Mechanisms of action of antimicrobials: focus on fluoroquinolones

Design, synthesis and activity against Toxoplasma gondii, Plasmodium spp., and Mycobacterium tuberculosis of new 6-fluoroquinolones

This paper reports on the rational design of a series of new 6-fluoroquinolones by QSAR analysis against Toxoplasma (T.) gondii, their synthesis, their biological evaluation against T. gondii and Plasmodium (P.) spp., and their effect on Mycobacterium (M.) tuberculosis DNA gyrase and growth inhibition. Of the 12 computer-designed 8-ethyl(or methoxy)- and 5-ethyl-8-methoxy-6-fluoroquinolones predicted to be active against T. gondii, we succeeded in the synthesis of four 6-fluoro-8-methoxy-quinolones. The four 6-fluoro-8-methoxy-quinolones are active on T. gondii but only one is as active as predicted. One of these four compounds appears to be an antiparasitical drug of great potential with inhibitory activities comparable to or higher than that of trovafloxacin, gatifloxacin, and moxifloxacin. They also inhibit DNA supercoiling by M. tuberculosis gyrase with an efficiency comparable to that of the most active quinolones but are poor inhibitors of M. tuberculosis growth.

Synthesis, antibacterial and antitubercular activities of some 7-[4-(5-amino-[1,3,4]thiadiazole-2-sulfonyl)-piperazin-1-yl] fluoroquinolonic derivatives

In the present study, a series of 7-[4-(5-amino-1,3,4 thiadiazole-2-sulfonyl)]-1-piperazinyl fluoroquinolonic derivatives VIIa-d were synthesized in good yields and characterized by IR, (1)H-NMR, (13)C-NMR, FAB Mass spectral and elemental analyses. The compounds were evaluated for their preliminary in vitro antibacterial activity against some Gram-positive and Gram-negative bacteria and selected compounds VIIa, b were screened for antitubercular activity against Mycobacterium tuberculosis H(37)Rv strain by broth dilution assay method. The antibacterial data of the tested N-sulfonylfluoroquinolones VIIa-d indicated that all the synthesized compounds showed better activity against Gram-positive bacteria S. aureus, E. faecelis, Bacillus sp. (MIC=1-5 microg ml(-1), respectively) compared to reference drugs. The MIC values of tested derivatives connotes that the sparfloxacin and gatifloxacin derivatives VIIc, d were most active against the tested Gram-positive bacterial strains (MIC=1-5 microg ml(-1)). All the tested compounds VIIa-d showed poor activity against the Gram-negative bacteria. The in vitro antitubercular activity reports of selected compounds VIIa, b against M. tuberculosis strain H(37)Rv showed moderate activity at MIC of 10 microg ml(-1).

Levofloxacin use in the elderly: focus on pneumonia

Levofloxacin is a broad-spectrum, rapid-acting bactericidal agent that exhibits concentration-dependent killing activity as well as a postantibiotic effect. Its activity includes enteric Gram-negative bacilli, Acinetobacter spp., Pseudomonas aeruginosa, methicillin-susceptible Staphylococcus aureus and most species of streptococci, including Streptococcus pneumoniae. With increasing age, there is a natural decline in renal function by approximately 1 ml/min/year after the age of 30 years, or an average decrease in creatinine clearance of 40% by the age of 80 years. This decline in renal function can have a significant impact on antibiotics that are predominantly eliminated from the body via the kidneys, such as levofloxacin. The favorable pharmacodynamic, safety and efficacy profiles, in addition to in vitro activity versus the usual respiratory pathogens, make levofloxacin among the first-line agents for the management of pneumonia, and an option for other respiratory bacterial infections in which more resistant organisms are a consideration, such as in the elderly population.

Synthesis and antibacterial activity of N-[2-[5-(methylthio)thiophen-2-yl]-2-oxoethyl] and N-[2-[5-(methylthio)thiophen-2-yl]-2-(oxyimino)ethyl]piperazinylquinolone derivatives

A number of N-substituted piperazinylquinolone derivatives were synthesized and evaluated for antibacterial activity against Gram-positive and Gram-negative bacteria. Preliminary results indicated that most compounds tested in this study demonstrated comparable or better activity against Staphylococcus aureus and Staphylococcus epidermidis than their parent piperazinylquinolones as reference drugs. Among these derivatives, ciprofloxacin derivative 5a, containing N-[2-[5-(methylthio)thiophen-2-yl]-2-oxoethyl] residue, showed significant improvement of potency against staphylococci, maintaining Gram-negative coverage.

Design, synthesis, and evaluation of novel 6-chloro-/fluorochromone derivatives as potential topoisomerase inhibitor anticancer agents

6-Chloro-2-pyrrolidino-/morpholino-/piperidino-/N-methylpiperazino-3-formyl-chromones (13-16) and 6-fluoro-2,7-di-morpholino-/piperidino-/N-methylpiperazino-3-formylchromones (17-19) have been synthesized as potential topoisomerase inhibitor anticancer agents, and evaluated, in vitro, against Ehrlich ascites carcinoma (EAC) cells, and also in vivo on EAC bearing mice. The compounds displayed promising anticancer activity under these test systems and shall serve as useful 'leads' for further design.

Evaluation of antimycobacterial and DNA gyrase inhibition of fluoroquinolone derivatives

The antimycobacterial activity (both in vitro and in vivo) and DNA gyrase inhibition of newly synthesized fluoroquinolone derivatives were tested against Mycobacterium tuberculosis H(37)Rv and Mycobacterium smegmatis, respectively. Among the synthesized compounds, compound F11 was found to exhibit the most potent in vitro antimycobacterial activity with a MIC value of 0.78 microg/ml, and a selectivity index of more than 80 while not being cytotoxic to the Vero cell line up to 62.5 microg/ml. When evaluated for in vivo antimycobacterial activity, compound F11 demonstrated a paramount decrease of bacterial load in lung and spleen tissues compared to the control and better than the standard drug ciprofloxacin.

