Susceptibility of contemporary isolates to fosfomycin: a systematic review of the literature

ESKAPE in China: epidemiology and characteristics of antibiotic resistance

The escalation of antibiotic resistance and the diminishing antimicrobial pipeline have emerged as significant threats to public health. The ESKAPE pathogens - Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp. - were initially identified as critical multidrug-resistant bacteria, demanding urgently effective therapies. Despite the introduction of various new antibiotics and antibiotic adjuvants, such as innovative β-lactamase inhibitors, these organisms continue to pose substantial therapeutic challenges. People's Republic of China, as a country facing a severe bacterial resistance situation, has undergone a series of changes and findings in recent years in terms of the prevalence, transmission characteristics and resistance mechanisms of antibiotic resistant bacteria. The increasing levels of population mobility have not only shaped the unique characteristics of antibiotic resistance prevalence and transmission within People's Republic of China but have also indirectly reflected global patterns of antibiotic-resistant dissemination. What's more, as a vast nation, People's Republic of China exhibits significant variations in the levels of antibiotic resistance and the prevalence characteristics of antibiotic resistant bacteria across different provinces and regions. In this review, we examine the current epidemiology and characteristics of this important group of bacterial pathogens, delving into relevant mechanisms of resistance to recently introduced antibiotics that impact their clinical utility in China.

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.

Efficacy of a Novel Prophylactic Scheme of Fosfomycin Trometamol in Patients Undergoing Endoscopic Surgery for Benign Prostatic Hyperplasia: Findings from a Prospective Monocentric Single-Arm Study

This study aimed to assess the efficacy of a novel prophylactic scheme of fosfomycin trometamol in patients undergoing elective HoLEP (holmium laser enucleation of the prostate) or TURP (transurethral resection of the prostate) procedures for treating benign prostatic hyperplasia. Patients affected by benign prostatic hyperplasia and undergoing elective HoLEP or TURP procedures during the period February 2022-June 2023 were prospectively enrolled. Two 3 g oral fosfomycin trometamol doses 12 h apart were administered at 8.00 p.m. on day -1 (i.e., the day before HoLEP or TURP procedure) and at 8.00 a.m. on day 0 (i.e., the day of the surgical procedure). The following outcomes were assessed: prevalence of fever occurring in the first 48 h after surgical procedure; prevalence of urological complications occurring after the surgical procedure; prevalence of proven urinary tract infections (UTIs) and/or bloodstream infections (BSIs) at 14 days post-procedure; and prevalence of emergency department admission for UTI-related sepsis at 14 days post-procedure. Univariate analysis comparing patients with and without proven UTI, BSI, or emergency department admission at 14 days post-procedure was carried out. Overall, 96 patients (median age 70 years) undergoing HoLEP (82.3%) or TURP (17.7%) were prospectively included. Median (IQR) time of surgical procedure after the morning fosfomycin dose was 226.5 min (range 88.5-393.75 min). Fever in the post-surgical 48 h occurred in 3/96 patients (3.1%). Prevalence of proven UTI at 14 days was as low as 1.0% (1/96), whereas no patient had proven BSI or UTI-related sepsis requiring emergency department admission at 14 days. Our findings support the contention that a prophylactic scheme based on two doses of fosfomycin trometamol 12 h apart before surgical intervention may represent a valuable strategy for preventing infectious complications in urologic patients undergoing HoLEP or TURP. Larger definitive confirmatory studies are warranted.

Antibiotic prescription patterns in patients with suspected urinary tract infections in Ecuador

BACKGROUND

Urinary tract infections (UTI) are among the most common cause to prescribe antibiotics in primary care. Diagnosis is based on the presence of clinical symptoms in combination with the results of laboratory tests. Antibiotic therapy is the primary approach to the treatment of UTIs; however, some studies indicate that therapeutics in UTIs may be suboptimal, potentially leading to therapeutic failure and increased bacterial resistance.

METHODS

This study aimed to analyze the antibiotic prescription patterns in adult patients with suspected UTIs and to evaluate the appropriateness of the antibiotic prescription. This is a cross-sectional study of patients treated in outpatient centers and in a second-level hospital of the Ministry of Public Health (MOPH) in a city in Ecuador during 2019. The International Classification of Disease Tenth Revision (ICD-10) was used for the selection of the acute UTI cases. The patients included in this study were those treated by family, emergency, and internal medicine physicians.

RESULTS

We included a total of 507 patients in the analysis and 502 were prescribed antibiotics at first contact, constituting an immediate antibiotic prescription rate of 99.01%. Appropriate criteria for antibiotic prescription were met in 284 patients, representing an appropriate prescription rate of 56.02%. Less than 10% of patients with UTI had a urine culture. The most frequently prescribed antibiotics were alternative antibiotics (also known as second-line antibiotics), such as ciprofloxacin (50.39%) and cephalexin (23.55%). Factors associated with inappropriate antibiotic prescribing for UTIs were physician age over forty years, OR: 2.87 (95% CI, 1.65-5.12) p<0.0001, medical care by a general practitioner, OR: 1.89 (95% CI, 1.20-2.99) p = 0.006, not using point-of-care testing, OR: 1.96 (95% CI, 1.23-3.15) p = 0.005, and care at the first level of health, OR: 15.72 (95% CI, 8.57-30.88) p<0.0001.

CONCLUSIONS

The results of our study indicate an appropriate prescription rate of 56.02%. Recommended antibiotics such as nitrofurantoin and fosfomycin for UTIs are underutilized. The odds for inappropriate antibiotic prescription were 15.72 times higher at the first level of care compared to the second. Effective strategies are needed to improve the diagnosis and treatment of UTIs.

Metallo-β-lactamase-mediated antimicrobial resistance and progress in inhibitor discovery

Resistance to β-lactam antibiotics is rapidly growing, substantially due to the spread of serine-β-lactamases (SBLs) and metallo-β-lactamases (MBLs), which efficiently catalyse β-lactam hydrolysis. Combinations of a β-lactam antibiotic with an SBL inhibitor have been clinically successful; however, no MBL inhibitors have been developed for clinical use. MBLs are a worrying resistance vector because they catalyse hydrolysis of all β-lactam antibiotic classes, except the monobactams, and they are being disseminated across many bacterial species worldwide. Here we review the classification, structures, substrate profiles, and inhibition mechanisms of MBLs, highlighting current clinical problems due to MBL-mediated resistance and progress in understanding and combating MBL-mediated resistance.

The Use of Intravenous Fosfomycin in Clinical Practice: A 5-Year Retrospective Study in a Tertiary Hospital in Italy

Fosfomycin in intravenous (IV) formulation has re-emerged as a valuable tool in the treatment of multi-drug resistant (MDR) and extensively drug-resistant (XDR) infections because of its broad spectrum of antibacterial action and pharmacokinetic characteristics. This retrospective study aimed to evaluate how fosfomycin was used in patients admitted to the Polyclinic of Palermo between January 2017 and July 2022. Clinical indications, therapeutic associations, clinical outcomes, and any side effects were analyzed. Intravenous fosfomycin was used in 343 patients, 63% male, with a mean age of 68 years (range 15-95). Urinary tract infections (UTIs) and hospital-acquired pneumonia (HAP) were the main indications for treatment (19% and 18% of the total cases, respectively), followed by skin and soft tissue infections and sepsis. IV fosfomycin was administered in combination with other antibacterial agents, the most common of which were ceftazidime/avibactam (35%), meropenem (17%), and colistin (14%). Nineteen patients received it as monotherapy for UTIs. About 66% had resolution of the infectious process with clinical remission (cure or discharge). Electrolyte disturbances occurred in 2.6% and gastrointestinal symptoms occurred in 2.9%. The data showed that IV fosfomycin is a safe and effective therapeutic option in the treatment of infections with multidrug-resistant microorganisms.

