Fluoroquinolone antimicrobial agents

Evaluating the predictive power of combined gene expression dynamics from single cells on antibiotic survival

Heteroresistance and persistence are examples of mechanisms that can allow otherwise drug-susceptible bacteria to survive and resume growth after antibiotic exposure. These temporary forms of antibiotic tolerance can be caused by the upregulation of stress response genes or a decrease in cell growth rate. However, it is not clear how the expression of multiple genes contributes to tolerance phenotypes. Using fluorescent reporters for stress-related genes, we conducted real-time measurements of expression prior to, during, and after antibiotic exposure. We first identified relationships between growth rate and reporter levels based on auto- and cross-correlation analysis, revealing consistent patterns where changes in growth rate were anticorrelated with fluorescence following a delay. We then used pairs of stress gene reporters and time-lapse fluorescence microscopy to measure the growth rate and reporter levels in cells that survived or died following antibiotic exposure. Using these data, we asked whether combined information about reporter expression and growth rate could improve our ability to predict whether a cell would survive or die following antibiotic exposure. We developed a Bayesian inference model to predict how the combination of dual reporter expression levels and growth rate impacts ciprofloxacin survival in Escherichia coli. We found clear evidence of the impact of growth rate and gadX promoter activity on survival. Unexpectedly, our results also revealed examples where additional information from multiple genes decreased prediction accuracy, highlighting an important and underappreciated effect that can occur when integrating data from multiple simultaneous measurements.IMPORTANCETransient increases in bacterial antibiotic tolerance can result in treatment failure despite an infection initially presenting as susceptible, presenting a significant challenge in antibiotic therapy. This phenomenon can also provide a window of opportunity for bacteria to acquire permanent genetic resistance mutations. Although understanding the underlying mechanisms of these antibiotic tolerance phenotypes is crucial for developing effective approaches to treatment, current approaches for studying these transient phenotypes have limitations. Here, we use fluorescent reporters to monitor the expression of genes involved in stress response over time, aiming to link expression with antibiotic survival outcomes. Our results reveal a counterintuitive finding: monitoring multiple gene reporters does not necessarily improve our ability to predict antibiotic survival outcomes compared to single gene reporters. This result emphasizes the need for a deeper mechanistic understanding of the relationship between stress response gene expression and antibiotic tolerance.

Trends in fluoroquinolone prescribing in UK primary and secondary care between 2019 and 2023

INTRODUCTION

Fluoroquinolones are important antibiotics but have associations with a number of adverse outcomes. A recent (January 2024) decision by the UK drug regulator, the Medicines and Health Regulatory Authority (MHRA), restricted systemic use of these antibiotics to when 'absolutely necessary'. One stated reason for the ban was the failure of previous guidance (2019, 2023) to reduce prescribing, with the MHRA stating there had been 'no change in prescribing' of fluoroquinolones in relation to guidance.

METHODS

We evaluated the trend in prescribing of fluoroquinolones and comparator antibiotics using national data for all primary care practices in England from 2019 to 2023. We calculated the percent change in prescribing of fluoroquinolones using linear regression, comparing with other antibacterials. We also performed analysis on secondary care prescribing and included hospital inpatient stay data.

RESULTS

In primary care, there was a negative trend in fluoroquinolone item dispensing, with a 4.2% reduction in items dispensed per year (95% CI -5.2% to -3.3%; P = 6 × 10-13). This occurred despite no change in overall antibacterial prescription and no decrease in comparator antibiotics. Secondary care data showed stable prescription of fluoroquinolones, but comparator antibiotics increased, leading to relatively fewer prescriptions compared with other agents.

CONCLUSIONS

There was a reduction in fluoroquinolone prescribing in England in absolute and relative terms between 2019 and 2023 in primary care, and absolute terms in secondary care. These findings do not support the MHRA's claim that there has been no change in prescribing in response to warnings.

Fluoroquinolone-specific resistance trajectories in E. coli and their dependence on the SOS-response

BACKGROUND

Fluoroquinolones are indispensable antibiotics used in treating bacterial infections in both human and veterinary medicine. However, resistance to these drugs presents a growing challenge. The SOS response, a DNA repair pathway activated by DNA damage, is known to influence resistance development, yet its role in fluoroquinolone resistance is not fully understood. This study aims to unfold the mechanisms of fluoroquinolone resistance by investigating the impact of the SOS response on bacterial adaptation.

RESULTS

We exposed Escherichia coli to four fluoroquinolones-ciprofloxacin, enrofloxacin, levofloxacin, and moxifloxacin. Using a recA knockout mutant, deficient in the SOS response, as a control, we assessed how the presence or absence of this pathway affects resistance development. Our findings demonstrated that the rate of resistance evolution varied between the different fluoroquinolones. Ciprofloxacin, enrofloxacin, and moxifloxacin exposures led to the most evident reliance on the SOS response for resistance, whereas levofloxacin exposed cultures showed less dependency. Whole genome analysis indicated distinct genetic changes associated with each fluoroquinolone, highlighting potential different pathways and mechanisms involved in resistance.

CONCLUSIONS

This study shows that the SOS response plays a crucial role in resistance development to certain fluoroquinolones, with varying dependencies per drug. The characteristic impact of fluoroquinolones on resistance mechanisms emphasizes the need to consider the unique properties of each antibiotic in resistance studies and treatment strategies. These findings are essential for improving antibiotic stewardship and developing more effective, tailored interventions to combat resistance.

Unraveling Antimicrobial Resistance Dynamics in Mycoplasma gallisepticum: Insights Into Antibiotic and Disinfectant Interactions

A major risk to the poultry industry is antimicrobial resistance (AMR), specifically with regard to Mycoplasma gallisepticum (MG) infections. The sensitivity patterns of 100 MG isolates to biocides and antibiotics were examined in this study to clarify the interactions between antimicrobial agents and resistance mechanisms. The antimicrobial activity against MG was assessed using broth microdilution, and the results are shown as the minimum inhibitory concentration (MIC) for each strain, the MIC distribution (range), the MIC50, and/or the MIC90. The statistical associations between the MICs of the antibiotics and biocides were investigated using regression model analysis and correlation coefficients. The absence of a cell wall in MG inherently confers resistance to beta-lactams, thereby necessitating the utilization of enrofloxacin, difloxacin, flumequine, oxytetracycline, chlortetracycline, doxycycline, tylosin, tilmicosin, tylvalosin, erythromycin, spiramycin, tiamulin, lincomycin, spectinomycin and dihydrostreptomycin. These antibiotics exhibited MIC50 values of 0.5, 0.5, 0.12, 0.062, 0.12, 0.031, 0.016, 0.016, 0.062, 16, 1, 0.008, 2, 0.5 and 32, respectively. In addition to antibiotics, disinfectants have garnered attention for their contribution to the development of AMR in MG. Notably, formalin, phenol, NADES, Halamid, Virkon-S, MicroSet and SteriSet exhibited MIC50 values of 125, 500, 31.25, 15.63, 15.63, 7.81 and 62.5, respectively. Significant positive correlations and direct associations were identified between various biocides and the development of antibiotic resistance, with coefficients ranging from 0.098 to 1.176. This research highlights the intricate nature of resistance profiles in MG and underscores the necessity for a thorough understanding of antimicrobial interactions. This finding emphasizes the importance of managing emerging AMR stemming from disinfectant misuse in the poultry farms to prevent additional constraints on antibiotic treatment options.

