Urinary Tract Conditions Affect Fosfomycin Activity against Escherichia coli Strains Harboring Chromosomal Mutations Involved in Fosfomycin Uptake

Small Molecule IITR08367 Potentiates Antibacterial Efficacy of Fosfomycin against Acinetobacter baumannii by Efflux Pump Inhibition

Fosfomycin is a broad-spectrum single-dose therapy approved for treating lower urinary tract infections. Acinetobacter baumannii, one of the five major UTI-causing pathogens, is intrinsically resistant to fosfomycin. Reduced uptake and active efflux are major reasons for this intrinsic resistance. AbaF, a major facilitator superfamily class of transporter in A. baumannii, is responsible for fosfomycin efflux and biofilm formation. This study describes the identification and validation of a novel small-molecule efflux pump inhibitor that potentiates fosfomycin efficacy against A. baumannii. An AbaF inhibitor screening was performed against Escherichia coli KAM32/pUC18_abaF, using the noninhibitory concentration of 24 putative efflux pump inhibitors. The inhibitory activity of IITR08367 [bis(4-methylbenzyl) disufide] against fosfomycin/H+ antiport was validated using ethidium bromide efflux, quinacrine-based proton-sensitive fluorescence, and membrane depolarization assays. IITR08367 inhibits fosfomycin/H+ antiport activity by perturbing the transmembrane proton gradient. IITR08367 is a nontoxic molecule that potentiates fosfomycin activity against clinical strains of A. baumannii and prevents biofilm formation by inhibiting efflux pump (AbaF). The IITR08367-fosfomycin combination reduced bacterial burden by > 3 log10 in kidney and bladder tissue in the murine UTI model. Overall, fosfomycin, in combination with IITR08367, holds the potential to treat urinary tract infections caused by A. baumannii.

Acidic Urine pH and Clinical Outcome of Lower Urinary Tract Infection in Kidney Transplant Recipients Treated with Ciprofloxacin and Fosfomycin

Different factors, including antimicrobial resistance, may diminish the effectiveness of antibiotic therapy, challenging the management of post-transplant urinary tract infection (UTI). The association of acidic urine pH with microbiological and clinical outcomes was evaluated after fosfomycin or ciprofloxacin therapy in 184 kidney transplant recipients (KTRs) with UTI episodes by Escherichia coli (N = 115) and Klebsiella pneumoniae (N = 69). Initial urine pH, antimicrobial therapy, and clinical and microbiological outcomes, and one- and six-month follow-up were assessed. Fosfomycin was prescribed in 88 (76.5%) E. coli and 46 (66.7%) K. pneumoniae UTI episodes in the total cohort. When the urine pH ≤ 6, fosfomycin was prescribed in 60 (52.2%) E. coli and 29 (42.0%) K. pneumoniae. Initial urine pH ≤ 6 in E. coli UTI was associated with symptomatic episodes (8/60 vs. 0/55, p = 0.04) at one-month follow-up, with a similar trend in those patients receiving fosfomycin (7/47 vs. 0/41, p = 0.09). Acidic urine pH was not associated with microbiological or clinical cure in K. pneumoniae UTI. At pH 5, the ciprofloxacin MIC90 increased from 8 to >8 mg/L in E. coli and from 4 to >8 mg/L in K. pneumoniae. At pH 5, the fosfomycin MIC90 decreased from 8 to 4 mg/L in E. coli and from 512 to 128 mg/L in K. pneumoniae. Acidic urine is not associated with the microbiological efficacy of fosfomycin and ciprofloxacin in KTRs with UTI, but it is associated with symptomatic UTI episodes at one-month follow-up in E. coli episodes.

