High Rates of Fosfomycin Resistance in Gram-Negative Urinary Isolates from Israel

Skipped wells and scientific error during fosfomycin agar dilution and broth microdilution lead to inconsistent minimal inhibitory concentrations and may be cause for reevaluating testing methods for Klebsiella pneumoniae

Despite the first-line recommendation of fosfomycin for uncomplicated urinary tract infections (UTIs), there are pressing barriers for optimizing its use for the treatment of non-Escherichia coli Enterobacterales UTI. There are no approved breakpoints for oral use against other Enterobacterales, and the recommended agar dilution (AD) reference method for minimal inhibitory concentration (MIC) determination is largely impractical. Using 160 clinical Klebsiella pneumoniae isolates, we sought to understand rates of skipped wells and MIC imprecision in broth microdilution (BMD) and how that compares to rates of error using AD. Though the Clinical and Laboratory Standards Institute refers to the skipped well phenomena in their recommendation against the use of BMD, there is a paucity of data on its frequency. While AD and BMD produced similar MIC50/90 values (32/256 µg/mL for AD and 64/256 µg/mL for BMD), essential agreement was poor. No-growth wells at concentrations below the MIC occurred in up to 10.9% of wells at a given concentration, as the most frequent scientific error. Growth in concentrations above the measured MIC occurred in up to 3.3% of wells and was seen within three dilutions of the MIC for BMD. Observation of single colonies either at or beyond the measured MIC for AD was also common and occurred up to 8.3% and 2.5% of the time, respectively. The frequent scientific error in both testing methods should prompt re-evaluation of AD guidelines and expansion of MIC testing methods for fosfomycin susceptibility testing, as poor agreement with another method prone to scientific error should not be the main detractor from BMD use.IMPORTANCEDespite the recommendation of fosfomycin for uncomplicated urinary tract infections (UTIs), there are barriers for optimizing its use. There are no approved breakpoints for oral use against other Enterobacterales, and the recommended agar dilution (AD) reference method for MIC determination is largely impractical. The use of broth microdilution (BMD) for fosfomycin testing is not recommended by the Clinical and Laboratory Standards Institute due to unsatisfactory precision and skipped wells-occurrence of no-growth in a single well before the minimal inhibitory concentration (MIC)-and trailing endpoints. We sought to understand rates of skipped wells and growth at concentrations above measured MICs in BMD and how that compares to scientific error using AD. No-growth wells at concentrations below the MIC occurred in up to 10.9% of wells for BMD and single colonies at or beyond measured MICs for AD were also common. Frequent scientific error in both methods should prompt re-evaluation of both AD and BMD for fosfomycin susceptibility testing.

Urinary Tract Infections Caused by Uropathogenic Escherichia coli: Mechanisms of Infection and Treatment Options

Urinary tract infections (UTIs) are common bacterial infections that represent a severe public health problem. They are often caused by Escherichia coli (E. coli), Klebsiella pneumoniae (K. pneumonia), Proteus mirabilis (P. mirabilis), Enterococcus faecalis (E. faecalis), and Staphylococcus saprophyticus (S. saprophyticus). Among these, uropathogenic E. coli (UPEC) are the most common causative agent in both uncomplicated and complicated UTIs. The adaptive evolution of UPEC has been observed in several ways, including changes in colonization, attachment, invasion, and intracellular replication to invade the urothelium and survive intracellularly. While antibiotic therapy has historically been very successful in controlling UTIs, high recurrence rates and increasing antimicrobial resistance among uropathogens threaten to greatly reduce the efficacy of these treatments. Furthermore, the gradual global emergence of multidrug-resistant UPEC has highlighted the need to further explore its pathogenesis and seek alternative therapeutic and preventative strategies. Therefore, a thorough understanding of the clinical status and pathogenesis of UTIs and the advantages and disadvantages of antibiotics as a conventional treatment option could spark a surge in the search for alternative treatment options, especially vaccines and medicinal plants. Such options targeting multiple pathogenic mechanisms of UPEC are expected to be a focus of UTI management in the future to help combat antibiotic resistance.

