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We report in vitro susceptibility data from five consecutive annual SIDERO-WT surveillance studies (2014-2019) for cefiderocol and comparators tested against Gram-negative clinical isolates from North America and Europe. CLSI broth microdilution was used to determine MICs for Enterobacterales (n=31,896), Pseudomonas aeruginosa (n=7,700), Acinetobacter baumannii complex (n=5,225), Stenotrophomonas maltophilia (n=2,030), and Burkholderia cepacia complex (n=425). MICs were interpreted by CLSI-approved clinical breakpoints (February 2021). Cefiderocol inhibited 99.8%, 96.7%, 91.6%, and 97.7% of all Enterobacterales, meropenem-nonsusceptible, ceftazidime-avibactam-nonsusceptible, and ceftolozane-tazobactam-nonsusceptible isolates, respectively, at ≤4 μg/ml (susceptible breakpoint). Cefiderocol inhibited 99.9%, 99.8%, 100%, and 99.8% of all P. aeruginosa, meropenem-nonsusceptible, ceftazidime-avibactam-nonsusceptible, and ceftolozane-tazobactam-nonsusceptible isolates, respectively, at ≤4 μg/ml (susceptible breakpoint). Cefiderocol inhibited 96.0% of all A. baumannii complex isolates and 94.2% of meropenem-nonsusceptible isolates at ≤4 μg/ml (susceptible breakpoint), and 98.6% of S. maltophilia isolates at ≤1 μg/ml (susceptible breakpoint). B. cepacia complex isolates tested with a MIC50 of ≤0.03 μg/ml and MIC90 of 0.5 μg/ml. Annual cefiderocol percent susceptible rates for Enterobacterales (North America, range 99.6-100%/year; Europe, range 99.3-99.9%/year) and P. aeruginosa (99.8-100%; 99.9-100%) were unchanged from 2014 to 2019. Annual percent susceptible rates for A. baumannii complex demonstrated sporadic, non-directional differences (97.5-100%; 90.4-97.5%); the wider range for Europe (∼7%) was due to isolates from Russia. Annual percent susceptible rates for S. maltophilia showed minor, non-directional differences (96.4-100%; 95.6-100%). We conclude that clinical isolates of Enterobacterales (99.8% susceptible), P. aeruginosa (99.9%), A. baumannii (96.0%), and S. maltophilia (98.6%) collected in North America and Europe from 2014 to 2019 were highly susceptible to cefiderocol.

In 2017, the Clinical and Laboratory Standards Institute (CLSI) Subcommittee on Antimicrobial Susceptibility Testing approved the use of iron-depleted cation-adjusted Mueller-Hinton broth (ID-CAMHB) prepared with Chelex® 100 resin (Bio-Rad Laboratories, Hercules, CA) to determine MICs for cefiderocol. The current study examined the reproducibility of cefiderocol MICs generated for 19 clinical isolates of Gram-negative bacilli, with CAMHB produced by three manufacturers; each of the 19 isolates was tested for 10 replicates in ID-CAMHB from each manufacturer. When analyzed by individual media lot, greater than 95% of MIC results were within ± one doubling-dilution of the mode for each of the 19 isolates tested. The remaining 5.0% of MIC results were within ± two doubling-dilutions of the modal MIC. For all media lots combined, 92.2% of MIC results were within ± one doubling-dilution of the modal MIC for each isolate, 99.8% were within ± two doubling-dilutions and 100% were within three doubling-dilutions.

Cefiderocol (S-649266) is a parenteral siderophore cephalosporin in phase III of clinical development. In this study, we determined the in vitro susceptibility to cefiderocol and comparators of a 2015-2016 collection of 8954 clinical isolates of Gram-negative bacilli (GNB), provided by 100 clinical laboratories in North America and Europe, using the Clinical and Laboratory Standards Institute broth microdilution method. Iron-depleted cation-adjusted Mueller-Hinton broth was used to test cefiderocol. The concentration of cefiderocol inhibiting 90% of isolates (MIC90) was 0.5 mg/L (North America; n=2470) and 1 mg/L (Europe; n=3,543) for Enterobacteriaceae, 0.5 mg/L (North America; n=619) and 0.5 mg/L (Europe; n=921) for Pseudomonas aeruginosa, 1 mg/L (North America; n=308) and 2 mg/L (Europe; n=664) for Acinetobacter spp., 0.5 mg/L (North America; n=165) and 0.25 mg/L (Europe; n=175) for Stenotrophomonas maltophilia, and 0.12 mg/L (North America; n=40) and 0.5 mg/L (Europe; n=49) for Burkholderia cepacia complex spp. Cefiderocol MICs were ≤4 mg/L for 99.9% (6005/6013) of Enterobacteriaceae, 99.9% (1539/1540) of P. aeruginosa, 96.4% (937/972) of Acinetobacter spp., 99.4% (338/340) of S. maltophilia, and 94.4% (84/89) of Burkholderia cepacia complex spp. isolates tested. Against meropenem-non-susceptible isolates, MICs to cefiderocol were ≤4 mg/L for 99.6% (245/246) of Enterobacteriaceae, 99.7% (394/395) of P. aeruginosa, 96.1% (540/562) of Acinetobacter spp., and 87.1% (27/31) of B. cepacia complex spp. We conclude that cefiderocol demonstrated potent in vitro activity (MIC ≤4 mg/L) against the majority (99.4%, 8903/8954) of clinical isolates of GNB in a recent (2015-2016), multi-continent collection, including carbapenem-non-susceptible isolates.

Objectives The present study evaluated the sustained kill and the potential for resistance development of Stenotrophomonas maltophilia exposed to a human-simulated exposure of cefiderocol over 72 h in in vitro and in vivo infection models. Methods A total of seven S. maltophilia isolates with cefiderocol MICs of 0.03–0.5 mg/L were utilized. The sustained bactericidal activity compared with the initial inoculum and the appearance of resistance after the 72 h treatment were evaluated in both an in vitro chemostat model (four strains) and an in vivo murine thigh infection model (six strains) under the human-simulated exposure of cefiderocol (2 g every 8 h as a 3 h infusion). Results In the in vitro model, regrowth was observed for three of four tested isolates and resistance emergence (>2-dilution MIC increase) was observed for all of the four test isolates. Conversely, sustained killing over 72 h and no resistance emergence were observed for all of the six tested isolates in the in vivo models. The mechanism of all resistant isolates that appeared only in the in vitro chemostat studies was a mutation in the tonB-exbB-exbD region, which contributes to the energy transduction on the iron transporters. Conclusions The discrepancy in the sustained efficacy and resistance emergence between in vivo and in vitro models appears to be due to the resistance acquisition mechanism caused by mutation in the tonB-exbB-exbD region developing in the enriched media utilized in vitro. These studies reveal the in vivo bactericidal activity and the low potential for development of resistance among Stenotrophomonas evaluated under human-simulated exposures.