Fate and effects of enrofloxacin in aquatic systems under different light conditions

The fate and effects of fluoroquinolone antibacterials (FQ) in the environment is of significance because of apparent increased FQ resistance in environmental and clinical organisms. Here we simultaneously assessed the fate and effects of enrofloxacin (enro), an FQ often used in agriculture, on the chemistry and in situ microbial communities in receiving waters. We added enro to 25 microg/L in nine outdoor mesocosms maintained under three light conditions (in triplicate): full sunlight typical of the upper epilimnion (100% full-light exposure, FLE), partial shading typical of the lower epilimnion (28% FLE), and near-complete shading typical of the hypolimnion (0.5% FLE). Enro disappearance and ciprofloxacin (cipro) formation were monitored over time using LC/MS, and water chemistry and ambient microbial communities (using denaturing gradient gel electrophoresis; DGGE) were characterized. Enro half-lives were 0.8, 3.7, and 72 days for the 100%, 28%, and 0.5% FLE treatments, respectively, creating three distinct FQ exposure scenarios. Although FQ exposures ranged from approximately 6 microg/L for 24 h to approximately 21 microg/L for 30 days, no statistically significant exposure effects were noted in water quality or microbial communities (as indicated by whole-community 16S rDNA DGGE analysis and specific amplification of the QRDR region of gyrase A). Small changes in water chemistry were noted over time; however, changes could not be specifically attributed to FQs. In general, enro addition had minimal effect on water column conditions at the levels and durations used here; however, further investigation is needed to assess effects in aquatic sediments.

Squeezing the antibiotic balloon: the impact of antimicrobial classes on emerging resistance

The ongoing problem of emerging antimicrobial resistance has been likened to a balloon where settling one specific issue results in a 'bulge' of even worse problems. However, much has been learned about how to best use our critical antibacterial agents in ways to avoid or even repair some of the resistance damage that has been done. A compilation of current literature strongly suggests that to slow the development of resistance to antimicrobial agents it is optimal to use drugs with more than one mechanism of action or target, to prescribe those with demonstrated ability to minimise or reverse resistance problems, and to avoid underdosing of potent antibiotics. The most recent information also indicates that it is best to limit empirical use of beta-lactam plus fluoroquinolone combination therapy, since these two classes activate some common resistance responses, and using them together can facilitate multidrug resistance in important pathogens, particularly Pseudomonas aeruginosa and Acinetobacter species. This review discusses the role of each major antimicrobial class on resistance development and presents specific strategies for combating the growing problem of multidrug-resistant bacteria. We now have the knowledge to better manage our antimicrobial agent prescribing practices, but finding the will and resources to apply our understanding remains a formidable challenge.

Synthesis and antibacterial activity of N-(5-benzylthio-1,3,4-thiadiazol-2-yl) and N-(5-benzylsulfonyl-1,3,4-thiadiazol-2-yl)piperazinyl quinolone derivatives

A series of N-(5-benzylthio-1,3,4-thiadiazol-2-yl) and N-(5-benzylsulfonyl-1,3,4-thiadiazol-2-yl) derivatives of piperazinyl quinolones was synthesized and evaluated for antibacterial activity against Gram-positive and Gram-negative microorganisms. Some of these derivatives exhibit high activity against Gram-positive bacteria; Staphylococcus aureus and Staphylococcus epidermidis, comparable or more potent than their parent N-piperazinyl quinolones norfloxacin and ciprofloxacin as reference drugs. The SAR of this series indicates that both the structure of the benzyl unit and the S or SO(2) linker dramatically impact antibacterial activity.

Further analysis of the risk of adverse birth outcome after maternal use of fluoroquinolones

In a database cohort study, the risk of adverse birth outcome in Danish women who redeemed a fluoroquinolone prescription during pregnancy was examined. Among 87 women who redeemed a fluoroquinolone prescription at any time during the pregnancy, the prevalence ratio of preterm birth was 1.4 (95% confidence interval (CI), 0.6-3.2), one woman had a stillbirth, and no children died during the perinatal period. Among 130 women who redeemed a prescription during the first trimester or 30 days before conception, the prevalence ratio of congenital malformation was 0.7 (95% CI, 0.3-2.0) and the prevalence ratio of bone malformations was 2.2 (95% CI, 0.7-6.7). Our study raises the concern that prenatal fluoroquinolone exposure may be associated with an increased risk of bone malformations.

Antimicrosporidial activity of (fluoro)quinolones in vitro and in vivo

Microsporidia are a cause of emerging and opportunistic infections in humans and animals. Although two drugs are currently being used to treat microsporidiosis, concerns exist that albendazole is only selective for inhibiting some species of microsporidia that infect mammals, and fumagillin appears to have been found to be toxic. During a limited sequence survey of the Vittaforma corneae genome, a partial gene encoding for the ParC topoisomerase IV subunit was identified. The purpose of this set of studies was to determine if fluoroquinolones, which target topoisomerase IV, exert activity against Encephalitozoon intestinalis and V. corneae in vitro, and whether these compounds could prolong survival of V. corneae-infected athymic mice. Fifteen fluoroquinolones were tested. Of these, norfloxacin and ofloxacin inhibited E. intestinalis replication by more than 70% compared with non-treated control cultures, while gatifloxacin, lomefloxacin, moxifloxacin, and nalidixic acid (sodium salt) inhibited both E. intestinalis and V. corneae by at least 60% at concentrations not toxic to the host cells. These drugs were tested in vivo also, where gatifloxacin, lomefloxacin, norfloxacin, and ofloxacin prolonged survival of V. corneae-infected athymic mice (P < 0.05), whereas moxifloxacin and nalidixic acid failed to prolong survival. Therefore, these results support continued studies for evaluating the efficacy of the fluoroquinolones for treating microsporidiosis and for characterizing the target(s) of these fluoroquinolones in the microsporidia.

[Failure of levofloxacin therapy in two cases of community-acquired pneumonia caused by fluoroquinolone-resistant Streptococcus pneumoniae and complicated with empyema]

BACKGROUND

Community acquired pneumonia (CAP) due to Streptococcus pneumoniae is a frequent cause of morbidity and mortality. We communicate two cases of CAP with complications. In both cases levofloxacin-resistant S. pneumoniae was isolated in pleural effusion. Patient 1: A 51-year-old man who had not received previous treatment with quinolones was admitted to the hospital for CAP and initially treated with levofloxacin (500 mg/24h iv). Four days later pleural effusion developed and fluid culture isolated levofloxacin-resistant S. pneumoniae (MIC > 32 .g/ml). The outcome was favorable following chest tube placement and treatment with beta-lactam antibiotics. Patient 2: A 73-year-old man with a history of chronic obstructive pulmonary disease was admitted due to CAP and was initially treated with levofloxacin (500 mg/24 h iv). He was transferred to our hospital after 10 days of treatment with this antibiotic, following the development of pleural effusion with isolation of levofloxacin-resistant S. pneumoniae (MIC = 12 .g/ml). The patient was treated with chest tube placement and beta-lactam antibiotics with a favorable outcome.

CONCLUSIONS

Patients with CAP treated empirically must be closely followed, both clinically and radiologically, to facilitate early detection of complications due to bacterial resistance to the prescribed antibiotic. Patients with CAP who have received quinolones in the weeks before the development of pneumonia should not been treated empirically with these antibiotics because of the risk of resistance development.

