In vitro and in vivo activity of cefiderocol against Achromobacter spp. and Burkholderia cepacia complex, including carbapenem-non-susceptible isolates.

Achromobacter spp. and Burkholderia cepacia complex (Bcc) are rare but diverse opportunistic pathogens associated with serious infections, which are often multidrug resistant. This study compared the in vitro antibacterial activity of the siderophore antibiotic cefiderocol against Achromobacter spp. and Bcc isolates with that of other approved antibacterial drugs, including ceftazidime-avibactam, ciprofloxacin, colistin, imipenem-relebactam, and meropenem-vaborbactam. Isolates were collected in the SIDERO multinational surveillance program. Among 334 Achromobacter spp. isolates [76.6% from respiratory tract infections (RTIs)], cefiderocol had minimum inhibitory concentration (MIC)50/90 of 0.06/0.5 µg/mL overall and 0.5/4 µg/mL against 52 (15.6%) carbapenem-non-susceptible (Carb-NS) isolates. Eleven (3.3%) Achromobacter spp. isolates overall and 6 (11.5%) Carb-NS isolates were not susceptible to cefiderocol. Among 425 Bcc isolates (73.4% from RTIs), cefiderocol had MIC50/90 of ≤0.03/0.5 µg/mL overall and ≤0.03/1 µg/mL against 184 (43.3%) Carb-NS isolates. Twenty-two (5.2%) Bcc isolates overall and 13 (7.1%) Carb-NS isolates were not susceptible to cefiderocol. Cumulative MIC distributions showed cefiderocol to be the most active of the agents tested in vitro against both Achromobacter spp. and Bcc. In a neutropenic murine lung infection model and a humanized pharmacokinetic immunocompetent rat lung infection model, cefiderocol showed significant bactericidal activity against two meropenem-resistant Achromobacter xylosoxidans strains compared with untreated controls (P < 0.05) and vehicle-treated controls (P < 0.05), respectively. Meropenem, piperacillin-tazobactam, ceftazidime, and ciprofloxacin comparators showed no significant activity in these models. The results suggest that cefiderocol could be a possible treatment option for RTIs caused by Achromobacter spp. and Bcc.

In vitro activity of ceftazidime-avibactam against clinical isolates of Enterobacterales and Pseudomonas aeruginosa from sub-Saharan Africa: ATLAS Global Surveillance Program 2017-2021.

OBJECTIVES: To report the in vitro susceptibility of Enterobacterales (n = 3905) and Pseudomonas aeruginosa (n = 1,109) isolates, collected from patients in sub-Saharan Africa (four countries) in 2017-2021, to a panel of 10 antimicrobial agents with a focus on ceftazidime-avibactam activity against resistant phenotypes and ß-lactamase carriers. METHODS: MICs were determined by CLSI broth microdilution and interpreted using both 2022 CLSI and EUCAST breakpoints. ß-lactamase genes were identified in select ß-lactam-nonsusceptible isolate subsets using multiplex PCR assays. RESULTS: Among Enterobacterales, 96.2% of all isolates were ceftazidime-avibactam-susceptible (MIC90, 0.5 µg/mL), including all serine carbapenemase-positive (n = 127), 99.6% of ESBL-positive, carbapenemase-negative (n = 730), 91.9% of multidrug resistant (MDR; n = 1817), and 42.7% of DTR (difficult-to-treat resistance; n = 171) isolates. Metallo-ß-lactamase (MBL) genes were identified in most (n = 136; 91.2%) ceftazidime-avibactam-resistant isolates (3.5% of all Enterobacterales isolates). Ceftazidime-avibactam percent susceptible values ranged from 99.5% (Klebsiella species other than Klebsiella pneumoniae) to 92.5% (K. pneumoniae) for the various Enterobacterial taxa examined. Greater than 90% of Enterobacterales isolates from each country (Cameroon, Ivory Coast, Nigeria, South Africa) were ceftazidime-avibactam-susceptible. Among P. aeruginosa, 88.9% of all isolates were ceftazidime-avibactam-susceptible (MIC90, 16 µg/mL). Most (88.5%) MBL-negative, meropenem-resistant (n = 78), 68.1% of MDR (n = 385), and 19.2% of DTR isolates (n = 99) were ceftazidime-avibactam-susceptible. MBL genes were identified in 43.1% of ceftazidime-avibactam-resistant isolates (n = 53; 4.8% of all P. aeruginosa isolates). Country-specific ceftazidime-avibactam percent susceptible values for P. aeruginosa ranged from 94.1% (Cameroon) to 76.2% (Nigeria). CONCLUSION: Reference in vitro antimicrobial susceptibility testing demonstrated that most recent Enterobacterales (96%) and P. aeruginosa (89%) clinical isolates from four sub-Saharan African countries were ceftazidime-avibactam susceptible.

