Beta-lactamases in Enterobacteriaceae in broilers

Resistance to cephalosprins due to the production of extended spectrum beta-lactamases (ESBLs) or plasmid mediated AmpC beta-lactamases is increasingly found in infections in humans outside the hospital. The genes encoding for these beta-lactamases are located on mobile DNA (plasmids), which can be transferred between bacterial species. Although the source of these bacteria is unknown, a food-borne source cannot be excluded. From 2003 to 2007 cefotaxime resistance increases in bacteria from broilers, but not in isolates from calves, pigs and dairy cows. Cefotaxime resistance is indicative for the presence of ESBLs or plasmid mediated AmpC beta-lactamases. Molecular typing of the resistance genes and the plasmids of Escherichia coli and Salmonella isolates from broilers revealed the presence of a variety of ESBL/AmpC genes: blaCTX-M-1, blaCTX-M-2, blaTEM-52, blaSHV-2, blaTEM20, blaACC-1 and blaCMY-2, located on plasmids: IncI1, IncHI2/P, IncK and some untypeable plasmids. A study performed at 26 broiler farms and a study performed in the broiler production pyramid showed that ESBL/AmpC-producing isolates were ubiquitous present. All 26 broiler farms contained broilers with ESBL-producing Escherichia coli in their faeces. Also in faeces of broiler farmers ESBL/AmpC producers were frequently found (33% against 10% described in the general population). ESBL/AmpC-producing isolates were also present at every level in the broiler production pyramid. In addition, in a study on three broiler farms, ESBL/AmpC-producing E. coli were found in the environment of two of four poultry houses before arrival of the broilers at the broiler farm. At arrival, not all broilers carried ESBL/AmpC-producing isolates, but within one week these isolates could be cultured from faeces of all 25 broilers tested. blaCTX-M-1 and blaTEM-52 on IncI1 plasmids were also found in bacteria isolated from infections in Dutch patients and subtyping of IncI1 plasmids revealed that 19% of the E. coli infections in Dutch patients was due to genetically identical resistance genes and plasmids as found in the broiler isolates. In addition, 94% of broiler meat purchased at different stores in the Netherlands contained similar ESBL-producing bacteria. This shows a high potency of transfer via food to humans. ESBL/AmpC-producing isolates were also found among 2% of bacteria causing clinical infections in companion animals and horses. ESBL/AmpC genes found in these isolates are partly similar to the ones found in broilers, but also include types found more often in humans, which shows another possible route of these bacteria to humans. Due to the potential threat to human health it is important to control the spread of ESBL/AmpC-producing isolates in the broiler production pyramid. This is feasible by preventing transmission from the top to the bottom of the broiler production pyramid, by identifying risk factors leading to the presence of ESBL/AmpC-producing isolates, by reducing the selection pressure imposed by the use of antimicrobials and by preventing local recirculation within subsequent flocks. In the meantime hygienic measures at slaughterhouses, hygienic standards in preparing meat products at retail and hygienic measures taken in the kitchen by the consumer are important measures to reduce the possibility of obtaining these isolates