Intravenous fosfomycin—back to the future. Systematic review and meta-analysis of the clinical literature

Fosfomycin in the pediatric setting: Evidence and potential indications

To date, there has been little experience in using fosfomycin in children. However, its broad spectrum of action and excellent safety profile have renewed interest in this antibiotic, especially for treating infections by multidrug-resistant bacteria. The main indication for fosfomycin in pediatrics is currently community-acquired lower urinary tract infection. Given its good activity against bacteria, fosfomycin can also be useful in urinary infections caused by extended-spectrum beta-lactamase-producing enterobacteria. Fosfomycin presents very good dissemination to tissues including bone and is therefore an option in the combined therapy of osteomyelitis, especially in cases produced by methicillin-resistant Staphylococcus aureus (MRSA) or in cases with beta-lactam allergies. Fosfomycin can also be employed in combination for multidrug-resistant Gram-negative bacteremia (especially carbapenemase-producing enterobacteria), S. aureus (if there is a high suspicion of MRSA or complicated infections) and vancomycin-resistant Enterococcus spp. Other infections in which fosfomycin could be part of a combined therapy include staphylococcal endocarditis (in case of beta-lactam allergy or MRSA), central nervous system infections (mainly by MRSA, S. epidermidis, Listeria and resistant pneumococcus), nosocomial pneumonia and infections associated with mechanical ventilation.

Deciphering pharmacokinetics and pharmacodynamics of fosfomycin

Fosfomycin, a low molecular weight and hydrophilic drug with negligible protein binding, is eliminated almost exclusively by glomerular filtration, whose clearance is subject to patient renal function. The volume of distribution approximates to the extracellular body water (about 0.3 L/Kg) in healthy volunteers, but it is increased in critically ill patients with bacterial infections. Fosfomycin presents a high ability to distribute into many tissues, including inflamed tissues and abscess fluids. Based on PK/PD analysis and Monte Carlo simulations, we have evaluated different fosfomycin dosing regimen to optimize the treatment of septic patients due to Enterobacterales and Pseudomonas aeruginosa. As PK/PD targets, we selected %T>MIC > 70% for all pathogens, and AUC24/MIC > 24 and AUC24/MIC > 15 for net stasis of Enterobacterales and P. aeruginosa, respectively. Pharmacokinetic parameters in critically ill patients were obtained from the literature. Several dosing regimens were studied in patients with normal renal function: fosfomycin 2-8 g given every 6-12 hours, infused over 30 minutes- 24 hours. At the susceptibility EUCAST breakpoint for Enterobacterales and Staphylococcus spp. (MIC ≤ 32 mg/L), fosfomycin 4 g/8h or higher infused over 30 minutes achieved a probability of target attainment (PTA) > 90%, based in both %T>MIC and AUC24/MIC. For MIC of 64 mg/L, fosfomycin 6 g/6h in 30-minute infusion and 8 g/ 8h in 30-minute and 6 hours infusions also achieved PTA values higher than 90%. No fosfomycin monotherapy regimen was able to achieve PK/PD targets related to antimicrobial efficacy for P. aeruginosa with MICs of 256-512 mg/L.

The potential of fosfomycin for multi-drug resistant sepsis: an analysis of in vitro activity against invasive paediatric Gram-negative bacteria

PURPOSE

Antimicrobial resistance (AMR) is of increasing global concern, threatening to undermine recent progress in reducing child and neonatal mortality. Repurposing older antimicrobials is a prominent strategy to combat multidrug-resistant sepsis. A potential agent is fosfomycin, however, there is scarce data regarding its in vitro activity and pharmacokinetics in the paediatric population.

METHODOLOGY

We analysed a contemporary, systematically collected archive of community-acquired (CA) and hospital-acquired (HA) paediatric Gram-negative bacteraemia isolates for their susceptibility to fosfomcyin. MICs were determined using agar serial dilution methods and validated by disk diffusion testing where breakpoints are available. Disk diffusion antimicrobial susceptibility testing was also conducted for current empirical therapies (ampicillin, gentamicin, ceftriaxone) and amikacin (proposed in the literature as a new combination empirical therapeutic option).