Evaluating the predictive power of combined gene expression dynamics from single cells on antibiotic survival

Heteroresistance can allow otherwise drug-susceptible bacteria to survive and resume growth after antibiotic exposure. This temporary form of antibiotic tolerance can be caused by the upregulation of stress response genes or a decrease in cell growth rate. However, it is not clear how expression of multiple genes contributes to the tolerance phenotype. By using fluorescent reporters for stress related genes, we conducted real time measurements of expression prior to, during, and after antibiotic exposure. We first identified relationships between growth rate and reporter levels based on auto and cross correlation analysis, revealing consistent patterns where changes in growth rate were anticorrelated with fluorescence following a delay. We then used pairs of stress gene reporters and time lapse fluorescence microcopy to measure the growth rate and reporter levels in cells that survived or died following antibiotic exposure. Using these data, we asked whether combined information about reporter expression and growth rate could improve our ability to predict whether a cell would survive or die following antibiotic exposure. We developed a Bayesian inference model to predict how the combination of dual reporter expression levels and growth rate impact ciprofloxacin survival in Escherichia coli . We found clear evidence of the impact of growth rate and the gadX promoter activity on survival. Unexpectedly, our results also revealed examples where additional information from multiple genes decreased prediction accuracy, highlighting an important and underappreciated effect that can occur when integrating data from multiple simultaneous measurements.

Antibacterial Mechanisms and Clinical Impact of Sitafloxacin

Sitafloxacin is a 4th generation fluoroquinolone antibiotic with broad activity against a wide range of Gram-negative and Gram-positive bacteria. It is approved in Japan and used to treat pneumonia and urinary tract infections (UTIs) as well as other upper and lower respiratory infections, genitourinary infections, oral infections and otitis media. Compared to other fluoroquinolones, sitafloxacin displays a low minimal inhibitory concentration (MIC) for many bacterial species but also activity against anaerobes, intracellular bacteria, and persisters. Furthermore, it has also shown strong activity against biofilms of P. aeruginosa and S. aureus in vitro, which was recently validated in vivo with murine models of S. aureus implant-associated bone infection. Although limited in scale at present, the published literature supports the further evaluation of sitafloxacin in implant-related infections and other biofilm-related infections. The aim of this review is to summarize the chemical-positioning-based mechanisms, activity, resistance profile, and future clinical potential of sitafloxacin.

Antibiotic prescribing for acute uncomplicated cystitis among community pharmacists in Thailand

OBJECTIVES

This study aimed to evaluate the knowledge of community pharmacists toward acute uncomplicated cystitis regarding diagnosis, referral, and conformity to guidelines of the chosen antibiotic and to identify the associated factors with the pharmacist's knowledge.

METHODS

This was a descriptive cross-sectional survey using a questionnaire. Data was collected from 349 community pharmacies in upper southern Thailand between December 2021 and February 2022. Univariate logistic regression analysis was used to assess factors associated with an inappropriate diagnosis of acute uncomplicated cystitis. The variables with P-value < 0.2 were included in the multivariate model. The statistically significant level was set as P-value < 0.05.

KEY FINDINGS

Three hundred and forty-nine pharmacists from 349 community pharmacies were included. Approximately 65% and 69% of the participants had the knowledge to identify which patients should be considered for cystitis and which patients should be considered for acute uncomplicated cystitis. Ninety eight percentage of pharmacists could select the appropriate antibiotic for uncomplicated cystitis patients. The most prescribed antibiotics were ciprofloxacin (44.7%), norfloxacin (40.7%), and ofloxacin (10.3%). Inappropriate diagnosis was significantly related to age (P = 0.016) and role in the community pharmacy (P = 0.033).

CONCLUSION

The majority of participants had misconceptions about the differential diagnosis between complicated and uncomplicated cystitis. These were related to the community pharmacists' advanced age. Continuous pharmacy education should be established to advocate rational antibiotic use, especially in a country where community pharmacists are legally allowed to dispense antimicrobials without a prescription.

Antibiotic Efficacy against Methicillin-Susceptible Staphylococcus aureus Biofilms on Synthetic and Biological Vascular Grafts

BACKGROUND

Biofilm formation is one of the greatest challenges encountered in vascular graft infections. Our aim is to compare the efficacy of 5 antibiotics against methicillin-susceptible Staphylococcus aureus (MSSA) biofilms on the surface of 4 vascular grafts.

METHODS

In vitro study of 2 clinical MSSA strains (MSSA2 and MSSA6) and 4 vascular grafts (Dacron, Dacron-silver-triclosan (DST), Omniflow-II, and bovine pericardium). After a 24-hr incubation period, the graft samples were divided into 6 groups: growth control (no treatment), ciprofloxacin 4.5 mg/L, cloxacillin 100 mg/L, dalbavancin 300 mg/L, daptomycin 140 mg/L, and linezolid 20 mg/L. Quantitative cultures were obtained and results expressed as log10 colony-forming units per milliliter (CFU/mL). Analysis of variance was performed to compare biofilm formation between the different groups.

RESULTS

The mean ± standard deviation MSSA2 count on the growth control Dacron graft was 10.05 ± 0.31 CFU/mL. Antibiotic treatment achieved a mean reduction of 45%; ciprofloxacin was the most effective antibiotic (64%). Baseline MSSA2 counts were very low on the DST (0.50 ± 1.03 CFU/mL) and Omniflow-II (0.33 ± 0.78 CFU/mL) grafts. On the bovine pericardium patch, the count was 9.87 ± 0.50 CFU/mL, but this was reduced by a mean of 45% after antibiotic treatment (61% for ciprofloxacin). The mean MSSA6 count on the growth control Dacron graft was 9.63 ± 0.53 CFU/mL. Antibiotics achieved a mean reduction of 48%, with ciprofloxacin performing best (67% reduction). The baseline MSSA6 count on the DST graft was 8.54 ± 0.73 CFU/mL. Antibiotics reduced biofilm formation by 72%; cloxacillin was the most effective treatment (86%). The MSSA6 count on the untreated Omniflow-II graft was 1.17 ± 1.52 CFU/mL. For the bovine pericardium patch, it was 8.98 ± 0.67 CFU/mL. The mean reduction after antibiotic treatment was 46%, with cloxacillin achieving the greatest reduction (68%).

CONCLUSIONS

In this in vitro study, ciprofloxacin and cloxacillin performed best at reducing biofilms formed by clinical MSSA strains on the surface of biological and synthetic vascular grafts.

