In vitro and in vivo antibacterial activities of DK-507k, a novel fluoroquinolone

Emergence of Neisseria gonorrhoeae Clone with Reduced Susceptibility to Sitafloxacin in China: An In Vitro and Genomic Study

Drug-resistant Neisseria gonorrhoeae poses an urgent threat to public health. Recently, sitafloxacin, a new-generation fluoroquinolone, has shown high in vitro activity against drug-resistant N. gonorrhoeae. However, data on its effectiveness in clinical isolates remains limited. In this study, we collected 507 N. gonorrhoeae isolates from 21 hospitals in Shanghai, China, during 2020 and 2021. Antimicrobial susceptibility testing revealed that sitafloxacin minimum inhibitory concentrations (MICs) exhibited a bimodal distribution, ranging from <0.004 to 2 mg/L. The MIC50 and MIC90 for sitafloxacin were 0.125 mg/L and 0.5 mg/L, respectively, which are 32 and 16 times lower than those for ciprofloxacin (4 mg/L and 8 mg/L, respectively). Sitafloxacin demonstrated high in vitro activity against isolates resistant to either ceftriaxone, azithromycin, or both. Notably, among the isolates with reduced sitafloxacin susceptibility (MIC ≥ MIC90), 83.7% (36/43) were identified as sequence type (ST) 8123. Further phylogenetic analysis showed that ST8123 has evolved into two subclades, designated as subclade-I and subclade-II. A majority of the isolates (80%, 36/45) within subclade-I exhibited reduced susceptibility to sitafloxacin. In contrast, all isolates from subclade-II were found to be susceptible to sitafloxacin. Subsequent genomic investigations revealed that the GyrA-S91F, D95Y, and ParC-S87N mutations, which were exclusively found in ST8123 subclade-I, might be linked to reduced sitafloxacin susceptibility. Our study reveals that sitafloxacin is a promising antibiotic for combating drug-resistant N. gonorrhoeae. However, caution is advised in the clinical application of sitafloxacin for treating N. gonorrhoeae infections due to the emergence of a clone exhibiting reduced susceptibility.

Quinolone derivatives and their activities against methicillin-resistant Staphylococcus aureus (MRSA)

Methicillin-resistant Staphylococcus aureus (MRSA) is the most common pathogen both in hospital and community settings, and is capable of causing serious and even fatal infections. Several antibiotics have been approved for the treatment of infections caused by MRSA, but MRSA has already developed resistance to them. More than ever, it's imperative to develop novel, high effective and fast acting anti-MRSA agents. Quinolones are one of the most common antibiotics in clinical practice used to treat various bacterial infections, and some of them displayed excellent in vitro and in vivo anti-MRSA activities, so quinolone derivatives are one of the most promising candidates. This review summarizes the recent developments of quinolone derivatives with potential activity against MRSA, and the structure-activity relationship is also discussed.

Microbial Biofilms in Urinary Tract Infections and Prostatitis: Etiology, Pathogenicity, and Combating strategies

Urinary tract infections (UTIs) are one of the most important causes of morbidity and health care spending affecting persons of all ages. Bacterial biofilms play an important role in UTIs, responsible for persistent infections leading to recurrences and relapses. UTIs associated with microbial biofilms developed on catheters account for a high percentage of all nosocomial infections and are the most common source of Gram-negative bacteremia in hospitalized patients. The purpose of this mini-review is to present the role of microbial biofilms in the etiology of female UTI and different male prostatitis syndromes, their consequences, as well as the challenges for therapy.

Analysis of Mechanism-Based Inhibition of CYP 3A4 by a Series of Fluoroquinolone Antibacterial Agents

