Extended-spectrum beta-lactamases in North America, 1987-2006.

Extended-spectrum beta-lactamases (ESBLs) derived from the TEM-1 beta-lactamase were first identified in the USA in outbreak strains of Klebsiella pneumoniae in the middle to late 1980s, together with the SHV-5 ESBL. The TEM-10, TEM-12 and TEM-26 enzymes have remained in US hospitals, but have been joined by other ESBLs that are variants of the SHV-1 broad-spectrum beta-lactamase. In the most recent surveys from hospitals in the eastern part of the USA, the most prominent ESBLs have been the SHV-7 and SHV-12 enzymes. In Canada, a wider variety of ESBLs has been identified, with multiple members of the TEM, SHV and CTX-M classes being represented in surveillance isolates. SHV-type and CTX-M ESBLs have appeared in many Canadian isolates, with an outbreak of CTX-M-14-related enzymes from Calgary, but limited TEM-derived ESBLs. Surprisingly, few CTX-M ESBLs have yet been reported in the USA, in contrast to the rest of the world, where the CTX-M enzymes have become a predominant ESBL family.