Abstract
Salmonella genomic island 1 (SGI1) is an integrative mobilizable element integrated into the chromosome of bacteria, which plays an important role in the dissemination of antimicrobial resistance genes. Lots of SGI1 variants are found mainly in Salmonella enterica and Proteus mirabilis. In this study, a total of 157 S. enterica and 132 P. mirabilis strains were collected from food-producing animals in Sichuan Province of China between December 2016 and November 2017. Detection of the SGI1 integrase gene showed that three S. enterica and five P. mirabilis strains were positive for SGI1, which displayed different multidrug resistance profiles. Five different SGI1 variants, including two novel variants (SGI1-PmBC1123 and SGI1-PmSC1111), were characterized by whole genome sequencing and PCR linkage. In two novel SGI1 variants, IS26-mediated rearrangements resulted in large sequence inversions of the MDR regions extending outside the SGI1 backbone. The sul3-type III class 1 integron (5′CS-sat-psp-aadA2-cmlA1-aadA1-qacH-IS440-sul3) and gene cassettes aac(6′)-Ib-cr-blaOXA–1-catB3-arr-3 are found in SGI1-PmSC1111. Mobilization experiments indicated that three known variants were conjugally mobilized in trans to Escherichia coli with the help of a conjugative IncC plasmid. However, the two novel variants seemed to lose the mobilization, which might result from the sequence inversion of partial SGI1 backbone. The identification of the two novel SGI1 variants in this study suggested that IS26-mediated rearrangements promote the diversity of SGI1.
Highlights
Genomic islands (GIs), such as integrative and conjugative elements (ICEs) and integrative mobilizable elements (IMEs), are distinct regions integrated into the chromosome of bacteria and acquired via horizontal transfer (Bellanger et al, 2014; Partridge et al, 2018)
Detection and sequence analysis of SGI/PGI/AGI/GIPmi1 integrase gene showed that 3 S. enterica and 5 P. mirabilis strains were positive for Salmonella genomic island 1 (SGI1)
Three SGI1-containg S. enterica strains belonged to different STs (Table 1)
Summary
Genomic islands (GIs), such as integrative and conjugative elements (ICEs) and integrative mobilizable elements (IMEs), are distinct regions integrated into the chromosome of bacteria and acquired via horizontal transfer (Bellanger et al, 2014; Partridge et al, 2018). SGI1 (42.4 kb) is comprised of a backbone containing 28 ORFs (S001-S027 and S044) and a 13 kb MDR region that consists of a complex In4-type class 1 integron named In104 (Boyd et al, 2001; Levings et al, 2005). It can form extrachromosomal circular form and is mobilized in trans by conjugative IncA/C plasmids (Doublet et al, 2005; Douard et al, 2010). We characterized the SGI/PGI genomic islands in Salmonella enterica and P. mirabilis of food-producing animal origin in Sichuan Province of China and described two novel SGI1 variants in P. mirabilis
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