Nitrofurantoin Concentrations Research Articles

A new Ag‐based photocatalyst for efficient degradation of antibiotic nitrofurantoin

In this paper, a new 0D Ag(I)‐based coordination polymer [Ag2(dib)(H2L)2](1) is proposed as a photocatalyst for the photocatalytic degradation of nitrofurantoin (NFT) under ultraviolet irradiation. The catalytic 1 was analyzed by various methods such as PXRD, SEM, FT‐IR, TGA, UV–vis, DRS, and electrochemical tests. The experimental result shows that 1 is an n‐type semiconductor, which can effectively catalyze the photodegradation of NFT under ultraviolet irradiation. Under the optimal reaction conditions, the photodegradation rate of NFT was 97.95% within 60 min when the concentration of NFT was 30 ppm. The experiment of free radical capture shows that O2˙− is the main active substance for photodecomposition, and the possible mechanism of 1 catalytic degradation of NFT is proposed. This research will lay the foundation for Ag(I)‐based coordination polymers in the field of antibiotic photocatalytic degradation.

Pharmacokinetic and pharmacodynamic evaluation of nitrofurantoin against Escherichia coli in a murine urinary tract infection model.

The antimicrobial agent nitrofurantoin is becoming increasingly important for treatment of urinary tract infections (UTIs) due to widespread occurrence of multidrug-resistant Escherichia coli. Despite many years of use, little data on nitrofurantoin pharmacokinetics (PK) or -dynamics (PD) exist. The objective of this study was to (i) evaluate the pharmacokinetics of nitrofurantoin in a mouse model and (ii) use that data to design an in vivo dose fractionation study in an experimental model of UTI with E. coli for determination of the most predictive PK/PD index. Nitrofurantoin concentrations in urine were approximately 100-fold larger than concentrations in plasma after oral administration of 5, 10, and 20 mg/kg nitrofurantoin. The area under the curve over the minimum inhibitory concentration (AUC/MIC) was weakly correlated to bacterial reduction in urine (r2 = 0.24), while no such correlation was found for the time that nitrofurantoin stayed above the MIC (T > MIC). Increasing size of single-dose treatment was significantly correlated to eradication of bacteria in the urine, while this was not apparent when the same doses were divided in 2 or 3 doses 8 or 12 h apart. In conclusion, the results indicate that nitrofurantoin activity against E. coli in urine is driven by AUC/MIC.

Rapid Quantitative Detection for Nitrofurantoin Based on Nitrogen-Doped Highly Photoluminescent Carbon Dots.

Nitrogen-doped carbon dots (NCD) with high fluorescence retention and good stability were successfully fabricated using citric acid and urea via a facile and eco-friendly one-step microwave method, which exhibited superior specificity for detection of nitrofurantoin (NFT). Upon the addition of NFT, the fluorescence intensity of NCD at 450 nm was significantly decreased. Besides, a satisfactory linear relationship between the fluorescence quenching efficiency and concentrations of NFT was obtained. Especially, NCD was qualitatively and quantitatively applied for detection NFT in milk and meat extract samples with a high recovery rate. Consequently, it was suggested that the detection method had potential application in the specific detection of NFT, offering a novel approach for veterinary drug residue detection.

IS1-related large-scale deletion of chromosomal regions harbouring the oxygen-insensitive nitroreductase gene nfsB causes nitrofurantoin heteroresistance in Escherichia coli.

