[Comparison of the in vitro and in vivo effects of meropenem and ciprofloxacin on the morphology of Escherichia coli and Staphylococcus aureus]. / Comparación del efecto in vitro e in vivo de meropenem y ciprofloxacino sobre la morfología de Escherichia coli y Staphylococcus aureus.

In the treatment of infections, subinhibitory concentrations are commonly present and induce a wide range of effects. Some of these effects have been reported to improve the efficacy of these compounds. One of these effects, the change of the bacterial morphology, was assayed in this study both in vitro and in vivo, and their results were compared. Two antimicrobial agents (meropenem and ciprofloxacin) and two standard Gram-positive and Gram-negative strains (S. aureus y E. coli) were used. The methods employed included the in vitro exposure of microorganisms on Mueller-Hinton agar plates, and the in vivo intraperitoneal infection model in mice. With all the sub-MICs tested, the in vitro results showed that meropenem induced the formation of round cells (spheroplasts) on E. coli, while ciprofloxacin produced filaments. With S. aureus, the two antimicrobial agents induced the formation of cellular aggregates (clusters) with a diameter greater than 1 mm. The in vivo results confirmed those observed in vitro, but to a lesser extent. These results agree with those expected in relation with the mechanisms of action of each drug, and could be important in order to prevent a lost in efficacy when the levels of the drug are below the MIC.