Functional and structural characterization of Streptococcus pneumoniae pyruvate kinase involved in fosfomycin resistance.

Glycolysis is the primary metabolic pathway in the strictly fermentative Streptococcus pneumoniae, which is a major human pathogen associated with antibiotic resistance. Pyruvate kinase (PYK) is the last enzyme in this pathway that catalyzes the production of pyruvate from phosphoenolpyruvate (PEP) and plays a crucial role in controlling carbon flux; however, while S. pneumoniae PYK (SpPYK) is indispensable for growth, surprisingly little is known about its functional properties. Here, we report that compromising mutations in SpPYK confers resistance to the antibiotic fosfomycin, which inhibits the peptidoglycan synthesis enzyme MurA, implying a direct link between PYK and cell wall biogenesis. The crystal structures of SpPYK in the apo and ligand-bound states reveal key interactions that contribute to its conformational change as well as residues responsible for the recognition of PEP and the allosteric activator fructose 1,6-bisphosphate (FBP). Strikingly, FBP binding was observed at a location distinct from previously reported PYK effector binding sites. Furthermore, we show that SpPYK could be engineered to become more responsive to glucose 6-phosphate instead of FBP by sequence and structure-guided mutagenesis of the effector binding site. Together, our work sheds light on the regulatory mechanism of SpPYK and lays the groundwork for antibiotic development that targets this essential enzyme.

Raising the alarm: fosfomycin resistance associated with non-susceptible inner colonies imparts no fitness cost to the primary bacterial uropathogen.

IMPORTANCE: While fosfomycin resistance is rare, the observation of non-susceptible subpopulations among clinical Escherichia coli isolates is a common phenomenon during antimicrobial susceptibility testing (AST) in American and European clinical labs. Previous evidence suggests that mutations eliciting this phenotype are of high biological cost to the pathogen during infection, leading to current recommendations of neglecting non-susceptible colonies during AST. Here, we report that the most common route to fosfomycin resistance, as well as novel routes described in this work, does not impair virulence in uropathogenic E. coli, the major cause of urinary tract infections, suggesting a re-evaluation of current susceptibility guidelines is warranted.

Antibiotics efficacy in clinical and microbiological cure of uncomplicated urinary tract infection: a systematic review and network meta-analysis.

PURPOSE: Fosfomycin has been used more frequently in managing uncomplicated urinary tract infections (UTIs) due to decreased compliance and increased multidrug-resistant bacteria. The aim of this network meta-analysis was to assess the efficacy of Fosfomycin compared to Nitrofurantoin, Trimethoprim-Sulfamethoxazole (TMP-SMX), and Ciprofloxacin in terms of clinical and microbiological cure alongside with other measurements. MATERIALS AND METHODS: We searched MEDLINE, Embase, and Cochrane Central Register of Controlled Trials (CENTRAL). We included randomized control trials (RCTs) with uncomplicated UTI patients who received Fosfomycin, Nitrofurantoin, TMP-SMX, or Ciprofloxacin and reported the clinical or microbiological cure. We used Cochrane Risk of Bias Assessment Tool to assess the included studies' quality. R-software was used for all statistical analysis. We ranked all antibiotics using the netrank function which yielded P scores. Frequentist network meta-analysis was used to assess the efficacy of all outcomes. RESULTS: We included 13 RCTs with a total number of 3856 patients that showed Fosfomycin ranked the highest among the other antibiotics with respect to clinical cure (P-score = 0.99) and microbiological cure (P-score = 0.99) while Ciprofloxacin ranked the lowest (P-score = 0.11 and 0.02, respectively). Moreover, Ciprofloxacin yielded the highest relapse rate (P-score = 1), whereas TMP-SMX had the lowest relapse rate (P-score = 0.07). As for the adverse events, Ciprofloxacin demonstrated the highest adverse events as opposed to Fosfomycin (P-score = 0.98 and 0.05, respectively). CONCLUSION: The network meta-analysis demonstrated that Fosfomycin is the most effective antibiotic in treating uncomplicated UTIs with respect to clinical cure, microbiological cure, and adverse events profile.

