Sulbactam-durlobactam susceptibility test method development and quality control ranges for MIC and disk diffusion tests.

Sulbactam-durlobactam is a ß-lactam/ß-lactamase inhibitor combination developed to treat hospital-acquired and ventilator-associated bacterial pneumonia caused by Acinetobacter baumannii-calcoaceticus complex (ABC). Durlobactam is a diazabicyclooctane ß-lactamase inhibitor with potent activity against Ambler classes A, C, and D serine ß-lactamases and restores sulbactam activity against multidrug-resistant ABC. Studies were conducted to establish sulbactam-durlobactam antimicrobial susceptibility testing methods for both broth microdilution minimal inhibitory concentration (MIC) and disk diffusion tests as well as quality control (QC) ranges. To establish the MIC test method, combinations of sulbactam and durlobactam were evaluated using a panel of genetically characterized A. baumannii isolates which were categorized as predicted to be susceptible or resistant based on the spectrum of ß-lactamase inhibition by durlobactam. MIC testing with doubling dilutions of sulbactam with a fixed concentration of 4 µg/mL of durlobactam resulted in the greatest discrimination of the pre-defined susceptible and resistant strains. Similarly, the sulbactam/durlobactam 10/10 µg disk concentration showed the best discrimination as well as correlation with the MIC test. A. baumannii NCTC 13304 was selected for QC purposes because it assesses the activity of both sulbactam and durlobactam with clear endpoints. Multi-laboratory QC studies were conducted according to CLSI M23 Tier 2 criteria. A sulbactam-durlobactam broth MIC QC range of 0.5/4-2/4 µg/mL and a zone diameter QC range of 24-30 mm were determined for A. baumannii NCTC 13304 and have been approved by CLSI. These studies will enable clinical laboratories to perform susceptibility tests with accurate and reproducible methods.

Pharmacokinetic-Pharmacodynamic Target Attainment Analyses Evaluating Omadacycline Dosing Regimens for the Treatment of Patients with Community-Acquired Bacterial Pneumonia Arising from Streptococcus pneumoniae and Haemophilus influenzae.

Omadacycline, a novel aminomethylcycline with in vitro activity against Gram-positive and -negative organisms, including Streptococcus pneumoniae and Haemophilus influenzae, is approved in the United States to treat patients with community-acquired bacterial pneumonia (CABP). Using nonclinical pharmacokinetic-pharmacodynamic (PK-PD) targets for efficacy and in vitro surveillance data for omadacycline against S. pneumoniae and H. influenzae, and a population pharmacokinetic model, PK-PD target attainment analyses were undertaken using total-drug epithelial lining fluid (ELF) and free-drug plasma exposures to evaluate omadacycline 100 mg intravenously (i.v.) every 12 h or 200 mg i.v. every 24 h (q24h) on day 1, followed by 100 mg i.v. q24h on day 2 and 300 mg orally q24h on days 3 to 5 for patients with CABP. Percent probabilities of PK-PD target attainment on days 1 and 2 by MIC were assessed using the following four approaches for selecting PK-PD targets: (i) median, (ii) second highest, (iii) highest, and (iv) randomly assigned total-drug ELF and free-drug plasma ratio of the area under the concentration-time curve to the MIC (AUC/MIC ratio) targets associated with a 1-log10 CFU reduction from baseline. Percent probabilities of PK-PD target attainment based on total-drug ELF AUC/MIC ratio targets on days 1 and 2 were ≥91.1% for S. pneumoniae for all approaches but the highest target and ≥99.2% for H. influenzae for all approaches at MIC90s (0.12 and 1 µg/mL for S. pneumoniae and H. influenzae, respectively). Lower percent probabilities of PK-PD target attainment based on free-drug plasma AUC/MIC ratio targets were observed for randomly assigned and the highest free-drug plasma targets for S. pneumoniae and for all targets for H. influenzae. These data provided support for approved omadacycline dosing regimens to treat patients with CABP and decisions for the interpretive criteria for the in vitro susceptibility testing of omadacycline against these pathogens.

Determination of MIC Quality Control Ranges for Ceftibuten-Avibactam (Fixed 4 µg/mL), a Novel ß-Lactam/ß-Lactamase Inhibitor Combination.