Cefiderocol is a novel siderophore cephalosporin antibiotic with broad coverage against difficult-to-treat Gram-negative bacteria, including those resistant to carbapenems. Its activity against Stenotrophomonas maltophilia was investigated in vitro against clinical isolates and in lung infection models using strains either resistant (SR202006) or susceptible (SR201934, SR200614) to trimethoprim-sulfamethoxazole., Cefiderocol is a novel siderophore cephalosporin antibiotic with broad coverage against difficult-to-treat Gram-negative bacteria, including those resistant to carbapenems. Its activity against Stenotrophomonas maltophilia was investigated in vitro against clinical isolates and in lung infection models using strains either resistant (SR202006) or susceptible (SR201934, SR200614) to trimethoprim-sulfamethoxazole. Cefiderocol demonstrated potent in vitro activity against all 217 S. maltophilia clinical isolates tested (MIC50, 0.063 μg/ml; MIC90, 0.25 μg/ml). Cefiderocol also demonstrated low MICs against the trimethoprim-sulfamethoxazole-resistant S. maltophilia strains (i.e., SR202006; MIC, 0.125 μg/ml). In a neutropenic mouse lung infection model, cefiderocol (30 mg/kg body weight and 100 mg/kg) demonstrated a significant, dose-dependent reduction in the lung viable bacteria cell count compared with untreated controls in S. maltophilia infection and was the only antibiotic tested to show a similar significant effect in a trimethoprim-sulfamethoxazole-resistant S. maltophilia infection. In immunocompetent rat lung infection models of S. maltophilia, humanized dosing of cefiderocol (2 g every 8 h) and meropenem (1 g every 8 h) revealed pharmacokinetic profiles similar to those in human subjects, and the humanized cefiderocol dosing significantly reduced the lung viable bacteria cell count compared with baseline controls, which received no intervention. Together, the results from these studies suggest that cefiderocol could provide an effective alternative treatment option for S. maltophilia infections in the lower respiratory tract, particularly strains resistant to empirical antibiotics, such as trimethoprim-sulfamethoxazole or minocycline.

Activities of cefiderocol under simulated human plasma concentrations at the recommended dosing regimen of 2 g every 8 h with a 3-h infusion were evaluated using an in vitro chemostat model. Against a total of 6 meropenem-resistant Gram-negative strains with cefiderocol MICs of 0.5 to 4 μg/ml, including metallo-β-lactamase producers and carbapenem-resistant Acinetobacter baumannii, cefiderocol treatment showed a bactericidal effect within 8 h and sustained efficacy with no marked bacterial regrowth over 24 h.

ObjectivesMany carbapenem-resistant (CR) Gram-negative (GN) pathogens exhibit MDR, meaning few therapeutic options are available for CR-GN infections. Cefiderocol, a siderophore cephalosporin, has demonstrated in vitro efficacy against CR-GN bacteria. In the SIDERO-CR-2014–2016 surveillance study, European clinical isolates comprising carbapenem-non-susceptible (CarbNS) Enterobacterales and MDR non-fermenters were tested against cefiderocol and comparators.MethodsCefiderocol MICs were determined using iron-depleted CAMHB, and comparators using CAMHB, per recommended CLSI methodology. Carbapenemase gene profiles were determined using PCR.ResultsIsolates (N = 870) from 23 European countries comprised CarbNS Enterobacterales (n = 457), MDR Pseudomonas aeruginosa (n = 177) and MDR Acinetobacter baumannii (n = 236). The most common carbapenemases were KPC (52%), OXA-48-like (19%), VIM (14%) and NDM (8%) in Enterobacterales, VIM (41%) in P. aeruginosa and OXA-23-like (57%) and OXA-24/40-like (37%) in A. baumannii. Most carbapenemase-producing isolates (65%) co-carried ESBLs. Approximately half of P. aeruginosa isolates were negative for carbapenemases, compared with 10% of Enterobacterales and 3% of A. baumannii. A similar proportion of Enterobacterales were susceptible to cefiderocol (81.6%; 79.0% of VIM producers; 51.4% of NDM producers; based on EUCAST breakpoint values) compared with comparator antimicrobial agents, including colistin (76.4%; 93.5% of VIM producers; 78.4% of NDM producers) and ceftazidime/avibactam (76.6%; 1.6% of VIM producers; 2.7% of NDM producers). Of P. aeruginosa isolates, 98.3% were susceptible to cefiderocol (100% of VIM producers), similar to colistin (100%). Against A. baumannii, 94.9% had cefiderocol MIC ≤2 mg/L and 93.6% of isolates were susceptible to colistin.ConclusionsCefiderocol demonstrated potent activity against CarbNS and MDR GN bacteria, including non-fermenters and a wide variety of MBL- and serine-β-lactamase-producing strains.

OBJECTIVES We assessed the activity of the novel siderophore cephalosporin, cefiderocol and selected other antibacterial agents against Gram-negative bacterial isolates in Europe. METHODS Isolates were obtained between 2013 and 2018 from European countries participating in the SIDERO-WT and SIDERO-Proteeae multinational surveillance studies. Isolates were categorised by infection site, focusing on bloodstream infections, hospital-acquired/ventilator-associated bacterial pneumonia (HABP/VABP), complicated intra-abdominal infections and complicated urinary tract infections. Cefiderocol activity was compared with ceftazidime-avibactam, ceftolozane-tazobactam, colistin and meropenem using standard susceptibility testing methods. European Committee on Antimicrobial Susceptibility Testing (EUCAST) breakpoints were used to interpret susceptibility data. RESULTS Isolates (n = 20 911) were collected from 145 sites in 24 countries in Europe, the highest proportion (34%) being from patients with HABP/VABP. Enterobacterales (66.6% of isolates) were more frequent than glucose non-fermenting species (33.4%) overall, with some differences between infection sites. Across all infection sites, the MIC50/MIC90 for cefiderocol was ≤0.5/≤2 mg/L for Enterobacter spp., ≤0.25/

Objectives The siderophore cephalosporin cefiderocol possesses in vitro activity against MDR Gram-negative bacteria. The stability of cefiderocol against serine- and metallo-type carbapenemases has been reported previously, but little is known about how cefiderocol interacts with chromosomal AmpC β-lactamases. We investigated a number of features of cefiderocol, namely antibacterial activity against AmpC overproducers, stability against AmpC β-lactamases and propensity for AmpC induction using Pseudomonas aeruginosa and Enterobacter cloacae. Methods MICs were determined by broth microdilution according to CLSI guidelines. The MIC of cefiderocol was determined in iron-depleted CAMHB. Hydrolysis of the antibiotics was determined by monitoring the changes in the absorbance in the presence of AmpC β-lactamase, and AmpC induction was evaluated by double disc diffusion and nitrocefin degradation assays. Results The MICs of ceftazidime and cefepime for PAO1 increased 4- to 16-fold with inactivation of either ampD or dacB, whereas cefiderocol MICs were little affected by these inactivations (

