In vitro activity of fosfomycin against Gram-negative urinary pathogens and the biological cost of fosfomycin resistance

Impact of a Primary Care Antimicrobial Stewardship Program on Bacterial Resistance Control and Ecological Imprint in Urinary Tract Infections

Antimicrobial stewardship programs (ASPs) are a central component in reducing the overprescription of unnecessary antibiotics, with multiple studies showing benefits in the reduction of bacterial resistance. Less commonly, ASPs have been performed in outpatient settings, but there is a lack of available data in these settings. We implemented an ASP in a large regional outpatient setting to assess its feasibility and effectiveness. Over a 5-year post-implementation period, compared to the pre-intervention period, a significant reduction in antibiotic prescription occurred, with a reduction in resistance in E. coli urinary isolates. ASP activities also were found to be cost-effective, with a reduction in medication prescription.

Efficacy and Safety of Oral Fosfomycin-Trometamol in Male Urinary Tract Infections with Multidrug-Resistant Enterobacterales

Background: Antimicrobial drugs to treat male urinary tract infection (UTI) with multidrug-resistant Enterobacterales are limited. We studied oral fosfomycin-trometamol (FT) in this situation. The objective was to assess the clinical cure rate in patients presenting UTIs treated with oral FT. Methods: We conducted a single-center observational retrospective study from January 2017 to August 2018. The primary endpoint was clinical cure; and the secondary endpoints were incidence of recurrences, oral FT safety, and microbiological cure. Results: Sixteen male patients were included, presenting 21 UTI episodes. Fourteen patients (88%) have at least one underlying urologic disorder. We described 4 episodes of acute UTI and 17 episodes of chronic bacterial prostatitis (CBP). Sixteen out of twenty-one Enterobacterales were extended spectrum beta-lactamase (ESBL)-producers and all the patients presented a resistance to fluoroquinolones and trimethoprim/sulfamethoxazole. In acute UTI, the regimen was a daily dose of oral FT for a mean duration of 2.5 weeks (+/−7.0 days). Clinical and microbiological recovery was achieved in all patients, with no recurrence after 5.3 months follow-up on average (+/−10.4 days). In CBP, the regimen was one oral dose of fosfomycin every 24–48 h, for a mean duration of 5.5 weeks/UTI episodes (+/−15.3 days). Clinical and microbiological recovery was found in 16/17 cases. Seven of the twelve patients with CBP had relapsed and 3/12 had had a new episode of infection after an average follow-up of 5.8 months. Only 6/21 of patients presented minor or moderate adverse effects, such as digestive disorders. Conclusions: FT could be an alternative option to carbapenems in the treatment of multidrug-resistant Enterobacterales infections for male UTIs.

Novel Chromosomal Mutations Responsible for Fosfomycin Resistance in Escherichia coli

Fosfomycin resistance in Escherichia coli results from chromosomal mutations or acquisition of plasmid-mediated genes. Because these mechanisms may be absent in some resistant isolates, we aimed at decipher the genetic basis of fosfomycin resistance in E. coli. Different groups of isolates were studied: fosfomycin-resistant mutants selected in vitro from E. coli CFT073 (MIC = 1 mg/L) and two groups (wildtype and non-wildtype) of E. coli clinical isolates. Single-nucleotide allelic replacement was performed to confirm the implication of novel mutations into resistance. Induction of uhpT expression by glucose-6-phosphate (G6P) was assessed by RT-qPCR. The genome of all clinical isolates was sequenced by MiSeq (Illumina). Two first-step mutants were obtained in vitro from CFT073 (MICs, 128 mg/L) with single mutations: G469R in uhpB (M3); F384L in uhpC (M4). Second-step mutants (MICs, 256 mg/L) presented additional mutations: R282V in galU (M7 from M3); Q558^∗ in lon (M8 from M4). Introduction of uhpB or uhpC mutations by site-directed mutagenesis conferred a 128-fold increase in fosfomycin MICs, whereas single mutations in galU or lon were only responsible for a 2-fold increase. Also, these mutations abolished the induction of uhpT expression by G6P. All 14 fosfomycin-susceptible clinical isolates (MICs, 0.5-8 mg/L) were devoid of any mutation. At least one genetic change was detected in all but one fosfomycin-resistant clinical isolates (MICs, 32 - >256 mg/L) including 8, 17, 18, 5, and 8 in uhpA, uhpB, uhpC, uhpT, and glpT genes, respectively. In conclusion, novel mutations in uhpB and uhpC are associated with fosfomycin resistance in E. coli clinical isolates.

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSION

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

The Role of fosA in Challenges with Fosfomycin Susceptibility Testing of Multispecies Klebsiella pneumoniae Carbapenemase-Producing Clinical Isolates

With multidrug-resistant (MDR) Enterobacterales on the rise, a nontoxic antimicrobial agent with a unique mechanism of action such as fosfomycin seems attractive. However, establishing accurate fosfomycin susceptibility testing for non-Escherichia coli isolates in a clinical microbiology laboratory remains problematic. We evaluated fosfomycin susceptibility by multiple methods with 96 KPC-producing clinical isolates of multiple strains and species collected at a single center between 2008 and 2016.

With multidrug-resistant (MDR) Enterobacterales on the rise, a nontoxic antimicrobial agent with a unique mechanism of action such as fosfomycin seems attractive. However, establishing accurate fosfomycin susceptibility testing for non-Escherichia coli isolates in a clinical microbiology laboratory remains problematic. We evaluated fosfomycin susceptibility by multiple methods with 96 KPC-producing clinical isolates of multiple strains and species collected at a single center between 2008 and 2016. In addition, we assessed the presence of fosfomycin resistance genes from whole-genome sequencing (WGS) data using NCBI’s AMRFinder and custom HMM search. Susceptibility testing was performed using a glucose-6-phosphate-supplemented fosfomycin Etest and Kirby-Bauer disk diffusion (DD) assays, and the results were compared to those obtained by agar dilution. Clinical Laboratory and Standards Institute (CLSI) breakpoints for E. coli were applied for interpretation. Overall, 63% (60/96) of isolates were susceptible by Etest, 70% (67/96) by DD, and 88% (84/96) by agar dilution. fosA was detected in 80% (70/88) of previously sequenced isolates, with species-specific associations and alleles, and fosA-positive isolates were associated with higher MIC distributions. Disk potentiation testing was performed using sodium phosphonoformate to inhibit fosA and showed significant increases in the zone diameter of DD testing for isolates that were fosA positive compared to those that were fosA negative. The addition of sodium phosphonoformate (PPF) corrected 10/14 (71%) major errors in categorical agreement with agar dilution. Our results indicate that fosA influences the inaccuracy of susceptibility testing by methods readily available in a clinical laboratory compared to agar dilution. Further research is needed to determine the impact of fosA on clinical outcomes.