Nitrofurantoin is a broad-spectrum first-line antimicrobial used for managing uncomplicated urinary tract infection (UTI). Loss-of-function mutations in chromosomal genes nfsA, nfsB and ribE of Escherichia coli are known to reduce nitrofurantoin susceptibility. Here, we report the discovery of nitrofurantoin heteroresistance in E. coli clinical isolates and a novel genetic mechanism associated with this phenomenon. Subpopulations with lower nitrofurantoin susceptibility than major populations (hereafter, nitrofurantoin-resistant subpopulations) in two E. coli blood isolates (previously whole-genome sequenced) were identified using population analysis profiling. Each isolate was known to have a loss-of-function mutation in nfsA. From each isolate, four nitrofurantoin-resistant isolates were derived at a nitrofurantoin concentration of 32 mg l-1, and a comparator isolate was obtained without any nitrofurantoin exposure. Genomes of derived isolates were sequenced on Illumina and Nanopore MinION systems. Genetic variation between isolates was determined based on genome assemblies and read mapping. Nitrofurantoin minimum inhibitory concentrations (MICs) of both blood isolates were 64 mg l-1, with MICs of major nitrofurantoin-susceptible populations varying from 4 to 8 mg l-1. Two to 99 c.f.u. per million demonstrated growth at the nitrofurantoin concentration of 32 mg l-1, which is distinct from that of a homogeneously susceptible or resistant isolate. Derived nitrofurantoin-resistant isolates had 11-66 kb deletions in chromosomal regions harbouring nfsB, and all deletions were immediately adjacent to IS1-family insertion sequences. Our findings demonstrate that the IS1-associated large-scale genetic deletion is a hitherto unrecognized mechanism of nitrofurantoin heteroresistance and could compromise UTI management. Further, frequencies of resistant subpopulations from nitrofurantoin-heteroresistant isolates may challenge conventional nitrofurantoin susceptibility testing in clinical settings.

Assessing the urinary concentration of nitrofurantoin and its antibacterial activity against Escherichia coli, Staphylococcus pseudintermedius, and Enterococcus faecium isolated from dogs with urinary tract infections.

Nitrofurantoin, a broad-spectrum nitrofuran class antibiotic, is applied as a first-line antibiotic in treating human urinary tract infections (UTIs) due to its great efficacy and high achievable concentration. The interest in using this antibiotic in companion animals has increased due to the growing demand for effective antibiotics to treat UTIs caused by multidrug-resistant bacteria. Currently, the susceptibility interpretations for nitrofurantoin are based on the breakpoints set for humans, while the canine-specific breakpoints are still unavailable. In this study, we assessed the concentration of nitrofurantoin reaching the dog's urine using the recommended oral dosing regimen. In addition, we examined the efficacy of this breakpoint concentration against the common canine UTI pathogens, Escherichia coli, Staphylococcus pseudintermedius, and Enterococcus faecium. Eight experimental beagle dogs were treated with ~5 mg/kg of nitrofurantoin macrocrystal PO 8qh for 7 days. The urine samples were collected via cystocentesis at 2, 4, and 6 h after administration on day 2 and day 7 and used to quantify nitrofurantoin concentrations by ultra-high performance liquid chromatography. The results showed that 26.13-315.87 μg/mL nitrofurantoin was detected in the dogs' urine with a mean and median concentration of 104.82 and 92.75 μg/mL, respectively. Additionally, individual dogs presented with urinary nitrofurantoin concentrations greater than 64 μg/mL for at least 50% of the dosing intervals. This concentration efficiently killed E. coli, and S. pseudintermedius, but not E. faecium strains carrying an MIC90 value equal to 16, 16, and 128 μg/mL, respectively. Taken together, these results suggest that the value of 64 μg/mL may be set as a breakpoint against UTI pathogens, and nitrofurantoin could be an effective therapeutic drug against E. coli and S. pseudintermedius for canine UTIs.

Nitrofurantoin removal by the photo-Fenton process: degradation, mineralization, and biological inactivation

ABSTRACT Antibiotics may induce super-resistant bacteria if they are available in the environment. Therefore, the removal of aqueous nitrofurantoin (NFT), and more importantly, the removal of the remaining antimicrobial activity after treatment, by the photo-Fenton process, was herein studied. Degradation experiments were performed according to an experimental design (0.5% error; factors: concentrations of NFT, Fe3+, and H2O2). Degradation conditions were: 20 mg NFT L−1, 10 mg Fe3+ L−1, and 170 mg H2O2 L−1. Fixed parameters were: 100 mL of the NFT solution, pH 2.5, 15-min stirring, and 25.0 ± 0.5°C. The initial rate constant (k 0) and the maximum oxidation capacity (MOC) of the system were 0.61 min−1 and 100%, respectively (R 2 = 0.986). 97% of the NFT and 93% of the organic carbon initially present were removed. Five degradation products (DPs) were detected by HPLC-MS and their endpoints estimated by the ECOSAR (ECOlogical Structure–Activity Relationships) 2.0 software. NFT and its DPs presented no toxicity towards Lactuca sativa. The antimicrobial activity (Escherichia coli) of NFT and/or DPs was completely removed in 15 min. Structures were proposed for the detected DPs. In short, the tested advanced oxidation technology (AOP), besides being capable of removing and mineralizing aqueous NFT in a short time, 15 min, also rendered the treated water biologically inactive (no ecotoxicity, no antimicrobial activity).