A series of fluoroquinolone compounds (compounds 1-9), which contain a common quinolone scaffold, inactivated the metabolic activity of CYP3A. The purpose of this study was to identify mechanism-based inhibition (MBI) among these fluoroquinolone compounds by metabolite profiling to elucidate the association of the substructure and MBI potential. Reversibility of MBI after incubation with potassium ferricyanide differed among the test compounds. Representative quasi-irreversible inhibitors form a metabolite-intermediate (MI) complex with the heme of CYP3A4 according to absorption analysis. Metabolite profiling identified the cyclopropane ring-opened metabolites from representative irreversible inhibitors, suggesting irreversible binding of the carbon-centered radical species with CYP3A4. On the other hand, the oxime form of representative quasi-irreversible inhibitors was identified, suggesting generation of a nitroso intermediate that could form the MI complex. Metabolites of compound 10 with a methyl group at the carbon atom at the root of the amine moiety of compound 8 include the oxime form, but compound 10 did not show quasi-irreversible inhibition. The docking study with CYP3A4 suggested that a methyl moiety introduced at the carbon atom at the root of the primary amine disrupts formation of the MI complex between the heme and the nitroso intermediate because of steric hindrance. This study identified substructures of fluoroquinolone compounds associated with the MBI mechanism; introduction of substituted groups inducing steric hindrance with the heme of P450 can prevent formation of an MI complex. Our series of experiments may be broadly applicable to prevention of MBI at the drug discovery stage.

Bacterial Infections in the Elderly Patient: Focus on Sitafloxacin

Sitafloxacin (DU-6859a) is a new-generation oral fluoroquinolone with in vitro activity against a broad range of Gram-positive and -negative bacteria, including anaerobic bacteria, as well as against atypical bacterial pathogens. Particularly in Japan this antibiotic was approved in 2008 for treatment of a number of bacterial infections caused by Gram-positive cocci and Gram-negative cocci and rods, including anaerobia atypical bacterial pathogens. As compared to oral levofloxacin sitafloxacin was non-inferior in the treatment of community-acquired pneumonia and non-inferior in the treatment of complicated urinary tract infections, according to the results of randomized, double-blind, multicentre, non-inferiority trials. Non-comparative studies demonstrated the efficacy of oral sitafloxacin in otorhinolaryngological infections, urethritis in men, cervicitis in women and odontogenic infections. Most common adverse reactions were gastrointestinal disorders and laboratory abnormalities in patients receiving oral sitafloxacin; diarrhea and liver enzyme elevations were among the common. In the Japanese population sitafloxacin covers broad spectrum of bacteria as compared to carbapenems, whereas in the Caucasians its use is currently limited due to the potential for ultraviolet A phototoxicity. Sitafloxacin is a promising therapeutic agent which merits further investigation in randomized clinical trials of elderly patients.

Quinolone-Based Third-Line Therapy for Helicobacter pylori Eradication

Currently, a standard third-line therapy for Helicobacter pylori (H. pylori) eradication remains to be established. Quinolones show good oral absorption, no major side effects, and marked activity against H. pylori. Several authors have studied quinolone-based third-line therapy and reported encouraging results, with the reported H. pylori cure rates ranging from 60% to 84%. Resistance to quinolones is easily acquired, and the resistance rate is relatively high in countries with a high consumption rate of these drugs. We recently reported a significant difference in the eradication rate obtained between patients infected with gatifloxacin-susceptible and gatifloxacin-resistant H. pylori, suggesting that the selection of quinolones for third-line therapy should be based on the results of drug susceptibility testing. As other alternatives of third-line rescue therapies, rifabutin-based triple therapy, high-dose proton pump inhibitor/amoxicillin therapy and furazolidone-based therapy have been suggested.

Antimicrobial-resistant Streptococcus pneumoniae: trends and management

Management of pneumococcal infections has been challenged by the development of resistance and, more recently, the unexpected spread of resistant clones of serotypes, such as 19A, following the introduction of a conjugate pneumococcal vaccine for use in children in 2000. High-dose penicillin G and many other agents continue to be efficacious parenterally for pneumonia and bacteremia. However, treatment options for meningitis and for infections treated with oral agents, particularly in children, have been limited by resistance. Empiric treatment guidelines should reflect the emerging threats from increased drug resistance. Compliance with guidelines by physicians and patients is important to prevent further development of resistance as new classes of agents are unlikely to be available in the next decade.

In vitro activity of the quinolone WCK 771 against recent U.S. hospital and community-acquired Staphylococcus aureus pathogens with various resistance types

WCK 771 demonstrated MIC(50) and MIC(90)s of 0.03 and 1 microg/ml, respectively, against 297 recent U.S. community-acquired and hospital strains of Staphylococcus aureus, irrespective of quinolone or glycopeptide resistance. Against quinolone-resistant strains, MIC(90)s of WCK 771 and moxifloxacin were 1 and 16 microg/ml, respectively.

