Bacteria that produce enzymes called extended-spectrum beta-lactamases (ESBLs) are resistant to many penicillin and cephalosporin antibiotics and often to other types of antibiotic.
The 2 main bacteria that produce ESBLs are Escherichia coli (E. coli) and Klebsiella species. The ESBLs that E. coli most often produce are called CTX-M enzymes.
E. coli with ESBLs may cause urinary tract infections (UTIs) that can sometimes progress to more serious infections like blood poisoning, which can be life threatening. Resistance makes these infections more difficult to treat.