 -derivatives transposons in MDR Proteus mirabilis strains isolated from anal swabs of chicken and swine in China from 2015-2020. Methods: The Tn 7 tnsA gene was screened in 207 P. mirabilis isolates by polymerase chain reaction (PCR). These strains were subjected to antimicrobial susceptibility testing. Illumina Hiseq (200 x coverage) was used for genome sequencing. Transposon maps were completed by PCR and Sanger sequencing and analysed by BLAST. Results: The Tn 7 tnsA gene was detected in 21 strains by PCR. Eight novel Tn 7 -derivatives, named Tn 6667 , Tn 6668 , Tn 6669 , Tn 6670 , Tn 7095 , Tn 7096 , Tn 7097 and Tn 7098 , were characterised. Three types of hybrid class 2/1 integrons were found at the right end of Tn 7 derivatives. A novel Tn 7 -like transposon Tn 6666 with an active integrase gene intI2 , whose transposition module shows 93% nucleotide identity to the corresponding region of Tn 7 , was characterised in three strains. Tn 6666 is also found next to Tn 7097 or Tn 7098 in the chromosomes of two clonally related P. mirabilis strains. The number of resistance genes carried by the novel transposons varied from 1 to 18. A novel variant of class A extended-spectrum betalactamase gene, bla PER-16 , with eight base substitutions compared with bla PER-12 , was harboured by Tn 7098 . Conclusion: Our study characterised diverse novel Tn 7 -derivatives and a new Tn 7 -like transposon in P. mirabilis . An active integrase gene intI2 might promote the diversification of Tn 7 -like transposons. More attention should be paid to the prevalence and evolution of Tn 7 -derivatives and Tn 7 -like transposons and antimicrobial resistance genes they carry. (c) 2022 The Authors. Published by Elsevier Ltd on behalf of International Society for Antimicrobial Chemotherapy. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ )

Automated summary

This study aimed to clarify the characteristics of Tn 7-derivatives transposons in MDR Proteus mirabilis strains isolated from anal swabs of chicken and swine in China from 2015-2020. Various novel Tn 7-derivatives and a new Tn 7-like transposon were identified, along with a new variant of a resistance gene.