Action of quinolones on gene expression and bacterial membranes

Inhibitory effects of the quinolone antibiotics trovafloxacin, ciprofloxacin, and levofloxacin on osteoblastic cells in vitro

We studied the inhibitory effects of the fluoroquinolones levofloxacin, ciprofloxacin, and trovafloxacin on growth and extracellular matrix mineralization in MC3T3-E1 osteoblast-like cell cultures. Levofloxacin had the least inhibitory effect on cell growth, with a 50% inhibitory concentration of approximately 80 microg/ml at 48 and 72 hours. Ciprofloxacin had an intermediate degree of inhibition, with a 50% inhibitory concentration of 40 microg/ml at 48 and 72 hours. Trovafloxacin exerted a profound inhibitory effect on cell growth, with a 50% inhibitory concentration of 0.5 microg/ml, lower than clinically achievable serum levels. The decreased cell counts with up to 2.5 microg/ml of trovafloxacin and with up to 40 microg/ml of ciprofloxacin were not associated with decreased rates of 5-bromo-2'-deoxyuridine incorporation per cell. Alatrovafloxacin, the L-alanyl-l-alanine prodrug of trovafloxacin, exerted effects on proliferation and 5-bromo-2'-deoxyuridine incorporation similar to those of the parent compound. The quinolones evaluated also inhibited extracellular matrix mineralization by MC3T3-E1 cells. Treatment of confluent cultures with trovafloxacin, ciprofloxacin, or levofloxacin resulted in strong inhibition of calcium deposition, as determined on day 14 by alizarin red staining and biochemical analysis. The effect was apparent with 2.5-5 microg/ml of each of the three antibiotics tested and progressively increased to more than a 90% decline in the calcium/protein ratio with 20-40 microg/ml antibiotic concentration. Further in vivo studies are advocated to evaluate the relevance of the in vitro cytotoxicity reported here to bone healing in orthopaedic patients.

Precipitating Pseudomonas aeruginosa antibodies and antimicrobial therapy in cystic fibrosis patients

Forty patients with cystic fibrosis were studied bacteriologically and serologically. Precipitating Pseudomonas aeruginosa antibodies were monitored by crossed-immunoelectrophoresis (CIE) in order to evaluate the possibility of preventing chronic colonization by Pseudomonas aeruginosa by cycles of antimicrobial therapy. Sputum or pharyngeal aspirate and serum samples from all patients were analyzed by means of spread on selective media and CIE, respectively. Significant differences in the number of precipitins were obtained: noncolonized and intermittently colonized patients had no precipitins, whereas the number of precipitins in the chronically colonized patients varied from 11 to 44. An increase in the number of precipitins could be a good marker for initiation of therapy with antimicrobial agents that are either active against Pseudomonas aeruginosa or able to inhibit the release of virulence factors.

Effects of MICs and sub-MICs of antibiotics on production of capsular polysaccharide of Klebsiella pneumoniae

In the present study, we examined whether MICs and sub-MICs of antimicrobial agents belonging to two different classes, ciprofloxacin and ceftazidime, were able to influence the production and release of cell-associated and soluble (extracellular) capsular polysaccharide (CPS), respectively, in a heavily encapsulated strain of Klebsiella pneumoniae (B5055). Using a CPS-specific enzyme-linked immunosorbent assay, we found that the amount of cell-associated CPS increased in a dose-dependent manner by more than 10-fold under the influence of the MIC of ceftazidime and by more than 100-fold under the influence of the MIC of ciprofloxacin. The largest amounts of CPS were measured by using the MIC of either antibiotic substance. Electron microscopic studies showed that the diameter of the capsule was significantly increased compared with the diameter for untreated controls. Thus, both antimicrobial agents genuinely stimulated CPS production.

Effect of low concentrations of quinolone antibiotics on bacterial virulence mechanisms

Recent studies have shown that exposure to quinolone antibiotics at or below the minimal inhibitory concentration (MIC) results in reduction in the level of production or total elimination of certain factors that contribute to the virulence of bacteria. This study was designed to determine whether low concentrations of enoxacin, lomefloxacin, and ciprofloxacin altered the morphology or affected the production of various virulence factors in several different genera of bacteria. The factors studied were nuclease and a toxin production in Staphylococcus aureus, cell size, pili and fimbriae production, and adherence of Salmonella typhimurium, Escherichia coli, and Pseudomonas aeruginosa to urinary epithelial cells and dog bladder cells, and the major virulence factor in Yersinia pseudotuberculosis. In addition, the effect of growth in low levels of enoxacin on phagocytosis of S. aureus by human polymorphonuclear leukocytes (PMNs) was studied. Following exposure to subinhibitory levels of quinolones tested, significant reduction in activity or complete elimination was seen in all of those factors measured. Minor differences were noted in the efficiency of elimination among the three quinolones tested. At as low as 1/8 MIC there is significant enhancement of phagocytic activity by human PMNs. These data suggest that exposure to quinolones at concentrations below the MIC disrupts the regulatory mechanisms that control cell morphology, adherence as well as exocellular enzyme production and plasmid maintenance. This may mean that certain virulent organisms that survive exposure to quinolone antibiotics may be less likely to produce or maintain the disease state in susceptible hosts.

The susceptibility of conjugative resistance transfer in gram-negative bacteria to physicochemical and biochemical agents

Over thirty years of studies have established that conjugative transfer of plasmid-encoded resistance to drugs and heavy metals can take place at high frequency between various organisms under laboratory conditions. The detected transfer frequencies in soil, in aquatic environments, and in the urogenital and respiratory tracts of healthy animals and man have generally been low. However, the conversion of bacteria from susceptible to resistant to antibiotics has been observed often during antimicrobial therapy. This has formed a challenge for the antibacterial treatment of pathogenic bacteria and called for the evaluation of the extent of conjugative transfer in various environments. Several biochemical and physicochemical factors inhibit conjugation, show preferential toxicity against plasmid-bearing cells, or stimulate plasmid curing. These factors include various agents such as detergents, anesthetics, mutagens and antibiotics which affect membrane potential, membrane permeability, protein synthesis and the processing of DNA. The application of the data on these agents, summarized in this review, might be helpful in preventing drug multi-resistance from spreading. Also these data might be valuable in studies which use conjugation as a tool or which treat the molecular mechanisms involved in conjugation.

Correlation between pharmacokinetics, pharmacodynamics and efficacy of antibacterial agents in animal models

On the basis of a review of published literature it is demonstrated that pharmacokinetic parameters of antibacterial agents correlate well with therapeutic efficacy in animal models, provided pharmacodynamic parameters are taken into account. The time that serum levels exceed the MIC is the most significant parameter determining efficacy of beta-lactams, whereas the efficacy of aminoglycosides is dependent on serum concentrations and the area under the curve. The efficacy of quinolones tends to be correlated to the doses administered or drug levels achieved. However, specific pharmacodynamic properties contribute significantly to the therapeutic efficacy of a few quinolones only whereas other quinolones lack these specific pharmacodynamic attributes. Thus, the correlation of pharmacokinetic parameters with therapeutic efficacy provides important basic concepts for the design of preclinical and clinical studies in the course of which additional pharmacodynamic properties will become apparent.