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Chapter 6 : β-Lactamases: Historical Perspectives
Category: Bacterial Pathogenesis
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β-lactamases are arguably the most well-studied antibiotic resistance determinants that have been described, with over 450 unique enzymes currently identified. Molecular relationships, as well as functional relationships, exist between the β-lactamases and penicillin binding proteins (PBPs), the essential enzymes involved in the terminal stages of bacterial cell wall synthesis. Two sets of β-lactamases classification schemes have evolved, based on either structural or functional descriptions of the enzymes. Fortuitously, the two schemes fit together according to major divisions but show some diversity among various subgroups for each of the divisions as shown. Microbiological methods have traditionally indicated the potential for β-lactamase production, based on susceptibility profiles for β-lactam-containing agents. In multiple surveys conducted during the late 1970s the most commonly identified plasmid-encoded β-lactamases among the Enterobacteriaceae were the broad-spectrum (group 2b) SHV-1 and TEM-1 or TEM-2 β-lactamase, followed by the oxacillinhydrolyzing OXA-1 enzyme. In the current age of rapid nucleotide sequencing, molecular and epidemiological characterizations of numerous β-lactamase genes in a wide variety of organisms have been reported. The chapter describes important new enzymes characterized in the published literature since the year 2000. The reported incidence of these β-lactamases depends, in part, on the laboratory technique used for detection by the clinical laboratory, and the type of β-lactamase varies by country and by region. Finally, the search for new β-lactamases in environmental isolates will serve to expand this important family of enzymes that are expected to continue as a major chapter in the story on antibiotic resistance.
Summary of β-lactamase classification schemes
Chromosomally encoded β-lactamase genes discovered since 2000
Diversity of plasmid-mediated β-lactamases in various regions of the world