Unexpected Activity of Oral Fosfomycin against Resistant Strains of Escherichia coli in Murine Pyelonephritis

Fosfomycin tromethamine activity is well established for oral treatment of uncomplicated lower urinary tract infections, but little is known about its potential efficacy in pyelonephritis. Ascending pyelonephritis was induced in mice infected with 6 strains of Escherichia coli (fosfomycin MICs, 1 μg/ml to 256 μg/ml). The urine pH was 4.5 before infection and 5.5 to 6.0 during infection. Animals were treated for 24 h with fosfomycin (100 mg/kg of body weight subcutaneously every 4 h), and the CFU were enumerated in kidneys 24 h after the last fosfomycin injection. Peak (20.5 μg/ml at 1 h) and trough (3.5 μg/ml at 4 h) levels in plasma were comparable to those obtained in humans after an oral dose of 3 g. Fosfomycin treatment significantly reduced the bacterial loads in kidneys (3.65 log₁₀ CFU/g [range, 1.83 to 7.03 log₁₀ CFU/g] and 1.88 log₁₀ CFU/g [range, 1.78 to 5.74 log₁₀ CFU/g] in start-of-treatment control mice and treated mice, respectively; P < 10^-6). However, this effect was not found to differ across the 6 study strains (P = 0.71) or between the 3 susceptible and the 3 resistant strains (P = 0.09). Three phenomena may contribute to explain this unexpected in vivo activity: (i) in mice, the fosfomycin kidney/plasma concentration ratio increased from 1 to 7.8 (95% confidence interval, 5.2, 10.4) within 24 h in vitro when the pH decreased to 5, (ii) the fosfomycin MICs for the 3 resistant strains (64 to 256 μg/ml) decreased into the susceptible range (16 to 32 μg/ml), and (iii) maximal growth rates significantly decreased for all strains and were the lowest in urine. These results suggest that local fosfomycin concentrations and physiological conditions may favor fosfomycin activity in pyelonephritis, even against resistant strains.

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

BACKGROUND

Increasing antimicrobial resistance is a major problem worldwide. Many urinary tract infection (UTI) isolates are resistant to all oral antimicrobial agents, necessitating intravenous treatment even for cystitis. Fosfomycin is a broad-spectrum antibiotic that achieves high and prolonged urinary drug concentration and is considered first-line treatment for uncomplicated cystitis. Our aim was to investigate fosfomycin susceptibility among urinary isolates and search for demographic or bacterial characteristics associated with fosfomycin nonsusceptibility.

MATERIALS AND METHODS

This is a retrospective study of all Gram-negative urinary isolates at Padeh-Poriya Medical Center in northern Israel. A total of 1503 isolates were tested for fosfomycin susceptibility, as well as susceptibility to other antimicrobial agents, by VITEK2 system and disk diffusion testing. Demographic and clinical data were obtained from patient electronic files.

RESULTS

A total of 1,503 isolates from patients' urine were included. Mean patient age was 64.6 years, 937 (62.3%) were female, 913 (60.7%) were Jews, and in 1,058 (70.4%) cases, the infection was community acquired; 28.1% were extended-spectrum beta lactamase (ESBL)-positive. A total of 1099 (73.1%) isolates were susceptible to fosfomycin. Fosfomycin nonsusceptibility was significantly correlated to year: 124 (20.7%) in 2015 versus 280 (30.9%) in 2016; patient age: 17.6% in patients ≤50 years versus 30% in patients >50 years; hospital-acquired UTI: 34.2% versus 23.8%; and presence of ESBL positivity: 31.1% in ESBL-positive versus 20.9% in ESBL-negative isolates (p for all <0.001).

CONCLUSIONS

Fosfomycin nonsusceptibility among urine culture isolates is a worrisome phenomenon that is on the rise and is more often found in elderly patients, patients with nosocomial UTI, and isolates that are ESBL positive.

Nitrofurantoin and fosfomycin for resistant urinary tract infections: old drugs for emerging problems

Uncomplicated urinary tract infection is one of the most common indications for antibiotic use in the community However the Gram-negative organisms that can cause the infection are becoming more resistant to antibiotics

Many multidrug resistant organisms retain susceptibility to two old antibiotics nitrofurantoin and fosfomycin Advantages over newer drugs include their high urinary concentrations and minimal toxicity

Fosfomycin is a potential treatment option for patients with uncomplicated urinary tract infection due to resistant organisms Nitrofurantoin may be more effective and can be used for urinary infections in pregnant women

Resistance to fosfomycin: Mechanisms, Frequency and Clinical Consequences

Fosfomycin has been used for the treatment of infections due to susceptible and multidrug-resistant (MDR) bacteria. It inhibits bacterial cell wall synthesis through a unique mechanism of action at a step prior to that inhibited by β-lactams. Fosfomycin enters the bacterium through membrane channels/transporters and inhibits MurA, which initiates peptidoglycan (PG) biosynthesis of the bacterial cell wall. Several bacteria display inherent resistance to fosfomycin mainly through MurA mutations. Acquired resistance involves, in order of decreasing frequency, modifications of membrane transporters that prevent fosfomycin from entering the bacterial cell, acquisition of plasmid-encoded genes that inactivate fosfomycin, and MurA mutations. Fosfomycin resistance develops readily in vitro but less so in vivo. Mutation frequency is higher among Pseudomonas aeruginosa and Klebsiella spp. compared with Escherichia coli and is associated with fosfomycin concentration. Mutations in cAMP regulators, fosfomycin transporters and MurA seem to be associated with higher biological cost in Enterobacteriaceae but not in Pseudomonas spp. The contribution of fosfomycin inactivating enzymes in emergence and spread of fosfomycin resistance currently seems low-to-moderate, but their presence in transferable plasmids may potentially provide the best means for the spread of fosfomycin resistance in the future. Their co-existence with genes conferring resistance to other antibiotic classes may increase the emergence of MDR strains. Although susceptibility rates vary, rates seem to increase in settings with higher fosfomycin use and among multidrug-resistant pathogens.

Urinary Tract Conditions Affect Fosfomycin Activity against Escherichia coli Strains Harboring Chromosomal Mutations Involved in Fosfomycin Uptake

The steps by which Escherichia coli strains harboring mutations related to fosfomycin (FOS) resistance arise and spread during urinary tract infections (UTIs) are far from being understood. The aim of this study was to evaluate the effects of urine, pH, and anaerobiosis on FOS activity against a set of isogenic strains carrying the most prevalent chromosomal mutations conferring FOS resistance (ΔuhpT, ΔglpT, ΔcyaA, and ΔptsI), either singly or in combination. We also studied fosfomycin-resistant E. coli clinical isolates from patients with UTI. Our results demonstrate that urinary tract physiological conditions might have a profound impact on FOS activity against strains with chromosomal FOS resistance mutations. Specifically, acidic pH values and anaerobiosis convert most of the strains categorized as resistant to fosfomycin according to the international guidelines to a susceptible status. Therefore, urinary pH values may have practical interest in the management of UTIs. Finally, our results, together with the high fitness cost associated with FOS resistance mutations, might explain the low prevalence of fosfomycin-resistant E. coli variants in UTIs.

Biological cost of fosfomycin resistance in Escherichia coli in a murine model of urinary tract infection

Prevalence of fosfomycin resistance in E. coli clinical isolates from UTIs remains very low. Our hypothesis was that fosfomycin resistance may be associated with a biological cost. Three groups of strains of E. coli belonging to the B2 phylogenetic group were used: clinical wild-type (WT) isolates, clinical multidrug-resistant isolates and in vitro fosfomycin-resistant derivatives from the uropathogen clinical strain E. coli CFT073. In each group fosfomycin-susceptible and -resistant isolates were compared. In vitro, we found a significantly decreased growth rate for fosfomycin-resistant strains as compared with susceptible strains in the WT group. In a murine model of ascending UTI, there was a significant reduction in infection rates with fosfomycin-resistant isolates as compared with susceptible ones, in all 3 study groups, ranging from 28 to 39% (P<0.03). All fosfomycin-susceptible clinical strains were virulent in vivo (13/13), while fosfomycin-resistant clinical strains were either virulent (2/7) or non-virulent (5/7) (P<0.002). This difference was not explained by the number of virulence factors or pathogenicity-associated islands. In conclusion, fosfomycin resistance appears to carry some biological cost in E. coli, which may explain in part the apparent paradox of the low prevalence of fosfomycin resistance despite a high rate of spontaneous mutants.