Treating respiratory tract infections in ambulatory care in Belgium: fluoroquinolone consumption and resistance development

This study analyses consumption patterns of fluoroquinolones in treating respiratory tract infections in ambulatory care in Belgium and describes susceptibility of Streptococcus pneumoniae isolates to fluoroquinolones. Consumption data were obtained from IMS Health. Pneumococcal resistance was investigated in 600 blood isolates collected from 1998 to 2003. Although consumption of fluoroquinolones has increased rapidly over the last decade, this trend does not seem to persist more recently. Fluoroquinolones were mainly used to treat urinary and lower respiratory tract infections, but rarely in the management of upper respiratory tract infections. The use of new fluoroquinolones (levofloxacin, moxifloxacin) and the ongoing use of older fluoroquinolones have not led to increased pneumococcal resistance, which remained below 1% for levofloxacin and was 0% for moxifloxacin.

Quinolone resistance in bacteria: emphasis on plasmid-mediated mechanisms

Bacterial resistance to quinolones/fluoroquinolones has emerged rapidly and such resistance has traditionally been attributed to the chromosomally mediated mechanisms that alter the quinolone targets (i.e. DNA gyrase and topoisomerase IV) and/or overproduce multidrug resistance efflux pumps. However, the discovery of the plasmid-borne quinolone resistance determinant, named qnr, has substantially broadened our horizon on the molecular mechanisms of quinolone resistance. Several recent reports of Qnr or its homologues encoded by transferable plasmids in Gram-negative bacteria isolated worldwide highlight the significance of the emerging plasmid-mediated mechanism(s). This also alerts us to the potential rapid dissemination of quinolone resistance determinants. Qnr belongs to the pentapeptide repeat family and protects DNA gyrase from the action of quinolone agents including the newer fluoroquinolones. This protection interplays with chromosomal mechanisms to raise significantly the resistance levels. The qnr-bearing strains generate quinolone-resistant mutants at a much higher frequency than those qnr-free strains. Furthermore, the qnr-plasmids are integron-associated and carry multiple resistance determinants providing resistance to several classes of antimicrobials including beta-lactams and aminoglycosides. The high quinolone resistance rates in Escherichia coli are used to address issues of quinolone resistance, and possible strategies for minimising quinolone resistance are discussed.

Antimicrobial synergy between mRNA- and protein-level inhibitors

BACKGROUND

The few available distinct classes of antimicrobials limits the scope for single and combination drug treatment of resistant infections.

OBJECTIVE

To evaluate antimicrobial effectiveness from combinations of protein-specific drugs and mRNA-specific antisense inhibitors.

METHODS

Interactions between conventional antimicrobial drugs and mRNA-specific translation inhibiting antisense peptide nucleic acids were assessed in Escherichia coli and Staphylococcus aureus cultures using pairwise combinations in a chequerboard arrangement. Fractional inhibitory concentration indices (FICIs) were calculated and grouped according to the functional relationship between the inhibitor targets. Antisense specificity controls included different antisense sequences targeting the same mRNA, as well as biochemical quantification of active protein expressed from the essential fabI gene and from the lacZ reporter gene after single and combined inhibitor treatment.

RESULTS

FICIs were higher for inhibitor combinations with unrelated targets than for combinations with functionally related targets. Inhibitor combinations with shared genetic targets displayed the lowest FICIs, with several qualifying for the conservative definition of antimicrobial synergy (FICI < or = 0.5). Furthermore, low FICIs arise as the hyperbolic dose-response curves for each separate inhibitor are maintained in combination.

CONCLUSION

Interactions between mRNA- and protein-level inhibitors with the same genetic target can be synergistic and may provide a strategy to improve antimicrobial efficacy, facilitate drug mechanism of action studies and aid the search for new antimicrobials.

Penetration of moxifloxacin into the human aqueous humour after oral administration

AIMS

To determine the pharmacokinetics of moxifloxacin, a new generation fluoroquinolone, in the anterior chamber of the human uninflamed eye.

METHODS

35 patients undergoing cataract surgery received two doses of 400 mg of oral moxifloxacin with a 12 hour interval and were divided into six groups. Moxifloxacin levels in aqueous humour and serum were determined by a microbiological agar well diffusion technique at 2, 4, 6, 8, 10, and 12 hours after the second dose in each group respectively.

RESULTS

Mean moxifloxacin levels in the anterior chamber were 1.20 (SD 0.35) microg/ml at the 2 hours group, 1.22 (0.48) microg/ml at the 4 hours group, 1.20 (0.45) microg/ml at the 6 hours group, 1.58 (0.38) microg/ml at the 8 hours group, 1.37 (0.44) microg/ml at the 10 hours group, and 1.23 (0.55) microg/ml at the 12 hours group. The mean ratio of aqueous to serum moxifloxacin level was 38%.

CONCLUSION

Moxifloxacin penetrates well into the anterior chamber of the human uninflamed eye after oral administration, reaching early significant levels, which are maintained for at least 12 hours and are much higher than the MIC(90) values of Gram positive and Gram negative pathogens commonly implicated in intraocular infections with the exceptions of fluoroquinolone resistant staphylococci, MRSA, and Pseudomonas aeruginosa.

Antimicrobial susceptibility and molecular characterization of avian pathogenic Escherichia coli isolates

Ninety-five avian pathogenic Escherichia coli (APEC) isolates recovered from diagnosed cases of avian colibacillosis from North Georgia between 1996 and 2000 were serotyped and examined for typical virulence-factors, susceptibility to antimicrobials of human and veterinary significance, and genetic relatedness. Twenty different serotypes were identified, with O78 being the most common (12%). The majority of the avian E. coli isolates (60%), however, were non-typeable with standard O antisera. Eighty-four percent of isolates were PCR positive for the temperature-sensitive hemagglutinin (tsh) gene and 86% positive for the increased serum survival (iss) gene. Multiple antimicrobial-resistant phenotypes (> or =3 antimicrobials) were observed in 92% of E. coli isolates, with the majority of isolates displaying resistance to sulfamethoxazole (93%), tetracycline (87%), streptomycin (86%), gentamicin (69%), and nalidixic acid (59%). Fifty-six E. coli isolates displaying resistance to nalidixic acid were co-resistant to difloxacin (57%), enrofloxacin (16%), gatifloxacin (2%), and levofloxacin (2%). DNA sequencing revealed point mutations in gyrA (Ser83-Leu, Asp87-Tyr, Asp87-Gly, Asp87-Ala), gyrB (Glu466-Asp, Asp426-Thr), and parC (Ser80-Ile, Ser80-Arg). No mutations were observed in parE. Twelve of the quinolone-resistant E. coli isolates were tolerant to cyclohexane, a marker for upregulation of the acrAB multi-drug resistance efflux pump. Quinolone-resistant isolates were further genetically characterized via ribotyping. Twenty-two distinct ribogroups were identified, with 61% of isolates clustering into four major ribogroups, indicating that quinolone resistance has emerged among multiple avian pathogenic E. coli serogroups and chromosomal backgrounds.

