In vitro activity of fluoroquinolones against gram-positive bacteria

PHARMACOKINETICS OF RECTALLY AND ORALLY ADMINISTERED LEVOFLOXACIN IN ASIAN ELEPHANTS (ELEPHAS MAXIMUS)

Appropriate and effective antibiotic use is a critical component of veterinary medicine, but there are variations across species regarding dosage and administration of these drugs. Oral or rectal routes of administration are typically used in elephants, but not all medications can achieve adequate concentrations rectally. The fluoroquinolone antimicrobials are used in elephants because of their favorable antimicrobial spectrum and pharmacokinetics compared with other oral agents. They are commonly used as part of multiple antibiotic regimens for the treatment of tuberculosis (Mycobacterium tuberculosis). The objective of this study was to determine the pharmacokinetic profile of levofloxacin after oral and rectal administration in Asian elephants (Elephas maximus). Dosages of 5 mg/kg orally and 15 mg/kg rectally were evaluated in 13 Asian elephants. Blood was collected at various time points from 0 to 72 h for pharmacokinetic analysis. Pharmacokinetic parameters were determined and reached concentrations above minimum inhibitory concentrations of various bacterial organisms via both routes. A pharmacokinetic-pharmacodynamic assessment was used to estimate appropriate minimal inhibitory concentrations for bacteria that could be potentially treated with this antimicrobial. Based on these findings, levofloxacin may be a consideration for administration orally (5 mg/kg) and rectally (15 mg/kg) in Asian elephants. Antimicrobial stewardship principles, culture and susceptibility of suspected pathogens, and blood level monitoring should be used to tailor administration of levofloxacin in this species.

Pharmacokinetics of levofloxacin following oral administration of a generic levofloxacin tablet and intravenous administration to dogs

OBJECTIVE

To determine the pharmacokinetics of levofloxacin following oral administration of a generic levofloxacin tablet and IV administration to dogs and whether the achieved plasma levofloxacin concentration would be sufficient to treat susceptible bacterial infections.

ANIMALS

6 healthy adult Beagles.

PROCEDURES

Levofloxacin was administered orally as a generic 250-mg tablet (mean dose, 23.7 mg/kg) or IV as a solution (15 mg/kg) to each dog in a crossover study design, with treatments separated by a minimum 2-day washout period. Blood samples were collected at various points for measurement of plasma levofloxacin concentration via high-pressure liquid chromatography. Pharmacokinetic analysis was performed with compartmental modeling.

RESULTS

After oral administration of the levofloxacin tablet, mean (coefficient of variation) peak plasma concentration was 15.5 μg/mL (23.8%), mean elimination half-life was 5.84 hours (20.0%), and mean bioavailability was 104% (29.0%). After IV administration, mean elimination half-life (coefficient of variation) was 6.23 hours (14.7%), systemic clearance was 145.0 mL/kg/h (22.2%), and volume of distribution was 1.19 L/kg (17.1%).

CONCLUSIONS AND CLINICAL RELEVANCE

In these dogs, levofloxacin was well absorbed when administered orally, and a dose of approximately 25 mg/kg was sufficient to reach pharmacokinetic-pharmacodynamic targets for treating infections with susceptible Enterobacteriaceae (ie, ≤ 0.5 μg/mL) or Pseudomonas aeruginosa (ie, ≤ 1 μg/mL) according to clinical breakpoints established by the Clinical and Laboratory Standards Institute.

Correlation between pH and molar iron/ligand ratio during ciprofloxacin degradation by photo-Fenton process: Identification of the main transformation products

