Evolution and spread of SHV extended-spectrum β-lactamases in Gram-negative bacteria

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Abstract
Resistance to β-lactam antibiotics has been a problem for as long as these drugs have been used in clinical practice. In clinically significant bacteria the most important mechanism of resistance is the production of one or more β-lactamases, enzymes that hydrolyse the β -lactam bond characteristic of this family of antibiotics. Prominent among the β -lactamases produced by the Enterobacteriaceae is the SHV family. The first reported SHV β-lactamase had a narrow spectrum of activity. By the accumulation of point mutations at sites that affect the active site of the enzyme, a family of derivatives of SHV-1 has evolved. Derivatives of SHV-1 either have an extended spectrum of activity, capable of inactivating third-generation cephalosporins, or are resistant to β-lactamase inhibitors. This review describes the evolution and spread of the SHV family of β-lactamases, introducing the structure–function analysis made possible by DNA sequence analysis. It also reviews the methods used to characterize members of this family of β-lactamases, indicating some of the difficulties involved.

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