RESULTS

Fosfomycin was highly active against invasive Gram-negative isolates, including 90  % (202/224) of Enterobacteriaceae and 96  % (22/23) of Pseudomonas spp. Fosfomycin showed high sensitivity against both CA isolates (94 %, 142/151) and HA isolates (81 %, 78/96; P =0.0015). CA isolates were significantly more likely to be susceptible to fosfomycin than the current first-line empirical therapy (96  % vs 59  %, P <0.0001). Extended spectrum β-lactamases (ESBL) production was detected in 34  % (85/247) of isolates with no significant difference in fosfomycin susceptibility between ESBL-positive or -negative isolates [73/85 (86  %) vs 147/162 (91  %) respectively, P =0.245]. All isolates were susceptible to a fosfomycin-amikacin combination.

CONCLUSION

Gram-negative paediatric bacteraemia isolates are highly susceptible to fosfomycin, which could be combined with aminoglycosides as a new, carbapenem-sparing regimen to achieve excellent coverage to treat antimicrobial-resistant neonatal and paediatric sepsis.

Intraperitoneal administration of fosfomycin, metronidazole, and granulocyte-macrophage colony-stimulating factor in patients undergoing appendectomy is safe: a phase II clinical trial

We aimed to investigate the safety of intraperitoneal administration of the combination of fosfomycin, metronidazole, and recombinant human granulocyte-macrophage colony-stimulating factor (rhGM-CSF) in patients undergoing appendectomy. We conducted a prospective phase II clinical trial in 14 otherwise healthy men suffering from uncomplicated appendicitis. After appendectomy, the trial treatment was administered intraperitoneally and left in the abdominal cavity. Trial treatment consisted of 4 g fosfomycin, 1 g metronidazole, and 50 µg rhGM-CSF in a total volume of 500 ml. Safety was evaluated through white blood cell count where a toxic effect was predefined. We evaluated harms and adverse events, repeated biochemical markers, vital signs, and length of stay. White blood cell count did not drop below the toxic range. The recorded harms were dizziness, discomfort when breathing deeply, no flatus, and bloating. Adverse events included three patients with diarrhoea after discharge and one patient with a hypotensive episode. No serious adverse events or infectious complications occurred. Intraperitoneal administration of fosfomycin, metronidazole, and rhGM-CSF was safe in otherwise healthy men undergoing laparoscopic appendectomy. There were some possible harms and adverse events but we were unable to assess if they were related to anaesthesia, surgery, or the trial treatment.

Treatment of Infections Due to MDR Gram-Negative Bacteria

The treatment of multidrug-resistant Gram-negative bacteria (MDR-GNB) infections in critically ill patients presents many challenges. Since an effective treatment should be administered as soon as possible, resistance to many antimicrobial classes almost invariably reduces the probability of adequate empirical coverage, with possible unfavorable consequences. In this light, readily available patient's medical history and updated information about the local microbiological epidemiology remain critical for defining the baseline risk of MDR-GNB infections and firmly guiding empirical treatment choices, with the aim of avoiding both undertreatment and overtreatment. Rapid diagnostics and efficient laboratory workflows are also of paramount importance both for anticipating diagnosis and for rapidly narrowing the antimicrobial spectrum, with de-escalation purposes and in line with antimicrobial stewardship principles. Carbapenem-resistant Enterobacteriaceae, Pseudomonas aeruginosa, and Acinetobacter baumannii are being reported with increasing frequencies worldwide, although with important variability across regions, hospitals and even single wards. In the past few years, new treatment options, such as ceftazidime/avibactam, meropenem/vaborbactam, ceftolozane/tazobactam, plazomicin, and eravacycline have become available, and others will become soon, which have provided some much-awaited resources for effectively counteracting severe infections due to these organisms. However, their optimal use should be guaranteed in the long term, for delaying as much as possible the emergence and diffusion of resistance to novel agents. Despite important progresses, pharmacokinetic/pharmacodynamic optimization of dosages and treatment duration in critically ill patients has still some areas of uncertainty requiring further study, that should take into account also resistance selection as a major endpoint. Treatment of severe MDR-GNB infections in critically ill patients in the near future will require an expert and complex clinical reasoning, of course taking into account the peculiar characteristics of the target population, but also the need for adequate empirical coverage and the more and more specific enzyme-level activity of novel antimicrobials with respect to the different resistance mechanisms of MDR-GNB.