Fosfomycin Disk Diffusion Testing among Klebsiella pneumoniae Results in Frequent Inner Colonies and Categorical Disagreement Based on Conflicting Breakpoint Organization Recommendations

Recent studies indicate that discrete inner colonies (ICs) arise during fosfomycin disk diffusion (DD) testing. CLSI and EUCAST have contradicting recommendations on the interpretation of ICs; CLSI recommends considering them while EUCAST recommends ignoring them when interpreting DD results. We sought to compare the categorical agreement of DD and agar dilution (AD) MIC and to assess the implications of ICs interpretation on zone diameter readings. A convenience sample of 80 Klebsiella pneumoniae clinical isolates with varied phenotypic profiles collected from 3 United States locations was included. Susceptibility was determined in duplicate, using both organization recommendations and interpretations for Enterobacterales. Correlations between methods were calculated using EUCASTIV AD as the reference method. MIC values ranged from 1 to >256 μg/mL with an MIC50/90 of 32/256 μg/mL. Extrapolating EUCASToral and CLSI AD Escherichia coli breakpoints, 12.5% and 83.8% of isolates were susceptible, respectively, whereas 66.3% were susceptible by EUCASTIV AD-which applies to K. pneumoniae. CLSI DD measurements were 2 to 13 mm smaller than EUCAST measurements due to 66 (82.5%) isolates producing discrete ICs. Categorical agreement with EUCASTIV AD was greatest for CLSI AD (65.0%) and poorest for EUCASToral DD (6.3%). Isolates among this collection were frequently classified into different interpretive categories based on varying breakpoint organization recommendations. The more conservative oral breakpoints of EUCAST resulted in more isolates categorized as resistant despite frequent ICs. Differing zone diameter distributions and poor categorical agreement highlight issues of extrapolating E. coli breakpoints and methods to other Enterobacterales, and the clinical relevance of this issue warrants further investigation. IMPORTANCE Fosfomycin susceptibility testing recommendations are complex. Both the Clinical and Laboratory Standards Institute and the European Committee on Antimicrobial Susceptibility Testing (EUCAST) recognize agar dilution as the reference method, but they also support disk diffusion as an approved method for Escherichia coli. However, these two organizations have conflicting recommendations for the interpretation of inner colonies that arise during disk diffusion testing which can lead to varying zone diameters and interpretations despite isolates having identical MIC values. Using a collection of 80 Klebsiella pneumoniae isolates, we found that a large (82.5%) portion produced discrete inner colonies during disk diffusion and isolates were frequently classified into different interpretive categories. The more conservative breakpoints of EUCAST resulted in more isolates categorized as resistant despite frequent inner colonies. Differing zone diameter distributions and poor categorical agreement highlight issues of extrapolating E. coli breakpoints and methods to other Enterobacterales, and the clinical relevance of this issue warrants further investigation.

Comparison of in vitro fosfomycin susceptibility testing methods with agar dilution for carbapenem resistant Klebsiella pneumoniae and Escherichia coli

PURPOSE

The emergence of Extensively drug resistant (XDR) pathogens like Carbapenem Resistant Klebsiella pneumoniae (CR Kpn) and Carbapenem Resistant Escherichia coli (CR Eco) has limited therapeutic options for treating them. Fosfomycin a broad-spectrum antibiotic, has emerged as a potential treatment option in combination with other agents. It is therefore important that accurate drug susceptibility testing (DST) results of fosfomycin should be available to all clinical microbiology laboratories. Agar dilution which is the recommended method for fosfomycin DST is not convenient to adopt in a routine set-up. This study aimed to determine the susceptibility pattern of CR Kpn and CR Eco to fosfomycin and to evaluate the discrepancies of the available manual MIC based alternative methods.

METHODS

Agar dilution (AD), broth microdilution (BMD), E-test and Ezy MIC test were performed on 235 CR-Kpn and Eco isolates respectively.

RESULTS

Of 177 CR Kpn, 31.63% (n ​= ​56/177) of the isolates were susceptible by AD. Categorical Agreement (CA) by BMD, E-test and Ezy MIC were lower than the acceptable limit while Very Major Errors (VMEs) and Major Errors (MEs) were beyond the acceptable limits. In the case of CR Eco, 96.55% (n ​= ​56/58) were susceptible by AD. CA of 100% (n ​= ​58/58) was shown by both BMD and Ezy MIC while 86.20% (n ​= ​50/58) was shown by E-test, with no VME observed for CR Eco. ME was only observed for E-test method.

CONCLUSION

The alternative methods were in poor agreement with AD method for CR Kpn and for CR Eco, BMD and Ezy MIC have shown reliable results.

Prevalence of Fosfomycin Resistance Among Enterobacterales Isolates in A Tertiary Care Hospital from Turkey

Objective

Urinary tract infections are one of the most common causes of morbidity around the world. Fosfomycin is a specific broad-spectrum antibiotic used to treat these infections. However, in recent years, many studies have reported increased fosfomycin resistance in Enterobacterales isolates. Therefore, this study aimed to evaluate the distribution of pathogens isolated from urine samples and find the fosfomycin resistance rates over nine years (2012-2020).

Materials and Methods

A total of 18,884 uropathogenic Enterobacterales isolates were included in the study between 2012 and 2020. The isolates were identified by VITEK® 2 Compact (bioMérieux, Marcy l'Etoile, France), and the antimicrobial susceptibilities of the isolates were also evaluated using the VITEK® MS automated system (bioMérieux, Marcy l'Etoile, France).

Results

Escherichia coli (64.04%) was the most common bacteria among Enterobacterales. Fosfomycin resistance rates were 1.98%, 21.64%, and 10.36% in E. coli, Klebsiella pneumoniae, and all bacteria, respectively. The 34.97% of isolates were extended-spectrum β-lactamase (ESBL)-producing Enterobacterales, and the fosfomycin resistance rate was 13.08% in these isolates. In addition, fosfomycin resistance rates were found as 3.06% and 23.84% in ESBL-producing E. coli and ESBL-producing K. pneumoniae, respectively.

Conclusion

Fosfomycin seems a good option for effectively treating UTIs caused by E. coli. On the other hand, we found that fosfomycin resistance tends to increase over the years. Therefore, we recommend further studies to evaluate fosfomycin resistance.

Assessment of the Susceptibility of Clinical Gram-Negative and Gram-Positive Bacterial Strains to Fosfomycin and Significance of This Antibiotic in Infection Treatment

Multidrug resistance of bacteria has prompted intensive development work on new medicines, but also the search for effective options among the oldest antibiotics. Although intravenous fosfomycin (IVFOS) seems to be an interesting proposal, the recommended agar dilution method for susceptibility determination poses a major problem in routine diagnostic testing. As a consequence, there is a lack of comprehensive data on the frequency of isolation of susceptible or resistant strains. This fact triggered the disposition of EUCAST concerning the revision of IVFOS breakpoints (BPs), including withdrawal of BPs for Enterobacterales (excluding E. coli) and coagulase-negative staphylococci. Therefore, the aim of this study was to assess the activity of fosfomycin against numerous clinical strains using recommended methods. Materials and methods: A total of 997 bacterial strains were tested from the following genera: Enterobacterales, Pseudomonas spp., Staphylococcus spp., Acinetobacter spp., and Enterococcus spp., for which there are currently no BPs. The strains were isolated from various clinical materials from patients hospitalized in five hospitals. During the investigation, the recommended agar dilution method was used. Susceptibility to other antibiotics and resistance mechanisms were determined using an automatic method (Phoenix) the disk diffusion method, and E-tests. MIC values of fosfomycin were estimated for all strains and for susceptible and multidrug-resistant (MDR) strains individually. Results: Except for Acinetobacter and Enterococcus, 83% of the strains were susceptible to IVFOS, including the largest percentage of S. aureus and E. coli. Klebsiella spp. turned out to be the least susceptible strains (66%). The highest proportion of susceptibility to fosfomycin was found among strains that were sensitive to other antibiotics (80.9%), and the lowest was found among Gram-negative carbapenemase-producing bacteria (55.6%) and ESBL+ bacteria (61.6%). The MIC evaluation revealed the lowest MIC₅₀ and MIC₉₀ values for S. aureus (0.5 mg/L and 1 mg/L, respectively) and E. coli (4 mg/L and 32 mg/L, respectively). The highest values of MIC₅₀ were found for Acinetobacter spp. (256 mg/L), while the highest values of MIC₉₀ were found for Acinetobacter spp. and Klebsiella spp. (256 mg/L and 512 mg/L, respectively). Conclusions: IVFOS appears to be suitable for the treatment of many infections, including the empirical treatment of polymicrobial infections and those caused by MDR strains, since the sensitivity of the studied strains to this antibiotic in different groups ranged from 66% to as much as 99%. Sensitivity to fosfomycin was also demonstrated by 60% of carbapenem-resistant strains; therefore, IVFOS is one of the few therapeutic options that can be effective against the most resistant Gram-negative rods. In light of the general consultation posted by EUCAST, obtaining data such as IVFOS MIC value distributions may be vital for the decision of implementing fosfomycin into breakpoint tables.