In vitro activity of cefiderocol against MBL-producing Gram-negative bacteria collected in North America and Europe in five consecutive annual multinational SIDERO-WT surveillance studies (2014-2019).

OBJECTIVES: To evaluate the in vitro antibacterial activity of cefiderocol, a siderophore cephalosporin against MBL-producing clinical isolates. METHODS: MBL-producing strains were selected from clinical isolates of Enterobacterales, Pseudomonas aeruginosa and Acinetobacter baumannii complex collected in North America and Europe in five consecutive annual multinational SIDERO-WT surveillance studies from 2014 to 2019. MICs of cefiderocol and comparator agents were determined by the broth microdilution method according to the CLSI guideline. RESULTS: A total of 452 MBL-producing strains consisting of 200 Enterobacterales, 227 P. aeruginosa and 25 A. baumannii complex were identified. The highest number of MBL-producing Enterobacterales strains were detected in Greece. MBL-producing strains of both P. aeruginosa and A. baumannii complex were isolated most frequently in Russia. For Enterobacterales, 91.5% or 67.5% of MBL-producing strains had cefiderocol MIC values ≤4 mg/L (CLSI susceptibility breakpoint) or ≤2 mg/L (EUCAST susceptibility breakpoint), respectively. All MIC values of cefiderocol for MBL-producing P. aeruginosa strains were ≤4 mg/L (CLSI susceptibility breakpoint), and 97.4% of them had cefiderocol MIC values ≤2 mg/L (EUCAST susceptibility breakpoint). For A. baumannii complex, 60.0% or 44.0% of MBL-producing strains had cefiderocol MIC values ≤4 mg/L (CLSI susceptibility breakpoint) or ≤2 mg/L (EUCAST pharmacokinetic-pharmacodynamic susceptibility breakpoint), respectively. Against all types of MBL-producing strains, MIC distribution curves of cefiderocol were located in the lowest numerical values, compared with other ß-lactams and ß-lactam/ß-lactamase inhibitor combinations tested and ciprofloxacin. CONCLUSIONS: Although the types of MBL-producing strains isolated by country varied, cefiderocol showed potent in vitro activity against all types of MBL-producing Gram-negative bacteria regardless of the bacterial species.

In Vitro Activity of Cefiderocol Against Meropenem-Nonsusceptible Gram-Negative Bacilli with Defined ß-Lactamase Carriage: SIDERO-WT Surveillance Studies, 2014-2019.

We examined the in vitro susceptibility of meropenem-nonsusceptible Enterobacterales, Pseudomonas aeruginosa, and Acinetobacter baumannii complex isolates from five consecutive annual SIDERO-WT surveillance studies (2014-2019) to cefiderocol and comparator agents in the context of their carbapenemase carriage. 1,003 Enterobacterales, 1,758 P. aeruginosa, and 2,809 A. baumannii complex isolates from North America and Europe that were meropenem nonsusceptible (CLSI M100, 2022) were molecularly characterized for ß-lactamase content by PCR followed by Sanger sequencing or by whole genome sequencing. Among Enterobacterales, 91.5% of metallo-ß-lactamase (MBL)-producing, 98.4% of KPC-producing, 97.3% of OXA-48 group-producing, and 98.7% of carbapenemase-negative, meropenem-nonsusceptible isolates were cefiderocol susceptible (MIC ≤4 mg/L). Among P. aeruginosa, 100% of MBL-producing, 100% of GES carbapenemase-producing, and 99.8% of carbapenemase-negative, meropenem-nonsusceptible isolates were cefiderocol susceptible (MIC ≤4 mg/L). Among A. baumannii complex, 60.0% of MBL-producing, 95.6% of OXA-23 group-producing, 89.5% of OXA-24 group-producing, 100% of OXA-58 group-producing, and 95.5% of carbapenemase-negative, meropenem-nonsusceptible isolates were cefiderocol susceptible (MIC ≤4 mg/L). Cefiderocol was inactive against A. baumannii complex isolates carrying a PER or VEB ß-lactamase (n = 103; 15.5% susceptible). Ceftazidime-avibactam and ceftolozane-tazobactam were inactive against MBL-carrying and A. baumannii complex isolates; ceftolozane-tazobactam was also inactive against serine carbapenemase-carrying Enterobacterales and P. aeruginosa. In summary, cefiderocol was highly active in vitro against Gram-negative isolates carrying MBLs and serine carbapenemases, as well as carbapenemase-negative, meropenem-nonsusceptible isolates.