Oral administration of an extended-release formulation of nitrofurantoin results in high concentrations in the urine of dogs.

Sporadic bacterial cystitis in both dogs and humans is often caused by Escherichia coli. In humans, nitrofurantoin is a first-line antimicrobial for the treatment of bacterial cystitis but in dogs a lack of available data may be part of the reason it is only recommended as a second-line treatment. The objective of this preliminary study was to determine the plasma pharmacokinetics and urine concentrations of nitrofurantoin monohydrate-macrocrystalline in dogs. 8 healthy female hound dogs. From July 26 to July 28, 2021, dogs received a single oral dose of nitrofurantoin monohydrate-macrocrystalline 100 mg with food. Blood and urine were collected at predetermined times. Nitrofurantoin concentrations were assayed by UPLC-MS/MS and plasma data were analyzed using noncompartmental methods. Plasma concentrations were low for all dogs with a mean ± SD maximum concentration (Cmax) of 0.242 ± 0.098 μg/mL (range, 0.14 to 0.42 µg/mL) occurring between 2 and 24 hours. Urine concentrations were manyfold higher than for plasma. Cmax in urine was 134 ± 54 µg/mL (range, 49.1 to 218 µg/mL) occurring between 6 and 36 hours. As seen in other species, nitrofurantoin concentrated in urine with concentrations being 500 times higher than the concentration in plasma. Results suggested that nitrofurantoin monohydrate-macrocrystalline formulation of nitrofurantoin should be effective in treating bacterial cystitis caused by susceptible uropathogens.

Effect of Sub-Inhibitory Concentrations of Nitrofurantoin, Ciprofloxacin, and Trimethoprim on In Vitro Biofilm Formation in Uropathogenic Escherichia coli (UPEC).

The purpose of this study was to determine the effect of sublethal concentrations of nitrofurantoin, ciprofloxacin, and trimethoprim on biofilm formation in 57 uropathogenic Escherichia coli strains (UPEC). The minimum inhibitory concentration of nitrofurantoin, ciprofloxacin, and trimethoprim was determined and the biofilm formation for each isolate with and without sub-lethal concentrations of each antibiotic was then quantified. The statistical significance of changes in biofilm formation was ascertained by way of a Dunnett's test. A total of 22.8% of strains were induced to form stronger biofilms by nitrofurantoin, 12% by ciprofloxacin, and 19% by trimethoprim; conversely 36.8% of strains had inhibited biofilm formation with nitrofurantoin, 52.6% with ciprofloxacin, and 38.5% with trimethoprim. A key finding was that even in cases where the isolate was resistant to an antibiotic as defined by EUCAST, many were induced to form a stronger biofilm when grown with sub-MIC concentrations of antibiotics, especially trimethoprim, where six of the 22 trimethoprim resistant strains were induced to form stronger biofilms. These findings suggest that the use of empirical treatment with trimethoprim without first establishing susceptibility may in fact potentiate infection in cases where a patient who is suffering from a urinary tract infection (UTI) caused by trimethoprim resistant UPEC is administered trimethoprim. This emphasizes the need for laboratory-guided treatment of UTI.

Exploring the in situ evolution of nitrofurantoin resistance in clinically derived uropathogenic Escherichia coli isolates.