Characteristics of bloodstream infection and initial antibiotic use in critically ill burn patients and their impact on patient prognosis

To investigate the bacterial epidemiology of blood cultures taken during the treatment of critically ill burn patients, the use of antibiotics at admission and before the observation of positive blood cultures, and their effect on prognosis. A retrospective study method was used. From January 1, 2010, to December 31, 2019, burn patients who met the inclusion criteria and were treated at the Burn Department, Ruijin Hospital, Shanghai Jiaotong University School of Medicine, were enrolled in the study. Data were collected from the patients' electronic medical records. General patient information, including length of hospital stay, length of intensive care unit (ICU) stay, in-hospital mortality, the bacteria epidemiological characteristics of blood cultures, and the use of antibiotics within 24 h after admission and before a positive blood culture was observed, was collected. Independent sample t tests and χ² tests were used to compare the effects of a positive blood culture and the use of appropriate antibiotics within 24 h after admission and before the observation of a positive blood culture on prognosis. (1) The three most frequently detected bacteria in the blood cultures were Klebsiella pneumoniae, Pseudomonas aeruginosa, and Acinetobacter baumannii, and the amount of K. pneumoniae detected increased gradually. (2) Compared with the group of patients who were negative for bloodstream infection , the positive bloodstream infection group had a larger total body burn surface area (TBSA) (t = - 5.097, P = 0.000) and third-degree burn area (t = - 5.133, P = 0.000), a significantly longer length of hospital stay (t = 3.003, P = 0.003) and the length of ICU stay (t = 4.258, P = 0.000), and a significantly higher rate of in-hospital mortality (χ² = 8.485, P = 0.004). When K. pneumoniae was detected, the length of hospital stay (t = 2.148, P = 0.035) and the length of ICU stay (t = 2.880, P = 0.005) were significantly prolonged. (3) The two antibiotics that were most frequently used in patients with acute burns within 24 h after admission were lincomycin (90 cases, 29.32%) and carbapenems (79 cases, 25.73%). Comparing the clinical characteristics of the lincomycin group and the carbapenem group, the TBSA (t = - 3.34, P = 0.001) and the third-degree burn area (t = - 6.08, P = 0.000) of the patients in the carbapenem group were larger, and the length of hospital stay (t = - 2.136, P = 0.035) and length of ICU stay (t = - 5.18, P = 0.000) were longer, but the difference in in-hospital mortality was not statistically significant (χ² = 1.983, P = 0.159). (4) Comparing the group with appropriate initial antibiotic use within 24 h of admission to the inappropriate use group, the TBSA (t = - 0.605, P = 0.547), the third-degree burn area (t = 0.348, P = 0.729), the length of hospital stay (t = - 0.767, P = 0.445), the length of ICU stay (t = - 0.220, P = 0.827) and in-hospital mortality (χ² = 1.271, P = 0.260) were not significantly different. (5) Comparing the group with appropriate antibiotic use before a positive blood culture was observed to the group with inappropriate antibiotic use, the TBSA (t = - 0.418, P = 0.677), the third-degree burn area (t = 0.266, P = 0.791), the length of hospital stay, the length of ICU stay (t = 0.995, P = 0.322) and in-hospital mortality (χ² = 1.274, P = 0.259) were not significantly different. We found that patients with a positive blood culture had a larger burn area and a worse prognosis; that the greater the amount of K. pneumoniae in the bloodstream of burn patients was, the longer the hospital and ICU stays were; that whether appropriate antibiotics were administered to acute critical burn patients 24 h after admission had no effect on the prognosis; and that whether appropriate antibiotics were administered before a positive blood culture was observed had no effect on prognosis.

A Literature Overview of Secondary Peritonitis Due to Carbapenem-Resistant Enterobacterales (CRE) in Intensive Care Unit (ICU) Patients

This comprehensive review of the recently published literature offers an overview of a very topical and complex healthcare problem: secondary peritonitis from multidrug-resistant pathogens, especially carbapenem-resistant Enterobacterales (CRE). Spontaneous secondary peritonitis and postsurgical secondary peritonitis are among the major causes of community- and healthcare- acquired sepsis, respectively. A large number of patients enter ICUs with a diagnosis of secondary peritonitis, and a high number of them reveal infection by CRE, P. aeruginosa or A. baumannii. For this reason, we conceived the idea to create a synthetic report on this topic including updated epidemiology data, a description of CRE resistance patterns, current strategies of antimicrobial treatment, and future perspectives. From this update it is clear that antimicrobial stewardship and precision medicine are becoming essential to fight the emergence of antimicrobial resistance and that even if there are new drugs effective against CRE causing secondary peritonitis, these drugs have to be used carefully especially in empirical therapy.

Treatment of Severe Infections Due to Metallo-Betalactamases Enterobacterales in Critically Ill Patients

Metallo-beta-lactamases-producing (MBL) Enterobacterales is a growing problem worldwide. The optimization of antibiotic therapy is challenging. The pivotal available therapeutic options are either the combination of ceftazidime/avibactam and aztreonam or cefiderocol. Colistin, fosfomycin, tetracyclines and aminoglycosides are also frequently effective in vitro, but are associated with less bactericidal activity or more toxicity. Prior to the availability of antibiotic susceptibility testing, severe infections should be treated with a combination therapy. A careful optimization of the pharmacokinetic/pharmacodynamic properties of antimicrobials is instrumental in severe infections. The rules of antibiotic therapy are also reported and discussed. To conclude, treatment of severe MBL infections in critically ill patients is difficult. It should be individualized with a close collaboration of intensivists with microbiologists, pharmacists and infection control practitioners.

Clonal Dissemination of Clinical Carbapenem-Resistant Klebsiella pneumoniae Isolates Carrying fosA3 and bla KPC-2 Coharboring Plasmids in Shandong, China

Treatment strategies of infection by carbapenem-resistant Klebsiella pneumoniae (CRKP) are limited. Fosfomycin, a broad-spectrum antibiotic, has attracted renewed interest in combination therapy to fight K. pneumoniae infections. However, reports on fosfomycin-resistant K. pneumoniae are increasing. Among the 57 CRKP strains, 40 (70.2%) were resistant to fosfomycin. Thus, whole-genome sequencing and bioinformatics analysis were conducted to reveal molecular characteristics of fosfomycin-resistant K. pneumoniae. Twenty-three isolates coharbored fosA^kp and fosA3, with K. pneumoniae carbapenemase (KPC)-producing ST11-KL64-wzi64-O2 (n = 13) and ST11-KL47-wzi209-OL101 (n = 8), the predominating clonal groups, while fosA3 was not detected in isolates carrying class B carbapenemase genes. Twenty-two (out of 26) ST11-KL64 strains were positive for rmpA2, of which 12 carried fosA3. Four of the 23 fosA3-positive isolates could successfully transfer their fosfomycin-resistant determinants to Escherichia coli J53Azi^R. All four strains belonged to ST11-KL47 with the same pulsed-field gel electrophoresis profile, and their transconjugants acquired fosfomycin, carbapenem, and aminoglycoside resistance. A 127-kb conjugative pCT-KPC-like hybrid plasmid (pJNKPN52_KPC_fosA) coharboring fosA3, bla_KPC–2, bla_CTX–M–65, bla_SHV–12, rmtB, and bla_TEM–1 was identified. ST11-KL64 and ST11-KL47 K. pneumoniae, with higher resistance and virulence, should be critically monitored to prevent the future dissemination of resistance.

Quantification of Fosfomycin in Combination with Nine Antibiotics in Human Plasma and Cation-Adjusted Mueller-Hinton II Broth via LCMS

Fosfomycin-based combination therapy has emerged as an attractive option in our armamentarium due to its synergistic activity against carbapenem-resistant Gram-negative bacteria (CRGNB). The ability to simultaneously measure fosfomycin and other antibiotic drug levels will support in vitro and clinical investigations to develop rational antibiotic combination dosing regimens against CRGNB infections. We developed an analytical assay to measure fosfomycin with nine important antibiotics in human plasma and cation-adjusted Mueller–Hinton II broth (CAMHB). We employed a liquid-chromatography tandem mass spectrometry method and validated the method based on accuracy, precision, matrix effect, limit-of-detection, limit-of-quantification, specificity, carryover, and short-term and long-term stability on U.S. Food & Drug Administration (FDA) guidelines. Assay feasibility was assessed in a pilot clinical study in four patients on antibiotic combination therapy. Simultaneous quantification of fosfomycin, levofloxacin, meropenem, doripenem, aztreonam, piperacillin/tazobactam, ceftolozane/tazobactam, ceftazidime/avibactam, cefepime, and tigecycline in plasma and CAMHB were achieved within 4.5 min. Precision, accuracy, specificity, and carryover were within FDA guidelines. Fosfomycin combined with any of the nine antibiotics were stable in plasma and CAMHB up to 4 weeks at −80 °C. The assay identified and quantified the respective antibiotics administered in the four subjects. Our assay can be a valuable tool for in vitro and clinical applications.

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.