Adverse events during intravenous fosfomycin therapy in a real-life scenario. Risk factors and the potential role of therapeutic drug monitoring.

BACKGROUND: Intravenous fosfomycin (IVFOF) is gaining interest in severe infections. Its use may be limited by adverse events (AEs). Little experience exists on IVFOF therapeutic drug monitoring (TDM) in real-life setting. PATIENTS AND METHODS: Retrospective study of patients receiving IVFOF for > 48 h at Policlinico Hospital (Milan, Italy) from 01/01/2019 to 01/01/2023. AEs associated to IVFOF graded CTCAE ≥ II were considered. Demographic and clinical risk factors for IVFOF-related AEs were analysed with simple and multivariable regression models. The determination of IVFOF TDM was made by a rapid ultraperformance liquid chromatography mass spectrometry method (LC-MS/MS) on plasma samples. The performance of TDM (trough levels (Cmin) in intermittent infusion, steady state levels (Css) in continuous infusion) in predicting AEs ≤ 5 days after its assessment was evaluated. RESULTS: Two hundred and twenty-four patients were included. At IVFOF initiation, 81/224 (36.2%) patients were in ICU and 35/224 (15.7%) had septic shock. The most frequent infection site was the low respiratory tract (124/224, 55.4%). Ninety-five patients (42.4%) experienced ≥ 1AEs, with median time of 4.0 (2.0-7.0) days from IVFOF initiation. Hypernatremia was the most frequent AE (53/224, 23.7%). Therapy discontinuation due to AEs occurred in 38/224 (17.0%). ICU setting, low respiratory tract infections and septic shock resulted associated with AEs (RRadjusted 1.59 (95%CI:1.09-2.31), 1.46 (95%CI:1.03-2.07) and 1.73 (95%CI:1.27-2.37), respectively), while IVFOF daily dose did not. Of the 68 patients undergone IVFOF TDM, TDM values predicted overall AEs and hypernatremia with AUROC of 0.65 (95%CI:0.44-0.86) and 0.91 (95%CI:0.79-1.0) respectively for Cmin, 0.67 (95%CI:0.39-0.95) and 0.76 (95%CI:0.52-1.0) respectively for Css. CONCLUSIONS: We provided real world data on the use of IVFOF-based regimens and associated AEs. IVFOF TDM deserves further research as it may represent a valid tool to predict AEs. KEY POINTS: Real world data on intravenous fosfomycin for severe bacterial infections. AEs occurred in over 40% (therapy discontinuation in 17%) and were related to baseline clinical severity but not to fosfomycin dose. TDM showed promising results in predicting AEs.

Fosfomycin as salvage therapy for persistent methicillin-resistant Staphylococcus aureus bacteremia: A case series and review of the literature.

Methicillin-resistant Staphylococcus aureus (MRSA) bacteremia can be persistent and refractory; however, the optimal approach for its treatment has not been determined. Although fosfomycin (FOM) has been shown to have synergistic effects with anti-MRSA agents in vitro, clinical experience with FOM combination therapy is limited. Thus, we present cases of persistent MRSA bacteremia that improved with the addition of FOM. In case 1, a 48-year-old man with prosthetic vascular graft infection developed persistent MRSA bacteremia despite vancomycin (VCM) and daptomycin (DAP) administration. On day 46, after the first positive blood culture, we added FOM to DAP. The blood culture became negative on day 53. In case 2, an 85-year-old woman presented with pacemaker-related MRSA bacteremia. She was treated with VCM, followed by DAP and DAP plus rifampicin. However, the bacteremia persisted for 32 days because of difficulties in immediate pacemaker removal. After adding FOM to DAP, the blood culture became negative on day 38. In case 3, a 57-year-old woman developed persistent MRSA bacteremia due to pulmonary valve endocarditis and pulmonary artery thrombosis after total esophagectomy for esophageal cancer. The bacteremia continued for 50 days despite treatment with DAP, followed by VCM, VCM plus minocycline, DAP plus linezolid (LZD), and VCM plus LZD. She was managed conservatively because of surgical complications. After adding FOM to VCM on day 51, the blood culture became negative on day 58. FOM combination therapy may be effective in eliminating bacteria and can serve as salvage therapy for refractory MRSA bacteremia.

