Deciphering the Efficacy of ß-Lactams in the Face of Metallo-ß-Lactamase-Derived Resistance in Enterobacterales: Supraphysiologic Zinc in the Broth Is the Culprit.

Background: In vitro-in vivo discordance in ß-lactams' activities against metallo-ß-lactamase (MBL)-producing Enterobacterales has been described. We aimed to assess whether this discordance is attributed to the supra-physiologic zinc concentration in in vitro testing media. Methods: A clinical and microbiological observational study of patients with bloodstream infections due to New Delhi metallo-ß-lactamase-producing Klebsiella pneumoniae was performed. Outcomes of patients treated empirically with non-MBL-active ß-lactam therapy (carbapenems and ceftazidime/avibactam) and MBL-active ß-lactam therapy (ceftazidime/avibactam + aztreonam) were documented. The patients' isolates were used to induce septicemia in mice, and survival upon meropenem treatment was recorded. Meropenem minimum inhibitory concentrations (MICs) were determined in standard media and in the presence of physiological zinc concentrations. Results: Twenty-nine patients receiving empiric non-MBL-active ß-lactams (median duration, 4 days) were compared with 29 receiving MBL-active ß-lactams. The 14-day mortality rates were 21% and 14%, respectively. In the murine septicemia model, meropenem treatment resulted in protection from mortality (P < .0001). Meropenem MICs in the physiologic zinc concentration broth were 1- to >16-fold lower vs MICs in zinc-unadjusted broth (≥64 mg/L). Conclusions: Our data provide foundational support to establish pharmacokinetic/pharmacodynamic relationships using MICs derived in physiologic zinc concentration, which may better predict ß-lactam therapy outcome.

Imipenem/funobactam (formerly XNW4107) in vivo pharmacodynamics against serine carbapenemase-producing Gram-negative bacteria: a novel modelling approach for time-dependent killing.

BACKGROUND: Imipenem/funobactam (formerly XNW4107) is a novel ß-lactam/ß-lactamase inhibitor with activity against MDR Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacterales strains. Using a neutropenic murine thigh infection model, we aimed to determine the pharmacokinetic/pharmacodynamic (PK/PD) index, relative to funobactam exposure, that correlated most closely with the in vivo efficacy of imipenem/funobactam combination and the magnitude of index required for efficacy against serine carbapenemase-producing clinical strains. METHODS: Dose-fractionation was conducted against three strains. Imipenem human-simulated regimen (HSR, 500 mg q6h 1 h infusion) efficacy in combination with escalating funobactam exposures against seven A. baumannii, four P. aeruginosa and four Klebsiella pneumoniae (imipenem/funobactam MICs 0.25-16 mg/L) was assessed as 24 h change in log10cfu/thigh. RESULTS: Increased funobactam fractionation enhanced efficacy, indicating time-dependent killing. Changes in log10cfu/thigh versus %fT > MIC were poorly predictive of efficacy; bactericidal activity was observed at %fT > MIC = 0%. Across different threshold plasma funobactam concentrations (CTs), %fT > CT(1 mg/L) had the highest correlation with efficacy. Normalizing the %fT > CT = 1 mg/L index to the respective isolate imipenem/funobactam MIC ([%fT > CT]/MIC) allowed integration of the isolate's susceptibility, which further enhanced the correlation. Median (%fT > CT[1 mg/L])/MIC values associated with 1-log reductions were 9.82 and 9.90 for A. baumannii and P. aeruginosa, respectively. Median (%fT > CT[1 mg/L])/MIC associated with stasis was 55.73 for K. pneumoniae. Imipenem/funobactam 500/250 mg q6h 1 h infusion HSR produced >1-log kill against 6/7 A. baumannii, 4/4 P. aeruginosa and stasis against 4/4 K. pneumoniae. CONCLUSIONS: Imipenem/funobactam showed potent in vivo efficacy against serine carbapenemase-producers. The novel PK/PD index (%fT > CT)/MIC appeared to best describe in vivo activity.

In vivo pharmacokinetic/pharmacodynamic evaluation of cefepime/taniborbactam combination against cefepime-non-susceptible Enterobacterales and Pseudomonas aeruginosa in a murine pneumonia model.

