Improving nitrofurantoin resistance prediction in Escherichia coli from whole-genome sequence by integrating NfsA/B enzyme assays.

Nitrofurantoin resistance in Escherichia coli is primarily caused by mutations damaging two enzymes, NfsA and NfsB. Studies based on small isolate collections with defined nitrofurantoin MICs have found significant random genetic drift in nfsA and nfsB, making it extremely difficult to predict nitrofurantoin resistance from whole-genome sequence (WGS) where both genes are not obviously disrupted by nonsense or frameshift mutations or insertional inactivation. Here, we report a WGS survey of 200 oqxAB-negative E. coli from community urine samples, of which 34 were nitrofurantoin resistant. We characterized individual non-synonymous mutations seen in nfsA and nfsB among this collection using complementation cloning and NfsA/B enzyme assays in cell extracts. We definitively identified R203C, H11Y, W212R, A112E, and A112T in NfsA and R121C, Q142H, F84S, P163H, W46R, K57E, and V191G in NfsB as amino acid substitutions that reduce enzyme activity sufficiently to cause resistance. In contrast, E58D, I117T, K141E, L157F, A172S, G187D, and A188V in NfsA and G66D, M75I, V93A, and A174E in NfsB are functionally silent in this context. We identified that 9/166 (5.4%) nitrofurantoin-susceptible isolates were "pre-resistant," defined as having loss of function mutations in nfsA or nfsB. Finally, using NfsA/B enzyme assays and proteomics, we demonstrated that 9/34 (26.5%) ribE wild-type nitrofurantoin-resistant isolates also carried functionally wild-type nfsB or nfsB/nfsA. In these cases, NfsA/B activity was reduced through downregulated gene expression. Our biological understanding of nitrofurantoin resistance is greatly improved by this analysis but is still insufficient to allow its reliable prediction from WGS data.

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.

Drug-Drug Binary Solids of Nitrofurantoin and Trimethoprim: Crystal Engineering and Pharmaceutical Properties.

With the aim of developing multidrug solids through a tuned crystal engineering approach, we have selected two antiurinary infective drugs, namely, nitrofurantoin (NF) and trimethoprim (TMP) and isolated eight binary drug-drug solid solvates along with a nonsolvated cocrystal. Crystal structure analyses were performed for eight of these solids and rationalized in terms of known supramolecular synthons formed by pyrimidine, imide, and amine functionalities. Notably, the TMP-NF anhydrous cocrystal and its ionic cocrystal hydrate exhibit enhanced equilibrium solubilities compared to pure NF or the simple NF hydrate. Furthermore, the ionic cocrystal hydrate exhibits greater antibacterial activity against the Gram-negative bacteria, E. coli, compared to the parent TMP and NF at the lowest concentration of 3.9 µg/mL. This study indicates initial pathways using the cocrystal methodology that would help to eventually arrive at an antiurinary cocrystal with optimal properties.

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.

Efficacy of mecillinam against clinical multidrug-resistant Escherichia coli in a murine urinary tract infection model.

Pivmecillinam, a pro-drug of mecillinam, has been used extensively in Scandinavia for the treatment of acute lower urinary tract infections (UTIs) caused by Enterobacterales. It is still an attractive first-line drug for the empirical treatment of UTIs owing to the low prevalence of resistance as well as its favourable impact on the intestinal microbiota as a pro-drug and good in vitro efficacy against extended-spectrum ß-lactamase (ESBL)- and plasmid-mediated AmpC ß-lactamase-producing Escherichia coli. However, optimal dosing of pivmecillinam as well as its in vivo efficacy against UTIs caused by multidrug-resistant (MDR) broad-spectrum ß-lactamase-producing E. coli has not been thoroughly studied. In this study, the efficacy of two mimicked human dosing regimens of pivmecillinam (200 mg and 400 mg three times daily) against clinical E. coli strains, including isolates producing ESBLs (CTX-M-14 and CTX-M-15), plasmid-mediated AmpCs (CMY-4 and CMY-6) and carbapenemases (NDM-1 and VIM-29), in a murine UTI model was compared. Both dosing regimens reduced the number of CFU/mL in urine for all strains, including mecillinam-resistant strains. Combining the effect for all six strains showed no significant differences in effect between doses for all three fluids/organs, but for each dose there was a highly significant effect in urine, kidney and bladder compared with vehicle-treated mice. Overall, this highlights the need for further studies to elucidate the role of mecillinam in the treatment of infections caused by MDR E. coli producing broad-spectrum ß-lactamases, including specific carbapenemases.

