# Beta-lactamase
**Beta-lactamase** (also written β-lactamase) is any bacterial enzyme that inactivates β-lactam antibiotics, such as penicillins, cephalosporins, carbapenems, and monobactams, by hydrolyzing the peptide bond of the characteristic four-membered β-lactam ring, rendering the antibiotic ineffective.[1](https://pubmed.ncbi.nlm.nih.gov/12195735/) These enzymes are the primary resistance mechanism against β-lactam antibiotics in [Gram-negative bacteria](https://www.edgepedia.org/gram-negative-bacteria), and they have driven antibiotic discovery and inhibitor development programs since the 1940s.[2](https://pmc.ncbi.nlm.nih.gov/articles/PMC6153792/)
| Key fact | Detail |
|---|---|
| Reaction | Hydrolysis of the β-lactam ring's peptide bond, producing products that lack antibacterial activity[1](https://pubmed.ncbi.nlm.nih.gov/12195735/) • [3](https://www.ncbi.nlm.nih.gov/books/n/nap10651/pdf/) |
| First report | 1940, by Abraham and Chain, an enzyme from *Bacillus coli* (now *Escherichia coli*) able to destroy penicillin[2](https://pmc.ncbi.nlm.nih.gov/articles/PMC6153792/) • [4](https://journals.asm.org/doi/10.1128/cmr.00037-09) |
| Classification | Ambler system (1980): classes A, B, C, and D; classes A, C, and D use a serine active site, class B are zinc-dependent metallo-β-lactamases[5](https://era.ed.ac.uk/server/api/core/bitstreams/6653268c-b97d-4198-b021-04b8b8ec7799/content) • [6](https://ecronicon.net/assets/ecmi/pdf/ECMI-16-00900.pdf) |
| Clinically important enzymes | TEM, SHV, CTX-M, KPC, and GES in class A; NDM metallo-β-lactamases in class B[7](https://pmc.ncbi.nlm.nih.gov/articles/PMC10235803/) • [8](https://arxiv.org/abs/1702.01239) |
| First inhibitors | Clavulanate, sulbactam, and tazobactam, introduced to protect amoxicillin, ampicillin, piperacillin, and ticarcillin[4](https://journals.asm.org/doi/10.1128/cmr.00037-09) |
| Newer inhibitors | Avibactam, vaborbactam, and relebactam, paired with ceftazidime, meropenem, and imipenem respectively, active against KPC-producing Enterobacterales[9](https://www.cambridge.org/core/services/aop-cambridge-core/content/view/694D38B773600296815B871899B034A7/S2732494X21002175a.pdf/div-class-title-evaluating-the-clinical-effectiveness-of-new-beta-lactam-beta-lactamase-inhibitor-combination-antibiotics-a-systematic-literature-review-and-meta-analysis-div.pdf) |
## Mechanism
A β-lactam antibiotic kills bacteria by mimicking the D-alanine residues of peptidoglycan peptides and irreversibly binding the transpeptidase enzymes (penicillin-binding proteins, PBPs) that cross-link the bacterial cell wall. β-lactamases defeat this by attacking the drug itself. The serine enzymes open the β-lactam ring with an active-site serine: in the prototypical enzyme TEM-1, the hydroxyl group of S70 opens the ring to form a covalent acyl-enzyme complex, and a water molecule positioned by the general base E166 then attacks the ester bond to release the hydrolyzed, inactive product.[10](https://pmc.ncbi.nlm.nih.gov/articles/PMC10075085/pdf/nihms-1885868.pdf) The hydrolytic reaction produces fragments with no antibacterial activity.[3](https://www.ncbi.nlm.nih.gov/books/n/nap10651/pdf/)
The catalytic proficiency of these enzymes approaches that of a fully efficient enzyme with diffusion-limited reaction rates, which is why even potent β-lactams are destroyed rapidly in producing cells.[2](https://pmc.ncbi.nlm.nih.gov/articles/PMC6153792/)
## Origin and evolution
β-lactamases evolved from the membrane-anchored PBPs themselves. Their evolution required the development of a diacylation step that releases the inactivated β-lactam substrate from the catalytic pocket and, in many cases, the loss of the membrane anchor.[7](https://pmc.ncbi.nlm.nih.gov/articles/PMC10235803/) TEM-1 retains the protein scaffold and active-site consensus sequences of its PBP ancestor but carries a longer Ω-loop bearing the key catalytic residue E166.[10](https://pmc.ncbi.nlm.nih.gov/articles/PMC10075085/pdf/nihms-1885868.pdf)
Resistance has tracked each new β-lactam into clinical use. Penicillinase-producing staphylococci emerged in the early 1950s, particularly in hospitals, and by the late 1960s more than 80 percent of both community and hospital-acquired *Staphylococcus aureus* strains were penicillin-resistant.[11](https://pmc.ncbi.nlm.nih.gov/articles/PMC5369031/) In 1976, β-lactamase-producing gonococci were isolated in England and the United States, contributing to the abandonment of penicillin as first-line therapy for gonorrhea in most of the world.[11](https://pmc.ncbi.nlm.nih.gov/articles/PMC5369031/)