ZTI-01 (fosfomycin for injection) in the treatment of hospitalized patients with complicated urinary tract infections

Fosfomycin is a bactericidal antibiotic available since the 1970s whose intravenous formulation has been available in many countries outside the USA. Given the rise in drug-resistant bacteria, its introduction into the US market has become a necessity for addressing these organisms. This review provides an overview of the microbiology, clinical pharmacology and initial clinical experiences of the intravenous fosfomycin product (ZTI-01) that is undergoing clinical development in the USA for the treatment of complicated urinary tract infections and acute pyelonephritis.

Small-Molecule Inhibitor of FosA Expands Fosfomycin Activity to Multidrug-Resistant Gram-Negative Pathogens

The spread of multidrug or extensively drug-resistant Gram-negative bacteria is a serious public health issue. There are too few new antibiotics in development to combat the threat of multidrug-resistant infections, and consequently the rate of increasing antibiotic resistance is outpacing the drug development process. This fundamentally threatens our ability to treat common infectious diseases. Fosfomycin (FOM) has an established track record of safety in humans and is highly active against Escherichia coli, including multidrug-resistant strains. However, many other Gram-negative pathogens, including the "priority pathogens" Klebsiella pneumoniae and Pseudomonas aeruginosa, are inherently resistant to FOM due to the chromosomal fosA gene, which directs expression of a metal-dependent glutathione S-transferase (FosA) that metabolizes FOM. In this study, we describe the discovery and biochemical and structural characterization of ANY1 (3-bromo-6-[3-(3-bromo-2-oxo-1H-pyrazolo[1,5-a]pyrimidin-6-yl)-4-nitro-1H-pyrazol-5-yl]-1H-pyrazolo[1,5-a]pyrimidin-2-one), a small-molecule active-site inhibitor of FosA. Importantly, ANY1 potentiates FOM activity in representative Gram-negative pathogens. Collectively, our study outlines a new strategy to expand FOM activity to a broader spectrum of Gram-negative pathogens, including multidrug-resistant strains.

Intravenous fosfomycin for the treatment of multidrug-resistant pathogens: what is the evidence on dosing regimens?

INTRODUCTION

The intravenous (IV) formulation of fosfomycin has been re-introduced in clinical practice mainly to overcome treatment failures against multidrug-resistant (MDR) bacteria. Appropriate dosing schedules of the IV formulation have not yet been established. Areas covered: The mechanism of action and resistance development, commercial IV formulations, pharmacokinetic/pharmacodynamic (PK/PD) properties, IV dosing regimens for the treatment of MDR infections along with efficacy and safety issues were reviewed. Data regarding specific MDR pathogens, daily doses and patients' outcomes, gaps in the current literature, and in progress research agenda are presented. Expert opinion: The doses of fosfomycin IV range between 12 and 24 grams/day depending on the severity of infection. The efficacy and safety of the commonly administered doses have been shown mainly in observational non-comparative trials. The optimal dose ensuring maximal efficacy with minimal toxicity along with the most appropriate co-administered antibiotic(s) need further evaluation. The pharmacokinetic/pharmacodynamic parameter associated with maximum efficacy has not yet been established, although, the ratio of the area under the concentration-time curve (AUC) for the free unbound fraction of fosfomycin versus the MIC (fAUC/MIC) may be linked to optimal treatment. RCTs and other comparative studies are underway to address gaps of knowledge in adult patients and neonates.

Epistatic control of intrinsic resistance by virulence genes in Listeria

Elucidating the relationships between antimicrobial resistance and virulence is key to understanding the evolution and population dynamics of resistant pathogens. Here, we show that the susceptibility of the gram-positive bacterium Listeria monocytogenes to the antibiotic fosfomycin is a complex trait involving interactions between resistance and virulence genes and the environment. We found that a FosX enzyme encoded in the listerial core genome confers intrinsic fosfomycin resistance to both pathogenic and non-pathogenic Listeria spp. However, in the genomic context of the pathogenic L. monocytogenes, FosX-mediated resistance is epistatically suppressed by two members of the PrfA virulence regulon, hpt and prfA, which upon activation by host signals induce increased fosfomycin influx into the bacterial cell. Consequently, in infection conditions, most L. monocytogenes isolates become susceptible to fosfomycin despite possessing a gene that confers high-level resistance to the drug. Our study establishes the molecular basis of an epistatic interaction between virulence and resistance genes controlling bacterial susceptibility to an antibiotic. The reported findings provide the rationale for the introduction of fosfomycin in the treatment of Listeria infections even though these bacteria are intrinsically resistant to the antibiotic in vitro.