[Antimicrobial Susceptibility Patterns in Outpatient Urinary Tract Infection in the District of Coimbra, Portugal: A Cross-Sectional Study]. / Perfil de Sensibilidade aos Antibióticos na Infeção Urinária em Ambulatório no Distrito de Coimbra: Um Estudo Transversal.

INTRODUCTION: Urinary tract infections in the community setting are quite common. It is necessary to be aware of antibiotic susceptibility patterns in order to provide rational empirical therapy. The aim of this study is to determine the frequency and antimicrobial susceptibility of the strains responsible for urinary tract infections in primary health care, in the district of Coimbra, Portugal. MATERIAL AND METHODS: In this observational and cross-sectional study, we analyzed 7134 positive urine cultures of outpatient laboratories in the district of Coimbra, over one year. In most cases, a positive culture was defined by a threshold of 105 colony-forming units per milliliter and was conducted by the automated system VITEK® 2, by bioMérieux. We used descriptive and inferential statistics to determine the prevalence and antimicrobial susceptibility of bacteria and to ascertain whether there were differences associated with sex and age. RESULTS: From the total of positive cultures, 83.4% pertained to females and 41.0% to individuals over 75 years old. Escherichia coli was the most frequent strain (63.9%), although its prevalence was lower (p < 0.001) in males and individuals over 75 years old. Its susceptibility to fosfomycin and nitrofurantoin was higher than 95% and with ciprofloxacin and trimethoprim/sulfamethoxazole it was lower than 80%. Resistances were more frequent (p < 0.001) in males and in the elderly. DISCUSSION: Escherichia coli was the most frequent strain, revealing less resistance to fosfomycin and nitrofurantoin. Antimicrobial susceptibility was lower in the elderly and in males, populations in whom empirical therapy may be less successful. CONCLUSION: In order to improve clinical results, we recommend periodic surveillance of antimicrobial susceptibility, which could enable the provision of efficient information to clinicians, namely those who prescribe empirically for such infections, as well as standardization of identification methods of bacterial strains diagnosis and of the antibiotic kits to be tested.

Introdução: As infeções do trato urinário são muito frequentes na comunidade. É essencial conhecer o padrão de sensibilidade aos antibióticos para uma terapêutica empírica racional. O objetivo deste estudo é determinar a prevalência e o perfil de suscetibilidade aos antibióticos dos microrganismos implicados em infeções urinárias a nível dos cuidados primários de saúde, no distrito de Coimbra.Material e Métodos: Neste estudo observacional e transversal, analisámos 7134 uroculturas positivas de laboratórios de ambulatório do distrito de Coimbra, no período de um ano. Na maioria dos casos, a urocultura positiva foi definida por um limiar de 105 unidadesformadoras de colónias por mililitro e executada através do sistema automatizado VITEK® 2, da bioMérieux. Usámos estatística descritiva e inferencial para determinar a prevalência e a sensibilidade aos antibióticos dos microrganismos e averiguar a relação destas com o sexo e com a idade.Resultados: Do total de uroculturas positivas, 83,4% pertencia ao sexo feminino e 41,0% pertencia à população acima dos 75 anos. A Escherichia coli foi o microrganismo mais frequente (63,9%), mas a sua prevalência foi inferior (p < 0,001) no sexo masculino e acima dos 75 anos. A sua sensibilidade à fosfomicina e à nitrofurantoína foi superior a 95% e à ciprofloxacina e ao cotrimoxazol foi inferior a 80%. As resistências foram mais frequentes (p < 0,001) no sexo masculino e nos mais idosos.Discussão: A Escherichia coli foi o microrganismo mais frequente, verificando-se menores percentagens de resistência desta à fosfomicina e à nitrofurantoína. A sensibilidade aos antibióticos foi menor em idades mais avançadas e também no sexo masculino (p < 0,001), populações onde a antibioterapia empírica pode ter maior risco de insucesso.Conclusão: Recomendamos a monitorização periódica do perfil de sensibilidade aos antibióticos, para eficaz informação aos médicos que têm de proceder a terapêutica empírica deste tipo de infeções, bem como a uniformização das técnicas de identificação das estirpes bacterianas e dos conjuntos de antibióticos a serem testados nos antibiogramas.