Biosynthesis of fosfomycin in pseudomonads reveals an unexpected enzymatic activity in the metallohydrolase superfamily.

The epoxide-containing phosphonate natural product fosfomycin is a broad-spectrum antibiotic used in the treatment of cystitis. Fosfomycin is produced by both the plant pathogen Pseudomonas syringae and soil-dwelling streptomycetes. While the streptomycete pathway has recently been fully elucidated, the pseudomonad pathway is still mostly elusive. Through a systematic evaluation of heterologous expression of putative biosynthetic enzymes, we identified the central enzyme responsible for completing the biosynthetic pathway in pseudomonads. The missing transformation involves the oxidative decarboxylation of the intermediate 2-phosphonomethylmalate to a new intermediate, 3-oxo-4-phosphonobutanoate, by PsfC. Crystallographic studies reveal that PsfC unexpectedly belongs to a new class of diiron metalloenzymes that are part of the polymerase and histidinol phosphatase superfamily.

FosA8-producing E. coli ST131: clinical cases in Italy, February 2023.

Fosfomycin-resistant FosA8-producing Enterobacterales are uncommon strains with extremely low incidence in Europe, based on only three reports in the literature. We detected FosA8-producing Escherichia coli ST131 in clinical isolates from two patients admitted in February 2023 to a rehabilitation unit in Italy. The occurrence of rare fosA-like genes in the high-risk clone ST131 is of clinical relevance. The dissemination of FosA-producing E. coli, although still at low levels, should be continuously monitored.

Genotypic Evolution of Klebsiella pneumoniae Sequence Type 512 during Ceftazidime/Avibactam, Meropenem/Vaborbactam, and Cefiderocol Treatment, Italy.

In February 2022, a critically ill patient colonized with a carbapenem-resistant K. pneumoniae producing KPC-3 and VIM-1 carbapenemases was hospitalized for SARS-CoV-2 in the intensive care unit of Policlinico Umberto I hospital in Rome, Italy. During 95 days of hospitalization, ceftazidime/avibactam, meropenem/vaborbactam, and cefiderocol were administered consecutively to treat 3 respiratory tract infections sustained by different bacterial agents. Those therapies altered the resistome of K. pneumoniae sequence type 512 colonizing or infecting the patient during the hospitalization period. In vivo evolution of the K. pneumoniae sequence type 512 resistome occurred through plasmid loss, outer membrane porin alteration, and a nonsense mutation in the cirA siderophore gene, resulting in high levels of cefiderocol resistance. Cross-selection can occur between K. pneumoniae and treatments prescribed for other infective agents. K. pneumoniae can stably colonize a patient, and antimicrobial-selective pressure can promote progressive K. pneumoniae resistome evolution, indicating a substantial public health threat.

The efficacy of mesenchymal stem cell treatment and colistin-fosfomycin combination on colistin-resistant Acinetobacter baumannii sepsis model.

