Tn6026 and Tn6029 are found in complex resistance regions mobilised by diverse plasmids and chromosomal islands in multiple antibiotic resistant Enterobacteriaceae.

Transposons flanked by direct copies of IS26 are important contributors to the evolution of multiple antibiotic resistance. Tn6029 and Tn6026 are examples of composite transposons that have become widely disseminated on small and large plasmids with different incompatibility markers in pathogenic and commensal Escherichia coli and various serovars of Salmonella enterica. Some of the plasmids that harbour these transposons also carry combinations of virulence genes. Recently, Tn6029 and Tn6026 and derivatives thereof have been found on chromosomal islands in both established and recently emerged pathogens. While Tn6029 and Tn6026 carry genes encoding resistance to older generation antibiotics, they also provide a scaffold for the introduction of genes encoding resistance to a wide variety of clinically relevant antibiotics that are mobilised by IS26. As a consequence, Tn6029 and Tn6026 or variants are likely to increasingly feature in complex resistance regions in multiple antibiotic resistant Enterobacteriaceae that threaten the health of humans and food production animals.

Molecular Analysis of an IncF ColV-Like Plasmid Lineage That Carries a Complex Resistance Locus with a Trackable Genetic Signature.

IncF ColV plasmids are important plasmid incompatibility group that are currently restricted to the Enterobacteriaceae. These plasmids carry an important repertoire of virulence-associated genes (VAGs) that contribute to the ability of avian pathogenic Escherichia coli to cause disease in poultry. VAGs found on ColV plasmids have also been linked to urosepsis and meningitis in humans but the mechanisms that elicit these disease conditions are not well understood. Recently we described the sequence of a ColV plasmid pSDJ2009-52F that carried the typical repertoire of VAGs and a complex resistance gene locus flanked by IS26, an insertion element that plays an important role in mobilizing antibiotic resistance genes on plasmids and genomic islands. We recovered complete ColV-like plasmid sequences from public databases that shared >80% sequence identity with pSDJ2009-52F in geographically diverse regions of the world over a 20-year timeframe. Previously we noted that pSDJ2009-52F carries a unique genetic signature in the class 1 integron within the complex resistance locus that was presumably created by the action of IS26. Here we show that most ColV-like plasmids that are closely related to pSDJ2009-52F also carry the same signature. Our studies provide insight into how these signature-bearing plasmids and the mobile genetic elements they carry traffic between E. coli sequence types over large geographic distances.

Genomic analysis of multidrug-resistant Escherichia coli ST58 causing urosepsis.

Sequence type 58 (ST58) phylogroup B1 Escherichia coli have been isolated from a wide variety of mammalian and avian hosts but are not noted for their ability to cause serious disease in humans or animals. Here we determined the genome sequences of two multidrug-resistant E. coli ST58 strains from urine and blood of one patient using a combination of Illumina and Single Molecule, Real-Time (SMRT) sequencing. Both ST58 strains were clonal and were characterised as serotype O8:H25, phylogroup B1 and carried a complex resistance locus/loci (CRL) that featured an atypical class 1 integron with a dfrA5 (trimethoprim resistance) gene cassette followed by only 24 bp of the 3'-CS. CRL that carry this particular integron have been described previously in E. coli from cattle, pigs and humans in Australia. The integron abuts a copy of Tn6029, an IS26-flanked composite transposon encoding blaTEM, sul2 and strAB genes that confer resistance to ampicillin, sulfathiazole and streptomycin, respectively. The CRL resides within a novel Tn2610-like hybrid Tn1721/Tn21 transposon on an IncF, ColV plasmid (pSDJ2009-52F) of 138 553 bp that encodes virulence associated genes implicated in life-threatening extraintestinal pathogenic E. coli (ExPEC) infections. Notably, pSDJ2009-52F shares high sequence identity with pSF-088-1, a plasmid reported in an E. coli ST95 strain from a patient with blood sepsis from a hospital in San Francisco. These data suggest that extraintestinal infections caused by E. coli carrying ColV-like plasmids, irrespective of their phylogroup or ST, may pose a potential threat to human health, particularly to the elderly and immunocompromised.