Nitrofurantoin has been re-introduced as a first-choice antibiotic to treat uncomplicated acute urinary tract infections in England and Wales. Highly effective against common uropathogens such as Escherichia coli, its use is accompanied by a low incidence (<10%) of antimicrobial resistance. Resistance to nitrofurantoin is predominantly via the acquisition of loss-of-function, step-wise mutations in the nitroreductase genes nfsA and nfsB. To explore the in situ evolution of NitR in E. coli isolates from 17 patients participating in AnTIC, a 12-month open label randomized controlled trial assessing the efficacy of antibiotic prophylaxis in reducing urinary tract infections (UTIs) incidence in clean intermittent self-catheterizing patients. The investigation of NitR evolution in E. coli used general microbiology techniques and genetics to model known NitR mutations in NitS E. coli strains. Growth rate analysis identified a 2%-10% slower doubling time for nitrofurantoin resistant strains: NitS: 20.8 ± 0.7 min compared to NitR: 23 ± 0.8 min. Statistically, these data indicated no fitness advantage of evolved strains compared to the sensitive predecessor (P-value = 0.13). Genetic manipulation of E. coli to mimic NitR evolution, supported no fitness advantage (P-value = 0.22). In contrast, data argued that a first-step mutant gained a selective advantage, at sub-MIC (4-8 mg/L) nitrofurantoin concentrations. Correlation of these findings to nitrofurantoin pharmacokinetic data suggests that the low incidence of E. coli NitR, within the community, is driven by urine-based nitrofurantoin concentrations that selectively inhibit the growth of E. coli strains carrying the key first-step loss-of-function mutation.

Stability study of extemporaneously compounded nitrofurantoin oral suspensions for pediatric patients.

To evaluate the stability of nitrofurantoin suspended in different extemporaneously compounded vehicles after storage at 4°C and at 25°C. To formulate an effective, readily available vehicle that can guarantee extended stability and precise dosing.

Formation and Parallel Manipulation of Gradient Droplets on a Self-Partitioning SlipChip for Phenotypic Antimicrobial Susceptibility Testing

Flexible, robust, and user-friendly screening systems with a large dynamic range are highly desired in scientific research, industrial development, and clinical diagnostics. Droplet-based microfluidic systems with gradient concentrations of chemicals have been demonstrated as promising tools to provide confined microenvironments for screening tests with small reaction volumes. However, the generation and manipulation of gradient droplets, such as droplet merging, generally require sophisticated fluidic manipulation systems, potentially limiting their application in decentralized settings. We present a gradient-droplet SlipChip (gd-SlipChip) microfluidic device that enables instrument-free gradient droplet formation and parallel manipulation. The device can establish a gradient profile by free interfacial diffusion in a continuous fluidic channel. With a simple slipping step, gradient droplets can be generated by a surface tension-driven self-partitioning process. Additional reagents can be introduced in parallel to these gradient droplets with further slipping operations to initiate screening tests of the droplets over a large concentration range. To profile the concentration in the gradient droplets, we establish a numerical simulation model and verify it with hydrogen chloride (HCl) diffusion, as tested with a dual-color pH indicator (methyl orange and aniline blue). As a proof of concept, we tested this system with a gradient concentration of nitrofurantoin for the phenotypic antimicrobial susceptibility testing (AST) of Escherichia coli. The results of our gd-SlipChip-based AST on both reference and clinical strains of E. coli can be indicated by the bacterial growth profile within 3 h and are consistent with the clinical culture-based AST.

In-vitro antibacterial activity of Fosfomycin and Nitrofurantoin against Pseudomonas aeruginosa and Acinetobacter baumannii against clinical isolates collected from Indian tertiary care hospitals