INTRODUCTION: This study examines the role of mesenchymal stem cells (MSCs) in an experimental sepsis model developed with colistin-resistant Acinetobacter baumannii (CRAB). MATERIALS AND METHODS: BALB-c mice were divided into treatment groups (MSC, MSC + colistin (C)-fosfomycin (F), and C-F and control groups (positive and negative)). CRAB was administered to mice through intraperitoneal injection. Three hours later, C, F, and MSC were given intraperitoneally to the treatment groups. Colistin administration was repeated every 12 h, F administration was done every 4 h, and the second dose of MSC was administered after 48 h. Mice were sacrificed at 24 and 72 h. The bacterial load was determined as colony-forming units per gram (cfu/g). Histopathological examination was conducted on the left lung, liver, and both kidneys. IL-6 and C-reactive protein (CRP) levels in mouse sera were determined by enzyme-linked immunosorbent assay. RESULTS: Among the treatment groups, the C-F group had the lowest colony count in the lung (1.24 ± 1.66 cfu/g) and liver (1.03 ± 1.08 cfu/g). The highest bacterial clearance was observed at 72 h compared to 24 h in the MSC-treated groups (p = 0.008). The MSC + C-F group showed the lowest histopathological score in the liver and kidney (p = 0.009). In the negative control group, the IL-6 level at the 24th hour was the lowest (p < 0.001). Among the treatment groups, the CRP level was the lowest in the MSC + C-F group at 24 and 72 h. CONCLUSION: In a CRAB sepsis model, adding MSCs to a colistin-fosfomycin treatment may be beneficial in terms of reducing bacterial loads and preventing histopathological damage.

First trimester pregnancy exposure to fosfomycin and risk of major congenital anomaly: a comparative study in the EFEMERIS database.

PURPOSE: Fosfomycin trometamol has been recommended as first-line bactericidal antibiotic for urinary tract infections in pregnant women since 2015 in France. However, studies assessing fosfomycin safety in pregnancy are sparse. This study aimed to assess the risk of major Congenital Anomaly (CA) after fosfomycin exposure during the first trimester of pregnancy. METHODS: We performed a comparative study in EFEMERIS, the French database including expecting mothers covered by the French Health Insurance System of Haute-Garonne from July 1st, 2004 to December 31th, 2018. EFEMERIS contains prescribed and dispensed reimbursed medications during pregnancy and pregnancy outcomes. Logistic regressions have been conducted to compare three groups: (1) pregnancies exposed at least once to fosfomycin; (2) pregnancies exposed at least once to nitrofurantoin; and (3) pregnancies exposed neither to fosfomycin nor to nitrofurantoin, another antibiotic prescribed for urinary infections, before and during pregnancy. RESULTS: A total of 2724 (2.0%) pregnant women received at least one fosfomycin prescription during the first trimester, 650 (0.5%) received nitrofurantoin during the first trimester, and 133,502 (97.5%) pregnant women were not exposed to fosfomycin nor to nitrofurantoin. First trimester pregnancy exposure to fosfomycin was not associated with an increased risk of major CA, compared to first trimester exposure to nitrofurantoin (2.0% versus 2.5%; ORa = 0.80 [0.44-1.47]), or to pregnancies unexposed to fosfomycin and nitrofurantoin (2.0% versus 2.1%; ORa = 0.97 [0.73-1.30]). CONCLUSION: This is the first large comparative study assessing fosfomycin safety in pregnancy. It does not exhibit an increased risk of major CA after fosfomycin exposure during the first trimester of pregnancy.

Isolation of Hafnia paralvei co-harbouring blaNDM-1 and blaVIM-1 in a woman who underwent allogeneic hematopoietic stem cell transplantation.

Metallo-ß-lactamases (MBL) are a threat to public health, since they dramatically limit the use of ß-lactams. We report the isolation of a multidrug-resistant Hafnia paralvei strain from urine and a rectal swab of a female patient after allogeneic hematopoietic stem cell transplantation for myelodysplastic syndrome. Antimicrobial susceptibility testing yielded resistance to trimethoprim/sulfamethoxazole, colistin, fosfomycin and all ß-lactams, except cefiderocol. Whole genome sequencing revealed the presence of plasmid-encoded NDM-1 and VIM-1 carbapenemases. This finding highlights the importance of epidemiological surveillance and new therapeutic options for MBL.

High incidence of fosfomycin-resistant uropathogenic E. coli among children.