Benzenesulfonamide analogs of fluoroquinolones. Antibacterial activity and QSAR studies

The structure-activity relationships (SAR) of new antibacterial benzenesulfonamidefluoroquinolones (BSFQs), coming from derivatization of N4-piperazinyl of ciprofloxacin (CIP) were studied. The behavior of the new BSFQ series was similar to the previously norfloxacin (NOR) analogs reported, making possible a quantitative structure-activity relationships (QSAR) analysis of the complete set of BSFQs. The presence of the benzenesulfonylamido (BS) groups shifted the activity of classic antimicrobial fluoroquinolones from being more active against Gram-negative to Gram-positive strains. QSAR studies through Hansch analysis showed a linear correlation of the activity with electronic and steric parameters. Small electron-donor groups would increase the in vitro activity against Gram-positive bacteria. Hydrophobic properties played a minor role when activity is measured as minimum inhibitory concentration (MIC). QSAR analysis also reinforces previous biological findings about the presence of new interactions with target topoisomerases.

Increased antibacterial activity of DW286, a novel fluoronaphthyridone antibiotic, against Staphylococcus aureus strains with defined mutations in DNA gyrase and topoisomerase IV

To investigate the activity of DW286, a new fluoronaphthyridone, the quinolone resistance determining regions (QRDRs) of gyrA, gyrB, grlA and grlB genes in 64 Staphylococcus aureus clinical isolates were analyzed and the MICs of DW286 and comparator quinolones determined. Double and triple mutants in gyrA and grlA were resistant to ciprofloxacin, sparfloxacin, trovafloxacin and gemifloxacin but susceptible to DW286 (MIC 0.25-0.5 mg/l). The fourth alteration, Ser85Pro of GyrA was required to make a strain resistant to DW286 (MIC 4-32 mg/l). For a strain with the mutations at GyrA Ser84Leu and GrlA Ser80Phe, the MBC of DW286 was two-fold higher than its corresponding MIC, in contrast to ciprofloxacin which was not bactericidal.

Mutations in the quinolone-resistance determining region (QRDR) of Salmonella strains isolated from pigs in Spain

Quinolone-resistance determining region (QRDR) of Gyrase A gene was sequenced in 54 Salmonella strains of pig origin that have different quinolone-resistance patterns. Those strains accounted for 12 different serotypes. Mutations at Ser83 or Asp87 were predominant in the studied isolates. However, for serotypes Anatum and Virchow, resistance to quinolones seemed to be linked to specific mutations, namely, Ser83-->Tyr and Ser83-->Phe, respectively. Other mutations found in different positions did not seem to have clinical significance except for changes at Asp82.

Ofloxacin-like antibiotics inhibit pneumococcal cell wall-degrading virulence factors

The search for new drugs against Streptococcus pneumoniae (pneumococcus) is driven by the 1.5 million deaths it causes annually. Choline-binding proteins attach to the pneumococcal cell wall through domains that recognize choline moieties, and their involvement in pneumococcal virulence makes them potential targets for drug development. We have defined chemical criteria involved in the docking of small molecules from a three-dimensional structural library to the major pneumococcal autolysin (LytA) choline binding domain. These criteria were used to identify compounds that could interfere with the attachment of this protein to the cell wall, and several quinolones that fit this framework were found to inhibit the cell wall-degrading activity of LytA. Furthermore, these compounds produced similar effects on other enzymes with different catalytic activities but that contained a similar choline binding domain; that is, autolysin (LytC) and the phage lytic enzyme (Cpl-1). Finally, we resolved the crystal structure of the complex between the choline binding domain of LytA and ofloxacin at a resolution of 2.6 Angstroms. These data constitute an important launch pad from which effective drugs to combat pneumococcal infections can be developed.

Synthesis and biological activity of fluoroquinolone-pyrrolo[2,1-c][1,4]benzodiazepine conjugates

Fluoroquinolones have been synthesized and linked to DC-81 at C8 position through different alkyl chain spacers. These PBD conjugates have exhibited good DNA binding affinity, and a representative compound shows promising in vitro anticancer activity.

Mutant prevention concentrations for single-step fluoroquinolone-resistant mutants of wild-type, efflux-positive, or ParC or GyrA mutation-containing Streptococcus pneumoniae isolates

Three fluoroquinolone-susceptible and five fluoroquinolone-resistant (two with ParC Ser79Phe mutations, one with a GyrA Ser81Phe mutation, and two that were efflux positive) Streptococcus pneumoniae isolates were exposed to one, two, four, eight, and sixteen times the MICs of ciprofloxacin, gatifloxacin, gemifloxacin, levofloxacin, and moxifloxacin. Mutational frequencies were calculated at each multiple of the MIC for which growth was observed. Mutant prevention concentrations (MPCs) and the multiple of the MIC at the MPC (MP(MIC)) were evaluated. All resulting mutants were sequenced for quinolone resistance-determining region changes in GyrA and ParC and were evaluated for reserpine-sensitive efflux. The MPC order was generally ciprofloxacin > levofloxacin > gatifloxacin > moxifloxacin > gemifloxacin. The MP(MIC) order varied depending on the genetic constitution of the original isolates from which the mutants were generated. For those mutants created from fluoroquinolone-susceptible isolates (those that had wild-type ParC and GyrA and were efflux negative), the MP(MIC) order was ciprofloxacin = moxifloxacin > gemifloxacin > levofloxacin > gatifloxacin. The MP(MIC)s of each fluoroquinolone for mutants created from isolates with a ParC mutation (with wild-type GyrA and efflux negative) were similar. A similar occurrence was observed with the mutants created from the efflux-positive isolates (with wild-type ParC and GyrA). The MP(MIC) order for the mutants created from the isolate with a GyrA mutation (with wild-type ParC and efflux negative) was ciprofloxacin = gemifloxacin > levofloxacin = moxifloxacin > gatifloxacin. Gatifloxacin, levofloxacin, and moxifloxacin may be intrinsically more able to prevent the development of resistance by fluoroquinolone-susceptible isolates, isolates that are efflux positive, or isolates that carry a GyrA mutation. However, once a ParC mutation is present, the MPC increases dramatically for all fluoroquinolones.