Ciprofloxacin has been determined with high frequency in studies involving environmental waters matrixes. However, no study evaluating the correlation between the initial pH and molar iron/organic ligand ratio has been published. This paper describes the degradation of the antibiotic ciprofloxacin by the photo-Fenton process using different sources of iron (Fe²⁺, Fe³⁺ and Fe³⁺-citrate and Fe³⁺-oxalate, named FeCit and FeOx, respectively) and molar iron/organic ligand ratios at initial pH values of 2.5 and 6.5. The best results at initial pH 2.5 were achieved using FeCit and FeOx at molar iron/organic ligand ratios of 1:1 and 1:3 respectively, when the ciprofloxacin concentration reached values below the quantitation limit of the HPLC after 20 min of treatment. However, at initial pH 6.5, improvements in the results (15% for FeCit, and 46% for FeOx) were achieved by increasing the molar iron/organic ligand ratios to 1:4 (FeCit) and 1:9 (FeOx), respectively. Three transformation products, (C₁₇H₁₉FN₃O₄, m/z 348; C₁₇H₂₁FN₃O₅, m/z 366; and C₁₃H₁₂FN₂O₃, m/z 263) of ciprofloxacin degradation were identified, one of them not yet being reported in the literature (C₁₇H₂₁FN₃O₅, m/z 366). Their formation and degradation was monitored and the initial steps of their formation and degradation were proposed. The results show that the piperazine ring is more susceptible to hydroxyl radical attack than the quinolone ring, which persists in the intermediates identified. Therefore, this process can be a good alternative for the treatment of this type of pollutant at near-neutral conditions.

Medicinal potential of ciprofloxacin and its derivatives

Ciprofloxacin (CP) is a fluoroquinolone that is highly active against diverse microorganisms. At concentrations less than 1 µg/ml it is active against a diverse types of bacteria, including Staphylococcus aureus, Staphylococcus epidermidis, Bacillius subtilius, Escherichia coli and Mycobacterium tuberculosis. In addition, it has shown to be effective against other diseases such as malaria, cancer and AIDS. The extended antimicrobial activity, lack of plasmid-mediated resistance, large volume of distribution and minimal adverse effects of CP are therapeutically advantageous. In the pursuit of increasing their effectiveness against these diseases and prevent unwanted resistance, researchers have begun to synthesize a class of organic, inorganic and organometallic derivatives, which have displayed interesting activities. This review describes the development and recent advances on the evaluation of CP and its derivatives as a new class of drugs with potential for clinical development.

Resistance pattern of ciprofloxacin against different pathogens

OBJECTIVES

Ciprofloxacin is a broad-spectrum antibiotic widely prescribed in clinical and hospital settings. The emergence of antimicrobial resistance against effective antibiotics is a global issue. The objective of study is the surveillance of ciprofloxacin against common pathogens.

METHODS

To investigate the present status of antimicrobial resistance against ciprofloxacin, five hundred and twenty four clinical isolates of Escherichia coli (30%), Staphylococcus aureus (33%), Salmonella typhi (9%), Klebsiella pneumonia (14%) and Pseudomonas aeruginosa (14%) were collected during study from January, 2008 to February, 2009 from different pathological laboratories running in and out side hospitals located in Karachi, Pakistan. These pathogens were isolated from specimens of both in and out patients. The in-vitro antimicrobial activity of ciprofloxacin was carried out by Disc Diffusion Method (Kirby-Bauer test).

RESULTS

Showed that ciprofloxacin is 27.02%, 21.95%, 16.66%, 72.22% and 44.44% resistant to Escherichia coli, Staphylococcus aureus, Salmonella typhi, Klebsiella pneumonia and Pseudomonas aeruginosa respectively.

CONCLUSION

It is concluded that these clinical isolates have started developing resistance against ciprofloxacin due to its irrational and inappropriate use. Continuous surveillance is crucial to monitor the antimicrobial resistance among pathogens.

Piperine, a phytochemical potentiator of ciprofloxacin against Staphylococcus aureus

Piperine, a trans-trans isomer of 1-piperoyl-piperidine, in combination with ciprofloxacin markedly reduced the MICs and mutation prevention concentration of ciprofloxacin for Staphylococcus aureus, including methicillin-resistant S. aureus. The enhanced accumulation and decreased efflux of ethidium bromide in the wild-type and mutant (CIPr-1) strains in the presence of piperine suggest its involvement in the inhibition of bacterial efflux pumps.

Comparative activity of quinolones (ciprofloxacin, levofloxacin, moxifloxacin and garenoxacin) against extracellular and intracellular infection by Listeria monocytogenes and Staphylococcus aureus in J774 macrophages

OBJECTIVES

Quinolones accumulate in eukaryotic cells and show activity against a large array of intracellular organisms, but systematic studies aimed at examining their pharmacodynamic profile against intracellular bacteria are scarce. The present work aims at comparing intracellular-to-extracellular activities in this context.