Treatment of extended-spectrum β-lactamase-producing Enterobacteriaceae (ESBLs) infections: what have we learned until now?

The spread of extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae (ESBL-PE) has dramatically increased worldwide, and this “evolving crisis” is currently regarded as one of the most important public health threats. The growing problem of ESBL-PE antimicrobial resistance seems to have a dual face between “Scylla and Charybdis”: on one hand the potential for rapid spread and dissemination of resistance mechanisms and on the other hand the injudicious overuse of antimicrobial agents and the inadequate infection control measures, especially in the health-care setting. Given the World Health Organization’s warning against a “post antibiotic era”, health-care providers are at a critical standpoint to find a “balance” between safe and effective ESBL-PE treatment and avoidance of inducing further resistance mechanisms. The aim of the review is to summarize the updated published knowledge in an attempt to answer basic everyday clinical questions on how to proceed to effective and the best ESBL-PE treatment options based on the existing published data.

Intravenous Fosfomycin: An Assessment of Its Potential for Use in the Treatment of Systemic Infections in Canada

Fosfomycin is a bactericidal agent that inhibits cell wall synthesis using a mechanism of action distinct from β-lactams or other antimicrobial agents. It is a broad-spectrum agent that is frequently active against antimicrobial-resistant bacterial pathogens including methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE), multidrug-resistant (MDR) Enterobacteriaceae, and some isolates of MDR Pseudomonas aeruginosa. Intravenous fosfomycin has been prescribed for a wide variety of infections in many countries for >40 years. It is most frequently used in combination with other antimicrobial agents (e.g., β-lactams, carbapenems, and aminoglycosides) and has an excellent safety profile, including in neonates and children, even with long-term administration (weeks). Fosfomycin achieves extensive tissue distribution including difficult to reach compartments such as aqueous humor, vitreous humor, abscess fluid, and CSF. Available data, to date, suggest no clinically relevant pharmacological interactions between fosfomycin and other agents, including drugs, stimulants, or food. Intravenous fosfomycin's role in therapy in Canada is likely as an agent used alone or in combination for complicated urinary tract infections in hospitalized patients as well as hospitalized patients with MDR infections who have not responded to first-, and potentially, second-line antimicrobials or in patients who cannot tolerate (due to adverse effects) first- and second-line antimicrobials.

Wagenlehner F, Zimmer KP, Chakraborty T. Treatment Options for Carbapenem- Resistant Gram-Negative Infections

BACKGROUND

Rates of colonization and infection with carbapenem-resistant Gram-negative pathogens are on the rise, particularly in southeastern European countries, and this is increasingly true in Germany as well. The organisms in question include enterobacteriaceae such as Klebsiella pneumoniae and Escherichia coli and non-fermenting bacteria such as Pseudomonas aeruginosa and Acinetobacter baumannii. As the carbapenems have been the gold standard to date for the systemic treatment of serious infections with Gram-negative bacteria, carbapenem resistance presents new and difficult challenges in therapeutic decision-making, particularly because of the high frequency of coresistance.

METHODS

This review is based on pertinent publications retrieved by a selective search in PubMed and on other applicable literature.

RESULTS

Multiresistant Gram-negative (MRGN) pathogens are classified in Germany according to their resistance to four different classes of antibiotics; fluoroquinolones, piperacillin, third-generation cephalosporins, and carbapenems. Quadruple MRGN pathogens are resistant to all four groups, triple MRGN pathogens to three of them. There are a number of therapeutic alternatives to carbapenems that can be applied with the aid of sensitive microbiological and/or molecular genetic testing. The following antibiotics are often the only ones that can be used to treat quadruple MRGN pathogens: colistin, aminoglycosides, tigecycline, fosfomycin, ceftazidime/avibactam, and ceftolozan/tazobactam. Carbapenems, too, may still be an option in certain situations. There is also evidence that combinations of antibiotics against which the pathogen is resistant individually can some- times be a valid treatment option; these include combinations of colistin with one or two carbapenems.