Background Metallo-β-lactamases (MBLs; eg, NDM, VIM, and IMP) can inactivate most commonly-used β-lactam antibiotics, including carbapenems. Infections caused by MBL producers are difficult to treat due to their resistance to many antibiotics. Cefiderocol (CFDC) is a siderophore cephalosporin antibiotic approved in the USA in 2019, with potent activity against carbapenem-resistant Gram-negative bacteria (GNB), including both serine- and metallo-carbapenemase positive strains. We evaluated the in vitro activity of CFDC and comparator agents against MBL-producing strains of GNB from North America and Europe in 3 years’ of consecutive surveillance studies (SIDERO-WT-2014–2016). Methods Susceptibility testing for CFDC, ceftazidime-avibactam (CZA), ceftolozane-tazobactam (C/T), meropenem (MEM), cefepime (FEP), ciprofloxacin (CIP), and colistin (CST) was performed by broth microdilution according to CLSI guidance. CFDC was tested in iron-depleted medium. A total of 275 MBL-producing strains, consisting of 120 Enterobacterales (45 NDM; 75 VIM), 5 NDM-producing Acinetobacter baumannii, and 150 Pseudomonas aeruginosa (134 VIM; 16 IMP), identified among 4985 (654 Enterobacterales and 4331 non-fermenters) MEM non-susceptible (based on CLSI breakpoints) strains were used for the current analysis. Results The minimum inhibitory concentration (MIC) range and MIC90 for CFDC and comparators for each MBL-producing organism group are shown in the Table. Against NDM-producing Enterobacterales, of which 42% and 33% were isolated in Turkey and Russia, respectively, CFDC inhibited the growth of 84% of isolates tested at ≤4 µg/mL. CFDC MIC90 was 4 μg/mL for VIM-producing Enterobacterales (41% and 31% isolated in Greece and Italy, respectively), 1 μg/mL for VIM-producing P. aeruginosa (50% isolated in Russia), and 4 μg/mL for IMP-producing P. aeruginosa (88% isolated in Czech Republic). Other comparators (except for CST) were not active against these MBL producers. Table. MIC range and MIC90 (μg/mL) for CFDC and comparators of MBL-producing organisms Conclusion CFDC inhibited the growth of 100% of MBL-positive GNB at ≤8 mg/mL and showed MIC90 of 4 μg/mL against all 275 MBL producers, indicating that CFDC has high potential for treating infections caused by these difficult-to-treat strains. Disclosures Miki Takemura, MSc, Shionogi & Co., Ltd. (Employee) Krystyna Kazmierczak, PhD, Shionogi & Co., Ltd. (Independent Contractor) Daniel F. Sahm, PhD, IHMA (Employee)Pfizer, Inc. (Consultant)Shionogi & Co., Ltd. (Independent Contractor) Roger Echols, MD, Shionogi Inc. (Consultant) Yoshinori Yamano, PhD, Shionogi & Co., Ltd. (Employee)

Carbapenem-resistant gram-negative bacteria including Enterobacteriaceae as well as nonfermenters, such as Pseudomonas aeruginosa and Acinetobacter baumannii, have emerged as significant global clinical threats. Although new agents have recently been approved, none are active across the entire range of resistance mechanisms presented by carbapenem-resistant gram-negative bacteria. Cefiderocol, a novel siderophore cephalosporin, has been shown in large surveillance programs and independent in vitro studies to be highly active against all key gram-negative causative pathogens isolated from patients with hospital-acquired or ventilator-associated pneumonia, bloodstream infections, or complicated urinary tract infections. The improved structure, the novel mode of entry into bacteria, and its stability against carbapenemases enables cefiderocol to exhibit high potency against isolates that produce carbapenemases of all classes or are resistant due to porin channel mutations and/or efflux pump overexpression. Resistance to cefiderocol is uncommon and appears to be multifactorial.

The pharmacokinetic (PK) and pharmacodynamic (PD) parameters which correlated with the in vivo efficacy of cefiderocol were evaluated using neutropenic murine thigh and lung infection models in which the infections were caused by a variety of Gram-negative bacilli., The pharmacokinetic (PK) and pharmacodynamic (PD) parameters which correlated with the in vivo efficacy of cefiderocol were evaluated using neutropenic murine thigh and lung infection models in which the infections were caused by a variety of Gram-negative bacilli. The dose fractionation study using the thigh infection model in which the infection was caused by Pseudomonas aeruginosa showed that the cumulative percentage of a 24-h period that the free drug concentration in plasma exceeds the MIC (%fT>MIC) rather than the free peak level divided by the MIC (fCmax/MIC) and the area under the free concentration-time curve over 24 h divided by the MIC (fAUC/MIC) was the PK/PD parameter that best correlated with efficacy. The study with multiple carbapenem-resistant strains revealed that the %fT>MIC determined in iron-depleted cation-adjusted Mueller-Hinton broth (ID-CAMHB) better reflected the in vivo efficacy of cefiderocol than the %fT>MIC determined in cation-adjusted Mueller-Hinton broth (CAMHB). The mean %fT>MIC of cefiderocol required for a 1-log10 reduction against 10 strains of Enterobacteriaceae and 3 strains of Pseudomonas aeruginosa in the thigh infection models were 73.3% and 77.2%, respectively. The mean %fT>MIC for Enterobacteriaceae, P. aeruginosa, Acinetobacter baumannii, and Stenotrophomonas maltophilia in the lung infection model were 64.4%, 70.3%, 88.1%, and 53.9%, respectively. These results indicate that cefiderocol has potent efficacy against Gram-negative bacilli, including carbapenem-resistant strains, irrespective of the bacterial species, in neutropenic thigh and lung infection models and that the in vivo efficacy correlated with the in vitro MIC under iron-deficient conditions.

Herein, we evaluated sustainability of humanized exposures of cefiderocol in vivo over 72 h against pathogens with cefiderocol MICs of 0.5 to 16 μg/ml in the neutropenic murine thigh model. In Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacteriaceae displaying MICs of 0.5 to 8 μg/ml (n = 11), sustained kill was observed at 72 h among 9 isolates., Herein, we evaluated sustainability of humanized exposures of cefiderocol in vivo over 72 h against pathogens with cefiderocol MICs of 0.5 to 16 μg/ml in the neutropenic murine thigh model. In Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacteriaceae displaying MICs of 0.5 to 8 μg/ml (n = 11), sustained kill was observed at 72 h among 9 isolates. Postexposure MICs revealed a single 2-dilution increase in one animal compared with controls (1/54 samples, 1.8%) at 72 h. Adaptive resistance during therapy was not observed.

S-649266 is a novel siderophore cephalosporin antibiotic with a catechol moiety on the 3-position side chain. Two sets of clinical isolate collections were used to evaluate the antimicrobial activity of S-649266 against Enterobacteriaceae . These sets included 617 global isolates collected between 2009 and 2011 and 233 β-lactamase-identified isolates, including 47 KPC-, 49 NDM-, 12 VIM-, and 8 IMP-producers. The MIC 90 values of S-649266 against the first set of Escherichia coli , Klebsiella pneumoniae , Serratia marcescens , Citrobacter freundii , Enterobacter aerogenes , and Enterobacter cloacae isolates were all ≤1 μg/ml, and there were only 8 isolates (1.3%) among these 617 clinical isolates with MIC values of ≥8 μg/ml. In the second set, the MIC values of S-649266 were ≤4 μg/ml against 109 strains among 116 KPC-producing and class B (metallo) carbapenemase-producing strains. In addition, S-649266 showed MIC values of ≤2 μg/ml against each of the 13 strains that produced other types of carbapenemases such as SME, NMC, and OXA-48. The mechanisms of the decreased susceptibility of 7 class B carbapenemase-producing strains with MIC values of ≥16 μg/ml are uncertain. This is the first report to demonstrate that S-649266, a novel siderophore cephalosporin, has significant antimicrobial activity against Enterobacteriaceae , including strains that produce carbapenemases such as KPC and NDM-1.

