Contribution of hypermutation to fosfomycin heteroresistance in Escherichia coli

Bacteriological and molecular study of fosfomycin resistance in uropathogenic Escherichia coli

The identification of genes associated with resistance has the potential to facilitate the development of novel diagnostic tests and treatment methods. The objective of this study was to examine the antibiotic resistance and Fosfomycin resistance genes in uropathogenic Escherichia coli (UPEC) in patients in Baghdad, Iraq. After analyzing 250 urine samples using various identification methods, including the examination of morphological characteristics, biochemical tests, and genetic detection, it was determined that E. coli was the most common bacteria present, accounting for 63.6% of the samples. Antibiotic susceptibility testing showed a significant prevalence of resistance to various antibiotics, with 99.3% of E. coli isolates exhibiting multiple drug resistance (MDR). Fosfomycin showed antibacterial properties against UPEC. The minimum inhibitory concentration (MIC) ranged from 512 to 1024 μg/mL, while the minimum bactericidal concentration (MBC) was 2048 μg/mL. In the time-kill assay, fosfomycin was effective against fosfomycin-resistant isolates within 8-12 h. The genetic determinants associated with fosfomycin resistance were examined through the utilization of polymerase chain reaction (PCR). The findings indicated that the genes murA, glpT, and cyaA were detected in all the isolates when genomic DNA was used as a template. However, all the tests yielded negative results when plasmid was used as a template. The genes fosA3 and fosA4 were detected in 8.6% and 5% of the isolates when genomic DNA was used as a template. When plasmid was used as a template, the genes fosA3 and fosA4 were found in 5.7% and 2.9% of the isolates, respectively. In conclusion, there is an increasing problem with antibiotic resistance in UPEC, with elevated rates of resistance to several antibiotics. The study also offers novel insights into the genetic foundation of fosfomycin resistance in UPEC.

Retrospective assessment of antimicrobial stewardship initiative in outpatient use of ertapenem for uncomplicated extended spectrum beta lactamase Enterobacteriaceae urinary tract infections

BACKGROUND

Urinary tract infections (UTI) are often over-diagnosed and over-treated, which can induce and select for resistant pathogens. After observing wide-spread outpatient use of ertapenem, a broad-spectrum antibiotic, a structured antimicrobial stewardship initiative (ASI) to improve appropriate antimicrobial prescribing was undertaken. ASI objectives were to achieve a goal of reducing ertapenem utilization for extended spectrum beta lactamase Enterobacteriaceae (ESBL-EB) UTI by 10% and evaluate the clinical outcomes associated with the ASI.

METHODS

A pre-to-post cohort study was conducted at a single-center integrated healthcare system between November 1, 2014 and February 26, 2017. An intensive, 90-day, pharmacist-driven, structured ASI was implemented between November 1, 2015 and January 29, 2016. Female patients aged ≥18 years who were treated for an uncomplicated, ESBL-EB urinary tract infection (UTI) were included. Primary outcome was clinical resolution defined as cure, persistence, relapse and recurrence. Secondary outcome measured was monthly ertapenem use expressed as number of days of therapy (DOT)/1000 adjusted patient days (APD). Segmented regression analysis for interrupted time series was performed to estimate ASI intervention effect.

RESULTS

A total of 184 patients were included in the study. Ertapenem utilization decreased from 0.0145 DOT/1000 APD in Nov. 2014 to 0.0078 DOT/1000 APD Feb. 2017(p < 0.01). The mean ertapenem DOT declined 19% overall from the pre vs. post intervention periods (32 vs 26, p < 0.01). Frequency of recurrent UTIs between treatments did not significantly differ and no adverse effects were reported in patients treated with aminoglycosides.

CONCLUSIONS

A structured ASI for uncomplicated ESBL-EB UTI was associated with a clinically meaningful decrease in ertapenem utilization and once-daily, 5-day aminoglycoside treatment was well-tolerated.