Urinary pH and antibiotics, choose carefully. A systematic review

Uncomplicated urinary tract infection (UTI) is the most common bacterial infection in women. Since 1948, the relationship between urinary pH and antibiotics (ABs) has been established. We aimed to search for the best urinary pH for each family of antibiotics and to assess whether pH changes bacterial susceptibility to them. We included in vitro research and in vivo studies including one or more bacterial species and tested the effect of one or more ABs at different pH values. We also included randomized controlled clinical trials (RCTs) in uncomplicated UTI (EAU guidelines 2019 definition), choosing the ABs based on urinary pH or using an antibiotic plus urinary pH modifiers (L-methionine, vitamin C…) vs. an antibiotic and a placebo. Quadas-2 tool was used as a quality assessment of the studies and PRISMA set of items for systematic reviews. Two authors independently screened and evaluated the papers, while two additional authors individually repeated the search. A fifth researcher acted as an arbiter, and another author collaborated as a hospital pharmaceutical consultant. Alkaline-friendly antibiotics are most fluoroquinolones, aminoglycosides, trimethoprim. Acidic-friendly antibiotics are fosfomycin, tetracycline, nitrofurantoin and some β-lactams. We suggest performing urine cultures with antibiogram tests, in both acidic and alkaline media, to define the bacterial susceptibility profile. There is insufficient in vivo evidence to support whether choosing an antibiotic based on a patient's urinary pH or adding urinary pH modifiers will lead to a higher cure rate.

Pervasive genotype-by-environment interactions shape the fitness effects of antibiotic resistance mutations

The fitness effects of antibiotic resistance mutations are a major driver of resistance evolution. While the nutrient environment affects bacterial fitness, experimental studies of resistance typically measure fitness of mutants in a single environment only. We explored how the nutrient environment affected the fitness effects of rifampicin-resistant rpoB mutations in Escherichia coli under several conditions critical for the emergence and spread of resistance-the presence of primary or secondary antibiotic, or the absence of any antibiotic. Pervasive genotype-by-environment (GxE) interactions determined fitness in all experimental conditions, with rank order of fitness in the presence and absence of antibiotics being strongly dependent on the nutrient environment. GxE interactions also affected the magnitude and direction of collateral effects of secondary antibiotics, in some cases so drastically that a mutant that was highly sensitive in one nutrient environment exhibited cross-resistance to the same antibiotic in another. It is likely that the mutant-specific impact of rpoB mutations on the global transcriptome underpins the observed GxE interactions. The pervasive, mutant-specific GxE interactions highlight the importance of doing what is rarely done when studying the evolution and spread of resistance in experimental and clinical work: assessing fitness of antibiotic-resistant mutants across a range of relevant environments.

Fosfomycin Resistance Evolutionary Pathways of Stenotrophomonas maltophilia in Different Growing Conditions

The rise of multidrug-resistant Gram-negative pathogens and the lack of novel antibiotics to address this problem has led to the rescue of old antibiotics without a relevant use, such as fosfomycin. Stenotrophomonas maltophilia is a Gram-negative, non-fermenter opportunistic pathogen that presents a characteristic low susceptibility to several antibiotics of common use. Previous work has shown that while the so-far described mechanisms of fosfomycin resistance in most bacteria consist of the inactivation of the target or the transporters of this antibiotic, as well as the production of antibiotic-inactivating enzymes, these mechanisms are not selected in S. maltophilia fosfomycin-resistant mutants. In this microorganism, fosfomycin resistance is caused by the inactivation of enzymes belonging to its central carbon metabolism, hence linking metabolism with antibiotic resistance. Consequently, it is relevant to determine how different growing conditions, including urine and synthetic sputum medium that resemble infection, could impact the evolutionary pathways towards fosfomycin resistance in S. maltophilia. Our results show that S. maltophilia is able to acquire high-level fosfomycin resistance under all tested conditions. However, although some of the genetic changes leading to resistance are common, there are specific mutations that are selected under each of the tested conditions. These results indicate that the pathways of S. maltophilia evolution can vary depending on the infection point and provide information for understanding in more detail the routes of fosfomycin resistance evolution in S. maltophilia.

