Functional Classification

Group 1

CEPHALOSPORINASE, Molecular Class A
Molecular Class C (not inhibited by clavulanic acid) Group 1 is cephalosporinases not inhibited by clavulanic acid, belonging to the molecular class C

Group 2

Group 2 are penicillinases, cephalosporinases, or both inhibited by clavulanic acid, corresponding to the molecular classes A and D reflecting the original TEM and SHV genes. However, because of the increasing number of TEM- and SHV-derived {beta}-lactamases, they were divided into two subclasses, 2a and 2b.

GROUP 2a

PENICILLINASE, Molecular Class A
The 2a subgroup contains just penicillinases.

GROUP 2b

BROAD SPECTRUM, Molecular Class A 2b Opposite to 2a, 2b are broad-spectrum {beta}-lactamases, meaning that they are capable of inactivating penicillins and cephalosporins at the same rate. Furthermore, new subgroups were segregated from subgroup 2b:

GROUP 2be

EXTENDED SPECTRUM, Molecular Class A Subgroup 2be, with the letter "e" for extended spectrum of activity, represents the ESBLs, which are capable of inactivating third-generation cephalosporins (ceftazidime, cefotaxime, and cefpodoxime) as well as monobactams (aztreonam)

GROUP 2br

INHIBITOR RESISTANT, Molecular Class A (diminished inhibition by clavulanic acid) The 2br enzymes, with the letter "r" denoting reduced binding to clavulanic acid and sulbactam, are also called inhibitor-resistant TEM-derivative enzymes; nevertheless, they are commonly still susceptible to tazobactam, except where an amino acid replacement exists at position met69.

GROUP 2c

CARBENICILLINASE, Molecular Class A Later subgroup 2c was segregated from group 2 because these enzymes inactivate carbenicillin more than benzylpenicillin, with some effect on cloxacillin.yht

GROUP 2d

CLOXACILANASE, Molecular Class D or A Subgroup 2d enzymes inactivate cloxacillin more than benzylpenicillin, with some activity against carbenicillin; these enzymes are poorly inhibited by clavulanic acid, and some of them are ESBLs The correct term is "OXACILLINASE". These enzymes are able to inactivate the oxazolylpenicillins like oxacilli, cloxacilli, dicloxacillin. The enzymes belong to the molecular class D not molecular class A.

GROUP 2e

CEPHALOSPORINASE, Molecular Class A Subgroup 2e enzymes are cephalosporinases that can also hydrolyse monobactams, and they are inhibited by clavulanic acid

GROUP 2f

CARBAPENAMASE, Molecular Class A Subgroup 2f was added because these are serine-based carbapenemases, in contrast to the zinc-based carbapenemases included in group 3

Group 3

METALLOENZYME, Molecular Class B (not inhibited by clavulanic acid) Group 3 are the zinc based or metallo {beta}-lactamases, corresponding to the molecular class B, which are the only enzymes acting by the metal ion zinc, as discussed above. Metallo B-lactamases are able to hydrolyse penicillins, cephalosporins, and carbapenems. Thus, carbapenems are inhibited by both group 2f (serine-based mechanism) and group 3 (zinc-based mechanism)

Group 4

PENICILLINASE, No Molecular Class (not inhibited by clavulanic acid) Group 4 are penicillinases that are not inhibited by clavulanic acid, and they do not yet have a corresponding molecular class.

GROUP 2e

CEPHALOSPORINASE, Molecular Class A Subgroup 2e enzymes are cephalosporinases that can also hydrolyse monobactams, and they are inhibited by clavulanic acid