METHODS

We assessed the activities of ciprofloxacin, levofloxacin, moxifloxacin and garenoxacin against the extracellular (broth) and intracellular (infected J774 macrophages) forms of Listeria monocytogenes (cytosolic infection) and Staphylococcus aureus (phagolysosomal infection) using a range of clinically meaningful extracellular concentrations (0.06-4 mg/L).

RESULTS

All four quinolones displayed concentration-dependent bactericidal activity against extracellular and intracellular L. monocytogenes and S. aureus for extracellular concentrations in the range 1-4-fold their MIC. Compared at equipotent extracellular concentrations, intracellular activities against L. monocytogenes were roughly equal to those that were extracellular, but were 50-100 times lower against S. aureus. Because quinolones accumulate in cells (ciprofloxacin, approximately 3 times; levofloxacin, approximately 5 times; garenoxacin, approximately 10 times, moxifloxacin, approximately 13 times), these data show that, intracellularly, quinolones are 5-10 times less potent against L. monocytogenes (P=0.065 [ANCOVA]), and at least 100 times less potent (P < 0.0001) against S. aureus. Because of their lower MICs and higher accumulation levels, garenoxacin and moxifloxacin were, however, more active than ciprofloxacin and levofloxacin when compared at similar extracellular concentrations.

CONCLUSIONS

Quinolone activity is reduced intracellulary. This suggests that either only a fraction of cell-associated quinolones exert an antibacterial effect, or that intracellular activity is defeated by the local environment, or that intracellular bacteria only poorly respond to the action of quinolones.

Phenotypic resistance of Staphylococcus aureus, selected Enterobacteriaceae, and Pseudomonas aeruginosa after single and multiple in vitro exposures to ciprofloxacin, levofloxacin, and trovafloxacin

The phenotypic resistance of selected organisms to ciprofloxacin, levofloxacin, and trovafloxacin was defined as a MIC of > or =4 microg/ml. The dynamics of resistance were studied after single and sequential drug exposures: clinical isolates of methicillin-susceptible and methicillin-resistant Staphylococcus aureus (MSSA and MRSA), Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae, Serratia marcescens, and Pseudomonas aeruginosa were utilized. After a single 48-h exposure of a large inoculum to four times the initial MIC for the organism, the frequency of selection of resistant mutants of MSSA was greater for trovafloxacin than levofloxacin (P = 0.008); for E. cloacae, the frequency was highest for ciprofloxacin and lowest for levofloxacin and trovafloxacin; for S. marcescens, the frequency was highest for trovafloxacin and lowest for ciprofloxacin (P = 0.003). The results of serial passage experiments were analyzed both by the Kaplan-Meier product-limited method as well as by analysis of variance of mean inhibitory values. By both methods, MSSA and MRSA expressed mutants resistant to ciprofloxacin after fewer passages than were required for either levofloxacin or trovafloxacin. For the aerobic gram-negative bacilli, two general patterns emerged. Mutants resistant to trovafloxacin appeared sooner and reached higher mean MICs than did mutants resistant to levofloxacin or ciprofloxacin. Mutants resistant to ciprofloxacin appeared later and reached mean MICs lower than the MICs of the other two drugs studied. Even though individual strain variation occurred, the mean MICs were reproduced when the serial passage experiment was repeated using an identical panel of E. coli isolates. In summary, the dynamic selection of fluoroquinolone-resistant bacteria can be demonstrated in experiments that employ serial passage of bacteria in vitro.

Moxifloxacin, a new antibiotic designed to treat community-acquired respiratory tract infections: a review of microbiologic and pharmacokinetic-pharmacodynamic characteristics