Molecular mechanism of a triazole-containing inhibitor of Mycobacterium tuberculosis DNA gyrase

Antimicrobial resistance remains a persistent and pressing public health concern. Here, we describe the synthesis of original triazole-containing inhibitors targeting the DNA gyrase, a well-validated drug target for developing new antibiotics. Our compounds demonstrate potent antibacterial activity against various pathogenic bacteria, with notable potency against Mycobacterium tuberculosis (Mtb). Moreover, one hit, compound 10a, named BDM71403, was shown to be more potent in Mtb than the NBTI of reference, gepotidacin. Mechanistic enzymology assays reveal a competitive interaction of BDM71403 with fluoroquinolones within the Mtb gyrase cleavage core. High-resolution cryo-electron microscopy structural analysis provides detailed insights into the ternary complex formed by the Mtb gyrase, double-stranded DNA, and either BDM71403 or gepotidacin, providing a rational framework to understand the superior in vitro efficacy on Mtb. This study highlights the potential of triazole-based scaffolds as promising gyrase inhibitors, offering new avenues for drug development in the fight against antimicrobial resistance.

Biliary excretion and pharmacokinetics of several fluoroquinolones after intravenous injection in rabbits

The aim of this study was to measure the concentrations of enrofloxacin (ERFX) and other fluoroquinolones; orbifloxacin (OBFX), marbofloxacin (MBFX), and ofloxacin (OFLX) in the plasma and bile of rabbits after a single intravenous (IV) injection. Twenty male rabbits were divided into four groups and given each drug by IV injection into the ear vein at a dose of 5.0 mg/kg BW. The concentration of ERFX, ciprofloxacin (CPFX), OBFX, MBFX and OFLX in plasma and bile were determined by HPLC. CPFX, metabolite of ERFX, was also measured by HPLC in plasma and bile of rabbits receiving ERFX. Several pharmacokinetic parameters in plasma were calculated and biliary clearance (CLbile) was calculated from extent of biliary excretion and accumulation of AUC of each drug. After IV injection, elimination half-life (t1/2β) was 4.13, 3.68, 6.60, 5.14 hr; volume of distribution at a steady state (Vdss) was 1.24, 0.503, 0.771, 1.02 L/kg; and total body clearance (CLtot) was 1.05, 0.418, 0.271, 0.453 L/kg/hr, respectively. The values for CLbile for ERFX, OBFX, MBFX, and OFLX were 0.0048, 0.0050, 0.0057, and 0.0094 L/kg/hr, respectively. These values represent 0.48%, 1.2%, 2.1%, and 2.3% of the total body clearance (CLtot) of each drug, respectively. The biliary clearance of CPFX was also measured and found to be 0.0199 L/kg/hr with ERFX administration. The results showed that ERFX, OBFX, MBFX, and OFLX were not excreted into the bile to a significant extent, making them safe drugs to use in rabbits.

Prevalence of Salmonella infection in village chickens and determination of the tetracycline resistance genes in the Salmonella isolates in the Sistan region, Iran

Recently, an increasing number of multi drug resistant Salmonella species have been emerged due to overuse of antibiotics in veterinary and human medicine which has adverse consequences on public health. The present study was conducted with the aim of investigating the prevalence of Salmonella infection in village chickens in Sistan region and determining the prevalence of the antibiotic resistance genes in Salmonella isolated from these birds. In this study, 100 chickens were randomly selected from five counties of Sistan region. A cloacal swab sample was taken from each bird and also information about age, gender, breed, proximity with other birds, proximity with waterfowl, proximity with livestock, and receiving different antibiotics especially tetracycline were obtained using a questionnaire. Conventional culture methods used for Salmonella detection and isolation. Then, amplification of invA gene by PCR was used to confirm Salmonella colonies. Finally, 27 samples were confirmed to be infected with Salmonella by both culture and PCR methods. Disk diffusion method was used to determine the sensitivity to 4 antibiotics including; tetracycline, gentamicin, cefepime, and difloxacin. The results of the present study showed that proximity to waterfowl (OR = 0.273) significantly mitigates the risk of Salmonella infection. For the isolates, the highest resistance was recorded against cefepime and the highest susceptibility was to difloxacin. The presence proportion of tetA and tetB in tetracycline resistant isolates was higher than that in susceptible ones but this difference was not statistically significant.

Seasonal analysis of commonly prescribed antibiotics in Istanbul city

Antibiotics are among the most common medicine groups since they are used to treat infectious diseases, as nutritional supplements in livestock breeding, and for preservation in the food industry. Turkey is among the highest antibiotic consumers in the world. In the present study, the most popular 14 antibiotics available in Turkey were monitored in one hospital sewage and two urban wastewater treatment plant influents and effluents seasonally in Istanbul province, the largest metropolitan center in Turkey. The present research aimed to develop a robust analytical method to determine 14 antibiotics, including six chemical groups, in environmental matrices which are considered significant antibiotic pollution sources, namely hospital sewage and urban wastewater. Solid-phase extraction (SPE) and UPLC-MS/MS analysis parameters included optimized column temperature, eluent, mobile phase, and flow rate. Three SPE cartridges were employed in recovery studies. The antibiotic recovery rates varied between 40 and 100%, and all analytes were identified within 3 min with UPLC-MS/MS under optimal conditions. It was determined that method detection limits (MDLs) varied between 0.07 and 2.72 µg/L for the antibiotics. In all seasons, the highest beta-lactam group antibiotic concentrations were identified in hospital sewage. The season with the greatest variety of antibiotics in urban wastewater was spring. Clarithromycin and ciprofloxacin were the antibiotics determined at the highest concentration in the influent and effluent of the wastewater treatment plant in all seasons. This study showed that the most widely used beta-lactam group antibiotics were found in high amounts in hospital sewage wastewater but in low concentrations in the treatment plants, and hence, it is seen that the degradability of beta-lactam group antibiotics was high. The presence of clarithromycin, ciprofloxacin, lincomycin, levofloxacin, and trimethoprim antibiotics in hospital sewage in higher amounts and also in inlet and outlet of wastewater treatment plants proves that those are resistant antibiotics.

Effect of Methyl-β-Cyclodextrin on the Interaction of Fluoroquinolones with Human Serum Albumin

Abstract—

The influence of the structure of fluoroquinolones (on the example of ciprofloxacin and levofloxacin) and their complexation with methyl-β-cyclodextrin on the interaction of the drug with human serum albumin was studied. It was found that the binding of the drug molecule with albumin is significantly affected by the structure of fluoroquinolone, as well as the presence of methyl-β-cyclodextrin. It was discovered that of the two fluoroquinolones, the more hydrophobic ciprofloxacin molecule interacts more strongly with the protein, using circular dichroism and fluorescence spectroscopy methods. It has also been shown that binding of albumin to the drug causes quenching of protein fluorescence, and this effect is more pronounced for ciprofloxacin. The complexation of fluoroquinolones with methyl-β-cyclodextrin leads to a change in the interaction of fluoroquinolones with the protein: in the case of complexes, more pronounced interactions are observed for levofloxacin. The results obtained will help to bring the use of fluoroquinolones to a new level in clinical practice, by creating new highly effective drugs with improved properties.

