Antibacterial effect of meropenem and imipenem on Proteus mirabilis.
Phase-contrast microscopy, killing-curves and turbidimetric growth-curves were used in a comparative study of the antibacterial effects of a new carbapenem, meropenem (SM 7338) and imipenem on five strains of Proteus mirabilis. Despite the low MIC (0.2 mg/l) of imipenem for the five strains included in our study, the MBC remained relatively high (4.4 mg/l). During the first few hours of incubation, imipenem induced large lemon-shaped cells while the turbidity increased without substantial changes in culture viability. Later, most of the cell-wall deficient bacteria generated small spheroplasts until the antibiotic concentration exceeded 32 times the MIC. The MIC of meropenem was lower (0.03 mg/l) with an MBC (0.08 mg/l) very close to the MIC. Meropenem also induced large bodies but these cell-wall deficient bacteria did not generate small round bodies as observed with imipenem. In conclusion, imipenem produced in strains of Pr. mirabilis an amdinocillin-like change in cell morphology, responsible for the discrepancies observed between MIC and MBC. This effect was not observed with meropenem.
Yourassowsky
E
E
Department of Microbiology, Brugmann University Hospital, Brussels, Belgium.
Van der Linden
M P
MP
Crokaert
F
F
D015378:Imipenem / Q000494:pharmacology*; D000077731:Meropenem; D008858:Microscopy, Phase-Contrast; D009391:Nephelometry and Turbidimetry; D011513:Proteus mirabilis / Q000187:drug effects* / Q000254:growth & development; D013045:Species Specificity; D013845:Thienamycins / Q000494:pharmacology*
D013845:Thienamycins; D015378:Imipenem; D000077731:Meropenem