The remarkable increase in resistance to currently available antibiotics to Gram-negative pathogens particularly multidrug resistant (MDR) Pseudomonas aeruginosa and Acinetobacter baumannii, This has resulted in increasing use of older under evaluated antibiotics such as fosfomycin, nitrofurantoin, and Trimethoprime-Sulfamethoxazole for the treatment of infections caused by MDR pathogens. However, limited in-vitro pharmacodynamic data for fosfomycin and nitrofurantoin against Pseudomonas Spp., and Acinetobacter Spp., is available in literature. The current study demonstrates in-vitro activities of fosfomycin and nitrofurantoin against Pseudomonas and Acinetobacter pathogens (425 Pseudomonas Spp., and 352 Acinetobacter Spp., Total: 777 Strains), isolated from Indian tertiary care hospitals. The minimum inhibitory concentration (MIC50/90) of fosfomycin and nitrofurantoin along with comparator antibiotics were determined using Clinical and Laboratory Standards Institute recommended agar dilution method. Fosfomycin demonstrated excellent in-vitro activity against Pseudomonas while in nitrofurantoin demonstrated poor activity against Pseudomonas Spp.,. Fosfomycin and nitrofurantoin did not show promising activities against Acinetobacter Spp.,. By applying E. coli breakpoints, the susceptibility rates of fosfomycin for Pseudomonas Spp., and Acinetobacter Spp., were 72.4%, and 14.8%, respectively. By applying respective breakpoints, the susceptibility rates of comparator drugs, including imipenem and meropenem, were lower than fosfomycin. Susceptibility rate of nitrofurantoin for Pseudomonas Spp., and Acinetobacter Spp., was &lt;1.2% suggesting its poor activity. The susceptibility rate of fosfomycin was &gt; 70% for Pseudomonas isolates, including strains expressing carbapenemases is encouraging finding and supports its potential use. Nitrofurantoin did not show activity against both the Spp., with susceptibility rates &lt;1.2%.&#x0D; Keywords: Fosfomycin, Nitrofurantoin Gram-negative, Multi Drug Resistant, A. baumannii and P. aeruginosa.

Highly sensitive and selective fluorescence sensing of nitrofurantoin based on water-soluble copper nanoclusters

In this contribution, dopamine-protected copper nanoclusters as a novel fluorescent nanosensor was employed to detect nitrofurantoin (NFT) for the first time, which were prepared by using dopamine as the stabilizing agent and sodium borohydride (NaBH4) and hydrazine hydrate (N2H4·H2O) as the reducing agents. A series of methods were used to analyze the structure and optical properties of as-prepared Cu NCs, such as UV-Vis absorption spectroscopy, fluorescence spectroscopy, Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). It possessed high dispersion, excellent water solubility, good photostability and strong green fluorescence under UV lamp (365 nm). Significantly, the FL intensities of Cu NCs were quenched with addition of NFT. The analytical method possessed good linear relationship between the relative fluorescence intensity (F0/F) and the NFT concentrations (range from 5 to 120 μM), and the limit of detection (LOD) could reach 0.73 μM. The fluorescence detection mechanisms were attributed to the static quenching and inner filter effect (IFE). In addition, this proposed fluorescence sensor has been successfully used for the detection of NFT in bovine serum samples.

Nitrofurantoin, monoliths and taboos

In 1968, Joseph Sachs et al. published a report in the New England Journal of Medicine on urinary concentrations of nitrofurantoin after its oral administration to an unspecified number of hospitalized individuals, some of whom required treatment for active urinary tract infection [1]. Recovery of nitrofurantoin from the urine appeared to be linearly related to creatinine clearance. In ‘uraemic’ individuals, whose creatinine clearances were not reported, the highest nitrofurantoin concentrations reached were considered probably too low to inhibit the growth of uropathogens, although neither MICs nor microbiological or clinical outcomes were reported.

Exposure to sub-inhibitory ciprofloxacin and nitrofurantoin concentrations increases recA gene expression in uropathogenic Escherichia coli: The role of RecA protein as a drug target

Sub-inhibitory concentrations (sub-MIC) of antimicrobial agents can lead to genetic changes in bacteria, modulating the expression of genes related to bacterial stress and leading to drug resistance. Herein we describe the impact of sub-MIC of ciprofloxacin and nitrofurantoin on three uropathogenic Escherichia coli strains. Disk-diffusion assays with different antimicrobial agents were tested to detect phenotype alterations, and quantitative real-time PCR (qRT-PCR) was performed to analyze the expression of ompF and recA genes. Significant reduction on the susceptibility to ciprofloxacin and nitrofurantoin was detected on disk diffusion test. The qRT-PCR results revealed a 1.2–4.7 increase in recA expression in all E. coli studied, while the ompF expression varied. Because RecA was pointed as an important component to the development of drug resistance, molecular docking studies were performed with three experimentally known inhibitors of this enzyme. These studies aimed to understand the inhibitory binding mode of such compounds. The results confirmed the ADP/ATP binding site as a potential site of inhibitor recognition and a binding mode based on π-stacking interactions with Tyr103 and hydrogen bonds with Tyr264. These findings can be useful for guiding the search and design of new antimicrobial agents, mainly concerning the treatment of infections with resistant bacterial strains.

