Author(s): Johann DD Pitout 1 1
carbapenemases; CTX-M-[beta]-lactamases; ExPEC ; extraintestinal pathogenic Escherichia coli; KPC ; laboratory detection; NDM; OXA-48; plasmid-mediated AmpC [beta]-lactamases; treatment options
Escherichia coli is an incredibly diverse bacterial species that shows considerable metabolic versatility with the ability to colonize numerous hosts as nonpathogenic commensal bacteria that form part of the normal intestinal flora of humans and various animals  . However, several pathogenic variants of E. coli have the ability to cause infections of the gastrointestinal system (these are referred to as intestinal pathogenic E. coli ), while different pathogenic variants cause infections outside the gastrointestinal system (referred to as extraintestinal pathogenic E. coli [ExPEC] isolates). ExPEC incorporates the following variants: avian pathogenic E. coli , uropathogenic E. coli (UPEC) and those isolates responsible for septicemia and neonatal meningitis  .
The presence of several putative virulence genes has been positively linked to the pathogenicity of ExPEC. Phylogenetic analyses have shown that intestinal E. coli and ExPEC fall into four main phylogenetic groups, namely, A, B1, B2 and D  . ExPEC belongs mainly to group B2 and, to a lesser extent, to group D, while intestinal commensal isolates tend to belong to groups A and B1. ExPEC isolates exhibit considerable genome diversity and possess a broad range of virulence-associated factors, including toxins, adhesions, lipopolysaccharides, polysaccharide capsules, proteases and invasins, which are frequently encoded by genes in pathogenic islands or other mobile DNA islands. It seems that these putative virulence factors contribute to fitness (e.g., iron-uptake systems, bacteriocins, proteases and adhesins) of ExPEC and increase the adaptability, competitiveness and ability to colonize the human body, rather than being typical virulence factors directly involved in infection  .
ExPEC, especially the UPEC variants, are most commonly associated with human infections outside the intestinal system  and are important causes of lower urinary tract infections (UTIs) and systemic infections in humans. The systemic infections include upper UTIs, bacteremia, nosocomial pneumonia, cholecystitis, cholangitis, peritonitis, cellulitis, osteomyelitis, infectious arthritis and neonatal meningitis. UPEC are the primary causes of community-acquired UTIs, with an estimated 20% of women over the age of 18 years suffering from a UTI during their lifetime  . UPEC is responsible for 70-95% of community-onset UTIs and approximately 50% of nosocomial UTIs, hence accounting for substantial morbidity, mortality and medical expenses  . Recurrent or relapsing UTIs are especially problematic in many individuals. The primary reservoir of UPEC is believed to be the human intestinal tract and isolates act as opportunistic pathogens that employ a diverse repertoire of virulence factors to colonize and infect the urinary tract in an ascending fashion  . However, community-onset clonal outbreaks of UTIs, possibly due to the consumption of food contaminated with UPEC have also been described  . Additionally, there is some evidence that UPEC isolates can also be transmitted via sexual activities  .
The aim of this article is to highlight recent aspects of antimicrobial resistance in ExPEC, including the laboratory detection of these isolates and to briefly describe treatment options for infections due to antimicrobial resistant ExPEC....