Ceftibuten/ARX-1796 (avibactam prodrug) is a novel oral antibacterial combination in early clinical development for the treatment of complicated urinary tract infections (cUTI) including pyelonephritis. ARX-1796 is the novel avibactam prodrug being combined with ceftibuten for oral dosing that is converted to active avibactam in vivo. A Clinical and Laboratory Standards Institute (CLSI) M23 (2018) tier 2 broth microdilution quality control (QC) study was conducted with ceftibuten-avibactam to establish MIC QC ranges. Ceftibuten-avibactam broth microdilution QC ranges were approved for Escherichia coli ATCC 25922 (0.016/4 to 0.12/4 µg/mL), E. coli NCTC 13353 (0.03/4 to 0.12/4 µg/mL), Klebsiella pneumoniae ATCC 700603 (0.06/4 to 0.25/4 µg/mL), K. pneumoniae ATCC BAA-1705 (0.03/4 to 0.25/4 µg/mL), and K. pneumoniae ATCC BAA-2814 (0.12/4 to 0.5/4 µg/mL) by the CLSI Subcommittee on Antimicrobial Susceptibility Testing in January 2022. Approved ceftibuten-avibactam QC ranges will support future clinical development, device manufacturers, and routine patient care.

In vitro activity of sulopenem and comparator agents against Enterobacterales and anaerobic clinical isolates collected during the SENTRY Antimicrobial Surveillance Program.

OBJECTIVES: Physicians must leverage several factors when making antibiotic therapy decisions, including route of administration and duration of therapy. Oral administration provides several potential advantages including increased accessibility, prevention of hospitalizations and earlier discharges. Sulopenem-a broad-spectrum, synthetic penem ß-lactam agent-uniquely possesses both oral and IV formulations along with noted stability among antimicrobial-resistant subsets. This study evaluated the in vitro activity of sulopenem and comparator agents against contemporary Enterobacterales and anaerobic clinical isolates predominantly from patients with bloodstream, intra-abdominal and urinary tract infections. METHODS: A contemporary collection of 1647 Enterobacterales and 559 anaerobic isolates was assembled from medical centres in Europe and the USA. Isolates were susceptibility tested using the CLSI reference methods: broth microdilution for Enterobacterales and agar dilution for anaerobes. RESULTS: Sulopenem demonstrated potent in vitro antimicrobial activity (MIC50/90, 0.03/0.25 mg/L) against Enterobacterales isolates regardless of infection type, inhibiting 99.2% of isolates at ≤1 mg/L. This activity was conserved against resistant phenotypes including ESBL-phenotype Escherichia coli (MIC50/90, 0.03/0.06 mg/L) and ESBL-phenotype Klebsiella pneumoniae (MIC50/90, 0.06/1 mg/L). Sulopenem maintained activity against ciprofloxacin-, nitrofurantoin- and trimethoprim/sulfamethoxazole-non-susceptible subsets (MIC50/90, 0.03-0.06/0.12-0.5 mg/L). Against anaerobic isolates, sulopenem (98.9% inhibited at ≤4 mg/L) and meropenem [98.4% susceptible (CLSI)] were the most active compounds tested. CONCLUSIONS: The potent in vitro activity of sulopenem against this large collection of recent Enterobacterales and anaerobic clinical isolates from multiple infection types supports its further clinical evaluation in the treatment of intra-abdominal and urinary tract infections.

Antimicrobial activity of ceftibuten-avibactam against a global collection of Enterobacterales from patients with urinary tract infections (2021).

We evaluated the in vitro activity of ceftibuten-avibactam against Enterobacterales causing urinary tract infection (UTI). A total of 3216 isolates (1/patient) were consecutively collected from patients with UTI in 72 hospitals from 25 countries in 2021 then susceptibility tested by CLSI broth microdilution. Ceftibuten-susceptible breakpoints currently published by EUCAST (≤ 1 mg/L) and CLSI (≤ 8 mg/L) were applied to ceftibuten-avibactam for comparison. The most active agents were ceftibuten-avibactam (98.4%/99.6% inhibited at ≤ 1/ ≤ 8 mg/L), ceftazidime-avibactam (99.6% susceptible [S]), amikacin (99.1%S), and meropenem (98.2%S). Ceftibuten-avibactam (MIC50/90, 0.03/0.06 mg/L) was fourfold more potent than ceftazidime-avibactam (MIC50/90, 0.12/0.25 mg/L) based on MIC50/90 values. The most active oral agents were ceftibuten (89.3%S; 79.5% inhibited at ≤ 1 mg/L), levofloxacin (75.4%S), and trimethoprim-sulfamethoxazole (TMP-SMX; 73.4%S). Ceftibuten-avibactam inhibited 97.6% of isolates with an extended-spectrum ß-lactamase phenotype, 92.1% of multidrug-resistant isolates, and 73.7% of carbapenem-resistant Enterobacterales (CRE) at ≤ 1 mg/L. The second most active oral agent against CRE was TMP-SMX (24.6%S). Ceftazidime-avibactam was active against 77.2% of CRE isolates. In conclusion, ceftibuten-avibactam was highly active against a large collection of contemporary Enterobacterales isolated from patients with UTI and exhibited a similar spectrum to ceftazidime-avibactam. Ceftibuten-avibactam may represent a valuable option for oral treatment of UTI caused by multidrug-resistant Enterobacterales.