Urinary antibacterial activity of fosfomycin and nitrofurantoin at registered dosages in healthy volunteers

Given emerging uropathogen resistance to more recent antibiotics, old antibiotics used for uncomplicated urinary tract infection (UTI) warrant re-examination. In this study, the urinary antibacterial activities of fosfomycin and nitrofurantoin were investigated by determining the urinary inhibitory titre and urinary bactericidal titre against uropathogens in urine samples from female volunteers following administration of single-dose fosfomycin (3 g) or nitrofurantoin (50 mg q6h or 100 mg q8h). Urine samples were collected over 48 h (fosfomycin) or 6 or 8 h (nitrofurantoin), with drug levels quantified with every void. Fosfomycin concentrations ranged from <0.75 mg/L [lower limit of quantification (LLOQ)] to 5729.9 mg/L and nitrofurantoin concentrations ranged from <4 mg/L (LLOQ) to 176.3 mg/L (50 mg q6h) or 209.4 mg/L (100 mg q8h). There was discrepancy in the response to fosfomycin between Escherichia coli and Klebsiella pneumoniae, with fosfomycin displaying strong bactericidal activity for 48 h against E. coli but moderate bactericidal activity for 18 h against K. pneumoniae. This effect was not related to the strain's baseline minimum inhibitory concentration but rather to the presence of a resistant subpopulation. Maximum titres of nitrofurantoin were obtained during the first 2 h, but no antibacterial effect was found in most samples regardless of the dose. In the rare samples in which antibacterial activity was detectable, titres were comparable for both species tested. These findings confirm doubts regarding fosfomycin administration in UTIs caused by K. pneumoniae and reveal a discrepancy between nitrofurantoin's measurable ex vivo activity and its clinical effect over multiple dosing intervals.

Nutrition Related Stress Factors Reduce the Transfer of Extended-Spectrum Beta-Lactamase Resistance Genes between an Escherichia coli Donor and a Salmonella Typhimurium Recipient In Vitro.

The transfer of extended spectrum β-lactamase (ESBL)-genes occurs frequently between different bacteria species. The aim of this study was to investigate the impact of nutrition related stress factors on this transfer. Thus, an Escherichia coli donor and a Salmonella Typhimurium recipient were co-incubated for 4 h in media containing different levels of the stress factors’ pH, osmolality, copper, zinc and acetic, propionic, lactic, and n-butyric acid, as well as subtherapeutic levels of cefotaxime, sulfamethoxazole/trimethoprim, and nitrofurantoin. Conjugation frequencies were calculated as transconjugants per donor, recipient, and total bacterial count. A correction factor for the stress impact on bacterial growth was used. Acetic, lactic, and n-butyric, acid, as well as pH, showed no significant impact. In contrast, increasing concentrations of propionate, zinc, copper, and nitrofurantoin, as well as increased osmolality reduced conjugation frequencies. Sulfamethoxazole/trimethoprim and cefotaxime showed increased transconjugants per donor, which decreased after correction for stress. This study showed, for the model mating pair, that conjugation frequencies decreased under different physiological stress conditions, and, thus, the hypothesis that stress factors may enhance conjugation should be viewed with caution. Furthermore, for studies on in vitro gene transfer, it is vital to consider the impact of studied stressors on bacterial growth.

Pharmacodynamics of nitrofurantoin at different pH levels against pathogens involved in urinary tract infections.

