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Class C β-Lactamases: Molecular Characteristics.

Alain Philippon1, Guillaume Arlet2, Roger Labia3

  • 1Faculté de Médecine, Bactériologie, Université de Paris, Paris, France.

Clinical Microbiology Reviews
|April 18, 2022
PubMed
Summary
This summary is machine-generated.

Class C β-lactamases, or cephalosporinases, show molecular variability and are widespread in bacteria. New research questions their classification and highlights genetic changes driving resistance to critical antibiotics.

Keywords:
AmpC β-lactamasesESACcephalosporinasesextended-spectrumphylogenyprimary structure

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Area of Science:

  • Microbiology
  • Enzymology
  • Molecular Biology

Background:

  • Class C β-lactamases (cephalosporinases) exhibit significant molecular diversity and are prevalent in bacteria, particularly Proteobacteria.
  • These enzymes are typically encoded by chromosomal, inducible genes and are identified by conserved catalytic motifs (e.g., 64SXSK, 150YXN, 315KTG).
  • Over 70 conserved amino acid residues, many near catalytic sites, aid in their identification.

Purpose of the Study:

  • To investigate the classification and evolutionary relationships of Class C β-lactamases.
  • To explore the genetic modifications contributing to the emergence of extended-spectrum AmpC β-lactamases (ESACs).
  • To understand the mechanisms underlying bacterial resistance to β-lactam antibiotics, including carbapenems and avibactam.

Main Methods:

  • Comparative sequence analysis of β-lactamase enzymes.
  • Identification of conserved amino acid residues and motifs.
  • Analysis of genetic modifications (mutations, insertions, deletions) in enzyme evolution.
  • Examination of regulatory genes (e.g., ampR, ampD, ampG) involved in resistance.

Main Results:

  • A distinct cluster of enzymes from genera like *Legionella* and *Bradyrhizobium* challenges existing β-lactamase classification, suggesting a potential C2 subclass.
  • Significant genetic variations, particularly in Ω- and H-10/R2-loops and the 150YXN motif, are observed in ESAC evolution.
  • Conserved deletions in *Acinetobacter* and *Hafnia* species support the concept of natural ESACs.
  • Emergence of high-level resistance to β-lactams and avibactam is linked to complex gene regulation and combined resistance mechanisms like porin loss and efflux system activation.

Conclusions:

  • The classification of Class C β-lactamases may require revision due to newly identified distant clusters.
  • Genetic plasticity in key enzyme regions drives the emergence of clinically relevant ESACs.
  • Bacterial resistance to advanced antibiotics is a multifactorial issue involving enzyme evolution, regulation, and other resistance strategies.