Β-lactam Β-lactamase Inhibitor Research Articles

Survival of infection with TEM β-lactamase-producing Escherichia coli with Pan-β-lactam resistance

Antimicrobial resistance is a critical global health issue, significantly contributing to patient mortality. Recent antibiotic developments have aimed to counteract carbapenemase-producing Enterobacterales; however, the impact of their use on the emergence of antibiotic resistance is unknown. This study investigates the first case of a non-carbapenemase-producing, pan-β-lactam-resistant Escherichia coli strain from a patient previously treated with ceftolozane-tazobactam and cefiderocol. This study describes the clinical progression of a 39-year-old ICU patient who developed multiple infections, culminating in the isolation of a pan-β-lactam-resistant E. coli strain (EC554). The resistance profile was characterised through MIC determination, whole-genome sequencing, the use of the β-lactam inactivation method, RT-qPCR, efflux pump inhibition assays, outer membrane protein analysis, and blaTEM transformation. The EC554 isolate displayed resistance to all tested β-lactams and β-lactam-β-lactamase inhibitor combinations. Whole-genome sequencing revealed four plasmids in EC554, with the only β-lactamase gene being blaTEM-252 on the pEC554-PBR-X1-X1 plasmid. We found that the extremely resistant phenotype was attributable to a combination of different mechanisms: a high expression of TEM-252, efflux pump activity, porin loss, and PBP3 mutations. The findings illustrate the complex interplay of multiple resistance mechanisms in E. coli, highlighting the potential for high-level resistance even without carbapenemase production. This study underscores the importance of comprehensively characterising resistance mechanisms in order to inform effective treatment strategies and mitigate the spread of resistant strains.

Contrasting methods to operationalize antibiotic exposure in clinical research: a real-world application on healthcare-associated Clostridioides difficile infection.

The goal of this article is to summarize common methods of antibiotic operationalization used in clinical research and demonstrate methods for exposure variable selection. We demonstrate three methods for modeling exposure, using data from a case-control study on Clostridioides difficile infection in hospitalized patients: 1) factor analysis, 2) logistic regression models, and 3) Least Absolute Shrinkage and Selection Operator (LASSO) regression. The factor analysis identified 8 variables contributing the most variation in the dataset: any antibiotic exposure; number of antibiotic classes; number of antibiotic courses; dose; and specific classes monobactam, 𝛽-lactam 𝛽-lactamase inhibitors, rifamycin, and cephalosporin. The logistic regression models resulting in the best model fit used predictors representing any antibiotic exposure and the proportion of a patient's hospitalization on antibiotics. The LASSO model selected 22 variables for inclusion in the predictive model, of which 10 were antibiotic exposure variables, including: any antibiotic exposure; classes 𝛽-lactam 𝛽-lactamase inhibitors, carbapenem, cephalosporin, fluoroquinolone, monobactam, rifamycin, sulfonamides, and miscellaneous; and proportion of hospitalization on antibiotics. Investigators studying antibiotic use should consider multiple characteristics of exposure informed by their research question and the theory on how antibiotics may impact the distribution of the outcome in their target population.

Novel β-lactam-β-lactamase inhibitors as monotherapy versus combination for the treatment of drug-resistant Pseudomonas aeruginosa infections: A multicenter cohort study

BackgroundData comparing the clinical outcomes of novel β-lactam-β-lactamase inhibitors given in combination versus monotherapy for the treatment of multidrug-resistant (MDR) P. aeruginosa infections are lacking. MethodThis retrospective cohort study included patients who received novel β-lactam–β-lactamase inhibitors as monotherapy or in combination for the treatment of MDR P. aeruginosa infections. The study was conducted between 2017 and 2022 in 6 tertiary care hospitals in Saudi Arabia. Overall in-hospital mortality, 30-day mortality, clinical cure, and acute kidney injury (AKI) were compared between recipients of monotherapy versus combination using multivariate logistic regression analysis. Result118 patients and 82 patients were included in monotherapy and combination therapy arms, respectively. The cohort represented an ill population with 56% in the intensive care unit and 37% in septic shock. A total of 19% of patients presented with bacteremia. Compared to monotherapy, combination therapy did not significantly differ in clinical cure (57% vs. 68%; P = 0.313; OR, 0.63; 95% CI, 0.36–1.14) in-hospital mortality (45% vs. 37%; P = 0.267; OR, 1.38; 95% CI, 0.78–2.45), or 30-day mortality (27% vs. 24%; P = 0.619; OR, 1.18; 95% CI, 0.62–1.25). However, AKI (32% vs. 12%; P = 0.0006; OR, 3.45; 95% CI, 1.67–7.13) was significantly more common in patients who received combination therapy. ConclusionNovel β-lactam–β-lactamase inhibitors when used in combination with other antibiotics did not add clinical benefit compared to their use as monotherapy in the treatment of MDR P. aeruginosa infections. A Combination regimen was associated with an increased risk of nephrotoxicity.

