Biochemical and genetic characteristics of TEM-29B, a novel extended spectrum beta-lactamase

A clinical strain of Escherichia coli (strain Ec 41553) that was resistant to ceftazidime produced a TEM-type beta-lactamase with a pI of 5.4. Clavula nic acid restored the ceftazidime activity, thus suggesting an extended spe ctrum beta-lactamase (ESBL). The gene encoding ESBL was located in a plasmi d of 57 kb. After cloning and sequencing, the ESBL (TEM-29B) showed one ami no acid replacement with respect to the TEM-1 sequence, Arg-164 to His. Thi s change increased mainly the rate of hydrolysis of ceftazidime but not of cefotaxime and aztreonam. The relevance of this substitution in the increas e of ceftazidime MIC is thus stressed. (C) 1999 Federation of European Micr obiological Societies. Published by Elsevier Science B.V. All rights reserv ed.