## Classification
The Ambler system, proposed in 1980, remains the principal structural classification and divides β-lactamases into four classes based on sequence.[5](https://era.ed.ac.uk/server/api/core/bitstreams/6653268c-b97d-4198-b021-04b8b8ec7799/content)
- **Class A** is the most diverse subgroup and contains some of the most clinically concerning enzymes, including TEM and SHV (in *Escherichia coli* and *Klebsiella pneumoniae* respectively), GES, KPC, and CTX-M.[7](https://pmc.ncbi.nlm.nih.gov/articles/PMC10235803/)
- **Class B** are metallo-β-lactamases, which require zinc for catalysis; the New Delhi metallo-β-lactamase NDM-1 hydrolyzes a wide range of antibiotics including carbapenems.[6](https://ecronicon.net/assets/ecmi/pdf/ECMI-16-00900.pdf) • [8](https://arxiv.org/abs/1702.01239)
- **Class C** enzymes, such as AmpC, are typically encoded by chromosomal genes, use a serine active site, and are inducible; the gene is not easily transferable between species.[6](https://ecronicon.net/assets/ecmi/pdf/ECMI-16-00900.pdf)
- **Class D** includes the OXA enzymes, some of which confer carbapenem resistance in *Acinetobacter baumannii*.[4](https://journals.asm.org/doi/10.1128/cmr.00037-09)
The structural split between serine enzymes and metallo-enzymes produces distinct hydrolytic mechanisms that shape each enzyme's activity spectrum and its susceptibility to inhibitor compounds.[7](https://pmc.ncbi.nlm.nih.gov/articles/PMC10235803/)
## Clinical significance
In Gram-negative bacteria, β-lactamases are the primary resistance mechanism against β-lactam antibiotics, although clinical resistance is often multifactorial, combining enzyme production with permeability changes or efflux pump upregulation.[12](https://pmc.ncbi.nlm.nih.gov/articles/PMC6723624) Extended-spectrum β-lactamase (ESBL) producing Enterobacterales are a major challenge; ESBL producers generally remain susceptible to carbapenems, which became the standard treatment for severe infections.[13](https://academic.oup.com/cid/article/72/7/e169/5940736)
The choice between carbapenems and carbapenem-sparing β-lactam/β-lactamase inhibitor combinations has been re-examined in randomized evidence. The MERINO trial refuted earlier observational studies, some of which had shown equivalence between the two strategies for bloodstream infection caused by ceftriaxone-resistant *E. coli* or *Klebsiella* species.[14](https://pubmed.ncbi.nlm.nih.gov/31834029/) Non-carbapenemase-producing carbapenem-resistant Enterobacterales typically arise from amplification of non-carbapenemase β-lactamase genes such as blaCTX-M and ampC combined with loss of outer membrane porins.[15](https://www.idsociety.org/practice-guideline/amr-guidance?n=%40)
In [Gram-positive bacteria](https://www.edgepedia.org/gram-positive-bacteria) the picture differs: in *S. aureus*, strains carrying altered penicillin-binding proteins (PBP-2a, encoded by mecA) have largely superseded β-lactamase production as the primary β-lactam resistance mechanism.[12](https://pmc.ncbi.nlm.nih.gov/articles/PMC6723624) Some organisms have no confirmed β-lactamases at all, notably *S. pneumoniae*, *Streptococcus pyogenes*, *Helicobacter pylori*, [Mycoplasma](https://www.edgepedia.org/mycoplasma) species, and the Chlamydiae.[2](https://pmc.ncbi.nlm.nih.gov/articles/PMC6153792/)
## β-lactamase inhibitors
The first countermeasure was to pair a β-lactam with an inhibitor. Clavulanate, sulbactam, and tazobactam were introduced into clinical practice and greatly enhanced the efficacy of their partner β-lactams (amoxicillin, ampicillin, piperacillin, and ticarcillin) against [Enterobacteriaceae](https://www.edgepedia.org/enterobacteriaceae) and penicillin-resistant staphylococci.[4](https://journals.asm.org/doi/10.1128/cmr.00037-09) Selective pressure from heavy use then accelerated the emergence of resistance to these combinations, and β-lactamases from other classes that resist inhibition increased in prevalence.[4](https://journals.asm.org/doi/10.1128/cmr.00037-09)
A newer generation pairs β-lactams with diazabicyclooctane and boronic acid inhibitors. Avibactam protects aztreonam and ceftazidime against hydrolysis by ESBL enzymes, and avibactam works against TEM-1 by trapping the enzyme in a covalent complex from which it cannot execute the hydrolysis needed to free itself.[15](https://www.idsociety.org/practice-guideline/amr-guidance?n=%40) • [10](https://pmc.ncbi.nlm.nih.gov/articles/PMC10075085/pdf/nihms-1885868.pdf) Meropenem-vaborbactam and imipenem-relebactam combine a carbapenem with an inhibitor effective against KPC-producing Enterobacterales, and clinical trials have shown these combinations are not inferior to standard therapies for complicated intra-abdominal infections, complicated urinary tract infections, and hospital- or ventilator-associated pneumonia.[9](https://www.cambridge.org/core/services/aop-cambridge-core/content/view/694D38B773600296815B871899B034A7/S2732494X21002175a.pdf/div-class-title-evaluating-the-clinical-effectiveness-of-new-beta-lactam-beta-lactamase-inhibitor-combination-antibiotics-a-systematic-literature-review-and-meta-analysis-div.pdf) Treatment guidance suggests reserving these agents preferentially for infections caused by carbapenem-resistant organisms.[15](https://www.idsociety.org/practice-guideline/amr-guidance?n=%40)
