Impermeability to quinolones in gram-positive and gram-negative bacteria

Evaluating LC-MS/MS To Measure Accumulation of Compounds within Bacteria

A general method for determining bacterial uptake of compounds independent of antibacterial activity would be a valuable tool in antibacterial drug discovery. LC-MS/MS assays have been described, but it has not been shown whether the data can be used directly to inform medicinal chemistry. We describe the evaluation of an LC-MS/MS assay measuring association of compounds with bacteria, using a set of over a hundred compounds (inhibitors of NAD-dependent DNA ligase, LigA) for which in vitro potency and antibacterial activity had been determined. All compounds were active against an efflux-deficient strain of Escherichia coli with reduced LigA activity ( E. coli ligA251 Δ tolC). Testing a single compound concentration and incubation time, we found that, for equipotent compounds, LC-MS/MS values were not predictive of antibacterial activity. This indicates that measured bacteria-associated compound was not necessarily exposed to the target enzyme. Our data suggest that, while exclusion from bacteria is a major reason for poor antibacterial activity of potent compounds, the distribution of compound within the bacterial cell may also be a problem. The relative importance of these factors is likely to vary from one chemical series to another. Our observations provide directions for further study of this difficult issue.

Poly(N-acryloyl ciprofloxacin-co-acrylic acid) grafted magnetite nanoparticles for microbial decontamination of collagen solution: have we conquered the problem of antimicrobial residues?

A strategy to avoid antimicrobial residues in decontaminated collagen solution is provided.

Design, synthesis, and biological evaluation of a novel series of quercetin diacylglucosides as potent anti-MRSA and anti-VRE agents

A series of novel quercetin diacylglucosides were designed and first synthesized by Steglich esterification on the basis of MRSA strains inhibiting natural compound A. The in vitro inhibition of different multi-drug resistant bacterial strains and Escherichia coli DNA gyrase B was investigated. In the series, compound 10h was up to 128-fold more potent against vancomycin-resistant enterococci and more effective than A, which represents a promising new candidate as a potent anti-MRSA and anti-VRE agent.

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.

Characterization of pyrazinamide and ofloxacin resistance among drug resistant Mycobacterium tuberculosis isolates from Singapore

OBJECTIVES

To evaluate rapid molecular approaches for the detection of pyrazinamide (PZA) and ofloxacin resistance, by screening 100 known drug-resistant Mycobacterium tuberculosis isolates.

METHODS

Mycobacterium tuberculosis isolates were tested for phenotypic resistance to pyrazinamide and ofloxacin using the BACTEC 460 radiometric method and the E-test, respectively. Mutation screening was done by amplifying the pncA, gyrA, and gyrB genes by the polymerase chain reaction (PCR) and direct automated sequencing.

RESULTS

Twelve isolates were PZA-resistant and 8 of 12 (66.7%) isolates had missense mutations or deletions at the pncA gene, suggesting that mutation or deletion at the pncA gene is the major molecular mechanism of PZA resistance among the Singaporean isolates. Using the E-test, 48 isolates were resistant to ofloxacin, with minimum inhibitory concentrations of 4 microg/mL or higher. No mutations were observed at the quinolone resistance-determining region (QRDR) of gyrA in all isolates. At the QRDR of gyrB, mutations were present in 1 of 48 ofloxacin-resistant isolates and 0 of 19 ofloxacin-susceptible isolates.

CONCLUSIONS

In Singapore, genotypic analysis of resistance to PZA and ofloxacin is inadequate and should be complemented by conventional methods.