Activity of the Novel Aminomethylcycline KBP-7072 and Comparators against 1,057 Geographically Diverse Recent Clinical Isolates from the SENTRY Surveillance Program, 2019.

KBP-7072 is a novel broad-spectrum tetracycline (aminomethylcycline) antibacterial in clinical development (oral and intravenous formulations) for the treatment of acute bacterial skin and skin structure infections, community-acquired bacterial pneumonia, and complicated intra-abdominal infections. KBP-7072 is active against many of the World Health Organization priority pathogens. In this study, KBP-7072 and tetracycline class comparators were susceptibility tested against 1,057 geographically diverse surveillance isolates from 2019 according to Clinical and Laboratory Standards Institute (CLSI) guidelines. KBP-7072 demonstrated potent in vitro activity against Gram-positive and Gram-negative bacterial pathogens. KBP-7072 was active against Staphylococcus aureus (MIC50/90, 0.06/0.12 mg/liter), methicillin-resistant S. aureus (MIC50/90, 0.06/0.12 mg/liter), S. lugdunensis (MIC50/90, 0.03/0.03 mg/liter), and other coagulase-negative staphylococci (MIC50/90, 0.06/0.25 mg/liter). KBP-7072 was active against Enterococcus faecalis (MIC50/90, 0.03/0.06 mg/liter) and vancomycin-susceptible and -nonsusceptible E. faecium (MIC50/90, 0.03/0.03 mg/liter); Streptococcus pneumoniae (MIC50/90, ≤0.015/0.03 mg/liter), including penicillin- and tetracycline-resistant strains; S. agalactiae (MIC50/90, 0.03/0.06 mg/liter), including macrolide-resistant strains; S. pyogenes (MIC50/90, 0.03/0.03 mg/liter); and viridans group streptococci, including S. anginosus group (MIC50/90, ≤0.015/0.03 mg/liter) isolates. KBP-7072 inhibited 90.2% (MIC50/90, 0.25/2 mg/liter) of all Enterobacterales isolates, including expanded-spectrum ß-lactamase-phenotype strains at ≤2 mg/liter. KBP-7072 demonstrated potent activity against Acinetobacter baumannii-calcoaceticus species complex and Stenotrophomonas maltophilia isolates (MIC50/90 values, 0.5/1 mg/liter), Haemophilus influenzae (MIC50/90, 0.12/0.25 mg/liter; 100.0% inhibited at ≤0.25 mg/liter), and Moraxella catarrhalis (MIC50/90, 0.06/0.06 mg/liter). Based on MIC90 values, KBP-7072 in vitro activity was generally superior to that the other tetracycline class comparators tested. The potent activity of KBP-7072, including resistant organism groups, merits further clinical investigation in infections where these organisms are likely to occur.

Antimicrobial activity of dalbavancin against Gram-positive bacteria isolated from patients hospitalized with bloodstream infection in United States and European medical centers (2018-2020).

Dalbavancin and comparators were susceptibility tested against 8643 Gram-positive bacteria from 74 hospitals located in Europe and the United States by broth microdilution method. The most common organisms were Staphylococcus aureus (45.2%), Enterococcus faecalis (12.2%), and Staphylococcus epidermidis (8.9%), but rank order varied markedly by geographic region. Dalbavancin demonstrated potent activity and broad spectrum, with MIC90 values of 0.03 mg/L for Staphylococcus aureus, ß-haemolytic streptococci, and viridans group streptococci; 0.06 mg/L for Enterococcus faecalis and Staphylococcus epidermidis; and 0.12 mg/L for vancomycin-susceptible Enterococcus faecium. All organisms, except vancomycin-resistant enterococci and 1 Staphylococcus haemolyticus isolate, were inhibited at ≤ 0.25 mg/L of dalbavancin.

Surveillance of Omadacycline Activity Tested against Clinical Isolates from the United States and Europe: Report from the SENTRY Antimicrobial Surveillance Program, 2016 to 2018.

