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In page Β-Lactam antibiotic:

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If the bacterium produces the enzyme β-lactamase or the enzyme penicillinase, the enzyme will hydrolyse the β-lactam ring of the antibiotic, rendering the antibiotic ineffective.[1] (An example of such an enzyme is New Delhi metallo-beta-lactamase 1, discovered in 2009.) The genes encoding these enzymes may be inherently present on the bacterial chromosome or may be acquired via plasmid transfer (plasmid-mediated resistance), and β-lactamase gene expression may be induced by exposure to β-lactams.[citation needed]