Real-Life Comparison of Fosfomycin to Nitrofurantoin for the Treatment of Uncomplicated Lower Urinary Tract Infection in Women

In this study, we compared the failure rates of fosfomycin and nitrofurantoin for uncomplicated urinary tract infections. We used Meuhedet Health Services’ large database to collect data on all female patients, older than 18 years, who were prescribed either antibiotic during 2013–2018. Treatment failure was a composite endpoint of hospitalization, emergency-room visit, IV antibiotic treatment, or prescription of a different antibiotic, within seven days of the initial prescription. Reinfection was considered when one of these endpoints appeared 8–30 days following the initial prescription. We found 33,759 eligible patients. Treatment failure was more common in the fosfomycin group than the nitrofurantoin group (8.16% vs. 6.87%, p-value < 0.0001). However, reinfection rates were higher among patients who received nitrofurantoin (9.21% vs. 7.76%, p-value < 0.001). Among patients younger than 40 years, patients treated with nitrofurantoin had more reinfections (8.68% vs. 7.47%, p value = 0.024). Treatment failure rates were mildly higher in patients treated with fosfomycin, despite having less reinfections. We suggest that this effect is related to a shorter duration of treatment (one vs. five days) and encourage clinicians to be more patient before declaring fosfomycin failure and prescribing another antibiotic.

Antimicrobial Susceptibilities of Urinary Extended-spectrum β-lactamase Escherichia coli to Fosfomycin

Objectives

Escherichia coli (E. coli)-induced urinary tract infection (UTI) is a common infection associated with frequent use of antibiotics and the increase in global antibiotic resistances. We aimed to determine the susceptibility profile of extended-spectrum β-lactamase (ESBL) producing E. coli isolated from the urinary samples to fosfomycin and other antibiotics.

Methods

We retrospectively analyzed urine samples with ESBL-producing E. coli isolates obtained between January 2018 and December 2019 in the Microbiology Section, Salmaniya Medical Complex, Bahrain. We collected and analyzed all the E. coli urinary isolates' data and their antibiotic susceptibility patterns.

Results

The study included 3044 E. coli isolates with 50.6% obtained in 2018 and 49.4% in 2019; 38.1% (1161 isolates) were ESBL E. coli, and 0.7% (21 isolates) were carbapenem-resistant ^{Enterobacteriaceae} (CRE). There were 1161 (38.1%) isolates with ESBL-producing E. coli, with 37.3% isolated in 2018 and 39.0% isolated in 2019. The antibiotic susceptibility of ESBL-producing E. coli during the study period showed susceptibility to trimethoprim/sulfamethoxazole in 46.1% of isolates (50.2% in 2018 dropped to 41.9% in 2019), to ciprofloxacin in 49.0% of isolates (49.5% in 2018 dropped to 48.4% in 2019), to nitrofurantoin in 91.8% of isolates (94.3 in 2018 dropped to 89.3% in 2019), and to fosfomycin in 97.6% of isolates (98.8% in 2018 dropped to 96.3% in 2019).

Conclusions

ESBL-producing E. coli is an important cause of UTI in Bahrain. Fosfomycin is a very effective oral antimicrobial that retains high efficacy against ESBL-producing E. coli, which helps decrease the need for parenteral therapy and, consequently, hospitalization.

Antimicrobial Susceptibilities of Urinary Extended-spectrum β-lactamase Escherichia coli to Fosfomycin

OBJECTIVES

Escherichia coli (E. coli)-induced urinary tract infection (UTI) is a common infection associated with frequent use of antibiotics and the increase in global antibiotic resistances. We aimed to determine the susceptibility profile of extended-spectrum β-lactamase (ESBL) producing E. coli isolated from the urinary samples to fosfomycin and other antibiotics.

METHODS

We retrospectively analyzed urine samples with ESBL-producing E. coli isolates obtained between January 2018 and December 2019 in the Microbiology Section, Salmaniya Medical Complex, Bahrain. We collected and analyzed all the E. coli urinary isolates' data and their antibiotic susceptibility patterns.

RESULTS

The study included 3044 E. coli isolates with 50.6% obtained in 2018 and 49.4% in 2019; 38.1% (1161 isolates) were ESBL E. coli, and 0.7% (21 isolates) were carbapenem-resistant ^{Enterobacteriaceae} (CRE). There were 1161 (38.1%) isolates with ESBL-producing E. coli, with 37.3% isolated in 2018 and 39.0% isolated in 2019. The antibiotic susceptibility of ESBL-producing E. coli during the study period showed susceptibility to trimethoprim/sulfamethoxazole in 46.1% of isolates (50.2% in 2018 dropped to 41.9% in 2019), to ciprofloxacin in 49.0% of isolates (49.5% in 2018 dropped to 48.4% in 2019), to nitrofurantoin in 91.8% of isolates (94.3 in 2018 dropped to 89.3% in 2019), and to fosfomycin in 97.6% of isolates (98.8% in 2018 dropped to 96.3% in 2019).

CONCLUSIONS

ESBL-producing E. coli is an important cause of UTI in Bahrain. Fosfomycin is a very effective oral antimicrobial that retains high efficacy against ESBL-producing E. coli, which helps decrease the need for parenteral therapy and, consequently, hospitalization.

