Beta-Lactamase and Ambler classification

β-lactamase enzymes are capable of hydrolysing the β-lactam rings (the active site) of β-lactam antibiotics; thereby deactivating their antibacterial properties.

  • It is observed in both gram-positive and gram-negative bacteria.
  • They are plasmid coded, and transferred from one bacterium to other mostly by conjugation, (except in Staphylococcus aureus where they are transferred by transduction).
  • Beta lactamases can be classified in two ways:
    • Ambler’s classification (structural or molecular classification).
    • Bush Jacoby Medeiros classification or functional (phenotypic)—Advanced and complex classification.

Beta-Lactamase and Ambler classification

Ambler classification of beta-lactamases

Class A-ESBL (Extended spectrum β-lactamases)

Organisms producing ESBL enzymes are resistant to all Penicillins and 1st, 2nd and 3rd generation cephalosporins and monobactams, however remain sensitive to carbapenems and cephamycins.

  • Resistance can be overcome by β-lactam + β-lactamase inhibitor (e.g. sulbactum or clavulanic acid).
  • Detected by Combination disk test (Ceftazidime and cetftazidime + clavulanic acid), Three dimensional test (best method).

Class B-MBL (Metallo beta-lactamase)

These organisms are resistant to all those antibiotics to which AmpC beta-lactamase producers are resistant plus they are resistant to carbapenems.

  • Resistance cannot be overcome by β-lactam + β-lactamase inhibitor combination.
  • Detected by EDTA disk synergy test, modified Hodge test.

Class C- AmpC beta-lactamase

These organisms are resistant to all those antibiotics to which ESBL producers are resistant plus they are resistant to cephamycins (e.g. cefoxitin and cefotetan ). But they are sensitive to carbapenems.

  • Resistance cannot be overcome by β-lactam + β-lactamase inhibitor combination.
  • Detected by AmpC disk test using cefoxitin disk.

Class D- oxacillinase

  • Resistance can be overcome by β-lactam + β-lactamase inhibitor combination.

About Author

Photo of author

Sagar Aryal

Sagar Aryal is a microbiologist and a scientific blogger. He attended St. Xavier’s College, Maitighar, Kathmandu, Nepal, to complete his Master of Science in Microbiology. He worked as a Lecturer at St. Xavier’s College, Maitighar, Kathmandu, Nepal, from Feb 2015 to June 2019. After teaching microbiology for more than four years, he joined the Central Department of Microbiology, Tribhuvan University, to pursue his Ph.D. in collaboration with Helmholtz-Institute for Pharmaceutical Research Saarland (HIPS), Saarbrucken, Germany. He is interested in research on actinobacteria, myxobacteria, and natural products. He has published more than 15 research articles and book chapters in international journals and well-renowned publishers.

1 thought on “Beta-Lactamase and Ambler classification”

Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.