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.

Susceptibility of carbapenemase-producing Enterobacterales (CPE) to nitroxoline.

BACKGROUND: Infections caused by carbapenemase-producing Enterobacterales (CPE) constitute a major global health concern and are associated with increased morbidity and mortality. Nitroxoline is an old antibiotic, which has recently been re-launched for the treatment of uncomplicated urinary tract infection. Because of low resistance rates it could be an interesting option for treatment of MDR isolates, yet data on CPE susceptibility are scarce. OBJECTIVES: To analyse the in vitro activity of nitroxoline against CPE. METHODS: MICs of nitroxoline were determined by agar dilution for a collection of well-characterized carbapenemase producers (n = 105), producing OXA-48-like (n = 36), VIM (n = 21), IMI (n = 9), IMP (n = 6), NDM (n = 22), KPC (n = 11), OXA-58 (n = 2) and GES (n = 2). For comparison, MICs of ertapenem, imipenem and meropenem were determined by agar gradient diffusion. RESULTS: For all 105 isolates, the MIC50/90 of nitroxoline was 8/16 mg/L. All Escherichia coli isolates (30/30, 100%) showed low MICs of 2-8 mg/L and were susceptible to nitroxoline. MICs of 32 mg/L were recorded for five isolates of VIM- and IMI-producing Enterobacter cloacae (n = 3) and OXA- and VIM-producing Klebsiella pneumoniae (n = 2). CONCLUSIONS: Nitroxoline exhibited excellent in vitro activity against most isolates producing common and rare carbapenemases. If the current EUCAST susceptibility breakpoint of ≤16 mg/L for E. coli in uncomplicated urinary tract infections was applied, 95.2% (100/105) of isolates would be classified as susceptible. Nitroxoline could therefore be an alternative oral option for treatment of uncomplicated urinary tract infections caused by CPE.

Efflux pumps AcrAB and OqxAB contribute to nitrofurantoin resistance in an uropathogenic Klebsiella pneumoniae isolate.

Klebsiella pneumoniae is a common cause of urinary tract infections (UTIs). Nitrofurantoin (NIT), with high therapeutic concentrations in urine, is recommended as the first-line drug for both empiric treatment and chemoprophylaxis of UTIs. Although NIT resistance in K. pneumoniae is relatively high, the resistance mechanism is not well understood. This study collected a NIT-resistant K. pneumoniae [NRKP, minimum inhibitory concentration (MIC)=128 mg/L] and investigated the resistance mechanism. Addition of efflux pump inhibitors increased the susceptibility of NRKP to NIT (MIC decreased from 128 to 32 mg/L), implying the important role of efflux pumps in NIT resistance. Quantitative reverse transcriptase polymerase chain reaction analysis showed that NRKP had >100-fold increased expression of ramA, which was demonstrated to be caused by ramR mutation. Deletion of ramA led to a four-fold decrease in the MIC of NIT, and the expression levels of efflux pumps acrB and oqxB were downregulated by four- to seven-fold. Complementation of ramA restored both the MIC value and the expression level of acrB and oqxB in the ramA mutant strain. In order to confirm the role of acrB and oqxB in NIT resistance, gene knockout strains were constructed. Deletion of acrB or oqxB alone led to a four-fold decrease in the MIC of NIT, and deletion of acrB and oqxB simultaneously led to a 16-fold decrease in the MIC of NIT. These results demonstrate that AcrAB and OqxAB contribute to NIT resistance in K. pneumoniae.

In vitro activity of mecillinam and nitroxoline against Neisseria gonorrhoeae - re-purposing old antibiotics in the multi-drug resistance era.