BACKGROUND: There are few epidemiological or molecular data on Escherichia coli (E. coli) strains resistant to fosfomycin. In this study, we described the occurrence and characterization of fosfomycin-resistant uropathogenic E. coli (UPEC) isolated from children. MATERIALS AND METHODS: This study was carried out on 96 E. coli isolates obtained from children with urinary tract infections. Two methods were performed to detect fosfomycin resistance: The agar dilution method and the rapid fosfomycin test. The disc diffusion method was done to detect the antimicrobial susceptibility pattern of all isolates. The phylogenetic grouping of all isolates was done according to the modified Clermont method. Conventional PCR was performed to detect plasmid-mediated fosfomycin-resistant genes (fos genes) and the blaCTX-M gene. RESULTS: Analyses of data were performed by SPSS software. A high percentage of fosfomycin resistance (37/96; 38.5%) was reported among UPEC isolates. The fosfomycin-resistant strains showed a higher resistance rate than fosfomycin-susceptible isolates to different antibiotics. E group (62.2%) was the most predominant phylogenetic group among the fosfomycin-resistant UPEC isolates, followed by Group B2 (21.6%) and group D (13.5%). The fos genes were detected in 21 isolates with the fosA3 gene as the most frequent, which was detected in 11 isolates followed by fosA (8), fosC2 (4), fosA4(1), and fosA5(1) genes. CONCLUSION: This is the first report of a high prevalence of plasmid-mediated fosfomycin-resistant UPEC in Egypt. All of these isolates were multidrug-resistant to the tested antibiotics. Close monitoring of such strains is mandatory to prevent widespread dissemination of the genes code for antibiotic resistance.

Fosfomycin-induced agranulocytosis: a case report and review of the literature.

BACKGROUND: The intravenous form of fosfomycin, a bactericide antibiotic used to treat multiresistant bacterial infections is little prescribed. The most common reported adverse effects are hypokaliemia and hypernatremia. We describe a case of agranulocytosis, a rarely described side effect that may be fatal. CASE PRESENTATION: A 45 year-old woman was admitted to the intensive care unit for post-surgical meningitis following meningioma resection. Meropenem and vancomycin were first introduced. A DRESS-syndrom with meropenem was suspected. Neutropenia was diagnosed three days after the introduction of parenteral fosfomycin and agranulocytosis four days later. Eosinophilia was also observed. A bone marrow aspiration was performed showing a disappearance of the neutrophil granulocyte line and a significant eosinophilia. Meropenem was discontinued. Fosfomycin was maintained and filgrastim was added. As filgrastim had no effect, the relationship with fosfomycin was suspected, so it was then withheld. An increase of the neutrophil count was observed. Because of the complexity of the case, the unfavorable course of the illness and the urgent need for revision surgery, a rechallenge with fosfomycin was done followed by a decrease of the neutrophil count. CONCLUSION: This is the third paper reporting agranulocytosis induced by fosfomycin, and the first detailed description of a case. Based on chronological and semiological criteria and bibliographic data, the event was qualified as probable with the Naranjo adverse drug probability scale. Literature data is scarce. The summary of product characteristics mentions that only a few cases of transient neutropenia and agranulocytosis have been reported. An analysis of the FDA Adverse Event Reporting System Database highlighted a higher than expected frequency of agranulocytosis in patients treated with fosfomycin. Parenteral fosfomycin is often used in patients receiving other medications, so that it is rarely the only suspect. In our case, the results of the bone marrow aspiration, the sudden drop of the neutrophil count with concomitant eosinophilia and the absence of improvement despite the dose decrease, point towards an immuno-allergic mechanism. However, the overlap between the suspected DRESS induced by meropenem and the agranulocytosis do not allow to conclude with certainty on the causality. Awareness should be raised about this side effect.

Population plasma and urine pharmacokinetics and the probability of target attainment of fosfomycin in healthy male volunteers.

