土井 洋平

Twenty patients with carbapenem-resistant Enterobacteriaceae (CRE) infections were treated with meropenem-vaborbactam. Thirty-day clinical success and survival rates were 65% (13/20) and 90% (18/20), respectively. Thirty-five percent of patients had microbiologic failures within 90 days. One patient developed a recurrent infection due to meropenem-vaborbactam non-susceptible, ompK36 porin mutant Klebsiellapneumoniae.

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

The case of a patient with left ventricular assist device (LVAD)-associated endocarditis involving multiple clones of Staphylococcus aureus is presented. Different clones with distinct colony morphology were identified from blood cultures collected on the same day and showed diverse antimicrobial resistance patterns. In addition, a difference in antimicrobial susceptibility was observed even within an identical clone recovered 400 days apart due to the loss of SCCmec for methicillin and modification of the 23S rRNA target site for linezolid during a long-term treatment course.

Carbapenem-resistant (CR) Gram-negative infections, including those caused by Enterobacteriaceae and the non-fermenters, represent the greatest unmet need for new effective treatments. The clinical development of new antibiotics for the treatment of CR infections is challenging and should focus on the individual pathogens irrespective of the infection site. However, the drug approval pathway is generally infection-site specific and rarely includes such drug-resistant pathogens. To overcome this limitation, a streamlined clinical development program may include a pathogen-focused clinical study, such as the CREDIBLE-CR study, to meet the expectations of some health authorities (ie, the European Medicines Agency [EMA]) and the medical community. Cefiderocol is a novel siderophore cephalosporin designed to target CR pathogens, including CR strains of Enterobacteriaceae (CRE), Pseudomonas aeruginosa, Acinetobacter baumannii, and also Stenotrophomonas maltophilia, which is intrinsically CR. The CREDIBLE-CR study was planned to evaluate cefiderocol in patients with CR Gram-negative infections regardless of species or infection-site source. Rapid diagnostic testing and/or selective media were provided to facilitate detection of CR pathogens to rapidly enroll patients with nosocomial pneumonia, bloodstream infection/sepsis, or complicated urinary tract infection. Patients were randomized 2:1 to receive cefiderocol or best available therapy. There were no pre-specified statistical hypotheses for this study, as the sample size was driven by enrollment feasibility and not based on statistical power calculations. The objective of the CREDIBLE-CR study was to provide descriptive evidence of the efficacy and safety of cefiderocol for the target population of patients with CR infections, including the non-fermenters. The CREDIBLE-CR study is currently the largest pathogen-focused, randomized, open-label, prospective, Phase 3 clinical study to investigate a new antibiotic in patients with CR Gram-negative infections. Here we describe the design of this pathogen-focused study and steps taken to aid patient enrollment into the study within an evolving regulatory environment. ClinicalTrialsgov registration: NCT02714595. EUDRA-CT registration: 2015-004703-23.

The efficacy and safety of intrathecal (ITH) or intraventricular (IVT) colistin in addition to intravenous (IV) colistin for meningitis and ventriculitis due to carbapenem-resistant Acinetobacter baumannii (CRAB) is unclear. In this retrospective observational study of 40 patients with post-neurosurgical meningitis and ventriculitis due to CRAB, 33 patients without concomitant infection received appropriate dosage regimens of IV colistin. Of the 33 patients, 17 received additional ITH/IVT colistin and 16 received only IV colistin. The 14-day, 30-day and in-hospital mortality rates were nominally lower for patients who received ITH/IVT colistin adjunctive therapy versus patients who received only IV colistin (24% vs. 38%, 29% vs. 56% and 29% vs. 56%, respectively). The costs of treatment were significantly lower, the lengths of hospital and intensive care unit (ICU) stay were significantly shorter, and the number of ventilator days was significantly less among patients who received ITH/IVT colistin compared with patients who did not receive ITH/IVT colistin. The initial Acute Physiology and Chronic Health Evaluation (APACHE) II and Glasgow Coma Scale (GCS) scores were associated with 30-day mortality with odds ratios (95% confidence intervals) of 1.21 (1.08–1.46) and 0.77 (0.44–0.85), respectively. Chemical meningitis from ITH/IVT colistin was mild and resolved spontaneously. Treatment of post-neurosurgical CRAB meningitis and ventriculitis with ITH/IVT colistin as an adjunct to IV colistin was associated with shorter lengths of hospital and ICU stay and a trend to lower mortality, especially among severely ill patients.

We report here the draft genome sequences of four blaKPC-containing bacteria identified as Klebsiella aerogenes, Citrobacter freundii, and Citrobacter koseri. Additionally, we report the draft genome sequence of a K. aerogenes strain that did not contain a blaKPC gene but was isolated from the patient who had the blaKPC-2- containing K. aerogenes strain.

