Comparative in vitro activities of 20 fluoroquinolones against Mycobacterium leprae

Drug Resistance in Nontuberculous Mycobacteria: Mechanisms and Models

The genus Mycobacteria comprises a multitude of species known to cause serious disease in humans, including Mycobacterium tuberculosis and M. leprae, the responsible agents for tuberculosis and leprosy, respectively. In addition, there is a worldwide spike in the number of infections caused by a mixed group of species such as the M. avium, M. abscessus and M. ulcerans complexes, collectively called nontuberculous mycobacteria (NTMs). The situation is forecasted to worsen because, like tuberculosis, NTMs either naturally possess or are developing high resistance against conventional antibiotics. It is, therefore, important to implement and develop models that allow us to effectively examine the fundamental questions of NTM virulence, as well as to apply them for the discovery of new and improved therapies. This literature review will focus on the known molecular mechanisms behind drug resistance in NTM and the current models that may be used to test new effective antimicrobial therapies.

Leprosy: current situation, clinical and laboratory aspects, treatment history and perspective of the uniform multidrug therapy for all patients

In this review, the most relevant and current epidemiological data, the main clinical, laboratory and therapeutical aspects of leprosy are presented. Detailed discussion of the main drugs used for leprosy treatment, their most relevant adverse effects, evolution of the therapeutic regimen, from dapsone as a monotherapy to the proposed polychemotherapy by World Health Organization (WHO) can be found in this CME. We specifically highlight the drug acceptability, reduction in treatment duration and the most recent proposal of a single therapeutic regimen, with a fixed six months duration, for all clinical presentations, regardless of their classification.

Whole cell screen for inhibitors of pH homeostasis in Mycobacterium tuberculosis

Bacterial pathogens like Mycobacterium tuberculosis (Mtb) encounter acidic microenvironments in the host and must maintain their acid-base homeostasis to survive. A genetic screen identified two Mtb strains that cannot control intrabacterial pH (pH_IB) in an acidic environment; infection with either strain led to severe attenuation in mice. To search for additional proteins that Mtb requires to survive at low pH, we introduced a whole-cell screen for compounds that disrupt pH_IB, along with counter-screens that identify ionophores and membrane perturbors. Application of these methods to a natural product library identified four compounds of interest, one of which may inhibit novel pathway(s). This approach yields compounds that may lead to the identification of pathways that allow Mtb to survive in acidic environments, a setting in which Mtb is resistant to most of the drugs currently used to treat tuberculosis.

Synthesis of N-substituted 2-[(1E)-alkenyl]-4-(1H)-quinolone derivatives as antimycobacterial agents against non-tubercular mycobacteria

In an effort to improve biological activities and to examine antimycobacterial-lipophilicity relationships of 2-[(1E)-alkenyl)]-4-(1H)-quinolones, we have synthesized a series of 30 quinolones by introducing several alkyl groups, an alkenyl and an alkynyl group at N-1. All synthetic compounds were first tested in vitro against Mycobacterium smegmatis and the most active compounds (MIC values ∼3.0–7.0 μM) were further examined against three other rapidly growing strains of mycobacteria using a microtiter broth dilution assay. The Clog P values of the synthetic compounds were calculated to provide an estimate of their lipophilicity. Compounds 18e, 19a and 19b displayed the most potent inhibitory effect against M. smegmatis mc²155 with an MIC value of ∼1.5 μM, which was twenty fold and thirteen fold more potent than isoniazid and ethambutol, respectively. On the other hand, compounds 17e, 18e and 19a were most active against Mycobacterium fortuitum and Mycobacterium phlei with an MIC value of ∼3.0 μM. In the human diploid embryonic lung cell line MRC-5 cytotoxicity assay, the derivatives showed moderate to strong cytotoxic activity. Although the antimycobacterial activity of our synthetic compounds could not be correlated with the calculated log P values, an increase in lipophilicity enhances the antimycobacterial activity and C₁₃–C₁₅ total chain length at positions 1 and 2 is required to achieve optimal inhibitory effect against the test strains.