Genomic Analysis of Global Staphylococcus argenteus Strains Reveals Distinct Lineages With Differing Virulence and Antibiotic Resistance Gene Content

Infections due to Staphylococcus argenteus have been increasingly reported worldwide and the microbe cannot be distinguished from Staphylococcus aureus by standard methods. Its complement of virulence determinants and antibiotic resistance genes remain unclear, and how far these are distinct from those produced by S. aureus remains undetermined. In order to address these uncertainties, we have collected 132 publicly available sequences from fourteen different countries, including the United Kingdom, between 2005 and 2018 to study the global genetic structure of the population. We have compared the genomes for antibiotic resistance genes, virulence determinants and mobile genetic elements such as phages, pathogenicity islands and presence of plasmid groups between different clades. 20% (n = 26) isolates were methicillin resistant harboring a mecA gene and 88% were penicillin resistant, harboring the blaZ gene. ST2250 was identified as the most frequent strain, but ST1223, which was the second largest group, contained a marginally larger number of virulence genes compared to the other STs. Novel S. argenteus pathogenicity islands were identified in our isolates harboring tsst-1, seb, sec3, ear, selk, selq toxin genes, as well as chromosomal clusters of enterotoxin and superantigen-like genes. Strain-specific type I modification systems were widespread which would limit interstrain transfer of genetic material. In addition, ST2250 possessed a CRISPR/Cas system, lacking in most other STs. S. argenteus possesses important genetic differences from S. aureus, as well as between different STs, with the potential to produce distinct clinical manifestations.

Emerging Carbapenem-Resistant Enterobacteriaceae Infection, Its Epidemiology and Novel Treatment Options: A Review

Infections due to multidrug-resistant Enterobacteriaceae have become major international public health problem due to the inadequate treatment options and the historically lagged pace of development of novel antimicrobial drugs. Inappropriate antimicrobial use in humans and animals coupled with increased global connectivity aided to the transmission of drug-resistant Enterobacteriaceae infections. Carbapenems are the medications of choice for extended-spectrum beta-lactamase and AmpC producers, but alternatives are currently needed because carbapenem resistance is increasing globally. This review pointed to discuss emerging drug-resistant Enterobacteriaceae, its epidemiology and novel treatment options for infections, which date back from 2010 to 2019 by searching Google Scholar, PubMed, PMC, Hinari and other different websites. The occurrence of carbapenem-resistant Enterobacteriaceae is reported worldwide with great regional variability. The rise of carbapenem-resistant Enterobacteriaceae poses a threat to all nations. Enzyme synthesis, efflux pumps, and porin mutations are the main methods by which Enterobacteriaceae acquire resistance to carbapenems. The major resistance mechanism among these is enzyme synthesis. Most carbapenem resistance is caused by three enzyme groups: Klebsiella pneumoniae carbapenemase (Ambler class A), metallo-ß-lactamases (Ambler class B), and oxacillinase-48 (Ambler class D). Ceftazidime–avibactam, which was newly licensed for carbapenemase producers, is the most common treatment option for infections. Meropenem–vaborbactam, imipenem–relebactam, plazomicin, cefiderocol, eravacycline, and aztreonam–avibactam are recently reported to be active against carbapenem-resistant Enterobacteriaceae; and are also in ongoing trials for different populations and combinations with other antibacterial agents. Overall, treatment must be tailored to the patient’s susceptibility profile, type and degree of infection, and personal characteristics.

Fosfomycin susceptibility of uropathogens at Charlotte Maxeke Johannesburg Academic Hospital

Background

Multidrug-resistant uropathogens are becoming widespread both in community and hospital setting. Safe yet effective treatments are a priority. Fosfomycin is an antibacterial that displays good activity against most bacteria causing urinary tract infections (UTIs), including multidrug-resistant bacteria. The aim of this study was to evaluate fosfomycin susceptibility for uropathogens isolated from a microbiology laboratory at a tertiary academic hospital. In addition, this was compared to the susceptibility of other oral antimicrobials.

Methods

We conducted a retrospective analysis of laboratory reports for uropathogens isolated at Charlotte Maxeke Johannesburg Academic Hospital from September 2015 to August 2017. Antimicrobial susceptibility testing of the isolates was performed using the Kirby–Bauer disk diffusion method or the Vitek^® 2 system according to the Clinical and Laboratory Standards Institute.

Results

Overall susceptibility of fosfomycin for the 4700 Enterobacteriaceae isolates was 95.7%; 95% confidence interval (CI) 95.1–96.2. The overall susceptibility for fosfomycin against the gram-positives was 98.6%. There were 37.9% multidrug-resistant Enterobacteriaceae (MDRE) isolated during the study period. Fosfomycin displayed activity against 94.4% of extended-spectrum β-lactamase (ESBL) producers and 90.7% for carbapenem-resistant Enterobacteriaceae (CRE). None of the methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus isolates tested was fosfomycin resistant. The overall in vitro susceptibility was significantly higher for fosfomycin (p = 0.0001) compared to amoxicillin/clavulanic acid, cephalexin, cefuroxime, ciprofloxacin, trimethoprim/sulfamethoxazole and nitrofurantoin.

Conclusion

This study confirmed the high susceptibility of fosfomycin against UTI pathogens isolated at our institution. In an era of increasing antimicrobial resistance, fosfomycin represents a potential option for the treatment of UTIs at Charlotte Maxeke Johannesburg Academic Hospital.

Pharmacokinetic/pharmacodynamic analysis of oral fosfomycin against Enterobacterales, Pseudomonas aeruginosa and Enterococcus spp. in an in vitro bladder infection model: impact on clinical breakpoints

OBJECTIVES

Fosfomycin is an established treatment for uncomplicated urinary tract infections (UTIs), yet evidence supporting susceptibility breakpoints is limited. We examine the UTI susceptibility criteria.

METHODS

Fosfomycin susceptibility, heteroresistance and in vitro growth in a bladder infection model, after a single 3 g dose of oral fosfomycin, were bridged to human pharmacokinetics with pharmacokinetic/pharmacodynamic and Monte Carlo analyses. Data from common uropathogens (24 Escherichia coli, 20 Klebsiella pneumoniae, 4 Enterobacter cloacae, 14 Pseudomonas aeruginosa, 8 Enterococcus faecalis and 8 Enterococcus faecium) were compared and analysed to ascertain species-specific PTA.

RESULTS

Glucose-6-phosphate (G6P) increased MICs of E. coli, K. pneumoniae and E. cloacae (median 2-fold dilutions 3-5), but not of P. aeruginosa and Enterococcus. Atypical E. coli lacking G6P potentiation were killed in the bladder infection model despite high MICs (32-128 mg/L). Fosfomycin heteroresistance was uncommon in E. coli (MIC > 2 mg/L) but was detected in the majority of K. pneumoniae (MIC > 1 mg/L) and P. aeruginosa (MIC >8 mg/L). For these species, baseline heteroresistance was a strong predictor for treatment failure in the model. No heteroresistance was found in Enterococcus. The fAUC/MIC targets for stasis were 1935, 3393, 9968, 2738 and 283 for typical E. coli, K. pneumoniae, E. cloacae, P. aeruginosa and E. faecalis, respectively (synthetic human urine medium alone promoted a 1 log10 kill in E. faecium). A >95% PTA for stasis was only found at MIC ≤ epidemiological cut-off (ECOFF) for E. coli (4 mg/L). For other species, PTAs were low for WT populations.

CONCLUSIONS

With the exception of E. coli, fosfomycin is a poor target for other uropathogen species. A reduction in oral fosfomycin UTI breakpoints is supported.

Characteristics of fosA-carrying plasmids in E. coli and Klebsiella spp. isolates originating from food and environmental samples

OBJECTIVES

Fosfomycin is an important antibiotic for the treatment of MDR Enterobacteriaceae infections. High susceptibility rates are, however, threatened by the spread of plasmids encoding fosfomycin-modifying enzymes. In this study, we sought to characterize the genetic context of fosA in plasmids from Escherichia coli and Klebsiella spp. isolates recovered from food, wastewater and surface water in Switzerland.

METHODS

E. coli and Klebsiella spp. isolates collected between 2012 and 2019 in Switzerland were screened for fosfomycin resistance. Presence of fosA was verified by PCR and sodium phosphonoformate (PPF) disc potentiation testing, and transferability was tested using conjugation assays. Whole-genome sequences including complete fosA-containing plasmids were determined using long- and short-read sequencing.

RESULTS

In 11 E. coli and two Klebsiella spp. isolates, high-level fosfomycin resistance was mediated by plasmids containing fosA3 (n = 12) or fosA8 (n = 1). Four isolates harboured a near-identical 45 kb IncN plasmid with fosA3, while replicon types varied in the remaining plasmids. The fosA genes were typically embedded in IS26-bounded transposition units and frequently located in the proximity of blaCTX-M transposition units.

CONCLUSIONS

Although fosfomycin resistance rates are currently low, the presence of fosA-encoding plasmids circulating in the Enterobacteriaceae population suggests that fosfomycin resistance may rapidly spread upon increased selection pressure. Transposition mobility of fosA and co-location on plasmids with other resistance genes may further promote its dissemination.