Mutations of the Transporter Proteins GlpT and UhpT Confer Fosfomycin Resistance in Staphylococcus aureus

With the increasing spread of methicillin-resistant Staphylococcus aureus worldwide, fosfomycin has begun to be used more often, either alone or in combination with other antibiotics, for treating methicillin-resistant S. aureus infections, resulting in the emergence of fosfomycin-resistant strains. Fosfomycin resistance is reported to be mediated by fosfomycin-modifying enzymes (FosA, FosB, FosC, and FosX) and mutations of the target enzyme MurA or the membrane transporter proteins UhpT and GlpT. Our previous studies indicated that the fos genes might not the major fosfomycin resistance mechanism in S. aureus, whereas mutations of glpT and uhpT seemed to be more related to fosfomycin resistance. However, the precise role of these two genes in S. aureus fosfomycin resistance remains unclear. The aim of the present study was to investigate the role of glpT and uhpT in S. aureus fosfomycin resistance. Homologous recombination was used to knockout the uhpT and glpT genes in S. aureus Newman. Gene complementation was generated by the plasmid pRB473 carrying these two genes. The fosfomycin minimal inhibitory concentration (MIC) of the strains was measured by the E-test to observe the influence of gene deletion on antibiotic susceptibility. In addition, growth curves were constructed to determine whether the mutations have a significant influence on bacterial growth. Deletion of uhpT, glpT, and both of them led to increased fosfomycin MIC 0.5 μg/ml to 32 μg/ml, 4 μg/ml, and >1024 μg/ml, respectively. By complementing uhpT and glpT into the deletion mutants, the fosfomycin MIC decreased from 32 to 0.5 μg/ml and from 4 to 0.25 μg/ml, respectively. Moreover, the transporter gene-deleted strains showed no obvious difference in growth curves compared to the parental strain. In summary, our study strongly suggests that mutations of uhpT and glpT lead to fosfomycin resistance in S. aureus, and that uhpT mutation may play a more important role. The high resistance and low biological fitness cost resulting from uhpT and glpT deletion suggest that these strains might have an evolutionary advantage in a fosfomycin-rich clinical situation, which should be closely monitored.

Fosfomycin: Mechanism and Resistance

Fosfomycin, a natural product antibiotic, has been in use for >20 years in Spain, Germany, France, Japan, Brazil, and South Africa for urinary tract infections (UTIs) and other indications and was registered in the United States for the oral treatment of uncomplicated UTIs because of Enterococcus faecalis and Escherichia coli in 1996. It has a broad spectrum, is bactericidal, has very low toxicity, and acts as a time-dependent inhibitor of the MurA enzyme, which catalyzes the first committed step of peptidoglycan synthesis. Whereas resistance to fosfomycin arises rapidly in vitro through loss of active transport mechanisms, resistance is rarely seen during therapy of UTIs, seemingly because of the low fitness of the resistant organisms. Recently, interest has grown in the use of fosfomycin against multidrug-resistant (MDR) pathogens in other indications, prompting the advent of development in the United States of a parenteral formulation for use, initially, in complicated UTIs. Whereas resistance has not been problematic in the uncomplicated UTI setting, it remains to be seen whether resistance remains at bay with expansion to other indications.

Trends in Antibiotic Resistance in Urologic Practice

CONTEXT

The significant global upsurge in antimicrobial resistance, particularly among Enterobacteriaceae, represents a serious threat to health care systems. The implications for urologic practice are of particular concern.

OBJECTIVE

To review trends in antibiotic resistance in urologic practice.

EVIDENCE ACQUISITION

We report current European trends of resistance in Gram-negative uropathogens.

EVIDENCE SYNTHESIS

In addition to β-lactam resistance, Gram-negative pathogens are often resistant to multiple drug classes, including aminoglycosides, fluoroquinolones, and carbapenems, commonly used to treat urologic infections. Interest is renewed in old antibiotics, and several new antibiotics are in the pipeline to meet the challenge of treating these infections. In this review, we summarise emerging trends in antimicrobial resistance and its impact on urologic practice. We also review current guidelines on the treatment and prevention of urologic infections with these organisms, and some key antibiotics in the era of resistance.

CONCLUSIONS

Increasing antimicrobial resistance represents a challenge to urologic practice for both treatment and prophylaxis. Antibiotic choice should be determined according to risk factors for multidrug resistance. Good knowledge of the local microbial prevalence and resistance profile is required to guide antimicrobial therapy.

PATIENT SUMMARY

Antimicrobial resistance represents a challenge in urology. We summarise emerging trends in antimicrobial resistance and review current guidelines on the treatment and prevention of urologic infections, as well as some key antibiotics in the era of resistance.

Fosfomycin: A First-Line Oral Therapy for Acute Uncomplicated Cystitis

Fosfomycin is a new agent to Canada approved for the treatment of acute uncomplicated cystitis (AUC) in adult women infected with susceptible isolates of E. coli and Enterococcus faecalis. We reviewed the literature regarding the use of oral fosfomycin for the treatment of AUC. All English-language references from 1975 to October 2015 were reviewed. In Canada, fosfomycin tromethamine is manufactured as Monurol® and is available as a 3-gram single dose sachet. Fosfomycin has a unique chemical structure, inhibiting peptidoglycan synthesis at an earlier site compared to β-lactams with no cross-resistance with other agents. Fosfomycin displays broad-spectrum activity against ESBL-producing, AmpC-producing, carbapenem-non-susceptible, and multidrug-resistant (MDR) E. coli. Resistance to fosfomycin in E. coli is rare (<1%). Fosfomycin is excreted unchanged in the urine by glomerular filtration with peak urinary concentration ~4000 µg/mL and remains at concentrations >100 µg/mL for 48 hours after a single 3-gram oral dose. No dosage adjustments are required in elderly patients, in pregnant patients, or in either renal or hepatic impairment. Fosfomycin demonstrates a favorable safety profile, and clinical trials have demonstrated efficacy in AUC that is comparable to ciprofloxacin, nitrofurantoin, and trimethoprim-sulfamethoxazole. Fosfomycin's in vitro activity against common uropathogens, including MDR isolates, its favorable safety profile including pregnancy patients, drug interactions, and clinical trials data demonstrating efficacy in AUC, has resulted in Canadian, US, and European guidelines/authorities recommending fosfomycin as a first line agent for the treatment of AUC.