Moxifloxacin (BAY 12-8039) is a new 8-methoxy-fluoroquinolone antibacterial agent. The minimum inhibitory concentration for 90% of organisms (MIC90) is less than 0.25 mg/L for commonly isolated community-acquired respiratory tract pathogens including penicillin-susceptible and -resistant Streptococcus pneumoniae, Haemophilus sp, and Moraxella catarrhalis, and less than 1.0 mg/L for atypical pathogens such as Mycoplasma pneumoniae, Chlamydia pneumoniae, and Legionella pneumophila. To date, emergence of resistance to moxifloxacin has been uncommon, including selection of resistance under experimental conditions (methicillin-sensitive Staphylococcus aureus, S. pneumoniae). A postantibiotic effect is observed for both gram-positive and gram-negative bacteria. Human pharmacokinetics in healthy volunteers after a single 400-mg oral dose were mean maximum concentration (Cmax) 3.2 mg/L, area under the curve (AUC) 37 mg x hour/L, and terminal elimination half-life 12.0 hours. At steady-state, Cmax and AUC were approximately 4.5 mg/L and 48 mg x hour/L, respectively. Because of a balanced system of excretion, no dosage adjustments are required in patients with renal or hepatic impairment. Moxifloxacin also has excellent penetration into upper and lower respiratory tissues. Laboratory pharmacodynamic models suggest that MIC and AUC values predict therapeutic response. Notably, the drug can be administered once/day and is not associated with drug interactions secondary to altered hepatic metabolism. In addition, since its metabolism does not involve the cytochrome P450 system, many common drug interactions are absent. The agent is being investigated in clinical trials and shows promise as a safe and effective once-daily treatment of respiratory infections. In addition, its chemical structure and pharmacokinetic and pharmacodynamic properties indicate that it has enhanced potential to minimize emergence of bacterial resistance, which should make it an excellent choice for treating respiratory tract infections now and in the future.

Engineering the specificity of antibacterial fluoroquinolones: benzenesulfonamide modifications at C-7 of ciprofloxacin change its primary target in Streptococcus pneumoniae from topoisomerase IV to gyrase

We have examined the antipneumococcal mechanisms of a series of novel fluoroquinolones that are identical to ciprofloxacin except for the addition of a benzenesulfonylamido group to the C-7 piperazinyl ring. A number of these derivatives displayed enhanced activity against Streptococcus pneumoniae strain 7785, including compound NSFQ-105, bearing a 4-(4-aminophenylsulfonyl)-1-piperazinyl group at C-7, which exhibited an MIC of 0.06 to 0.125 microg/ml compared with a ciprofloxacin MIC of 1 microg/ml. Several complementary approaches established that unlike the case for ciprofloxacin (which targets topoisomerase IV), the increased potency of NSFQ-105 was associated with a target preference for gyrase: (i) parC mutants of strain 7785 that were resistant to ciprofloxacin remained susceptible to NSFQ-105, whereas by contrast, mutants bearing a quinolone resistance mutation in gyrA were four- to eightfold more resistant to NSFQ-105 (MIC of 0.5 microg/ml) but susceptible to ciprofloxacin; (ii) NSFQ-105 selected first-step gyrA mutants (MICs of 0.5 microg/ml) encoding Ser-81-to-Phe or -Tyr mutations, whereas ciprofloxacin selects parC mutants; and (iii) NSFQ-105 was at least eightfold more effective than ciprofloxacin at inhibiting DNA supercoiling by S. pneumoniae gyrase in vitro but was fourfold less active against topoisomerase IV. These data show unequivocally that the C-7 substituent determines not only the potency but also the target preference of fluoroquinolones. The importance of the C-7 substituent in drug-enzyme contacts demonstrated here supports one key postulate of the Shen model of quinolone action.

Activity of newer fluoroquinolones in vitro against gram-positive bacteria

Several newer fluoroquinolones, which have been recently introduced or are under investigation, display substantially greater potency against gram-positive organisms than the older generation agents of this class. Nevertheless, for problem organisms including methicillin-resistant strains of Staphylococcus aureus and many Enterococcus faecium, concentrations of newer antimicrobials required to inhibit 90% of organisms in the collections studied remain above those that are projected to be achievable with clinical use. Nevertheless, enhanced potency of several newer quinolones may result in a favourable pharmacodynamic profile leading to improved outcomes against gram-positive infections and possibly to the delayed or diminished emergence of resistance to these agents.

