ESBLs are enzymes produced by bacteria, which make the bacteria resistant to a variety of antimicrobials. Vertical and horizontal spread of ESBL-producers in the production pyramid, in combination with antibiotic use at hatcheries and production farms, has led to a high level of colonization in the animals and in meat. When people come into contact with ESBL-producing bacteria, e.g. through the food chain, it can pose a risk to human health. An obvious solution to the ESBL problem would be to stop the use of antibiotics in poultry, so that ESBLs will slowly disappear.
Reduction of antibiotic usage in hatcheries has indeed resulted in a decrease, but the problem has not yet been solved. A complication is that antibiotic resistance can spread (horizontally) between bacteria by plasmids, which can prevent a reduction in ESBLs or even increase their number in absence of antibiotics. This has been shown in the laboratory and in live animals. Stopping the usage of antibiotics will therefore not be enough, and active interventions are needed.