Activity of imipenem on aerobic bacteria

Imipenem is a new carbapenem antibiotic with a broad spectrum of activity on Gram-positive and Gram-negative bacteria. It is a potent inhibitor of plasmid- and chromosomally-mediated beta-lactamases. The purpose of this study was to evaluate the in vitro activity of imipenem on clinical isolates classified according to their susceptibility to beta-lactam antibiotics. On penicillin G-susceptible bacteria, imipenem is comparable to penicillin. On streptococci, pneumococci, Staphylococcus aureus and Listeria the MICs were 0.02 to 0.06 mg/l. On gonococci, MICs were 0.04 to 0.25 mg/l. Gram-negative bacteria susceptible to beta-lactam antibiotics or naturally resistant to certain of them (e.g. Klebsiella pneumoniae resistant to ampicillin and carbenicillin) were highly susceptible to imipenem with MICs from 0.06 to 0.5 mg/l. It was slightly less active on Haemophilus influenzae, compared to ampicillin. On beta-lactam-resistant bacteria, imipenem maintained a remarkable activity. For penicillin-resistant pneumococci (MIC 16 mg/l) the imipenem MIC was 1 mg/l. Imipenem was equally effective on beta-lactamase-producing and non-producing Haemophilus influenzae and gonococci. Among 12 Nocardia asteroides tested, 11 had MIC less than 1 mg/l. When tested at 30 degrees, the MIC of imipenem for oxacillin-resistant Staphylococcus aureus ranged from 8 to 64 mg/l in contrast to 0.03 to 0.06 mg/l for oxacillin-sensitive isolates. Eighteen strains of enterococci (17 faecium, 2 faecalis) resistant to ampicillin (MIC 128 mg/l) were more resistant to imipenem (MIC 16 to 256 mg/l). Imipenem was very active on beta-lactam-resistant Gram-negative bacteria, including multiply-resistant Salmonella typhi., with MICs in a range from 0.06 to 4 mg/l).(ABSTRACT TRUNCATED AT 250 WORDS)