Development of in vitro susceptibility testing methods for gemifloxacin (formerly LB20304a or SB-265805), an investigational fluoronaphthyridone

Potent investigational fluoroquinolones require convenient, but accurate, diagnostic tests for initially applied clinical trials. For this purpose, gemifloxacin (formerly SB-265805, LB20304a) was tested by the reference dilution tests and standardized disk diffusion methods of the National Committee for Clinical Laboratory Standards (NCCLS) to establish interpretive criteria. For rapid-growing pathogens, 986 organisms were tested by broth microdilution MIC, and 5- and 10-microgram disk diffusion tests. Correlation (r) between 5- and 10-microgram disk zone diameters was 0.99 (y = -0.12 to 0.99x) and the preferred 5-microgram disk zone/MIC scattergram produced a regression of y = 14.8 to 0.41x (r = 0.93). At potential pharmacodynamics (Cmax = 1.3 micrograms/mL for 320 mg dose) validated breakpoints of < or = 0.5 microgram/mL for susceptible and > or = 2 micrograms/mL for resistant, correlate zones of > or = 17 mm and < or = 13 mm produced rare serious interpretive errors (0.1%) and 96.7% absolute categorical agreement. For 304 Streptococcus pneumoniae and 305 strains of other streptococci, the same breakpoints produced 100 and 99.1% categorical accuracy even when testing levofloxacin-resistant (MIC, > or = 4 micrograms/mL) strains. Interpretive breakpoints were proposed for Hemophilus influenzae (300 strains tested), with complete correlation between tests. Etest (AB BIODISK, Solna, Sweden) was compared in all experiments with the fastidious species and showed a trend toward higher values (twofold). Gemifloxacin in vitro susceptibility test methods seem to be accurate and with very acceptable intermethod agreement, supported by previously reported functional quality control guidelines.

Multiple novel inhibitors of the NorA multidrug transporter of Staphylococcus aureus

The multidrug transporter NorA contributes to the resistance of Staphylococcus aureus to fluoroquinolone antibiotics by promoting their active extrusion from the cell. Previous studies with the alkaloid reserpine, the first identified inhibitor of NorA, indicate that the combination of a chemical NorA inhibitor with a fluoroquinolone could improve the efficacy of this class of antibiotics. Since reserpine is toxic to humans at the concentrations required to inhibit NorA, we sought to identify new inhibitors of NorA that may be used in a clinical setting. Screening of a chemical library yielded a number of structurally diverse inhibitors of NorA that were more potent than reserpine. The new inhibitors act in a synergistic manner with the most widely used fluoroquinolone, ciprofloxacin, by substantially increasing its activity against both NorA-overexpressing and wild-type S. aureus isolates. Furthermore, the inhibitors dramatically suppress the emergence of ciprofloxacin-resistant S. aureus upon in vitro selection with this drug. Some of these new inhibitors, or their derivatives, may prove useful for augmentation of the antibacterial activities of fluoroquinolones in the clinical setting.

Antimicrobial resistance in Staphylococcus aureus

Recognized since 1883 as a common cause of infection, Staphylococcus aureus' preantimicrobial-era bacteremia mortality rate was 82%. The mortality of that era threatens to return as evidence of growing vancomycin resistance undermines the utility of vancomycin therapy. Successful treatment of S. aureus infections requires knowledge of its antimicrobial resistance capacity.

Comparative efficacies of levofloxacin and ciprofloxacin against Streptococcus pneumoniae in a mouse model of experimental septicaemia

The in vivo efficacies of levofloxacin and ciprofloxacin were compared against three clinical isolates of Streptococcus pneumoniae, using a mouse protection model. Two strains (SP 22 and SP 28) were penicillin-sensitive while one strain (SP 46) was penicillin-resistant. Each strain had identical susceptibility to both drugs. Using mice with renal impairment induced by uranyl nitrate injection, the elimination half-life of each antibiotic was prolonged to approximate human pharmacokinetic profiles of the drugs. The dosing regimen of each drug that yielded serum levels in mice which mimic human therapeutic concentrations of the drugs, were designed. One hour after intraperitoneal inoculation with minimum lethal dose of each strain, either levofloxacin at a dosing regimen of 10.6 mg/kg every 8 h or ciprofloxacin at 9.5 mg/kg every 8 h was subcutaneously administered for a total of six or 15 doses. In treatment, monitored daily for 5-8 days, levofloxacin resulted in higher survival compared with ciprofloxacin for the three strains. For example, percent survival following levofloxacin treatment recorded at day 4 postinfection with SP 22, SP 28 and SP 46 were 41, 90 and 30%, respectively, while the corresponding values after ciprofloxacin treatment were 27, 75 and 16%, respectively. However, statistical analysis did not reveal a significant difference (p > 0.05). The lack of significant difference observed in the efficacies of both drugs reflected the comparability of their 24-h AUC/MIC ratios. It is suggested that, with some strains of S. pneumoniae, the efficacy of levofloxacin may be equivalent to that of ciprofloxacin in the treatment of systemic pneumococcal infections caused by susceptible strains of the organism.

