Extended-spectrum beta-lactamase-producing Klebsiella spp.

Extended-spectrum beta-lactamases (ESBLs) are associated particularly with Klebsiella spp. These enzymes have arisen by mutation of the genes coding for clavulanate-sensitive, plasmid-mediated beta-lactamases such as TEM-1, TEM-2 and SHV-1. Amino acid changes in ESBLs confer enhanced hydrolysis of oxyimino-aminothiazolyl beta-lactams and aztreonam. Enzyme hyperproduction and loss of porins contribute to hydrolytic efficiency. ESBLs are highly susceptible to inhibition by clavulanate, and their presence can be detected by the disc-approximation test, using amoxycillin/clavulanate and an ESBL-susceptible antibiotic. Other manual procedures have been used and commercial tests to detect the enzymes include Etest, Vitek and Dade Microscan products. The epidemiology of ESBLs is complex, and epidemic and sporadic strains may be encountered in the same hospital. Spread between hospitals--even countries--has been documented. ESBL activity is carried on large plasmids that often carry determinants for resistance to aminoglycosides and other antibiotics, and this is transmissible to Escherichia coli and other species of Enterobacteriaceae in which ESBLs have been detected.