Ofloxacin-loaded liposomes: in vitro activity and drug accumulation in bacteria

Different ofloxacin-loaded unilamellar vesicles were prepared by the extrusion technique, and their antimicrobial activities were determined in comparison to those of the free drug by means of MIC determinations with both American Type Culture Collection standards and wild-type bacterial strains (six strains of Enterococcus faecalis, seven strains of Escherichia coli, six strains of Staphylococcus aureus, and six strains of Pseudomonas aeruginosa). The accumulation of ofloxacin and liposome-ofloxacin was measured by determining the amount of the drug inside the bacteria as a function of time. Encapsulated fluoroquinolone yielded MICs which were at least twofold lower than those obtained with the free drug. In particular, liposomes made up of dimyristoylphosphatidylcholine-cholesterol-dipalmitoylphosphatidylser ine and dimyristoylphosphatidylcholine-cholesterol-dihexadecylphosphate (4:3:4 molar ratio) provided the best improvement in antimicrobial activity against the various bacterial strains investigated. The liposome formulation produced higher intracellular fluoroquinolone concentrations than those achieved simultaneously with the free drug in both E. coli and P. aeruginosa.

Systematic study of parameters influencing the action of Rose Bengal with visible light on bacterial cells: comparison between the biological effect and singlet-oxygen production

As part of a project to study different methods for the disinfection of effluent water, the inactivation of different microorganisms (Escherichia coli, Deinococcus radiodurans and spores of Bacillus subtilis) using a combination of a photosensitizer (Rose Bengal) with simulated sunlight and oxygen was determined under various environmental conditions (temperature, pH index). In parallel, the singlet-oxygen (1O2) production was also measured under the same conditions. Whereas the vegetative cells could be inactivated much more efficiently at increased temperature and altered index of pH, the production of 1O2 remained essentially the same under these alterations. Additionally, the relations among the sensitivities of different cell types to be killed by our photodynamic treatments (PDT) were opposite to those found after exposure to ionizing radiation. The results of photodynamic experiments do not reflect the cells' capacity to repair DNA strand breaks. Spores of B. subtilis, as a nonvegetative system, could not be inactivated by illuminations up to 100 J cm-2. Together, these findings indicate that DNA is not the primary target, the inactivation of which leads to the killing of our test organisms. Instead, the cellular envelope appears to be the component being assaulted by our PDT.

Resolution of high-molecular-weight components in lipopolysaccharides of Escherichia coli, Morganella morganii, Citrobacter freundii and Citrobacter diversus strains with sodium dodecyl sulfate polyacrylamide gels

The use of 0.5% sodium dodecyl sulfate in polyacrylamide separation gels allowed the resolution in several bands of high-molecular-mass components in smooth lipopolysaccharide of bacterial outer membrane from Escherichia coli, Morganella morganii, Citrobacter freundii and Citrobacter diversus. With or without 0.1% SDS, however, such a result was not possible.

Antibiotic resistance in community-acquired respiratory tract infections: current issues

OBJECTIVE

In recent years, antibiotic resistance has emerged as an important global problem. The major goal of this review is to update important issues pertaining to antibiotic resistance, with an emphasis on antibiotic resistance involving community-acquired respiratory pathogens. In addition, this review examines potential reasons why antibiotic resistance has increased in recent years, how clinicians can better understand commonly used laboratory antibiotic resistance tests, and possible solutions to the increasing problem of antibiotic resistance. The article emphasizes the diagnosis, therapy, and prevention of antibiotic-resistant infections.

DATA SOURCES

We identified relevant English-language articles through MEDLINE search (1966 to March 1998). All articles related to antibiotic resistance and the scope of the articles included original investigative articles, reviews, letters, and editorials. In addition, we selected additional references from the bibliographies of the identified articles.

STUDY SELECTION

We selected articles for detailed review if they provided direct insight into the cause of antibiotic resistance, testing for antibiotic resistance, or the treatment of antibiotic resistance. Most, but not all, of the articles selected pertained to antibiotic resistance and respiratory tract infections. We performed a detailed review on approximately 40% of the originally selected articles.

RESULTS

Multiple factors that play a significant role in the development of antibiotic resistance include the overuse of antibiotics in both humans and animals, situations such as day care that enhance transmission via frequent close personal contact, and widespread dissemination of resistant strains via global travel. Most respiratory pathogens have developed resistance to commonly used antibiotics either by producing beta-lactamase or by altering binding site proteins.