Omadacycline is a broad-spectrum aminomethylcycline approved in October 2018 by the U.S. Food and Drug Administration for treating acute bacterial skin and skin structure infections and community-acquired pneumonia as both an oral and intravenous once-daily formulation. In this report, the activities of omadacycline and comparators were tested against 49,000 nonduplicate bacterial isolates collected prospectively during 2016 to 2018 from medical centers in Europe (24,500 isolates, 40 medical centers [19 countries]) and the United States (24,500 isolates, 33 medical centers [23 states and all 9 U.S. census divisions]). Omadacycline was tested by broth microdilution following the methods in Clinical and Laboratory Standards Institute document M07 (Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria That Grow Aerobically; Approved Standard, 11th ed., 2018). Omadacycline (MIC50/90, 0.12/0.25 mg/liter) inhibited 98.6% of Staphylococcus aureus isolates at ≤0.5 mg/liter, including 96.3% of methicillin-resistant S. aureus isolates and 99.8% of methicillin-susceptible S. aureus isolates. Omadacycline potency was comparable for Streptococcus pneumoniae (MIC50/90, 0.06/0.12 mg/liter), viridans group streptococci (MIC50/90, 0.06/0.12 mg/liter), and beta-hemolytic streptococci (MIC50/90, 0.12/0.25 mg/liter), regardless of species and susceptibility to penicillin, macrolides, or tetracycline. Omadacycline was active against all Enterobacterales tested (MIC50/90, 1/8 mg/liter; 87.5% of isolates were inhibited at ≤4 mg/liter) except Proteus mirabilis (MIC50/90, 16/>32 mg/liter) and indole-positive Proteus spp. (MIC50/90, 8/32 mg/liter) and was most active against Escherichia coli (MIC50/90, 0.5/2 mg/liter), Klebsiella oxytoca (MIC50/90, 1/2 mg/liter), and Citrobacter spp. (MIC50/90, 1/4 mg/liter). Omadacycline inhibited 92.4% of Enterobacter cloacae species complex and 88.5% of Klebsiella pneumoniae isolates at ≤4 mg/liter. Omadacycline was active against Haemophilus influenzae (MIC50/90, 0.5/1 mg/liter), regardless of ß-lactamase status, and against Moraxella catarrhalis (MIC50/90, ≤0.12/0.25 mg/liter). The potent activity of omadacycline against Gram-positive and -negative bacteria indicates that omadacycline merits further study in serious infections in which multidrug resistance and mixed Gram-positive and Gram-negative bacterial infections may be a concern.

In Vitro Activity of KBP-7072, a Novel Third-Generation Tetracycline, against 531 Recent Geographically Diverse and Molecularly Characterized Acinetobacter baumannii Species Complex Isolates.

KBP-7072 is a novel third-generation tetracycline (aminomethylcycline) antibacterial that overcomes common efflux and ribosomal protection resistance mechanisms that cause resistance in older-generation tetracyclines. KBP-7072 completed phase 1 clinical development studies for safety, tolerability, and pharmacokinetics (ClinicalTrials.gov identifier NCT02454361) and multiple ascending doses in healthy subjects (ClinicalTrials.gov identifier NCT02654626) in December 2015. Both oral and intravenous formulations of KBP-7072 are being developed. In this study, we evaluated the in vitro activities of KBP-7072 and comparator agents by CLSI document M07 (2018) broth microdilution against 531 recent geographically diverse and/or molecularly characterized Acinetobacter baumannii-A. calcoaceticus species complex (A. baumannii) isolates from the United States, Europe, Asia-Pacific (excluding China), and Latin America. A. baumannii isolates included carbapenem-resistant, colistin-resistant, tetracycline-resistant, and extended-spectrum-ß-lactamase (ESBL)- and metallo-ß-lactamase (MBL)-producing isolates. Overall, KBP-7072 (MIC50/90, 0.25/1 mg/liter) was comparable in activity to colistin (92.8%/92.8% susceptible [S] [CLSI/EUCAST]) against A. baumannii isolates, inhibiting 99.2% of isolates at ≤2 mg/liter and 97.6% of isolates at ≤1 mg/liter. KBP-7072 was equally active against A. baumannii isolates, including carbapenem-resistant, colistin-resistant, and tetracycline-resistant isolates, regardless of geographic location, and maintained activity against ESBL- and MBL-producing isolates. KBP-7072 outperformed comparator agents, including ceftazidime (40.3% S [CLSI]), gentamicin (48.2%/48.2% S [CLSI/EUCAST]), levofloxacin (39.5%/37.9% S [CLSI/EUCAST]), meropenem (42.0%/42.0% S [CLSI/EUCAST]), piperacillin-tazobactam (33.3% S [CLSI]), and all tetracycline-class comparator agents, which include doxycycline (67.3% S [CLSI]), minocycline (73.8% S [CLSI]), tetracycline (37.2% S [CLSI]), and tigecycline (79.5% inhibited by ≤2 mg/liter). The potent in vitro activity of KBP-7072 against recent geographically diverse, molecularly characterized, and drug-resistant A. baumannii isolates supports continued clinical development for the treatment of serious infections, including those caused by A. baumannii.

Antimicrobial Activity of Omadacycline Tested against Clinical Bacterial Isolates from Hospitals in Mainland China, Hong Kong, and Taiwan: Results from the SENTRY Antimicrobial Surveillance Program (2013 to 2016).

