A Short Note On Classification Of Β -lactamases

1197 Words Aug 23rd, 2014 5 Pages
1.6.1 Classification of β-lactamases
Two major schemes for classification of β-lactamases are currently in use. The molecular classification of β-lactamases is based on the amino acid sequence homology dividing them into four classes A through D. The enzymes belonging to class A, C and D utilize serine residue for substrate hydrolysis while class B enzymes (metallo-β-lactamases) utilize divalent zinc ions for β-lactam hydrolysis [Ambler R. P. et al, 1991]. The functional classification is based on the substrate and inhibitor profiles of the enzymes [Bush K. et al, 1995; Bush & Jacoby, 2010]. The inhibitors used in this scheme are Clavulanic acid, tazobactam and EDTA. The β-lactamases can be loosely identified based on their substrate
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However with the advent of each new class of antibiotic used to treat bacterial infections, new β-lactamases emerged that caused resistance to that particular class of drug. It is assumed that the overuse of new antibiotics in the treatment of patients created a selective pressure eventually selecting for new variants of β-lactamase.
One of the new classes of antibiotics introduced was the oximino-cephalosporins which owing to their excellent activity became widely used for the treatment of serious infections due to gram negative bacteria in the 1980s. Not surprisingly, resistance due to production of β-lactamases against this expanded spectrum β-lactam antibiotics soon emerged. These β-lactamases were named as extended-spectrum β-lactamases (ESBLs) because of their increased spectrum of activity especially against the oximino-cephalosporins. The first ESBL capable of hydrolyzing the newer β-lactams was SHV-2 found in a strain Klebsiella ozaenae in
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