CONCLUSIONS

In many regions of the United States, the level of antibiotic resistance has impacted the clinical management of common respiratory pathogens. Future efforts to curtail antibiotic resistance will require a concerted effort in multiple areas, particularly enhanced epidemiologic surveillance to better detect resistance trends, judicious use of antibiotics, and new drug development.

Resistance mechanism of Acinetobacter spp. strains resistant to DW-116, a new quinolone

DW-116 is a new fluoroquinolone antimicrobial agent with a broad spectrum. In order to elucidate the resistance mechanism to DW-116 in Acinetobacter spp. bacteria, total chromosomal DNA was isolated from 10 strains of Acinetobacter spp. resistant to DW-116. Quinolone resistance determinant region (QRDR) of DNA gyrase gene was amplified by PCR. The 345 bp nucleotide fragment yielded was inserted into pKF 3 which was used as the vector. Comparisons of the DNA sequences of 8 strains with that of the wild type strain revealed a Ser-83 to Leu mutation in mutants and all ten strains contained one silent mutation(T-->G) in QRDR. From Acinetobacter MB4-8 strain, DNA gyrase was isolated and purified, through no-vobiocin-sepharose, heparin-sepharose affinity column chromatography. The enzyme was composed of two subunits and the molecular mass of subunits A and B were 75.6 and 51.9 kDa, respectively. The supercoiling activity of the reconstituted DNA gyrase composed of subunit A from Acinetobacter MB4-8 and subunit B from E. coli was not inhibited by 128 micrograms/ml of ciprofloxacin. It might be said that one of the resistance mechanisms to DW-116 in A-cinetobacter MB4-8 was subunit A alteration of DNA gyrase.

Gyrase mutations in laboratory-selected, fluoroquinolone-resistant mutants of Mycobacterium tuberculosis H37Ra

To characterize mechanisms of resistance to fluoroquinolones by Mycobacterium tuberculosis, mutants of strain H37Ra were selected in vitro with ofloxacin. Their quinolone resistance-determining regions for gyrA and gyrB were amplified and sequenced to identify mutations in gyrase A or B. Three types of mutants were obtained: (i) one mutant (TKp1) had no mutations in gyrA or gyrB; (ii) mutants that had single missense mutations in gyrA, and (iii) mutants that had two missense mutations resulting in either two altered gyrase A residues or an altered residue in both gyrases A and B. The TKp1 mutant had slightly reduced levels of uptake of [14C]norfloxacin, which was associated with two- to fourfold increases in the MICs of ofloxacin, ciprofloxacin, and sparfloxacin. Gyrase mutations caused a much greater increase in the MICs of fluoroquinolones. For mutants with single gyrA mutations, the increases in the MICs were 4- to 16-fold, and for mutants with double gyrase mutations, the MICs were increased 32-fold or more compared with those for the parent. A gyrA mutation in TKp1 secondary mutants was associated with 32- to 128-fold increases in the MICs of ofloxacin and ciprofloxacin compared with the MICs for H37Ra and an eight-fold increase in the MIC of sparfloxacin. Sparfloxacin was the most active fluoroquinolone tested. No sparfloxacin-resistant single-step mutants were selected at concentrations of > 2.5 micrograms/ml, and high-level resistance (i.e., MIC, > and = 5 micrograms/ml) was associated with two gyrase mutations. Mutations in gyrB and possibly altered levels of intracellular accumulation of drug are two additional mechanisms that may be used by M. tuberculosis in the development of fluoroquinolone resistance. Because sparfloxacin is more active in vitro and selection of resistance appears to be less likely to occur, it may have important advantage over ofloxacin or ciprofloxacin for the treatment of tuberculosis.