Carbapenem-resistant Enterobacterales susceptibility patterns to new antimicrobials: A single-center analysis

Background: Multidrug-resistant bacteria are of high concern, and empiric antimicrobial choice for infections caused by these pathogens, while awaiting susceptibilities, is increasingly encountered. We describe the susceptibility patterns of ceftazidime-avibactam (CZA), imipenem-rel-ebactam (I-R), meropenem-vaborbactam (MVB), cefiderocol (FDC), ceftolozone-tazobactam (C/T), minocycline (MIN), and tigecycline (TGC) for carbapenem-resistant Enterobacterales at an academic medical center. Methods: We performed a single-center analysis of Enterobacterales isolates from 110 hospitalized adult patients who had CZA, I-R, MVB, FDC, MIN, or TGC susceptibility testing performed between October 2020 and September 2022. The study included 1 isolate per patient per infection site per year. Isolates were divided into carbapenem susceptible and non susceptible categories. For carbapenem nonsusceptible isolates, phenotypic confirmatory testing of carbapenem nonsusceptibility was performed using disk diffusion, gradient diffusion, and/or broth microdilution. Interpretive categories were applied using CLSI- or FDA-approved break-points where applicable. Carbapenemase testing was also performed using the modified carbapenem inactivation method (mCIM) and, where applicable, this testing was confirmed at the Massachusetts State Public Health Laboratory using genotypic methods. Results: In total, 125 unique isolates were reviewed: 34 meropenem-susceptible and 91 meropenem-intermediate or resistant isolates. CZA, I-R, MVB, and FDC were active against all tested meropenem-susceptible isolates; however, 50% of tested isolates were susceptible to C/T. MIN and TGC, when tested, were active against 2 of 11 isolates (18%) and 14 of 16 isolates (86%), respectively. Of 91 meropenem-nonsusceptible isolates, most tested isolates were susceptible to MVB (59 of 72, 82%), followed by CZA (63 of 82, 77%), I-R (8 of 11, 73%), FDC (9 of 16, 56%), and C/T (1 of 12, 8%). TGC retained activity against 78 of 81 (96%) tested isolates. In contrast, MIN retained activity against 8 of 45 isolates (18%). Additionally, all (28 of 28, 100%) isolates that were nonsusceptible to at least 1 novel agent (CZA, I-R, MVB, FDC, or C/T) remained susceptible to TGC. State laboratory confirmatory testing was available for 75 isolates. Of 43 mCIM-positive isolates, all 28 KPC-producing isolates were susceptible to CZA, I-R, MVB, FDC and TGC. Conclusions: Among Enterobacterales, CZA, MVB, and I-R retained activity against most non-NDM CRE isolates in this local analysis, with comparable susceptibilities. TGC demonstrated excellent susceptibility for CRE and meropenem-susceptible isolates, offering an alternative for nonbloodstream infections. Choice of empiric agent with a newβ-lactam, β-lactam–β-lactamase inhibitors, or TGC appear to be reasonable empiric therapeutic options at our institution. CT and MIN warrant confirmatory testing prior to use due to low susceptibility rates among meropenem nonsusceptible isolates.Disclosures: None

Characterization of a Novel Pathogen in Immunocompromised Patients: Elizabethkingia anophelis-Exploring the Scope of Resistance to Contemporary Antimicrobial Agents and β-lactamase Inhibitors.

Elizabethkingia anophelis is an emerging Gram-negative nonlactose fermenter in the health care setting, where it causes life-threatening infections in immunocompromised patients. We aimed to characterize the molecular mechanisms of antimicrobial resistance and evaluate the utility of contemporary antibiotics with the intent to offer targeted therapy against an uncommonly encountered pathogen. Whole-genome sequencing (WGS) was conducted to accurately identify isolate species and elucidate the determinants of β-lactam resistance. Antimicrobial susceptibility testing was performed using broth microdilution and disk diffusion assays. To assess the functional contribution of the major metallo-β-lactamase (MBL) encoding genes to the resistance profile, bla BlaB was cloned into pBCSK(-) phagemid vector and transformed into Escherichia coli DH10B. WGS identified the organism as E. anophelis. MBL genes bla BlaB-1 and bla GOB-26 were identified, in addition to bla CME-2, which encodes for an extended-spectrum β-lactamase (ESBL). Plasmids were not detected. The isolate was nonsusceptible to all commonly available β-lactams, carbapenems, newer β-lactam β-lactamase inhibitor combinations, and to the combination of aztreonam (ATM) with ceftazidime-avibactam (CAZ-AVI). Susceptibility to the novel siderophore cephalosporin cefiderocol was determined. A BlaB-1 transformant E. coli DH10B isolate was obtained and demonstrated increased minimum inhibitory concentrations to cephalosporins, carbapenems, and CAZ-AVI, but not ATM. Using WGS, we accurately identified and characterized an extensively drug-resistant E. anophelis in an immunocompromised patient. Rapid evaluation of the genetic background can guide accurate susceptibility testing to better inform antimicrobial therapy selection.