Fosfomycin resistance in community-acquired urinary pathogens from Western Cape, South Africa

Oral fosfomycin is commonly used to treat uncomplicated urinary tract infections (UTI) and whilst resistance has been reported in many healthcare facilities in South Africa, the current prevalence remains unknown. This study investigated the prevalence and mechanisms of fosfomycin resistance amongst urinary pathogens in the Western Cape, South Africa. Of the 200 isolates collected during the study period (2019–2020), seven (3.5%) were fosfomycin resistant. Mutations in the glpT and uhpT transporter genes were the most common mechanism of resistance detected. These findings support the ongoing use of fosfomycin as an empiric antibiotic choice for the treatment of community-acquired UTI in this setting.

OUP accepted manuscript

Introduction

The use of oral fosfomycin for urinary tract infections (UTIs) caused by non-Escherichia coli uropathogens is uncertain, including Klebsiella pneumoniae, the second most common uropathogen.

Methods

A multicompartment bladder infection in vitro model was used with standard media and synthetic human urine (SHU) to simulate urinary fosfomycin exposure after a single 3 g oral dose (fAUC_0–72 16884 mg·h/L, t_½ 5.5 h) against 15 K. pneumoniae isolates including ATCC 13883 (MIC 2 to >1024 mg/L) with a constant media inflow (20 mL/h) and 4-hourly voiding of each bladder. The impact of the media (CAMHB + G6P versus SHU) on fosfomycin MIC measurements, drug-free growth kinetics and regrowth after fosfomycin administration was assessed. A low and high starting inoculum (5.5 versus 7.5 log₁₀ cfu/mL) was assessed in the bladder infection model.

Results

Compared with CAMHB, isolates in SHU had a slower growth rate doubling time (37.7 versus 24.1 min) and reduced growth capacity (9.0 ± 0.3 versus 9.4 ± 0.3 log₁₀ cfu/mL), which was further restricted with increased inflow rate (40 mL/h) and more frequent voids (2-hourly). Regrowth was commonly observed in both media with emergence of fosfomycin resistance promoted by a high starting inoculum in CAMHB (MIC rise to ≥1024 mg/L in 13/14 isolates). Resistance was rarely detected in SHU, even with a high starting inoculum (MIC rise to ≥1024 mg/L in 2/14 isolates).

Conclusions

Simulated in an in vitro UTI model, the regrowth of K. pneumoniae urinary isolates was inadequately suppressed following oral fosfomycin therapy. Efficacy was further reduced by a high starting inoculum.

First Detection of Klebsiella pneumoniae Isolate Co-Harboring Fosfomycin Resistance Gene fosA3 and blactx-m Among Gram Negative Urine Isolates in a Turkish Hospital

The most common gram-negative pathogens in urinary tract infections are Escherichia coli and Klebsiella pneumoniae. Therapy that is often empirical relies on local antibiotic resistance data, hence monitorization of antimicrobial resistance periodically in each hospital is a requirement. In this study, antibiotic susceptibility profiles of consecutive urinary isolates (E. coli [n = 235] and K. pneumoniae [n = 56]) of adult patients collected between February 2018 and February 2019 from inpatients in Hacettepe University Hospital were assessed. Isolates resistant to fosfomycin (minimum inhibitory concentration >32 mg/L) were further investigated for the presence of fosA, fosA3, and fosC2. Fosfomycin susceptibility was determined by agar dilution method. Broth microdilution method was performed for amikacin, gentamicin, ceftazidime, ceftriaxone, meropenem, ciprofloxacin, tigecycline, trimethoprim/sulfamethoxazole (TMP/SMX), colistin, and piperacillin/tazobactam (PIP/TAZ). PCR method was employed to investigate fosA, fosA3, fosC2, and bla_CTX-M. Existence of fosA3 gene was confirmed by sequencing. Resistance rates to amikacin, gentamicin, ceftazidime, ceftriaxone, meropenem, ciprofloxacin, tigecycline, TMP/SMX, colistin, and PIP/TAZ were 2.7%, 18.5%, 25.4%, 33.0%, 3.4%, 45.4%, 2.4%, 43.6%, 6.2%, and 23.7%, respectively. Sixteen isolates (5.5%) were resistant to fosfomycin. Resistance was most frequently observed in K. pneumoniae (n = 9). fosA3 gene was detected in one fosfomycin-resistant K. pneumoniae isolate. This isolate also carried bla_CTX-M. fosC2 and fosA genes could not be detected in any of the isolates. In this study, we report for the first time the existence of fosA3 in Turkey and its association with the bla_CTX-M gene. As a result of increasing bla_CTX-M producing Enterobacterales isolates globally, increase in fosfomycin resistance may be expected in near future.

