In-vitro antibacterial activity of imipenem compared with four other beta-lactam antibiotics (ceftazidime, cefotaxime, piperacillin and azlocillin) against 828 separate clinical isolates from a Portuguese hospital.

An agar dilution technique was used to determine the MIC50 and MIC90 of imipenem in comparison with ceftazidime, cefotaxime, piperacillin and azlocillin. Eight hundred and eighteen of the 828 (98.8%) unselected Gram-positive cocci and Gram-negative bacilli were inhibited by imipenem at a concentration of 8 mg/l or less. Imipenem was shown to be superior to the other four beta-lactam antibiotics against Acinetobacter calcoaceticus (40 strains), all the Staphylococcus aureus (80 strains, 10 of them penicillin- and methicillin-resistant), Streptococcus faecalis (20 strains) and Salmonella spp. (50 strains). Imipenem and cefotaxime were the most active against Str. pneumoniae (20 strains). Against Escherichia coli (52 strains) the activity of imipenem was similar to that of ceftadizime and superior to the other three antibiotics. Imipenem was two-fold inferior to cefotaxime and four-fold inferior to ceftazidime against Serratia marcescens (52 strains) and superior to piperacillin and azlocillin. Against Pseudomonas aeruginosa (300 strains), Ps. cepacia (104 strains) and indole positive Proteus (52 strains), only ceftazidime was better than imipenem. This study confirms published results that point to the impressive spectrum of activity offered by imipenem.