Oral fosfomycin for treating lower urinary tract infections due to multidrug-resistant Escherichia coli in female adolescents

Fosfomycin trometamol (FT) has shown promising in vitro activity against multidrug-resistant (MDR) uropathogens; however, clinical data are limited in pediatric patients. We conducted a retrospective study to describe the clinical and microbiological outcomes of uncomplicated lower urinary tract infections (LUTIs) due to MDR Escherichia coli treated with oral FT in female adolescents. A total of 70 outpatients, with a median age of 13 years (range 12-16 years), were included. FT was initiated as definitive treatment of UTIs in all patients due to documented resistance against alternative oral agents. All patients received a single dose of 3 g oral FT. The post-treatment clinical and microbiological cure rates were 97% (68/70) and 94% (66/70), respectively. Only two (3%) patients reported mild, self-limited diarrhea. UTI relapse occurred in two (3%) patients. Our results suggest that oral FT might be an alternative option for outpatient treatment of uncomplicated LUTIs due to MDR E. coli in female adolescents.

The role of combination therapy in the treatment of severe infections caused by carbapenem resistant gram-negatives: a systematic review of clinical studies

BACKGROUND

Effective treatment of sepsis due to carbapenem-resistant Gram-negative bacteria (CR-GNB) remains a challenge for clinicians worldwide. In recent years, the combination of antibiotics has become the preferred treatment strategy for CR-GNB infection. However, robust evidence to support this approach is lacking. This systematic review aimed at critically evaluating all available antibiotic options for CR-GNB sepsis with particular focus on combination.

METHODS

We systematically searched published literature from January 1945 until December 2018 for observational comparative and non-comparative studies and randomized trials examining any antibiotic option for CR-GNB. Studies were included if reporting microbiologically-confirmed infection caused by Acinetobacter baumannii, Enterobacteriaceae/Klebsiella spp., or Pseudomonas aeruginosa, reporting at least one of the study outcomes, and definitive antibiotic treatment. Carbapenem-resistance was defined as phenotypically-detected in vitro resistance to at least one of the following carbapenems: doripenem, ertapenem, imipenem, meropenem. Each antibiotic regimen was classified as "defined" when at least the molecular class(es) composing the regimen was detailed. Primary outcomes were 30-day and attributable mortality. Bayesian network meta-analysis (NMA) approach was selected for quantitative synthesis to explore feasibility of pooling data on antibiotic regimens.

RESULTS

A total of 6306 records were retrieved and 134 studies including 11,546 patients were included: 54 studies were on Acinetobacter, 52 on Enterobacteriaceae/Klebsiella, 21 on mixed Gram-negative, and 7 on Pseudomonas. Nine (7%) were RCTs; 19 prospective cohorts (14%), 89 (66%) retrospective, and 17 (13%) case series. Forty-one studies (31%) were multicentric. Qualitative synthesis showed an heterogeneous and scattered reporting of key-clinical and microbiological variables across studies. Ninety-two distinct antibiotic regimens were identified with 47 of them (51%, 5863 patients) not reporting any details on numbers, type, dosage and in vitro activity of the included antibiotic molecules. The NMAs could not be performed for any of the selected outcome given the presence of too many disconnected components.

CONCLUSION

The existing evidence is insufficient to allowing for the formulation of any evidence-based therapeutic recommendation for CR-GNB sepsis. Future studies must provide a standardized definition of antibiotic regimen to drive recommendations for using combination of antibiotics that can be reliably applied to clinical practice.

Emerging Treatment Options for Multi-Drug-Resistant Bacterial Infections

Antimicrobial resistance (AMR) remains one of the top public health issues of global concern. Among the most important strategies for AMR control there is the correct and appropriate use of antibiotics, including those available for the treatment of AMR pathogens. In this article, after briefly reviewing the most important and clinically relevant multi-drug-resistant bacteria and their main resistance mechanisms, we describe the emerging antimicrobial options for both MDR Gram-positive cocci and Gram-negative bacilli, including recently marketed agents, molecules just approved or under evaluation and rediscovered older antibiotics that have regained importance due to their antimicrobial spectrum. Specifically, emerging options for Gram-positive cocci we reviewed include ceftaroline, ceftobiprole, tedizolid, dalbavancin, and fosfomycin. Emerging treatment options for Gram-negative bacilli we considered comprise ceftolozane-tazobactam, ceftazidime-avibactam, meropenem-vaborbactam, imipenem-relebactam, aztreonam-avibactam, minocycline, fosfomycin, eravacycline, plazomicin, and cefiderocol. An exciting scenario is opening today with the long awaited growing availability of novel molecules for the treatment of AMR bacteria. Knowledge of mechanisms of action and resistance patterns allows physicians to increasingly drive antimicrobial treatment towards a precision medicine approach. Strict adherence to antimicrobial stewardship practices will allow us to preserve the emerging antimicrobials for our future.

Characterization of fosfomycin resistance and molecular epidemiology among carbapenem-resistant Klebsiella pneumoniae strains from two tertiary hospitals in China

Background

Fosfomycin has been proven to be a vital choice to treat infection caused by multidrug resistance bacteria, especially carbapenem-resistant Klebsiella pneumoniae (CRKP). However, fosfomycin resistant cases has been reported gradually. In this study, we reported the fosfomycin-resistant rate in CRKP strains and further revealed the molecular mechanisms in resistance gene dissemination.

Results

A total of 294 non-duplicated CRKP strains were collected. And 55 fosfomyin-resistant strains were detected, 94.5% of which were clustered to sequence type (ST) 11 by PCR followed up sequencing. PFGE further revealed two major groups and four singletons. The positive rates of genes responsible to fosfomycin and carbapenem resistance were 81.8% (fosA3), 12.7% (fosA5) and 94.5% (bla_KPC-2), respectively. Genomic analysis confirmed insertion sequence (IS) 26 was the predominant structure surrounding fosA3. The fosA3 genes in six isolates were located on plasmids which were able to transfer to E. coli J53 recipient cells by means of conjugation.

Conclusions

Although the resistant rate of CRKP to fosfomycin is relatively low in our area, considering its gene is located on transferrable plasmid and inserted in IS structure, continuous monitoring is still needed.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-021-02165-7.

Present and Future Perspectives on Therapeutic Options for Carbapenemase-Producing Enterobacterales Infections

Carbapenem-resistant Enterobacterales (CRE) are included in the list of the most threatening antibiotic resistance microorganisms, being responsible for often insurmountable therapeutic issues, especially in hospitalized patients and immunocompromised individuals and patients in intensive care units. The enzymatic resistance to carbapenems is encoded by different β-lactamases belonging to A, B or D Ambler class. Besides compromising the activity of last-resort antibiotics, CRE have spread from the clinical to the environmental sectors, in all geographic regions. The purpose of this review is to present present and future perspectives on CRE-associated infections treatment.

fosM, a New Family of Fosfomycin Resistance Genes Identified in Bacterial Species Isolated from Human Microbiota

Fosfomycin is a decades-old antibiotic, currently reused because of its activity against multidrug-resistant bacteria. Here, we used a combined in vitro/in silico approach to search for fosfomycin resistance determinants in 25 new bacterial species isolated from the human microbiota. Putative resistance genes were cloned into a susceptible Escherichia coli strain. MIC values increased from 1 μg/ml to 1,024 μg/ml. Here, we report a new family of potential chromosomal fosfomycin resistance genes, named fosM.

Therapeutic Options for Metallo-β-Lactamase-Producing Enterobacterales

The spread of metallo-β-lactamase (MBL)-producing Enterobacterales worldwide without the simultaneous increase in active antibiotics makes these organisms an urgent public health threat. This review summarizes recent advancements in diagnostic and treatment strategies for infections caused by MBL-producing Enterobacterales. Adequate treatment of patients infected with MBL-producing Enterobacterales relies on detection of the β-lactamase in the clinic. There are several molecular platforms that are currently available to identify clinically relevant MBLs as well as other important serine-β-lactamases. Once detected, there are several antibiotics that have historically been used for the treatment of MBL-producing Enterobacterales. Antimicrobials such as aminoglycosides, tetracyclines, fosfomycin, and polymyxins often show promising in vitro activity though clinical data are currently lacking to support their widespread use. Ceftazidime-avibactam combined with aztreonam is promising for treatment of infections caused by MBL-producing Enterobacterales and currently has the most clinical data of any available antibiotic to support its use. While cefiderocol has displayed promising activity against MBL-producing Enterobacterales in vitro and in preliminary clinical studies, further clinical studies will better shed light on its place in treatment. Lastly, there are several promising MBL inhibitors in the pipeline, which may further improve the treatment of MBL-producing Enterobacterales.

A peptide-based aggregation-induced emission bioprobe for selective detection and photodynamic killing of Gram-negative bacteria

A bioprobe with aggregation-induced emission characteristics is developed, which can visualize and photodynamically ablate Gram-negative bacteria in a selective manner.