A prodrug approach toward the development of water soluble fluoroquinolones and structure--activity relationships of quinoline-3-carboxylic acids

A fluoroquinolone prodrug, PA2808, was prepared and shown to convert to the highly active parent drug PA2789. In vitro and in vivo activation of PA2808 by alkaline phosphatase was demonstrated using disk diffusion and rat lung infection models. The water solubility of PA2808 showed a marked increase compared to PA2789 over a pH range suitable for aerosol drug delivery. A total of 48 analogues based on PA2789 were prepared and screened against a panel of Gram-positive and Gram-negative pathogens. Incorporating a cyclopropane-fused pyrrolidine (amine) at C-7 resulted in some of the most active analogues.

Mechanisms of quinolone resistance and clonal relationship among Aeromonas salmonicida strains isolated from reared fish with furunculosis

The mechanisms of resistance to quinolone and epidemiological relationships among A. salmonicida strains isolated from diseased fish in French marine farms from 1998 to 2000 were investigated. The quinolone resistance-determining regions of the gyrA and parC genes of 12 clinical A. salmonicida isolates with different levels of quinolone susceptibility were sequenced. MICs were determined in the presence of the efflux pump inhibitor (EPI) Phe-Arg beta-naphthylamide and E(max) values (MIC without EPI/MIC in the presence of EPI) were calculated. Isolates fell into two classes: (i) those that had a wild-type gyrA gene with oxolinic acid MIC </= 0.5, flumequine MIC </= 1 and ciprofloxacin MIC </= 0.25 micro g ml(-1); and (ii) those that had a single mutation in gyrA encoding Asp-87 --> Asn with oxolinic acid MIC >/= 2, flumequine MIC >/= 4 and ciprofloxacin MIC >/= 0.125 micro g ml(-1). No mutations were found in parC. High E(max) values obtained for flumequine and oxolinic acid (up to 16 and 8, respectively, for the most resistant isolates of the two classes) indicated an important contribution of efflux to the resistance phenotype. Flumequine accumulation experiments confirmed that high E(max) values were associated with a much lower level of accumulation. PCR/RFLP assays conducted on 34 additional isolates showed the presence of a mutation at codon 87 of gyrA in nearly all the quinolone-resistant isolates. This finding, together with PFGE typing results, strongly suggests a common clonal origin of these quinolone-resistant isolates.

Antibiotic-resistant gram-negative bacteria in hospitalized children

Antibiotic-resistant Gram-negative bacilli are a prominent and growing problem among hospitalized children. Epidemics caused by these organisms have been implicated in many outbreaks in children's hospitals, primarily in neonatal intensive care units. These epidemics are characterized by efficient patient-to-patient transmission of the outbreak clone via the hands of caregivers and through exposure of contaminated inanimate sources. The epidemiology of these resistant organisms in pediatric hospitals during endemic periods is more complex. The isolates cultured from hospitalized individuals in the absence of an outbreak usually are unique to each individual and are derived from the patient's endogenous flora or other disparate sources. As in adults, chronic care facilities for children represent significant reservoirs of antibiotic-resistant bacilli that are circulated back into the acute care hospital environment when the child becomes ill.

Chemometric Studies on the Bactericidal Activity of Quinolones via an Extended VolSurf Approach

An extended VolSurf approach, that additionally includes SHAPE descriptors, was applied to a dataset of 55 quinolones. Bactericidal activity was measured at Bayer AG, Germany, for Gram-negative (Escherichia coli and Pseudomonas aeruginosa) and Gram-positive bacteria (Staphylococcus aureus and Enterococcus faecalis). Chemometric analysis was first approached via a classical VolSurf approach. The following descriptors were found most important: bactericidal activity particularly increases with high values of the best volume (BV11(OH2)) and the minimum energy (Emin1(OH2)) of the water probe, high values of the integy moment (ID(DRY)) of the lipophilic probe, and high values of the hydrophilic region (W(O)) of the hydrogen bond acceptor probe. Best volume (BV31(OH2)) of the water probe and best volume (BV12(DRY)) and lipophilic regions (D(DRY)) of the lipophilic probe as well as H-bonding capacity derived with the CO probe (HB(O)) are inversely related to activity. PLS analysis yields a five-component model with an r(2) of 0.83 and a q(2) of 0.43 after variable selection via fractional factorial design (FFD). Chemometric modeling could be improved by including newly derived SHAPE descriptors, which were merged with the VolSurf descriptors and subjected to PLS analysis. The global model of this extended VolSurf approach is optimal with two components and exhibits a significantly improved statistical quality; a marginally reduced r(2) (0.75 versus 0.83) is more than compensated by a highly improved predictivity with a q(2) of 0.63 versus 0.43. To prove model quality, external prediction of seven test set quinolones was performed. The precise prediction of all test set molecules nicely demonstrates the robustness and statistical significance of the obtained chemometric model using the extended VolSurf approach.

Enhanced Production of Functional Proteins from Defective Genes

Nonsense mutations are associated with a host of genetic disorders. The protein products encoded by genes containing these mutations are either truncated or completely missing. Recently, members of the aminoglycoside family of antibiotics have been found to induce the ribosome to read past these inappropriately inserted stop codons, albeit at extremely modest efficiencies. We report herein a strategy that enhances the production of functional proteins from the corresponding mutated genes.

Analysis of the gyrA gene of clinical Yersinia ruckeri isolates with reduced susceptibility to quinolones

Antimicrobial susceptibility of seven clinical strains of Yersinia ruckeri representative of those isolated between 1994 and 2002 from a fish farm with endemic enteric redmouth disease was studied. All isolates displayed indistinguishable pulsed-field gel electrophoresis restriction patterns, indicating that they represented a single strain. However, considering both inhibition zone diameters (IZD) and MICs, the isolates recovered in 2001-2002 formed a separate cluster with lower levels of susceptibility to all the quinolones tested, especially nalidixic acid (NA) and oxolinic acid (OA), compared with the isolates recovered between 1994 and 1998. Analysis of the PCR product of the quinolone resistance-determining region of the gyrA gene from clinical isolates of Y. ruckeri with reduced susceptibility to OA and NA revealed a single amino acid substitution, Ser-83 to Arg-83 (Escherichia coli numbering). Identical substitution was observed in induced OA-resistant mutant strains, which displayed IZD and MICs of quinolones similar to those of the clinical isolates of Y. ruckeri with reduced susceptibility to these antimicrobial agents. These data indicate in that for Y. ruckeri, the substitution of Ser by Arg at position 83 of the gyrA gene is associated with reduced susceptibility to quinolones.

Ribosomal alterations contribute to bacterial resistance against the dipeptide antibiotic TAN 1057

TAN 1057-resistant Staphylococcus aureus and Escherichia coli strains were selected to elucidate the mechanism of resistance and the mode of action of this dipeptide antibiotic. Cell-free translation with isolated ribosomes and S150 fractions from sensitive and resistant S. aureus strains demonstrated that alterations in the ribosomes contribute to the resistance of the bacteria.

