Influence of ciprofloxacin on the ultrastructure of gram-negative and gram-positive bacteria

Killing curves were performed in pooled active human serum using serum resistant Escherichia coli C14, Pseudomonas aeruginosa 220 and Staphylococcus aureus 25151 as test organisms. Ciprofloxacin (a quinoline-carboxylic acid derivative, Bay o 9867) was added in concentrations of 0.025-4.0 micrograms/ml. Samples were taken at different times to determine the number of viable bacteria and to prepare specimens for transmission electron microscopy. The following drug concentration-dependent results were obtained: In the early phase of the bactericidal process in Escherichia coli C14 distinct loosenings of the peripheral cytoplasm occurred. With Pseudomonas aeruginosa 220 osmiophilic condensations were detected in the less dense areas where the bacterial DNA may be located. At low concentrations, elongation of gram-negative bacterial cells was observed, whereas at higher concentrations rupture and lysis occurred. In staphylococci, severe disturbances of septum formation and surface deformations could be found; in the final stage proteolysis and empty envelopes were observed.