Omadacycline is a derivative of minocycline and the first agent of the aminomethylcycline class. A total of 3,282 organisms (1 per patient) were consecutively collected from patients hospitalized in China (including Hong Kong) and Taiwan. Susceptibility testing was performed by broth microdilution methods in a central laboratory (JMI Laboratories). The collection included Gram-positive and Gram-negative organisms from patients with pneumonia, bloodstream, skin, community-acquired respiratory, and other infections. Omadacycline was very potent against Staphylococcus aureus (n = 689; MIC50/90, 0.12/0.25 mg/liter), including methicillin-resistant Staphylococcus aureus (MRSA; n = 299; MIC50/90, 0.12/0.5 mg/liter), and had similar activity across geographic regions. Omadacycline was very active against Streptococcus pneumoniae (highest MIC, 0.25 mg/liter), ß-hemolytic streptococci (highest MIC, 1 mg/liter), viridans group streptococci (highest MIC, 0.25 mg/liter), and Enterococcus spp. (highest MIC, 0.5 mg/liter) from all geographic regions. Overall, 53.8% of S. pneumoniae isolates were penicillin resistant (penicillin MIC, ≥2 mg/liter) and 10.7% of enterococci (21.2% among E. faecium isolates) were vancomycin resistant. Omadacycline was active against Haemophilus influenzae (MIC50/90, 0.5/1 mg/liter) regardless of ß-lactamase production and was active against Moraxella catarrhalis (MIC50/90, ≤0.12/0.25 mg/liter). Against Enterobacteriaceae, omadacycline was most active against Escherichia coli (MIC50/90, 1/2 mg/liter), Klebsiella oxytoca (MIC50/90, 1/4 mg/liter), and Enterobacter cloacae (MIC50/90, 2/4 mg/liter). Omadacycline had potent in vitro activity against Gram-positive and Gram-negative pathogens isolated from China and Taiwan and retained activity against problem pathogens, such as MRSA, vancomycin-resistant enterococci (VRE), penicillin-resistant S. pneumoniae (PRSPN), and extended-spectrum ß-lactamase-producing E. coli The observed MIC profile in Chinese isolates was very similar to that seen in the U.S. and European surveillance studies.

Determination of MIC Quality Control Ranges for the Novel Gyrase Inhibitor Zoliflodacin.

This report describes the results of two different, multilaboratory quality control (QC) studies that were used to establish QC ranges for the novel gyrase inhibitor zoliflodacin against the ATCC strains recommended by the Clinical and Laboratory Standards Institute (CLSI). Following the completion of an eight-laboratory, CLSI document M23-defined tier 2 study, the agar dilution MIC QC range for zoliflodacin against the Neisseria gonorrhoeae QC strain ATCC 49226 was defined as 0.06 to 0.5 µg/ml and was approved by the CLSI Subcommittee on Antimicrobial Susceptibility Testing. This QC range will be used for in vitro susceptibility testing of zoliflodacin during phase 3 human clinical trials and surveillance studies, and eventually it will be implemented in clinical labs. In a separate study, broth microdilution MIC quality control ranges for zoliflodacin against additional QC strains were determined to be 0.12 to 0.5 µg/ml for Staphylococcus aureus ATCC 29213, 0.25 to 2 µg/ml for Enterococcus faecalis ATCC 29212, 1 to 4 µg/ml for Escherichia coli ATCC 25922, 0.12 to 0.5 µg/ml for Streptococcus pneumoniae ATCC 49619, and 0.12 to 1 µg/ml for Haemophilus influenzae ATCC 49247. These MIC QC ranges were also approved by CLSI for use in future in vitro susceptibility testing studies against organisms other than N. gonorrhoeae.

Development of Broth Microdilution MIC and Disk Diffusion Antimicrobial Susceptibility Test Quality Control Ranges for the Combination of Cefepime and the Novel ß-Lactamase Inhibitor Enmetazobactam.