Synthesis and Coordination Properties of a Water-Soluble Material by Cross-Linking Low Molecular Weight Polyethyleneimine with Armed Cyclotriveratrilene

In this study, a full organic and water-soluble material was synthesized by coupling low molecular weight polyethylenimine (PEI-800) with cyclotriveratrilene (CTV). The water-soluble cross-linked polymer contains hydrophobic holes with a high coordination capability towards different organic drug molecules. The coordinating capability towards hydrophilic drugs (doxorubicin, gatifloxacin and sinomenine) and hydrophobic drugs (camptothecin and celastrol) was analyzed in an aqueous medium by using NMR, UV-Vis and emission spectroscopies. The coordination of drug molecules with the armed CTV unit through hydrophobic interactions was observed. In particular, celastrol exhibited more ionic interactions with the PEI moiety of the hosting system. In the case of doxorubicin, the host-guest detachment was induced by the addition of ammonium chloride, suggesting that the intracellular environment can facilitate the release of the drug molecules.

Lipophilic quinolone derivatives: Synthesis and in vitro antibacterial evaluation

This paper reports on the design of a series of 10 novel lipophilic piperazinyl derivatives of the 1-cyclopropyl-6-fluoro-8-methoxy-4-oxo-1,4-dihydroquinoline-3-carboxylic acid, their synthesis, their characterisation by ¹H, ¹³C and ¹⁹F NMR, IR spectroscopy and HRMS, as well as their biological activity against bacteria of medical interest. Among these derivatives, 2 were as potent as the parent quinolone against Neisseriagonorrhoeae whereas all the compounds displayed lower activity than the parent quinolone against other bacteria of medical interest. Our results showing that the increased lipophilicity was deleterious for antibacterial activity may help to design new quinolone derivatives in the future, especially lipophilic quinolones which have been poorly investigated previously.

Adverse effects of oxytetracycline and enrofloxacin on the fertility of Saanen bucks

This study aimed to determine the adverse effects of oxytetracycline and enrofloxacin application on the fertility of Saanen bucks. For this purpose, twenty-four bucks were divided into three groups. Group I (control group) received only 5 ml of 0.9% NaCl for 7 days, group II was given a single dose of 20 mg/kg oxytetracycline and group III was given at a dose of 2.5 mg/kg per day for 7 days intramuscularly. Serum and semen samples were collected from the bucks at post-treatment 1, 3, 5, 7, and 9 days and examined spermatological parameters (quantity, motility, density, abnormal sperm ratio, and live-dead sperm ratio), serum testosterone levels (with ELISA) and sperm DNA parameters (with Comet assay). The results showed no change in sperm volume, abnormal sperm rate, and dead-live sperm ratio in group II and III following oxytetracycline and enrofloxacin administration. However, a decrease in sperm density, sperm motility, mass activity, and testosterone levels, and an increase in sperm DNA damage were detected. These spermatological parameters (density, motility, mass activity) and testosterone levels were less decreased and sperm DNA damage was less increased in group II than group III. The greater damage in group III may be attributed to the longer duration of enrofloxacin administration compared to oxytetracycline and the effect of enrofloxacin on DNA. The results obtained from this study suggest that usage of oxytetracycline and especially enrofloxacin should be restricted and antibiotics with fewer side effects on sperm should be preferred in Saanen bucks during the reproduction period.

Fluoroquinolones: Blessings Or Curses

Fluoroquinolones are one of the world's most valuable and popularly used categories of antimicrobial agents. This paper attempts to review the substantial progress of fluoroquinolones from their discovery to black box warning. Antibiotic drug choice will remain difficult in the presence of increasing resistance, but the introduction of fluoroquinolones has created a new and exciting era in antimicrobial treatment. These are a synthetic heterogeneous group of compounds used in both hospital and community practices to treat numerous severe infections. The era of quinolone antibiotics began with the serendipitous discovery of the quinolone prototype in 1962. The chronological development of fluoroquinolone reported that nalidixic acid was the first quinolone that gained popular choice for the treatment of urinary tract infection. The subsequent agents like levofloxacin, ofloxacin, norfloxacin, gatifloxacin, moxifloxacin, clinafloxacin, sparfloxacin, and ciprofloxacin were derived through side chain and nuclear manipulation from basic pharmacophore. The fluoroquinolone motifs have been found as a milestone, effective in certain infections that are respiratory tract infection, urinary tract infection, bone disorders, meningococcal and mycobacterial infections, sexually transmitted diseases, skin infections, etc. Fluoroquinolones are first entirely man-made antibiotics that exhibit antibacterial activity through the inhibition of topoisomerase II, topoisomerase IV and deoxyribonucleic acid gyrase, which is vital for chromosome replication and function. The post-marketing surveillance pointed out the favorable side effects associated with fluoroquinolones such as phototoxicity, QT interval prolongation and anaphylaxis. The discovery, development and clinical use of fluoroquinolone antibiotics in the last century contributed to a decline in morbidity and mortality rates.

Membrane active 7-thiazoxime quinolones as novel DNA binding agents to decrease the genes expression and exert potent anti-methicillin-resistant Staphylococcus aureus activity

A novel class of 7-thiazoxime quinolones was developed as potential antimicrobial agents for the sake of bypassing resistance of quinolones. Biological assays revealed that some constructed 7-thiazoxime quinolones possessed effective antibacterial efficiency. Methyl acetate oxime derivative 6l exhibited 32-fold more active than ciprofloxacin against MRSA, which also possessed rapidly bactericidal ability and low toxicity towards mammalian cells. The combination use of 7-thiazoxime quinolone 6l and ciprofloxacin was able to improve antibacterial potency and effectively alleviate bacterial resistance. The preliminarily mechanism exploration revealed that compound 6l could destroy the cell membrane and insert into MRSA DNA to bind with DNA gyrase, then decrease the expression of gyrB and femB genes. The above results strongly suggested that methyl acetate oxime derivative 6l held a promise for combating MRSA infection.

Microbial Keratitis After Corneal Collagen Cross-Linking for Corneal Ectasia

PURPOSE

The aim of this study was to report the clinical profile and microbiological of patients with microbial keratitis post accelerated corneal collagen cross-linking (CXL).

METHODS

A retrospective case series of all patients diagnosed with microbial keratitis post-CXL who attended the Sydney Eye Hospital, Australia from January 1, 2012 to December 31, 2019 were included. Patients were identified from hospital coding and pathology data. Data were extracted from patients' medical records.

RESULTS

Eleven eyes from 10 patients with a mean age of 29 ± 11 years (range 16-48) were included. The median time of infection after CXL surgery was 4 days [interquartile range (IQR) 3-83]. Median initial and final Visual acuity at presentation were 1.3 logMAR (IQR 1-2.0) and 0.8 logMAR (IQR 0.6-1.2), respectively. The culture positivity rate was 92%, identifying 13 isolates, predominately made up of coagulase-negative Staphylococcus (n = 6, 50%) and Staphylococcus aureus (n = 3, 25%). The median epithelial healing time was 30 days (IQR 15-53).