PURPOSE: A population pharmacokinetic model of fosfomycin was developed in healthy volunteers after intravenous administration, and different dosing regimens were evaluated in terms of the probability of target attainment for Escherichia coli using both plasma and urinary pharmacokinetic/pharmacodynamic targets. METHODS: Eight healthy men received fosfomycin as both intermittent 8 g q8h and continuous infusion 1 g/h with a loading dose of 8 g in a crossover study design. Dense sampling was conducted during both regimens. Population pharmacokinetic modelling was performed using NONMEM. Monte Carlo simulations were conducted to evaluate the Probability of Target Attainment (PTA) of different dosing regimens using bactericidal (AUC24h/MIC of 83 and 75%T>MIC) and bacteriostatic (AUC24h/MIC of 25) plasma targets and bacteriostatic (AUC24h/MIC of 3994) urine target. RESULTS: A total of 176 plasma and 86 urine samples were available for PK analysis. A two-compartment model with a urine compartment best described the data. Glomerular filtration rate (GFR) showed a significant correlation with renal clearance and was implemented in the final model. Simulation results show that the dose of 4 g q8h reached 100% of PTA using bactericidal and bacteriostatic targets for MIC up to 16 mg/L. CONCLUSION: For the clinical breakpoint of 32 mg/L, the standard dosing regimen (4 g q8h) might not be sufficient to reach the bactericidal target. Higher dosing of 8 g q8h as an intermittent infusion or 0.75 g/h as a continuous infusion might be required. Continuous infusion resulted in better attainment of the %T>MIC target than intermittent infusion.

Cotransfer of resistance to cephalosporins, colistin, and fosfomycin mediated by an IncHI2/pSH16G4928-like plasmid in ESBL-producing monophasic Salmonella Typhimurium strains of pig origin.

AIMS: To assess the co-transmission risk of phenotypic and genetic resistance to cephalosporins, colistin, and fosfomycin in Salmonella strains collected along the whole pork production chain. METHODS AND RESULTS: From a total of 107 Salmonella isolates from samples collected in pig slaughterhouses and markets, 15 ESBL-producing Salmonella strains resistant to cefotaxime were identified by broth microdilution method and clavulanic acid inhibition test, including 14 monophasic Salmonella Typhimurium strains and one Salmonella Derby strain. Whole genome sequence analysis showed that nine monophasic S. Typhimurium strains coresistant to colistin and fosfomycin carried the resistance genes blaCTX-M-14, mcr-1, and fosA3. Conjugational transfer tests demonstrated that the phenotypic and genetic resistance to cephalosporins, colistin, and fosfomycin could cotransfer back and forth between Salmonella and Escherichia coli via an IncHI2/pSH16G4928-like plasmid. CONCLUSIONS: This study reports the cotransmission of phenotypic and genetic resistance to cephalosporins, colistin, and fosfomycin via an IncHI2/pSH16G4928-like plasmid in Salmonella strains of animal origin, giving an alarm for the prevention of the development and spread of bacterial multidrug resistance.

Cerebrospinal fluid penetration of fosfomycin in patients with ventriculitis: an observational study.

BACKGROUND: For treatment of ventriculitis, vancomycin and meropenem are frequently used as empiric treatment but cerebrospinal fluid (CSF) penetration is highly variable and may result in subtherapeutic concentrations. Fosfomycin has been suggested for combination antibiotic therapy, but data are sparse, so far. Therefore, we studied CSF penetration of fosfomycin in ventriculitis. METHODS: Adult patients receiving a continuous infusion of fosfomycin (1 g/h) for the treatment of ventriculitis were included. Routine therapeutic drug monitoring (TDM) of fosfomycin in serum and CSF was performed with subsequent dose adaptions. Demographic and routine laboratory data including serum and CSF concentrations for fosfomycin were collected. Antibiotic CSF penetration ratio as well as basic pharmacokinetic parameters were investigated. RESULTS: Seventeen patients with 43 CSF/serum pairs were included. Median fosfomycin serum concentration was 200 [159-289] mg/L and the CSF concentration 99 [66-144] mg/L. Considering only the first measurements in each patient before a possible dose adaption, serum and CSF concentrations were 209 [163-438] mg/L and 104 [65-269] mg/L. Median CSF penetration was 46 [36-59]% resulting in 98% of CSF levels above the susceptibility breakpoint of 32 mg/L. CONCLUSION: Penetration of fosfomycin into the CSF is high, reliably leading to appropriate concentrations for the treatment of gram positive and negative bacteria. Moreover, continuous administration of fosfomycin appears to be a reasonable approach for antibiotic combination therapy in patients suffering from ventriculitis. Further studies are needed to evaluate the impact on outcome parameters.