Third-generation cephalosporin resistance among Enterobacteriaceae, mediated by the spread of extended-spectrum ß-lactamases (ESBLs), is a very serious medical concern with limited therapeutic options. Enmetazobactam (formerly AAI101) is a novel penicillanic sulfone ß-lactamase inhibitor active against a wide range of ESBLs. The combination of enmetazobactam and cefepime has entered phase 3 development in patients with complicated urinary tract infections. Using the Clinical and Laboratory Standards Institute (CLSI) M23 tier 2 study design, broth microdilution MIC and disk diffusion quality control (QC) ranges were determined for cefepime-enmetazobactam. Enmetazobactam was tested at a fixed concentration of 8 µg/ml in the MIC assay, and a cefepime-enmetazobactam disk mass of 30/20 µg was used in the disk diffusion assay. Escherichia coli ATCC 25922, E. coli ATCC 35218, E. coli NCTC 13353, Klebsiella pneumoniae ATCC 700603, and Pseudomonas aeruginosa ATCC 27853 were chosen as reference strains. The CTX-M-15-producing E. coli NCTC 13353 isolate is recommended for routine testing to control for inhibition of ESBL activity by enmetazobactam. Broth microdilution MIC QC ranges spanned 3 to 4 doubling dilutions and contained 99.6% to 100.0% of obtained MIC values for the five reference strains. Disk diffusion yielded inhibition zone diameter QC ranges that spanned 7 mm and encompassed 97.1% to 100.0% of the obtained values. Quality control ranges were approved by the CLSI in 2017 (broth microdilution MIC) and 2019 (disk diffusion). The established QC ranges will ensure that appropriate assay performance criteria are attained using CLSI reference methodology when determining the susceptibility of clinical isolates to cefepime-enmetazobactam.

Surveillance of Omadacycline Activity Tested against Clinical Isolates from the United States and Europe as Part of the 2016 SENTRY Antimicrobial Surveillance Program.

Omadacycline was tested against 21,000 bacterial isolates collected prospectively from medical centers in Europe and the United States during 2016. Omadacycline was active against Staphylococcus aureus (MIC50/MIC90, 0.12/0.25 mg/liter), including methicillin-resistant S. aureus (MRSA); streptococci (MIC50/MIC90, 0.06/0.12 mg/liter), including Streptococcus pneumoniae, viridans group streptococci, and beta-hemolytic streptococci; Enterobacteriaceae, including Escherichia coli (MIC50/MIC90, 0.5/2 mg/liter); Haemophilus influenzae (MIC50/MIC90, 1/1 mg/liter); and Moraxella catarrhalis (MIC50/MIC90, 0.25/0.25 mg/liter). Omadacycline merits further study in serious infections where resistant pathogens may be encountered.

A Systematic Approach to the Selection of the Appropriate Avibactam Concentration for Use with Ceftazidime in Broth Microdilution Susceptibility Testing.

Selection of the avibactam concentration to combine with ceftazidime in susceptibility testing was determined using Gram-negative isolates with characterized ß-lactamases predefined as susceptible or resistant, based on the known inhibition spectrum of avibactam. MIC values were determined by broth microdilution of ceftazidime with fixed concentrations and ratios of avibactam. A constant concentration of 4 µg/ml of avibactam was selected for susceptibility testing with ceftazidime because of its ability to correctly categorize susceptible and resistant isolates while minimizing categorical errors.

Assessment of 30/20-Microgram Disk Content versus MIC Results for Ceftazidime-Avibactam Tested against Enterobacteriaceae and Pseudomonas aeruginosa.

We evaluated the correlation between MIC and disk diffusion inhibition zones when testing ceftazidime-avibactam, using the 30/20-µg disk and the disk diffusion and MIC breakpoints established by the U.S. FDA and the Clinical and Laboratory Standards Institute (CLSI). Organisms used included 2 groups of Enterobacteriaceae isolates and 2 groups of Pseudomonas aeruginosa isolates; 1 group of each consisted of randomly selected isolates and the second group consisted of a challenge group from thousands of surveillance isolates with an increased proportion of organisms displaying ceftazidime-avibactam MIC values close to the breakpoints. Broth microdilution, disk diffusion tests, and data analysis were performed according to reference standardized methods. Ceftazidime-avibactam breakpoints of ≤8/4 (susceptible) and ≥16/4 µg/ml (resistant) for MIC and ≥21/≤20 mm for disk diffusion, as established by the U.S. FDA and the CLSI, were applied for Enterobacteriaceae and P. aeruginosa Ceftazidime-avibactam MIC and disk zone (30/20-µg disk) correlation were acceptable when testing Enterobacteriaceae (overall, very major [VM] and major [Ma] error rates of 0.4% and 0.0%, respectively) and nearly so when testing P. aeruginosa (2.3% VM and 2.9% Ma errors). In summary, disk diffusion and broth microdilution testing results demonstrated good categorical agreement for ceftazidime-avibactam against Enterobacteriaceae and P. aeruginosa, using 30/20-µg disks.

Meropenem-Vaborbactam Tested against Contemporary Gram-Negative Isolates Collected Worldwide during 2014, Including Carbapenem-Resistant, KPC-Producing, Multidrug-Resistant, and Extensively Drug-Resistant Enterobacteriaceae.