BACKGROUND: Cefepime/taniborbactam is a cephalosporin/bicyclic boronate ß-lactamase inhibitor combination in clinical development for nosocomial pneumonia due to MDR Gram-negative bacteria. A murine pneumonia model was used to characterize cefepime/taniborbactam in vivo pharmacodynamics against Enterobacterales and Pseudomonas aeruginosa strains. METHODS: Clinical cefepime-non-susceptible Enterobacterales and P. aeruginosa strains expressing serine carbapenemases and/or other cefepime-hydrolysing ß-lactamases with cefepime/taniborbactam combination MICs of 0.12-16 mg/L were used. Cefepime and taniborbactam human-simulated regimens equivalent to clinical doses (i.e. 2/0.5 g q8h) were established in the pneumonia model. The in vivo activity of the cefepime human-simulated regimen given alone or concomitantly with escalating taniborbactam exposures against eight Enterobacterales and four P. aeruginosa strains was assessed. Taniborbactam pharmacokinetics were evaluated to determine systemic exposures of regimens used; taniborbactam fAUC0-24/MIC values required for efficacy were estimated using the Hill equation. In addition, the in vivo activity of the cefepime/taniborbactam combination human-simulated regimen was assessed against 18 strains. RESULTS: Among Enterobacterales, median taniborbactam fAUC0-24/MIC values associated with stasis and 1 log kill were 0.96 and 4.03, respectively, while for P. aeruginosa, requirements were 1.35 and 3.02 for stasis and 1 log kill, respectively. The cefepime/taniborbactam human-simulated regimen produced >2 log kill in 14/18 strains and >1 log kill in 18/18 strains. CONCLUSIONS: Cefepime/taniborbactam produced marked in vivo bactericidal activity against cefepime-non-susceptible Enterobacterales and P. aeruginosa isolates with cefepime/taniborbactam MICs up to and including 16 mg/L in the pneumonia model. Assessments of the probability of clinical attainment of the identified targets should be undertaken to support the selected cefepime/taniborbactam dose for treatment of nosocomial pneumonia.

Assessment of sustained efficacy and resistance emergence under human-simulated exposure of cefiderocol against Acinetobacter baumannii using in vitro chemostat and in vivo murine infection models.

Objectives: This study evaluated the sustained kill and potential for resistance development of Acinetobacter baumannii exposed to human-simulated exposure of cefiderocol over 72 h in in vitro and in vivo infection models. Methods: Seven A. baumannii isolates with cefiderocol MICs of 0.12-2 mg/L were tested. The sustained bactericidal activity compared with the initial inoculum and the resistance appearance over 72 h treatment were evaluated in both an in vitro chemostat and an in vivo murine thigh infection model under the human-simulated exposure of cefiderocol (2 g every 8 h as 3 h infusion). Results: In the in vitro model, regrowth was observed against all seven tested isolates and resistance emergence (>2 dilution MIC increase) was observed in five test isolates. Conversely, sustained killing over 72 h and no resistance emergence were observed in six of seven tested isolates in vivo. The mechanism of one resistant isolate that appeared only in the in vitro chemostat studies was a mutation in the tonB-exbB-exbD region, which contributes to the energy transduction on the iron transporters. The resistance acquisition mechanisms of other isolates have not been identified. Conclusions: The discrepancy in the sustained efficacy and resistance emergence between in vitro and in vivo models was observed for A. baumannii. Although the resistance mechanisms in vitro have not been fully identified, sustained efficacy without resistance emergence was observed in vivo for six of seven isolates. These studies reveal the in vivo bactericidal activity and the low potential for development of resistance among A. baumannii evaluated under human-simulated exposures.

In vivo efficacy of WCK 6777 (ertapenem/zidebactam) against carbapenemase-producing Klebsiella pneumoniae in the neutropenic murine pneumonia model.