1812. Impact of removing ESBL testing report on the selection of antibiotics for the treatment and 30-day mortality of patients infected with ESBL-producing organisms

Abstract Background The rising burden of carbapenem-resistant organisms is well recognized as a global crisis. Several studies have identified preceding carbapenem use as a risk factor for the subsequent development of infections with carbapenem-resistant, gram- negative organisms. We characterized the impact of removal of the ESBL designation from microbiology reports on inpatient antibiotic prescribing. Methods A historical control study, interventional analysis study was conducted at Ramathibodi Hospital) to compared 1 year before removal ESBL designation (period1, August 1, 2019 to July 31, 2020) and 1 year post removal ESBL designation (period 2, August 1, 2020 to July 31, 2021) on inpatient antibiotic prescribing. Categorical variables were compared using the Fisher exact test. Continuous variables were evaluated using the Wilcoxon rank-sum test. All statistical tests were 2-tailed, and a P < .05 was considered statistically significant. Results The primary outcome definitive prescribing of carbapenems decreased from 56.5% to 41.3% afterward (P= .01). Prescription of cefepime was also decreased from 13.6% to 3.5% (P< .05), respectively. Whereas piperacillin-tazobactam use significantly increased from 10.4% to 28.7% (P< .05). Trimethoprim-sulfamethoxazole was prescribed more frequently, i.e., increased from 0 to 2.8%, but this change was not statistically significant. The secondary outcome 30-day mortality from any cause was no different between the two groups, with 22 of 154 patients (14.3%) in group 1 and 24 of 143 (16.8%) in group 2 (P = .55). Conclusion Definitive prescribing of carbapenems was decreased and β-lactam–β-lactamase inhibitor combination was increased after removal ESBL report. Our findings confirm the importance of collaboration between microbiology and antimicrobial stewardship programs. Disclosures All Authors: No reported disclosures.

Role of Enzymatic Activity in the Biological Cost Associated with the Production of AmpC β-Lactamases in Pseudomonas aeruginosa.

ABSTRACTIn the current scenario of growing antibiotic resistance, understanding the interplay between resistance mechanisms and biological costs is crucial for designing therapeutic strategies. In this regard, intrinsic AmpC β-lactamase hyperproduction is probably the most important resistance mechanism of Pseudomonas aeruginosa, proven to entail important biological burdens that attenuate virulence mostly under peptidoglycan recycling alterations. P. aeruginosa can acquire resistance to new β-lactam–β-lactamase inhibitor combinations (ceftazidime-avibactam and ceftolozane-tazobactam) through mutations affecting ampC and its regulatory genes, but the impact of these mutations on the associated biological cost and the role that β-lactamase activity plays per se in contributing to the above-mentioned virulence attenuation are unknown. The same questions remain unsolved for plasmid-encoded AmpC-type β-lactamases such as FOX enzymes, some of which also provide resistance to new β-lactam–β-lactamase inhibitor combinations. Here, we assessed from different perspectives the effects of changes in the active center and, thus, in the hydrolytic spectrum resistance to inhibitors of AmpC-type β-lactamases on the fitness and virulence of P. aeruginosa, using site-directed mutagenesis; the previously described AmpC variants T96I, G183D, and ΔG229-E247; and, finally, blaFOX-4 versus blaFOX-8. Our results indicate the essential role of AmpC activity per se in causing the reported full virulence attenuation (in terms of growth, motility, cytotoxicity, and Galleria mellonella larvae killing), although the biological cost of the above-mentioned AmpC-type variants was similar to that of the wild-type enzymes. This suggests that there is not an important biological burden that may limit the selection/spread of these variants, which could progressively compromise the future effectiveness of the above-mentioned drug combinations.IMPORTANCE The growing antibiotic resistance of the top nosocomial pathogen Pseudomonas aeruginosa pushes research to explore new therapeutic strategies, for which the resistance-versus-virulence balance is a promising source of targets. While resistance often entails significant biological costs, little is known about the bases of the virulence attenuations associated with a resistance mechanism as extraordinarily relevant as β-lactamase production. We demonstrate that besides potential energy and cell wall alterations, the enzymatic activity of the P. aeruginosa cephalosporinase AmpC is essential for causing the full attenuation associated with its hyperproduction by affecting different features related to pathogenesis, a fact exploitable from the antivirulence perspective. Less encouraging, we also show that the production of different chromosomal/plasmid-encoded AmpC derivatives conferring resistance to some of the newest antibiotic combinations causes no significantly increased biological burdens, which suggests a free way for the selection/spread of these types of variants, potentially compromising the future effectiveness of these antipseudomonal therapies.