CONCLUSIONS

Post-CXL microbial keratitis was predominately associated with gram-positive bacteria and in some cases delayed epithelialization. Microbial keratitis post-CXL may lead to moderate to poor patient outcomes.

Quinolones: Mechanism, Lethality and Their Contributions to Antibiotic Resistance

Fluoroquinolones (FQs) are arguably among the most successful antibiotics of recent times. They have enjoyed over 30 years of clinical usage and become essential tools in the armoury of clinical treatments. FQs target the bacterial enzymes DNA gyrase and DNA topoisomerase IV, where they stabilise a covalent enzyme-DNA complex in which the DNA is cleaved in both strands. This leads to cell death and turns out to be a very effective way of killing bacteria. However, resistance to FQs is increasingly problematic, and alternative compounds are urgently needed. Here, we review the mechanisms of action of FQs and discuss the potential pathways leading to cell death. We also discuss quinolone resistance and how quinolone treatment can lead to resistance to non-quinolone antibiotics.

Synthesis of Novel Ciprofloxacin-Based Hybrid Molecules toward Potent Antimalarial Activity

Antimalarial drug resistance is a serious obstacle in the persistent quest to eradicate malaria. There is a need for potent chemical agents that are able to act on drug-resistant Plasmodium falciparum populations at reasonable concentrations without any related toxicity to the host. By rational drug design, we envisaged to address this issue by generating a novel hybrid drug possessing two pharmacophores that can act on two unique and independent targets within the cell. We synthesized a new class of ciprofloxacin-based hybrid molecules, which have been integrated with acridine, quinolone, sulphonamide, and cinnamoyl pharmacophores (1-4). We realized a potent chloroquinolone-ciprofloxacin-based antimalarial hybrid (2, CQ-CFX) whose mechanism of action is unlike that of its parent molecules indicating a unique biological target. CQ-CFX is not only potent against CQ-resistant and susceptible strains of Plasmodium falciparum at low nanomolar concentrations (IC₅₀ values are 63.17 ± 1.2 nM and 25.52 ± 4.45 nM, respectively) but is also not toxic to mammalian and bacterial systems up to 20 μM and 1 μM, respectively.

Mutant Prevention Concentration of Ciprofloxacin against Klebsiella pneumoniae Clinical Isolates: An Ideal Prognosticator in Treating Multidrug-Resistant Strains

Background

Fluoroquinolone-resistant Klebsiella pneumoniae poses a therapeutic challenge when implicated in urinary tract infections, pyelonephritis, pneumonia, skin infections, osteomyelitis, and respiratory infections. The mutant prevention concentration (MPC) represents a concentration threshold above which increase of resistant mutants occurs rarely. The aim of the present study is to determine the MPC among ciprofloxacin-resistant K. pneumoniae clinical isolates.

Materials and Methods

A total of 240 clinical isolates of K. pneumoniae were collected from a tertiary care hospital. The MPCs were determined for 24 selected strains using an inoculum of 10¹⁰ CFU/ml in Müller-Hinton agar plates with serial/various concentrations (0.003-100 μg) of ciprofloxacin. In addition to the MPC, phenotypic screening for ESBL, AmpC, and carbapenemase was performed. The detection of qnr genes for 24 isolates and DNA sequencing for six isolates were performed.

Results

Ciprofloxacin resistance was observed in 19.6% of the K. pneumoniae clinical isolates. Among the ciprofloxacin-resistant isolates, 14 isolates showed an MPC value of more than 100 μg. The MPC ranged between 100 μg and 20 μg for ciprofloxacin-resistant isolates. ESBL producers and qnr gene-producing strains had a high MPC. 11 isolates showed the presence of either qnrB or qnrS genes. None of the samples showed the presence of the qnrA gene.

Conclusion

From our study, we infer that ESBL producers and qnr gene-possessing strains are frequently resistant to ciprofloxacin. Estimation of the MPC in the case of multidrug-resistant isolates in the clinical setup may help in treating these drug-resistant strains.

Pharmacokinetic and tissue analyses of levofloxacin in sheep (Ovis aries Linnaeus) after multiple-dose administration

The aim of this study was to assess the pharmacokinetic profile of LFX in sheep after intravenous (IV) and oral (PO) administration of 2 mg/kg LFX once a day for 5 days and to evaluate its tissue depletion in the muscles, heart, liver, lungs, and kidneys. Twenty healthy female sheep were randomly divided into two equal groups. Each group was further randomly subdivided into two equal subgroups (n = 5). Group 1 was used for blood collection and underwent a crossover design (2 × 2 Latin square). Group 2 was randomly subdivided into two equal subgroups (n = 5) for IV and PO route respectively, and used for tissue collection. A single sheep was sacrificed at each time point and the organs were harvested. Samples were analyzed using a validated HPLC method with fluorescence detection. LFX administered orally was rapidly absorbed with a peak plasma concentration of 2866 ± 239 ng/mL and an absolute oral bioavailability of 114 ± 27.7%. The pharmacokinetic estimates were comparable between PO and IV administration. According to the pharmacokinetic/pharmacodynamic surrogate index (area under the curve / minimum inhibitory concentration) of 100-125, LFX has the potential to be an effective treatment for infections caused by bacteria with a MIC of 0.049-0.061 μg/mL. LFX was detected for up to 48 h in all the tissues samples. The kidney had the highest LFX concentration after IV and PO administration. The AUC_{tissue/plasma} ratio was lower than 1 in all tissues indicating absence of LFX tissue accumulation.

Salmonella enterica persister cells form unstable small colony variants after in vitro exposure to ciprofloxacin

Persistence phenotype and small colony variants (SCVs) can be part of a bacterial bet-hedging strategy for survival under environmental stresses, such as antimicrobial exposure. These phenotypes are of particular concern in persistent and relapsing infections, since cells resume to normal growth after cessation of the stressful condition. In this context, we found persisters and unstable SCVs as phenotypic variants of Salmonella enterica that were able to survive ciprofloxacin exposure. A high heterogeneity in persister levels was observed among S. enterica isolates grown under planktonic and biofilm conditions and exposed to ciprofloxacin or ceftazidime, which may indicate persistence as a non-multidrug-tolerant phenotype. Nevertheless, a comparable variability was not found in the formation of SCVs among the isolates. Indeed, similar proportions of SCV in relation to normal colony phenotype (NCP) were maintained even after three successive cycles of ciprofloxacin exposure testing colonies from both origins (SCV or NCP). Additionally, we found filamentous and dividing cells in the same scanning electron microscopy images from both SCV and NCP. These findings lead us to hypothesize that besides variability among isolates, a single isolate may generate distinct populations of persisters, where cells growing under distinct conditions may adopt different and perhaps complementary survival strategies.