Expression and purification of an active form of the Mycobacterium leprae DNA gyrase and its inhibition by quinolones

Mycobacterium leprae, the causative agent of leprosy, is noncultivable in vitro; therefore, evaluation of antibiotic activity against M. leprae relies mainly upon the mouse footpad system, which requires at least 12 months before the results become available. We have developed an in vitro assay for studying the activities of quinolones against the DNA gyrase of M. leprae. We overexpressed in Escherichia coli the M. leprae GyrA and GyrB subunits separately as His-tagged proteins by using a pET plasmid carrying the gyrA and gyrB genes. The soluble 97.5-kDa GyrA and 74.5-kDa GyrB subunits were purified by nickel chelate chromatography and were reconstituted as an enzyme with DNA supercoiling activity. Based on the drug concentrations that inhibited DNA supercoiling by 50% or that induced DNA cleavage by 25%, the 13 quinolones tested clustered into three groups. Analysis of the quinolone structure-activity relationship demonstrates that the most active quinolones against M. leprae DNA gyrase share the following structural features: a substituted carbon at position 8, a cyclopropyl substituent at N-1, a fluorine at C-6, and a substituent ring at C-7. We conclude that the assays based on DNA supercoiling inhibition and drug-induced DNA cleavage on purified M. leprae DNA gyrase are rapid, efficient, and safe methods for the screening of quinolone derivatives with potential in vivo activities against M. leprae.

Mycobacterium leprae is naturally resistant to PA-824

Leprosy responds very slowly to the current multidrug therapy, and hence there is a need for novel drugs with potent bactericidal activity. PA-824 is a 4-nitroimidazo-oxazine that is currently undergoing phase I clinical trials for the treatment of tuberculosis. The activity of PA-824 against Mycobacterium leprae was tested and compared with that of rifampin in axenic cultures, macrophages, and two different animal models. Our results conclusively demonstrate that PA-824 has no effect on the viability of M. leprae in all three models, consistent with the lack of the nitroimidazo-oxazine-specific nitroreductase, encoded by Rv3547 in the M. leprae genome, which is essential for activation of this molecule.

The continuing challenges of leprosy

Leprosy is best understood as two conjoined diseases. The first is a chronic mycobacterial infection that elicits an extraordinary range of cellular immune responses in humans. The second is a peripheral neuropathy that is initiated by the infection and the accompanying immunological events. The infection is curable but not preventable, and leprosy remains a major global health problem, especially in the developing world, publicity to the contrary notwithstanding. Mycobacterium leprae remains noncultivable, and for over a century leprosy has presented major challenges in the fields of microbiology, pathology, immunology, and genetics; it continues to do so today. This review focuses on recent advances in our understanding of M. leprae and the host response to it, especially concerning molecular identification of M. leprae, knowledge of its genome, transcriptome, and proteome, its mechanisms of microbial resistance, and recognition of strains by variable-number tandem repeat analysis. Advances in experimental models include studies in gene knockout mice and the development of molecular techniques to explore the armadillo model. In clinical studies, notable progress has been made concerning the immunology and immunopathology of leprosy, the genetics of human resistance, mechanisms of nerve injury, and chemotherapy. In nearly all of these areas, however, leprosy remains poorly understood compared to other major bacterial diseases.

Antimycobacterial activities of novel levofloxacin analogues

In order to investigate structure-activity relationships between antimycobacterial activities and basic substituents at the C-10 position of levofloxacin (LVFX), we synthesized a series of pyridobenzoxazine derivatives by replacement of the N-methylpiperazinyl group of LVFX with various basic substituents. A compound with a 3-aminopyrrolidinyl group had one-half the activity of LVFX against Mycobacterium avium, M. intracellulare, and M. tuberculosis. Mono- and dimethylation of the 3-amino moiety of the pyrrolidinyl group increased the activities against M. avium and M. intracellulare but not those against M. tuberculosis. On the other hand, dialkylation at the C-4 position of the 3-aminopyrrolidinyl group enhanced the activities against M. avium, M. intracellulare, and M. tuberculosis. Thus, introduction of an N-alkyl or a C-alkyl group(s) into the 3-aminopyrrolidinyl group may contribute to an increase in potency against M. avium, M. intracellulare, and/or M. tuberculosis, probably through elevation of the lipophilicity. However, among the compounds synthesized, compound VII, which was a 2,8-diazabicyclo[4.3.0]nonanyl derivative with relatively low lipophilicity, showed the most potent activity against mycobacterial species: the activity was 4- to 32-fold more potent than that of LVFX and two to four times as potent as that of gatifloxacin. These results suggested that an increase in the lipophilicity of LVFX analogues in part contributed to enhancement of antimycobacterial activities but that lipophilicity of the compound was not a critical factor affecting the potency.