Contribution of hypermutation to fosfomycin heteroresistance in Escherichia coli

OBJECTIVES

To explore the effect of combining defects in DNA repair systems with the presence of fosfomycin-resistant mechanisms to explain the mechanisms underlying fosfomycin heteroresistance phenotypes in Enterobacteriaceae.

MATERIALS AND METHODS

We used 11 clinical Escherichia coli isolates together with isogenic single-gene deletion mutants in the E. coli DNA repair system or associated with fosfomycin resistance, combined with double-gene deletion mutants. Fosfomycin MICs were determined by gradient strip assay (GSA) and broth microdilution (BMD). Mutant frequencies for rifampicin (100 mg/L) and fosfomycin (50 and 200 mg/L) were determined. Using two starting inocula, in vitro fosfomycin activity was assessed over 24 h in growth (0.5-512 mg/L) and time-kill assays (64 and 307 mg/L).

RESULTS

Strong and weak mutator clinical isolates and single-gene deletion mutants, except for ΔuhpT and ΔdnaQ, were susceptible by GSA. By BMD, the percentage of resistant clinical isolates reached 36%. Single-gene deletion mutants showed BMD MICs similar to those for subpopulations by GSA. Strong mutators showed a higher probability of selecting fosfomycin mutants at higher concentrations. By combining the two mechanisms of mutation, MICs and ranges of resistant subpopulations increased, enabling strains to survive at higher fosfomycin concentrations in growth monitoring assays. In time-kill assays, high inocula increased survival by 37.5% at 64 mg/L fosfomycin, compared with low starting inocula.

CONCLUSIONS

The origin and variability of the fosfomycin heteroresistance phenotype can be partially explained by high mutation frequencies together with mechanisms of fosfomycin resistance. Subpopulations should be considered until clinical meaning is established.

Novel Chromosomal Mutations Responsible for Fosfomycin Resistance in Escherichia coli

Fosfomycin resistance in Escherichia coli results from chromosomal mutations or acquisition of plasmid-mediated genes. Because these mechanisms may be absent in some resistant isolates, we aimed at decipher the genetic basis of fosfomycin resistance in E. coli. Different groups of isolates were studied: fosfomycin-resistant mutants selected in vitro from E. coli CFT073 (MIC = 1 mg/L) and two groups (wildtype and non-wildtype) of E. coli clinical isolates. Single-nucleotide allelic replacement was performed to confirm the implication of novel mutations into resistance. Induction of uhpT expression by glucose-6-phosphate (G6P) was assessed by RT-qPCR. The genome of all clinical isolates was sequenced by MiSeq (Illumina). Two first-step mutants were obtained in vitro from CFT073 (MICs, 128 mg/L) with single mutations: G469R in uhpB (M3); F384L in uhpC (M4). Second-step mutants (MICs, 256 mg/L) presented additional mutations: R282V in galU (M7 from M3); Q558^∗ in lon (M8 from M4). Introduction of uhpB or uhpC mutations by site-directed mutagenesis conferred a 128-fold increase in fosfomycin MICs, whereas single mutations in galU or lon were only responsible for a 2-fold increase. Also, these mutations abolished the induction of uhpT expression by G6P. All 14 fosfomycin-susceptible clinical isolates (MICs, 0.5-8 mg/L) were devoid of any mutation. At least one genetic change was detected in all but one fosfomycin-resistant clinical isolates (MICs, 32 - >256 mg/L) including 8, 17, 18, 5, and 8 in uhpA, uhpB, uhpC, uhpT, and glpT genes, respectively. In conclusion, novel mutations in uhpB and uhpC are associated with fosfomycin resistance in E. coli clinical isolates.