Background Cefiderocol (CFDC) is a siderophore cephalosporin with broad coverage of aerobic Gram-negative (GN) bacteria. Provisional breakpoints (BP) were approved by CLSI in 2018, with FDA and EUCAST providing clinical BP in 2019 and 2020, respectively; however, BPs differ markedly between organizations, reflecting differences in labelling, PK/PD standards and availability of clinical study data during regulatory review. Here we compare susceptibility rates based on these different BPs. Methods Susceptibility rates for each bacterial species were determined using CFDC BP from each organization and the MICs of 28,629 GN clinical isolates from 3 consecutive years of SIDERO-WT surveillance studies (2014–17). The analysis used all isolates and sub-grouped isolates based on meropenem (MEM) susceptibility (CLSI BP) or carbapenemase production. Results Within the overall Enterobacterales group, ≥98.5% isolates were interpreted as susceptible to CFDC regardless of BP used. However, the proportion of susceptible differed significantly (82.5–98.6%) when applied to MEM-non-susceptible (NS) isolates. Similarly, against most carbapenemase producers, susceptibility ranged from 80 to 100%, however for NDM producers, only 51% of isolates were defined as susceptible by FDA or EUCAST BP vs 84% using the CLSI BP. Against Pseudomonas aeruginosa including MEM-NS isolates, susceptibility was ≥94% despite different BPs recommended by FDA (1 mg/L), EUCAST (2 mg/L) and CLSI (4 mg/L). This changed the proportion of IMP-producing isolates classified as susceptible from 100% (CLSI) and 81% (EUCAST) to only 19% (FDA). Against other non-fermenters, susceptibility was ≥91% irrespective of BP used. Table 1. Susceptibility rates against Enterobacterales based on breakpoints from each organization Table 2. Susceptibility rates against non-fermenters based on breakpoints from each organization Conclusion Differences in BPs between FDA, CLSI and EUCAST could impact on the reporting of susceptibility or resistance to CFDC, particularly for MEM-NS isolates. PK/PD model simulations support 100% fT >MIC up to an MIC of 4 mg/L, and in Phase 3 trials the mean trough concentration of unbound cefiderocol was >4 mg/L. The potential impact of these differences on clinical decision making are important as the greatest clinical utility for CDFC is expected to be in patients with carbapenem-resistant GN infections due to limited treatment options. Disclosures Yoshinori Yamano, PhD, Shionogi & Co., Ltd. (Employee) Miki Takemura, MSc, Shionogi & Co., Ltd. (Employee) Christopher Longshaw, PhD, Shionogi B.V. (Employee) Roger Echols, MD, Shionogi Inc. (Consultant)

The structure-activity relationship (SAR) for a novel series of catechol conjugated siderophore cephalosporins is described with their in vitro activities against multi-drug resistant Gram-negative pathogens including Pseudomonas aeruginosa, Acinetobacter baumannii, Stenotrophomonas maltophilia and Enterobacteriaceae. Cefiderocol (3) was one of the best molecules which displayed well-balanced and potent activities against multi-drug resistant Gram-negative pathogens including carbapenem resistant bacteria among the prepared compounds with the modified C-7 side chain and the modified C-3 side chain. Cefiderocol (3) is a highly promising parenteral cephalosporin for the treatment of multi-drug resistant Gram-negative infection.

The in vitro activity of the investigational siderophore cephalosporin, cefiderocol (formerly S-649266), was determined against a 2014–2016, 52-country, worldwide collection of clinical isolates of carbapenem-nonsusceptible Enterobacteriaceae ( n = 1,022), multidrug-resistant (MDR) Acinetobacter baumannii ( n = 368), MDR Pseudomonas aeruginosa ( n = 262), Stenotrophomonas maltophilia ( n = 217), and Burkholderia cepacia ( n = 4) using the Clinical and Laboratory Standards Institute (CLSI) standard broth microdilution method. Iron-depleted cation-adjusted Mueller-Hinton broth (ID-CAMHB), prepared according to a recently approved (2017), but not yet published, CLSI protocol, was used to test cefiderocol; all other antimicrobial agents were tested using CAMHB. The concentration of cefiderocol inhibiting 90% (MIC 90 ) of isolates of carbapenem-nonsusceptible Enterobacteriaceae was 4 μg/ml; cefiderocol MICs ranged from 0.004 to 32 μg/ml, and 97.0% (991/1,022) of isolates demonstrated cefiderocol MICs of ≤4 μg/ml. The MIC 90 s for cefiderocol for MDR A. baumannii , MDR P. aeruginosa , and S. maltophilia were 8, 1, and 0.25 μg/ml, respectively, with 89.7% (330/368), 99.2% (260/262), and 100% (217/217) of isolates demonstrating cefiderocol MICs of ≤4 μg/ml. Cefiderocol MICs for B. cepacia ranged from 0.004 to 8 μg/ml. We conclude that cefiderocol demonstrated potent in vitro activity against a 2014–2016, worldwide collection of clinical isolates of carbapenem-nonsusceptible Enterobacteriaceae , MDR A. baumannii , MDR P. aeruginosa , S. maltophilia , and B. cepacia isolates as 96.2% of all (1,801/1,873) isolates tested had cefiderocol MICs of ≤4 μg/ml.

Background DTR organisms are defined as nonsusceptible to all high-efficacy, low-toxicity antibiotics (penicillins, cephalosporins, carbapenems, and quinolones), leaving physicians with limited first-line treatment options. Analyses of electronic health records have shown that patients with DTR Gram-negative bacterial infections are more likely to receive inappropriate antibiotic therapy, have longer hospital stay and increased risk of mortality. CFDC is a novel parenteral siderophore cephalosporin with potent activity against aerobic Gram-negative pathogens, including carbapenem-resistant strains. We evaluated the in vitro activity of CFDC and comparators against DTR pathogens collected by the SIDERO-WT surveillance study. Methods A total of 30,459 clinical isolates of Gram-negative bacilli were systematically collected from United States, Canada, and 11 EU countries during 2014–2017. MICs were determined by broth microdilution for a panel of 7 antibiotics, including CFDC, ceftazidime–avibactam (CZA), ceftolozane–tazobactam (C/T), colistin (CST), cefepime (FEP), meropenem (MEM), and ciprofloxacin (CIP) according to CLSI guidelines. All antibiotics were tested in cation-adjusted Mueller–Hinton broth (CAMHB) except CFDC, for which iron-depleted CAMHB was used. Susceptibility was determined according to CLSI interpretive breakpoints except CST, where EUCAST breakpoints were used. DTR pathogens were defined as being nonsusceptible to FEP, MEM, and CIP according to CLSI breakpoints. Results Among 30,459 Gram-negative isolates collected between 2014 and 2017, 9.3% were nonsusceptible to FEP, MEM, and CIP and could be defined as DTR. DTR was most frequently observed in Acinetobacter spp. (55.5%), followed by Burkholderia spp. (19%), Pseudomonas aeruginosa (9.5%), and Enterobacterales (2.7%). Of the 1,173 Stenotrophomonas maltophilia tested, 97% had MEM MIC of ≥8 mg/L; however, only 2.9% could be defined as DTR. Cefiderocol was the most active antibiotic tested against DTR isolates with 94.5% DTR-Acinetobacter spp., 98.3% DTR-P. aeruginosa, and 99.8% DTR-Enterobacterales susceptible (Table 1). Conclusion CFDC demonstrated potent activity against DTR Gram-negative pathogens with limited first-line treatment options. Disclosures All authors: No reported disclosures.