In Vitro Activity of New β-Lactam-β-Lactamase Inhibitor Combinations and Comparators against Clinical Isolates of Gram-Negative Bacilli: Results from the China Antimicrobial Surveillance Network (CHINET) in 2019.

ABSTRACTNovel β-lactam–β-lactamase inhibitor combinations (BLBLIs) are in clinical development for the treatment of infections caused by carbapenem-resistant and difficult-to-treat resistant (DTR) (defined as resistance to all tested β-lactams and fluoroquinolones) Gram-negative bacilli. This study evaluated the in vitro activities of cefepime-zidebactam, ceftazidime-avibactam, cefepime-tazobactam, ceftolozane-tazobactam, and other comparators against 4,042 nonduplicate Gram-negative clinical isolates collected from different regions of China (46 hospitals) in 2019. Based on the pharmacokinetic-pharmacodynamic (PK-PD) breakpoints, cefepime-zidebactam inhibited 98.5% of Enterobacterales and 98.9% of Pseudomonas aeruginosa isolates, respectively. Against carbapenem-resistant and difficult-to-treat resistant Gram-negative bacilli, cefepime-zidebactam demonstrated better activity against Enterobacterales (96% and 97.2%, respectively) and P. aeruginosa (98.2% and 96.9%, respectively). Among the 379 carbapenem-resistant Enterobacterales isolates, the most common carbapenemase genes detected were blaKPC-2 (64.1%) and blaNDM (30.9%). Cefepime-zidebactam showed an MIC90 of ≤2 mg/L for 98.8% of blaKPC-positive isolates and 89.7% of blaNDM-positive isolates. Ceftazidime-avibactam also showed efficient in vitro activity against Enterobacterales (93.6%) and P. aeruginosa (87.7%). Ceftazidime-avibactam was active against 97.5% of blaKPC-positive isolates and 100% of blaOXA-232-positive isolates. Cefepime-zidebactam inhibited 97.3% of Acinetobacter baumannii isolates with an MIC50/90 of 16/32 mg/L. Our study systematically evaluated the in vitro activities of these new BLBLIs against a variety of Gram-negative bacilli, provided preclinical data for the approval of these BLBLIs in China, and supported cefepime-zidebactam and ceftazidime-avibactam as potential efficient therapies for infections caused by carbapenem-resistant Enterobacterales (CRE), carbapenem-resistant P. aeruginosa (CRPA), and DTR isolates.IMPORTANCE Enterobacterales, Pseudomonas aeruginosa, and Acinetobacter baumannii are the most common Gram-negative bacilli to cause nosocomial infections throughout the world. Due to their large public health and societal implications, carbapenem-resistant A. baumannii (CRAB), carbapenem-resistant P. aeruginosa (CRPA), and carbapenem-resistant and third-generation-cephalosporin-resistant Enterobacteriaceae were regarded by the World Health Organization (WHO) as a global priority for investment in new drugs in 2017. The present study showed the potent in vitro activity of these novel BLBLIs and other comparators against Gram-negative bacillus isolates, including carbapenem-resistant or difficult-to-treat resistant phenotypes. Polymyxins, tigecycline, and ceftazidime-avibactam (except for blaNDM-positive isolates) were available for the treatment of infections caused by CRE isolates. Currently, cefepime-zidebactam and other BLBLIs have not yet been approved for use in China. Here, our study aimed to evaluate the in vitro activities of BLBLIs against Gram-negative bacillus isolates, especially CRE, before clinical use.

Evaluation of the in vitro synergy of polymyxin B-based combinations against polymyxin B -resistant gram-negative bacilli

ObjectivesThis study aimed to evaluate the in vitro synergy of polymyxin B (PMB) combined with 11 other antibiotics against PMB-resistant gram-negative bacilli (GNBs). MethodsThirty-six clinical isolates of PMB-resistant GNBs were used. The MICs of all the antimicrobials tested were determined by the broth microdilution method and the checkerboard assay method. Carbapenemase genes were detected by PCR. In vitro synergy results were interpreted using the fractional inhibitory concentration index (FICI). Four combinations that showed positive interactions were subsequently evaluated in a time-kill study. ResultsAmong the 36 strains, 15 harboured the carbapenemase gene, and blaKPC was the predominant carbapenemase. The resistance rates of the 36 strains to tigecycline, meropenem, ceftazidime, and cefepime were 100% (36/36), 97% (35/36), 94% (34/36), and 97% (35/36), respectively. For Enterobacteriaceae and Pseudomonas aeruginosa, the resistance rates to aztreonam and ceftazidime-avibactam (avibactam at a fixed concentration of 4 mg/L) were 95% (19/20) and 25% (5/20), respectively. The PMB-based combinations exhibited synergism to a certain degree. The most synergistic combinations were PMB plus meropenem-avibactam (avibactam at a fixed concentration of 4 mg/L) and PMB plus tigecycline, with the synergy rates of 83.3% and 80.6%, respectively. Compared to tazobactam- and sulbactam-based β-lactam–β-lactamase inhibitor combinations (BL-BLIs), PMB with avibactam-based BL-BLIs exhibited a better synergistic effect. For Acinetobacter baumannii, PMB plus sulbactam exhibited a strong synergism with a 2∼7-fold MIC reduction of PMB. In time-kill studies, the highest degree of synergism was observed for PMB with cefepime-avibactam on all the tested isolates. For isolates with low-level resistance to PMB, PMB combined with other partner antimicrobials also showed a certain degree of synergism. ConclusionsPMB in combination with tigecycline and avibactam-based BL-BLIs could be a potential clinical option for clinical treatment of infections caused by PMB -resistant GNBs.

