IN-VITRO ANTIBACTERIAL ACTIVITY AND BETA-LACTAMASE STABILITY OF SY5555, A NEW ORAL PENEM ANTIBIOTIC

The antibacterial activity of SY5555, a new oral penem antibiotic, was compared with those of cefaclor, cefixime, and cefteram. SY5555 was m ore active than the comparison agents against methicillin-susceptible Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus pneum oniae, Enterococcus faecalis, Citrobacter freundii, Enterobacter cloac ae, Morganella morganii, Acinetobacter calcoaceticus, Clostridium spp. , and Bacteroides fragilis. Against Providencia spp., Proteus spp., an d Haemophilus influenzae, SY5555 was less active than cefixime or ceft eram. SY5555 was inactive against methicillin-resistant S. aureus, Ent erococcus faecium, Serratia marcescens, Pseudomonas aeruginosa, and Xa nthomonas maltophilia, as were the comparison agents. The bactericidal activities of SY5555, cefixime, and cefteram were at or slightly grea ter than the MICs for clinical isolates of Escherichia coli and Klebsi ella pneumoniae. SY5555 was not hydrolyzed by various types of beta-la ctamases. However, SY5555 and the comparison agents were hydrolyzed by X. maltophilia (L-1) and P. aeruginosa/pMS354 beta-lactamases, two Bu sh group 3 beta-lactamases. SY5555 showed a high affinity, as did cefi xime and cefteram, for cephalosporinases from C. freundii GN7391 and E . cloacae GN7471 strains. These results suggest that SY5555 may be mor e specific than existing beta-lactam antibiotics.