CONCLUSION

The treatment of severe infection with carbapenem-resistant pathogens should be individualized and carried out in an interdisciplinary framework, in consideration of antibiotic pharmacokinetics and pharmacodynamics in each case. The treat- ment options are based on evidence from in vitro studies, retrospective studies, and case series, which must be interpreted with caution. Randomized clinical trials are needed to test each of the various combined approaches.

Pharmacokinetic and Pharmacodynamic Considerations of Antibiotics of Last Resort in Treating Gram-Negative Infections in Adult Critically Ill Patients

PURPOSE OF REVIEW

We provide an overview of antimicrobials that are considered last resort for the treatment of resistant gram-negative infections in adult critically ill patients. The role in therapy, pharmacodynamic (PD) goals, and pharmacokinetic (PK) changes in critical illness for aminoglycosides, polymyxins, tigecycline, fosfomycin, and fluoroquinolones are summarized.

RECENT FINDINGS

Altered PK in septic patients in the intensive care unit (ICU) is observed with many of our agents of last resort. Based on the available literature, dosage adjustments may be required to optimize PK parameters and meet PD targets for most effective bacterial killing. Data is limited, studies are conducted in heterogeneous patient populations, and conclusions are frequently conflicting. Strategic dosing regimens such as high-dose extended interval dosing of aminoglycosides or loading doses with colistin and polymyxin B are examples of ways to optimize antibiotic PK in critically ill patients. Benefits of these strategies must be balanced with risks of increased toxicity. Patients with resistant gram-negative infections may present with septic shock in the ICU. Sepsis can significantly alter the PK of antibiotics and require dosage adjustments to attain optimal drug levels. An understanding of PK and PD properties of these agents of last resort will help to maximize therapeutic efficacy while minimizing toxic effects.

Influence of different peritoneal dialysis fluids on the in vitro activity of fosfomycin against Escherichia coli, Staphylococcus aureus, Staphylococcus epidermidis, and Pseudomonas aeruginosa

Peritonitis is still the main infectious complication among patients on peritoneal dialysis. For treatment of peritoneal dialysis-related peritonitis, the intraperitoneal administration of antibiotics admixed to peritoneal dialysis fluids (PDFs) should be preferred. However, the influence of diverse PDFs on the activity of frequently used antibiotics has been investigated insufficiently. Thus, the present study set out to investigate the in vitro activity of fosfomycin against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus epidermidis, and Staphylococcus aureus in commercially available PDFs. Time-kill curves in four different PDFs (Dianeal®, Extraneal®, Nutrineal®, and Physioneal®) were performed over 24 h with two different concentrations of fosfomycin (150 and 400 mg/L) and without antibiotics as control. Cation-adjusted Mueller Hinton broth (CA-MHB) was used as a comparator solution. In blank PDFs, bacterial growth of each organism evaluated was reduced when compared to CA-MHB. For S. aureus in blank Physioneal®, a reduction under the limit of detection was observed within 24 h. The activity of fosfomycin was reduced in all PDFs when compared to CA-MHB except for P. aeruginosa in Nutrineal® where the activity of fosfomycin was increased when investigated at 400 mg/L. Against E.coli, bactericidal activity was demonstrated in Extraneal®, Nutrineal®, and Physioneal®. Fosfomycin resistance (MIC > 1024 mg/L) was observed for P. aeruginosa in CA-MHB at both concentrations and in Nutrineal® at 150 mg/L. Fosfomycin is active in PDFs particularly against the frequently isolated enterobacterium E. coli. The choice of the respective PDF considerably influences the microbiological outcome in vitro. Further studies are warranted to investigate the clinical relevance of these findings.