In Vitro Activity of Ceftibuten-Avibactam against ß-Lactamase-Positive Enterobacterales from the ATLAS Global Surveillance Program.

Ceftibuten is an established, oral, third-generation cephalosporin in early clinical development in combination with an oral prodrug of avibactam for the treatment of complicated urinary tract infections, including acute pyelonephritis. We evaluated the in vitro activity of ceftibuten-avibactam against 1,165 Enterobacterales isolates selected from the 2016-2020 ATLAS global surveillance program based upon their ß-lactamase genotype, ß-lactam-susceptible phenotype, species identification, and specimen source (95.8% urine). MICs were determined by CLSI broth microdilution. Avibactam was tested at a fixed concentration of 4 µg/mL. Molecular methods were used to identify ß-lactamase genes. Ceftibuten-avibactam inhibited 90% (MIC90) of ESBL-producing (n = 645), KPC-producing (n = 60), chromosomal AmpC-positive (n = 100), OXA-48-like-producing (n = 50), and acquired AmpC-producing (n = 110) isolates at concentrations of 0.12, 0.5, 1, 2, and 4 µg/mL, respectively. At concentrations of ≤1 and ≤8 µg/mL, ceftibuten-avibactam inhibited 98.4 and 99.2% of ESBL-positive isolates; 96.7 and 100% of KPC-positive isolates; 91.0 and 99.0% of chromosomal AmpC-positive isolates; 86.0 and 96.0% of OXA-48-like-positive isolates; and 85.5 and 91.8% of acquired AmpC-positive isolates. Against ESBL-producing, KPC-producing, chromosomal AmpC-positive, OXA-48-like-producing, and acquired AmpC-producing isolates, ceftibuten-avibactam was 256-, 128-, >64-, >32-, and > 16-fold more potent than ceftibuten alone. The potency of ceftibuten-avibactam was 4-fold greater than ceftazidime-avibactam against ESBL-producing (ceftibuten-avibactam MIC90, 0.12 µg/mL; ceftazidime-avibactam MIC90, 0.5 µg/mL) and KPC-producing (0.5 µg/mL; 2 µg/mL) isolates, equivalent to ceftazidime-avibactam (MIC90, 2 µg/mL) against OXA-48-like-producing isolates, 2-fold less active than ceftazidime-avibactam (1 µg/mL; 0.5 µg/mL) against chromosomal AmpC-positive isolates, and 4-fold less active than ceftazidime-avibactam (4 µg/mL; 1 µg/mL) against acquired AmpC-producing isolates. Continued development of ceftibuten-avibactam appears justified.

In Vitro Activity of Cefepime-Taniborbactam and Comparators against Clinical Isolates of Gram-Negative Bacilli from 2018 to 2020: Results from the Global Evaluation of Antimicrobial Resistance via Surveillance (GEARS) Program.

Taniborbactam is a novel cyclic boronate ß-lactamase inhibitor in clinical development in combination with cefepime. We assessed the in vitro activity of cefepime-taniborbactam and comparators against a 2018-2020 collection of Enterobacterales (n = 13,731) and Pseudomonas aeruginosa (n = 4,619) isolates cultured from infected patients attending hospitals in 56 countries. MICs were determined by CLSI broth microdilution. Taniborbactam was tested at a fixed concentration of 4 µg/mL. Isolates with cefepime-taniborbactam MICs of ≥16 µg/mL underwent whole-genome sequencing. ß-lactamase genes were identified in meropenem-resistant isolates by PCR/Sanger sequencing. Against Enterobacterales, taniborbactam reduced the cefepime MIC90 value by >64-fold (from >16 to 0.25 µg/mL). At ≤16 µg/mL, cefepime-taniborbactam inhibited 99.7% of all Enterobacterales isolates; >97% of isolates with multidrug-resistant (MDR) and ceftolozane-tazobactam-resistant phenotypes; ≥90% of isolates with meropenem-resistant, difficult-to-treat-resistant (DTR), meropenem-vaborbactam-resistant, and ceftazidime-avibactam-resistant phenotypes; 100% of VIM-positive, AmpC-positive, and KPC-positive isolates; 98.7% of extended-spectrum ß-lactamase (ESBL)-positive; 98.8% of OXA-48-like-positive; and 84.6% of NDM-positive isolates. Against P. aeruginosa, taniborbactam reduced the cefepime MIC90 value by 4-fold (from 32 to 8 µg/mL). At ≤16 µg/mL, cefepime-taniborbactam inhibited 97.4% of all P. aeruginosa isolates; ≥85% of isolates with meropenem-resistant, MDR, and meropenem-vaborbactam-resistant phenotypes; >75% of isolates with DTR, ceftazidime-avibactam-resistant, and ceftolozane-tazobactam-resistant phenotypes; and 87.4% of VIM-positive isolates. Multiple potential mechanisms, including carriage of IMP, certain alterations in PBP3, permeability (porin) defects, and possibly, upregulation of efflux were present in most isolates with cefepime-taniborbactam MICs of ≥16 µg/mL. We conclude that cefepime-taniborbactam exhibited potent in vitro activity against Enterobacterales and P. aeruginosa and inhibited most carbapenem-resistant isolates, including those carrying serine carbapenemases or NDM/VIM metallo-ß-lactamases (MBLs).

