Bench-to-bedside review: The role of β-lactamases in antibiotic-resistant Gram-negative infections

Table 2 Major groups of β-lactamases in Gram-negative bacteria that threaten the role of β-lactam antibiotics

			β-Lactams to which resistance is conferred
Functional group^a	Molecular class^b	Common name	Primary^c	Secondary^d
1	C	Cephalosporinase	Penicillins, cephalosporins	Carbapenems, monobactams
2b	A	Penicillinase	Penicillins, early cephalosporins	β-lactamase inhibitor combinations
2be	A	Extended-spectrum β-lactamase	Penicillins, cephalosporins, monobactams, β-lactamase inhibitor combinations	None
2d	D	Cloxacillinase	Penicillins, including oxacillin and cloxacillin	None
2df	D	Carbapenemase	Carbapenems and other β-lactams	None
2f	A	Carbapenemase	All current β-lactams	None
3	B	Metallo-β-lactamase	All β-lactams except monobactams	None

^aClassification based on Bush, Jacoby, and Medeiros [11] and Bush and Jacoby [7]. ^bClassified according to primary amino acid sequence [8–10]. ^cβ-lactams that are resistant solely as a function of β-lactamase production. ^dβ-lactams that are resistant as a function of β-lactamase production, usually at high levels, in combination with efflux or porin modifications.

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