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.

Prevalence and mechanisms of fosfomycin resistance among KPC-producing Klebsiella pneumoniae clinical isolates in China

The threat of antibiotic resistance has increased dramatically in recent years. Fosfomycin, an old antibiotic agent, has been re-introduced to fight infections caused by Klebsiella pneumoniae carbapenemase-producing K. pneumoniae (KPC-KP). However, the trend of fosfomycin resistance among KPC-KP strains is increasing. In this study, 80 KPC-KP clinical isolates were collected from three teaching hospitals during 2014-2017 in China and were subjected to whole-genome sequencing (WGS). The fosfomycin resistance phenotype and resistance mechanisms were investigated by antimicrobial susceptibility testing and carbon source growth test, respectively. Among all KPC-KP strains, 80.0% (64/80) were resistant to fosfomycin and 36.3% (29/80) were positive for the mobile fosfomycin resistance gene fosA3. Among the 63 strains that were unable to grow in M9 basic medium with glycerol-3-phosphate (G3P) as the sole carbon source (mediated by mutation of the target gene glpT), there was no significant difference regarding the MIC distribution of fosfomycin between fosA3-positive and fosA3-negative strains (P = 0.577). Among the 50 strains that were negative for fosA3 but positive for fosA, the fosfomycin MICs of strains unable to grow in M9 basic medium with G3P as the sole carbon source were significantly higher (P < 0.001) than in strains that were able to grow in M9 basic medium with G3P as the sole carbon source. Our findings indicate that fosfomycin resistance among KPC-KP in China is an emerging problem and the two major mechanisms of resistance identified were plasmid-mediated fosfomycin resistance gene fosA3 and mutation of the target gene glpT.

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.

Synergistic Effect of Propolis and Antibiotics on Uropathogenic Escherichia coli

Urinary tract infections (UTIs) are the most common bacterial infections around the world. Uropathogenic Escherichia coli (UPEC) is among the main pathogens isolated in UTIs. The rate of UPEC with high resistance towards antibiotics and multidrug-resistant bacteria have increased dramatically and conduct to the difficulty to treat UTIs. Due to the rarefaction of new antibiotics molecules, new alternative strategies must be evaluated. Since many years, propolis has demonstrated an interesting antibacterial activity against E. coli. Here, we evaluated its activity added to antibiotics on a panel of UPEC with different resistance mechanisms. Minimal inhibitory concentrations (MICs) and time-kill curves of fosfomycin, ceftriaxone, ertapenem and ofloxacin, with and without propolis, were determined. Significant diminution of the MICs was observed using ceftriaxone or ofloxacin + propolis. Propolis alone had a bacteriostatic activity with time-dependent effect against UPEC. The addition of this nutraceutical improved the effect of all the antibiotics evaluated (except fosfomycin) and showed a synergistic bactericidal effect (fractional inhibitory concentrations index ≤ 0.5 and a decrease ≥ 2 log CFU/mL for the combination of propolis plus antibiotics compared with the antibiotic alone). Propolis is able to restore in vitro antibiotic susceptibility when added to antibiotics against UPEC. This study showed that propolis could enhance the efficiency of antibiotics used in UTIs and could represent an alternative solution.

Characterization of Fosfomycin and Nitrofurantoin Resistance Mechanisms in Escherichia coli Isolated in Clinical Urine Samples

Fosfomycin and nitrofurantoin are antibiotics of choice to orally treat non-complicated urinary tract infections (UTIs) of community origin because they remain active against bacteria resistant to other antibiotics. However, epidemiologic surveillance studies have detected a reduced susceptibility to these drugs. The objective of this study was to determine possible mechanisms of resistance to these antibiotics in clinical isolates of fosfomycin- and/or nitrofurantoin-resistant UTI-producing Escherichia coli. We amplified and sequenced murA, glpT, uhpT, uhpA, ptsI, cyaA, nfsA, nfsB, and ribE genes, and screened plasmid-borne fosfomycin-resistance genes fosA3, fosA4, fosA5, fosA6, and fosC2 and nitrofurantoin-resistance genes oqxA and oqxB by polymerase chain reaction. Among 29 isolates studied, 22 were resistant to fosfomycin due to deletion of uhpT and/or uhpA genes, and 2 also possessed the fosA3 gene. Some modifications detected in sequences of NfsA (His11Tyr, Ser33Arg, Gln67Leu, Cys80Arg, Gly126Arg, Gly154Glu, Arg203Cys), NfsB (Gln44His, Phe84Ser, Arg107Cys, Gly192Ser, Arg207His), and RibE (Pro55His), and the production of truncated NfsA (Gln67 and Gln147) and NfsB (Glu54), were associated with nitrofurantoin resistance in 15/29 isolates; however, the presence of oqxAB plasmid genes was not detected in any isolate. Resistance to fosfomycin was associated with the absence of transporter UhpT expression and/or the presence of antibiotic-modifying enzymes encoded by fosA3 plasmid-mediated gene. Resistance to nitrofurantoin was associated with modifications of NfsA, NfsB, and RibE proteins. The emergence and spread of these resistance mechanisms, including transferable resistance, could compromise the future usefulness of fosfomycin and nitrofurantoin against UTIs. Furthermore, knowledge of the genetic mechanisms underlying resistance may lead to rapid DNA-based testing for resistance.

Fosfomycin, Applying Known Methods and Remedies to A New Era

The exponential increase in the numbers of isolates of Carbapenem-Resistant Enterobacteriaceae (CRE) creates the need for using novel therapeutic approaches to save the lives of patients. Fosfomycin has long been considered a rational option for the treatment of CRE to be used as part of a combined therapy scheme. However, the assessment of fosfomycin susceptibility in the laboratory presents a great challenge due to the discrepancies found between different methodologies. Thus, our goal was to evaluate fosfomycin susceptibility in a group of 150 Enterobacteriaceae bacterial isolates using agar dilution as the gold standard technique to compare the results with those obtained by disk diffusion. We found a fosfomycin susceptibility of 79.3% in general terms. By comparing both methodologies, we reported a categorical agreement of 96% without Very Major Errors (VMEs) or Major Errors (MEs) and 4% of minor Errors (mEs). Our results suggest that fosfomycin could provide a rational alternative treatment for those patients that are infected by a Multidrug-Resistant (MDR) microorganism that is currently untreatable and that the disk diffusion and classical agar dilution techniques are adequate to assess the resistance profile of CRE to fosfomycin.

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.

Oral fosfomycin for the treatment of chronic bacterial prostatitis

Background

Chronic bacterial prostatitis (CBP) is a difficult-to-treat infection as only a few antibiotics achieve therapeutic concentrations in the prostate. Data on the efficacy and safety of oral fosfomycin for the treatment of CBP are limited.

Objectives

To analyse the efficacy and safety of fosfomycin in CBP due to MDR pathogens.

Methods

In a prospective observational study, an oral regimen of 3 g of fosfomycin q24h for 1 week followed by 3 g q48h for a treatment duration of 6–12 weeks was administered. The outcome was clinical and microbiological cure rate at the end of treatment (EOT) and rate of relapse at 3 and 6 months.

Results

The study included 44 patients. The most common pathogen was Escherichia coli (66%), followed by Klebsiella spp. (14%) and Enterococcus faecalis (14%). Most strains were MDR (59%) and 23% had an ESBL phenotype; 33 of 44 strains were resistant to fluoroquinolones, but all were susceptible to fosfomycin (median MIC for Gram-negative pathogens 1.5 mg/L). In 25 patients, treatment was administered for 6 weeks, whereas in the remaining 19 patients it was prolonged to 12 weeks based on the presence of calcifications in the prostate. Cure rate was 82% at EOT and 80% and 73% at 3 and 6 months accordingly. Microbiological eradication was achieved in 86% and 77% at EOT and at 6 months, respectively. Failure was observed in 12 patients. The most common adverse event was diarrhoea (18%).

Conclusions

Oral fosfomycin, particularly in the era of MDR prevalence, represents an attractive, safe and effective alternative to fluoroquinolones for the treatment of CBP.