Background Cefiderocol (CFDC) is a new siderophore cephalosporin with potent in vitro activity against a broad range of Gram-negative (GN) pathogens, including carbapenem-nonsusceptible (Carb-NS) strains. We evaluated the in vitro activity of CFDC and comparator agents against recent clinical Carb-NS GN respiratory isolates collected from North America and Europe as part of the multi-national SIDERO-WT surveillance program. Methods A total of 2831 Carb-NS GN respiratory isolates collected from 2014 to 2017 were tested centrally (IHMA, Inc., Schaumburg, IL). Minimum inhibitory concentrations (MIC) were determined for CFDC, cefepime (FEP), ceftazidime–avibactam (CZA), ceftolozane-tazobactam (C/T), ciprofloxacin (CIP), colistin (CST), and meropenem (MEM) by broth microdilution and interpreted according to the 2018 CLSI guidelines. CFDC MICs were tested in iron-depleted cation-adjusted Mueller–Hinton broth, and interpreted according to the 2018 CLSI provisional breakpoints. Carb-NS strains were defined as MEM MIC of ≥2 µg/mL for Enterobacteriaceae (ENB) and of ≥4 µg/mL for nonfermenters (NF). Results CFDC exhibited predictable in vitro activity against 2807 clinically relevant Carb-NS GN isolates (214 ENB, 1086 A. baumannii complex, 693 P. aeruginosa, 794 S. maltophilia, and 20 Burkholderia cepacia) isolated from respiratory infections. CFDC was the most active agent against Carb-NS ENB with 97.7% susceptibility followed by 78.0% CZA, 59.4% CST, and 16.4% CIP. Against Carb-NS A. baumannii complex, CFDC demonstrated 94% susceptibility vs. 83.7% for CST. CFDC was the most active agent against Carb-NS P. aeruginosa with 99.9% susceptibility followed by 97.8% CST, 77.6% C/T, and 77.5% CZA. 99.7% of S. maltophilia and 100% of B. cepacia isolates had CFDC MICs of ≤4 µg/mL. The MIC90s of tested compounds for clinically relevant pathogens are shown in the table. Conclusion In a multinational collection of Carb-NS GN respiratory isolates, CFDC demonstrated potent in vitro activity with MIC90 of ≤4 µg/mL for all clinically relevant ENB and NF. These findings suggest that CFDC can be a potential option for the treatment of respiratory infections caused by Carb-NS ENB, A. baumannii complex, P. aeruginosa, S. maltophilia, and B. cepacia. Disclosures All authors: No reported disclosures.

Cefiderocol (S-649266) is a novel siderophore cephalosporin with potent in vitro activity against clinically encountered multidrug-resistant (MDR) Gram-negative isolates; however, its spectrum of antibacterial activity against these difficult-to-treat isolates remains to be fully explored in vivo . Here, we evaluated the efficacy of cefiderocol humanized exposures in a neutropenic murine thigh model to support a suitable MIC breakpoint. Furthermore, we compared cefiderocol's efficacy with humanized exposures of meropenem and cefepime against a subset of these phenotypically diverse isolates. Ninety-five Gram-negative isolates were studied. Efficacy was determined as the change in log 10 CFU at 24 h compared with 0-h controls. Bacterial stasis or ≥1 log reduction in 67 isolates with MICs of ≤4 μg/ml was noted in 77, 88, and 85% of Enterobacteriaceae , Acinetobacter baumannii , and Pseudomonas aeruginosa , respectively. For isolates with MICs of ≥8 μg/ml, bacterial stasis or ≥1 log 10 reduction was observed in only 2 of 28 (8 Enterobacteriaceae , 19 A. baumannii , and 1 P. aeruginosa ) strains. Against highly resistant meropenem and cefepime organisms, cefiderocol maintained its in vivo efficacy. Overall, humanized exposures of cefiderocol produced similar reductions in bacterial density for organisms with MICs of ≤4 μg/ml, whereas isolates with MICs of ≥8 μg/ml generally displayed bacterial growth in the presence of the compound. Data derived in the current study will assist with the delineation of MIC susceptibility breakpoints for cefiderocol against these important nosocomial Gram-negative pathogens; however, additional clinical data are required to substantiate these observations.

Cefiderocol (formerly S-649266) is an investigational siderophore cephalosporin. Iron-depleted cation-adjusted Mueller-Hinton broth (ID-CAMHB) was prepared according to the Clinical and Laboratory Standards Institute (CLSI) protocol and used to perform broth microdilution testing of cefiderocol against a 2014-2015 collection of clinical isolates of Gram-negative bacilli from North America ( n = 4,239) and Europe ( n = 4,966). The concentrations of cefiderocol inhibiting 90% of isolates tested (MIC 90 s) were 0.5 μg/ml (North America; n = 3,007) and 1 μg/ml (Europe; n = 3,080) for all isolates of Enterobacteriaceae ; 1 μg/ml (North America; n = 30) and 4 μg/ml (Europe; n = 139) for meropenem-nonsusceptible (MIC ≥ 2 μg/ml) isolates of Enterobacteriaceae ; 0.5 μg/ml for both North American ( n = 765) and European ( n = 765) isolates of Pseudomonas aeruginosa ; 0.5 μg/ml (North America; n = 151) and 1 μg/ml (Europe; n = 202) for meropenem-nonsusceptible (MIC ≥ 4 μg/ml) isolates of P. aeruginosa ; 1 μg/ml for both North American ( n = 309) and European ( n = 839) isolates of all Acinetobacter baumannii strains as well as for both North American ( n = 173) and European ( n = 595) isolates of meropenem-nonsusceptible A. baumannii ; and 0.5μg/ml (North America; n = 152) and 0.25 μg/ml (Europe; n = 276) for isolates of Stenotrophomonas maltophilia . MICs of cefiderocol were ≤4 μg/ml for 99.9% (6,078/6,087) of all Enterobacteriaceae , 97.0% (164/169) of meropenem-nonsusceptible Enterobacteriaceae , 99.9% (1,529/1,530) of all P. aeruginosa isolates, 100% (353/353) of meropenem-nonsusceptible P. aeruginosa isolates, 97.6% (1,120/1,148) of all A. baumannii isolates, 96.9% (744/768) of meropenem-nonsusceptible A. baumannii isolates, 100% of isolates of S. maltophilia (428/428) and 93.8% of isolates of Burkholderia cepecia (11/12). We conclude that cefiderocol demonstrated potent in vitro activity against a recent collection of clinical isolates of commonly encountered Gram-negative bacilli, including carbapenem-nonsusceptible isolates.