In Vitro Activity of Cefepime-Taniborbactam against Carbapenemase-Producing Enterobacterales and Pseudomonas aeruginosa Isolates Recovered in Spain.

Novel β-lactam-β-lactamase inhibitor combinations currently approved for clinical use are poorly active against metallo-β-lactamase (MBL)-producing strains. We evaluated the in vitro activity of cefepime-taniborbactam (FTB [formerly cefepime-VNRX-5133]) and comparator agents against carbapenemase-producing Enterobacterales (n = 247) and carbapenem-resistant Pseudomonas species (n = 170) clinical isolates prospectively collected from different clinical origins in patients admitted to 8 Spanish hospitals. FTB was the most active agent in both Enterobacterales (97.6% MICFTB, ≤8/4 mg/L) and Pseudomonas (67.1% MICFTB, ≤8/4 mg/L) populations. The MICFTB was >8 mg/L in 6/247 (2.4%) Enterobacterales isolates (3 KPC-producing Klebsiella pneumoniae isolates, 1 VIM-producing Enterobacter cloacae isolate, 1 IMP-producing E. cloacae isolate, and 1 NDM-producing Escherichia coli isolate) and in 56/170 (32.9%) Pseudomonas isolates, 19 of them carbapenemase producers (15 producers of VIM, 2 of GES, 1 of GES+VIM, and 1 of GES+KPC). Against the Enterobacterales isolates with meropenem MICs of >2 mg/L (138/247), FTB was the most active agent against both serine-β-lactamases (107/138) and MBL producers (31/138) (97.2 and 93.5% MICFTB, ≤8/4 mg/L, respectively), whereas the activity of comparators was reduced, particularly against the MBL producers (ceftazidime-avibactam, 94.4 and 12.9%, meropenem-vaborbactam, 85.0 and 64.5%, imipenem-relebactam, 76.6 and 9.7%, ceftolozane-tazobactam, 1.9 and 0%, and piperacillin-tazobactam, 0 and 0%, respectively). Among the meropenem-resistant Pseudomonas isolates (163/170; MIC, >2 mg/L), the activities of FTB against serine-β-lactamase (35/163) and MBL (43/163) producers were 88.6 and 65.1%, respectively, whereas the susceptibilities of comparators were as follows: ceftazidime-avibactam, 88.5 and 16.0%, meropenem-vaborbactam, 8.5 and 7.0%, imipenem-relebactam, 2.9 and 2.3%, ceftolozane-tazobactam, 0 and 2.3%, and piperacillin-tazobactam, 0 and 0%, respectively. Microbiological results suggest FTB as a potential therapeutic option in patients infected with carbapenemase-producing Enterobacterales and carbapenem-resistant Pseudomonas isolates, including MBL producers.

Evaluation of Ceftolozane/Tazobactam, Ceftazidime/Avibactam and Meropenem/Vaborbactam Against Multidrug-Resistant (MDR) Pseudomonas

Background: Data on the patient outcomes for newer β-lactam–β-lactamase inhibitor (BLBI) drugs compared to carbapenem-containing combination antibiotics for multidrug-resistant (MDR)–Pseudomonas aeruginosa infections are limited. Methods: This retrospective, case–control observational study was based on chart review of the patients managed at the University of Kentucky. Results: In total, 143 patients with MDRO Pseudomonas aeruginosa infections were identified and divided into 2 groups: 1 group received newer BLBI combinations with or without aminoglycosides or polymyxins, for at least 72 hours, and the control group received carbapenem containing combination antibiotics or other antibiotics. Baseline characteristics and patient outcomes are shown in Table 1. Discussion: The newer BLBI combinations group consisted of 60.8% MDR Pseudomonas bacteremia, whereas the control group had 68.4% of MDR Pseudomonas respiratory cultures. Overall, the use of newer BLBI combinations such as ceftazidime/avibactam, ceftolozane/tazobactam, and meropenem/vaborbactam was associated with lower rates of acute kidney injury (AKI), shorter LOS, and lower mortality rates compared to the control group, and these differences were statistically significant. Because the 2 populations of patient differed significantly based on the site of infection (sepsis vs pneumonia), the data were reanalyzed to evaluate the impact of therapy on the occurrence of AKI, LOS, and mortality based on the site of infection. Only those patients with sepsis who received the newer combination drugs had significantly better rates of AKI, lower LOS, and had lower rates of mortality. The 2 treatment arms were not statistically different when comparing patients with pneumonia. Additionally, the use of these new combination therapies did not make a difference regarding readmission rates or duration of bacteremia for the patients included in the study.Funding: NoDisclosures: None

