Evaluation of the in vitro bactericidal action of ciprofloxacin on cells of Escherichia coli in the logarithmic and stationary phases of growth

Abstract

Cells of Escherichia coli Neumann and E. coli KL16 were suspended in phosphate-buffered saline pH 7.4 and allowed to reach stationary growth conditions. Ciprofloxacin was added at different concentrations, and time-kill curves were constructed. It could be demonstrated that the number of viable cells was reduced quickly by several logs for E. coli Neumann, whereas a weak and slow killing effect was observed with E. coli KL16. When ciprofloxacin or norfloxacin was added to logarithmically growing cultures of E. coli Neumann or E. coli KL16, no principal differences in the killing rate for the two strains could be observed. Ciprofloxacin, however, was more bactericidal than norfloxacin. It was also demonstrated that the bactericidal action of ciprofloxacin on cells in the stationary growth phase was better at pH 7.4 than at pH 8.6. This dependence is different from that observed in MIC studies, in which the MIC were lower at pH 8.0 than at pH 7.2. It was also found that the bactericidal action of ciprofloxacin or norfloxacin on cells of E, coli Neumann in the stationary phase of growth could not be reduced by the addition of chloramphenicol, whereas under conditions of logarithmic growth the rapid killing effect of ciprofloxacin was reduced in the presence of chloramphenicol.Ciprofloxacin, a new quinolone derivative with a broad antibacterial spectrum (1,3,5,7,9), has become the subject of many in vitro studies. Ciprofloxacin has been characterized by its extraordinary killing effect on bacteria which are in a stationary phase of growth (10). Furthermore, it has been shown that the killing effect of ciprofloxacin or norfloxacip on actively growing cells is antagonized in the presence of chloramphenicol or rifampin (4,7,8). It was also reported that ciprofloxacin or ofloxacin must have an additional bactericidal action, which makes these two quinolones more independent from the antagonistic influence of chloramphenicol or rifampin (8). This paper reports results that concern the killing activity of ciprofloxacin on cells of different strains of Escherichia coli in the stationary phase of growth. The effect of pH and the influence of chloramphenicol under such conditions are also described and compared with those under normal growth conditions in broth. MATERIALS AND METfIODSOrganisms. The test strains used were isolates from the strain collection of the Institute of Chemotherapy, Bayer AG, Wuppertal, Federal Republic of Germany. E. coli KL16 (6) was originally obtained from J. T. Smith, School of Pharmacy, University of London, London, England.Antibacterial agents. The test substances were ciprofloxacin, norfloxacin (synthesized at Bayer AG), and chloramphenicol (Sigma Chemical Co.).MICs. MICs were measured by broth dilution techniques in microtiter trays (Greiner). Serial dilutions of 0.1 ml of the agents used were prepared in Isosensitest broth (Oxoid). To these were added 0.1 ml of a 1:1,000 dilution of an overnight culture of organisms, ending in a final inoculum of 1 x 105 to 2 x 105 CFU/ml. The microtiter pla...

Correlation between In Vivo and In Vitro Efficacy of Antimicrobial Agents against Foreign Body Infections

“…The low performance of ciprofloxacin on nongrowing bacteria was surprising since Zeiler and Grohe [20] showed a high efficacy of this antibiotic on Escherichiacoli in1he stationary phase. However, this quality of ciprofloxacin was later shown to be specific for some gram-negative rods [21,22]. The low antistaphylococcal activity of cyprofloxacin has also been confirmed byclinical data.…”

Isolation and characterization of an Escherichia coli strain exhibiting partial tolerance to quinolones

“…Also, a gyrA mutant strain of E. coli selected with nalidixic acid appears to be partially tolerant to quinolones (6,29). Second, bacterial killing by quinolones is blocked by chloramphenicol, rifampin, 2,4-dinitrophenol, or nutrient starvation (6,9,27,29,35), all of which inhibit protein synthesis, suggesting that synthesis of a protein may be required for quinolone killing. Such a requirement may explain the paradoxical effect of decreased killing of some bacterial strains by high concentrations of quinolone (7,10,27,29,32), because low drug concentrations inhibit DNA synthesis, whereas high concentrations inhibit RNA and protein synthesis as well (14,29,32).…”

“…There are, in addition, differences in bactericidal activity among quinolones. Analog 17606 is only bacteriostatic (29), and ofloxacin and ciprofloxacin, in comparison with norfloxacin and nalidixic acid, produce greater killing of E. coli in the presence of chloramphenicol (27) or nutrient starvation (35).…”

Identification of a pKM101 region which confers a slow growth rate and interferes with susceptibility to quinolone in Escherichia coli AB1157

“…4-Qs less effectively kill nondividing E. coli (20,26,27), Enterococcus faecalis (13), and staphylococci (14) than exponentially growing cells. Reduced killing of Pseudomonas aeruginosa in the stationary phase of growth by 4-Qs has also been reported elsewhere (6).…”