ESBL is an abbreviation of Extended Spectrum Beta-Lactamase. Beta-Lactamase is an enzyme made by some bacteria that live in the bowel.
The enzyme breaks down certain antibiotics and stops them from working. 

ESBL producing bacteria can cause infections in the urine, in wounds and in the bloodstream.
Most commonly these bacteria can reside in your bowel without causing any harm which is referred to as colonisation. 

Problems only occur when ESBL gets into the body through wounds or into a part of the body that is normally sterile such as the bladder.

For those people who are vulnerable because they are already unwell or have injuries or surgical wounds, the risk of developing an infection is higher. This is why ESBL is taken seriously when people come into hospital. 

More information on ESBL in hospital and healthcare environments