1593. Antimicrobial Activity of Ceftazidime-Avibactam and Comparator Agents Against OXA-48 β-lactamase–Producing Enterobacterales Collected in International Medical Centers, Including the United States, in 2017–2018

BackgroundOXA-48 is a carbapenemase with low-level hydrolytic activity toward cephalosporins. This study evaluated in vitro activities of ceftazidime-avibactam (CAZ-AVI), meropenem (MEM), meropenem-vaborbactam (MVB), ceftolozane-tazobactam (C/T), and other antimicrobial agents against 113 OXA-48-producing Enterobacterales with multiple resistance mechanisms collected in a 2017–2018 global surveillance program.MethodsNonduplicate clinical isolates of 113 Enterobacterales were collected from medical centers in 25 countries in 2017–2018. In vitro susceptibility tests were performed by broth microdilution with a custom-made panel consisting of CAZ-AVI, ceftazidime (CAZ), MEM, MVB, C/T, colistin (COL), gentamicin (GEN), levofloxacin (LEV), and amikacin (AMK). Whole genome sequencing or quantitative PCR data were used to analyze resistance mechanisms, such as OXA-48, extended-spectrum β-lactamase (ESBL), original-spectrum β-lactamase (OSBL), and AmpC β-lactamase. Clinical and Laboratory Standards Institute breakpoints were applied for susceptibility interpretations.ResultsOf 113 OXA-48–producing clinical isolates, 20 carried OXA-48 alone. The remaining 93 isolates carried additional β-lactamases, including 63 with ESBL (CTX-M-15) + OSBL (SHV, TEM), 15 with AmpC (DHA, AAC, CMY) + ESBL (CTX-M-15), and 15 with OSBL (SHV, TEM). 99.1% (all but 1) of all isolates tested were susceptible to CAZ-AVI, whereas 71.7%, 17.7%, and 14.2% were susceptible to MVB, MEM, and C/T, respectively. Among isolates harboring multiple resistance mechanisms (OXA-48 + ESBL + OSBL; n=63), 98.4%, 69.8%, 11.1%, and 7.9% were susceptible to CAZ-AVI, MVB, MEM, and C/T, respectively. Among isolates carrying OXA-48 + AmpC + ESBL + OSBL (n=15), 100%, 66.7%, 13.3%, and 13.3% were susceptible to CAZ-AVI, MVB, MEM, and C/T, respectively (Table). Aminoglycosides (AMK and GEN) and other β-lactams (eg, CAZ) were 20%–90% active against these isolates. COL was the second most effective comparator, inhibiting 83.2% of these isolates.Table ConclusionCAZ-AVI was the most effective agent in this study compared with other antibiotics, including β-lactams, β-lactam–β-lactamase inhibitor combinations, aminoglycosides, and COL, against OXA-48-producing Enterobacterales carrying multiple β-lactamases.DisclosuresLynn-Yao Lin, MS, AbbVie (Employee) Dmitri Debabov, PhD, AbbVie (Employee) William Chang, BS, AbbVie (Employee)

Intrapulmonary Pharmacokinetics of Cefepime and Enmetazobactam in Healthy Volunteers: Towards New Treatments for Nosocomial Pneumonia.

Cefepime-enmetazobactam is a novel β-lactam-β-lactamase inhibitor combination with broad-spectrum antimicrobial activity against a range of multidrug-resistant Enterobacteriaceae This agent is being developed for a range of serious hospital infections. An understanding of the extent of partitioning of β-lactam-β-lactamase inhibitor combinations into the human lung is required to better understand the potential role of cefepime-enmetazobactam for the treatment of nosocomial pneumonia. A total of 20 healthy volunteers were used to study the intrapulmonary pharmacokinetics of a regimen of 2 g cefepime-1 g enmetazobactam every 8 h intravenously (2 g/1 g q8h i.v.). Each volunteer contributed multiple plasma samples and a single epithelial lining fluid (ELF) sample, obtained by bronchoalveolar lavage. Concentrations of cefepime and enmetazobactam were quantified using liquid chromatography-tandem mass spectrometry. The pharmacokinetic data were modeled using a population methodology, and Monte Carlo simulations were performed to assess the attainment of pharmacodynamic targets defined in preclinical models. The concentration-time profiles of both agents in plasma and ELF were similar. The mean ± standard deviation percentage of partitioning of total drug concentrations of cefepime and enmetazobactam between plasma and ELF was 60.59% ± 28.62% and 53.03% ± 21.05%, respectively. Using pharmacodynamic targets for cefepime of greater than the MIC and free enmetazobactam concentrations of >2 mg/liter in ELF of 20% of the dosing interval, a regimen of cefepime-enmetazobactam of 2 g/0.5 g q8h i.v. infused over 2 h resulted in a probability of target attainment of ≥90% for Enterobacteriaceae with cefepime-enmetazobactam MICs of ≤8 mg/liter. This result provides a rationale to further consider cefepime-enmetazobactam for the treatment of nosocomial pneumonia caused by multidrug-resistant Enterobacteriaceae.

