Abstract: The antibacterial activity of beta-lactam antibiotics or their combinations with inhibitor sulbactum against non-lactamase-producing strains, lactamase-producing and ESBLs-producing isolates was evaluated with two-fold dilution method after pathogens isolated from pigs and chickens were detected, respectively, for beta-lactamase and extended-spectrum beta-lactamases(ESBLs).The results revealed that most of the 43 clinically isolated strains could produce beta-lactamase and 3 strains of Shigella isolated from chicken samples produced ESBLs. Ａll of the 30 lactamase-producing strains isolated and only one of the 16 non-lactamase-producing strains were resistant to amoxicillin and ampicillin. MICs of ampicillin against lactamase-producing isolates decreased by 10-40 and 10-20 times, respectively, when it was conbined with sulbactam at ratio of 1∶2 and 1∶4. All clinical isolates were susceptible to third-generation cephalosporins.The MICs of third-generation cephalosporins against lactamase-producing isolates did not change when they were conbined with sulbactam. MICs of ceftiofur and ceftriaxone against ESBLs-producing isolates decreased by 2-4 times when they were conbined with sulbactam.

Key words: Beta-lactamase, Extended-spectrum beta-lactamase, Inhibitor, Antibiotic susceptibility test