In vitro and in vivo antibacterial activities of DC-159a, a new fluoroquinolone

DC-159a is a new 8-methoxy fluoroquinolone that possesses a broad spectrum of antibacterial activity, with extended activity against gram-positive pathogens, especially streptococci and staphylococci from patients with community-acquired infections. DC-159a showed activity against Streptococcus spp. (MIC(90), 0.12 microg/ml) and inhibited the growth of 90% of levofloxacin-intermediate and -resistant strains at 1 microg/ml. The MIC 90s of DC-159a against Staphylococcus spp. were 0.5 microg/ml or less. Against quinolone- and methicillin-resistant Staphylococcus aureus strains, however, the MIC 90 of DC-159a was 8 microg/ml. DC-159a was the most active against Enterococcus spp. (MIC 90, 4 to 8 microg/ml) and was more active than the marketed fluoroquinolones, such as levofloxacin, ciprofloxacin, and moxifloxacin. The MIC 90s of DC-159a against Haemophilus influenzae, Moraxella catarrhalis, and Klebsiella pneumoniae were 0.015, 0.06, and 0.25 microg/ml, respectively. The activity of DC-159a against Mycoplasma pneumoniae was eightfold more potent than that of levofloxacin. The MICs of DC-159a against Chlamydophila pneumoniae were comparable to those of moxifloxacin, and DC-159a was more potent than levofloxacin. The MIC 90s of DC-159a against Peptostreptococcus spp., Clostridium difficile, and Bacteroides fragilis were 0.5, 4, and 2 microg/ml, respectively; and among the quinolones tested it showed the highest level of activity against anaerobic organisms. DC-159a demonstrated rapid bactericidal activity against quinolone-resistant Streptococcus pneumoniae strains both in vitro and in vivo. In vitro, DC-159a showed faster killing than moxifloxacin and garenoxacin. The bactericidal activity of DC-159a in a murine muscle infection model was revealed to be superior to that of moxifloxacin. These activities carried over to the in vivo efficacy in the murine pneumonia model, in which treatment with DC-159a led to bactericidal activity superior to those of the other agents tested.

Tissue and Fluid Penetration of Garenoxacin in Surgical Patients

BACKGROUND AND PURPOSE

Garenoxacin is a novel des-F(6)-quinolone that exhibits broad-spectrum activity against a wide range of aerobic and anaerobic pathogens of clinical importance. This study examined the penetration of garenoxacin into sinus mucosa, incisional skin, subcutaneous tissue, bile, adipose tissue, striated muscle, bone, gallbladder wall, liver, small and large bowel mucosa, and mesenteric lymph nodes relative to the plasma concentration after an oral 600 mg dose.

METHODS

A series of 30 patients, ages 20 to 83 years, undergoing elective surgery were enrolled. Patients received a single 600 mg oral dose of garenoxacin before surgery. Blood and tissue specimens were collected at surgery 3-5 h post-dose, and garenoxacin concentrations were determined using validated liquid chromatography/tandem mass spectrometry assays designed specifically for each tissue and biofluid.

RESULTS

The mean plasma or bile (mcg/mL) and tissue (mcg/g) concentrations ( +/- standard deviation) were plasma 5.71 +/- 3.44, bile 7.59 +/- 9.96, adipose tissue 0.90 +/- 0.54, subcutaneous tissue 1.19 +/- 1.23, incisional skin 3.06 +/- 1.74, striated muscle 3.92 +/- 2.54, bone 2.82 +/- 2.42, sinus mucosa 5.26 +/- 3.84, liver 1.84 +/- 0.75, gallbladder 11.59 +/- 11.94, large intestine 12.13 +/- 9.34, small intestine 15.66 +/- 19.20, and mesenteric lymph node 3.10 +/- 2.44.

CONCLUSION

After a single 600 mg oral dose, garenoxacin penetrates well into selected tissues and fluids. In addition, the tissue and fluid concentrations at 3-5 hours post-dose exceeded the minimum inhibitory concentration-90% of most targeted pathogens, suggesting that garenoxacin would be effective in the treatment of sinus, skin and skin structure, and intra-abdominal infections.

Anti-MRSA agents: under investigation, in the exploratory phase and clinically available

Staphylococcal infections are difficult to treat due to the rapid emergence of methicillin-resistant staphylococci and, unfortunately, vancomycin-intermediate or -resistant staphylococci. Numerous alternative treatments are urgently required. In this special report, intensive research of new molecules is highlighted--in known antibacterial families and new medicinal chemical entities.