Investigation of in vitro efficacy of meropenem/polymyxin B and meropenem/fosfomycin combinations against carbapenem resistant Klebsiella pneumoniae strains.

The incidence of infections caused by carbapenem-resistant Klebsiella pneumoniae (CRKP) is increasing worldwide, and very limited number of effective antibiotics are available for therapy. In our study, the in vitro efficacy of meropenem/polymyxin B and meropenem/fosfomycin combinations against CRKP strains was investigated. The efficiency of meropenem/polymyxin B and meropenem/fosfomycin combinations was tested by checkerboard microdilution and checkerboard agar dilution methods, respectively, against 21 CRKP strains containing major carbapenem resistant genes (7 blaKPC, 7 blaOXA-48 gene, and 7 blaOXA-48+ blaNDM), and seven additional CRKP strains without carbapenemase genes.Among the 28 CRKP strains, the meropenem/polymyxin B combination was synergistic in ten (35.7%), partially synergistic in 12 (42.8%), and indifferent in six (21.4%) isolates. The meropenem/fosfomycin combination was found to be synergistic in three isolates (10.7%), partially synergistic in 20 (71.4%), and indifferent in five (17.8%). In 21 strains containing carbapenem resistance genes, meropenem/polymyxin B and meropenem/fosfomycin combinations exhibited synergistic/partial synergistic effects in 15 (71.4%) and 16 (76.2%) strains, respectively, compared to 100% synergistic/partial synergistic efficiency in both combinations in seven strains free of carbapenemase genes. No antagonistic effect was detected in either combination.Regardless of presence or absence of carbapenem resistance genes, meropenem/polymyxin B and meropenem/fosfomycin combinations both demonstrated high synergistic and partial synergistic activity against 78.4% and 82.1% of CRKP strains, respectively. Also, they have no antagonistic effects and can be used successfully to prevent therapeutic failure with monotherapy, according to our in vitro studies.

Susceptibility to Fosfomycin and Nitrofurantoin of ESBL-Positive Escherichia coli and Klebsiella pneumoniae Isolated From Urine of Pediatric Patients.

BACKGROUND: Pediatric urinary tract infection (UTI) caused by extended-spectrum ß-lactamase (ESBL)-positive gram-negative bacilli (GNB) has limited options for oral antibiotic treatment. The purpose of this study was to investigate the susceptibility of ESBL-positive Escherichia coli and Klebsiella pneumoniae isolates from pediatric urine samples to two oral antibiotics (fosfomycin and nitrofurantoin). METHODS: From November 2020 to April 2022, ESBL-positive E. coli and K. pneumoniae isolates from urine samples were collected at Samsung Medical Center, Seoul, Korea. Patients over 18 years of age or with malignancy were excluded. For repeated isolates from the same patient, only the first isolate was tested. Minimum inhibitory concentrations (MICs) were measured using agar (fosfomycin) or broth (nitrofurantoin) dilution methods. MIC50 and MIC90 were measured for fosfomycin and nitrofurantoin in both E. coli and K. pneumoniae. RESULTS: There were 117 isolates from 117 patients, with a median age of 7 months (range, 0.0-18.5 years). Among 117 isolates, 92.3% (108/117) were E. coli and 7.7% (9/117) were K. pneumoniae. Isolates from the pediatric intensive care unit (PICU) and general ward (GW) was 11.1% (13/117) and 88.9% (104/117), respectively. Among 108 E. coli isolates, MIC50 and MIC90 for fosfomycin were 0.5 µg/mL and 2 µg/mL, respectively. Fosfomycin susceptibility rate was 97.2% (105/108) with a breakpoint of 128 µg/mL. Fosfomycin susceptibility rate was significantly lower in PICU isolates than in GW isolates (81.8% vs. 99.0%, P = 0.027). For nitrofurantoin, both the MIC50 and MIC90 were 16 µg/mL. Nitrofurantoin susceptibility rate was 96.3% (104/108) with a breakpoint of 64 µg/mL based on Clinical and Laboratory Standards Institute guidelines. Among the nine K. pneumoniae isolates, the MIC50 and MIC90 for fosfomycin was 2 µg/mL and 32 µg/mL, respectively. MIC50 and MIC90 for nitrofurantoin were 64 µg/mL and 128 µg/mL, respectively. CONCLUSION: For uncomplicated UTI caused by ESBL-positive GNB in Korean children, treatment with fosfomycin and nitrofurantoin for E. coli infections can be considered as an effective oral therapy option.