Fosfomycin for bacterial prostatitis: a review

There has been growing interest in fosfomycin for the treatment of bacterial prostatitis due to evidence suggesting that it achieves adequate prostatic concentrations for antimicrobial effect, has activity against resistant micro-organisms, and has a low-toxicity profile. This review evaluated the current clinical evidence for fosfomycin in acute and chronic bacterial prostatitis to elucidate the clinical implications of fosfomycin in an era of increasing antimicrobial resistance. PubMed, Scopus, EMBASE, Web of Science, Google Scholar and ClinicalTrials.gov were searched for studies published in the English language from January 1984 to November 2019. The inclusion criteria were met if the study reported the use of fosfomycin (more than one dose) to treat bacterial prostatitis. Ten observational studies were identified that met the inclusion criteria. The evidence for the use of fosfomycin in acute bacterial prostatitis is sparse. The majority of the available evidence is for chronic bacterial prostatitis caused by Escherichia coli. Despite the implementation of variable dosing regimens, extended courses of fosfomycin appear to be safe and effective in achieving clinical and microbiological cure. In these studies, the use of fosfomycin was restricted to cases of treatment failure, intolerance to first-line therapy, or multi-resistant organisms. However, given the development of resistant organisms and the undesirable adverse effects of many first-line therapeutic options, fosfomycin has the potential to be considered as an effective first-line alternative for acute and chronic bacterial prostatitis in the future. Further studies, including randomized controlled trials, would be helpful to firmly establish its optimal dosing regimen, efficacy and place in therapy.

The combined antimicrobial activity of citrus honey and fosfomycin on multidrug resistant Pseudomonas aeruginosa isolates

Infections with Pseudomonas aeruginosa (P. aeruginosa) have become a real fear in hospital-acquired infections, especially in critically ill and immunocompromised patients. Thus, advance of novel anti-infectives is currently pursued. The aim of the present study was to evaluate the antibacterial effect of each of citrus honey and fosfomycin in comparison to the combined effect of both of them on multidrug resistant (MDR) P. aeruginosa. 50 MDR P. aeruginosa isolates were tested for the antibacterial effect of citrus honey. Screening for potential synergistic activity of fosfomycin and honey combinations by E test. Molecular detection of the virulent exoenzyme U (exoU) genotype by conventional PCR was done. The present study found that 50 % (v/v) concentration of citrus honey was sufficient to inhibit the growth of most isolates (33/50, 66%). Minimal inhibitory concentration (MIC) for fosfomycin tested by E test was found to be >128 µg/mL in 50(100%) of MDR P. aeruginosa isolates but after repeating E test with Mueller-Hinton agar (MHA) containing sublethal concentration of citrus honey (29/50,58%) isolates were sensitive. Also, there was a significant correlation between the presence of exoU gene and positive synergy of citrus honey-fosfomycin combination. This study showed that citrus honey has antibacterial effect and synergy with fosfomycin antibiotic against MDR P. aeruginosa isolates. Also, exoU positive genotype is associated with MDR phenotype. In conclusion, our results revealed that the citrus honey-fosfomycin combination showed highly statistically significant effect on MDR P. aeruginosa fosfomycin susceptibility pattern. exoU positive P. aeruginosa isolates were detected mostly in burn unit and ICUs. Also, there was a statistically significant correlation between the presence of exoU gene and positive result of honey-fosfomycin combination E test.

Molecular Mechanisms and Epidemiology of Fosfomycin Resistance in Staphylococcus aureus Isolated From Patients at a Teaching Hospital in China

Staphylococcus aureus is a major cause of hospital- and community-acquired infections placing a significant burden on the healthcare system. With the widespread of multidrug-resistant bacteria and the lack of effective antibacterial drugs, fosfomycin has gradually attracted attention as an "old drug." Thus, investigating the resistance mechanisms and epidemiology of fosfomycin-resistant S. aureus is an urgent requirement. In order to investigate the mechanisms of resistance, 11 fosfomycin-resistant S. aureus isolates were analyzed by PCR and sequencing. The genes, including fosA, fosB, fosC, fosD, fosX, and tet38, as well as mutations in murA, glpT, and uhpT were identified. Quantitative real-time PCR (qRT-PCR) was conducted to evaluate the expression of the target enzyme gene murA and the efflux pump gene tet38 under the selection pressure of fosfomycin. Furthermore, multilocus sequence typing (MLST) identified a novel sequence type (ST 5708) of S. aureus strains. However, none of the resistant strains carried fosA, fosB, fosC, fosD, and fosX genes in the current study, and 12 distinct mutations were detected in the uhpT (3), glpT (4), and murA (5) genes. qRT-PCR revealed an elevated expression of the tet38 gene when exposed to increasing concentration of fosfomycin among 8 fosfomycin-resistant S. aureus strains and reference strain ATCC 29213. MLST analysis categorized the 11 strains into 9 STs. Thus, the mutations in the uhpT, glpT, and murA genes might be the primary mechanisms underlying fosfomycin resistance, and the overexpression of efflux pump gene tet38 may play a major role in the fosfomycin resistance in these isolates.

Potential of fosfomycin in treating multidrug-resistant infections in children

In an era of increasing antimicrobial resistance, there are limited treatment options available to treat multidrug-resistant organisms in paediatric patients. Fosfomycin is an antibiotic defined as 'critically important' by The World Health Organization due to its potential efficacy against multidrug-resistant bacteria and is increasingly cited in the international literature as a promising antimicrobial for combating sepsis in an era of increasing antimicrobial resistance. With broad-spectrum cover that includes both Gram-positive and Gram-negative organisms and both parenteral and oral formulations available, fosfomycin provides a promising treatment option for paediatric patients. This review summarises fosfomycin's spectrum of activity, published efficacy in paediatric patients, safety considerations and pharmacokinetic data, as well as identifying current clinical trials delineating pharmacokinetic parameters and safety parameters in neonatal sepsis which will provide further information regarding the use of fosfomycin in neonatal and paediatric infections. Limitations regarding the current standards for fosfomycin susceptibility definitions, variations in dosing regimens and the potential mechanisms for resistance are also discussed.

Fosfomycin-trometamol for Urinary Tract Infections in Kidney Transplant Recipients

BACKGROUND

The treatment of urinary tract infections (UTIs) in kidney transplant recipients (KTRs) with oral antibiotics is complicated by increasing resistance to trimethoprim-sulfamethoxazole, amoxicillin/clavulanic acid, and ciprofloxacin. Fosfomycin-trometamol (FT) could be an alternative, but evidence on clinical effectiveness is scarce. We evaluated the use, effectiveness and safety of FT for UTI in KTRs.

METHODS

Data were retrospectively collected in 2 Dutch transplant hospitals from adult KTRs that were treated with FT as initial treatment for lower UTI or asymptomatic bacteriuria (ASB) or as stepdown treatment for upper UTI after initial intravenous antibiotics. Exclusion criteria were in vitro resistance to FT or concomitant antibiotic treatment. Endpoints were clinical cure within 14 days and severe clinical failure, microbiological cure, relapse, recurrence, and acquired resistance within 90 days postend of treatment.

RESULTS

Fifty-three episodes in 40 KTRs were included (ASB, n = 15; lower UTI, n = 33; upper UTI, n = 5). Fosfomycin-trometamol was used for a median short duration in a heterogeneous gift interval. Fosfomycin-trometamol resulted in microbiological cure in 25%, 28%, and 100% of ASB, lower UTI and upper UTI with initial positive culture and follow-up culture performed, respectively. Clinical cure rates were 67% for lower UTI and 80% for upper UTI. Relapses or recurrences occurred in 31% and 24% of symptomatic UTI episodes, without severe clinical failure. Acquired resistance to fosfomycin was observed in 6 episodes.

CONCLUSIONS

Fosfomycin-trometamol has a reasonable effectiveness as last-resort oral treatment for lower UTI and stepdown treatment for upper UTI in KTRs. Randomized controlled trials with optimal dosage regimens are warranted. Use of FT is not recommended for ASB.

Optimizing therapy of bloodstream infection due to extended-spectrum β-lactamase-producing Enterobacteriaceae

PURPOSE OF REVIEW

Infections due to extended-spectrum β-lactamase-producing Enterobacteriaceae (ESBL-E) are increasing worldwide. Carbapenems are usually regarded as the antibiotics of choice for the treatment of serious ESBL infections. However, because of the alarming emergence or carbapenem resistance, interest in effective alternatives has emerged. The present review summarizes the findings published on the antibiotics currently available for treatment of patients with an ESBL-E bloodstream infection (BSI).

RECENT FINDINGS

Meropenem and imipenem are the drugs recommended for treatment of ESBL BSIs in critically ill patients, and in infections with high bacterial loads or elevated β-lactam minimum inhibitory concentrations. Ertapenem should be reserved for patients with less severe presentations, and should be used at high doses. In milder presentations or BSIs from low-risk sources, other carbapenem-sparing alternatives could be considered: cephamycins, fluoroquinolones, and particularly a β-lactam/β-lactam inhibitor combination (particularly piperacillin/tazobactam). Optimized dosing of piperacillin/tazobactam is recommended (high doses and extended infusion). There are few data on the use of the promising newly available drugs (e.g. ceftolozane/tazobactam, ceftazidime/avibactam, cefiderocol, and plazomicin), and it seems reasonable to reserve them as last-resort drugs.