In 2018, the European Centre for Disease Prevention and Control reported the first cases of extensively drug-resistant Neisseria gonorrhoeae infections in Europe. Seeking new options for antimicrobial therapy we investigated the susceptibility of N. gonorrhoeae to nitroxoline (NIT) and mecillinam (MCM), both of which are currently only indicated to treat uncomplicated urinary tract infections. Clinical N. gonorrhoeae isolates with non-susceptibility to penicillin from two German medical centres were included (n =27). Most isolates were also non-susceptible to a range of other anti-gonococcal antimicrobials (cefotaxime, ciprofloxacin, azithromycin, tetracycline). All isolates were further characterized by multi-locus sequence typing. MICs of penicillin and cefotaxime were determined by agar gradient diffusion. Production of penicillinase was tested by cefinase disk test. Susceptibility of MCM was investigated by agar dilution, NIT by agar dilution and disk diffusion. Penicillin MICs ranged from 0.125 to 64 mg l-1 and MICs of cefotaxime ranged from < 0.016 to 1 mg l-1 . Five isolates were penicillinase-producers. MICs of MCM ranged from 16 to > 128 mg l-1 whereas MICs of NIT ranged from 0.125 to 2 mg l-1 . NIT disk diffusion (median zone diameter 32 mm) correlated well with results from agar dilution. We demonstrated excellent in vitro activity of NIT against clinical N. gonorrhoeae isolates with non-susceptibility to standard anti-gonococcal antibiotics. MCM activity was unsatisfactory. Correlation of agar dilution and disk diffusion in NIT susceptibility testing is an important aspect with potential clinical implications.

Ibuprofen lacks direct antimicrobial properties for the treatment of urinary tract infection isolates.

The high incidence of urinary tract infection (UTI) among women and children, in combination with a lack of antibiotic efficacy with regard to pathogen eradication and recurrence prevention, as well as the negative side effects associated with antibiotics, has led researchers to explore the role of non-steroidal anti-inflammatory drugs as a primary management strategy. The aim of this study was to determine whether ibuprofen (IBU) or one of its major metabolites, 2-carboxyibuprofen (CIBU), could affect the growth and adhesion of the two most common uropathogens, Escherichia coli and Enterococcus faecalis. The bacterial growth and adhesion to the urothelial cells of E. coli UTI89 and E. faecalis 1131 in the presence of physiologically relevant concentrations of IBU and CIBU were assessed. The effect of IBU on bacterial adhesion to urothelial cells was also assessed following exposure to trimethoprim/sulfamethoxazole (TMP/SMX) and nitrofurantoin. Bacterial growth was not affected by IBU. Further, only at high levels of IBU not regularly found in the bladder was there a significant increase in E. faecalis 1131 attachment at growth inhibitory concentrations of TMP/SMX. There was no effect on the attachment of E. faecalis or E. coli to urothelial cells in the presence of nitrofurantoin. These studies indicate that the beneficial effects of IBU for UTI management are likely mediated through its anti-inflammatory properties rather than direct interactions with uropathogens in the bladder.

Emerging clinical role of pivmecillinam in the treatment of urinary tract infections caused by Extended Spectrum ßeta-lactamase (ESBL) producing Enterobacteriaceae.

BACKGROUND: Extended Spectrum ßeta-lactamase (ESBL)-producing Enterobacteriaceae causing urinary tract infections (UTIs) appear resistant to many common oral agents. There is a growing need to discover new antibiotics to combat with emerging antibiotic resistance problem. Until the discovery of new antimicrobials, we can bring back forgotten antibiotics to our clinical formulary. Pivmecillinam (prodrug of mecillinam), an oral antimicrobial agent is effective against ESBL producing organisms. We analysed the sensitivity rates of ESBL-producing Enterobacteriaceae from urine samples to mecillinam and to document if pivmecillinam is a suitable alternative option in the treatment of UTI. MATERIALS/METHODS: This retrospective study was conducted from September 2015 to September 2017. Data were collected from the pathology information system. Antimicrobial sensitivity testing on ESBL-producing Enterobacteriaceae isolates was carried out by disc diffusion method in accordance with The European Committee on Antimicrobial Susceptibility Testing. RESULTS: A total of 986 ESBL-producing Enterobacteriaceae were tested for mecillinam during the study period. Of 986 organisms, Escherichia coli was the most common organism (889); followed by Klebsiella species (71) and others Enterobacteriaceae (26). Mecillinam sensitivity was found in 96% Escherichia coli (855/889 isolates), 83% Klebsiella species (59/71 isolates) and 88% other Enterobacteriaceae (23/26 isolates). Overall 95% (935/986 isolates) of ESBL-producing urinary isolates were sensitive to mecillinam. CONCLUSIONS: Pivmecillinam appears to be suitable option to treat ESBL-producing Enterobacteriaceae causing uncomplicated UTI. Our results showed low resistance rate to mecillinam. We recommend the use of pivmecillinam in uncomplicated UTIs because of ESBL-producing Enterobacteriaceae. More studies on in vitro activity of mecillinam against ESBL producing organism and its use and clinical outcome should be tried in future.