Synergistic Antimicrobial Activity of Eugenol in Combination with Fosfomycin to Combat Escherichia coli and Potential Effect on Plasmid-Mediated Fosfomycin Resistance Genes.

The presence of multidrug-resistant pathogenic microorganisms makes it challenging to cure bacterial illnesses. Syzygium aromaticum has been used for medicinal purposes since ancient times. The objective of this study was to investigate the potential synergistic effect of the combination of Eugenol and Fosfomycin against clinically Uropathogenic Escherichia coli (UPEC) and their possible co-treatment as well as their contribution to plasmid-mediated Fosfomycin resistance (fosA3 and fosA4) genes using molecular assays. Eugenol was extracted from clove (Syzygium aromaticum) plants using steam distillation by Clevenger and analyzed by high-performance liquid chromatography (HPLC). UPEC accounted for 63.6 % of all isolates. Specifically, 99.3 % of the UPEC isolates exhibited resistance to multiple types of antibiotics [multidrug-resistant (MDR)]. The MIC for Eugenol was 1.25-5 µg/mL, and Fosfomycin was 512-1024 µg/mL, while the MBC for Eugenol was 5-10 µg/mL and Fosfomycin was 2048 µg/mL. The synergistic effects were considerable, with 1/4 MIC of Eugenol resulting in 1/8 MIC Fosfomycin. Eugenol inhibited most of the UPEC isolates at 4-8 hours, Fosfomycin at 8-12 hours, and co-treatment at 4-8 hours. The fosA3 and fosA4 genes were detected in 5.7 % and 2.9 % of the isolates, respectively. The results showed variable gene expression changes in response to the different treatments.

Fosfomycin-meropenem synergistic combination against NDM carbapenemase-producing Klebsiella pneumoniae strains.

Carbapenemase-producing Enterobacteriaceae (CPE) are an increasing threat to global public health. Treatment of CPE isolates, like New Delhi metallo-ß-lactamase (NDM), is limited and often necessitates combination therapies. The aim of this study was to evaluate the synergistic meropenem/fosfomycin combination against K.pneumoniae-producing NDM isolates. Fosfomycin/meropenem, fosfomycin/colistin and meropenem/colistin were tested alone and in combination, using e-test and time-kill assay against 20 clinical carbapenemase-producing K. pneumonia (CPKp NDM) isolates collected from September 2022 to December 2022. K. pneumoniae strains were resistant to meropenem, ceftazidime/avibactam and ceftolozano/tazobactam, 75% and 80% of isolates were susceptible for cefiderocol and for colistin respectively. Fosfomycin/meropenem combination was synergic in 95% (n=19) strains. Fosfomycin/colistin and colistin/meropenem combination showed only 10% synergistic combination strains. In 16 isolates (80%) indifference action for fosfomycin/colistin and colistin/meropenem was reported. For 0.8% of CpKP NDM isolates colistin/meropenem and fosfomycin/colistin combinations found to be antagonistic. In this study, time kill assay showed combination therapies action versus K.pneumoniae metallo-b-lactamase producing (NDM) strains and confirmed the synergistic action of fosfomycin/meropenem combination. In vitro synergy testing should be routinely performed in multidrug resistance infections and combo therapies can be used as a possible alternative in targeted patients with the goal of reducing overall antibiotic costs.