In vitro antibacterial activities of cefiderocol against Gram-negative clinical strains isolated from China in 2020.

OBJECTIVES: Cefiderocol (CFDC) is a parenteral siderophore cephalosporin that is active against Gram-negative bacteria, including carbapenem-resistant isolates. We report the in vitro activity of CFDC and other antibiotics against 1738 clinical isolates of Gram-negative bacilli (GNB) provided by five medical centres in five provinces of China in 2020 METHODS: Antibiotic susceptibility testing was performed using the Clinical and Laboratory Standards Institute broth microdilution method. RESULTS: Against Pseudomonas aeruginosa and Acinetobacter Spp., the CFDC concentration inhibiting the growth of 90% of the isolates (MIC90) (0.5 µg/mL) was identical and did not change by the carbapenem resistance phenotype. The susceptibility rate of P. aeruginosa and Acinetobacter Spp. to CFDC was high (> 98%) and was similar against isolates with and without meropenem resistance. The MIC of CFDC for all Stenotrophomonas maltophilia isolates (20 isolates) was ≤1 µg/mL and the MIC90 was 0.12 µg/mL. Considerable differences were noted in the susceptibility to CFDC between all tested Enterobacterales isolates and meropenem-non-susceptible Enterobacterales isolates. The MIC90 of CFDC was 1 µg/mL for all tested Enterobacterales isolates and 8 µg/mL for meropenem-non-susceptible Enterobacterales isolates. CONCLUSIONS: CFDC demonstrated potent in vitro activity against a recent collection of clinical isolates, including meropenem-non-susceptible isolates, obtained from medical centres in mainland China.

Ceftibuten-Ledaborbactam Activity against Multidrug-Resistant and Extended-Spectrum-ß-Lactamase-Positive Clinical Isolates of Enterobacterales from a 2018-2020 Global Surveillance Collection.

Ceftibuten-ledaborbactam etzadroxil is a cephalosporin-boronate ß-lactamase inhibitor prodrug combination under development as an oral treatment for complicated urinary tract infections caused by multidrug-resistant (MDR) Enterobacterales producing serine ß-lactamases (Ambler class A, C, and D). In vivo, ledaborbactam etzadroxil (formerly VNRX-7145) is cleaved to the active inhibitor ledaborbactam (formerly VNRX-5236). To more completely define the breadth of ceftibuten-ledaborbactam's activity against important antimicrobial-resistant pathogens, we assessed its in vitro activity against phenotypic and genotypic subsets from a 2018-2020 global culture collection of 3,889 clinical isolates of Enterobacterales, including MDR organisms, extended-spectrum-ß-lactamase (ESBL)-positive organisms, and organisms that are nonsusceptible and resistant to other antimicrobials. MICs were determined by CLSI broth microdilution and interpreted using both CLSI and EUCAST breakpoints. Ledaborbactam was tested at a fixed concentration of 4 µg/mL. ß-Lactamase genes were characterized by PCR followed by Sanger sequencing or whole-genome sequencing for selected ß-lactam-resistant isolate subsets. At ≤1 µg/mL, ceftibuten-ledaborbactam (MIC90, 0.25 µg/mL) inhibited 89.7% of MDR isolates, 98.3% of isolates with a presumptive ESBL-positive phenotype, and 92.6% of trimethoprim-sulfamethoxazole-nonsusceptible, 91.7% of levofloxacin-nonsusceptible, 88.1% of amoxicillin-clavulanate-nonsusceptible, 85.7% of ceftibuten-resistant (MIC >1 µg/mL), and 54.1% of carbapenem-nonsusceptible isolates. Against specific ESBL genotype-positive isolates (AmpC negative, serine carbapenemase negative, and metallo-ß-lactamase negative), ceftibuten-ledaborbactam inhibited 96.3% of CTX-M-9 group (MIC90, 0.25 µg/mL), 91.5% of CTX-M-1 group (MIC90, 0.5 µg/mL), and 88.2% of SHV-positive (MIC90, 2 µg/mL) isolates at ≤1 µg/mL. Against specific serine carbapenemase genotype-positive isolates, ceftibuten-ledaborbactam inhibited 85.9% of KPC-positive (MIC90, 2 µg/mL) and 82.9% of OXA-48-group-positive (MIC90, 2 µg/mL) isolates at ≤1 µg/mL. Continued development of ceftibuten-ledaborbactam appears warranted.