Active efflux of fluoroquinolones in Mycobacterium smegmatis mediated by LfrA, a multidrug efflux pump

The lfrA gene cloned from chromosomal DNA of quinolone-resistant Mycobacterium smegmatis mc2-552 conferred low-level resistance to fluoroquinolones when present on multicopy plasmids. Sequence analysis suggested that lfrA encodes a membrane efflux pump of the major facilitator family (H. E. Takiff, M. Cimino, M. C. Musso, T. Weisbrod, R. Martinez, M. B. Delgado, L Salazar, B. R. Bloom, and W. R. Jacbos, Jr., Proc. Natl. Acad. Sci. USA 93:362-366, 1996). In this work, we studied the role of LfrA in the accumulation of fluoroquinolones by M. smegmatis. The steady-state accumulation level of a hydrophilic quinolone, norfloxacin, by M. smegmatis harboring a plasmid carrying the lfrA gene was about 50% of that by the parent strain but was increased to the same level as that of the parent strain by addition of a proton conductor, carbonyl cyanide m-chorophenylhydrazone. Norfloxacin efflux mediated by LfrA was competed for strongly by ciprofloxacin but not by nalidixic acid. Furthermore, we showed that portions of norfloxacin accumulated by starved cells were pumped out upon reenergization of the cells, and the rates of this efflux showed evidence of saturation at higher intracellular concentrations of the drug. These results suggest that the LfrA polypeptide catalyzes the active efflux of several quinolones.

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.

Pefloxacine mesilate- and ofloxacin-loaded polyethylcyanoacrylate nanoparticles: characterization of the colloidal drug carrier formulation

The entrapment of fluoroquinolones, perfloxacine mesilate (PFX) and ofloxacin (OFX), in polyalkylcyanoacrylate (PECA) nanoparticles could offer some advantages for their biological application; for examples, increasing their bioavailability, controlling the drug time-release in blood, and reducing the formation of bacterial resistance. To load these two drugs in PECA polymeric bulk, the incorporation or adsorption method was performed. These two methods were capable of influencing nanoparticle size, molecular weight, release profile, and drug-polymer association. The incorporation method, particularly for the OFX system, achieved PECA nanoparticle suspensions with a mean size value three times higher than that obtained in the absence of the drug. In contrast, negligible changes were observed for PFX systems. This preparation process also influenced the nanoparticle storage stability. The molecular weight values of the various nanoparticle preparations were also influenced; that is, the PFX-loaded systems showed an enhancement in the average molecular weight values, whereas a reduction was observed for OFX-loaded systems. The adsorption method showed no particular difference in particle size, molecular weight, and storage stability compared with nanoparticles prepared without the drugs. The nanoparticle loading capacity was higher for the colloidal systems obtained following the incorporation preparation procedure. The release of drug from the nanoparticles was biphasic for both preparation processes. The fluoro-quinolone-loaded nanoparticles showed an enhancement of the antimicrobial activity against standard bacteria strains from 2- to 50-fold compared with the free drugs.

Cloning of multidrug resistance gene pqrA from Proteus vulgaris

The multiple antibiotic resistance gene pqrA was cloned from the chromosomal DNA of a clinical isolate of Proteus vulgaris 881051 into Escherichia coli KY2563. The MICs of quinolones tetracycline, cephalosporin, and chloramphenicol for transformant strain DNS7020 were from 8 to 32 times higher than those for the parent strain, KY2563. The level of expression of outer membrane protein F (OmpF) by DNS7020 was lower than that of KY2563 but not as low as that of an OmpF-deficient control strain. The 1.4-kb fragment containing the pqrA gene had an open reading frame encoding a polypeptide of 122 amino acid residues with a molecular weight of about 14,000, which was consistent with the experimental value identified by the Maxicell method. The putative PqrA polypeptide showed significant amino acid sequence similarity to the E. coli proteins SoxS and MarA. These polypeptides are strongly conserved in predicted helix-turn-helix DNA binding domains. The MarA protein, which is responsible for multiple antibiotic resistance in E. coli, also decreases OmpF expression. Moreover, the SoxS protein, which is characterized as a superoxide response regulon of E. coli, has also been shown to increase resistance to many structurally unrelated antibiotics. The soxS gene increases superoxide dismutase levels in addition to decreasing OmpF expression. The expression level of superoxide dismutase with DNS7020 was about 1.5 times higher than that with KY2563. These findings suggest that the pqrA gene in P. vulgaris confers multidrug resistance in a way similar to that of the soxS and marA genes in E. coli.