Bactericidal activity of a single-dose combination of ofloxacin plus minocycline, with or without rifampin, against Mycobacterium leprae in mice and in lepromatous patients

To develop a fully supervisable, monthly administered regimen for treatment of leprosy, the bactericidal effect of a single-dose combination of ofloxacin (OFLO) and minocycline (MINO), with or without rifampin (RMP), against Mycobacterium leprae was studied in the mouse footpad system and in previously untreated lepromatous leprosy patients. Bactericidal activity was measured by the proportional bactericidal method. In mouse experiments, the activity of a single dose of the combination OFLO-MINO was dosage related; the higher dosage of the combination displayed bactericidal activity which was significantly inferior to that of a single dose of RMP, whereas the lower dosage did not exhibit a bactericidal effect. In the clinical trial, 20 patients with previously untreated lepromatous leprosy were treated with a single dose consisting of either 600 mg of RMP plus 400 mg of OFLO and 100 mg of MINO or 400 mg of OFLO plus 100 mg of MINO. The OFLO-MINO combination exhibited definite bactericidal activity in 7 of 10 patients but was less bactericidal than the RMP-OFLO-MINO combination. Both combinations were well tolerated. Because of these promising results, a test of the efficacy of multiple doses of ROM in a larger clinical trial appears justified.

Pathology of iris in leprosy

AIM

The histopathological features of the iris in leprosy were studied by light microscopy.

METHOD

Formalin fixed and paraffin embedded iris tissue excised during cataract surgery from 20 leprosy patients were sectioned and studied with haematoxylin and eosin stain and modified Fite Faraco's stain for acid fast bacilli (AFB).

RESULTS

Chronic inflammatory reactions were seen in the iris of 11 patients, seven of whom did not have any clinically demonstrable evidence of iridocyclitis. Smooth muscle disruption and destruction were seen in two specimens. AFB were found in the iris tissue of a polar lepromatous patient whose skin smears were negative for AFB and who had completed the WHO recommended antileprosy multidrug therapy (MDT).

CONCLUSION

Histopathology discloses far more silent chronic iridocyclitis in leprosy patients than are diagnosed clinically. AFB can persist in the iris tissue even after completion of MDT. Smooth muscle disruption and destruction, a cause of the miotic pupil in leprosy has been conclusively demonstrated histopathologically.

Sparfloxacin worldwide in vitro literature: isolate data available through 1994

Sparfloxacin is a piperazinyl, cyclopropyl-fluoroquinolone with broad-spectrum antibacterial activity. Compared to other quinolones, sparfloxacin displays improved activity against a variety of pathogens including Staphylococcus, Streptococcus, Enterococcus, Chlamydia, Mycoplasma, Ureaplasma, and Mycobacteria species. Other susceptible organism group include Haemophilus, Legionella, Moraxella, Neisseria, Aeromonas, Acinetobacter, Bordetella, Brucella, Campylobacter, Gardnerella, and Helicobacter species. Most Enterobacteriaceae are also susceptible, whereas most isolates of Pseudomonas aeruginosa are not. Sparfloxacin is bactericidal. Activity is generally stable to variations of inoculum, pH, and cation concentration, and it is unchanged in the presence of 5% sodium cholate or 70% human serum. Susceptibility to the drug is diminished in urine. Cross-resistance, although incomplete, has been documented with other quinolones, but not with other antimicrobic classes.

Chemotherapy of lepromatous leprosy: recent developments and prospects for the future

Leprosy is a major debilitating infectious disease, primarily of the developing world. In this paper the current status and future prospects of antimicrobial therapy of the severe anergic lepromatous form of the disease are reviewed. Until the last few years only dapsone, rifampicin, clofazimine and ethionamide have had practical application in its therapy, and only rifampicin was bactericidal. Recently, antibiotics from three different classes have been found to be bactericidal in lepromatous patients: a tetracycline (minocycline), a macrolide (clarithromycin), and several fluoroquinolones (including pefloxacin, ofloxacin and sparfloxacin). Against a background of drug resistance and bacterial persistence, recommendations for multidrug therapy and the means to devise rationally based therapy for the future are discussed.

Effectiveness of various antimicrobial agents against Mycobacterium avium complex in the beige mouse model

The results of five chemotherapeutic experiments in beige mice infected with organisms of the Mycobacterium avium complex are presented. After monotherapy with various antimicrobial agents for 4 weeks, only clarithromycin, amikacin, and ethambutol displayed definite bactericidal effects; sparfloxacin and clofazimine showed modest bacteriostatic effects; and rifampin and rifabutin were totally inactive against the isolate tested. After treatment for 4 weeks, the large quantities of clofazimine that had accumulated in the organs of mice seriously interfered with the enumeration of the CFU and assessment of the efficacy of the treatment. The in vitro synergistic effects of drug combinations against M. avium complex were not confirmed in beige mice. In combination with clarithromycin, amikacin could prevent the selection of clarithromycin-resistant mutants, whereas minocycline could not.

