Detection of Tn 7-Like Transposons and Antibiotic Resistance in Enterobacterales From Animals Used for Food Production With Identification of Three Novel Transposons Tn 6813, Tn 6814, and Tn 6765

Abstract

Enterobacterales are widely distributed in the gastro-intestinal system of animals and may cause opportunistic infections. Worse still, multidrug-resistant Enterobacterales also poses a serious threat to public health. Tn7-like transposons have been found in several species of the Enterobacterales order and play an important role in dissemination of antibiotic resistance. This study aimed to investigate the distribution and genetic characterization of Tn7-like transposons in Enterobacterales isolates from food animals and their association with antibiotic resistance. Enterobacterales isolated from the samples were identified and classified according to the 16S rDNA sequence. Tn7-like transposons and associated integrons were detected by polymerase chain reaction (PCR) and sequencing. The antibiotic resistance of each Tn7-like transposon positive isolate was detected according to the Kirby-Bauer disk diffusion method. Then, six representative strains were selected to study the genetic environment by whole-genome sequencing (WGS). In total, we isolated 377 Tn7-like transposons positive strains of Enterobacterales. Class 2 integrons were detected in 99.5% of the isolates, and there were high frequency mutation sites especially in base 535, a stop mutation. Many isolates (54.9%) were multidrug-resistant and observed high resistance rates to trimethoprim/sulfamethoxazole and streptomycin. Among these strains, we found three new types of Tn7-like transposons, named Tn6813, Tn6814, and Tn6765. This is the first comprehensive survey that shows Tn7-like transposons in Enterobacterales from animals used for food production in different regions of China. This study also provides an insight into the horizontal transfer of resistance genes associated with Tn7-like transposons.

Keywords: Enterobacterales; Tn7-like transposons; animals used for food production; antibiotic resistance; class 2 integrons.

Figure 1

The Weblogo of repeats of intI2. The sequences were each mutation site of the integrase gene of class 2 integrons.

Figure 2

Genetic structure of Tn6813, Tn6814, and Tn6817. The physical maps were generated using Easyfig 2.2.3 and DNAMAN Version 8.0. Linear comparison of Tn6813 region in E. coli strain SFE8 with Tn6814 region in E. coli strain SCZE5, and Tn6817 region in S. enterica strain SCFS4. Genes and open reading frames (ORFs) are shown as arrows, and their orientations of transcription are indicated by the arrowheads. Horizontal lines, different regions corresponding to Tn7, Tn1721, Tn3, Tn5393, and integrons. Antimicrobial resistance genes are in yellow, transposase are in blue, and integrase genes are in red. The IS elements are indicated by gray arrows. Other functions or putative proteins are in green. Shared regions with 99% identity are indicated by shading.

Figure 3

Genetic structure of Tn6763, Tn6764, and Tn6765. The physical maps were generated using Easyfig 2.2.3 and DNAMAN Version 8.0. Linear comparison of Tn6765 region in p1.1.2 with Tn6763 region in P. mirabilis strain, Tn6764 region in E. coli strain and Tn6450 region in P. mirabilis strain SNYG17 (GenBank accession number MF805806). Genes and ORFs are shown as arrows, and their orientations of transcription are indicated by the arrowheads. Horizontal lines, different regions corresponding to Tn7, Tn1721, Tn21, and integrons. Antimicrobial resistance genes are in yellow, transposase are in blue, and integrase genes are in red. The IS elements are indicated by gray arrows. Other functions or putative proteins are in green. Shared regions with 99% identity are indicated by shading.

Figure 4

Circular representation of plasmid p1.1.2. The physical map of p1.1.2 was generated using BRIG v0.95.

Figure 5

Genetic structure of cfr-containing region and in p1.1.1. The physical maps were generated using Easyfig 2.2.3 and DNAMAN Version 8.0. Linear comparison of the cfr-containing region in p1.1.1 with the cfr-containing region in P. cibarius strain G11 (Genebank number CP047287) and in M. morganii strain BCMM24 (Genebank number MG832661). Genes and ORFs are shown as arrows, and their orientations of transcription are indicated by the arrowheads. Antimicrobial resistance genes are in red. The IS elements are indicated by yellow arrows. Putative proteins are in green. Shared regions with 99% identity are indicated by shading.