In Vitro Activity of Sulbactam-Durlobactam against Global Isolates of Acinetobacter baumannii-calcoaceticus Complex Collected from 2016 to 2021.

Sulbactam-durlobactam is a ß-lactam-ß-lactamase inhibitor combination designed to treat serious Acinetobacter baumannii-calcoaceticus complex (ABC) infections, including carbapenem-non-susceptible and multidrug-resistant (MDR) isolates. The current study characterized the in vitro activity of sulbactam-durlobactam against a collection of 5,032 ABC clinical isolates collected in 33 countries across the Asia/South Pacific region, Europe, Latin America, the Middle East, and North America from 2016 to 2021. The sulbactam-durlobactam MIC50 and MIC90 were 1 and 2 µg/mL, respectively, for all ABC isolates tested. The addition of durlobactam (at a fixed concentration of 4 µg/mL) to sulbactam decreased its MIC50 by 8-fold (from 8 to 1 µg/mL) and its MIC90 by 32-fold (from 64 to 2 µg/mL) for all ABC isolates. The in vitro activity of sulbactam-durlobactam was maintained across individual ABC species, years, global regions of collection, specimen sources, and resistance phenotypes, including MDR and extensively drug-resistant (XDR) isolates. At 4 µg/mL (preliminary sulbactam-durlobactam susceptible MIC breakpoint), sulbactam-durlobactam inhibited 98.3% of all ABC isolates and >96% of sulbactam-, imipenem-, ciprofloxacin-, amikacin-, and minocycline-non-susceptible isolates; as well as colistin-resistant, MDR, and XDR isolates. Most imipenem-non-susceptible ABC isolates (96.8%, 2,488/2,570) were carbapenem-resistant A. baumannii (CRAB); 96.9% (2,410/2,488) of CRAB isolates were sulbactam-durlobactam-susceptible. More than 80% of ABC isolates had sulbactam-durlobactam MIC values that were ≥2 doubling-dilutions (4-fold) lower than sulbactam alone. Only 1.7% (84/5,032) of ABC isolates from 2016 to 2021 had sulbactam-durlobactam MIC values of >4 µg/mL. Of the 84 isolates, 94.0% were A. baumannii, 4.8% were A. pittii, and 1.2% were A. nosocomialis. In summary, sulbactam-durlobactam demonstrated potent antibacterial activity against a 2016 to 2021 collection of geographically diverse clinical isolates of ABC isolates, including carbapenem-non-susceptible and MDR isolates.

Antimicrobial activity of ceftazidime-avibactam and comparators against levofloxacin-resistant Escherichia coli collected from four geographic regions, 2012-2018.

BACKGROUND: Increases in resistance to fluoroquinolones have been correlated with the use of levofloxacin in the treatment of infections caused by Escherichia coli. The analysis presents the in vitro activity of ceftazidime-avibactam and comparator agents against 10,840 levofloxacin-resistant E. coli isolates collected from four geographic regions (Africa/Middle East, Europe, Asia/South Pacific, Latin America) between 2012 and 2018. METHODS: Non-duplicate clinical isolates of E. coli were collected from participating centres and shipped to IHMA, Inc., (Schaumburg, IL, USA). Susceptibility testing was performed with frozen broth microdilution panels manufactured by IHMA, according to CLSI guidelines. Levofloxacin-resistance was defined at a minimum inhibitory concentration of ≥ 2 mg/L. Isolates collected between 2012 and 2015 were tested for extended-spectrum ß-lactamase (ESBL) activity by determining susceptibility to cefotaxime, cefotaxime-clavulanate, ceftazidime, and ceftazidime-clavulanate as recommended by CLSI guidelines. Isolates collected between 2016 and 2018 were identified as ESBL-positive by genotype using multiplex polymerase chain reaction assays. RESULTS: A total of 74.8% of levofloxacin-resistant E. coli isolates in the analysis were from three culture sources: urinary tract infections (N = 3229; 29.8%), skin and skin structure infections (N = 2564; 23.7%) and intra-abdominal infections (N = 2313; 21.3%). Susceptibility rates to ceftazidime-avibactam were consistently high in all regions against both ESBL-positive (97.0% in Asia/South Pacific to 99.7% in Africa/Middle East and Latin America) and ESBL-negative isolates (99.4% in Asia/South Pacific to 100% in Latin America). Susceptibility was also high in each region among ESBL-positive and ESBL-negative isolates to colistin (≥ 98.5%), imipenem (≥ 96.5%), meropenem (≥ 96.5%) and tigecycline (≥ 94.1%). CONCLUSIONS: Antimicrobial susceptibility to ceftazidime-avibactam among levofloxacin-resistant E. coli isolates, including ESBL-positive isolates, collected from four geographical regions between 2012 and 2018 was consistently high. Susceptibility to the comparator agents colistin, tigecycline, imipenem and meropenem was also high.