Adding Insult to Injury: Mechanistic Basis for How AmpC Mutations Allow Pseudomonas aeruginosa To Accelerate Cephalosporin Hydrolysis and Evade Avibactam.

Pseudomonas aeruginosa is a leading cause of nosocomial infections worldwide and notorious for its broad-spectrum resistance to antibiotics. A key mechanism that provides extensive resistance to β-lactam antibiotics is the inducible expression of AmpC β-lactamase. Recently, a number of clinical isolates expressing mutated forms of AmpC have been found to be clinically resistant to the antipseudomonal β-lactam-β-lactamase inhibitor (BLI) combinations ceftolozane-tazobactam and ceftazidime-avibactam. Here, we compare the enzymatic activity of wild-type (WT) AmpC from PAO1 to those of four of these reported AmpC mutants, bearing mutations E247K (a change of E to K at position 247), G183D, T96I, and ΔG229-E247 (a deletion from position 229 to 247), to gain detailed insights into how these mutations allow the circumvention of these clinically vital antibiotic-inhibitor combinations. We found that these mutations exert a 2-fold effect on the catalytic cycle of AmpC. First, they reduce the stability of the enzyme, thereby increasing its flexibility. This appears to increase the rate of deacylation of the enzyme-bound β-lactam, resulting in greater catalytic efficiencies toward ceftolozane and ceftazidime. Second, these mutations reduce the affinity of avibactam for AmpC by increasing the apparent activation barrier of the enzyme acylation step. This does not influence the catalytic turnover of ceftolozane and ceftazidime significantly, as deacylation is the rate-limiting step for the breakdown of these antibiotic substrates. It is remarkable that these mutations enhance the catalytic efficiency of AmpC toward ceftolozane and ceftazidime while simultaneously reducing susceptibility to inhibition by avibactam. Knowledge gained from the molecular analysis of these and other AmpC resistance mutants will, we believe, aid in the design of β-lactams and BLIs with reduced susceptibility to mutational resistance.

Resistance to Ceftazidime/Avibactam plus Meropenem/Vaborbactam When Both Are Used Together Is Achieved in Four Steps in Metallo-β-Lactamase-Negative Klebsiella pneumoniae.

Serine β-lactamases are dominant causes of β-lactam resistance in Klebsiella pneumoniae isolates. Recently, this has driven clinical deployment of the β-lactam-β-lactamase inhibitor pairs ceftazidime/avibactam and meropenem/vaborbactam. We show that four steps, i.e., ompK36 and ramR mutation plus carriage of OXA-232 and KPC-3-D178Y variant β-lactamases, confer ceftazidime/avibactam and meropenem/vaborbactam resistance when both pairs are used together. These findings have implications for decision making about sequential and combinatorial use of these β-lactam-β-lactamase inhibitor pairs to treat K. pneumoniae infections.

Impact of removing ESBL designation from culture reports on the selection of antibiotics for the treatment of infections associated with ESBL-producing organisms.

We characterized the impact of removal of the ESBL designation from microbiology reports on inpatient antibiotic prescribing. Definitive prescribing of carbapenems decreased from 48.4% to 16.1% (P = .01) and β-lactam-β-lactamase inhibitor combination increased from 19.4% to 61.3% (P = .002). Our findings confirm the importance of collaboration between microbiology and antimicrobial stewardship programs.

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 β-lactam-β-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-β-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.

A novel mechanism-based pharmacokinetic-pharmacodynamic (PKPD) model describing ceftazidime/avibactam efficacy against β-lactamase-producing Gram-negative bacteria.