We evaluated the activity of meropenem-vaborbactam against contemporary nonfastidious Gram-negative clinical isolates, including Enterobacteriaceae isolates with resistance phenotypes and carbapenemase genotypes. Meropenem-vaborbactam (inhibitor at 8 µg/ml) and comparators were susceptibility tested by reference broth microdilution methods against 14,304 Gram-negative clinical isolates collected worldwide during 2014. Carbapenemase-encoding genes were screened by PCR and sequencing. Meropenem-vaborbactam (MIC50/90, ≤0.015/0.06 µg/ml) inhibited 99.1 and 99.3% of the 10,426 Enterobacteriaceae isolates tested at ≤1 and ≤2 µg/ml, respectively. Meropenem inhibited 97.3 and 97.7% of these isolates at the same concentrations. Against Enterobacteriaceae isolates displaying carbapenem-resistant Enterobacteriaceae (CRE) (n = 265), multidrug-resistant (MDR) (n = 1,210), and extensively drug-resistant (XDR) (n = 161) phenotypes, meropenem-vaborbactam displayed MIC50/90 values of 0.5/32, 0.03/1, and 0.5/32 µg/ml, respectively, whereas meropenem activities were 16/>32, 0.06/32, and 0.5/32 µg/ml, respectively. Among all geographic regions, the highest meropenem-vaborbactam activities were observed for CRE and MDR isolates from the United States (MIC50/90, 0.03/1 and 0.03/0.12 µg/ml, respectively). Meropenem-vaborbactam was very active against 135 KPC producers, and all isolates were inhibited by concentrations of ≤8 µg/ml (133 isolates by concentrations of ≤2 µg/ml). This combination had limited activity against isolates producing metallo-ß-lactamases (including 25 NDM-1 and 16 VIM producers) and/or oxacillinases (27 OXA-48/OXA-163 producers) that were detected mainly in Asia-Pacific and some European countries. The activity of meropenem-vaborbactam was similar to that of meropenem alone against Pseudomonas aeruginosa, Acinetobacter spp., and Stenotrophomonas maltophilia Meropenem-vaborbactam was active against contemporary Enterobacteriaceae isolates collected worldwide, and this combination demonstrated enhanced activity compared to those of meropenem and most comparator agents against CRE isolates and KPC producers, the latter of which are often MDR.

Pseudomonas aeruginosa Antimicrobial Susceptibility Results from Four Years (2012 to 2015) of the International Network for Optimal Resistance Monitoring Program in the United States.

Pseudomonas aeruginosa represents a major cause of health care-associated infections, and inappropriate initial antimicrobial therapy is associated with increased morbidity and mortality. The International Network for Optimal Resistance Monitoring (INFORM) program monitors the in vitro activity of ceftazidime-avibactam and many comparator agents. We evaluated the antimicrobial susceptibility of 7,452 P. aeruginosa isolates collected from 79 U.S. medical centers in 2012 to 2015. The isolates were collected and tested consecutively for susceptibility by broth microdilution method. Infection types included mainly pneumonia (50.5%), skin and skin structure (24.0%), urinary tract (7.8%), and bloodstream (7.7%) infections. The only compounds with >90% susceptibility rates were colistin (MIC50/90, 1/2 mg/liter, respectively; 99.4% susceptible), ceftazidime-avibactam (MIC50/90, 2/4 mg/liter, respectively; 97.0% susceptible), and amikacin (MIC50/90, 2/8 mg/liter, respectively; 97.0/93.0% susceptible [CLSI/EUCAST, respectively]). The addition of avibactam to ceftazidime increased the percentage of susceptible P. aeruginosa isolates from 84.3% to 97.0%. Multidrug resistance (MDR) and extensive drug resistance (XDR) phenotypes were observed among 1,151 (15.4%) and 698 (9.4%) isolates, respectively, and ceftazidime-avibactam inhibited 82.1 and 75.8% of these isolates at ≤8 mg/liter, respectively. High rates of cross-resistance were observed with ceftazidime, meropenem, and piperacillin-tazobactam, whereas ceftazidime-avibactam retained activity against isolates nonsusceptible to ceftazidime (81.0% susceptible), meropenem (86.2% susceptible), and piperacillin-tazobactam (85.4% susceptible), as well as isolates nonsusceptible to these three ß-lactams (71.2% susceptible). The only antimicrobial combinations that provided a better overall anti-Pseudomonas coverage than ceftazidime-avibactam (97.0% susceptibility rate) were those including amikacin (97.0 to 98.4% coverage). Susceptibility rates remained stable during the study period. The results of this investigation highlight the challenge of optimizing empirical antimicrobial therapy for P. aeruginosa infections.

Surveillance of Omadacycline Activity against Clinical Isolates from a Global Collection (North America, Europe, Latin America, Asia-Western Pacific), 2010-2011.

