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=== Types ===
{{Redirect|Amp resistance|resistance to antimicrobial peptides|AMP resistance}}
==== TEM beta-lactamases (class A) ====
TEM-1 is the most commonly encountered beta-lactamase in [[gram-negative bacteria]]. Up to 90% of ampicillin resistance in [[Escherichia coli|''E. coli'']] is due to the production of TEM-1.<ref name="pmid2193616">{{cite journal | vauthors = Cooksey R, Swenson J, Clark N, Gay E, Thornsberry C | title = Patterns and mechanisms of beta-lactam resistance among isolates of Escherichia coli from hospitals in the United States | journal = Antimicrobial Agents and Chemotherapy | volume = 34 | issue = 5 | pages = 739–45 | date = May 1990 | pmid = 2193616 | pmc = 171683 | doi = 10.1128/AAC.34.5.739 }}</ref> Also responsible for the ampicillin and penicillin resistance that is seen in ''[[H. influenzae]]'' and ''[[N. gonorrhoeae]]'' in increasing numbers. Although TEM-type beta-lactamases are most often found in ''[[Escherichia coli|E. coli]]'' and ''[[K. pneumoniae]]'', they are also found in other species of gram-negative bacteria with increasing frequency. The amino acid substitutions responsible for the [[#Extended-spectrum beta-lactamase (ESBL)|extended-spectrum beta lactamase (ESBL)]] phenotype cluster around the active site of the enzyme and change its configuration, allowing access to oxyimino-beta-lactam substrates. Opening the active site to beta-lactam substrates also typically enhances the susceptibility of the enzyme to β-lactamase inhibitors, such as clavulanic acid. Single amino acid substitutions at positions 104, 164, 238, and 240 produce the ESBL phenotype, but ESBLs with the broadest spectrum usually have more than a single amino acid substitution. Based upon different combinations of changes, currently 140 TEM-type enzymes have been described. TEM-10, TEM-12, and TEM-26 are among the most common in the United States.<ref name="pmid14576117">{{cite journal | vauthors = Paterson DL, Hujer KM, Hujer AM, Yeiser B, Bonomo MD, Rice LB, Bonomo RA | title = Extended-spectrum beta-lactamases in Klebsiella pneumoniae bloodstream isolates from seven countries: dominance and widespread prevalence of SHV- and CTX-M-type beta-lactamases | journal = Antimicrobial Agents and Chemotherapy | volume = 47 | issue = 11 | pages = 3554–60 | date = November 2003 | pmid = 14576117 | pmc = 253771 | doi = 10.1128/AAC.47.11.3554-3560.2003 }}</ref><ref name="pmid11585791">{{cite journal | vauthors = Bradford PA | title = Extended-spectrum beta-lactamases in the 21st century: characterization, epidemiology, and detection of this important resistance threat | journal = Clinical Microbiology Reviews | volume = 14 | issue = 4 | pages = 933–51, table of contents | date = October 2001 | pmid = 11585791 | pmc = 89009 | doi = 10.1128/CMR.14.4.933-951.2001 }}</ref><ref name="pmid15673804">{{cite journal | vauthors = Jacoby GA, Munoz-Price LS | title = The new beta-lactamases | journal = The New England Journal of Medicine | volume = 352 | issue = 4 | pages = 380–91 | date = January 2005 | pmid = 15673804 | doi = 10.1056/NEJMra041359 }}</ref> The term TEM comes from the name of the Athenian patient (Temoniera) from which the isolate was recovered in 1963.<ref>{{cite journal | doi = 10.3201/eid2404.et2404 | title = Etymologia: TEM | year = 2018 | vauthors = Ruiz J | journal = Emerging Infectious Diseases | volume = 24 | issue = 4 | page = 709 | doi-access = free | pmc = 5875283 }}</ref>
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==Evolution==
Beta-lactamases are ancient bacterial enzymes. Metallo β-lactamases ("class B") are all structurally similar to [[RNase Z]] and may have evolved from it. Of the three subclasses B1, B2, and B3, B1 and B2 are theorized to have evolved about one [[Bya|billion years ago]], while B3 seems to have arisen independently, possibly before the divergence of the gram-positive and gram-negative eubacteria about two billion years ago.<ref name=Hall2004>{{cite journal | vauthors = Hall BG, Salipante SJ, Barlow M | title = Independent origins of subgroup Bl + B2 and subgroup B3 metallo-beta-lactamases | journal = Journal of Molecular Evolution | volume = 59 | issue = 1 | pages = 133–41 | date = July 2004 | pmid = 15383916 | doi = 10.1007/s00239-003-2572-9 | bibcode = 2004JMolE..59..133H | s2cid = 30833168 }}</ref> PNGM-1 (Papua New Guinea Metallo-β-lactamase-1) has both metallo-β-lactamase (MBL) and tRNase Z activities, suggesting that PNGM-1 is thought to have evolved from a tRNase Z, and that the B3 MBL activity of PNGM-1 is a promiscuous activity and subclass B3 MBLs are thought to have evolved through PNGM-1 activity.<ref>{{cite journal | vauthors = Lee JH, Takahashi M, Jeon JH, Kang LW, Seki M, Park KS, Hong MK, Park YS, Kim TY, Karim AM, Lee JH, Nashimoto M, Lee SH | title = Dual activity of PNGM-1 pinpoints the evolutionary origin of subclass B3 metallo-''β''-lactamases: a molecular and evolutionary study | journal = Emerging Microbes & Infections | volume = 8 | issue = 1 | pages = 1688–1700 | year = 2019 | pmid = 31749408 | pmc = 6882493 | doi = 10.1080/22221751.2019.1692638 | doi-access = free }}</ref> Subclasses B1 and B3 has been further subdivided.<ref>{{cite journal | vauthors = Berglund F, Johnning A, Larsson DG, Kristiansson E | title = An updated phylogeny of the metallo-β-lactamases | journal = The Journal of Antimicrobial Chemotherapy | volume = 76 | issue = 1 | pages = 117–123 | date = January 2021 | pmid = 33005957 | doi = 10.1093/jac/dkaa392 }}</ref>
Serine beta-lactamases (classes A, C, and D) appear to have evolved from [[DD-Transpeptidase|<small>DD</small>-transpeptidase]]s, which are [[penicillin-binding protein]]s involved in cell wall biosynthesis, and as such are one of the main targets of beta-lactam antibiotics.<ref>{{InterPro|IPR012338}}</ref> These three classes show undetectable sequence similarity with each other, but can still be compared using structural homology. Groups A and D are sister taxa and group C diverged before A and D.<ref name=Hall2003>{{cite journal | vauthors = Hall BG, Barlow M | title = Structure-based phylogenies of the serine beta-lactamases | journal = Journal of Molecular Evolution | volume = 57 | issue = 3 | pages = 255–60 | date = September 2003 | pmid = 14629035 | doi = 10.1007/s00239-003-2473-y | s2cid = 187389 }}</ref> These serine-based enzymes, like the group B betalactamases, are of ancient origin and are theorized to have evolved about two billion years ago.<ref name="pmid15158767">{{cite journal | vauthors = Hall BG, Barlow M | title = Evolution of the serine beta-lactamases: past, present and future | journal = Drug Resistance Updates | volume = 7 | issue = 2 | pages = 111–23 | date = April 2004 | pmid = 15158767 | doi = 10.1016/j.drup.2004.02.003 }}</ref>
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