Lactic acid polymers as biodegradable carriers of fluoroquinolones: an in vitro study

A biodegradable polymer of DL-dilactide that facilitates release of ciprofloxacin or pefloxacin at levels exceeding MICs for the causative microorganisms of chronic osteomyelitis is described. Duration and peak of release were found to depend on the molecular weight of the polymer. Its characteristics make it promising for treating chronic bone infections.

Clinical applications of quinolones

The quinolone antimicrobials are the class of inhibitors of bacterial topoisomerases that has been developed most fully for clinical use in human medicine. Initial members of the class had their greatest potency against Gram-negative bacteria, but newly developed members have exhibited increased potency against Gram-positive bacteria and soon agents will be available with additional activity against anaerobic bacteria, providing a broad spectrum of potency. After nalidixic acid, the earliest member of the class which was used for treatment of urinary tract infections, the later fluoroquinolone congeners have had sufficient potency, absorption, and distribution into tissue for additional uses in treatment of sexually transmitted diseases, infections of the gastrointestinal tract, respiratory tract, skin, and bones and joints. Tolerability of these agents in usual doses has been good. Acquired bacterial resistance resulting from clinical uses has occurred in particular among staphylococci and Pseudomonas aeruginosa. Intense drug use and ability of resistant pathogens to spread have also contributed to development of resistance in initially more susceptible pathogens such as Escherichia coli and Neisseria gonorrhoeae in certain settings. Preservation of the considerable clinical utility of the quinolone class for the long term will be affected by the extent to which their use is judicious.

In vitro activity of quinupristin/dalfopristin and newer quinolones combined with gentamicin against resistant isolates of Enterococcus faecalis and Enterococcus faecium

In a study designed to obtain data on compounds active against enterococci, the minimum inhibitory concentrations (MICs) of quinupristin/dalfopristin (RP 59500) and the novel quinolones DU-6859a, trovafloxacin, levofloxacin, and sparfloxacin were determined for 122 Enterococcus faecalis and seven Enterococcus faecium isolates. In addition, 15 Enterococcus faecalis isolates resistant to gentamicin, DU-6859a, and trovafloxacin were exposed over time to combinations of DU-6859a plus gentamicin and trovafloxacin plus gentamicin. DU-6859a and trovafloxacin were found to be the most active compounds against Enterococcus faecalis and DU-6859a and RP 59500 against Enterococcus faecium. Synergy between either DU-6859a or trovafloxacin and gentamicin was observed with 27 to 35% of the isolates. It is concluded that DU-6859a and trovafloxacin are very potent against enterococci, especially when combined with gentamicin.

In vitro activity of BAY 12-8039, a new fluoroquinolone, against species representative of respiratory tract pathogens

The in vitro antibacterial activity of BAY 12-8039, a novel 8-methoxy-quinolone, was compared with those of other quinolones, amoxicillin/clavulanate, cefuroxime and erythromycin against species commonly implicated in respiratory tract infections as well as viridans group streptococci. The new compound was highly active against methicillin-susceptible staphylococci (MIC90 0.125 microgram/ml), penicillin-susceptible and penicillin-resistant pneumococci (MIC90 0.5 and MIC50 0.25 microgram/ml, respectively), penicillin-susceptible and penicillin-resistant viridans group streptococci (MIC90 0.5 and 0.25 microgram/ml, respectively), group A streptococci (MIC90 0.25 microgram/ml), M. catarrhalis (MIC90 0.125 microgram/ml) and H. influenzae (MIC90 0.063 microgram/ml), irrespective of beta-lactamase production. It was, however, less active against methicillin-resistant staphylococci (MIC50 and MIC90, 2 and 4 micrograms/ml, respectively). The new compound demonstrated bactericidal activity at concentrations 2, 4, 8 times the MIC against representative isolates of the above collection. At a concentration of eight times the MIC, the frequency of spontaneous resistance ranged from 2.5 x 10(-7) to < 4 x 10(-8). These results suggested that BAY 12-8039 would be a promising agent for the eradication of respiratory tract pathogens and that clinical trials assessing its efficacy for the management of infections caused by these organisms are warranted.