Management of community-acquired pneumonia: a focus on conversion from hospital to the ambulatory setting

Patients with community-acquired pneumonia (CAP) are treated in hospital or in the ambulatory care setting depending on the severity of illness. Despite numerous guidelines proposed, there is no agreement on specific criteria for hospitalization other than the clinicians' experience. The purpose of this review is to discuss the importance of the appropriate choice and timely administration of antibacterial agents, either in the hospital or in the outpatient setting. Since a high proportion of CAP patients will not have an etiologic agent identified at the time of initiation of treatment, the choice of antibacterial therapy is usually empiric. Antibacterial agents with activity against pneumococci and atypical pathogens causing pneumonia are the preferred choices. Macrolides, doxycycline, or respiratory fluoroquinolones have been recommended by various guidelines committees in North America for the treatment of pneumonia in patients with or without underlying comorbidities. Because of the increasing resistance to beta-lactams as well other antibacterial agents such as macrolides, doxycycline, and sulfamethoxazole/trimethoprim (cotrimoxazole), it is important that clinicians are aware of local statistics on resistance to Streptococcus pneumoniae, as infection with this bacterium is associated with high rates of morbidity and mortality. More recently, fluoroquinolone resistance has been reported, but the percentage of pneumococcal strains resistant to this agent is relatively low compared with the other antibacterial agents. Switch (intravenous to oral) therapy is recommended for hospitalized patients with CAP to facilitate early discharge, which has been shown to improve patient satisfaction and reduce hospital costs. Early conversion to oral therapy has not been shown to be associated with increased complications or higher mortality. Following prompt intravenous therapy and stabilization, patients with CAP should be treated with oral therapy in the ambulatory setting.

ATP-bound conformation of topoisomerase IV: a possible target for quinolones in Streptococcus pneumoniae

Topoisomerase IV, a C(2)E(2) tetramer, is involved in the topological changes of DNA during replication. This enzyme is the target of antibacterial compounds, such as the coumarins, which target the ATP binding site in the ParE subunit, and the quinolones, which bind, outside the active site, to the quinolone resistance-determining region (QRDR). After site-directed and random mutagenesis, we found some mutations in the ATP binding site of ParE near the dimeric interface and outside the QRDR that conferred quinolone resistance to Streptococcus pneumoniae, a bacterial pathogen. Modeling of the N-terminal, 43-kDa ParE domain of S. pneumoniae revealed that the most frequent mutations affected conserved residues, among them His43 and His103, which are involved in the hydrogen bond network supporting ATP hydrolysis, and Met31, at the dimeric interface. All mutants showed a particular phenotype of resistance to fluoroquinolones and an increase in susceptibility to novobiocin. All mutations in ParE resulted in resistance only when associated with a mutation in the QRDR of the GyrA subunit. Our models of the closed and open conformations of the active site indicate that quinolones preferentially target topoisomerase IV of S. pneumoniae in its ATP-bound closed conformation.

Synthesis and in vitro antibacterial activity of some N-(5-aryl-1,3,4-thiadiazole-2-yl)piperazinyl quinolone derivatives

A series of N-[5-(1-methyl-5-nitro-2-imidazolyl)-1,3,4-thiadiazole-2-yl] and N-[5-(nitrophenyl)-1,3,4-thiadiazole-2-yl] piperazinyl quinolone derivatives (5a-c and 5d-l) were synthesized and evaluated for in vitro antibacterial activity against some Gram-positive and Gram-negative bacteria. The antibacterial data revealed that all nitroimidazole derivatives (5a-c) showed interesting activity against tested Gram-positive bacteria (minimum inhibitory concentration, MIC=0.008-0.03 microg/ml) while they did not show good activity against Gram-negative organisms. Despite the significant activity of nitroimidazole series, all nitrophenyl analogues (5d-l) were inactive against both Gram-positive and Gram-negative bacteria. Among all of the tested compounds, 5a (ciprofloxacin derivative in nitroimidazole series) exhibited excellent activity against Staphylococcus aureus and Staphylococcus epidermidis (MIC=0.008 microg/ml).

Synthesis and in vitro antibacterial evaluation of N-[5-(5-nitro-2-thienyl)-1,3,4-thiadiazole-2-yl] piperazinyl quinolones

A series of N-[5-(5-nitro-2-thienyl)-1,3,4-thiadiazole-2-yl]piperazinyl quinolones (7a-c) were synthesized and evaluated for in vitro antibacterial activity against some Gram-positive and Gram-negative bacteria. The antibacterial data revealed that compounds 7a-c had strong and better activity against tested Gram-positive organisms than the reference quinolones such as ciprofloxacin, norfloxacin and enoxacin. However, all three compounds were nearly inactive against Gram-negative bacteria. Compound 7a (ciprofloxacin analogue) was the most active compound against Gram-positive bacteria (MIC=0.008-0.015 mug mL(-1)).

Fluoroquinolones, tuberculosis, and resistance

Although the fluoroquinolones are presently used to treat tuberculosis primarily in cases involving resistance or intolerance to first-line antituberculosis therapy, these drugs are potential first-line agents and are under study for this indication. However, there is concern about the development of fluoroquinolone resistance in Mycobacterium tuberculosis, particularly when administered as monotherapy or as the only active agent in a failing multidrug regimen. Treatment failures as well as relapses have been documented under such conditions. With increasing numbers of fluoroquinolone prescriptions and the expanded use of these broad-spectrum agents for many infections, the selective pressure of fluoroquinolone use results in the ready emergence of fluoroquinolone resistance in a diversity of organisms, including M tuberculosis. Among M tuberculosis, resistance is emerging and may herald a significant future threat to the long-term clinical utility of fluoroquinolones. Discussion and education regarding appropriate use are necessary to preserve the effectiveness of this antibiotic class against the hazard of growing resistance.

Selection and characterization of fluoroquinolone-resistant mutants of Campylobacter jejuni using enrofloxacin

Significant levels of fluoroquinolone resistance were obtained in Campylobacterjejuni isolates after an unique step of selection using enrofloxacin. An Asp90-to-Asn and a Thr86-to-Ile change in the gyrase subunit GyrA were found associated with a low (MIC < or = 8 /microg/ml) or a high (MIC > or = 16 microg/ml) level of resistance to ciprofloxacin, respectively. An association of both mutations conferred a higher level of resistance (MIC > or = 128 microg/ml). Further steps of selection increased the MICs of fluoroquinolones but did not result in a multiple antibiotic resistance phenotype. The Thr86-to-Ile change was found to confer different levels of resistance, pointing out other mechanisms of resistance. However, sequencing revealed no mutation in gyrB, and several attempts did not enable any amplification of the parC gene coding for topoisomerase IV, suggesting an absence of this secondary target in C. jejuni. In addition, no difference in the major outer membrane protein expression was found among the isolates. Furthermore, the use of the recently identified efflux pump inhibitor Phe-Arg-beta-naphthylamide did not result in a significant decrease of fluoroquinolone MICs or change in the frequency of isolation of enrofloxacin-resistant mutants, and thus appears ineffective against fluoroquinolone-resistant C. jejuni isolates. Results obtained during ciprofloxacin accumulation studies confirmed that efflux probably plays a minor role in fluoroquinolone resistance of C. jejuni.