Spatial structure facilitates the accumulation and persistence of antibiotic-resistant mutants in biofilms

The emergence and spread of antibiotic resistance in bacterial pathogens are a global crisis. Because many bacterial infections are caused by pathogens that reside in biofilms, we sought to investigate how biofilms influence the evolution of antibiotic resistance. We hypothesize that the inherent spatial structure of biofilms facilitates the accumulation and persistence of spontaneously evolved antibiotic-resistant mutants. To test this, we tracked the frequency of mutants resistant to kanamycin and rifampicin in biofilm populations of Escherichia coli before, during, and after an antibiotic treatment regimen. Our results show that biofilms accumulate resistant mutants even in the absence of antibiotics. This resistance was found to be heritable and thus unlike the phenotypic plasticity of so-called "persister cells" that have been shown to occur in biofilms. Upon exposure to an antibiotic, resistant mutants swept to high frequency. Following the conclusion of treatment, these resistant mutants remained at unexpectedly high frequencies in the biofilms for over 45 days. In contrast, when samples from kanamycin-treated biofilms were used to found well-mixed liquid cultures and propagated by serial transfer, the frequency of resistant cells dramatically decreased as they were outcompeted by sensitive clones. These observations suggest that the emergence of antibiotic resistance through spontaneous mutations in spatially structured biofilms may significantly contribute to the emergence and persistence of mutants that are resistant to antibiotics used to treat bacterial infections.

Optimization of the electrochemical degradation process of the antibiotic ciprofloxacin using a double-sided β-PbO2 anode in a flow reactor: kinetics, identification of oxidation intermediates and toxicity evaluation

The electrochemical degradation of ciprofloxacin-CIP (50 mg L^-1 in 0.10 mol L^-1 Na₂SO₄) was investigated using a double-sided Ti-Pt/β-PbO₂ anode in a filter-press flow reactor, with identification of oxidation intermediates and follow-up of antimicrobial activity against Escherichia coli. The effect of solution pH, flow rate, current density, and temperature on the CIP removal rate was evaluated. All of these parameters did affect the CIP removal performance; thus, optimized electrolysis conditions were further explored: pH = 10, q_V = 6.5 L min^-1, j = 30 mA cm^-2, and θ = 25 °C. Therefore, CIP was removed within 2 h, whereas ~75% of the total organic carbon concentration (TOC) was removed after 5 h and then, the solution no longer presented antimicrobial activity. When the electrochemical degradation of CIP was investigated using a single-sided boron-doped diamond (BDD) anode, its performance in TOC removal was similar to that of the Ti-Pt/β-PbO₂ anode; considering the higher oxidation power of BDD, the surprisingly good comparative performance of the Ti-Pt/β-PbO₂ anode was ascribed to significantly better hydrodynamic conditions attained in the filter-press reactor used with this electrode. Five initial oxidation intermediates were identified by LC-MS/MS and completely removed after 4 h of electrolysis; since they have also been determined in other degradation processes, there must be similarities in the involved oxidation mechanisms. Five terminal oxidation intermediates (acetic, formic, oxamic, propionic, and succinic acids) were identified by LC-UV and all of them (except acetic acid) were removed after 10 h of electrolysis.

Adsorption/desorption study of antibiotic and anti-inflammatory drugs onto bioactive hydroxyapatite nano-rods

The use of high doses of antibacterial and anti-inflammatory drugs for patients with bone diseases, associated to implants or bone filling, can develop adverse effects; and consequently, it promotes to think new strategies to avoid this problem. In this work, it has been described the adsorption/release (or desorption) behavior of two drugs, ciprofloxacin (CIP) and ibuprofen (IBU), onto hydroxyapatite (nano-HA) at 37 °C. Through Ultraviolet-Visible (UV-Vis) spectroscopy, the concentrations of both drugs in adsorption, kinetic and desorption processes were obtained. The Fourier Transformed-Infrared (FT-IR) spectroscopy, Zeta-potential (ζ-potential), High-Resolution Transmission Electron Microscopy (H-TEM) and x-Ray Diffraction (xRD) were also used to characterize bared nanoparticles and those with adsorbed drugs. Five adsorption models (Langmuir, Freundlich, Sips, Temkin and Dubinin-Radushkevich) were used for describing the behavior of both active compounds. The adsorption processes (CIP/nano-HA and IBU/nano-HA) were better predicted by the Sips model than by the others. The kinetic adsorption data were processed, for both active agents, by application of Avrami's model. Desorption/release process (of both drugs) was evaluated though Korsmeyer-Peppas (K-P) model. Owing to the predictability of these systems, we propose the use of these active ceramics as potential bone filler for improving the treatment against bacterial bone infections and to avoid its associated inflammatory process.

Copper(ii) complexes based on levofloxacin and 2N-donor ligands: synthesis, crystal structures and in vitro biological evaluation

The molecular structures and in vitro biological applications of two cationic copper(ii) complexes are reported.

The role of various transporters in the placental uptake of ofloxacin in an in vitro model of human villous trophoblasts

Introduction

Six years after the US Food and Drug Administration approval of the broad-spectrum antibiotic ofloxacin (OFLX), the chiral switching of this racemic mixture resulted in a drug composed of the L-optical isomer levofloxacin (LVFX). Since both fluoroquinolones (FQs) were introduced to the pharmaceutical market, they have been widely prescribed by physicians, with careful administration during pregnancy and breastfeeding. Therefore, the role of the influx and efflux placental transporters in the concentrations of these drugs that permeate through human placental barrier model was investigated in this study.

Methods

The contribution of major carriers on the transplacental flux of OFLX and LVFX uptake into choriocarcinoma BeWo cells was evaluated in the presence vs absence of well-known inhibitors.

Results

Our results reveal that neither the influx transporters such as organic cation transporters, organic anion transporters, and monocarboxylate transporters nor the efflux transporters such as P-glycoprotein or breast cancer resistance protein significantly affected the transport of OFLX. In contrast, multiple transporters revealed pronounced involvement in the transfer of the levorotatory enantiomer in and out of the in vitro placental barrier. These data suggest a non-carrier-mediated mechanism of transport of the racemic mixture, while LVFX is subjected to major influx and efflux passage through the placental brush border membranes.

Conclusion

This study provides underlying insights to elucidate the governing factors that influence the flux of these FQs through organ barriers, in view of the controversial safety profile of these drugs in pregnant population.