Antimicrobial pharmacokinetics and preclinical in vitro models to support optimized treatment approaches for uncomplicated lower urinary tract infections

INTRODUCTION

Urinary tract infections (UTIs) are extremely common. Millions of people, particularly healthy women, are affected worldwide every year. One-in-two women will have a recurrence within 12-months of an initial UTI. Inadequate treatment risks worsening infection leading to acute pyelonephritis, bacteremia and sepsis. In an era of increasing antimicrobial resistance, it is critical to provide optimized antimicrobial treatment.

AREAS COVERED

Literature was searched using PubMed and Google Scholar (up to 06/2020), examining the etiology, diagnosis and oral antimicrobial therapy for uncomplicated UTIs, with emphasis on urinary antimicrobial pharmacokinetics (PK) and the application of dynamic in vitro models for the pharmacodynamic (PD) profiling of pathogen response.

EXPERT OPINION

The majority of antimicrobial agents included in international guidelines were developed decades ago without well-described dose-response relationships. Microbiology laboratories still apply standard diagnostic methodology that has essentially remained unchanged for decades. Furthermore, it is uncertain how relevant standard in vitro susceptibility is for predicting antimicrobial efficacy in urine. In order to optimize UTI treatments, clinicians must exploit the urine-specific PK of antimicrobial agents. Dynamic in vitro models are valuable tools to examine the PK/PD and urodynamic variables associated with UTIs, while informing uropathogen susceptibility reporting, optimized dosing schedules, clinical trials and treatment guidelines.

Detection of Low-Level Fosfomycin-Resistant Variants by Decreasing Glucose-6-Phosphate Concentration in Fosfomycin Susceptibility Determination

Mutations that confer low-level fosfomycin resistance (LLFR) but not clinical resistance in Escherichia coli are increasingly reported. LLFR strains can become clinically resistant under urinary tract physiological conditions or may act as gateways for highly resistant subpopulations by the selection of additional LLFR mutations. Nevertheless, most LLFR strains are impossible to detect under routine fosfomycin susceptibility determinations. Here, we have explored the possibility of detecting LLFR variants by reducing glucose-6-phosphate (G6P) concentration in fosfomycin susceptibility testing for E. coli strains. As a proof of concept, fosfomycin minimal inhibitory concentrations (MICs) and disk diffusion susceptibility tests were performed for E. coli strain BW25113 and 10 isogenic derivatives carrying the most prevalent LLFR chromosomal mutations (∆uhpT, ∆glpT, ∆cyaA, and ∆ptsI) and their double combinations. Whereas standard G6P concentrations detected only ∆uhpT single and double variants, assays with reduced G6P detected all LLFR variants. In addition, G6P levels were determined to be ≤5 µg/mL in urine samples from 30 patients with urinary tract infection (UTI) caused by E. coli and 10 healthy volunteers, suggesting that most bacterial cells in uncomplicated UTIs are facing fosfomycin under low G6P concentration. Reducing G6P allows for the detection of LLFR variants, which may suppose a risk for future resistance development, especially in UTIs.