Resistance to fluoroquinolones in Pseudomonas aeruginosa and Klebsiella pneumoniae

The fluoroquinolone sensitivity of Pseudomonas aeruginosa and Klebsiella pneumoniae was studied by determinations of Minimum Inhibitory Concentrations (MICs) of norfloxacin and ciprofloxacin in consecutive clinical isolates. In P. aeruginosa, resistance or reduced susceptibility (MIC > or = 8 mg/l for norfloxacin and > or = 2 mg/l for ciprofloxacin) was found in 17% (9/54) of the isolates. Reduced susceptibility (MIC > or = 2 mg/l for norfloxacin) was found in 12% (10/84) of K. pneumoniae isolates. P. aeruginosa strains isolated in 1991 had reduced susceptibility to both norfloxacin and ciprofloxacin significantly more often than isolates from 1984-85 (p = 0.02). 10/84 K. pneumoniae strains from 1991 had reduced susceptibility to norfloxacin, compared with 1/34 from 1984-85. This difference was not statistically significant (p = 0.11).

Sequential acquisition of norfloxacin and ofloxacin resistance by methicillin-resistant and -susceptible Staphylococcus aureus

The acquisition of ofloxacin resistance by a susceptible clinical Staphylococcus aureus strain was found to be achieved in two sequential steps: the first step was accompanied by 4-fold increases in the ofloxacin MIC and 8- to 16-fold increases in the norfloxacin MIC. The second step was accompanied by further increases in both the ofloxacin and the norfloxacin MICs. A mutation of the gyrA gene resulting in an amino acid substitution was found in the second-step but not in the first-step resistant subclone. On the other hand, there was no difference in the accumulation of norfloxacin in the parent strain and the resistant subclones of each step. The rates of mutation to resistance in the steps were (1.58 to 6.81) x 10(-9) and (0.71 to 2.59) x 10(-9), respectively, and did not depend on whether the parent strain was resistant to methicillin. Some implications of these observations for clinical as well as mechanistic aspects of the prevalence of methicillin- and ofloxacin-resistant S. aureus are discussed.

Quinolone accumulation in Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus

The accumulation of quinolones by Escherichia coli JF568, Pseudomonas aeruginosa PAO1, and Staphylococcus aureus ATCC 29213 was measured by a modified fluorometric assay (J. S. Chapman and N. H. Georgopapadakou, Antimicrob. Agents Chemother. 33:27-29, 1989). The quinolones examined were fleroxacin, pefloxacin, norfloxacin, difloxacin, A56620, ciprofloxacin, ofloxacin, and Ro 09-1168. In all three organisms, uptake was complete in less than 5 min and was proportional to extracellular quinolone concentrations between 2 and 50 micrograms/ml, which is consistent with simple diffusion. Washing cells with quinolone-free buffer decreased accumulation by up to 70% in E. coli and P. aeruginosa but not in S. aureus. Similarly, incubation with the uncouplers 2,4-dinitrophenol and carbonyl cyanide m-chlorophenylhydrazone increased accumulation up to fourfold in E. coli and P. aeruginosa, though not in S. aureus, suggesting endogenous, energy-dependent efflux. High quinolone hydrophobicity was generally associated with decreased accumulation in E. coli and P. aeruginosa (except in the case of pefloxacin) but was associated with increased accumulation in S. aureus (except in the case of difloxacin). Ciprofloxacin had the highest accumulation in E. coli and P. aeruginosa, while pefloxacin had the highest accumulation in S. aureus.