Fosfomycin trometamol: a review of its use as a single-dose oral treatment for patients with acute lower urinary tract infections and pregnant women with asymptomatic bacteriuria

Fosfomycin trometamol (fosfomycin tromethamine) [Monuril(®), Monurol(®), Monural(®)] is approved in numerous countries worldwide, mainly for the treatment of uncomplicated urinary tract infections (UTIs). Fosfomycin has good in vitro activity against common uropathogens, such as Escherichia coli (including extended-spectrum β-lactamase-producing E. coli), Proteus mirabilis, Klebsiella pneumoniae and Staphylococcus saprophyticus, and the susceptibility of uropathogens to fosfomycin has remained relatively stable over time. A single oral dose of fosfomycin trometamol 3 g (the approved dosage) achieves high concentrations in urine. Results of recent randomized trials indicate that single-dose fosfomycin trometamol had similar clinical and/or bacteriological efficacy to 3- to 7-day regimens of ciprofloxacin, norfloxacin, cotrimoxazole or nitrofurantoin in women with uncomplicated lower UTIs. In addition, single-dose fosfomycin trometamol had similar bacteriological efficacy to a 5-day course of cefuroxime axetil or a 7-day course of amoxicillin/clavulanic acid in pregnant women with asymptomatic bacteriuria, and similar clinical and/or bacteriological efficacy to a 5-day course of cefuroxime axetil or amoxicillin/clavulanic acid or a 3-day course of ceftibuten in pregnant women with a lower UTI. Single-dose fosfomycin trometamol was generally well tolerated, with gastrointestinal adverse events (e.g. diarrhoea, nausea) reported most commonly. In conclusion, single-dose fosfomycin trometamol is an important option for the first-line empirical treatment of uncomplicated lower UTIs.

Efficacy of fosfomycin compared to vancomycin in treatment of implant-associated chronic methicillin-resistant Staphylococcus aureus osteomyelitis in rats

Fosfomycin monotherapy was compared to therapy with vancomycin for the treatment of implant-associated methicillin-resistant Staphylococcus aureus (MRSA) osteomyelitis in an experimental rat model. The proximal tibiae were inoculated with 15 μl of a suspension containing 1×10(8) to 5×10(8) CFU/ml of a clinical isolate of MRSA with simultaneous insertion of a titanium wire. Four weeks later, treatment was started for 28 days with either 50 mg/kg of body weight vancomycin intraperitoneally twice daily (n=11) or 75 mg/kg fosfomycin intraperitoneally once daily (n=10). Eleven animals were left untreated. After treatment, quantitative cultures from bone were found to be positive for MRSA in all animals in the untreated group (median, 3.29×10(6) CFU/g of bone) and the vancomycin group (median, 3.03×10(5) CFU/g of bone). In the fosfomycin group, MRSA was detectable in 2 out of 10 (20%) animals (3.42×10(2) and 1.51×10(3) CFU/g of bone). Vancomycin was superior to the no-drug control (P=0.002), and fosfomycin was superior to the no-drug control and vancomycin (P<0.001). The cultures from the wires were positive in all untreated animals (median, 2.5×10(3) CFU/implant), in 10 animals in the vancomycin group (median, 1.15×10(3) CFU/implant), and negative in all animals in the fosfomycin group. Based on the bacterial counts from the implants, vancomycin was not superior to the no-drug control (P=0.324), and fosfomycin was superior to the no-drug control and vancomycin (P<0.001). No emergence of resistance was observed. In conclusion, it was demonstrated that fosfomycin monotherapy is highly effective for the treatment of experimental implant-associated MRSA osteomyelitis.

Increasing Resistance According to Patient's Age and Sex inEscherichia coliIsolated from Urine in Italy

The prevalence of Escherichia coli among the uropathogens routinely isolated in non-hospital laboratories (Labs) and its susceptibility profiles were investigated. Thirty-three Labs were selected throughout Italy. In vitro assays were performed by means of disk diffusion according to the CLSI. Females were prevalent (79.9%) and the mean patient age was 58.6 (sd 20.4) years. Overall, the prevalence of E. coli was 55.3% (1375 strains), with Enterococcus spp 10.2 %, Proteus mirabilis 4.8%, coagulase-negative staphylococci 4.3% and Klebsiella 3.8% being the next most frequently encountered species. High compliance with quality control program was observed. Susceptibility figures in E. coli were consistently low for many antimicrobial agents such as ampicillin (51.3%) and co-trimoxazole (74.6%) and higher for others such as gentamicin (87.9%) and ceftazidime (95.1%). Resistance rates were higher among male patients and increased according to the patient's age.

Role of the CpxAR two-component signal transduction system in control of fosfomycin resistance and carbon substrate uptake

Although fosfomycin is an old antibiotic, it has resurfaced with particular interest. The antibiotic is still effective against many pathogens that are resistant to other commonly used antibiotics. We have found that fosfomycin resistance of enterohemorrhagic Escherichia coli (EHEC) O157:H7 is controlled by the bacterial two-component signal transduction system CpxAR. A cpxA mutant lacking its phosphatase activity results in constitutive activation of its cognate response regulator, CpxR, and fosfomycin resistance. We have shown that fosfomycin resistance requires CpxR because deletion of the cpxR gene in the cpxA mutant restores fosfomycin sensitivity. We have also shown that CpxR directly represses the expression of two genes, glpT and uhpT, which encode transporters that cotransport fosfomycin with their native substrates glycerol-3-phosphate and glucose-6-phosphate, and repression of these genes leads to a decrease in fosfomycin transport into the cpxA mutant. However, the cpxA mutant had an impaired growth phenotype when cultured with glycerol-3-phosphate or glucose-6-phosphate as a sole carbon substrate and was outcompeted by the parent strain, even in nutrient-rich medium. This suggests a trade-off between fosfomycin resistance and the biological fitness associated with carbon substrate uptake. We propose a role for the CpxAR system in the reversible control of fosfomycin resistance. This may be a beneficial strategy for bacteria to relieve the fitness burden that results from fosfomycin resistance in the absence of fosfomycin.

Evaluation of fosfomycin activity against uropathogens in a fosfomycin-naive population in South India: a prospective study

AIM

The aim was to evaluate the in vitro activity of fosfomycin against common uropathogens in a fosfomycin-naive population in India.

METHODS

The authors prospectively collected and tested all consecutive isolates of Escherichia coli and Enterococcus spp. from urine samples between December 2009 and April 2010.

RESULTS

A total of 3141 isolates were included in the study, 2416 E. coli and 725 Enterococcus spp. Fosfomycin was the most active antibiotic against both pathogens with an overall susceptibility of 83 and 99% for E. coli and Enterococcus spp, respectively. Among E. coli, 47.6% of the isolates were extended-spectrum β-lactamase producing, of which 81% were susceptible to fosfomycin, while 51.5% were multidrug resistant, with 75.7% of this portion being susceptible to fosfomycin.

CONCLUSION

Fosfomycin exhibits good in vitro activity against both the uropathogens tested. Therefore, it might be considered as a treatment option for urinary tract infections in India; however, clinical trials should first reinforce the in vitro findings.

Activities of fosfomycin and rifampin on planktonic and adherent Enterococcus faecalis strains in an experimental foreign-body infection model

Enterococcal implant-associated infections are difficult to treat because antibiotics generally lack activity against enterococcal biofilms. We investigated fosfomycin, rifampin, and their combinations against planktonic and adherent Enterococcus faecalis (ATCC 19433) in vitro and in a foreign-body infection model. The MIC/MBClog values were 32/>512 μg/ml for fosfomycin, 4/>64 μg/ml for rifampin, 1/2 μg/ml for ampicillin, 2/>256 μg/ml for linezolid, 16/32 μg/ml for gentamicin, 1/>64 μg/ml for vancomycin, and 1/5 μg/ml for daptomycin. In time-kill studies, fosfomycin was bactericidal at 8× and 16× MIC, but regrowth of resistant strains occurred after 24 h. With the exception of gentamicin, no complete inhibition of growth-related heat production was observed with other antimicrobials on early (3 h) or mature (24 h) biofilms. In the animal model, fosfomycin alone or in combination with daptomycin reduced planktonic counts by ≈4 log10 CFU/ml below the levels before treatment. Fosfomycin cleared planktonic bacteria from 74% of cage fluids (i.e., no growth in aspirated fluid) and eradicated biofilm bacteria from 43% of cages (i.e., no growth from removed cages). In combination with gentamicin, fosfomycin cleared 77% and cured 58% of cages; in combination with vancomycin, fosfomycin cleared 33% and cured 18% of cages; in combination with daptomycin, fosfomycin cleared 75% and cured 17% of cages. Rifampin showed no activity on planktonic or adherent E. faecalis, whereas in combination with daptomycin it cured 17% and with fosfomycin it cured 25% of cages. Emergence of fosfomycin resistance was not observed in vivo. In conclusion, fosfomycin showed activity against planktonic and adherent E. faecalis. Its role against enterococcal biofilms should be further investigated, especially in combination with rifampin and/or daptomycin treatment.