Optimizing dosing of nitrofurantoin from a PK/PD point of view: What do we need to know?

Nitrofurantoin is an old antibiotic and an important first-line oral antibiotic for the treatment of uncomplicated urinary tract infections. However despite its long term use for over 60 years, little information is available with respect to its dose justification and this may be the reason of highly variable recommended doses and dosing schedules. Furthermore, nitrofurantoin is not a uniform product -crystal sizes of nitrofurantoin, and therefore pharmacokinetic properties, differ significantly by product. Moreover, pharmacokinetic profiling of some products is even lacking, or difficult to interpret because of its unstable chemical properties. Pharmacokinetic and pharmacodynamic data is now slowly becoming available. This review provides an overview of nitrofurantoins antibacterial, pharmacokinetic and pharmacodynamic properties. This shows that a clear rationale of current dosing regimens is scanty.

Antimicrobial resistance patterns in urinary E. coli isolates after a change in a single center's guidelines for uncomplicated cystitis in ambulatory settings.

Recommending nitrofurantoin to treat uncomplicated cystitis was associated with increased nitrofurantoin use from 3.53 to 4.01 prescriptions per 1,000 outpatient visits, but nitrofurantoin resistance in E. coli isolates remained stable at 2%. Concomitant levofloxacin resistance was a significant risk for nitrofurantoin resistance in E. coli isolates (odds ratio [OR], 2.72; 95% confidence interval [CI], 1.04-7.17).

Methenamine's journey of 160 years: Repurposal of an old urinary antiseptic for treatment and hypoxic radiosensitization of cancers and glioblastoma.

Methenamine (hexamethylenetetramine, hexamine, urotropine) is a compound discovered in 1859, which is still currently being used as a urinary antiseptic. Methenamine is highly soluble in water and polar solvents, and its molecular constitution is similar to adamantane compounds with tetrahedral cage like structure. In acidic conditions, methenamine decomposes to formaldehyde and ammonia. Recently, methenamine has gained a renewal of interest due to antibiotic-resistant bacteria urinary tract infections; interestingly, bacteria cannot gain resistance to formaldehyde. In 1968, David and Burkitt reported remarkable regression of four Burkitt Lymphoma patients in eight subjects who were treated with septicemine (a solution containing 6.3 g of methenamine iodomethylate and 1 g of methenamine sodium benzoate in 100 cc distilled water). Unfortunately, these striking observations did not gain interest in the medical community; despite experimental models that showed that methenamine synergized with hyperthermia, radiation, and chemotherapy to block cancer growth. As the hypoxic core of tumours have an acidic pH, it would be plausible to expect that methenamine would selectively target dormant, non-proliferative, and treatment-resistant cancer clones in large tumours. Moreover, previous data suggests that methenamine can be safely used intravenously and for treatment of infections of the central nervous system. It may therefore be an effective adjuvant in treatment of systemic cancers and glioblastoma.

Resistance of uropathogens to antibacterial agents: Emerging threats, trends and treatments.

Urinary tract infections are among the most common infectious diseases in humans. Today, resistance to nearly all antimicrobial classes is dramatically growing, and extremely drug-resistant or even pan-drug resistant pathogens are increasingly isolated around the world. It is foreseen that in the next decades the world will be facing a major medical emergency generated by the rapid spread of pathogens carrying resistance determinants of unprecedented power. Carbapenemase-producing Enterobacteriaceae, multidrug- resistant Enterococci and fluoroquinolone resistance determinants in both Gram-negative and Gram-positive uropathogens are among the greatest emergencies. In this article, the major emerging threats of particular interest to urologists are reviewed, worldwide resistance trends are illustrated, and novel and older - but still active - recommended drugs are summarized.

Unravelling mechanisms of nitrofurantoin resistance and epidemiological characteristics among Escherichia coli clinical isolates.