Mycobacterial cell wall: structure and role in natural resistance to antibiotics

Mycobacteria show a high degree of intrinsic resistance to most antibiotics and chemotherapeutic agents. The low permeability of the mycobacterial cell wall, with its unusual structure, is now known to be a major factor in this resistance. Thus hydrophilic agents cross the cell wall slowly because the mycobacterial porin is inefficient in allowing the permeation of solutes and exists in low concentration. Lipophilic agents are presumably slowed down by the lipid bilayer which is of unusually low fluidity and abnormal thickness. Nevertheless, the cell wall barrier alone cannot produce significant levels of drug resistance, which requires synergistic contribution from a second factor, such as the enzymatic inactivation of drugs.

Clinical trial of sparfloxacin for lepromatous leprosy

Nine previously untreated patients with lepromatous leprosy were treated with 200 mg of sparfloxacin daily for 12 weeks to determine whether this drug is bactericidal for Mycobacterium leprae in humans. The efficacy of therapy was monitored both clinically and by measuring changes in morphological index, mouse footpad infectivity, and the radiorespirometric activity of M. leprae organisms obtained from serial biopsy specimens and also by determining titers of phenolic glycolipid-I in serum. Most patients showed clinical improvement within 2 weeks of treatment; this was accompanied by significant reductions in the morphological index, mouse footpad infectivity, and bacillary radiorespirometric activity. After 4 weeks of treatment, all patients had a morphological index of zero and specimens from most patients were noninfectious for mice, while the median decrease in radiorespirometric activity was > 99%. Overall results by the rapid radiorespirometric assay paralleled those of the mouse footpad and morphological index assays. Sparfloxacin given at 200 mg once daily appears to be rapidly bactericidal in humans, with activity similar to that observed in a previous clinical trial with 400 mg of ofloxacin.

Development of an in vitro drug screening system for Mycobacterium leprae based on the determination of the intrabacterial sodium to potassium ratio of individual bacterial organisms

In vitro drug effects on Mycobacterium leprae (M. leprae) in a cell-free system have been monitored by mass spectrometric determination of the ratio of the intrabacterial concentrations of the sodium and potassium ions (Na(+), K(+) ratio) of a limited number of individual bacteria per sample. From the drug-induced increase of the median values of the distributions of the Na(+), K(+) ratio, information on the concentration and time dependence of drug effects as well as on antagonistic or synergistic interactions of drugs has been obtained. Moreover, absolute values for the percentage of killed bacteria (% kill) have been derived from the distribution of the Na(+), K(+) ratios within a bacterial population. For this, the limiting value of the Na(+), K(+) ratio (up to which bacteria are viable) -which had been determined as 0.45 for cultivable bacteria - has been presumed to be valid also for M. leprae. Highest killing rates have been observed for fusidic acid and clarithromycin, followed by rifabutine, rifampin, and clofazimine. Minocycline and dapsone have shown only moderate killing effects and isoniazid and - probably due to the restricted metabolism of M. leprae in a cell-free medium - ofloxacin have been completely inactive. Strong ofloxacin effects, however, have been observed for cultivable mycobacteria and intracellular M. leprae phagocytized by a murine macrophage cell line.

Chemotherapy of leprosy--current status and future prospects

The introduction of multi-drug therapy (MDT) by the World Health Organization in 1982 has proved to be the most important advance in the management and control of leprosy since the first use of the sulphone drugs 40 years earlier. For the first time, the number of registered leprosy cases has shown a decline from a peak of 5.37 million in 1985 to 3.1 million in February 1992. The 2 standard MDT regimens have proved simple to apply in most parts of the world, are relatively cheap, generally acceptable, and have shown remarkably few toxic side-effects. Nevertheless, difficulties have arisen in distinguishing between multibacillary and paucibacillary leprosy, especially when skin smears are of poor quality. Relapses in paucibacillary leprosy have proved difficult to distinguish from late reversal reactions. In multibacillary leprosy, the duration of treatment, 2-10 years in lepromatous leprosy, is a source of difficulty, and in addition light-skinned patients dislike the skin discolouration caused by clofazimine, for fear that their diagnosis might be discovered. The discovery that 3 different groups of drugs are highly bactericidal for the leprosy bacillus, although not so rapidly bactericidal as rifampicin, raises the possibility of having simplified, shorter, or better supervised regimens in the future as second generation MDT. These drugs include the 4-fluoroquinolones, pefloxacin, ofloxacin and sparfloxacin, the tetracycline minocycline, and the macrolide clarithromycin. Finally, in low-prevalence areas it is opportune to consider chemoprophylaxis and immunoprophylaxis for child contacts of lepromatous patients.