Resistance Trends and Treatment Options in Gram-Negative Ventilator-Associated Pneumonia

PURPOSE OF REVIEW

Hospital-acquired and ventilator-associated pneumonia (VAP) are frequent causes of infection among critically ill patients. VAP is the most common hospital-acquired bacterial infection among mechanically ventilated patients. Unfortunately, many of the nosocomial Gram-negative bacteria that cause VAP are increasingly difficult to treat. Additionally, the evolution and dissemination of multi- and pan-drug resistant strains leave clinicians with few treatment options. VAP patients represent a dynamic population at risk for antibiotic failure and under-dosing due to altered antibiotic pharmacokinetic parameters. Since few antibiotic agents have been approved within the last 15 years, and no new agents specifically targeting VAP have been approved to date, it is anticipated that this problem will worsen. Given the public health crisis posed by resistant Gram-negative bacteria, it is essential to establish a firm understanding of the current epidemiology of VAP, the changing trends in Gram-negative resistance in VAP, and the current issues in drug development for Gram-negative bacteria that cause VAP.

RECENT FINDINGS

Rapid identification technologies and phenotypic methods, new therapeutic strategies, and novel treatment paradigms have evolved in an attempt to improve treatment outcomes for VAP; however, clinical data supporting alternative treatment strategies and adjunctive therapies remain sparse. Importantly, new classes of antimicrobials, novel virulence factor inhibitors, and beta-lactam/beta-lactamase inhibitor combinations are currently in development. Conscientious stewardship of new and emerging therapeutic agents will be needed to ensure they remain effective well into the future.

Treatment of Infections Caused by Extended-Spectrum-Beta-Lactamase-, AmpC-, and Carbapenemase-Producing Enterobacteriaceae

Therapy of invasive infections due to multidrug-resistant Enterobacteriaceae (MDR-E) is challenging, and some of the few active drugs are not available in many countries. For extended-spectrum β-lactamase and AmpC producers, carbapenems are the drugs of choice, but alternatives are needed because the rate of carbapenem resistance is rising. Potential active drugs include classic and newer β-lactam-β-lactamase inhibitor combinations, cephamycins, temocillin, aminoglycosides, tigecycline, fosfomycin, and, rarely, fluoroquinolones or trimethoprim-sulfamethoxazole. These drugs might be considered in some specific situations. AmpC producers are resistant to cephamycins, but cefepime is an option. In the case of carbapenemase-producing Enterobacteriaceae (CPE), only some "second-line" drugs, such as polymyxins, tigecycline, aminoglycosides, and fosfomycin, may be active; double carbapenems can also be considered in specific situations. Combination therapy is associated with better outcomes for high-risk patients, such as those in septic shock or with pneumonia. Ceftazidime-avibactam was recently approved and is active against KPC and OXA-48 producers; the available experience is scarce but promising, although development of resistance is a concern. New drugs active against some CPE isolates are in different stages of development, including meropenem-vaborbactam, imipenem-relebactam, plazomicin, cefiderocol, eravacycline, and aztreonam-avibactam. Overall, therapy of MDR-E infection must be individualized according to the susceptibility profile, type, and severity of infection and the features of the patient.

A Cohort Study of Risk Factors That Influence Empirical Treatment of Patients with Acute Pyelonephritis

The aim of the current study was to compare community-acquired acute pyelonephritis (CA-APN) with health care-associated acute pyelonephritis (HCA-APN), describe the outcomes, and identify variables that could predict antimicrobial susceptibility. We conducted an observational study that included all consecutive episodes of acute pyelonephritis (APN) in adults during 2014 at a Spanish university hospital. From each episode, demographic data, comorbidities, clinical presentation, microbiological data, antimicrobial therapy, and outcome were recorded. A multivariable logistic regression model was performed to define the variables associated with antimicrobial resistance. A total of 607 patients, 503 (82.9%) with CA-APN and 104 (17.1%) with HCA-APN, were included in the study. Patients with HCA-APN were older than patients with CA-APN (70.4 versus 50.6 years; P < 0.001) and had higher rates of previous urinary tract infections (UTIs) (56.5% versus 24.5%; P < 0.001) and previous antibiotic use (56.8% versus 22.8%; P < 0.001). Escherichia coli was more frequently isolated from patients with CA-APN than from patients with HCA-APN (79.9% versus 50.5%; P < 0.001). The rates of resistance of Escherichia coli strains from CA-APN patients versus HCA-APN patients were as follows: amoxicillin-clavulanic acid, 22.4% versus 53.2% (P = 0.001); cefuroxime, 7.7% versus 43.5% (P = 0.001); cefotaxime, 4.3% versus 32.6% (P < 0.001); ciprofloxacin, 22.8% versus 74.5% (P < 0.001); and co-trimoxazole, 34.5% versus 58.7% (P = 0.003). The site of acquisition, recurrent UTIs, and previous antibiotic use were independent risk factors for antimicrobial resistance. Relapse rates were significantly higher when definitive antimicrobial treatment was not adequate (37.1% versus 9.3% when definitive antimicrobial treatment was adequate; P < 0.001). Our study reflects the rise of resistance to commonly used antibiotics in acute pyelonephritis. In order to choose the adequate empirical antibiotic therapy, risk factors for resistance should be considered.