[Quinolones]

Quinolones act by inhibiting enzymes (topoisomerases), which are indispensable to DNA synthesis. Their bactericidal activity is concentration-dependent. Their spectrum has become broader, especially since the introduction of a fluorine atom at position 6 (fluoroquinolones). They are used as the treatment of choice or as alternative therapy in a wide variety of infections, both in the hospital and non-hospital setting. Depending on the compound, they are used in urinary tract infections, sexually transmitted diseases, chronic osteomyelitis, respiratory tract infections, and severe systemic infections, among others. The upsurge and extent of quinolone resistance has limited the use of these agents in some cases and in future may determine their use in others. There are strategies to minimize the spread of resistance. Quinolones are safe and well tolerated. The most frequent adverse effects are gastrointestinal and those affecting the central nervous system.

Structural and functional changes by Ciprofloxacin of rat submandibular gland

In the present study, the effects of Ciprofloxacin (Cipro), a fluoroquinolone antibiotic, on rat submandibular gland structure and function were examined in an acute experiment. Cipro was administered intraperitoneally at various doses (20, 40 and 80 mg/kg). Pure submandibular saliva was collected intraorally by micropolyethylene tubes under anaesthesia using a dissecting microscope. After collection of saliva, submandibular glands were removed and weighed. Flow rate, amylase activity, total protein and electrolyte concentrations were measured in saliva. Concentrations of DNA and protein were measured in the gland. All doses of Cipro (20, 40, 80 mg/kg) reduced salivary flow rate. Concentrations of salivary total protein and calcium and gland DNA were reduced by all doses of Cipro. Treatment by Cipro (80 mg/kg) induced an increase in salivary sodium and potassium concentrations. Histopathological examination of glands revealed that Cipro at doses of 40 mg/kg and 80 mg/kg induces morphological changes in the glands including irregular shape of the cerous and mucous bobbles, lack of nucleus in some cells, damage of the cytoplasmic and cell walls and presence of oncocytes in secretory ducts. It is concluded that Cipro inhibits rat submandibular gland functions consistent with structural damages to the gland that might be observed as a side effect in humans. Properties of fluoroquinolones to alter intracellular cAMP and their ability to suppress DNA and protein synthesis of acinar cells might be possible reasons for observed changes.

[Phenotypes of resistance in community urinary tract isolates of Escherichia coli: therapeutic implications]

BACKGROUND AND OBJECTIVE

Urinary tract infectious (UTI) are very frequent in the community and are managed through empirical treatment guidelines. The knowledge of patterns of susceptibility of patients at the time of establishing an empirical treatment is fundamental to avoid therapeutic failures. The aim of this study was to know the pattern of resistance to betalactams and other antimicrobials used in the treatment of non-complicated urinary infections in the area 11 of Madrid.

PATIENTS AND METHOD

Retrospective study of susceptibility of Escherichia coli isolated in cultures of urine of outpatients of area 11 of Madrid during a period of 12 months.

RESULTS

We found high rates of resistance to ampicillin and trimethoprim-sulfamethoxazole (57 and 29%, respectively). We observed high rates of resistance to cefuroxime (24%) and amoxicillin-clavulanic acid (27%). Resistance to ciprofloxacine was 16%. Resistance to phosphomicin and nitrofurantoin was very low (5 and 4%). Most frequent resistance association was ampicillin + cephalothin (20,2%). The mechanisms of resistance having more clinical relevance was the production and hyper-production of betalactamase.

CONCLUSIONS

Changes were detected as to the pattern of susceptibility of certain antimicrobials frequently used in the empirical treatment of UTI such as cefuroxime and amoxicillin-clavulanic acid. It is important to support a condition of active surveillance for the evolution of resistances.

Contribution of the 8-methoxy group to the activity of gatifloxacin against type II topoisomerases of Streptococcus pneumoniae

The inhibitory activities (50% inhibitory concentrations [IC(50)s]) of gatifloxacin and other quinolones against both DNA gyrase and topoisomerase IV of the wild-type Streptococcus pneumoniae IID553 were determined. The IC(50)s of 10 compounds ranged from 4.28 to 582 microg/ml against DNA gyrase and from 1.90 to 35.2 microg/ml against topoisomerase IV. The inhibitory activity against DNA gyrase was more varied than that against topoisomerase IV among fluoroquinolones. The IC(50)s for DNA gyrase of the 8-methoxy quinolones gatifloxacin and AM-1147 were approximately seven times lower than those of their 8-H counterparts AM-1121 and ciprofloxacin, whereas the IC(50)s for topoisomerase IV were 1.5 times lower. Moreover, the IC(50) ratios (IC(50) for DNA gyrase/IC(50) for topoisomerase IV) of gatifloxacin, AM-1147, and moxifloxacin, which possess 8-methoxy groups, were almost the same. The 8-methoxy quinolones showed higher antibacterial activity and less mutant selectivity against IID553 than their 8-H counterparts. These results suggest that the 8-methoxy group enhances both target inhibition, especially for DNA gyrase, leading to potent antipneumococcal activity and dual inhibition against both DNA gyrase and topoisomerase IV in the bacterial cell.

Topoisomerase targeting with and resistance to gemifloxacin in Staphylococcus aureus

Gemifloxacin, a novel quinolone with potent activity against Staphylococcus aureus, was 8- to 16-fold more active against wild-type S. aureus than ciprofloxacin. The two- to fourfold increase in the MIC of gemifloxacin in genetically defined grlBA mutants and the twofold increase in a single gyrA mutant, supported by the low frequency of selection of resistant mutants at twice the MIC (7.4 x 10(-11) to 1.1 x 10(-10)), suggested similar targeting of the two enzymes by gemifloxacin. Dual mutations in both gyrase and topoisomerase IV caused a 64- to 128-fold increase in the MIC of gemifloxacin, similar to that seen with ciprofloxacin. Gemifloxacin also had similar activity in vitro against topoisomerase IV and gyrase purified from S. aureus (50% inhibitory concentrations of 0.25 and 0.31 micro g/ml, respectively). This activity was 10- to 20-fold higher than that of ciprofloxacin for topoisomerase IV and 33-fold higher than that for gyrase. In contrast to the in vitro findings, only topoisomerase IV mutants were selected in first-step mutants. Overexpression of the NorA efflux pump had a minimal effect on resistance to gemifloxacin, and a mutation in the promoter region of the gene for NorA was selected only in the sixth step of serial selection of mutants. Our data show that although gemifloxacin targets purified topoisomerase IV and gyrase similarly in vitro, topoisomerase IV is the preferred target in the bacteria. Selection of novel resistance mutations in grlA requires further expansion of quinolone-resistance-determining regions, and their study may provide increased insight into enzyme-quinolone interactions.

