Β-lactamases

Definition

• Bacteria containing a plasmid that codes for an extended-spectrum beta-lactamase (ESBL)
• Most common with Escherichia coli and Klebsiella

Classification

• Classes A, B, and C: serine β-lactamases
  • Class A: inhibited by clavulanic acid or tazobactam
    • Constitutively expressed plasmid
    • Most common ESBL in Gram-negative bacteria
    • Resistance to 2nd and 3rd generation cephalosporins
    • Examples include penicillinase, TEM-1 (common in GNBs), CTX-M, K. pneumoniae carbapenemase (KPC) family
    • Common in E. coli, Klebsiella, and Proteus spp.
  • Class C: not inhibited by clavulanic acid or EDTA, resistant to cefoxitin, inhibited by clox in vitro
    • AmpC = chromosomal
    • Often an inducible AmpC gene present in the genome
    • Common in Citrobacter, Serratia, and Enterobacter
  • Class D: not inhibited by EDTA, variably inhibited by clavulanic acid; hard to identify
    • Common in Acinetobacter
• Class B: metallo-β-lactamase, inhibited by EDTA, not inhibited by clavulanic acid
  • Examples include New Delhi metallo-beta-lactamase (NDM-1)

Management

• Antibiotic therapy tailored to the resistance pattern
• Carbapenems, aminoglycosides, fluoroquinolones, and Septra typically work well