Adherence to guideline recommendations for urinary tract infections in adult women: a cross-sectional study

AIM

To study whether changes in drug preferences in the Dutch guideline for the treatment of Urinary Tract Infection (UTI) for General Practitioners (GPs) in 2013, resulted in corresponding changes in antibiotic dispensing.

BACKGROUND

For the treatment of uncomplicated UTI, nitrofurantoin remained the first choice, while fosfomycin became the second choice and changed ranks with trimethoprim. For a subsequent febrile UTI, ciprofloxacin became the first choice and changed ranks with amoxicillin/clavulanic acid, co-trimoxazole remained the third choice.

METHODS

In this observational cross-sectional study, routinely collected dispensing data from the Dutch Foundation of Pharmaceutical Statistics from 2012 to 2017 were used. The number of women 18 years and older, treated with one of the guideline antibiotics for uncomplicated UTI and subsequent febrile UTI were analysed annually. Proportions were calculated. Data were stratified for age categories. Failure of uncomplicated UTI treatment was defined as the dispensing of an antibiotic for febrile UTI within 14 days after the dispensing of an antibiotic for uncomplicated UTI.

FINDINGS

Data were available from 81% of all pharmacies in 2012 to 89% in 2017. Percentages of women dispensed nitrofurantoin were relatively stable with 87.4% in 2012 and 84.4% in 2017. Percentages of women dispensed fosfomycin increased from 5.4% in 2012 to 21.8% in 2017, whereas percentages of women dispensed trimethoprim decreased from 17.8% to 8.0%. Within age categories, the percentage of women dispensed fosfomycin increased from 12.4% in women 18-30 years old to 36.7% in women above 80 years old. Percentages of women dispensed antibiotics for febrile UTI remained stable at 5% annually. Percentages of women receiving ciprofloxacin increased from 1.9% in 2012 to 3.3% in 2017, while those receiving amoxicillin/clavulanic acid decreased from 2.9% to 1.8%. New guideline recommendations resulted in corresponding changes in dispensed antibiotics for uncomplicated UTI and subsequent febrile UTI. Drug choices differed for age categories.

Risk factors of multidrug-resistant bacteria in community-acquired urinary tract infections

Background

Urinary tract infections (UTIs) are one of the most seen infection among community.

Objectives

In this cross-sectional study we aimed to investigate the risk factors of multidrug-resistant (MDR) bacteria that caused community-acquired UTI (CA-UTI).

Methods

Consecutive patients admitted to the Urology and Infectious Diseases policlinics with the diagnosis of CA-UTI were included in the study. A standard form including possible predisposing factors for MDR bacteria was applied.

Results

In total, 240 patients (51.3% females) were enrolled in the study. The mean age of participants were 59.8 ± 18.3 years old. Escherichia coli (n =166; 69.2%)was the most frequently isolated bacteria and its incidence was higher in females than in males (p=0.01). In total, 129 (53.8%) of the identified pathogens were MDR bacteria. According to multivariate analysis, the use of antibiotics three or more times increased the risk of infection with MDR bacteria by 4.6 times, the history of urinary tract infection in the last 6 months by 2 times, being male and over 65 years old by 3 times.

Conclusion

Doctors should consider prescribing broad-spectrum antibiotics in patients with severe UTIs with a history of UTI, advanced age, male gender, and multiple antibiotic usage, even if they have a CA-UTI.

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.

Effective Treatment for Uncomplicated Urinary Tract Infections with Oral Fosfomycin, Single Center Four Year Retrospective Study

Fosfomycin represents a relatively old antibiotic, but it is experiencing a comeback in recent years. According to some studies, the increasing therapeutic use of this drug led to a rapid increase in the levels of resistance in bacteria causing urinary tract infection. In the presented study, levels of resistance to fosfomycin in more than 3500 bacterial isolates before and after fosfomycin introduction into therapeutic use in the Czech Republic and the clinical efficacy of treatment in 300 patients using this drug were assessed. The results show that the resistance levels to fosfomycin in Escherichia coli isolates before and after the drug registration were not significantly different (3.4% and 4.4%, respectively). In some other Gram-negative rods, such as otherwise susceptible Enterobacter, resistance to fosfomycin increased significantly from 45.6% to 76.6%. Fosfomycin treatment of urinary tract infections showed an excellent seven-day clinical efficacy (79.7%). However, when used to treat recurrent or complicated urinary tract infections, fosfomycin treatment was associated with high levels of infection relapse, leading to relapse in a total of 20.4% of patients during the first two months. This indicates that fosfomycin exhibits good efficacy only for the treatment of uncomplicated urinary tract infections

The role of fosfomycin for multidrug-resistant gram-negative infections

PURPOSE OF REVIEW

In the last decade, an increasing interest in using fosfomycin for the treatment of multidrug-resistant gram-negative (MDR-GNB) infections have been registered, especially when none or only a few other active alternatives remained available.

