Escherichia coli sequence type 131 (ST131) is a globally disseminated, multidrug resistant (MDR) clone responsible for a high proportion of urinary tract and bloodstream infections. The rapid emergence and successful spread of E. coli ST131 is strongly associated with several factors, including resistance to fluoroquinolones, high virulence gene content, the possession of the type 1 fimbriae FimH30 allele, and the production of the CTX-M-15 extended spectrum β-lactamase (ESBL). Here, we used genome sequencing to examine the molecular epidemiology of a collection of E. coli ST131 strains isolated from six distinct geographical locations across the world spanning 2000-2011. The global phylogeny of E. coli ST131, determined from whole-genome sequence data, revealed a single lineage of E. coli ST131 distinct from other extraintestinal E. coli strains within the B2 phylogroup. Three closely related E. coli ST131 sublineages were identified, with little association to geographic origin. The majority of single-nucleotide variants associated with each of the sublineages were due to recombination in regions adjacent to mobile genetic elements (MGEs). The most prevalent sublineage of ST131 strains was characterized by fluoroquinolone resistance, and a distinct virulence factor and MGE profile. Four different variants of the CTX-M ESBL-resistance gene were identified in our ST131 strains, with acquisition of CTX-M-15 representing a defining feature of a discrete but geographically dispersed ST131 sublineage. This study confirms the global dispersal of a single E. coli ST131 clone and demonstrates the role of MGEs and recombination in the evolution of this important MDR pathogen. bacterial evolution | genomics | phylogeography | genomic epidemiology M any multidrug-resistant (MDR) bacterial strains are now recognized as belonging to clones that originate in a specific locale, country, or even globally. Escherichia coli sequence type 131 (ST131) is one such recently emerged and globally disseminated MDR pandemic clone responsible for community and hospital-acquired urinary tract and bloodstream infections. E. coli ST131 was identified in 2008 as a major clone linked to the spread of the CTX-M-15 extended-spectrum β-lactamase (ESBL) resistance (1-3). Since then, E. coli ST131 has also been strongly associated with fluoroquinolone resistance, and coresistance to aminoglycosides and trimethoprim-sulfamethoxazole (4-6). Alarmingly, strains of E. coli ST131 resistant to carbapenems have also been reported (7, 8), further limiting treatment options for this clone.E. coli ST131 belongs to the B2 phylogenetic subgroup I, with most isolates characterized as serotype O25b:H4 (1). Epidemiology studies using pulse-field gel electrophoresis (PFGE) have demonstrated that E. coli ST131 strains exhibit diversity, with some dominant PFGE pulsotypes including the UK epidemic strain A (9) and pulsotype 968 (10, 11) widely distributed across the globe. More recently, a typing scheme using the type 1 fimbriae fimH adhesin gene revealed that a la...

Escherichia coli is one of the most-studied microorganisms worldwide but its characteristics are continually changing. Extraintestinal E. coli infections, such as urinary tract infections and neonatal sepsis, represent a huge public health problem. They are caused mainly by specialized extraintestinal pathogenic E. coli (ExPEC) strains that can innocuously colonize human hosts but can also cause disease upon entering a normally sterile body site. The virulence capability of such strains is determined by a combination of distinctive accessory traits, called virulence factors, in conjunction with their distinctive phylogenetic background. It is conceivable that by developing interventions against the most successful ExPEC lineages or their key virulence/colonization factors the associated burden of disease and health care costs could foreseeably be reduced in the future. On the other hand, one important problem worldwide is the increase of antimicrobial resistance shown by bacteria. As underscored in the last WHO global report, within a wide range of infectious agents including E. coli, antimicrobial resistance has reached an extremely worrisome situation that ‘threatens the achievements of modern medicine’. In the present review, an update of the knowledge about the pathogenicity, antimicrobial resistance and clinical aspects of this ‘old friend’ was presented.