Effects of fixation on polymerase chain reaction detection of Mycobacterium leprae

The effects of standard fixatives (10% neutral buffered formalin, ethanol and mercury based) on the detection of Mycobacterium leprae DNA by the polymerase chain reaction (PCR) were studied. Mercury-based fixatives (Zenker's and Carnoy-Lebrun's fluids) strongly inhibited PCR amplification of M. leprae DNA. Ten percent neutral buffered formalin was inhibitory, but significant inhibition was observed only when fixation times exceeded 24 h. Ethanol-based fixatives provided the best medium for holding specimens for subsequent PCR with both free bacilli and skin biopsy specimens containing M. leprae. The M. leprae-specific, 360-bp region of the 18-kDa protein gene could be amplified from paraffin-embedded sections of formalin-fixed skin biopsy specimens from patients with either multibacillary or paucibacillary infections when proper fixation conditions were used. Results of the study demonstrate that tissues properly fixed with two standard fixatives (10% neutral buffered formalin and 50 or 70% ethanol) can be analyzed by PCR for the presence of M. leprae with no loss in specificity and only minimal diminution in sensitivity compared with the specificities and sensitivities obtained by use of freshly prepared, unfixed specimens.

Activities of various quinolone antibiotics against Mycobacterium leprae in infected mice

Previously, pefloxacin and ofloxacin were found to be active against Mycobacterium leprae in vitro, in experimental animals, and in clinical trials of lepromatous leprosy patients. In this study, we compared certain more recently developed fluoroquinolones (lomefloxacin, PD 124816, WIN 57273, temafloxacin, and sparfloxacin) with pefloxacin and ofloxacin in M. leprae-infected mice at doses of 50, 150, and 300 mg/kg given five times weekly. All seven of the fluoroquinolones studies were active against M. leprae; temafloxacin and sparfloxacin were the most active, being fully bactericidal at all three dosage schedules. Additionally, sparfloxacin was found to be fully bactericidal at 15 and 30 mg/kg given five times weekly.

Fusidic acid is highly active against extracellular and intracellular Mycobacterium leprae

The activity of fusidic acid against Mycobacterium leprae was studied in axenic medium and in bacilli residing within mouse peritoneal macrophages. Activity was assessed by subsequent quantitation of bacillary radiorespirometric activity. Significant inhibition in both systems was observed at 0.156 micrograms/ml, and an approximately 50% reduction in activity occurred after exposure to 1.25 to 2.5 micrograms/ml. The excellent human pharmacokinetics and in vitro activity of fusidic acid against the leprosy bacillus warrant a clinical trial of this drug for leprosy.

Ofloxacin. A reappraisal of its antimicrobial activity, pharmacology and therapeutic use

Ofloxacin is a fluoroquinolone whose primary mechanism of action is inhibition of bacterial DNA gyrase. In vitro it has a broad spectrum of activity against aerobic Gram-negative and Gram-positive bacteria, although it is poorly active against anaerobes. Ofloxacin, unlike most other broad spectrum antibacterial drugs, can be administered orally as well as intravenously. Penetration into body tissues and fluids is highly efficient. Clinical trials with orally and intravenously administered ofloxacin have confirmed its potential for use in a wide range of infections, where it has generally proved as effective as standard treatments. Ofloxacin in well tolerated, and in comparison with other available fluoroquinolones is less likely to cause clinically relevant drug interactions. Ofloxacin thus offers a valuable oral treatment (with an option for intravenous administration if necessary) for use in a wide range of clinical infections, but with a particular advantage in more severe or chronic infections when recourse to parenteral broad spectrum agents would normally be required, thereby providing cost savings and additionally allowing outpatient treatment.