Diazabicyclooctanes (DBOs) are an increasingly important group of non β-lactam β-lactamase inhibitors, employed clinically in combinations such as ceftazidime/avibactam. The dose finding of such combinations is complicated using the traditional pharmacokinetic/pharmacodynamic (PK/PD) index approach, especially if the β-lactamase inhibitor has an antibiotic effect of its own. To develop a novel mechanism-based pharmacokinetic-pharmacodynamic (PKPD) model for ceftazidime/avibactam against Gram-negative pathogens, with the potential for combination dosage simulation. Four β-lactamase-producing Enterobacteriaceae, covering Ambler classes A, B and D, were exposed to ceftazidime and avibactam, alone and in combination, in static time-kill experiments. A PKPD model was developed and evaluated using internal and external evaluation, and combined with a population PK model and applied in dosage simulations. The developed PKPD model included the effects of ceftazidime alone, avibactam alone and an 'enhancer' effect of avibactam on ceftazidime in addition to the β-lactamase inhibitory effect of avibactam. The model could describe an extensive external Pseudomonas aeruginosa data set with minor modifications to the enhancer effect, and the utility of the model for clinical dosage simulation was demonstrated by investigating the influence of the addition of avibactam. A novel mechanism-based PKPD model for the DBO/β-lactam combination ceftazidime/avibactam was developed that enables future comparison of the effect of avibactam with other DBO/β-lactam inhibitors in simulations, and may be an aid in translating PKPD results from in vitro to animals and humans.

2288. Role of Β Lactam-Β Lactamase Inhibitors in Indian Tertiary Care Hospitals: Results from a Nationwide Survey

BackgroundBroad-spectrum antibiotics, particularly third-generation cephalosporins, are routinely used in the treatment of nosocomial infections. The emergence of Extended Spectrum Β-Lactamase (ESBL)-producing pathogens in Indian tertiary care hospitals warrants the need to reassess β-lactam–β-lactamase inhibitors (BL-BLIs) as better alternative treatments.MethodsAn online survey was conducted by Pfizer India to understand the usage of BL-BLIs across Indian hospitals. The survey was administered to 334 clinicians across multiple specialties out of which 195 were from tertiary care hospitals. Results were analyzed using MS-Excel statistical tools.ResultsOne-hundred ninety-five (195) clinicians from tertiary care hospitals completed the survey. About 78% of HCPs revealed the resistance to third-generation cephalosporins (e.g., ceftriaxone, ceftazidime) to be between 10–60% in their clinical settings. BL-BLIs were mostly preferred for treatment based on hospital antibiograms (64%) and used as first-line options for hospitalized adults with mild-moderate severe infections caused by ESBL-producing organisms (71%) and in mild-moderate infections caused by susceptible Gram-negative bacteria such as Enterobacteriaceae (54%). The average duration of IV BL-BLI treatment was 5–7 days (66%). The HCPs considerations while choosing BL-BLIs were mainly based on anti-microbial spectrum (81%), and rationality of BL/BLI combination (63%) and clinical experience with the BL-BLI molecule (63%). Cefoperazone-Sulbactam (CS) and Piperacillin–tazobactam (PT) were most commonly prescribed BL-BLIs and HCPs preferred the latter for pneumonia (67%), skin and soft-tissue infections (57%), bloodstream infections (67%) and cancer-associated febrile neutropenia (64%); while they preferred former for urinary tract infections (64%). CS and PT were preferred for intra-abdominal infections (57% and 64% respectively) and post-surgical infections (56% and 53% respectively).ConclusionCS and PT were the most commonly prescribed BL-BLIs probably due to their wide antimicrobial spectrum, rationality of the BL/BLI combination and the clinical experience with the molecules. BL-BLIs are still a mainstay of treatment for infections due to ESBL producing organisms. Disclosures All authors: No reported disclosures.

Pharmacodynamic modelling of β-lactam/β-lactamase inhibitor checkerboard data: illustration with aztreonam–avibactam

ObjectivesCheckerboard experiments followed by fractional inhibitory concentration (FIC) index determinations are commonly used to assess in vitro pharmacodynamic interactions between combined antibiotics, but FIC index cannot be determined in case of antibiotic/non-active compound combinations. The aim of this study was to use a simple modelling approach to quantify the in vitro activity of aztreonam-avibactam, a new β-lactam–β-lactamase inhibitor combination. MethodsMIC checkerboard experiments were performed with 12 Enterobacteriaceae with diverse β-lactamases profiles. Aztreonam MICs in the absence and presence of avibactam at different concentrations (ranging from 0.0625 to 4 mg/L) were determined. Aztreonam MIC versus avibactam concentrations were fitted by an inhibitory Emax model with a baseline effect parameter. ResultsA concentration-dependent relationship was observed with a steep initial reduction of aztreonam MIC at low avibactam concentrations and reaching a maximum at higher avibactam concentrations that was adequately fitted by the model. Maximum avibactam effect was characterized by the ratio of aztreonam MICs in the absence of avibactam (MIC0) and when avibactam concentration tends toward infinity (MIC∞), and this ratio ranged between 90 and 10 068 depending on the strain. Avibactam potency was characterized by avibactam concentrations corresponding to 50% of the maximum effect (IC50 values between 0.00022 and 0.053 mg/L). ConclusionsAn inhibitory Emax model with a baseline effect could quantify maximum avibactam effect and potency among various strains. This simple modelling approach can be used to compare the activity of other combinations of antibiotics with non-antibiotic drugs when FIC index is inappropriate.