## Surveillance
Because β-lactamase genes are mobile and spread readily, resistance surveillance tracks them at global scale. The WHO Global Antimicrobial Resistance and Use Surveillance System (GLASS) collects standardized data from national systems; its 2025 report analyzed more than 23 million bacteriologically confirmed infections reported by 104 countries in 2023 and produced adjusted global estimates for 93 infection type–pathogen–antibiotic combinations.[16](https://www.who.int/publications/i/item/9789240116337) In the United States, CDC's Multi-site Gram-negative Surveillance Initiative monitors carbapenem-resistant Enterobacterales, carbapenem-resistant *A. baumannii*, and ESBL-producing Enterobacterales to identify trends, resistance mechanisms, and risk factors.[17](https://cdc.gov/healthcare-associated-infections/php/haic-eip/mugsi.html)
## References
1. [Molecular analysis of beta-lactamase structure and function, PubMed](https://pubmed.ncbi.nlm.nih.gov/12195735/)
2. [Past and Present Perspectives on β-Lactamases, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC6153792/)
3. [Infectious diseases in an era of antibiotic resistance (National Academies executive summary)](https://www.ncbi.nlm.nih.gov/books/n/nap10651/pdf/)
4. [Drawz SM, Bonomo RA. Three Decades of β-Lactamase Inhibitors. Clinical Microbiology Reviews (2010)](https://journals.asm.org/doi/10.1128/cmr.00037-09)
5. [Metallo-β-lactamase mediated carbapenem resistance, University of Edinburgh thesis](https://era.ed.ac.uk/server/api/core/bitstreams/6653268c-b97d-4198-b021-04b8b8ec7799/content)
6. [bacterial resistance; a perspective on beta-lactamase enzymes](https://ecronicon.net/assets/ecmi/pdf/ECMI-16-00900.pdf)
7. [The biogenesis of β-lactamase enzymes, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC10235803/)
8. [Hydrolysis of Cephalexin and Meropenem by New Delhi Metallo-β-Lactamase, arXiv](https://arxiv.org/abs/1702.01239)
9. [Evaluating the clinical effectiveness of new beta-lactam/beta-lactamase inhibitor combination antibiotics, International Journal of Antimicrobial Agents (2020)](https://www.cambridge.org/core/services/aop-cambridge-core/content/view/694D38B773600296815B871899B034A7/S2732494X21002175a.pdf/div-class-title-evaluating-the-clinical-effectiveness-of-new-beta-lactam-beta-lactamase-inhibitor-combination-antibiotics-a-systematic-literature-review-and-meta-analysis-div.pdf)
10. [β-Lactamases Evolve against Antibiotics by Acquiring Large Active-Site Electric Fields, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC10075085/pdf/nihms-1885868.pdf)
11. [Penicillin's Discovery and Antibiotic Resistance: Lessons for the Future? Yale Journal of Biology and Medicine (2017)](https://pmc.ncbi.nlm.nih.gov/articles/PMC5369031/)
12. [β-Lactamases and β-Lactamase Inhibitors in the 21st Century, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC6723624)
13. [IDSA Guidance on the Treatment of ESBL-E, CRE, and DTR-P. aeruginosa, Clinical Infectious Diseases](https://academic.oup.com/cid/article/72/7/e169/5940736)
14. [Current evidence for therapy of ceftriaxone-resistant Gram-negative bacteremia, PubMed](https://pubmed.ncbi.nlm.nih.gov/31834029/)
15. [IDSA 2026 Guidance on the Treatment of Antimicrobial Resistant Gram-Negative Infections](https://www.idsociety.org/practice-guideline/amr-guidance?n=%40)
16. [Global antibiotic resistance surveillance report 2025, World Health Organization](https://www.who.int/publications/i/item/9789240116337)
17. [Multi-site Gram-negative Surveillance Initiative (MuGSI), CDC](https://cdc.gov/healthcare-associated-infections/php/haic-eip/mugsi.html)
---
*Topic: Encyclopedia › Life and health › Microorganisms and fungi › Bacteria › Antibiotic resistance and resistant strains*
*Initially written Sep 17, 2026 · Reviewed: Oct 21, 2026 · Edited: Oct 15, 2026; Oct 21, 2026 · Last review: Oct 21, 2026*
*Copyright 2026 EdgeChat AI, a subsidiary of Biostate AI.*
License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license