The Inactivation of Enzymes Belonging to the Central Carbon Metabolism Is a Novel Mechanism of Developing Antibiotic Resistance

Fosfomycin is a bactericidal antibiotic, analogous to phosphoenolpyruvate, that exerts its activity by inhibiting the activity of MurA. This enzyme catalyzes the first step of peptidoglycan biosynthesis, the transfer of enolpyruvate from phosphoenolpyruvate to uridine-diphosphate-N-acetylglucosamine. Fosfomycin is increasingly being used, mainly for treating infections caused by Gram-negative multidrug-resistant bacteria. The mechanisms of mutational resistance to fosfomycin in Stenotrophomonas maltophilia, an opportunistic pathogen characterized by its low susceptibility to commonly used antibiotics, were studied in the current work. None of the mechanisms reported so far for other organisms, which include the production of fosfomycin-inactivating enzymes, target modification, induction of an alternative peptidoglycan biosynthesis pathway, and the impaired entry of the antibiotic, are involved in the acquisition of such resistance by this bacterial species. Instead, the unique cause of resistance in the mutants studied is the mutational inactivation of different enzymes belonging to the Embden-Meyerhof-Parnas central metabolism pathway. The amount of intracellular fosfomycin accumulation did not change in any of these mutants, showing that neither inactivation nor transport of the antibiotic is involved. Transcriptomic analysis also showed that the mutants did not present changes in the expression level of putative alternative peptidoglycan biosynthesis pathway genes or any related enzyme. Finally, the mutants did not present an increased phosphoenolpyruvate concentration that might compete with fosfomycin for its binding to MurA. On the basis of these results, we describe a completely novel mechanism of antibiotic resistance based on mutations of genes encoding metabolic enzymes.IMPORTANCE Antibiotic resistance has been largely considered a specific bacterial response to an antibiotic challenge. Indeed, its study has been mainly concentrated on mechanisms that affect the antibiotics (mutations in transporters, efflux pumps, and antibiotic-modifying enzymes, or their regulators) or their targets (i.e., target mutations, protection, or bypass). Usually, antibiotic resistance-associated metabolic changes were considered a consequence (fitness costs) and not a cause of antibiotic resistance. Herein, we show that alterations in the central carbon bacterial metabolism can also be the cause of antibiotic resistance. In the study presented here, Stenotrophomonas maltophilia acquires fosfomycin resistance through the inactivation of glycolytic enzymes belonging to the Embden-Meyerhof-Parnas pathway. Besides resistance to fosfomycin, this inactivation also impairs the bacterial gluconeogenic pathway. Together with previous work showing that antibiotic resistance can be under metabolic control, our results provide evidence that antibiotic resistance is intertwined with the bacterial metabolism.

The intriguing biology and chemistry of fosfomycin: the only marketed phosphonate antibiotic

Recently infectious diseases caused by the increased emergence and rapid spread of drug-resistant bacterial isolates have been one of the main threats to global public health because of a marked surge in both morbidity and mortality. The only phosphonate antibiotic in the clinic, fosfomycin, is a small broad-spectrum molecule that effectively inhibits the initial step in peptidoglycan biosynthesis by blocking the enzyme, MurA in both Gram-positive and Gram-negative bacteria. As fosfomycin has a novel mechanism of action, low toxicity, a broad spectrum of antibacterial activity, excellent pharmacodynamic/pharmacokinetic properties, and good bioavailability, it has been approved for clinical use in the treatment of urinary tract bacterial infections in many countries for several decades. Furthermore, its potential use for difficult-to-treat bacterial infections has become promising, and fosfomycin has become an ideal candidate for the effective treatment of bacterial infections caused by multidrug-resistant isolates, especially in combination with other therapeutic drugs. Here we aim to present an overview of the biology and chemistry of fosfomycin including isolation and characterization, pharmacology, biosynthesis and chemical synthesis since its discovery in order to not only help scientists reassess the role of this exciting drug in fighting antibiotic resistance but also build the stage for discovering more novel phosphonate antibiotics in the future.

