Extended-spectrum beta-lactamase (ESBL) is an enzyme produced by certain bacteria that makes these bacteria resistant to antibiotics. Researchers from various institutes collaborating in a large consortium discovered that ESBL enzymes occur frequently in livestock, the food chain, the environment and in people, according to an announcement from Wageningen University & Research (WUR) in the Netherlands.
However, ESBL types in livestock and meat were found to be genetically different from those in people, WUR said. This means that people acquire ESBL only to a limited extent via livestock and through eating meat. The transmission mainly occurs among people.
These are the most important conclusions of the ESBLAT research consortium, part of the 1Health4Food program in the area of animal and human health. The results were presented during the ESBLAT symposium on Feb. 9.
ESBL ensures that bacteria become resistant to an important group of antibiotics. An infection with these resistant bacteria is more difficult to treat, which may be a problem for vulnerable people in particular.
Humans as a source
About 5% of the Dutch population carry ESBL in their intestines. The researchers found major similarities between ESBL from healthy carriers and people with an infection caused by these bacteria. This means that humans are an important source for the transmission of ESBL to other humans.
People who are occupationally exposed to animal sources as a result of their work, such as livestock farmers and abattoir employees, have a higher chance of carrying ESBL. Unlike the ESBL in livestock and other people, the ESBL of livestock farmers and their livestock do exhibit a high degree of similarity, WUR said. That is due to the intensive, direct contact between these risk groups and the livestock.
A total of 22 different reservoirs where bacteria accumulate were investigated, and ESBL was found in all of these reservoirs. For example, the researchers found ESBL in pets, wild birds, poultry, pigs, cattle and in surface water. However, the ESBL they found in livestock and meat showed little genetic similarity with the enzyme found in people, WUR noted, which means that livestock farming contributes less to ESBL carriership in humans than was previously assumed.
It is, therefore, a misconception that humans mainly acquire ESBL through eating meat (especially chicken meat), WUR said. If the meat is sufficiently cooked and adequate hygiene measures are taken in the kitchen, then the chance of people being exposed to ESBL is small.
ESBL occurrence in the environment was also studied during the research. Surface water often contains these enzymes, mainly due to the discharge of purified wastewater from the sewerage system but also because animal manure can end up in surface water. Nevertheless, WUR said the chances of people coming into contact with these — for example, through swimming — is small, because ESBL concentrations in water are low.
People who live near livestock farms are exposed to ESBL, for example via the air. However, they do not have an increased risk of carrying ESBL. The research demonstrates that the ESBL contribution of livestock farming via the environment is small as well, WUR noted.
The research consortium consists of WUR, Utrecht University, the Dutch National Institute for Public Health & the Environment, University Medical Center Utrecht and GD Animal Health. The research is part of 1Health4Food, a public/private research consortium in the area of animal and human health.