In vitro activity of sparfloxacin (CI-978, AT-4140, and PD 131501). A quinolone with high activity against gram-positive bacteria

Sparfloxacin (CI-978, AT-4140 and PD 131501) is a new antimicrobial agent of the piperazinyl quinolone class. Relative to other quinolones, it is a potent antistaphylococcal and antistreptococcal drug in vitro: The microbroth 90% minimum inhibitory concentration (MIC90) (in microgram/ml) was 0.25 vs 26 methicillin-resistant and -sensitive coagulase-positive and -negative staphylococci and 20 Streptococcus pneumoniae; 0.5 vs 20 strains each of S. pyogenes, S. agalactiae, and Enterococcus faecalis. The data indicate sparfloxacin to be generally superior to ciprofloxacin, ofloxacin, oxacillin, cefazolin, doxycycline, amikacin, and vancomycin against these Gram-positive bacterial groups. Additional MIC90s were determined for Haemophilus influenzae, Moraxella (Branhamella) catarrhalis, and Neisseria gonorrhoeae (less than or equal to 0.03); Enterobacteriaceae (0.5); and Listeria monocytogenes (1). Activity was generally unchanged with light, 50% human serum, aerobic-anaerobic atmosphere, 5% sodium cholate, cation supplementation, and 100-fold increased or decreased inoculum; as with other quinolones, potency was measurably diminished with decreasing pH (pH less than or equal to 6.0) and in 100% urine. Naturally occurring resistant mutants occurred at frequencies of 10(-8) or lower.

In vitro activities of aminoglycosides, lincosamides, and rifamycins against Mycobacterium leprae

The in vitro activities of a variety of aminoglycosides, lincosamides, and rifamycins against Mycobacterium leprae were evaluated with the BACTEC 460 system. At 20 micrograms/ml, gentamicin, kanamycin, tobramycin, streptomycin, and amikacin were inactive. Lincomycin was active at 20 micrograms/ml, and clindamycin was active at 0.31 micrograms/ml. Rifamycin SV, rifabutin, and rifampin were active at 3.1, 3.1 to 12.5, and 200 ng/ml, respectively. The in vitro assay correlates well with the in vivo response of M. leprae to antimicrobial agents, with the exception of the aminoglycosides.

Newly documented antimicrobial activity of quinolones

The improved antimicrobial activity of newer fluoroquinolones and novel applications recently found for the drugs already marketed are reviewed. Several new compounds are more active against gram-positive bacteria than the presently marketed fluoroquinolones. WIN 57273, the most potent compound in vitro on a weight basis, is 16 to 128 times more active than ciprofloxacin against various staphylococci, streptococci, Enterococcus spp., Corynebacterium spp., Listeria monocytogenes and Bacillus spp. BMY 40062, PD 117558, PD 127391, sparfloxacin, temafloxacin and tosufloxacin also show enhanced in vitro efficacy against these species. These drugs also possess increased activity against various anaerobes, notably Clostridium perfringens, Clostridium difficile and the Bacteroides fragilis group. Mycobacterium tuberculosis, rapidly growing mycobacteria other than Mycobacterium chelonae, and Mycobacterium leprae are often susceptible to quinolones displaying bactericidal activity which is potentially useful for curing difficult-to-treat mycobacteriosis. In addition, a number of new products, notably those containing a cyclopropyl group, are more active than reference fluoroquinolones against Mycobacterium leprae. Sparfloxacin, BMY 40062 and WIN 57273 compare favorably with older fluoroquinolones in the killing of intracellular Legionella spp., and several of the newer compounds have greater antichlamydial potency. Improved antibacterial activity has also been found against Mycoplasma hominis, Ureaplasma urealyticum, Acinetobacter spp. and Pseudomonas maltophilia. By contrast, the newer quinolones have similar or less activity against Pseudomonas aeruginosa and Enterobacteriaceae. Recently, pefloxacin, ofloxacin and ciprofloxacin were found to be active against protozoa, including Plasmodium spp., Trypanosoma cruzi and Leishmania donovani, but not against Toxoplasma gondii. In the near future, more specific research testing unusual pathogens may lead to the identification of quinolones with more selective activity.

A review of the antimicrobial activity of the fluoroquinolones

The evolution of the fluoroquinolones is described, and structure-activity relationships outlined. The in-vitro antimicrobial activities of ciprofloxacin, enoxacin, norfloxacin, ofloxacin and pefloxacin against a wide range of organisms are critically reviewed. In-vitro factors influencing fluoroquinolone activity are discussed. Reports of the acquisition of resistance to the fluoroquinolones are evaluated. Finally, possible future directions for this group of antibiotics are discussed.