Carbapenemase-producing Enterobacteriaceae (CPE) have been spreading worldwide and are a great concern among health care settings ([1][1]). Intriguingly, IMP-6 (encoded by the bla IMP-6 gene), one of the IMP-type metallo-carbapenemases, has been reported to confer the paradoxical imipenem

Background Antibiotic susceptibility surveillance is the foundation for selecting treatment options as well as immediate and long-term strategies for combating antimicrobial resistance. We have conducted three surveillance studies SIDERO-WT-2014/-2015/-2016 with approximately 30,000 Gram-negative strains isolated in North America and Europe between 2014 and 2017. Here, we present the latest data of molecular analysis on acquired carbapenemase genes and antibiotic susceptibility of 3691 meropenem-nonsusceptible strains in the surveillance studies. Methods Meropenem-nonsusceptible strains isolated in North America (n = 1009) and Europe (n = 2,682), consisting of 1,897 Acinetobacter baumannii, 1,154 Pseudomonas aeruginosa, 447 Klebsiella pneumoniae, and 193 other Enterobacteriaceae were tested. Conventional PCR was used to detect known carbapenemases. Cefiderocol MICs were determined by broth microdilution method using iron-depleted cation-adjusted Mueller–Hinton broth. Results The percentages of known carbapenemases detected in 3 main pathogens are shown in the Table. In A. baumannii complex, OXA-23 was predominant followed by OXA-24 in most countries. The detection rates of VIM in P. aeruginosa were ≥40% in Greece and Russia, but none of the strains in the United States carried VIM. In K. pneumoniae, the predominant carbapenemase varied among the countries, with KPC predominating in the USA, Greece and Italy, while OXA-48-like was dominant in Russia, Spain and Turkey. Cefiderocol MIC90 were ≤4 μg/mL against these 3 pathogens in all 6 countries, except for A. baumannii strains in Russia. Conclusion Carbapenemase detection rates, especially in P. aeruginosa and K. pneumoniae, were quite different among the countries. Cefiderocol demonstrated potent in vitro activity against meropenem-nonsusceptible strains irrespective of the presence of specific carbapenemases. Disclosures All authors: No reported disclosures.

Background The global rise of carbapenem resistant Gram-negative bacteria such as carbapenem-resistant Enterobacteriaceae (CRE) and carbapenem-resistant non-fermenting bacteria is alarming and become threats to patient as only a few drugs remain active (e.g. colistin). Cefiderocol (S-649266) is a novel parenteral siderophore cephalosporin with potent activity against a wide variety of Gram-negative pathogens including carbapenem-resistant strains. This study evaluated the in vitro activity of cefiderocol and comparator agents against clinical isolates collected from urinary track source from North America. Methods A total of 3,323 Enterobacteriaceae, 263 Acinetobacter spp, 509 Pseudomonas aeruginosa, and 38 Stenotrophomonas maltophilia collected from the USA and Canada in 2014–2016 were tested. MIC was determined for cefiderocol, cefepime (FEP), ceftazidime-avibactam (CZA), ceftolozane-tazobactam (C/T), ciprofloxacin (CIP), colistin (CST), and meropenem (MEM) by broth microdilution and interpreted according to CLSI 2016 guidelines. All testing was done at IHMA, Inc. As recommended by CLSI, cefiderocol was tested in iron-depleted cation-adjusted Mueller Hinton broth. Based upon CLSI breakpoints, carbapenem-non-susceptible (CarbNS) strains were defined as follows: MEM: MIC ≥2 µg/mL for Enterobacteriaceae, ≥4 µg/mL for non-fermenters. Quality control testing was performed on each day of testing by using E. coli ATCC25922 and P. aeruginosa ATCC27853. Results Cefiderocol exhibited in vitro activity against 4,133 strains of Gram-negative bacteria with an overall MIC90 of 0.5 µg/mL. At 4 µg/mL cefiderocol inhibited the growth of 99.9% of the all isolates. MIC90 of cefiderocol against CarbNS Enterobacteriaceae was 4 µg/mL although MIC90 of other comparators were >64 or >8 (CST) µg/mL. The cefiderocol MIC90value was 1 µg/mL for CarbNS non-fermeneters. Conclusion Cefiderocol demonstrated potent in vitro activity against Enterobacteriaceae, A. baumannii, P. aeruginosa, and S. maltophilia isolates collected from a UTI source, with greater than 99.9% of isolates having MIC values ≤4 µg/mL. These findings indicate that this agent has high potential for treating cUTI infections caused by these problematic organisms, including isolates resistant to colistin. Disclosures M. Tsuji, Shionogi & Co.: Employee, Salary; M. Hackel, IHMA: Employee, Salary; R. Echols, Shionogi & CO., LTD: Consultant, Consulting fee; Y. Yamano, Shionogi & Co.: Employee, Salary

Background Cefiderocol (S-649266, CFDC) is a novel siderophore cephalosporin against Gram-negatives, including carbapenem (CR)-resistant strains. Its spectrum includes both the Enterobacteriaceae but also nonfermenters, including Stenotrophomonas maltophilia—an opportunistic pathogen with intrinsic resistance to carbapenem antibiotics. In this study, in vitro activity and in vivo efficacy of CFDC and comparators against S. maltophilia were determined. Methods MICs of CFDC and comparators (trimethoprim/sulfamethoxazole (TMP/SMX), minocycline (MINO), tigecycline (TGC), ciprofloxacin (CPFX), cefepime (CFPM), meropenem (MEPM), and colistin (CL)) were determined by broth microdilution method as recommended by CLSI. The MIC against CFDC was determined using iron-depleted cation-adjusted Mueller–Hinton broth. In vivo efficacy of CFDC, CFPM, ceftazidime–avibactam (CAZ/AVI), MEPM, and CL was evaluated using neutropenic murine systemic infection model caused by strain SR21970. The 50% effective doses (ED50s) were calculated by the logit method using the survival number at each dose 7 days after infection. Results MIC90 of CFDC and comparators against the 216 clinical isolates from global countries collected in SIDERO-CR 2014/2016 study are shown in the table. CFDC, TMP/SMX, MINO, and TGC showed good activity with MIC90 of 0.5, 0.25/4.75, 1, and 2 µg/mL, respectively. CFDC, MINO, and TGC inhibited growth of all tested strains at ≤1, ≤4, and ≤8 µg/mL although two strains showed resistance to TMP/SMX. MICs of CFPM, CAZ/AVI, MEPM, and CL were ≥32 µg/mL. The ED50 of CFDC against S. maltophilia SR21970 with MIC of 0.125 mg/mL was 1.17 mg/kg/dose. Conversely, MICs of CFPM, CAZ/AVI, MEPM/CS, and CL against SR21970 were 32 μg/mL or higher, and ED50s were >100 mg/kg/dose, showing that CFDC had potent in vivo efficacy against S. maltophilia strain which was resistant to other antibiotics. Conclusion CFDC showed potent in vitro activity against S. maltophilia, including TMP/SMX-resistant isolates. CFDC also showed potent in vivo efficacy reflecting in vitro activity against S. maltophilia in murine systemic infection model. Disclosures A. Ito, Shionogi & Co., Ltd.: Employee, Salary. M. Ota, Shionogi & Co., Ltd.: Employee, Salary. R. Nakamura, Shionogi & Co., Ltd.: Employee, Salary. M. Tsuji, Shionogi & Co., Ltd.: Employee, Salary. T. Sato, Shionogi & Co., Ltd.: Employee, Salary. Y. Yamano, Shionogi & Co., Ltd.: Employee, Salary.