SUMMARY

Carbapenems should be used in patients with serious infections; alternatives could be used individually, particularly for definitive treatment of patients with milder presentations.

Oral Fosfomycin Efficacy with Variable Urinary Exposures following Single and Multiple Doses against Enterobacterales: the Importance of Heteroresistance for Growth Outcome

Oral fosfomycin trometamol is licensed as a single oral dose for the treatment of uncomplicated urinary tract infections, with activity against multidrug-resistant uropathogens. The impact of interindividual variability in urinary concentrations on antimicrobial efficacy, and any benefit of giving multiple doses, is uncertain. We therefore performed pharmacodynamic profiling of oral fosfomycin, using a dynamic bladder infection in vitro model, to assess high and low urinary exposures following a single oral dose and three repeat doses given every 72 h, 48 h, and 24 h against 16 clinical isolates with various MICs of fosfomycin (8 Escherichia coli, 4 Enterobacter cloacae, and 4 Klebsiella pneumoniae isolates). Baseline fosfomycin high-level-resistant (HLR) subpopulations were detected prior to drug exposure in half of the isolates (2 E. coli, 2 E. cloacae, and 4 K. pneumoniae isolates; proportion, 1 × 10^-5 to 5 × 10^-4% of the total population). Fosfomycin exposures were accurately reproduced compared to mathematical modeling (linear regression slope, 1.1; R ², 0.99), with a bias of 3.8% ± 5.7%. All 5/5 isolates with MICs of ≤1 μg/ml had no HLR and were killed, whereas 8/11 isolates with higher MICs regrew regardless of exposure to high or low urinary concentrations. A disk diffusion zone of <24 mm was a better predictor for baseline HLR and regrowth. Administering 3 doses with average exposures provided very limited additional kill. These results suggest that baseline heteroresistance is important for treatment response, while increased drug exposure and administering multiple doses may not be better than standard single-dose fosfomycin therapy.

Whole genome sequencing snapshot of multi-drug resistant Klebsiella pneumoniae strains from hospitals and receiving wastewater treatment plants in Southern Romania

We report on the genomic characterization of 47 multi-drug resistant, carbapenem resistant and ESBL-producing K. pneumoniae isolates from the influent (I) and effluent (E) of three wastewater treatment plants (WWTPs) and from Romanian hospital units which are discharging the wastewater in the sampled WWTPs. The K. pneumoniae whole genome sequences were analyzed for antibiotic resistance genes (ARGs), virulence genes and sequence types (STs) in order to compare their distribution in C, I and E samples. Both clinical and environmental samples harbored prevalent and widely distributed ESBL genes, i.e. bla_SHV, bla_OXA, bla_TEM and bla_{CTX M}. The most prevalent carbapenemase genes were bla_NDM-1, bla_OXA-48 and bla_KPC-2. They were found in all types of isolates, while bla_OXA-162, a rare bla_OXA-48 variant, was found exclusively in water samples. A higher diversity of carbapenemases genes was seen in wastewater isolates. The aminoglycoside modifying enzymes (AME) genes found in all types of samples were aac(6’), ant(2'')Ia, aph(3'), aaD, aac(3) and aph(6). Quinolone resistance gene qnrS1 and the multi-drug resistance oqxA/B pump gene were found in all samples, while qnrD and qnrB were associated to aquatic isolates. The antiseptics resistance gene qacEdelta1 was found in all samples, while qacE was detected exclusively in the clinical ones. Trimethroprim-sulfamethoxazole (dfrA, sul1 and sul2), tetracyclines (tetA and tetD) and fosfomycin (fosA6, known to be located on a transpozon) resistance genes were found in all samples, while for choramphenicol and macrolides some ARGs were detected in all samples (catA1 and catB3 / mphA), while other (catA2, cmIA5 and aac(6’)Ib / mphE and msrE) only in wastewater samples. The rifampin resistance genes arr2 and 3 (both carried by class I integrons) were detected only in water samples. The highly prevalent ARGs preferentially associating with aquatic versus clinical samples could ascribe potential markers for the aquatic (bla_SHV-145, qacEdelta1, sul1, aadA1, aadA2) and clinical (bla_OXA-1, bla_SHV-106,bla_TEM-150, aac(3)Iia, dfrA14, oqxA10; oqxB17,catB3, tetD) reservoirs of AR. Moreover, some ARGs (oqxA10; bla_SHV-145; bla_SHV-100, aac(6')Il, aph(3')VI, armA, arr2, cmlA5, bla_CMY-4, mphE, msrE, oqxB13, bla_OXA-10) showing decreased prevalence in influent versus effluent wastewater samples could be used as markers for the efficiency of the WWTPs in eliminating AR bacteria and ARGs. The highest number of virulence genes (75) was recorded for the I samples, while for E and C samples it was reduced to half. The most prevalent belong to three functional groups: adherence (fim genes), iron acquisition (ent, fep, fyu, irp and ybt genes) and the secretion system (omp genes). However, none of the genes associated with hypervirulent K. pneumoniae have been found. A total of 14 STs were identified. The most prevalent clones were ST101, ST219 in clinical samples and ST258, ST395 in aquatic isolates. These STs were also the most frequently associated with integrons. ST45 and ST485 were exclusively associated with I samples, ST11, ST35, ST364 with E and ST1564 with C samples. The less frequent ST17 and ST307 aquatic isolates harbored bla_OXA-162, which was co-expressed in our strains with bla_CTX-M-15 and bla_OXA-1.

Designing A Pathogen-Focused Study To Address The High Unmet Medical Need Represented By Carbapenem-Resistant Gram-Negative Pathogens - The International, Multicenter, Randomized, Open-Label, Phase 3 CREDIBLE-CR Study

Carbapenem-resistant (CR) Gram-negative infections, including those caused by Enterobacteriaceae and the non-fermenters, represent the greatest unmet need for new effective treatments. The clinical development of new antibiotics for the treatment of CR infections is challenging and should focus on the individual pathogens irrespective of the infection site. However, the drug approval pathway is generally infection-site specific and rarely includes such drug-resistant pathogens. To overcome this limitation, a streamlined clinical development program may include a pathogen-focused clinical study, such as the CREDIBLE-CR study, to meet the expectations of some health authorities (ie, the European Medicines Agency [EMA]) and the medical community. Cefiderocol is a novel siderophore cephalosporin designed to target CR pathogens, including CR strains of Enterobacteriaceae (CRE), Pseudomonas aeruginosa, Acinetobacter baumannii, and also Stenotrophomonas maltophilia, which is intrinsically CR. The CREDIBLE-CR study was planned to evaluate cefiderocol in patients with CR Gram-negative infections regardless of species or infection-site source. Rapid diagnostic testing and/or selective media were provided to facilitate detection of CR pathogens to rapidly enroll patients with nosocomial pneumonia, bloodstream infection/sepsis, or complicated urinary tract infection. Patients were randomized 2:1 to receive cefiderocol or best available therapy. There were no pre-specified statistical hypotheses for this study, as the sample size was driven by enrollment feasibility and not based on statistical power calculations. The objective of the CREDIBLE-CR study was to provide descriptive evidence of the efficacy and safety of cefiderocol for the target population of patients with CR infections, including the non-fermenters. The CREDIBLE-CR study is currently the largest pathogen-focused, randomized, open-label, prospective, Phase 3 clinical study to investigate a new antibiotic in patients with CR Gram-negative infections. Here we describe the design of this pathogen-focused study and steps taken to aid patient enrollment into the study within an evolving regulatory environment.

Treatment Options for Carbapenem-resistant Gram-negative Bacterial Infections

Antimicrobial resistance has become one of the greatest threats to public health, with rising resistance to carbapenems being a particular concern due to the lack of effective and safe alternative treatment options. Carbapenem-resistant gram-negative bacteria of clinical relevance include the Enterobacteriaceae, Pseudomonas aeruginosa, Acinetobacter baumannii, and more recently, Stenotrophomonas maltophilia. Colistin and tigecycline have been used as first-line agents for the treatment of infections caused by these pathogens; however, there are uncertainties regarding their efficacy even when used in combination with other agents. More recently, several new agents with activity against certain carbapenem-resistant pathogens have been approved for clinical use or are reaching late-stage clinical development. They include ceftazidime-avibactam, ceftolozane-tazobactam, meropenem-vaborbactam, imipenem-cilastatin-relebactam, plazomicin, eravacycline, and cefiderocol. In addition, fosfomycin has been redeveloped in a new intravenous formulation. Data regarding the clinical efficacy of these new agents specific to infections caused by carbapenem-resistant pathogens are slowly emerging and appear to generally favor newer agents over previous best available therapy. As more treatment options become widely available for carbapenem-resistant gram-negative infections, the role of antimicrobial stewardship will become crucial in ensuring appropriate and rationale use of these new agents.