The aim of this study was to investigate mechanisms of nitrofurantoin resistance and epidemiological characteristics in Escherichia coli clinical isolates. From a total of 1444 E. coli clinical isolates collected from our hospital in 2015, 18 (1.2%) nitrofurantoin-resistant E. coli isolates were identified with nitrofurantoin minimum inhibitory concentrations (MICs) ranging from 128 µg/mL to ≥512 µg/mL. The prevalence of the nfsA gene in nitrofurantoin-resistant, -intermediate and -susceptible isolates was 88.9%, 88.9% and 100%, respectively, and the prevalence of the nfsB gene was 66.7%, 61.1% and 100%, respectively. Eight nitrofurantoin-resistant isolates and two nitrofurantoin-intermediate isolates possessed oqxAB genes. In nitrofurantoin-resistant isolates, mutations in NfsA (the majority of mutated sites were I117T and G187D, accounting for 38.9%) and/or NfsB were detected, whereas only NfsA mutations were found in intermediate isolates and no sequence changes were detected in susceptible isolates. A ≥4-fold decrease in MIC was observed in eight nitrofurantoin-resistant isolates following addition of the efflux pump inhibitor carbonyl cyanide m-chlorophenylhydrazone (CCCP). The mean expression level of oqxB in nitrofurantoin-resistant isolates increased ca. 7-fold compared with intermediate isolates. Multilocus sequence typing (MLST) categorised the 18 nitrofurantoin-resistant isolates into 11 different sequence types. Pulsed-field gel electrophoresis (PFGE) analysis revealed that homology among the nitrofurantoin-resistant isolates was low and sporadic. In conclusion, mutations in nfsA and nfsB were the main mechanisms leading to nitrofurantoin resistance, and overexpression of the oqxAB gene might help to further increase the MIC of nitrofurantoin.

Trimethoprim susceptibility in E. coli community-acquired urinary tract infections in France.

OBJECTIVES: Trimethoprim has been recently included in the French guidelines for the treatment of urinary tract infections, but no epidemiological data supports its use. We aimed to determine the trimethoprim susceptibility of Escherichia coli isolates responsible for community-acquired urinary tract infections in women of childbearing age. MATERIALS AND METHODS: We conducted a national prospective survey. A total of 350 strains of E. coli isolated from urines in 35 laboratories were included. Antibiotic susceptibility testing was performed in each laboratory. RESULTS: We reported a susceptibility rate of 78%, and a similar clinical categorization between trimethoprim and cotrimoxazole for 97.4% of isolates. We pointed out an association between resistance to trimethoprim and other antibiotic classes. CONCLUSION: The results support trimethoprim as a second-line therapy based on antibiotic susceptibility testing results. We confirm that trimethoprim and cotrimoxazole susceptibility rates are very close.

Empirical treatment of lower urinary tract infections in the face of spreading multidrug resistance: in vitro study on the effectiveness of nitroxoline.

The spread of antimicrobial resistance challenges the empirical treatment of urinary tract infections (UTIs). Among others, nitrofurantoin is recommended for first-line treatment, but acceptance among clinicians is limited due to chronic nitrofurantoin-induced lung toxicity and insufficient coverage of Enterobacteriaceae other than Escherichia coli. Nitroxoline appears to be an alternative to nitrofurantoin owing to its favourable safety profile, however data on its current in vitro susceptibility are sparse. In this study, susceptibility to nitroxoline was tested against 3012 urinary clinical isolates (including multidrug-resistant bacteria and Candida spp.) by disk diffusion test and/or broth microdilution. At least 91% of all Gram-negatives (n = 2000), Gram-positives (n = 403) and yeasts (n = 132) had inhibition zone diameters for nitroxoline ≥18 mm. Except for Pseudomonas aeruginosa, nitroxoline MIC90 values were ≤16 mg/L and were 2- to >16-fold lower compared with nitrofurantoin. In extended-spectrum ß-lactamase (ESBL)-producing Enterobacteriaceae and methicillin-resistant Staphylococcus aureus (MRSA), MIC90 values of nitroxoline were two-fold higher compared with non-ESBL-producing enterobacteria and methicillin-susceptible S. aureus (MSSA). The in vitro efficacies of nitroxoline and nitrofurantoin against ATCC strains of E. coli, Enterococcus faecalis and Proteus mirabilis were compared by time-kill curves in Mueller-Hinton broth and artificial urine. Nitroxoline was non-inferior against E. coli, P. mirabilis and E. faecalis in artificial urine. In conclusion, nitroxoline showed a broad antimicrobial spectrum, with inhibition zone diameters and MICs of nitroxoline well below the EUCAST breakpoint for E. coli for most organisms, and thus may also be a target for therapy of uncomplicated UTIs.