Identification of Tn 6835 and a Novel Genomic Island, MMGI-1, in a Pan-Resistant Morganella morganii Strain

M organella morganii is a member of the Morganellaceae that shares closest fea- tures with the Proteus and Providencia genera (1) and is widespread in the environment and the intestinal tracts of animals and humans.It is also recognized as an opportunistic pathogen causing clinical infections (2).Acquisition of the bla NDM-1 gene in M. morganii strains that are intrinsically resistant to multiple antibiotics will make clinical treatment extremely difficult (2).Here, we report the isolation and identification of a highly drug-resistant M. morganii strain harboring a novel Tn7-like transposon and a peculiar genomic island, M. morganii genomic island 1 (MMGI-1).M. morganii GDMM86 was recovered from a fecal swab of a healthy chicken in the routine surveillance of animal-origin bacterial antimicrobial resistance in Guangdong Province, China.Antimicrobial susceptibility testing was performed and interpreted using CLSI reference broth microdilution (3).Strain GDMM86 was resistant to cefotaxime (MIC, .256mg/ ml), ceftazidime (.256 mg/ml), cefoxitin (.256mg/ml), cefepime (.256 mg/ml), piperacillin (.256 mg/ml), imipenem (.32mg/ml), meropenem (.64mg/ml), ertapenem (.64 mg/ ml), ciprofloxacin (.32mg/ml), levofloxacin (.64mg/ml), gentamicin (.128 mg/ml), amikacin (.64mg/ml), streptomycin (.128mg/ml), trimethoprim-sulfamethoxazole (.128mg/ml), chloramphenicol (.128mg/ml), and aztreonam (.128mg/ml).Whole-genome sequencing data were generated using short-read technology (Illumina, San Diego, CA) and MinION (Oxford Nanopore Technologies, Oxford, UK).Short and long reads were subjected to de novo hybrid assembly.A single contig, assembled with the Canu (version 1.8) protocol and corrected using Pilon (version 1.22), contained a full chromosome of 4,111,737 bp, with 3,890 putative coding sequences (Fig. 1A) (GenBank accession no.CP061513).The resistome was investigated using ResFinder 3.1 (https://cge.cbs.dtu.dk/services/ResFinder/).The chromosome-borne bla DHA-10 and catA2 genes were detected in the isolate, resulting in its intrinsic resistance to ampicillin and phenicols.Sequence analysis showed that 11 resistance genes were carried by a novel multidrugresistant (MDR) transposon that was designated Tn6835 (Fig. 1B), according to the nomenclature of transposons (4; http://transposon.lstmed.ac.uk/).Tn6835 contains a hybrid class 2/class 1 integron with a large IS26 flanked multiresistance region inserted.It is located at the usual Tn7 insertion site near glmS (encodes glucosamine 6-phosphate synthase), with a 5-bp direct repeat (AGATA) on both sides.Tn6835 is 41,915 bp (corresponding to bases 35338 to 77252 of GenBank accession no.CP061513) and harbors 11 resistance genes, including aadA1, aac(3)-IV, aadA2, aph(4)-Ia, aphA1, floR, lnu(F), dfrA1, dfrA12, sul1, and sul2.Tn7 contains a transposition module formed by the tnsA, tnsB, tnsC, tnsD, and tnsE genes, in which tnsD and tnsE encode transposition target site selection proteins (5,6).In this study, tnsD in Tn6835 was truncated by insertion of a fragment of Tn1721, and tnsE is missing.The transposition module (tnsA, tnsB, tnsC, and DtnsD) and the class 2 integrase gene of Tn6835 shows 99% nucleotide sequence identity to the Tn7 of M. morganii strain FDAARGOS_172 (CP014026).The truncation of tnsD and the loss of tnsE may enhance the