In vitro extracellular and intracellular activity of two newer and two earlier fluoroquinolones against Listeria monocytogenes

Two new fluoroquinolones (trovafloxacin and sparfloxacin) with enhanced activity against gram-positive pathogens and two earlier compounds (ciprofloxacin and ofloxacin) were tested for their in vitro inhibitory and bactericidal activity against 80 strains of Listeria monocytogenes. All strains were uniformly highly susceptible to trovafloxacin, the MIC90 being 0.25 mg/l. Resistance to sparfloxacin was not detected, however the MIC90 of sparfloxacin was eight times that of trovafloxacin. A few strains were resistant to ciprofloxacin and ofloxacin (MIC90 4 mg/l for both drugs). MBCs usually exceeded MICs by 2 to 4 times. The MBC90 of trovafloxacin (1 mg/l) was lower than that of the other three drugs (8 mg/l). After checking their ability to enter and grow within human enterocyte-like Caco-2 cells, four strains were used to study the intracellular activity and eradicating power of the four quinolones. Trovafloxacin was more active than sparfloxacin and the earlier fluoroquinolones in terms of both intracellular killing and inhibition of a cytopathogenic effect. The uniform high-level activity of trovafloxacin against Listeria monocytogenes isolates in conventional in vitro assays and its extracellular and intracellular killing of invasive strains suggest that this and maybe other new fluoroquinolones should be further investigated as possible anti-listerial agents.

Targeting of DNA gyrase in Streptococcus pneumoniae by sparfloxacin: selective targeting of gyrase or topoisomerase IV by quinolones

gyrA and parC mutations have been identified inn Streptococcus pneumoniae mutants stepwise selected for resistance to sparfloxacin, an antipneumococcal fluoroquinolone. GyrA mutations (at the position equivalent to resistance hot spot Ser-83 in Escherichia coli GyrA) were found in all 17 first-step mutants examined and preceded DNA topoisomerase IV parC mutations (at Ser-79 or Glu-83), which appeared only in second-step mutants. The targeting of gyrase by sparfloxacin in S. pneumoniae but of topoisomerase IV by ciprofloxacin indicates that target preference can be altered by changes in quinolone structure.

Involvement of topoisomerase IV and DNA gyrase as ciprofloxacin targets in Streptococcus pneumoniae

Ciprofloxacin-resistant mutants of Streptococcus pneumoniae 7785 were generated by stepwise selection at increasing drug concentrations. Sequence analysis of PCR products from the strains was used to examine the quinolone resistance-determining regions of the GyrA and GyrB proteins of DNA gyrase and the analogous regions of the ParC and ParE subunits of DNA topoisomerase IV. First-step mutants exhibiting low-level resistance had no detectable changes in their topoisomerase quinolone resistance-determining regions, suggesting altered permeation or another novel resistance mechanism. Nine of 10 second-step mutants exhibited an alteration in ParC at Ser-79 to Tyr or Phe or at Ala-84 to Thr. Third- and fourth-step mutants displaying high-level ciprofloxacin resistance were found to have, in addition to the ParC alteration, a change in GyrA at residues equivalent to Escherichia coli GyrA resistance hot spots Ser-83 and Asp-87 or in GyrB at Asp-435 to Asn, equivalent to E. coli Asp-426, part of a highly conserved EGDSA motif in GyrB. No ParE changes were observed. Complementary analysis of two S. pneumoniae clinical isolates displaying low-level resistance to ciprofloxacin revealed a ParC change at Ser-79 to Phe or Arg-95 to Cys but no changes in GyrA, GyrB, or ParE. A highly resistant isolate, in addition to a ParC mutation, had a GyrA alteration at the residue equivalent to E. coli Asp-87. Thus, in both laboratory strains and clinical isolates, ParC mutations preceded those in GyrA, suggesting that topoisomerase IV is a primary topoisomerase target and gyrase is a secondary target for ciprofloxacin in S. pneumoniae.