Pharmacokinetic and Pharmacodynamic Efficacy of Intrapulmonary Administration of Ciprofloxacin for the Treatment of Respiratory Infections

The pharmacokinetic and pharmacodynamic efficacy of intrapulmonary administration of ciprofloxacin (CPFX) for the treatment of respiratory infections caused by pathogenic microorganisms resisting sterilization systems of alveolar macrophages (AMs) was evaluated by comparison with an oral administration. The time-courses of the concentration of CPFX in AMs and lung epithelial lining fluid (ELF) following intrapulmonary administration of CPFX solution to rats (200 microg/kg) were markedly higher than that following oral administration (10 mg/kg). The time-course of the concentrations of CPFX in plasma following intrapulmonary administration was markedly lower than that in AMs and ELF. These results indicate that intrapulmonary administration is more effective in delivering CPFX to AMs and ELF, compared with oral administration, in spite of a low dose and it avoids distribution of CPFX to the blood. In addition, the antibacterial effects of CPFX in AMs and ELF following intrapulmonary administration were evaluated by pharmacokinetics/pharmacodynamics analysis. The concentration of CPFX in AMs and ELF-time curve (AUC)/minimum inhibitory concentration of CPFX (MIC) ratio and the maximum concentration of CPFX in AMs and ELF (Cmax)/MIC ratio were markedly higher than the effective values. The present study indicates that intrapulmonary administration of CPFX is an effective technique for the treatment of respiratory infections.

Investigational new drugs for the treatment of resistant pneumococcal infections

Antibiotic resistance in Streptococcus pneumoniae is not only increasing with penicillin but also with other antimicrobial classes including the macrolides, tetracyclines and sulfonamides. This trend with antibiotic resistance has highlighted the need for the further development of new anti-infectives for the treatment of pneumococcal infections, particularly against multi-drug resistant pneumococci. Several new drugs with anti-pneumococcal activity are at various stages of development and will be discussed in this review. Two new cephalosporins with activity against S. pneumoniae include ceftobiprole and RWJ-54428. Faropenem is in a new class of beta-lactam antibiotics called the penems. Structurally, the penems are a hybrid between the penicillins and cephalosporins. Sitafloxacin and garenoxacin are two new quinolones that are likely to have a role in treating pneumococcal infections. Oritavancin and dalbavancin are glycopeptides with activity against methicillin-resistant S. aureus and vancomycin-resistant Enterococcus spp. as well as multi-drug resistant pneumococci. Tigecycline is the first drug in a new class of anti-infectives called the glycycyclines that has activity against penicillin-resistant pneumococci.

The effect of treatment with moxifloxacin or azithromycin on acute bacterial rhinosinusitis in mice

OBJECTIVE

Acute bacterial rhinosinusitis, which is a major health problem, is treated with antibiotics. We developed a mouse model of acute bacterial rhinosinusitis to gain a better understanding of the pathophysiology of the disease. Our goal was to investigate the response to acute rhinosinusitis when treated with either a bactericidal or a bacteriostatic antibiotic.

METHODS

C57BL/6 mice were infected intranasally with Streptococcus pneumoniae. One day after inoculation, the mice were treated with either moxifloxacin (bactericidal) or azithromycin (bacteriostatic). Different groups were euthanized during the first five days post-inoculation. Bacterial counts from nasal lavage culture and the cell markers GR1, CD11b, CD3, CD4, and CD8 in sinus tissue were evaluated by flow cytometry.

RESULTS

Azithromycin led to rapid clearance of the bacteria and of the inflammation in contrast to placebo. Surprisingly, moxifloxacin showed a limited effect. Investigations of this limited effect of moxifloxacin suggested a high metabolic clearance, a low concentration at the site of infection, and low persistent post-antibiotic effects of moxifloxacin in mice.

CONCLUSION

Our animal model of acute sinusitis has great utility for studying the disease, but the difference between mice and man must always be considered in making extrapolations from animal experiments to the human experience.