Unexpected Activity of Oral Fosfomycin against Resistant Strains of Escherichia coli in Murine Pyelonephritis

Fosfomycin tromethamine activity is well established for oral treatment of uncomplicated lower urinary tract infections, but little is known about its potential efficacy in pyelonephritis. Ascending pyelonephritis was induced in mice infected with 6 strains of Escherichia coli (fosfomycin MICs, 1 μg/ml to 256 μg/ml). The urine pH was 4.5 before infection and 5.5 to 6.0 during infection. Animals were treated for 24 h with fosfomycin (100 mg/kg of body weight subcutaneously every 4 h), and the CFU were enumerated in kidneys 24 h after the last fosfomycin injection. Peak (20.5 μg/ml at 1 h) and trough (3.5 μg/ml at 4 h) levels in plasma were comparable to those obtained in humans after an oral dose of 3 g. Fosfomycin treatment significantly reduced the bacterial loads in kidneys (3.65 log₁₀ CFU/g [range, 1.83 to 7.03 log₁₀ CFU/g] and 1.88 log₁₀ CFU/g [range, 1.78 to 5.74 log₁₀ CFU/g] in start-of-treatment control mice and treated mice, respectively; P < 10^-6). However, this effect was not found to differ across the 6 study strains (P = 0.71) or between the 3 susceptible and the 3 resistant strains (P = 0.09). Three phenomena may contribute to explain this unexpected in vivo activity: (i) in mice, the fosfomycin kidney/plasma concentration ratio increased from 1 to 7.8 (95% confidence interval, 5.2, 10.4) within 24 h in vitro when the pH decreased to 5, (ii) the fosfomycin MICs for the 3 resistant strains (64 to 256 μg/ml) decreased into the susceptible range (16 to 32 μg/ml), and (iii) maximal growth rates significantly decreased for all strains and were the lowest in urine. These results suggest that local fosfomycin concentrations and physiological conditions may favor fosfomycin activity in pyelonephritis, even against resistant strains.

Nitrofurantoin and fosfomycin for resistant urinary tract infections: old drugs for emerging problems

Uncomplicated urinary tract infection is one of the most common indications for antibiotic use in the community However the Gram-negative organisms that can cause the infection are becoming more resistant to antibiotics

Many multidrug resistant organisms retain susceptibility to two old antibiotics nitrofurantoin and fosfomycin Advantages over newer drugs include their high urinary concentrations and minimal toxicity

Fosfomycin is a potential treatment option for patients with uncomplicated urinary tract infection due to resistant organisms Nitrofurantoin may be more effective and can be used for urinary infections in pregnant women

Development and validation of a LC-MS/MS method for quantitation of fosfomycin - Application to in vitro antimicrobial resistance study using hollow-fiber infection model

Extensive use and misuse of antibiotics over the past 50 years has contributed to the emergence and spread of antibiotic-resistant bacterial strains, rendering them as a global health concern. To address this issue, a dynamic in vitro hollow-fiber system, which mimics the in vivo environment more closely than the static model, was used to study the emergence of bacterial resistance of Escherichia coli against fosfomycin (FOS). To aid in this endeavor we developed and validated a liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay for quantitative analysis of FOS in lysogeny broth. FOS was resolved on a Kinetex HILIC (2.1 × 50 mm, 2.6 μm) column with 2 mm ammonium acetate (pH 4.76) and acetonitrile as mobile phase within 3 min. Multiple reaction monitoring was used to acquire data on a triple quadrupole mass spectrometer. The assay was linear from 1 to 1000 μg/mL. Inter- and intra-assay precision and accuracy were <15% and between ±85 and 115% respectively. No significant matrix effect was observed when corrected with the internal standard. FOS was stable for up to 24 h at room temperature, up to three freeze-thaw cycles and up to 24 h when stored at 4°C in the autosampler. In vitro experimental data were similar to the simulated plasma pharmacokinetic data, further confirming the appropriateness of the experimental design to quantitate antibiotics and study occurrence of antimicrobial resistance in real time. The validated LC-MS/MS assays for quantitative determination of FOS in lysogeny broth will help antimicrobial drug resistance studies.