Prevalence and Clinical Management of Complicated Urinary Tract Infections in Italy: a Prospective Multicenter Epidemiological Study in Urological Outpatients

The objectives of the study were to evaluate the prevalence of complicated urinary tract infections among Italian patients attending the urologist's office, to describe the frequency of different complication factors, the encountered bacterial pathogens and the clinical attitude of urologists in management of complicated urinary tract infections (CUTIs). The study was a prospective, multicenter study which was undertaken by office urologists throughout Italy. During the May-June 2002 timeframe, the prevalence of each urologist's diagnosis of CUTIs was noted for a 4-week slot. The prevalence of CUTIs in over 13,000 patients observed was 10.8% (n = 1201), with a trend (not statistically significant) of higher figures in the South/Islands (12.2%) with respect to Center (11.4%) or North (8.7%) of Italy. We have confirmed the significant relevance of CUTI among the Italian patients attending the urologist office and the clinical data collected may contribute to improve the diagnosis and empiric therapy of complicated urinary tract infections.

Antimicrobial Susceptibility Patterns of Contemporary Pathogens from Uncomplicated Urinary Tract Infections Isolated in a Multicenter Italian Survey: Possible Impact on Guidelines

During 2004 four Italian Laboratories assessed the prevalence of antimicrobial resistance among uropathogens causing acute uncomplicated cystitis in female out-patients. A total of 600 urine samples from individuals aged 18-65 were studied. The overall prevalence of Escherichia coli was 85.3%. Klebsiella pneumoniae, Staphylococcus saprophyticus, Proteus mirabilis, Enterococcus faecalis and other rarer species were far less represented. Determination of the antibiotic susceptibility pattern of the entire collection of E. coli (512 organisms) revealed that among the drugs analyzed ampicillin was the least active molecule with only 62.5% of the strains being inhibited. Amoxicillin-clavulanate and cefuroxime displayed a higher potency (87.7% and 89.2% respectively). Cotrimoxazole inhibited only 70.1% of the uropathogens. The three fluoquinolones tested had comparable activity ranging from 83.0% for ciprofloxacin, to 83.6% for levofloxacin and 84.9% for prulifloxacin, indicating an identical spectrum of cross resistance. Nitrofurantoin (96.7%) and fosfomycin (98.6%) were the most potent drugs. Against the whole collection of uropathogens, only cefuroxime, nitrofurantoin and fosfomycin overcame the threshold of 90% activity, with the fluoroquinolones and amoxicillin-clavulanate suffering from about 15% resistance. The results of this survey strongly support the conclusions of recent Italian guidelines concerning the best empiric treatment of UTI in this country today.

[Randomized comparative study for the assessment of a new therapeutic schedule of fosfomycin trometamol in postmenopausal women with uncomplicated lower urinary tract infection]

OBJECTIVES

To compare two therapeutic regimes in terms of bacterial eradication of post-menopausal with uncomplicated acute cystitis who complete antibiotic treatment.

MATERIALS AND METHOD

A multicenter, randomized, prospective and controlled study between two short antibiotic regimes: fosfomycin trometamol (FMT) 3g, 2 doses separated by 72hours and ciprofloxacin 250mg every 12hours for 3 days. A total of 118 post-menopausal women were enrolled in the study. They underwent an initial urine culture to know the responsible microorganism and susceptibility to treatment. This was repeated 5-7 days and 4 weeks after the treatment to evaluate bacterial eradication. Clinical symptoms and treatment safety were also evaluated.

RESULTS

There were microbiological data at the onset of the treatment in 82 women (69.49%). Of these, 27 did not have positive culture at the first visit (30.51%), 76 (64.41%) fulfilled all the protocol requirements and adverse effects from the treatment were collected in 113 (95.76%) of the patients enrolled in the study. The germs isolated most frequently were Escherichia coli (E. coli) (76.83%), Klebsiella pneumoniae (K. pneumoniae) (7.32%), Proteus mirabilis (P. mirabilis) (4.89%) and Enterococo sp. (3.66%). In terms of efficacy, no differences were detected in the proportion of patients who achieved bacterial eradication between the two study arms: 62.16% of the patients who received FMT and 58.97% of those treated with ciprofloxacin (chi-square, p=0.78). The proportion of patients who achieved clinical cure was also similar (86.49% for FMT and 82.05% for ciprofloxacin; square, p=0.59). These results indicate similar efficacy of both antibiotics in the treatment of uncomplicated lower tract urinary infection in post-menopausal women. In regards to safety data, the proportion of global adverse effects associated to the treatments was 3.45% for FMT and 9.09% for ciprofloxacin. Treatment compliance was 100% for FMT and 83.64% for ciprofloxacin.

CONCLUSIONS

The FMT administered at a dose of 3g every 72hours (2 total doses) and ciprofloxacin at a dose of 250mg every 12hours during 3 days (6 total doses) have a comparable efficacy profile in lower tract urinary infection in post-menopausal women who adequately comply with the treatment, also having comparable safety. The FMT has a better antimicrobial susceptibility profile and better rate of treatment compliance.

Genomewide overexpression screen for fosfomycin resistance in Escherichia coli: MurA confers clinical resistance at low fitness cost

To determine whether the overexpression of chromosomal genes can confer fosfomycin resistance, genomewide screening of a complete set of 5,272 plasmid-expressed open reading frames of Escherichia coli (ASKA collection) was performed. Major results are that (i) no clinical level of resistance is achieved by overexpressing chromosomal genes, except murA; (ii) this level is reached at a low fitness cost; and (iii) this cost is much lower than that imposed by other mutations conferring fosfomycin resistance.

Fosfomycin: evaluation of the published evidence on the emergence of antimicrobial resistance in Gram-negative pathogens

Fosfomycin has attracted renewed interest for the treatment of lower urinary tract and even systemic infections caused by Gram-negative pathogens with resistance to traditionally used agents. The main concern regarding the clinical utility of fosfomycin refers to the potential for the emergence of resistance during therapy. In this review, we evaluate the available published evidence regarding the mechanisms and the frequency of in vitro mutational resistance to fosfomycin in Gram-negative pathogens. We also review data regarding the emergence of resistance in clinical studies of fosfomycin therapy in various infectious syndromes and data from studies that evaluate the evolution of fosfomycin resistance over time. There appears to be discordance between the high frequency of mutational resistance to fosfomycin in vitro and the lower extent of this phenomenon in clinical studies. This discordance could at least partly be attributed to a biological cost associated with common mutations that confer resistance to fosfomycin, including decreased growth rate and low adherence to epithelial cells for the resistant mutants. The development of resistance appears to be more frequent both in vitro and in clinical studies for Pseudomonas aeruginosa in comparison with Escherichia coli, whereas relevant data for other Enterobacteriaceae are relatively scarce. The urinary tract seems to provide a favourable environment for the use of fosfomycin with a low associated likelihood for the emergence of resistance, owing to high drug concentrations and acidic pH. Additional data are needed to further clarify the optimal use of fosfomycin for different infectious syndromes caused by contemporary multidrug-resistant pathogens.