RECENT FINDINGS

Fosfomycin may remain active against a considerable proportion of MDR-GNB. In observational studies, a possible curative effect of oral fosfomycin monotherapy has been described for uncomplicated urinary tract infections (UTI) and bacterial prostatitis caused by MDR-GNB, whereas intravenous fosfomycin has been mostly used in combination with other agents for various type of severe MDR-GNB infections. The ZEUS randomized controlled trial (RCT) has started to provide high-level evidence about the possible use of fosfomycin for complicated UTI caused by extended-spectrum β-lactamase-producing GNB, but no results of large RCT are currently available to firmly guide the use of fosfomycin for carbapenem-resistant GNB.

SUMMARY

Fosfomycin is an important therapeutic option for MDR-GNB infections. Further pharmacokinetic/pharmacodynamic and clinical research is needed to optimize its use.

Coexistence of Fosfomycin Resistance Determinant fosA and fosA3 in Enterobacter cloacae Isolated from Pets with Urinary Tract Infection in Taiwan

To analyze the characteristics of fosA and fosA3 in Enterobacter cloacae isolated from aspirated and catheterized urine culture specimens of companion pets in Taiwan. A total of 19 E. cloacae isolates from pets with urinary tract infection were screened for the presence of fosA, fosA3, and fosC2 and for the genetic context of them by PCR amplification and sequencing. The transferability, resistance phenotypes, plasmid replicon typing properties and genetic environments of fosA- and/or fosA3-positive strains were characterized. Five E. cloacae isolates were positive for fosA and three coharbored fosA and fosA3. No fosC determinant was detected. Transconjugants of fosA3 were successfully acquired, while the acquisition of fosA transconjugants was failed. The minimum inhibitory concentrations (MICs) of the three fosA3-positive isolates and their transconjugants were ≥256 mg/L, whereas the MICs of the five fosA-positive isolates ranged from 64 mg/L to 256 mg/L. Three plasmid replicons (InCFrepB, InCL/M, and InCHI2) were identified in fosA- and fosA3-positive E. cloacae isolates. Different genetic contexts lay in the downstream region of fosA and fosA3, respectively. Eight distinct patterns based on the similarity value of more than 80% were typed for all the 8 fosA-positive isolates. In conclusion, the fosA concomitant with fosA3 were found in E. cloacae isolates. The fosA3 not only exhibits stronger activity of inactivating fosfomycin than fosA but also possesses stronger potential to spread than fosA. Different genetic backgrounds exist in these fosA- and fosA3-positive isolates, and different mobile elements may confer the dissemination of fosA and fosA3.

Characterization of fosfomycin heteroresistance among multidrug-resistant Escherichia coli isolates from hospitalized patients in Rio de Janeiro, Brazil

OBJECTIVES

Urinary tract infections (UTIs) caused by multidrug-resistant Escherichia coli have become a major medical concern. Old antibiotics such as fosfomycin have become an alternative therapeutic option due to their effectiveness and, as a result, fosfomycin is now used as a first-line drug for the treatment of UTIs in many countries. Despite low resistance rates, fosfomycin heteroresistance, defined as a phenomenon where subpopulations of bacteria are resistant to high antibiotic concentrations whereas most of the bacteria are susceptible, is an underestimated problem.

METHODS

The frequency of heteroresistance in E. coli isolated from hospitalized patients in Brazil and its effect on susceptibility of E. coli in biofilms was studied and the isolates were molecularly characterized to reveal the mechanisms behind their fosfomycin heteroresistance using whole-genome sequencing.

RESULTS

A higher frequency of fosfomycin heteroresistance compared with other studies was found. In biofilms, most heteroresistant isolates were less sensitive to fosfomycin than control isolates and showed overexpression of metabolic genes thereby increasing their survival rate. Molecular characterization showed that some resistant subpopulations derived from heteroresistant isolates had a defect in their fosfomycin uptake system caused by mutations in transporter and regulatory genes, whereas others overexpressed the murA gene. None to minor effects on bacterial fitness were observed. Oxidative stress protection, virulence and metabolic genes were differentially expressed in resistant subpopulations and heteroresistant isolates.