Identification by virtual screening and functional characterisation of novel positive and negative allosteric modulators of the α7 nicotinic acetylcholine receptor

Several previous studies have demonstrated that the activity of neurotransmitters acting on ligand-gated ion channels such as the nicotinic acetylcholine receptor (nAChR) can be altered by compounds binding to allosteric modulatory sites. In the case of α7 nAChRs, both positive and negative allosteric modulators (PAMs and NAMs) have been identified and have attracted considerable interest. A recent study, employing revised structural models of the transmembrane domain of the α7 nAChR in closed and open conformations, has provided support for an inter-subunit transmembrane allosteric binding site (Newcombe et al 2017). In the present study, we have performed virtual screening of the DrugBank database using pharmacophore queries that were based on the predicted binding mode of PAMs to α7 nAChR structural models. A total of 81 compounds were identified in the DrugBank database, of which the 25 highest-ranked hits corresponded to one of four previously-identified therapeutic compound groups (carbonic anhydrase inhibitors, cyclin-dependent kinase inhibitors, diuretics targeting the Na⁺-K⁺-Cl^- cotransporter, and fluoroquinolone antibiotics targeting DNA gyrase). The top-ranked compound from each of these four groups (DB04763, DB08122, furosemide and pefloxacin, respectively) was tested for its effects on human α7 nAChR expressed in Xenopus oocytes using two-electrode voltage-clamp electrophysiology. These studies, conducted with wild-type, mutant and chimeric receptors, resulted in all four compounds exerting allosteric modulatory effects. While DB04763, DB08122 and pefloxacin were antagonists, furosemide potentiated ACh responses. Our findings, supported by docking studies, are consistent with these compounds acting as PAMs and NAMs of the α7 nAChR via interaction with a transmembrane site.

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Identification of α7 nAChR positive and negative allosteric modulators.

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Furosemide is a positive allosteric modulator of α7 nAChRs.

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DB04763, DB08122 and pefloxacin are negative allosteric modulators of α7 nAChRs.

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Modulation of α7 nAChRs by an allosteric transmembrane site.

Isocratic Resolution of Fluoroquinolone-Based Antibiotics on the Phenylethyl-Bonded Phase under Nonaqueous Elution: A Consideration of the Separation Mechanism

This paper reports the isocratic resolution of 10 fluoroquinolone-based antibiotics and their precursors on the phenylethyl-bonded phase under the elution of the nonaqueous mobile phase composed of acetonitrile, methanol, acetic acid, and triethylamine. Most of the analytes were baseline resolved within 10 minutes. The interaction simulation and Fourier-transform infrared spectroscopy (FTIR) data indicated that the carbonyl-containing group, a secondary or tertiary amine of an analyte, was heavily involved in the retention, resulting in retention with residual silanol groups on the stationary phase. In some cases, the elution reversal or resolution enhancement of analytes was observed when the volume of acidic or basic additive in the mobile phase was dominant. However, the π-π complexation interaction between the fluorine-attached phenyl group of the analyte and the phenylethyl moiety on the stationary phase was not observed. Consequently, the resolution could not be reproduced either on the other stationary phase modified with C₁₈, phenyl, or phenylhexyl moiety under the same chromatographic conditions or under the aqueous elution.

Antibiotics in the aquatic environments: A review of lakes, China

The potential threat of antibiotics to the environment and human health has raised significant concerns in recent years. The consumption and production of antibiotics in China are the highest in the world due to its rapid economic development and huge population, possibly resulting in the high detection frequencies and concentrations of antibiotics in aquatic environments of China. As a water resource, lakes in China play an important role in sustainable economic and social development. Understanding the current state of antibiotics in lakes in China is important. Closed and semi-closed lakes provide an ideal medium for the accumulation of antibiotics and antibiotic resistance genes (ARGs). This review summarizes the current levels of antibiotic exposure in relevant environmental compartments in lakes. The ecological and health risks of antibiotics are also evaluated. This review concludes that 39 antibiotics have been detected in the aquatic environments of lakes in China. The levels of antibiotic contamination in lakes in China is relatively high on the global scale. Antibiotic contamination is higher in sediment than water and aquatic organisms. Quinolone antibiotics (QNs) pose the greatest risks. The contents of antibiotics in aquatic organisms are far lower than their maximum residual limits (MRLs), with the exception of the organisms in Honghu Lake. The lakes experience high levels of ARG contamination. A greater assessment of ARG presence and antibiotic exposure are urgent.

Effectiveness of Topical Antibiotics on Staphylococcus Aureus Biofilm in Vitro

Background

In vitro biofilm-producing capacity in isolates of Staphylococcus aureus and Pseudomonas aeruginosa collected from the sinus cavities after endoscopic sinus surgery (ESS) are associated with a poor outcome in patients with chronic rhinosinusitis (CRS). However, conventional oral antibiotic therapy is frequently ineffective in eradicating bacteria in the biofilm form. Increasing the concentration of antibiotics may offer a means of countering this resistance. The aim of this study was to determine the in vitro activity of moxifloxacin (MOXI) against S. aureus in biofilm form (recovered from patients with CRS at least 1 year post-ESS).

Method

This study was performed in a research microbiology laboratory, where five isolates of S. aureus with known biofilm-forming capacity were cultured in Tryptic Soy Broth 0.5% glucose in 96-well plates at 37°C for 24 hours. After visual confirmation of biofilm formation, plates were incubated in phosphate-buffered saline (PBS) or with MOXI at concentrations of 0.1×, 1×, 100×, and 1000× minimal inhibitory concentration (MIC) for an additional 24 hours. Biofilm from 3 wells of each concentration were collected and sonicated and the number of viable bacteria was determined by serial dilution and plating.

Results

After incubation, the number of viable bacteria was similar for nontreated and MOXI-treated biofilms at MIC and sub-MIC levels. However, MOXI at 1000X (0.1–0.2 mg/mL) gave a 2 to 2.5 log reduction in number of viable bacteria.

Conclusion

In vitro results show that increased concentrations of antibiotics, easily attainable in topical solutions, are effective in killing bacteria in bacterial biofilms. This suggests a role for topical antibiotic therapies in the treatment of biofilm infections.

Moxifloxacin versus levofloxacin or ciprofloxacin prophylaxis in acute myeloid leukemia patients receiving chemotherapy

PURPOSE

Patients receiving intensive chemotherapy regimens are at high risk for infectious complications due to prolonged neutropenia and hospital stay. Fluoroquinolone antibiotics, mainly levofloxacin and ciprofloxacin, are the mainstay of prophylactic therapy for these patients. There is limited data regarding the utilization of other quinolone antibiotics including moxifloxacin in this setting.

METHODS

A retrospective chart review was completed comparing the use of prophylactic moxifloxacin to that of levofloxacin or ciprofloxacin during periods of prolonged neutropenia. Adult patients admitted to a community teaching hospital while receiving induction or reinduction chemotherapy for acute myeloid leukemia were included.

RESULTS

One hundred and forty-one patients were included in this study. The two groups displayed slight heterogeneity: patients receiving moxifloxacin were approximately 10 years younger (54 vs. 64 years, p = 0.01), more likely to receive granulocyte colony stimulating factor (GCSF) (45 vs. 19%, p = 0.001), and neutropenic for a longer duration (23 vs. 19 days, p = 0.009). The incidence of febrile neutropenia (76 vs. 81%, RR 0.93, 95% CI 0.78-1.11, p = 0.42) and of documented infections (27 vs. 33%, RR 0.82, 95% CI 0.49-1.36, p = 0.44) was similar between those receiving moxifloxacin and levofloxacin/ciprofloxacin, respectively. Hospital readmission for an infectious issue within 30 days of hospital discharge (9 vs. 5%, p = 0.39) was also similar between groups as was the incidence of Clostridium difficile (9 vs. 9%, p = 0.96).

