Avian pathogenic Escherichia coli (APEC) cause widespread economic losses in poultry production and are potential zoonotic pathogens. Genome sequences of 95 APEC from commercial poultry operations in four Australian states that carried the class 1 integrase gene intI1, a proxy for multiple drug resistance (MDR), were characterized. Sequence types ST117 (22/95), ST350 (10/95), ST429 and ST57 (each 9/95), ST95 (8/95) and ST973 (7/95) dominated, while 24 STs were represented by one or two strains. FII and FIB repA genes were the predominant (each 93/95, 98 %) plasmid incompatibility groups identified, but those of B/O/K/Z (25/95, 26 %) and I1 (24/95, 25 %) were also identified frequently. Virulence-associated genes (VAGs) carried by ColV and ColBM virulence plasmids, including those encoding protectins [iss (91/95, 96 %), ompT (91/95, 96 %) and traT (90/95, 95 %)], iron-acquisition systems [sitA (88/95, 93 %), etsA (87/95, 92 %), iroN (84/95, 89 %) and iucD/iutA (84/95, 89 %)] and the putative avian haemolysin hylF (91/95, 96 %), featured prominently. Notably, mobile resistance genes conferring resistance to fluoroquinolones, colistin, extended-spectrum β-lactams and carbapenems were not detected in the genomes of these 95 APEC but carriage of the sulphonamide resistance gene, sul1 (59/95, 63 %), the trimethoprim resistance gene cassettes dfrA5 (48/95, 50 %) and dfrA1 (25/95, 27 %), the tetracycline resistance determinant tet(A) (51/95, 55 %) and the ampicillin resistance genes blaTEM-1A/B/C (48/95, 52 %) was common. IS26 (77/95, 81 %), an insertion element known to capture and mobilize a wide spectrum of antimicrobial resistance genes, was also frequently identified. These studies provide a baseline snapshot of drug-resistant APEC in Australia and their role in the carriage of ColV-like virulence plasmids.

Escherichia coli ST58 has recently emerged as a globally disseminated uropathogen that often progresses to sepsis. Unlike most pandemic extra-intestinal pathogenic E. coli (ExPEC), which belong to pathogenic phylogroup B2, ST58 belongs to the environmental/commensal phylogroup B1. Here, we present a pan-genomic analysis of a global collection of 752 ST58 isolates from diverse sources. We identify a large ST58 sub-lineage characterized by near ubiquitous carriage of ColV plasmids, which carry genes encoding virulence factors, and by a distinct accessory genome including genes typical of the Yersiniabactin High Pathogenicity Island. This sub-lineage includes three-quarters of all ExPEC sequences in our study and has a broad host range, although poultry and porcine sources predominate. By contrast, strains isolated from cattle often lack ColV plasmids. Our data indicate that ColV plasmid acquisition contributed to the divergence of the major ST58 sub-lineage, and different sub-lineages inhabit poultry, swine and cattle.

E. coli ST95 is one of five dominant ExPEC lineages globally and noted for causing urinary tract and bloodstream infections and neonatal meningitis in humans and colibacillosis in poultry. Using high-resolution phylogenomics, we show that F replicon sequence type is linked to ST95 clade structure and zoonotic potential.

This study sought to assess the genetic variability of Escherichia coli isolated from bloodstream infections (BSIs) presenting at Concord Hospital, Sydney during 2013–2016. Whole-genome sequencing was used to characterize 81 E. coli isolates sourced from community-onset (CO) and hospital-onset (HO) BSIs. The cohort comprised 64 CO and 17 HO isolates, including 35 multidrug-resistant (MDR) isolates exhibiting phenotypic resistance to three or more antibiotic classes. Phylogenetic analysis identified two major ancestral clades. One was genetically diverse with 25 isolates distributed in 16 different sequence types (STs) representing phylogroups A, B1, B2, C and F, while the other comprised phylogroup B2 isolates in subclades representing the ST131, ST73 and ST95 lineages. Forty-seven isolates contained a class 1 integron, of which 14 carried bla CTX -M- gene. Isolates with a class 1 integron carried more antibiotic resistance genes than isolates without an integron and, in most instances, resistance genes were localized within complex resistance loci (CRL). Resistance to fluoroquinolones could be attributed to point mutations in chromosomal parC and gyrB genes and, in addition, two isolates carried a plasmid-associated qnrB4 gene. Co-resistance to fluoroquinolone and broad-spectrum beta-lactam antibiotics was associated with ST131 (HO and CO), ST38 (HO), ST393 (CO), ST2003 (CO) and ST8196 (CO and HO), a novel ST identified in this study. Notably, 10/81 (12.3 %) isolates with ST95 (5 isolates), ST131 (2 isolates), ST88 (2 isolates) and a ST540 likely carry IncFII–IncFIB plasmid replicons with a full spectrum of virulence genes consistent with the carriage of ColV-like plasmids. Our data indicate that IncF plasmids play an important role in shaping virulence and resistance gene carriage in BSI E. coli in Australia.

Colistin is a last resort antibiotic used for the treatment of human infections associated with carbapenemase-producing Enterobacteriales. Here, we evaluated the occurrence of mcr-1 and -2 plasmid-mediated colistin resistance in colistin and/or carbapenem resistant human clinical Enterobacteriales and other gram-negative bacteria (n = 543) as well as third generation cephalosporin-resistant (3GCR) Escherichia coli isolates from poultry abattoir workers (n = 15) and poultry fecal samples (n = 92) collected from two geographically separate abattoirs in Romania. which revealed that mcr-1 was present within four sequence types (STs): ST744 (n = 7), ST57 (n = 7), ST156 (n = 2), and ST10 (n = 1). Within STs, serotypes were conserved and, notably, all except one of the mcr-1-positive isolates were found to exhibit fluoroquinolone-resistance (FQR) associated SNPs in both gyrA and parC. While there were variations in genotypes, all isolates belonging to ST744, ST57, and ST156 were rich in resistance determinants, carrying aminoglycoside-modifying enzymes genes, sulfonamide resistance gene blaTEM–1 as well as blaCMY–2 AmpC β-lactamase resistance genes. They also exhibited high similarity in carriage of virulence genes; ST10, however, only carried the mcr-1 gene. Whole genome sequencing (WGS) analysis also revealed that although the mcr-1 gene was identified in a diverse population of E. coli, two STs (ST57 and ST744) predominated and interestingly, were found in isolates across both abattoirs providing evidence for clonal transmission. Also, two main genomic contexts of mcr-1 isolates were revealed with all ST57 isolates harboring the mcr-1 gene between two copies of ISApl1 (or the Tn6330 transposon) whilst a common mcr-1 containing scaffold, highly similar to IncX type mcr-1-bearing plasmids (pWI2-mcr, Accession number: LT838201), was present among mcr-1 isolates of varying phylogenetic backgrounds (ST10, ST744 and ST156). The high prevalence of the mcr-1 gene in poultry E. coli isolates with co-resistance to cephalosporins and quinolones, in a country where antimicrobial use in food production species is poorly regulated, is concerning and the findings from this study should lead to better surveillance of antimicrobial resistance (AMR) in food-production animals in Romania.