Background Cefiderocol (S-649266, CFDC) is a novel siderophore cephalosporin with activity against a wide variety of Gram-negative bacteria including carbapenem-resistant strains. We previously reported that CFDC is efficiently transported into Pseudomonas aeruginosa via iron transporter PiuA. In this study, we examined frequency of resistance of P. aeruginosa to CFDC, and investigated the resistance mechanisms of appeared colonies. Methods Frequency of resistance (FoR) was determined by plating an overnight culture of P. aeruginosa PAO1 on Mueller–Hinton Agar containing 4× or 10×MIC of CFDC or ceftazidime (CAZ). Appeared colonies were analyzed by whole-genome sequencing (WGS) to identify genomic mutations. The mRNA expression was determined by real-time RT-PCR, and pyoverdine production was determined by MALDI-TOF/MS and expression of outer membrane protein was analyzed by SDS–PAGE and proteomic analysis. Results The FoR to CFDC was 2.9 × 10–8 and Conclusion The MIC increase of CFDC against P. aeruginosa occurred due to the mutation of iron transporter-related genes. The resistance acquisition risks should be low as the frequency of resistance to CFDC was lower and the MIC increase of CFDC against the mutants was smaller than that of CAZ. In addition, no cross-resistance between CFDC and CAZ was observed. Disclosures A. Ito, Shionogi & Co., Ltd.: Employee, Salary. T. Nishikawa, Shionogi & Co., Ltd.: Employee, Salary. R. Ishii, Shionogi & Co., Ltd.: Employee, Salary. M. Kuroiwa, Shionogi & Co., Ltd.: Employee, Salary. Y. Ishioka, Shionogi & Co., Ltd.: Employee, Salary. N. Kurihara, Shionogi & Co., Ltd.: Employee, Salary. I. Sakikawa, Shionogi & Co., Ltd.: Employee, Salary. T. Ota, Shionogi & Co., Ltd.: Employee, Salary. M. Rokushima, Shionogi & Co., Ltd.: Employee, Salary. M. Tsuji, SHIONOGI & CO., LTD.: Employee, Salary. T. Sato, SHIONOGI & CO., LTD.: Employee, Salary. Y. Yamano, SHIONOGI & CO., LTD.: Employee, Salary.

The pharmacokinetic (PK)/pharmacodynamic (PD) parameters and the antibacterial activity of S-013420, a novel bicyclolide, against Haemophilus influenzae and Streptococcus pneumoniae , including macrolide-resistant isolates, were investigated using an in vitro PD model. Various time-concentration curves were artificially constructed by modifying the PK data obtained in phase I studies. The activity against H. influenzae was evaluated using two parameters, that is, the area above the killing curve (AAC) and the viable cell reduction at 24 h. The relationships between the antibacterial activity of S-013420 and the three PK/PD parameters were investigated by fitting the data to the sigmoid maximum effective concentration model. The square of the correlation coefficient ( R 2 ) values for AAC versus the area under the concentration-time curve from 0 to 24 h (AUC 0-24 )/MIC, the peak concentration ( C max )/MIC, and the cumulative percentage of a 24-h period that the drug concentration exceeded the MIC under steady-state PK conditions (% T MIC ) were 0.92, 0.87, and 0.49, respectively. The R 2 values for viable cell reduction at 24 h versus AUC 0-24 /MIC, C max /MIC, and % T MIC were 0.93, 0.61, and 0.56, respectively. These results demonstrated that AUC 0-24 /MIC is the most significant parameter for evaluation of the antibacterial activity of S-013420. The values of AUC 0-24 /MIC required for maximum and static efficacy were 10.8 and 9.63, respectively, for H. influenzae and 16.3 to 22.3 and 4.66 to 9.01, respectively, for S. pneumoniae . This analysis is considered useful for determining the AUC value at the infection site, which would be required for efficacy in clinical use.

Objectives S-649266 is a parenteral siderophore cephalosporin antibiotic with a catechol moiety on its side chain. The in vitro antimicrobial activity of S-649266 against non-fermenting Gram-negative bacteria was evaluated and compared with the activities of meropenem, levofloxacin, cefepime, ceftazidime and piperacillin/tazobactam. Methods MIC values of S-649266 were determined in Mueller-Hinton broth or Iso-Sensitest broth supplemented with apo-transferrin. Results S-649266 showed potent in vitro activity against the non-fermenting Gram-negative bacteria Acinetobacter baumannii, Pseudomonas aeruginosa and Stenotrophomonas maltophilia, including MDR strains such as carbapenem-resistant A. baumannii and metallo-β-lactamase-producing P. aeruginosa. MIC90s of S-649266 for A. baumannii, P. aeruginosa and S. maltophilia were 2, 1 and 0.5 mg/L, respectively, whereas MIC90s of meropenem were >16 mg/L. S-649266 showed potent in vitro activities against A. baumannii producing carbapenemases such as OXA-type β-lactamases, and P. aeruginosa producing metallo-β-lactamases such as IMP type and VIM type. MIC90 values for these A. baumannii strains and P. aeruginosa strains were 8 and 4 mg/L, respectively. Conclusions S-649266 is a novel antibiotic with potent in vitro activity against a range of non-fermenting Gram-negative bacteria, including MDR strains.

The in vitro antibacterial activity of S-3578, a new parenteral cephalosporin, against clinical isolates was evaluated. The MICs of the drug at which 90% of the isolates were inhibited were 4 μg/ml for methicillin-resistant Staphylococcus aureus (MRSA) and 2 μg/ml for methicillin-resistant Staphylococcus epidermidis , which were fourfold higher than and equal to those of vancomycin, respectively. The anti-MRSA activity of S-3578 was considered to be due to its high affinity for penicillin-binding protein 2a (50% inhibitory concentration, 4.5 μg/ml). In time-kill studies with 10 strains each of MRSA and methicillin-susceptible S. aureus , S-3578 caused more than a 4-log 10 decrease of viable cells on the average at twice the MIC after 24 h of exposure, indicating that it had potent bactericidal activity. Furthermore, in population analysis of MRSA strains with heterogeneous or homogeneous resistance to imipenem, no colonies emerged from about 10 9 cells on agar plates containing twice the MIC of S-3578, suggesting the low frequency of emergence of S-3578-resistant strains from MRSA. S-3578 was also highly active against penicillin-resistant Streptococcus pneumoniae (PRSP), with a MIC 90 of 1 μg/ml, which was comparable to that of ceftriaxone. S-3578 also had antibacterial activity against a variety of gram-negative bacteria including Pseudomonas aeruginosa , though its activity was not superior to that of cefepime. In conclusion, S-3578 exhibited a broad antibacterial spectrum and, particularly, had excellent activity against gram-positive bacteria including methicillin-resistant staphylococci and PRSP. Thus, S-3578 was considered to be worthy of further evaluation.