CONCLUSIONS

Moxifloxacin may be an alternative to levofloxacin or ciprofloxacin in patients with a prolonged risk of febrile neutropenia requiring prophylaxis.

A spontaneous mutation in kdsD, a biosynthesis gene for 3 Deoxy-D-manno-Octulosonic Acid, occurred in a ciprofloxacin resistant strain of Francisella tularensis and caused a high level of attenuation in murine models of tularemia

Francisella tularensis, a gram-negative facultative intracellular bacterial pathogen, is the causative agent of tularemia and able to infect many mammalian species, including humans. Because of its ability to cause a lethal infection, low infectious dose, and aerosolizable nature, F. tularensis subspecies tularensis is considered a potential biowarfare agent. Due to its in vitro efficacy, ciprofloxacin is one of the antibiotics recommended for post-exposure prophylaxis of tularemia. In order to identify therapeutics that will be efficacious against infections caused by drug resistant select-agents and to better understand the threat, we sought to characterize an existing ciprofloxacin resistant (CipR) mutant in the Schu S4 strain of F. tularensis by determining its phenotypic characteristics and sequencing the chromosome to identify additional genetic alterations that may have occurred during the selection process. In addition to the previously described genetic alterations, the sequence of the CipR mutant strain revealed several additional mutations. Of particular interest was a frameshift mutation within kdsD which encodes for an enzyme necessary for the production of 3-Deoxy-D-manno-Octulosonic Acid (KDO), an integral component of the lipopolysaccharide (LPS). A kdsD mutant was constructed in the Schu S4 strain. Although it was not resistant to ciprofloxacin, the kdsD mutant shared many phenotypic characteristics with the CipR mutant, including growth defects under different conditions, sensitivity to hydrophobic agents, altered LPS profiles, and attenuation in multiple models of murine tularemia. This study demonstrates that the KdsD enzyme is essential for Francisella virulence and may be an attractive therapeutic target for developing novel medical countermeasures.

Direct Photolysis of Fluoroquinolone Antibiotics at 253.7 nm: Specific Reaction Kinetics and Formation of Equally Potent Fluoroquinolone Antibiotics

Three fluoroquinolone-to-fluoroquinolone antibiotic transformations were monitored during UV-C irradiation processes. In particular, the following reactions were observed: enrofloxacin-to-ciprofloxacin, difloxacin-to-sarafloxacin, and pefloxacin-to-norfloxacin. The apparent molar absorptivity and fluence-based pseudo-first-order rate constants for transformation of the six fluoroquinolones by direct photolysis at 253.7 nm were determined for the pH 2-12 range. These parameters were deconvoluted to calculate specific molar absorptivity and fluence-based rate constants for cationic, zwitterionic, and anionic fluoroquinolone species. For a typical disinfection fluence of 40 mJ/cm(2), the apparent transformation efficiencies were inflated by 2-8% when fluoroquinolone products were not considered; moreover, the overall transformation efficiencies at 400 mJ/cm(2) varied by up to 40% depending on pH. The three product antibiotics, namely ciprofloxacin, sarafloxacin, and norfloxacin, were found to be equally or more potent than the parent fluoroquinolones using an Escherichia coli-based assay. UV treatment of a solution containing difloxacin was found to increase antimicrobial activity due to formation of sarafloxacin. These results highlight the importance of considering antibiotic-to-antibiotic transformations in UV-based processes.

Prevalence of gyrA Mutations in Nalidixic Acid-Resistant Strains of Salmonella Enteritidis Isolated from Humans, Food, Chickens, and the Farm Environment in Brazil

Salmonella Enteritidis strains that are resistant to nalidixic acid and exhibit reduced susceptibility to fluoroquinolones have been increasing worldwide. In Brazil, few studies have been conducted to elucidate the quinolone resistance mechanisms of S. Enteritidis strains. This study analyzed the profile of gyrA, gyrB, parC, and parE mutations and plasmid-mediated quinolone resistance (PMQR) mechanisms in S. Enteritidis Nal^R strains isolated in Brazil. Moreover, the minimum inhibitory concentrations (MICs) of ciprofloxacin were evaluated in 84 Nal^R strains and compared with 20 Nal^S strains. The mutation profiles of the gyrA gene were accessed by high-resolution melting analysis and gyrB, parC, and parE by quinolone resistance-determining region sequencing. The MICs of ciprofloxacin were accessed with Etest^®. The strains were divided into five gyrA melting profiles. The Nal^R strains exhibited the following amino acid substitutions: Ser97→Pro, Ser83→Phe, Asp87→Asn, or Asp87→Tyr. The average MICs of ciprofloxacin was 0.006 μg/ml in the Nal^S and 0.09 μg/ml in the Nal^R strains. No points of mutation were observed in the genes gyrB, parC, and parE. The qnrB gene was found in two strains. In conclusion, the reduced susceptibility to ciprofloxacin observed in Nal^R strains may cause treatment failures once this drug is commonly used to treat Salmonella infections. Moreover, this reduced susceptibility in these Brazilian strains was provided by target alteration of gene gyrA and not by mobile elements, such as resistance plasmids.

The effects of ciprofloxacin on early life stages of common carp (Cyprinus carpio)

The authors performed a toxicity test with ciprofloxacin in fertilized eggs of common carp according to guideline 210 of the Organisation for Economic Co-operation and Development. The tested concentrations were 1 μg L(-1) , 100 μg L(-1) , 500 μg L(-1) , 1000 μg L(-1) , and 3000 μg L(-1) . Accelerated hatching was found in all groups exposed to ciprofloxacin, but significant growth reduction was found only in the group exposed to the highest concentration (3000 μg L(-1) ). Increased numbers of macroscopic morphological anomalies were observed on day 6 of the test (after hatching). The highest numbers of macroscopic morphological anomalies were observed in the groups of free embryos and larvae exposed to ciprofloxacin concentrations of 100 μg L(-1) , 500 μg L(-1) , 1000 μg L(-1) , and 3000 μg L(-1) (20-23% of tested samples). A gradual decrease in glutathione S-transferase activity was detected in all experimental groups exposed to ciprofloxacin, but significant differences (p < 0.01) were found only in groups treated with 500 μg L(-1) and 3000 μg L(-1) . Glutathione peroxidase and catalase exhibited increased activity in most of the tested concentrations (p < 0.01 and <0.05, respectively), whereas decreased glutathione reductase activity was found in the groups exposed to ciprofloxacin concentrations of 500 μg L(-1) and 3000 μg L(-1) (p < 0.05). The concentration of thiobarbituric acid-reactive substances was significantly lower (p < 0.01) in all experimental groups exposed to ciprofloxacin. The lowest-observed-effect concentration of ciprofloxacin was 1 μg L(-1) . These results suggest that hatching, early ontogeny, occurrence of morphological anomalies, antioxidant and biotransformation enzyme activity, and lipid peroxidation in fish can be affected by ciprofloxacin. Environ Toxicol Chem 2016;35:1733-1740. © 2015 SETAC.