Therapeutic options for infections with Enterobacteriaceae producing carbapenem-hydrolyzing enzymes

Enterobacteriaceae that produce serine carbapenemases or metallo-β-lactamases, such as KPC, OXA-48, VIM or NDM, respectively, are spreading mostly as nosocomial pathogens worldwide. Such strains are typically resistant to most if not all available antimicrobials. Specific relevant clinical data are scarce to guide the determination of the most appropriate treatment options. Data on antimicrobial susceptibility, resistance development, synergy, pharmacokinetic and pharmacodynamic parameters of the candidate regimens, as well as the experience from the treatment of infections with nonfermenting Gram-negative pathogens, can aid in this regard. Colistin and tigecycline are most likely to be active in vitro against Enterobacteriaceae producing carbapenem-hydrolyzing β-lactamases, but resistance development is of concern. Individual members of the aminoglycoside class can also be active in vitro, while carbapenems or aztreonam (specifically for metallo-β-lactamase producers) can have low minimum inhibitory concentrations. Current data do not reliably support the use of these agents as monotherapy for systemic infections. Several expanded-spectrum cephalosporins, such as ceftazidime, may be active against OXA-48 type producers. Fosfomycin might be useful as a last-resort option as part of combination regimens. Combination antimicrobial therapy with agents exhibiting synergy might also be of benefit, until novel effective agents could become clinically available.

Daptomycin, fosfomycin, or both for treatment of methicillin-resistant Staphylococcus aureus osteomyelitis in an experimental rat model

The in vivo activities of daptomycin, fosfomycin, and a combination of both antibiotics against a clinical isolate of methicillin-resistant Staphylococcus aureus (daptomycin MIC, 0.25 μg/ml; fosfomycin MIC, 0.5 μg/ml) were evaluated in a rat model of osteomyelitis. A total of 37 rats with experimental osteomyelitis were treated for 4 weeks with either 60 mg/kg of body weight of daptomycin subcutaneously once daily, 75 mg/kg fosfomycin intraperitoneally once daily, a combination of both drugs, or a saline placebo. After the completion of treatment, animals were euthanized, and the infected tibiae were processed for quantitative bacterial culture. Bone cultures were found to be positive for methicillin-resistant S. aureus in 9 of 9 (100%) animals of the placebo group, in 9 of 9 (100%) animals treated with daptomycin, in 1 of 10 (10%) fosfomycin-treated rats, and in 1 of 9 (22.2%) rats comprising the combination group. Results of bacterial counts in the bone samples were expressed as log(10) CFU/g of bone and analyzed by using the Mann-Whitney U test followed by Bonferroni's multiple-comparison test. Based on bacterial counts, treatment with daptomycin was significantly superior to placebo, although it remained inferior to treatment with fosfomycin. No synergistic or antagonistic effect was observed for the combination therapy. No development of resistance against daptomycin or fosfomycin was observed after the 4-week treatment period.

Antimicrobial susceptibilities of commonly encountered bacterial isolates to fosfomycin determined by agar dilution and disk diffusion methods

We studied the antimicrobial activity of fosfomycin against 960 strains of commonly encountered bacteria associated with urinary tract infection using standard agar dilution and disk diffusion methods. Species studied included 3 common species of Enterobacteriaceae, Pseudomonas aeruginosa, Acinetobacter baumannii, and Stenotrophomonas maltophilia; methicillin-susceptible and -resistant Staphylococcus aureus; and vancomycin-susceptible and resistant Enterococcus faecalis and E. faecium. MICs and inhibition zone diameters were interpreted in accordance with both the currently recommended Clinical and Laboratory Standards Institute (CLSI) criteria for urinary tract isolates of Escherichia coli and Enterococcus faecalis and the European Committee on Antimicrobial Susceptibility Testing (EUCAST) criteria for Enterobacteriaceae. Tentative zone diameter interpretive criteria were developed for species not currently published by CLSI or EUCAST. Escherichia coli was uniformly susceptible to fosfomycin, as were most strains of Klebsiella pneumoniae and Enterobacter cloacae. A. baumannii was resistant to fosfomycin, while the prevalence of resistance in P. aeruginosa and S. maltophilia was greatly affected by the choice of MIC breakpoint. New tentative zone diameter criteria for K. pneumoniae, E. cloacae, S. aureus, and E. faecium were able to be set, providing some interim laboratory guidance for disk diffusion until further breakpoint evaluations are undertaken by CLSI and EUCAST.

Efficacy of fosfomycin in experimental osteomyelitis due to methicillin-resistant Staphylococcus aureus

The activity of fosfomycin was evaluated in an experimental methicillin-resistant Staphylococcus aureus (MRSA) osteomyelitis model. Eighteen rats were treated for 4 weeks with 150 mg of fosfomycin/kg of body weight intraperitoneally once daily or with saline placebo. After treatment, animals were euthanized and the infected tibiae were processed for quantitative bacterial culture. Bone cultures were positive for methicillin-resistant S. aureus in all 9 (100%) untreated controls and in 2 of 9 (22.2%) fosfomycin-treated rats. Thus, fosfomycin treatment was significantly more efficacious than placebo. No development of resistance was observed after the 4-week treatment period.

Assessing the emergence of resistance: the absence of biological cost in vivo may compromise fosfomycin treatments for P. aeruginosa infections

BACKGROUND

Fosfomycin is a cell wall inhibitor used efficiently to treat uncomplicated urinary tract and gastrointestinal infections. A very convenient feature of fosfomycin, among others, is that although the expected frequency of resistant mutants is high, the biological cost associated with mutation impedes an effective growth rate, and bacteria cannot offset the obstacles posed by host defenses or compete with sensitive bacteria. Due to the current scarcity of new antibiotics, fosfomycin has been proposed as an alternative treatment for other infections caused by a wide variety of bacteria, particularly Pseudomonas aeruginosa. However, whether fosfomycin resistance in P. aeruginosa provides a fitness cost still remains unknown.

PRINCIPAL FINDINGS

We herein present experimental evidence to show that fosfomycin resistance cannot only emerge easily during treatment, but that it is also cost-free for P. aeruginosa. We also tested if, as has been reported for other species such as Escherichia coli, Klebsiella pneumoniae and Proteus mirabilis, fosfomycin resistant strains are somewhat compromised in their virulence. As concerns colonization, persistence, lung damage, and lethality, we found no differences between the fosfomycin resistant mutant and its sensitive parental strain. The probability of acquisition in vitro of resistance to the combination of fosfomycin with other antibiotics (tobramycin and imipenem) has also been studied. While the combination of fosfomycin with tobramycin makes improbable the emergence of resistance to both antibiotics when administered together, the combination of fosfomycin plus imipenem does not avoid the appearance of mutants resistant to both antibiotics.

CONCLUSIONS

We have reached the conclusion that the use of fosfomycin for P. aeruginosa infections, even in combined therapy, might not be as promising as expected. This study should encourage the scientific community to assess the in vivo cost of resistance for specific antibiotic-bacterial species combinations, and therefore avoid reaching universal conclusions from single model organisms.