Omadacycline is a broad-spectrum aminomethylcycline in late-stage clinical development for the treatment of acute bacterial skin and skin structure infections and community-acquired pneumonia as an oral and an intravenous once-daily formulation. In this study, omadacycline and comparators were tested against 69,246 nonduplicate bacterial isolates collected prospectively during 2010 and 2011 from medical centers in Asia-Pacific (11,397 isolates), Europe (23,490 isolates), Latin America (8,038 isolates), and North America (26,321 isolates). Omadacycline was tested by broth microdilution following Clinical and Laboratory Standards Institute M07-A10 (2015) methods. A total of 99.9% of Staphylococcus aureus isolates were inhibited by ≤2 µg/ml of omadacycline (MIC50/90, 0.12/0.25 µg/ml), including 100.0% of methicillin-susceptible S. aureus isolates and 99.8% of methicillin-resistant S. aureus isolates. Omadacycline potencies were comparable for Streptococcus pneumoniae (MIC50/90, 0.06/0.06 µg/ml), viridans group streptococci (MIC50/90, 0.06/0.12 µg/ml), and beta-hemolytic streptococci (MIC50/90, 0.06/0.12 µg/ml) regardless of species and susceptibility to penicillin. Omadacycline was active against Enterobacteriaceae and was most active against Escherichia coli (MIC50/90, 0.5/2 µg/ml), Enterobacter aerogenes (MIC50/90, 2/4 µg/ml), Klebsiella oxytoca (MIC50/90, 1/4 µg/ml), and Citrobacter spp. (MIC50/90, 1/4 µg/ml). Omadacycline was active against Haemophilus influenzae (MIC50/90, 1/1 µg/ml) regardless of ß-lactamase status and against Moraxella catarrhalis (MIC50/90, 0.12/0.25 µg/ml). The potent activity of omadacycline against Gram-positive and Gram-negative bacteria indicates that omadacycline merits further study in serious infections in which multidrug resistance and mixed Gram-positive and Gram-negative infections may be a concern.

Activities of Omadacycline and Comparator Agents against Staphylococcus aureus Isolates from a Surveillance Program Conducted in North America and Europe.

Omadacycline is a new broad-spectrum aminomethylcycline in late-stage clinical development for acute bacterial skin and skin structure infections and community-acquired bacterial pneumonia as a once-daily formulation taken orally or intravenously. In this study, omadacycline and comparator agents were tested against 502 isolates of Staphylococcus aureus selected from a 2014 global surveillance program, and the results were compared with those for 7,740 isolates from a 2010 surveillance program. For the 2014 isolates, testing was completed on 252 isolates from Europe and 250 isolates from North America. Each set of isolates was composed of ∼100 hospital-acquired methicillin-resistant Staphylococcus aureus (HA-MRSA) isolates (isolated >48 h after hospital admission), 100 community-acquired MRSA (CA-MRSA) isolates (isolated <48 h after hospital admission), and 50 methicillin-susceptible S. aureus (MSSA) isolates. The omadacycline MIC50 and MIC90 for all S. aureus collected during 2014 was 0.12 and 0.12 µg/ml, respectively. The MIC90 values were identical for MRSA, HA-MRSA, and CA-MRSA (0.12 µg/ml). The MIC90 values for isolates from 2010 for S. aureus, MRSA, and CA-MRSA were 0.25 µg/ml (0.5 µg/ml for HA-MRSA; 87.8% were at ≤0.25 µg/ml). All 2014 and 2010 MRSA isolates were susceptible to vancomycin, and ≥99.8% were susceptible to daptomycin, linezolid, and tigecycline. The activity of omadacycline was similar for North American and European isolates, including MRSA (CA-MRSA or HA-MRSA). There was no evidence for emerging resistance to omadacycline between 2010 and 2014. The potent activity of omadacycline against S. aureus indicates that omadacycline merits further study in serious infections where multidrug resistance may be a concern.

Determination of Disk Diffusion and MIC Quality Control Guidelines for High-Dose Cefepime-Tazobactam (WCK 4282), a Novel Antibacterial Combination Consisting of a ß-Lactamase Inhibitor and a Fourth-Generation Cephalosporin.

High-dose cefepime-tazobactam (1:1; WCK 4282), a novel antibacterial combination consisting of the ß-lactamase inhibitor tazobactam and a fourth-generation cephalosporin, is under clinical development for the treatment of serious Gram-negative infections. A quality control (QC) study was performed to establish disk diffusion and MIC ranges for cefepime-tazobactam for multiple QC reference strains. The cefepime-tazobactam QC ranges for a fixed tazobactam MIC of 8 µg/ml and disk diffusion (30/20-µg disk) test methods were approved by the CLSI Subcommittee on Antimicrobial Susceptibility Testing in January 2015 and January 2016. These QC ranges will be important for accurate in vitro activity evaluations of cefepime-tazobactam when tested against clinical Gram-negative bacteria during clinical studies and routine patient care.