The ecology of extended-spectrum b-lactamases (ESBLs) in the developed world

Background: Since the initial appearance in the 1980s, Enterobacteriaceae producing extended-spectrum b-lactamase (ESBL) have increased in prevalence and emerged as a major antimicrobial-resistant pathogen. The source of these antimicrobial-resistant bacteria in the developed world is an area of active investigation. Methods: A standard internet search was conducted with a focus on the epidemiology and potential sources of ESBL-producing Enterobacteriaceae in the developed world. Results: The last decade has witnessed several major changes in the epidemiology of these bacteria: replacement of TEM and SHV-type ESBLs by CTX-M-family ESBLs, emergence of Escherichia coli ST131 as a prevalent vehicle of ESBL, and spread of ESBL-producing E. coli in the community. The most studied potential sources of ESBL-producing Enterobacteriaceae in humans in the community include food and companion animals, the environment and personto- person transmission, though definitive links are yet to be established. Evidence is emerging that international travel may serve as a major source of introduction of ESBL-producing Enterobacteriaceae into the developed world. Conclusions: ESBL-producing Enterobacteriaceae has become a major multidrug-resistant pathogen in the last two decades, especially in the community settings. The multifactorial nature of its expansion poses a major challenge in the efforts to control them.