Background Cefiderocol (S-649266) is a novel siderophore cephalosporin under development by Shionogi (Osaka, Japan). Previous studies have demonstrated cefiderocol efficacy against a diverse population of Gram-negative bacteria with MICs ≤ 4 μg/mL. Our aim was to further define the agent’s clinical role by comparing the efficacy of humanized regimens of cefiderocol, FEP, and MEM against a subset of these Gram-negative isolates. Methods 15 Gram-negative isolates were studied. MICs were determined by broth microdilution in triplicate, using reference CLSI methods. Pharmacokinetic studies were conducted to reproduce the humanized exposures of cefiderocol 2g q8h (3h inf.), FEP 2g q8h (3h inf.), and MEM 2g q8h (3 hours inf.). Antibiotics were started 2h post thigh inoculation (0h) and continued for 24 hours in immunocompromised mice. Efficacy was determined as the change in log10CFU at 24h compared with 0 hour controls. Results 8 Enterobacteriaceae, 4 A. baumannii, and 3 P. aeruginosa isolates were studied. Cefiderocol, FEP, and MEM MICs were in the range of 0.12 to 8 μg/mL, ≤0.03 to >64 μg/mL, and ≤0.06 to >64 μg/mL, respectively. Three of the 15 isolates were susceptible to both meropenem and cefepime. All remaining isolates demonstrated in vitro resistance to one or both comparator agents. Cefiderocol was efficacious against all 15 isolates, regardless of FEP or MEM resistance, producing bacterial reductions from 0 hour between 0.89 to 3.04 log10 CFU. Against FEP and MEM susceptible isolates, cefiderocol treatment resulted in bacterial kill of 2.6 ± 0.5 and 2.1 ± 0.9 log10 CFU, respectively, similar to that of FEP (2.6 ± 0.5) and MEM (2.2 ± 0.6). Against MEM and FEP resistant isolates, cefiderocol produced a mean (± SD) bacterial reduction of 1.5 ± 0.4 log10 CFU at 24 hours. Conclusion Cefiderocol humanized exposures produced antibacterial efficacy similar to MEM and FEP for susceptible pathogens, while also displaying activity against Enterobacteriaceae, A. baumannii, and P. aeruginosa with phenotypic resistance to the comparator β-lactams. These studies support the potential clinical utility of cefiderocol against these difficult-to-treat multidrug-resistant pathogens. Disclosures M. Tsuji, Shionogi & Co.: Employee, Salary; Y. Yamano, Shionogi & Co.: Employee, Salary; R. Echols, Shionogi & Co.: Employee, Salary; D. P. Nicolau, Shionogi & Co.: Research Contractor, Research support

Background Cefiderocol (S-649266) is a novel siderophore cephalosporin active against a wide variety of Gram-negative bacteria, not only Enterobacteriaceae but also non-fermenting bacteria such as Pseudomonas aeruginosa and Acinetobacter spp., including carbapenem-resistant strains. This potent activity is due to its efficient penetration through the outer membrane via active iron transporter systems and its high stability to both serine- and metallo-carbapenemases.This study evaluated the in vitro activity of cefiderocol and comparator agents against carbapenem-resistant clinical isolates collected from urinary track source in 2014–2016 from global countries. Methods /Methods Carbapenem-resistant Enterobacteriaceae (CRE) and multidrug-resistant (MDR) non-fermenters (defined as resistant to imipenem, ciprofloxacin and amikacin) were collected globally from 2014 to 2016 by IHMA Inc. A total of 226 Enterobacteriaceae, 44 Acinetobacter baumannii, 45 P. aeruginosa, 7 Stenotrophomonas maltophilia and 1 Burkholderia cepacia isolated from a urinary track source were tested. MICs were determined for cefiderocol, cefepime (FEP), ceftazidime-avibactam (CZA), ceftolozane-tazobactam (C/T), ciprofloxacin (CIP), colistin (CST), and meropenem (MEM) by broth microdilution and interpreted according to CLSI 2016 guidelines. As recommended by CLSI, cefiderocol was tested in iron-depleted cation-adjusted Mueller Hinton broth. Quality control testing was performed on each day of testing by using E. coli ATCC25922 and P. aeruginosa ATCC27853. Results MIC90 of cefiderocol against carbapenem-resistant Enterobacteriaceae, MDR P. aeruginosa, MDR A. baumannii, and S. maltophilia were 4 µg/mL or less. However, MEM, C/T and CZA had MIC90s of >64µg/mL. Cefiderocol demonstrated potent in vitro activity against carbapenem-resistant Enterobacteriaceae, A. baumannii, and P. aeruginosa isolates collected from a UTI source. At 4 µg/mL or less, cefiderocol inhibited the growth of 95.8% of the isolates. Conclusion These results strongly indicated that cefiderocol is a promising candidate for the treatment of the serious infections caused by cUTI isolated Gram-negative bacteria including carbapenem-resistant strains. Disclosures M. Tsuji, Shionogi & Co.: Employee, Salary; M. Hackel, IHMA: Employee, Salary; R. Echols, Shionogi & CO., LTD.: Consultant, Consulting fee; Y. Yamano, Shionogi & Co.: Employee, Salary

The in vitro activity of S-013420, a novel bicyclolide, was investigated.All test strains for this study were isolated from Japanese medical facilities. MICs were determined by the microbroth dilution method or agar dilution method according to the CLSI guidelines. In time-kill kinetics, viable cells were measured at 1, 2.5, 4 and 6 h after exposure to antimicrobials. The frequencies of single-step resistance acquisition at 4x MIC and 8x MIC were determined using 10(7) cfu of bacterial cells.S-013420 showed MIC(90) values of 0.125, 0.125, 8 and 0.5 mg/L for Streptococcus pneumoniae, Streptococcus pyogenes, Haemophilus influenzae and Moraxella catarrhalis, respectively. S-013420 showed the most potent activity against erythromycin-intermediate and -resistant S. pneumoniae with an MIC(90) of 0.25 mg/L and inhibited the growth of all strains of S. pyogenes with macrolide resistance genes at 1 mg/L. The MICs of S-013420 for atypical pathogens such as erythromycin-susceptible Mycoplasma pneumoniae and Chlamydophila pneumoniae were 0.00049-0.001 and 0.0039 mg/L, respectively, although the activity of S-013420, as well as other macrolide agents, against erythromycin-resistant M. pneumoniae was significantly weak. S-013420 caused a 3 log(10) reduction in viable cells against all test strains of S. pneumoniae and H. influenzae. Acquisition of resistance to S-013420 was not observed for three strains of S. pneumoniae.S-013420 shows potent in vitro activity against respiratory tract pathogens. Against streptococci, including erythromycin-resistant strains, S-013420 demonstrated the most potent in vitro activity among the antimicrobials tested.

Van-M-02, a novel glycopeptide, was revealed to exert potent activities against Gram-positive bacteria, including vancomycin-resistant enterococci (VRE) and vancomycin-resistant Staphylococcus aureus (VRSA). A crude assay system was then used to study the mode of action of Van-M-02 as a peptidoglycan synthesis model of both vancomycin-susceptible and -resistant strains. The results suggested that Van-M-02 inhibits the synthesis of lipid intermediates irrespective of their termini. This inhibitory activity may contribute to the anti-VRE and anti-VRSA activities observed.