Fosfomycin maintains activity against most Escherichia coli clinical isolates, but the growth of E. coli colonies within the zone of inhibition around the fosfomycin disk is occasionally observed upon susceptibility testing. We aimed to estimate the frequency of such nonsusceptible inner colony mutants and identify the underlying resistance mechanisms. Disk diffusion testing of fosfomycin was performed on 649 multidrug-resistant E. coli clinical isolates collected between 2011 and 2015. For those producing inner colonies inside the susceptible range, the parental strains and their representative inner colony mutants were subjected to MIC testing, whole-genome sequencing, reverse transcription-quantitative PCR (qRT-PCR), and carbohydrate utilization studies. Of the 649 E. coli clinical isolates, 5 (0.8%) consistently produced nonsusceptible inner colonies. Whole-genome sequencing revealed the deletion of uhpT encoding hexose-6-phosphate antiporter in 4 of the E. coli inner colony mutants, while the remaining mutant contained a nonsense mutation in uhpA. The expression of uhpT was absent in the mutant strains with uhpT deletion and was not inducible in the strain with the uhpA mutation, unlike in its parental strain. All 5 inner colony mutants had reduced growth on minimal medium supplemented with glucose-6-phosphate. In conclusion, fosfomycin-nonsusceptible inner colony mutants can occur due to the loss of function or induction of UhpT but are rare among multidrug-resistant E. coli clinical strains. Considering that these mutants carry high biological costs, we suggest that fosfomycin susceptibility of strains that generate inner colony mutants can be interpreted on the basis of the zone of inhibition without accounting for the inner colonies.

FosA proteins confer fosfomycin resistance to Gram-negative pathogens via glutathione-mediated modification of the antibiotic. In this study, we assessed whether inhibition of FosA by sodium phosphonoformate (PPF) (foscarnet), a clinically approved antiviral agent, would reverse fosfomycin resistance in representative Gram-negative pathogens. The inhibitory activity of PPF against purified recombinant FosA from Escherichia coli (FosA3), Klebsiella pneumoniae (FosA(KP)), Enterobacter cloacae (FosA(EC)), and Pseudomonas aeruginosa (FosA(PA)) was determined by steadystate kinetic measurements. The antibacterial activity of PPF against FosA in clinical strains of these species was evaluated by susceptibility testing and time-kill assays. PPF increased the Michaelis constant (K-m) for fosfomycin in a dose-dependent manner, without affecting the maximum rate (V-max) of the reaction, for all four FosA enzymes tested, indicating a competitive mechanism of inhibition. Inhibitory constant (K-i) values were 22.6, 35.8, 24.4, and 56.3 mu M for FosA(KP), FosA(EC), FosA(PA), and FosA3, respectively. Addition of clinically achievable concentrations of PPF (similar to 667 mu M) reduced the fosfomycin MICs by >= 4-fold among 52% of the K. pneumoniae, E. cloacae, and P. aeruginosa clinical strains tested and led to a bacteriostatic or bactericidal effect in time-kill assays among representative strains. PPF inhibits FosA activity across Gram-negative species and can potentiate fosfomycin activity against the majority of strains with chromosomally encoded fosA. These data suggest that PPF may be repurposed as an adjuvant for fosfomycin to treat infections caused by some FosAproducing, multidrug-resistant, Gram-negative pathogens.

Antibiotics are unable to remove biofilms from surgical implants. This high antibiotic tolerance is related to bacterial persisters, a sub-population of bacteria phenotypically tolerant to antibiotics secondary to a reduced metabolic state. WLBU2 is an engineered cationic amphipathic peptide designed to maximize antimicrobial activity with minimal mammalian cell toxicity. The objective of this study was to test the ability of WLBU2 to remove Staphylococcus aureus surgical implant biofilms. WLBU2 effectively treated S. aureus biofilms formed by a variety of clinical MSSA and MRSA strains and created culture-negative implants in the in vitro biofilm model. Blocking bacterial metabolism by inhibiting oxidative phosphorylation did not affect WLBU2 killing compared to decreased killing by cefazolin. In the surgical implant infection animal model, WLBU2 decreased biofilm mass as compared to control, untreated samples. WLBU2 could rapidly eliminate implants in vitro and had sufficient efficacy in vivo with minimal systemic toxicity.

We describe regional differences in therapy for bloodstream infection (BSI) caused by extended-spectrum beta-lactamase-producing Enterobacteriaceae (ESBL-E) or carbapenemase-producing Enterobacteriaceae (CPE). Patients (n = 1482) in 12 countries from an observational study of BSI caused by ESBL-E or CPE were included. Multivariate logistic regression was used to calculate adjusted odds ratios (aORs) for the influence of country of recruitment on empirical use of beta-lactam/beta-lactamase inhibitors (BLBLIs) or carbapenems, targeted use of BLBLIs for ESBL-E and use of targeted combination therapy for CPE. Compared with Spain, BLBLI use for empirical therapy was least likely in sites from Israel (aOR 0.34, 95% CI 0.14-0.81), Greece (aOR 0.49, 95% CI 0.26-0.94) and Canada (aOR 0.31, 95% CI 0.11-0.88) but more likely in Italy (aOR 1.58, 95% CI 1.11-2.25) and Turkey (aOR 2.09, 95% CI 1.14-3.81). Empirical carbapenem use was more likely in sites from Taiwan (aOR 1.73, 95% CI 1.03-2.92) and USA (aOR 1.89, 95% CI 1.053.39) and less likely in Italy (aOR 0.44, 95% CI 0.28-0.69) and Canada (aOR 0.10, 95% CI 0.01-0.74). Targeted BLBLIs for ESBL-E was more likely in Italian sites. Treatment at sites within Israel, Taiwan, Turkey and Brazil was associated with less combination therapy for CPE. Although this study does not provide precise data on the relative prevalence of ESBL-E or CPE, significant variation in therapy exists across countries even after adjustment for patient factors. Better understanding of what influences therapeutic choices for these infections will aid antimicrobial stewardship efforts. (C) 2017 Elsevier B.V. and International Society of Chemotherapy. All rights reserved.