Table 1.
Classification of β-lactamases.
| Ambler Class |
Bush Group | Characteristics of β-Lactamases | Number of Enzymes |
|---|---|---|---|
| C | 1 | Often chromosomal enzymes in Gram-negative but some are plasmid coded. Not inhibited by clavulanic acid. | 51 |
| A | 2a | Staphylococcal and enterococcal penicillinases. | 23 |
| 2b | Broad-spectrum β-lactamases including TEM-1 and SHV-1, mainly occurring in Gram-negative. |
16 | |
| 2be | Extended-spectrum β-lactamases (ESBL). | 200 | |
| 2br | Inhibitor-resistant TEM (IRT) β-lactamases. | 24 | |
| 2c | Carbenicillin-hydrolyzing enzymes. | 19 | |
| 2d | Cloxacillin (oxacillin)-hydrolyzing enzymes. | 31 | |
| 2e | Cephalosporinases inhibited by clavulanic acid. | 20 | |
| 2f | Carbapenem-hydrolyzing enzyme inhibited by clavulanic acid. | 4 | |
| B | 3 | Metallo-enzymes that hydrolyze carbapenems and other β-lactams except monobactams. Not inhibited by clavulanic acid. |
24 |
| D | 4 | Miscellaneous enzymes that do not fit into other groups. | 9 |