Fosfomycin for the treatment of infections caused by Gram-positive cocci with advanced antimicrobial drug resistance: a review of microbiological, animal and clinical studies

BACKGROUND

The advancing antimicrobial drug resistance in Gram-positive cocci complicates the selection of appropriate therapy. The re-evaluation of older antibiotics may prove useful in expanding relevant therapeutic options.

OBJECTIVE

We sought to evaluate fosfomycin for the treatment of infections caused by methicillin-resistant staphylococci, vancomycin-resistant enterococci, and penicillin-non-susceptible pneumococci.

METHODS

We searched in PubMed, Scopus, and the Cochrane Library for studies evaluating the antimicrobial activity of fosfomycin against the above-mentioned pathogens, or the in vivo or clinical effectiveness of fosfomycin for the treatment of infections caused by these pathogens.

RESULTS/CONCLUSIONS

As reported in the identified studies, the susceptibility rate of methicillin-resistant Staphylococcus aureus to fosfomycin was > or = 90% in 12/22, and 50-90% in 7/22 studies; the cumulative susceptibility rate was 87.9% (4240/4892 isolates). The cumulative susceptibility rate of vancomycin-resistant enterococci to fosfomycin was 30.3% (183/604 isolates), and that of penicillin-non-susceptible pneumococci was 87.2% (191/219 isolates). Clinical data show that fosfomycin, primarily in combination regimens, has been associated with clinical success in 28/29 (96.6%) cases of infection (mainly pneumonia, bacteremia, and meningitis) by fosfomycin-susceptible isolates of methicillin-resistant S. aureus. The above data support further research on the role of fosfomycin against infections caused by Gram-positive cocci with advanced antimicrobial drug resistance.

Molecular mechanisms of fosfomycin resistance in clinical isolates of Escherichia coli

To clarify the molecular mechanisms of fosfomycin resistance in clinical isolates of Escherichia coli, the murA, glpT, uhpT, uhpA, ptsI and cyaA genes were sequenced from six fosfomycin-resistant isolates. Two strains were found to harbour a mutation in the murA gene that leads to an amino acid substitution (Asp369Asn or Leu370Ile) in the target protein. The remaining four strains carried specific mutations in the glpT gene; one strain possessed a mutation and the other three strains possessed truncated versions of the GlpT transporter owing either to the presence of insertion sequences or a deletion in the coding region of the gene. Two of the strains with truncated GlpT had also lost the entire uhpT gene, which encodes another fosfomycin transporter. Uptake of specific substrates for the transporters was either totally blocked or reduced in strains possessing truncated forms of GlpT or those lacking the uhpT gene. Escherichia coli strains expressing an amino-acid-substituted MurA were at least eight-fold more resistant to fosfomycin than the strain overproducing wild-type MurA. In conclusion, novel amino acid substitutions in MurA or the loss of function of transporters were identified as mechanisms of fosfomycin resistance in clinical isolates of E. coli.

Fosfomycin: an old, new friend?

Fosfomycin (FOM) is an antibiotic which has varying application indications across the globe. European, Japanese, South African and Brazilian usage practices are much broader, involving multiple formulations of FOM than the currently limited application of FOM in the United States, where uncomplicated urinary tract infection represents the only indication for FOM-tromethamine. Based on early difficulty in determining FOMs genuine in vitro activity, there was initial skepticism about its efficacy and application range. However, in the mid 1970s, correctly executed experiments coupled with an improved understanding of microbiological concepts opened the door for broader use of FOM. During the following 40 years FOM was evaluated in pre-clinical and clinical trials in a wide range of applications and in a multitude of settings. The gathering of pharmacokinetic and pharmacodynamic data was incorporated into large scale studies in which FOM efficacy was further explored and proven. Among European nations, intravenous FOM-disodium for patients presenting with soft tissue infections, sepsis or deep seated infectious processes has become well accepted over the last two decades. The recent emergence of bacterial strains, which impede and encumber pharmacotherapy, namely, MRSA, ESBL and MSSA, lends itself to the idea of reviving long-standing, sensibly used antimicrobial agents like FOM. This review provides a comprehensive conspectus on FOM's history, mode of action, tissue penetration characteristics, resistance, antibacterial activity, combination partners and clinical uses among other facets of interest.

Role of fosfomycin tromethamine in modulating non-specific defence mechanisms in chronic uremic patients towards ESBL-producing Escherichia coli

Antimicrobial agents and polymorphonuclear cells (PMNs) have the potential to interact in such a way that improve the therapy for infectious diseases. In immunocompromised patients highly susceptible to microbial infections with high morbidity and mortality, several metabolic and functional alterations in PMNs, mostly related to microbicidal activity, are observed. Therefore, the antibiotic of choice should have a good antimicrobial effect without impairing host defences. The aim of this study is to evaluate in vitro effects of sub-inhibiting fosfomycin tromethamine (FT) concentrations on the primary functions of PMNs from healthy subjects and immunocompromised patients (haemodialysed and renal transplant recipients), against an ESBL-producing Escherichia coli, the most common aetiological agent in urinary tract infections (UTIs). FT is considered a first line drug in the eradication of UTIs due to its appropriate antimicrobial spectrum, oral bioavailability and minimal risk of microbial resistance. Our results provide evidence that FT is able to induce enhancement of the depressed phagocytic response of PMNs from patients on chronic haemodialysis and from renal transplant recipients, restoring their primary functions in vitro against ESBL-producing E. coli. All these data permit the conclusion that uremic-infected patients might additionally benefit from the immunomodulating properties of FT.

In vitro activity of prulifloxacin against Escherichia coli isolated from urinary tract infections and the biological cost of prulifloxacin resistance

Minimum inhibitory concentrations (MICs) and mutant prevention concentrations (MPCs) of prulifloxacin against 30 strains of Escherichia coli isolated from urinary tract infections as well as the 'biological cost' related to acquisition of resistance to the same drug in 10 uropathogenic E. coli were assessed. In terms of MIC(90), prulifloxacin was more potent than ciprofloxacin and levofloxacin. Prulifloxacin produced lower or equal MPC values than the other two fluoroquinolones (93.3% and 73.3% compared with levofloxacin and ciprofloxacin, respectively). Compared with susceptible strains, prulifloxacin-resistant mutants showed a reduced rate of growth (ranging from 20.0% to 98.0% in different culture media and incubation conditions) and a decreased fitness index (ranging from 0.959 to 0.999). They were also impaired in their ability to adhere to uroepithelial cells and urinary catheters (11.7-66.4% and 16.3-78.3% reduction, respectively) and showed a lower surface hydrophobicity (51.2-76.0%). They were more susceptible to ultraviolet irradiation (30.6-93.8% excess mortality), showed increased resistance to colicins and diminished transfer of plasmids (<1-8.5x10(-8) vs. 3.3x10(-7)-2.4x10(-4)). Synthesis of haemolysin and type I fimbriae and production of flagella were also adversely affected. This study demonstrates a strict relationship between acquisition of prulifloxacin resistance and loss of important virulence traits. In this transition, E. coli pays a severe biological cost that entails a general reduction of fitness, thus compromising competition with susceptible wild-type strains in the absence of the drug.

[Fosfomycin trometamol: multiple-dose regimen for the treatment of lower urinary tract infections]

INTRODUCTION

A short antibiotic regimen is recommended for the treatment of uncomplicated lower urinary tract infection. Nevertheless, the treatment to follow in other situations is not so clearly defined. When the person affected by lower urinary tract infection is not a young woman, it is recommended to treat at least 7 days, and quinolones or cotrimoxazole are the antibiotics most often used. However, because of the frequency of drug resistance in this type if infection, it is advisable to apply antibiotics with lower rates of resistance, such as fosfomycin trometamol, for longer treatment periods than the often-used single dose.

