Extended-spectrum β-lactamase-producing<i>Escherichia coli</i>isolated from poultry: a review of current problems, illustrated with some laboratory findings

Extended-spectrum β-lactamase (ESBL)-producing Escherichia coli has been documented in humans as well as in food-producing birds, including chickens, and for unknown reasons the prevalence has increased significantly during the last decade. With E. coli as a major opportunistic pathogen in chickens and with a potential for zoonotic transfer to human beings, ESBL-producing E. coli represents a major risk both to poultry production and to human health. This review presents some of the current problems with ESBL-producing E. coli in relation to poultry production, with a focus on chickens. To illustrate issues in relation to screening and typing, two case studies are included where one collection of ESBL-producing E. coli isolates was obtained from asymptomatic carrier chickens while the other was obtained from lesions in chickens. Pulsed-field gel electrophoresis and multi-locus sequence typing revealed a highly heterogeneous population of ESBL-producing E. coli. All isolates harboured between one and three large plasmids (>100 kb). Among isolates associated with asymptomatic chickens, the ESBL types SHV and TEM dominated, while CTX-M-1 dominated in disease-associated isolates. The isolates from diseased birds were occasionally of sequence types often associated with human infections, such as ST131. With improved tools to trace and screen for ESBL-producing E. coli at farm level, strategies can be selected that aim to reduce or eliminate the presence of ESBL-producing E. coli in poultry and poultry products meant for human consumption.