be·ta-lac·ta·mase 
(bā′tə-lăktə-mās′, -māz′, bē′-)
(bā′tə-lăktə-mās′, -māz′, bē′-)n.
Any of various enzymes that hydrolyze and inactivate beta-lactam antibiotics such as penicillin, found in many antibiotic-resistant bacteria.
[beta-lactam, cyclic amide occurring in penicillins (BETA + LACT(ONE) + AM(IDE)) + -ASE.]