Structure and Dynamics of FosA-Mediated Fosfomycin Resistance in Klebsiella pneumoniae and Escherichia coli

Fosfomycin exhibits broad-spectrum antibacterial activity and is being reevaluated for the treatment of extensively drug-resistant pathogens. Its activity in Gram-negative organisms, however, can be compromised by expression of FosA, a metal-dependent transferase that catalyzes the conjugation of glutathione to fosfomycin, rendering the antibiotic inactive. In this study, we solved the crystal structures of two of the most clinically relevant FosA enzymes: plasmid-encoded FosA3 from Escherichia coli and chromosomally encoded FosA from Klebsiella pneumoniae (FosA^KP). The structure, molecular dynamics, catalytic activity, and fosfomycin resistance of FosA3 and FosA^KP were also compared to those of FosA from Pseudomonas aeruginosa (FosA^PA), for which prior crystal structures exist. E. coli TOP10 transformants expressing FosA3 and FosA^KP conferred significantly greater fosfomycin resistance (MIC, >1,024 μg/ml) than those expressing FosA^PA (MIC, 16 μg/ml), which could be explained in part by the higher catalytic efficiencies of the FosA3 and FosA^KP enzymes. Interestingly, these differences in enzyme activity could not be attributed to structural differences at their active sites. Instead, molecular dynamics simulations and hydrogen-deuterium exchange experiments with FosA^KP revealed dynamic interconnectivity between its active sites and a loop structure that extends from the active site of each monomer and traverses the dimer interface. This dimer interface loop is longer and more extended in FosA^KP and FosA3 than in FosA^PA, and kinetic analyses of FosA^KP and FosA^PA loop-swapped chimeric enzymes highlighted its importance in FosA activity. Collectively, these data yield novel insights into fosfomycin resistance that could be leveraged to develop new strategies to inhibit FosA and potentiate fosfomycin activity.

Management of KPC-producing Klebsiella pneumoniae infections

BACKGROUND

Klebsiella pneumoniae carbapenemase (KPC)-producing K. pneumoniae (KPC-KP) has become one of the most important contemporary pathogens, especially in endemic areas.

AIMS

To provide practical suggestion for physicians dealing with the management of KPC-KP infections in critically ill patients, based on expert opinions.

SOURCES

PubMed search for relevant publications related to the management of KPC-KP infections.

CONTENTS

A panel of experts developed a list of 12 questions to be addressed. In view of the current lack of high-level evidence, they were asked to provide answers on the bases of their knowledge and experience in the field. The panel identified several key aspects to be addressed when dealing with KPC-KP in critically ill patients (preventing colonization in the patient, preventing infection in the colonized patient and colonization of his or her contacts, reducing mortality in the infected patient by rapidly diagnosing the causative agent and promptly adopting the best therapeutic strategy) and provided related suggestions that were based on the available observational literature and the experience of panel members.

IMPLICATIONS

Diagnostic technologies could speed up the diagnosis of KPC-KP infections. Combination treatment should be preferred to monotherapy in cases of severe infections. For non-critically ill patients without severe infections, results from randomized clinical trials are needed for ultimately weighing benefits and costs of using combinations rather than monotherapy. Multifaceted infection control interventions are needed to decrease the rates of colonization and cross-transmission of KPC-KP.