In Vitro Activity of Ceftibuten/VNRX-5236 against Urinary Tract Infection Isolates of Antimicrobial-Resistant Enterobacterales.

Ceftibuten/VNRX-7145 is a cephalosporin/boronate ß-lactamase inhibitor combination under development as an oral treatment for complicated urinary tract infections caused by Enterobacterales producing serine ß-lactamases (Ambler class A, C, and D). In vivo, VNRX-7145 (VNRX-5236 etzadroxil) is cleaved to the active inhibitor, VNRX-5236. We assessed the in vitro activity of ceftibuten/VNRX-5236 against 1,066 urinary isolates of Enterobacterales from a 2014-2016 global culture collection. Each isolate tested was preselected to possess a multidrug-resistant (MDR) phenotype that included nonsusceptibility to amoxicillin-clavulanate and resistance to levofloxacin. MICs were determined by CLSI broth microdilution. VNRX-5236 was tested at a fixed concentration of 4 µg/ml. Ceftibuten/VNRX-5236 inhibited 90% of all isolates tested (MIC90) at 2 µg/ml; MIC90s for ESBL- (n = 566), serine carbapenemase- (n = 116), and acquired AmpC-positive (n = 58) isolate subsets were ≤0.25, >32, and 8 µg/ml, respectively. At concentrations of ≤1, ≤2, and ≤4 µg/ml, ceftibuten/VNRX-5236 inhibited 89.1, 91.7, and 93.1% of all isolates tested; 96.5, 97.7, and 98.4% of ESBL-positive isolates; 75.9, 81.9, and 81.9% of serine carbapenemase-positive isolates; and 70.7, 81.0, and 87.9% of acquired AmpC-positive isolates. Ceftibuten/VNRX-5236 at concentrations of ≤1, ≤2, and ≤4 µg/ml inhibited 85-89, 89-91, and 91-92% of isolates that were not susceptible (defined by CLSI and EUCAST breakpoint criteria) to nitrofurantoin, trimethoprim-sulfamethoxazole, and/or fosfomycin, (as part of their MDR phenotype), oral agents commonly prescribed to treat uncomplicated urinary tract infections. The potency of ceftibuten/VNRX-5236 (MIC90, 2 µg/ml) was similar (within one doubling-dilution) to intravenous-only agents ceftazidime-avibactam (MIC90 2 µg/ml) and meropenem-vaborbactam (MIC90 1 µg/ml). Continued investigation of ceftibuten/VNRX-5236 is warranted.

In Vitro Susceptibility of Gram-Negative Pathogens to Cefiderocol in Five Consecutive Annual Multinational SIDERO-WT Surveillance Studies, 2014 to 2019.

We report in vitro susceptibility data from five consecutive annual SIDERO-WT surveillance studies (2014 to 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 were 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 to 100%/year; Europe range, 99.3 to 99.9%/year) and P. aeruginosa (North America range, 99.8 to 100%; Europe range, 99.9 to 100%) were unchanged from 2014 to 2019. Annual percent susceptible rates for A. baumannii complex demonstrated sporadic, nondirectional differences (North America range, 97.5 to 100%; Europe range, 90.4 to 97.5%); the wider range for Europe (∼7%) was due to isolates from Russia. Annual percent susceptible rates for S. maltophilia showed minor, nondirectional differences (North America range, 96.4 to 100%; Europe range, 95.6 to 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 Vitro Activity of Gepotidacin against Gram-Negative and Gram-Positive Anaerobes.

Gepotidacin (formerly GSK2140944) is a first-in-class triazaacenaphthylene antibacterial currently in phase III clinical trials. When tested against Gram-negative (n = 333) and Gram-positive (n = 225) anaerobes by agar dilution, gepotidacin inhibited 90% of isolates at concentrations of 4 and 2 µg/mL, respectively. Given gepotidacin's in vitro activity against the anaerobic isolates tested, further study is warranted to better understand the utility of gepotidacin in the treatment of infections caused by clinically relevant anaerobic organisms.