Cloning and characterization of the parC and parE genes of Streptococcus pneumoniae encoding DNA topoisomerase IV: role in fluoroquinolone resistance

DNA topoisomerase IV mediates chromosome segregation and is a potential target for antibacterial agents including new antipneumococcal fluoroquinolones. We have used hybridization to a Staphylococcus aureus gyrB probe in concert with chromosome walking to isolate the Streptococcus pneumoniae parE-parC locus, lying downstream of a putative new insertion sequence and encoding 647-residue ParE and 823-residue ParC subunits of DNA topoisomerase IV. These proteins exhibited greatest homology respectively to the GrlB (ParE) and GrlA (ParC) subunits of S. aureus DNA topoisomerase IV. When combined, whole-cell extracts of Escherichia coli strains expressing S. pneumoniae ParC or ParE proteins reconstituted a salt-insensitive ATP-dependent decatenase activity characteristic of DNA topoisomerase IV. A second gyrB homolog isolated from S. pneumoniae encoded a 648-residue protein which we identified as GyrB through its close homology both to counterparts in S. aureus and Bacillus subtilis and to the product of the S. pneumoniae nov-1 gene that confers novobiocin resistance. gyrB was not closely linked to gyrA. To examine the role of DNA topoisomerase IV in fluoroquinolone action and resistance in S. pneumoniae, we isolated mutant strains stepwise selected for resistance to increasing concentrations of ciprofloxacin. We analysed four low-level resistant mutants and showed that Ser-79 of ParC, equivalent to resistance hotspots Ser-80 of GrlA and Ser-84 of GyrA in S. aureus, was in each case substituted with Tyr. These results suggest that DNA topoisomerase IV is an important target for fluoroquinolones in S. pneumoniae and establish this organism as a useful gram-positive system for resistance studies.

Ciprofloxacin. An updated review of its pharmacology, therapeutic efficacy and tolerability

Ciprofloxacin is a broad spectrum fluoroquinolone antibacterial agent. Since its introduction in the 1980s, most Gram-negative bacteria have remained highly susceptible to this agent in vitro; Gram-positive bacteria are generally susceptible or moderately susceptible. Ciprofloxacin attains therapeutic concentrations in most tissues and body fluids. The results of clinical trials with ciprofloxacin have confirmed its clinical efficacy and low potential for adverse effects. Ciprofloxacin is effective in the treatment of a wide variety of infections, particularly those caused by Gram-negative pathogens. These include complicated urinary tract infections, sexually transmitted diseases (gonorrhoea and chancroid), skin and bone infections, gastrointestinal infections caused by multiresistant organisms, lower respiratory tract infections (including those in patients with cystic fibrosis), febrile neutropenia (combined with an agent which possesses good activity against Gram-positive bacteria), intra-abdominal infections (combined with an antianaerobic agent) and malignant external otitis. Ciprofloxacin should not be considered a first-line empirical therapy for respiratory tract infections if penicillin-susceptible Streptococcus pneumoniae is the primary pathogen; however, it is an appropriate treatment option in patients with mixed infections (where S. pneumoniae may or may not be present) or in patients with predisposing factors for Gram-negative infections. Clinically important drug interactions involving ciprofloxacin are well documented and avoidable with conscientious prescribing. Recommended dosage adjustments in patients with impaired renal function vary between countries; major adjustments are not required until the estimated creatinine clearance is < 30 ml/min/1.73m2 (or when the serum creatinine level is > or = 2 mg/dl). Ciprofloxacin is one of the few broad spectrum antibacterials available in both intravenous and oral formulations. In this respect, it offers the potential for cost savings with sequential intravenous and oral therapy in appropriately selected patients and may allow early discharge from hospital in some instances. In conclusion, ciprofloxacin has retained its excellent activity against most Gram-negative bacteria, and fulfilled its potential as an important antibacterial drug in the treatment of a wide range of infections. Rational prescribing will help to ensure the continued clinical usefulness of this valuable antimicrobial drug.