Fosfomycin for the treatment of drug-resistant urinary tract infections: potential of an old drug not explored fully

INTRODUCTION

Increased emergence of bacterial resistance and the limited options of novel antimicrobial agents have necessitated the reintroduction of some old antimicrobial agents. One such drug is fosfomycin, but its potential has not been explored fully, especially in India.

AIMS AND OBJECTIVES

To analyze the in vitro activity of fosfomycin, against the urinary isolates and to compare it with in vitro activity of other orally administered antimicrobial agents.

MATERIALS AND METHODS

This was a prospective observational study conducted between July 2014 and June 2016. All consecutive, non-duplicate and clinically significant urinary isolates obtained from patients of all ages and both genders, diagnosed to have UTI, were included. Patients already on antibiotic therapy were excluded. Urine culture was performed by semiquantitative method on cysteine lactose electrolyte-deficient medium and the isolates obtained in significant count were subjected to antimicrobial sensitivity testing by the Kirby Bauer disk diffusion method as per CLSI guidelines.

RESULTS

A total of 3947 non-repeating urinary isolates were included in the study, of which 2684 (68%) isolates originated from adult outpatients and remaining 1236 (32%) isolates from pediatric patients. Of these 2783 isolates were from enterobacteriaceae family. Out of these 2730 (98.1%) were sensitive to fosfomycin. Most [375 of 385 (97.4%)] Pseudomonas spp were also susceptible to fosfomycin. A majority of ESBL- (96.5%) and MBL (91.9%)-producing isolates were also susceptible to fosfomycin and so were of Gram-positive isolates [698/707 (96%)] and MRSA [61/69 (88.4%)] were susceptible to fosfomycin.

CONCLUSIONS

Fosfomycin showed an excellent in vitro activity against all urinary pathogens, including the Gram-positive or Gram-negative, ESBL and MBL producers. Fosfomycin should be considered as a highly effective alternative in treatment UTIs in both adults and pediatric patients.

Widespread Fosfomycin Resistance in Gram-Negative Bacteria Attributable to the Chromosomal fosA Gene

Fosfomycin is a decades-old antibiotic which is being revisited because of its perceived activity against many extensively drug-resistant Gram-negative pathogens. FosA proteins are Mn²⁺ and K⁺-dependent glutathione S-transferases which confer fosfomycin resistance in Gram-negative bacteria by conjugation of glutathione to the antibiotic. Plasmid-borne fosA variants have been reported in fosfomycin-resistant Escherichia coli strains. However, the prevalence and distribution of fosA in other Gram-negative bacteria are not known. We systematically surveyed the presence of fosA in Gram-negative bacteria in over 18,000 published genomes from 18 Gram-negative species and investigated their contribution to fosfomycin resistance. We show that FosA homologues are present in the majority of genomes in some species (e.g., Klebsiella spp., Enterobacter spp., Serratia marcescens, and Pseudomonas aeruginosa), whereas they are largely absent in others (e.g., E. coli, Acinetobacter baumannii, and Burkholderia cepacia). FosA proteins in different bacterial pathogens are highly divergent, but key amino acid residues in the active site are conserved. Chromosomal fosA genes conferred high-level fosfomycin resistance when expressed in E. coli, and deletion of chromosomal fosA in S. marcescens eliminated fosfomycin resistance. Our results indicate that FosA is encoded by clinically relevant Gram-negative species and contributes to intrinsic fosfomycin resistance.IMPORTANCE There is a critical need to identify alternate approaches to treat infections caused by extensively drug-resistant (XDR) Gram-negative bacteria. Fosfomycin is an old antibiotic which is routinely used for the treatment of urinary tract infections, although there is substantial interest in expanding its use to systemic infections caused by XDR Gram-negative bacteria. In this study, we show that fosA genes, which encode dimeric Mn²⁺- and K⁺-dependent glutathione S-transferase, are widely distributed in the genomes of Gram-negative bacteria-particularly those belonging to the family Enterobacteriaceae-and confer fosfomycin resistance. This finding suggests that chromosomally located fosA genes represent a vast reservoir of fosfomycin resistance determinants that may be transferred to E. coli Furthermore, they suggest that inhibition of FosA activity may provide a viable strategy to potentiate the activity of fosfomycin against XDR Gram-negative bacteria.