Activity of imipenem/relebactam and comparators against gram-negative pathogens from patients with bloodstream infections in the United States and Canada - SMART 2018-2019.

Bloodstream infections (BSI) are often caused by drug-resistant pathogens, and novel antimicrobials are needed. We examined the activity of imipenem/relebactam against BSI pathogens from US and Canada: >99% of non-Morganellaceae Enterobacterales, including 100% of MDR isolates, and >94% of Pseudomonas aeruginosa were imipenem/relebactam-susceptible. Imipenem/relebactam could provide an important treatment option.

In vitro activity of ceftaroline against bacterial pathogens isolated from patients with skin and soft tissue and respiratory tract infections in the Middle East and Africa: AWARE global surveillance programme 2015-2018.

OBJECTIVES: To report antimicrobial susceptibility testing surveillance data for ceftaroline and comparative agents from the AWARE global surveillance programme for bacterial pathogens causing skin and soft tissue infections (SSTIs) and lower respiratory infections (RTIs) in Middle East and African countries from 2015 to 2018. METHODS: Pathogens were identified by MALDI-TOF/MS. Antimicrobial susceptibility testing was performed using the Clinical and Laboratory Standards Institute (CLSI) broth microdilution method. MICs were interpreted by both CLSI (M100, 2020) and European Committee on Antimicrobial Susceptibility Testing (EUCAST) (v 10.0, 2020) breakpoints. RESULTS: All MSSA (n = 1125) and 93.9% of MRSA (n = 1235) were susceptible to ceftaroline (MIC ≤ 1 µg/mL, CLSI and EUCAST). The maximum ceftaroline MIC observed for MRSA was 2 µg/mL; no ceftaroline-resistant MRSA were identified among SSTI (CLSI and EUCAST) and RTI (CLSI) isolates. All isolates of ß-haemolytic Streptococcus (n = 324), and penicillin-susceptible (PSSP) and -intermediate Streptococcus pneumoniae (PISP; n = 369) were susceptible to ceftaroline. Rates of susceptibility to ceftaroline for penicillin-resistant S. pneumoniae (penicillin MIC ≥ 2 µg/mL; n = 175), and ß-lactamase-negative (BLNHI; n = 224) and ß-lactamase-positive Haemophilus influenzae (n = 49) were 99.4%, 98.7%, and 98.0% (CLSI) and 92.6%, 98.2%, and 83.7% (EUCAST), respectively. Rates of susceptibility to ceftaroline for ESBL-negative Escherichia coli (n = 442), Klebsiella pneumoniae (n = 381), and Klebsiella oxytoca (n = 103) were 92.1%, 93.2%, and 96.1%, respectively. CONCLUSION: Ceftaroline-resistant isolates of MRSA causing SSTIs were not identified in Middle East and African countries in 2015-2018 using recently revised CLSI (in 2019) or EUCAST (in 2018) breakpoint criteria. Common bacterial pathogens causing SSTIs (Staphylococcus aureus, ß-haemolytic Streptococcus) and lower RTIs (PSSP, PISP, BLNHI) demonstrated no resistance or low levels of resistance (0-1.8%) to ceftaroline.

In Vitro Activity of WCK 5222 (Cefepime-Zidebactam) against Worldwide Collected Gram-Negative Bacilli Not Susceptible to Carbapenems.