CONCLUSION

Frequent detection of heteroresistance in UTIs may play a role in the failure of antibiotic treatments and should therefore be more carefully diagnosed.

Treatment of urinary tract infections in the era of antimicrobial resistance and new antimicrobial agents

Urinary tract infections (UTIs) caused by antibiotic-resistant Gram-negative bacteria are a growing concern due to limited treatment options. Knowledge of the common uropathogens in addition to local susceptibility patterns is essential in determining appropriate empiric antibiotic therapy of UTIs. The recommended first-line empiric antibiotic therapy for acute uncomplicated bacterial cystitis in otherwise healthy adult nonpregnant females is a 5-day course of nitrofurantoin, a 3-g single dose of fosfomycin tromethamine, or a 5-day course of pivmecillinam. High rates of resistance for trimethoprim-sulfamethoxazole and ciprofloxacin preclude their use as empiric treatment of UTIs in several communities, particularly if patients who were recently exposed to them or in patients who are at risk of infections with extended-spectrum β-lactamases (ESBLs)-producing Enterobacteriales. Second-line options include oral cephalosporins such as cephalexin or cefixime, fluoroquinolones and β-lactams, such as amoxicillin-clavulanate. Current treatment options for UTIs due to AmpC- β -lactamase-producing Enterobacteriales include nitrofurantoin, fosfomycin, pivmecillinam, fluoroquinolones, cefepime, piperacillin-tazobactam and carbapenems. Treatment oral options for UTIs due to ESBLs-E coli include nitrofurantoin, fosfomycin, pivmecillinam, amoxicillin-clavulanate, finafloxacin, and sitafloxacin while pivmecillinam, fosfomycin, finafloxacin, and sitafloxacin are treatment oral options for ESBLs- Klebsiella pneumoniae. Parenteral treatment options for UTIs due to ESBLs-producing Enterobacteriales include piperacillin-tazobactam (for ESBL-E coli only), carbapenems including meropenem/vaborbactam, imipenem/cilastatin-relebactam, and sulopenem, ceftazidime-avibactam, ceftolozane-tazobactam, aminoglycosides including plazomicin, cefiderocol, fosfomycin, sitafloxacin, and finafloxacin. Ceftazidime-avibactam, meropenem/vaborbactam, imipenem/cilastatin-relebactam, colistin, fosfomycin, aztreonam and ceftazidime-avibactam, aztreonam and amoxicillin-clavulanate, aminoglycosides including plazomicin, cefiderocol, tigecycline are treatment options for UTIs caused by carbapenem-resistant Enterobacteriales (CRE). Treatment options for UTIs caused by multidrug resistant (MDR)-Pseudomonas spp. include fluoroquinolones, ceftazidime, cefepime, piperacillin-tazobactam, carbapenems including imipenem-cilastatin/relebactam, meropenem, and fosfomycin, ceftolozane-tazobactam, ceftazidime-avibactam, aminoglycosides including plazomicin, aztreonam and ceftazidime-avibactam, cefiderocol, and colistin. It is important to use the new antimicrobials wisely for treatment of UTIs caused by MDR-organisms to avoid resistance development.

Prevalence of fosfomycin resistance among ESBL-producing Escherichia coli isolates in the community, Switzerland

Our aim was to evaluate the prevalence of fosfomycin-resistant strains among ESBL-producing Escherichia coli isolates recovered from community patients in Switzerland. A total of 1225 ESBL-producing E. coli isolates were collected between 2012 and 2013 from a private and community laboratory. Fosfomycin resistance was assessed by using the novel rapid fosfomycin/E. coli NP test and agar dilution method. Resistant isolates were further investigated for acquired resistance genes fosA1-7 by PCR and sequencing. Pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST) were performed to evaluate the clonal relationship among fosA3-carrying isolates. Out of the 1225 ESBL-producing E. coli isolates analyzed in this study, 1208 were fosfomycin susceptible while 17 were fosfomycin resistant. No discrepancy was observed between the rapid fosfomycin/E. coli NP test and the agar dilution method taken as the gold standard. Five out of the 17 resistant isolates carried a fosA-like gene. No clonal relationship was observed among those isolates. Here, the prevalence of fosfomycin resistance among ESBL-producing E. coli isolates in the community is reported for the first time in Switzerland, being ca. 1.4%. Among the five isolates carrying a fosA gene, four encoded the FosA3 enzyme, being the most prevalent fosfomycin-resistant determinant. An excellent correlation was observed between minimum inhibitory concentration-based susceptibility categorization and results of the rapid fosfomycin/E. coli NP test, further indicating the excellent sensitivity and specificity of this recently developed rapid test whose results are obtained in less than 2 h.