Activity of fosfomycin and amikacin against fosfomycin-heteroresistant Escherichia coli strains in a hollow-fiber infection model

Objectives:To evaluate human-like intravenous doses of fosfomycin (8g/Q8h) and amikacin (15mg/kg/Q24h) efficacy in monotherapy and in combination against six fosfomycin-heteroresistant Escherichia coli isolates using a hollow-fiber infection model (HFIM).Materials and methods:Six fosfomycin-heteroresistant E. coli isolates (4 with strong mutator phenotype) and the control strain E. coli ATCC 25922 were used. Mutant frequencies for rifampin (100mg/L), fosfomycin (50 and 200mg/L) and amikacin (32mg/L) were determined. Fosfomycin and amikacin MICs were assessed by agar dilution (AD), gradient strip (GSA) and broth microdilution (BMD) assays. Fosfomycin and amikacin synergies were studied by checkerboard and time-kill assays at different concentrations. Fosfomycin (8g/Q8h) and amikacin (15mg/kg/Q24h) efficacy alone and in combination were assessed using a HFIM.Results:Five isolates were resistant to fosfomycin by AD and BMD, but all susceptible by GSA. All isolates were considered susceptible to amikacin. Antibiotic combinations were synergistic in two isolates and no antagonism was detected. In time-kill assays, all isolates survived under fosfomycin at 64mg/L, although, at 307mg/L, only the normomutators and two hypermutators survived. Four isolates survived under 16mg/L amikacin and none at 45mg/L. No growth was detected under combination conditions. In HFIM, fosfomycin and amikacin monotherapies failed to sterilise bacterial cultures, however, fosfomycin and amikacin combination showed a rapid eradication.Conclusions.There may be a risk of treatment failure of fosfomycin-heteroresistant E. coli isolates using either amikacin or fosfomycin in monotherapy. These results support that the combination amikacin-fosfomycin can rapidly decrease bacterial burden and prevent the emergence of resistant subpopulations against fosfomycin-heteroresistant strains.

Interplay among Different Fosfomycin Resistance Mechanisms in Klebsiella pneumoniae

The objectives of this study were to characterize the role of the uhpT, glpT, and fosA genes in fosfomycin resistance in Klebsiella pneumoniae and evaluate the use of sodium phosphonoformate (PPF) in combination with fosfomycin. Seven clinical isolates of K. pneumoniae and the reference strain (ATCC 700721) were used, and their genomes were sequenced. ΔuhpT, ΔglpT, and ΔfosA mutants were constructed from two isolates and K. pneumoniae ATCC 700721. Fosfomycin susceptibility testing was done by the gradient strip method. Synergy between fosfomycin and PPF was studied by checkerboard assay and analyzed using SynergyFinder. Spontaneous fosfomycin mutant frequencies at 64 and 512 mg/liter, in vitro activity using growth curves with fosfomycin gradient concentrations (0 to 256mg/liter), and time-kill assays at 64 and 307 mg/liter were evaluated with and without PPF (0.623 mM). The MICs of fosfomycin against the clinical isolates ranged from 16 to ≥1,024 mg/liter. The addition of 0.623 mM PPF reduced fosfomycin MIC between 2- and 8-fold. Deletion of fosA led to a 32-fold decrease. Synergistic activities were observed with the combination of fosfomycin and PPF (most synergistic area at 0.623 mM). The lowest fosfomycin-resistant mutant frequencies were found in ΔfosA mutants, with decreases in frequency from 1.69 × 10^-1 to 1.60 × 10^-5 for 64 mg/liter of fosfomycin. In the final growth monitoring and time-kill assays, fosfomycin showed a bactericidal effect only with the deletion of fosA and not with the addition of PPF. We conclude that fosA gene inactivation leads to a decrease in fosfomycin resistance in K. pneumoniae The pharmacological approach using PPF did not achieve enough activity, and the effect decreased with the presence of fosfomycin-resistant mutations.