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Objective To study the infection condition of AmpC ? lactamases producing strains for reasonable use of antibiotics in clinic. Methods Adopting modified three dimensional extract test was adopted to detect enterobacteriaceae strains, and 12 antibiotics were determined by the antimicrobial disk diffusion susceptibility tests in specimen collected from 233 senile infectious patients. Results The total isolating rate of AmpC ? lactamases producing enterobacteriaceae strains in senile patients was 8 6%. The incidence of AmpC ? lactamases producing strains was found most often in E.cloacae. The AmpC ? lactamases producing strains were susceptive to imipenem and there the resistance rates to imipenem were 100 0%. The resistance rates to cefepime were 85%～100% to the third generation cephalosporins and aztreonam Conclusions The drug resistance of AmpC ? lactamases producing enterobacteriaceae is very serious. It is important to surveillance and control drug resistance of AmpC producing strains.