Recently approved and investigational antibiotics for treatment of severe infections caused by Gram-positive bacteria

The development of resistance in the major pathogenic Gram-positive genera Staphylococcus and Streptococccus has led to the need for new agents that are able to overcome existing resistance mechanisms or that have novel mechanisms of action. There is currently a dearth of new agents that are active against resistant bacterial species. Agents that have recently been approved for clinical use include linezolid, the first oxazolidinone in clinical use, daptomycin, the first lipopeptide in clinical use, and telithromycin, a ketolide that is derived from clarithromycin. Agents currently in clinical development include tigecycline, a broad-spectrum intravenous tetracycline, ceftobiprole, a broad-spectrum cephalosporin that has activity against methicillin-resistant staphylococci, DX-619 and WCK-771, which are potent quinolones that have activity against quinolone-resistant staphylococci, oritavancin and dalbavancin, both of which are new glycopeptides, and iclaprim, which is a diaminopyrimidine. Additional agents that are in preclinical development against Gram-positive pathogens include quinoline-naphthyridine agents, which target novel DNA gyrase sites, other novel quinolones that have high potency, peptide deformylase inhibitors, and new lincosamide, oxazolidinone, lipopeptide and cephalosporin derivatives. Misuse of potent new agents will, however, result in the inevitable development of resistance to these agents; responsible use of potent new agents is required to prevent continuation of this vicious cycle.

Noninvasive biophotonic imaging for monitoring of catheter-associated urinary tract infections and therapy in mice

Urinary tract infections (UTIs) are among the most common bacterial infections acquired by humans, particularly in catheterized patients. A major problem with catheterization is the formation of bacterial biofilms on catheter material and the risk of developing persistent UTIs that are difficult to monitor and eradicate. To better understand the course of UTIs and allow more accurate studies of in vivo antibiotic efficacy, we developed a catheter-based biofilm infection model with mice, using bioluminescently engineered bacteria. Two important urinary tract pathogens, Pseudomonas aeruginosa and Proteus mirabilis, were made bioluminescent by stable insertion of a complete lux operon. Segments of catheter material (precolonized or postimplant infected) with either pathogen were placed transurethrally in the lumen of the bladder by using a metal stylet without surgical manipulation. The bioluminescent strains were sufficiently bright to be readily monitored from the outside of infected animals, using a low-light optical imaging system, including the ability to trace the ascending pattern of light-emitting bacteria through ureters to the kidneys. Placement of the catheter in the bladder not only resulted in the development of strong cystitis that persisted significantly longer than in mice challenged with bacterial suspensions alone but also required prolonged antibiotic treatment to reduce the level of infection. Treatment of infected mice for 4 days with ciprofloxacin at 30 mg/kg of body weight twice a day cured cystitis and renal infection in noncatheterized mice. Similarly, ciprofloxacin reduced the bacterial burden to undetectable levels in catheterized mice but did not inhibit rebound of the infection upon cessation of antibiotic therapy. This methodology easily allows spatial information to be monitored sequentially throughout the entire disease process, including ascending UTI, treatment efficacy, and relapse, all without exogenous sampling, which is not possible with conventional methods.

The need for new therapeutic agents: what is in the pipeline?

There is a clinical need for new treatment options for serious Gram-positive infections. Recently introduced agents such as the newer fluoroquinolones and the ketolide telithromycin have limited use as they do not cover methicillin-resistant Staphylococcus aureus (MRSA) or glycopeptide-resistant enterococci (GRE). The clinical use of the streptogramin combination quinupristin/dalfopristin, which has activity against MRSA and vancomycin-resistant Enterococcus faecium, is limited because administration is via a slow infusion of a large volume. The oxazolidinone linezolid is active against MRSA and GRE but resistant organisms and treatment failures have been reported. A number of compounds currently in development show promise, the new glycopeptides oritavancin, dalbavancin and the glycolipodepsipeptide ramoplanin, as well as the new tetracyclines tigecycline and BAY73-7388. However, in some cases, there is concern that resistance may develop quickly to new compounds that are based on existing antimicrobial agents. Therefore daptomycin, a novel lipopeptide with a unique mode of action, is of particular interest. Daptomycin is active against MRSA (including vancomycin-resistant strains) and GRE. Daptomycin displays rapid concentration-dependent killing and is bactericidal even in the stationary phase of growth. Daptomycin-resistant strains are very difficult to generate in vitro. A dosage of 4 mg/kg intravenous once a day has been shown to be efficacious in two evaluator-blinded trials of complicated skin and soft tissue infections with clinical success rates similar for daptomycin and comparators (vancomycin or penicillinase-resistant penicillins). With its activity against key Gram-positive pathogens, including resistant strains, daptomycin has potential as a valuable addition to the available treatment options for serious Gram-positive infections.