METHODS

Using the data on urinary elimination of fosfomycin after a single dose obtained in a prior study in healthy volunteers, we simulated the urinary concentrations of this antibiotic following administration of two doses. In addition, we calculated the interval of administration required to achieve urinary concentrations greater than 16 mg/L, the critical concentration of sensitivity for Escherichia coli, one of the most commonly implicated microorganisms in these infections.

RESULTS

Fosfomycin concentrations in urine persisted above the defined cut-off for 161 hours after administration of two 3-g doses of fosfomycin trometamol, 72 hours apart. This implied an efficacy time of 66% in a period of 7 days.

CONCLUSION

From the pharmacokinetic viewpoint, the optimum dosage of fosfomycin trometamol to achieve appropriate urinary concentrations along 7 days is administration of two 3-g doses, 72 hours apart.

[Activity of fosfomycin against extended-spectrum beta-lactamase producing Escherichia coli and Klebsiella pneumoniae]

INTRODUCTION

Infection due to extended-spectrum beta-lactamase (ESBL)-producing microorganisms is an emerging problem in the community; a high proportion of these microorganisms have been isolated from urine samples of women with uncomplicated urinary tract infections (UTI). The options for oral treatment of uncomplicated UTI are limited because of the multiple drug resistance typical of ESBL-producing strains.

METHODS

The in vitro activity of fosfomycin (FOS) was determined against 428 ESBL-producing strains, including 290 (68%) E. coli and 138 (32%) K. pneumoniae. Activity of fosfomycin was compared with that of amoxicillin-clavulanate (AMC), ciprofloxacin (CIP) and cotrimoxazole (SxT). MICs of AMC, CIP, and SxT, and detection of ESBL production were tested by the broth microdilution method, whereas FOS MICs were determined by the agar dilution method. ESBLs were characterized by isoelectric focusing, polymerase chain reaction (PCR) and direct sequencing of encoding genes. The genetic relationship among the isolates was determined by REP-PCR.

RESULTS

Among the 428 ESBL-producing isolates studied, 417 (97.4%) were susceptible to FOS (MIC < or = 64 microg/mL). The resistance rate of E. coli to FOS was 0.3%, and was lower than resistance to AMC (11.7%), whereas the resistance rate of K. pneumoniae was 7.2% and was equal to resistance to AMC. SxT and CIP were the least active antibiotic agents against ESBL-producing isolates (sensitivity < 50%). There were no differences in fosfomycin activity against strains expressing different types of ESBLs.

CONCLUSION

Fosfomycin showed maintained activity against ESBL-producing strains and did not present co-resistance with other antimicrobial groups.

In vitro activity of fosfomycin against ciprofloxacin-resistant or extended-spectrum beta-lactamase-producing Escherichia coli isolated from urine and blood

In this study, we evaluated the in vitro activity of fosfomycin and 7 other comparator agents against 307 Escherichia coli isolates including ciprofloxacin-resistant or extended-spectrum beta-lactamase (ESBL)-producing isolates. Bacterial isolates were collected from urine and blood from patients at a Korean tertiary-care hospital. Among 307 E. coli isolates, 30.3% were resistant to ciprofloxacin (MIC(90), >32 mg/L) and 7.8% produced ESBLs. The highest resistance rate was observed in ampicillin (69.7%), followed by trimethoprim-sulfamethoxazole (43.0%), and then amoxicillin-clavulanate (32.2%). All isolates were susceptible to imipenem (MIC(90), 0.125 mg/L). All but 1 isolate was susceptible to fosfomycin (MIC(90), 16 mg/L), regardless of the collected sources, ciprofloxacin resistance, and ESBL production. The data showed excellent activity of fosfomycin against E. coli isolates including fluoroquinolone-resistant strains. The clinical usefulness of fosfomycin, as a 1st-line therapy for urinary tract infection, should be evaluated further, especially in regions where ciprofloxacin resistance rates are high.

In vitro activity of fosfomycin against extended-spectrum-beta-lactamase-producing Escherichia coli and Klebsiella pneumoniae: comparison of susceptibility testing procedures

The agar dilution, broth microdilution, and disk diffusion methods were compared to determine the in vitro susceptibility of 428 extended-spectrum-beta-lactamase (ESBL)-producing Escherichia coli and Klebsiella pneumoniae to fosfomycin. Fosfomycin showed very high activity against all ESBL-producing strains. Excellent agreement between the three susceptibility methods was found for E. coli, whereas marked discrepancies were observed for K. pneumoniae.

Second-line treatment of limb-threatening diabetic foot infections with intravenous fosfomycin

Diabetic foot infections (DFI) expanding to bones and joints are associated with a poor prognosis of limb salvage. The bactericidal epoxide fosfomycin accumulates in inflamed soft and bone tissue, and may represent a potential treatment option for targeting severe DFI. Fifty-two patients (35 men, 17 women, mean age 62.9 +/- SD 9.2 years) with limb-threatening DFI (that is, Wagner grade 3 and higher) were enrolled in a multi-center compassionate use program of fosfomycin. Twenty-two patients (42.4%) had unsuccessfully been pretreated with other antimicrobials. Besides standard treatment (topical wound care and surgical debridement), eligible subjects received a combination of 8 to 24 g fosfomycin daily, and a conventional antibiotic agent, usually a beta-lactam compound. Treatment duration averaged 14.4 +/- 8.3 days. Limb-sparing surgery was possible in 48 patients (92.3%, 95% confidence interval 81.5-97.9%). Only four participants faced mild drug-related side effects (nausea, rash). Logistic regression analysis showed a trend towards better results with prolonged treatment, whereas a dose increase above 12 g daily did not affect outcomes. In DFI being resistant to conventional antibiotic agents, intravenous fosfomycin offers an effective treatment choice that may increase the likelihood of limb preservation. The present data warrant a larger comparative trial to stabilize effect estimates.

Antibiotic abscess penetration: fosfomycin levels measured in pus and simulated concentration-time profiles

The present study was performed to evaluate the ability of fosfomycin, a broad-spectrum antibiotic, to penetrate into abscess fluid. Twelve patients scheduled for surgical or computer tomography-guided abscess drainage received a single intravenous dose of 8 g of fosfomycin. The fosfomycin concentrations in plasma over time and in pus upon drainage were determined. A pharmacokinetic model was developed to estimate the concentration-time profile of fosfomycin in pus. Individual fosfomycin concentrations in abscess fluid at drainage varied substantially, ranging from below the limit of detection up to 168 mg/liter. The fosfomycin concentrations in pus of the study population correlated neither with plasma levels nor with the individual ratios of abscess surface area to volume. This finding was attributed to highly variable abscess permeability. The average concentration in pus was calculated to be 182 +/- 64 mg/liter at steady state, exceeding the MIC(50/90)s of several bacterial species which are commonly involved in abscess formation, such as streptococci, staphylococci, and Escherichia coli. Hereby, the exceptionally long mean half-life of fosfomycin of 32 +/- 39 h in abscess fluid may favor its antimicrobial effect because fosfomycin exerts time-dependent killing. After an initial loading dose of 10 to 12 g, fosfomycin should be administered at doses of 8 g three times per day to reach sufficient concentrations in abscess fluid and plasma. Applying this dosing regimen, fosfomycin levels in abscess fluid are expected to be effective after multiple doses in most patients.