Vancomycin tolerance induced by erythromycin but not by loss of vncRS, vex3, or pep27 function in Streptococcus pneumoniae

Vancomycin-tolerant Streptococcus pneumoniae is a growing problem among drug-resistant human pathogens. Some vancomycin-tolerant pneumococci have been reported to carry mutations in loci encoding a two-component regulatory system designated VncRS or in a proximal ABC transporter, Vex. A model was advanced proposing that the tolerance phenotype resulted from the inability of a vncS mutant to respond to the Vex-transported Pep27 "death peptide" signal and dephosphorylate VncR, thereby preventing relief of repression of autolytic and other cell death functions in response to antibiotics. To explore this hypothesis, we constructed mutations in vncS, vncR, vex3, and pep27 in S. pneumoniae strain R6 and two additional genetic backgrounds. The lytic responses of the isogenic DeltavncS, Deltavex3, DeltavncR, and Deltapep27 mutants, but not a DeltalytA strain, to vancomycin were indistinguishable from that of the parent strain. DeltavncS strains also failed to exhibit tolerance to vancomycin at various doses in multiple media and showed wild-type sensitivity to other classes of autolysis-inducing antibiotics. In contrast, addition of subinhibitory levels of the antibiotic erythromycin led to tolerance to vancomycin during late, but not early, exponential-phase growth in a DeltavncS strain, in the parent strain R6, and in two other strains bearing erythromycin resistance markers, namely, a DeltavncR strain and an unrelated DeltacomD strain that is defective in competence-quorum sensing. Thus, this tolerance effect resulted from changes in cell growth or other erythromycin-dependent phenomena and not inactivation of vncS per se. Consistent with these results, and in contrast to a previous report, we found that a synthetic form of Pep27 did not elicit lytic or nonlytic killing of pneumococci. Finally, microarray transcriptional analysis and beta-galactosidase reporter assays revealed VncS-dependent regulation of the vex123 gene cluster but did not support a role for VncRS in the regulation of autolytic or other putative cell death loci. Based on these findings, we propose that vancomycin tolerance in S. pneumoniae does not result from loss of vncS function alone.

Dual targeting of DNA gyrase and topoisomerase IV: target interactions of garenoxacin (BMS-284756, T-3811ME), a new desfluoroquinolone

We determined the target enzyme interactions of garenoxacin (BMS-284756, T-3811ME), a novel desfluoroquinolone, in Staphylococcus aureus by genetic and biochemical studies. We found garenoxacin to be four- to eightfold more active than ciprofloxacin against wild-type S. aureus. A single topoisomerase IV or gyrase mutation caused only a 2- to 4-fold increase in the MIC of garenoxacin, whereas a combination of mutations in both loci caused a substantial increase (128-fold). Overexpression of the NorA efflux pump had minimal effect on resistance to garenoxacin. With garenoxacin at twice the MIC, selection of resistant mutants (<7.4 x 10(-12) to 4.0 x 10(-11)) was 5 to 6 log units less than that with ciprofloxacin. Mutations inside or outside the quinolone resistance-determining regions (QRDR) of either topoisomerase IV, or gyrase, or both were selected in single-step mutants, suggesting dual targeting of topoisomerase IV and gyrase. Three of the novel mutations were shown by genetic experiments to be responsible for resistance. Studies with purified topoisomerase IV and gyrase from S. aureus also showed that garenoxacin had similar activity against topoisomerase IV and gyrase (50% inhibitory concentration, 1.25 to 2.5 and 1.25 micro g/ml, respectively), and although its activity against topoisomerase IV was 2-fold greater than that of ciprofloxacin, its activity against gyrase was 10-fold greater. This study provides the first genetic and biochemical data supporting the dual targeting of topoisomerase IV and gyrase in S. aureus by a quinolone as well as providing genetic proof for the expansion of the QRDRs to include the 5' terminus of grlB and the 3' terminus of gyrA.

Demonstration of in vitro antagonism between fusidic acid and quinolones

Fusidic acid is an antibiotic active against staphylococci and other bacterial pathogens. It is used in the treatment of staphylococcal infections usually in combination with other antibacterial agents. Reports of the clinical effects of antimicrobial combinations containing fusidic acid have been somewhat inconsistent. The aim of this study was to investigate the in vitro antagonism of fusidic acid and quinolones. Twenty-six staphylococci strains isolated from various clinical samples were tested. After detecting the diameter of the zone of inhibition around fusidic acid, levofloxacin, ciprofloxacin, ofloxacin and moxifloxacin for each strain, in vitro antagonism between fusidic acid and each quinolone was investigated using disk approximation. In all 26 strains, quinolones and fusidic acid were antagonist in vitro. The reason for this antagonistic effect and its clinical implications are not known. However, care should be exercised in prescribing quinolones and fusidic acid in combination.

Fluoroquinolones for the treatment of outpatient community-acquired pneumonia

The increasing prevalence of beta-lactam and macrolide resistance in bacteria that cause respiratory infections has underscored the need for effective antimicrobial agents. The broad spectrum, excellent oral bioavailability, and once-daily dosing of fluoroquinolones contributed to the introduction of several new agents in the past decade. This class is among the world's most used antimicrobial therapies in community and hospital settings. Fluoroquinolones are generally well tolerated, but safety profiles differ widely among agents. Knowledge of in vitro activity, local microbiologic susceptibility and resistance patterns, adverse effects, and potential drug interactions should influence the selection of the best agent for individual patients. This overview of the fluoroquinolones directs particular attention to use in community-acquired pneumonia and safety.

Resistant pathogens in respiratory tract infections in older people

Bronchitis, bronchiectasis, and pneumonia are the most common respiratory tract infections observed in older people and are the leading causes of morbidity and mortality associated with infection. Accurate diagnosis of respiratory tract infections in older people is problematic because of the lack of clear symptoms and signs that are usually seen in younger patients. In addition, the increasing prevalence of bacterial resistance to antibiotic therapy highlights the importance of appropriate therapy. The following review examines the issues associated with the accurate diagnosis of respiratory tract infections, optimal therapy for older patients, and the mechanisms of emerging bacterial resistance to antibiotic therapy.