WCK 5222 (cefepime-zidebactam, 2 g + 1g, every 8 h [q8h]) is in clinical development for the treatment of infections caused by carbapenem-resistant and multidrug-resistant (MDR) Gram-negative bacilli. We determined the in vitro susceptibility of 1,385 clinical isolates of non-carbapenem-susceptible Enterobacterales, MDR Pseudomonas aeruginosa (also non-carbapenem susceptible), Stenotrophomonas maltophilia, and Burkholderia spp. collected worldwide (49 countries) from 2014 to 2016 to cefepime-zidebactam (1:1 ratio), ceftazidime-avibactam, imipenem-relebactam, ceftolozane-tazobactam, and colistin using the CLSI broth microdilution method. Cefepime-zidebactam inhibited 98.5% of non-carbapenem-susceptible Enterobacterales (n = 1,018) at ≤8 µg/ml (provisional cefepime-zidebactam-susceptible MIC breakpoint). Against the subset of metallo-ß-lactamase (MBL)-positive Enterobacterales (n = 214), cefepime-zidebactam inhibited 94.9% of isolates at ≤8 µg/ml. Further, it inhibited 99.6% of MDR P. aeruginosa (n = 262) isolates at ≤32 µg/ml (proposed cefepime-zidebactam-susceptible pharmacokinetic/pharmacodynamic MIC breakpoint), including all MBL-positive isolates (n = 94). Moreover, cefepime-zidebactam was active against the majority of isolates of Enterobacterales (≥95%) and P. aeruginosa (99%) that were not susceptible to ceftazidime-avibactam, ceftolozane-tazobactam, imipenem-relebactam, and colistin. Most isolates (99%) of S. maltophilia (n = 101; MIC50, 8 µg/ml; MIC90, 32 µg/ml) and Burkholderia spp. (n = 4; MIC range, 16 to 32 µg/ml) were also inhibited by cefepime-zidebactam at ≤32 µg/ml. The activity of cefepime-zidebactam against carbapenem-resistant Gram-negative bacteria is ascribed to its ß-lactam enhancer mechanism of action (i.e., zidebactam binding to penicillin binding protein 2 [PBP2] and its universal stability to both serine ß-lactamases and MBLs). The results from this study support the continued development of cefepime-zidebactam as a potential therapy for infections caused by Enterobacterales, P. aeruginosa, and other nonfermentative Gram-negative bacilli where resistance to marketed antimicrobial agents is a limiting factor.

Reduced susceptibility mechanism to cefiderocol, a siderophore cephalosporin, among clinical isolates from a global surveillance programme (SIDERO-WT-2014).

OBJECTIVE: To investigate possible mechanistic factors to explain cefiderocol (CFDC) non-susceptibility, we characterized 38 clinical isolates with a CFDC minimum inhibitory concentration (MIC) of >4µg/mL from a multi-national surveillance study. METHODS: The MIC measurement in the presence of ß-lactamase inhibitors and whole genome sequencing were performed. RESULTS: The MIC decrease of CFDC by ß-lactamase inhibitors was observed against all of the test isolates. Among the 38 isolates, NDM and PER genes were observed in 5 and 25 isolates, respectively. No other ß-lactamases responsible for high MIC were identified in the other eight isolates. The MIC of CDFC against Escherichia coli isogenic strains introduced with NDM and PER ß-lactamase increased by ≥16-fold, suggesting the contribution of NDM and PER to the non-susceptibility to CFDC. Against NDM producers, a ≥8-fold MIC increase was observed only when both serine- and metallo-type ß-lactamase inhibitors were added. In addition, many of the PER or NDM producers remained susceptible to CFDC. These results suggested that the presence of only NDM or PER would not lead to non-susceptibility to CFDC and that multiple factors would be related to CFDC resistance. CONCLUSION: Multiple factors including NDM and PER could be related to reduced susceptibility to CFDC.

In Vitro Activity of Sulbactam-Durlobactam against Acinetobacter baumannii-calcoaceticus Complex Isolates Collected Globally in 2016 and 2017.

Acinetobacter baumannii-calcoaceticus complex (ABC) organisms cause severe infections that are difficult to treat due to preexisting antibiotic resistance. Sulbactam-durlobactam (formerly sulbactam-ETX2514) (SUL-DUR) is a ß-lactam-ß-lactamase inhibitor combination antibiotic designed to treat serious infections caused by ABC organisms, including multidrug-resistant (MDR) strains. The in vitro antibacterial activities of SUL-DUR and comparator agents were determined by broth microdilution against 1,722 clinical isolates of ABC organisms collected in 2016 and 2017 from 31 countries across Asia/South Pacific, Europe, Latin America, the Middle East, and North America. Over 50% of these isolates were resistant to carbapenems. Against this collection of global isolates, SUL-DUR had a MIC50/MIC90 of 1/2 µg/ml compared to a MIC50/MIC90 of 8/64 µg/ml for sulbactam alone. This level of activity was found to be consistent across organisms, regions, sources of infection, and subsets of resistance phenotypes, including MDR and extensively drug-resistant isolates. The SUL-DUR activity was superior to those of the tested comparators, with only colistin having similar potency. Whole-genome sequencing of the 39 isolates (2.3%) with a SUL-DUR MIC of >4 µg/ml revealed that these strains encoded either the metallo-ß-lactamase NDM-1, which durlobactam does not inhibit, or single amino acid substitutions near the active site of penicillin binding protein 3 (PBP3), the primary target of sulbactam. In summary, SUL-DUR demonstrated potent antibacterial activity against recent, geographically diverse clinical isolates of ABC organisms, including MDR isolates.

Reproducibility of broth microdilution MICs for the novel siderophore cephalosporin, cefiderocol, determined using iron-depleted cation-adjusted Mueller-Hinton broth.

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.