Urinary tract infections are among the most common human infections. Due to the progressive increase in ESBL-producing bacteria and the unavailability of new antibiotics, re-evaluation of 'old' antibiotics is needed. However, the pharmacodynamics of nitrofurantoin under variable pH conditions are poorly understood. We determined the pharmacodynamic properties of nitrofurantoin at different pH levels using time-kill assays. Time-kill assays were performed at four pH levels (5.5, 6.5, 7.5 and 8.5), exposing the bacteria to 2-fold increasing concentrations from 0.125 to 32 times the MIC. Seven ESBL-positive and two ESBL-negative strains (MICs 8-32 mg/L) were used. The Δlog10 cfu/mL values at 6 and 24 h were plotted against each log10-transformed concentration and analysed with non-linear regression analysis using the sigmoid maximum effect model with variable slope. Geometric means normalized by the MIC of the EC50, stasis and 1 and 3 log10 cfu/mL kill were calculated. Minimum bactericidal effects differed significantly by species and pH level. At pH 5.5-6.5 bactericidal effects were observed at ≥ 0.5 × MIC for Escherichia coli and Enterobacter cloacae. At pH 8.5 only the two highest concentrations were considered bactericidal. Strong pH-dependent pharmacodynamic output parameters were observed in 6 h and especially 24 h modelling. At 24 h, pH 5.5-6.5 for E. coli and Klebsiella pneumoniae required significantly lower nitrofurantoin concentrations compared with pH 7.5 or 8.5. Although for E. cloacae similar strong decreasing trends were visible with decreasing pH, none of the tested pharmacodynamic parameters was significant. Nitrofurantoin bactericidal activity against Enterobacteriaceae significantly increases at lower pH levels. Bactericidal activity of nitrofurantoin may be overestimated or underestimated, which may have implications for therapy and the interpretation of clinical breakpoints.

Genetic diversity of Enterococcus faecalis isolated from environmental, animal and clinical sources in Malaysia.

Enterococcus faecalis ranks as one of the leading causes of nosocomial infections. A strong epidemiological link has been reported between E. faecalis inhabiting animals and environmental sources. This study investigates the genetic diversity, antibiotic resistance and virulence determinants in E. faecalis from three sources in Malaysia. A total of 250 E. faecalis isolates were obtained consisting of 120 isolates from farm animals, 100 isolates from water sources and 30 isolates from hospitalized patients. Pulse-field gel electrophoresis-typing yielded 63 pulsotypes, with high diversity observed in all sources (D=≥0.901). No pulsotype was common to all the three sources. Each patient room had its own unique PFGE pattern which persisted after six months. Minimum inhibitory concentrations of Vancomycin, Gentamicin, Penicillin, Tetracycline, Nitrofurantoin, Levofloxacin, Ciprofloxacin and Fosfomycin were evaluated. Resistance to Tetracycline was most prevalent in isolates from farm animals (62%) and water sources (49%). Water isolates (86%) had a higher prevalence of the asa1 gene, which encodes for aggregation substance, whereas clinical (78%) and farm animal isolates (87%) had a higher prevalence of the esp gene, encoding a surface exposed protein. This study generates knowledge on the genetic diversity of E. faecalis with antibiotic resistance and virulence characteristics from various sources in Malaysia.

Development and analysis of furazolidone-resistant Escherichia coli mutants.

Furazolidone-resistant mutants were obtained from four clinical isolates of diarrhoeagenic Escherichia coli. The stability of the resistance and the frequency of mutation were established. The minimal inhibitory concentration of furazolidone, nitrofurantoin, nalidixic acid, ampicillin, chloramphenicol and tetracycline was established both in the presence and absence of the efflux pump inhibitor Phe-Arg-β-Naphtylamyde. The presence of mutations in the nitroreductase genes nfsA and nfsB was analysed by PCR; sequencing and their enzymatic activity was assessed by a spectrophotometric assay. Alterations in outer membrane proteins were studied by SDS-PAGE. The frequency of mutation ranged from <9.6×10(-10) to 9.59×10(-7) . Neither an effect on efflux pumps inhibited by Phe-Arg-β-Naphtylamyde nor cross-resistance with the antibiotics studied was observed. Nineteen mutants (52.94%) presented mutations in the nitroreductase-encoding genes: 17 in the nfsA gene (15 mutants with an internal stop codon, 2 with amino acid changes), 2 in the nfsB (all amino acid changes). Alterations in the outer membrane proteins OmpA and OmpW were also observed. Although more studies are necessary to find other resistance mechanisms, present data showed the low potential of selecting furazolidone-resistant mutants, together with the lack of cross-resistance with unrelated antimicrobial agents.