Medical Laboratory Scientist (MLS) ASCP Practice Exam

The confirmatory test for the presence of extended spectrum beta-lactamases (ESBLs) is based on assessing the activity of cephalosporins in the presence of clavulanic acid. Clavulanic acid is a non-beta-lactam β-lactamase inhibitor that can restore the activity of certain cephalosporins against bacteria that produce ESBLs.

In the case of ESBL-producing organisms, these enzymes can hydrolyze extended-spectrum cephalosporins, leading to resistance and decreased activity of these antibiotics. However, when clavulanic acid is added to the testing medium, it inhibits the ESBLs, allowing cefotaxime and similar antibiotics to retain their antibacterial activity. This enhanced activity in the presence of clavulanic acid is used to confirm the production of ESBLs.

Other choices do not serve as confirmatory methods. The option regarding decreased activity of cephalosporins is more of a characteristic observed in initial susceptibility testing, rather than a confirmatory test itself. Increased activity of penicillin without inhibitors does not relate to ESBL confirmation, as ESBLs primarily affect cephalosporins. Lastly, a blanket resistance to all beta-lactam antibiotics does not