OBJECTIVES: Ertapenem has proven to be an effective antimicrobial; however, increasing enzyme-mediated resistance has been noted. Combination with zidebactam, a ß-lactam enhancer, is restorative. Human-simulated regimens (HSRs) of ertapenem and zidebactam alone and in combination (WCK 6777; 2 g/2 g q24h) were assessed for efficacy against carbapenemase-producing Klebsiella pneumoniae (CP-KP) in the pneumonia model. METHODS: Infected ICR mice were rendered neutropenic and exposed to various doses of ertapenem and zidebactam alone and in combination to develop the HSRs that were subsequently confirmed in additional pharmacokinetic studies. Twenty-one CP-KP (KPC or OXA-48-like producers) with WCK 6777 MICs of 1-8 mg/L were utilized. Mice were treated for 24 h with saline or HSRs of ertapenem, zidebactam and WCK 6777. Efficacy was defined as change in mean lung bacterial density relative to 0 h. RESULTS: Confirmatory pharmacokinetic analysis showed agreement between predicted human exposures (%fT>MIC) and those achieved in vivo for all three HSRs. The 0 h bacterial density across all isolates was 6.69 ±â€Š0.31 log10 cfu/lungs. At 24 h, densities increased by 2.57 ±â€Š0.50, 2.2 ±â€Š0.60 and 2.05 ±â€Š0.71 log10 cfu/lungs in the 24 h control, ertapenem HSR and zidebactam HSR groups, respectively. Overall, 18/21 of the isolates exposed to the WCK 6777 HSR displayed a killing profile that exceeded the translational benchmark for efficacy of a 1 log10 cfu reduction. Among the remaining three isolates, two displayed ∼0.5 log10 kill and stasis was observed in the third. CONCLUSIONS: Human-simulated exposures of WCK 6777 demonstrated potent in vivo activity against CP-KP, including those with WCK 6777 MICs up to 8 mg/L.

Murine Model for Measuring Effects of Humanized-Dosing of Antibiotics on the Gut Microbiome.

There is a current need for enhancing our insight in the effects of antimicrobial treatment on the composition of human microbiota. Also, the spontaneous restoration of the microbiota after antimicrobial treatment requires better understanding. This is best addressed in well-defined animal models. We here present a model in which immune-competent or neutropenic mice were administered piperacillin-tazobactam (TZP) according to human treatment schedules. Before, during and after the TZP treatment, fecal specimens were longitudinally collected at established intervals over several weeks. Gut microbial taxonomic distribution and abundance were assessed through culture and molecular means during all periods. Non-targeted metabolomics analyses of stool samples using Quadrupole Time of Flight mass spectrometry (QTOF MS) were also applied to determine if a metabolic fingerprint correlated with antibiotic use, immune status, and microbial abundance. TZP treatment led to a 5-10-fold decrease in bacterial fecal viability counts which were not fully restored during post-antibiotic follow up. Two distinct, relatively uniform and reproducible restoration scenarios of microbiota changes were seen in post TZP-treatment mice. Post-antibiotic flora could consist of predominantly Firmicutes or, alternatively, a more diverse mix of taxa. In general, the pre-treatment microbial communities were not fully restored within the screening periods applied. A new species, closely related to Eubacterium siraeum, Mageeibacillus indolicus, and Saccharofermentans acetigenes, became predominant post-treatment in a significant proportion of mice, identified by 16S rRNA gene sequencing. Principal component analysis of QTOF MS of mouse feces successfully distinguished treated from non-treated mice as well as immunocompetent from neutropenic mice. We observe dynamic but distinct and reproducible responses in the mouse gut microbiota during and after TZP treatment and propose the current murine model as a useful tool for defining the more general post-antibiotic effects in the gastro-intestinal ecosystem where humanized antibiotic dosing may ultimately facilitate extrapolation to humans.

Discrepancy in sustained efficacy and resistance emergence under human-simulated exposure of cefiderocol against Stenotrophomonas maltophilia between in vitro chemostat and in vivo murine infection models.

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

Comparative in vivo activity of human-simulated plasma and epithelial lining fluid exposures of WCK 5222 (cefepime/zidebactam) against KPC- and OXA-48-like-producing Klebsiella pneumoniae in the neutropenic murine pneumonia model.

OBJECTIVES: This was a comparative assessment of WCK 5222 (cefepime/zidebactam 2/1 g as a 1 h infusion every 8 h) efficacy using human-simulated plasma and ELF exposures against serine-carbapenemase-producing Klebsiella pneumoniae in the neutropenic murine pneumonia model. METHODS: Ten clinical isolates were utilized: eight were serine-carbapenemase-producing (KPC, n = 4; OXA-48-like, n = 4) Enterobacterales with WCK 5222 MICs (1:1) ranging from 1 to 4 mg/L; and two were previously studied MDR isolates serving as quality controls. Lungs of mice were inoculated with 50 µL of 107 cfu/mL. Treatment mice received human-simulated regimens of cefepime, zidebactam or WCK 5222 derived from plasma or epithelial lining fluid (ELF) profiles obtained from healthy subjects. Lung bacterial densities resulting from the humanized exposures in plasma and ELF were compared. RESULTS: Initial lung bacterial densities ranged from 6.06 to 6.87 log10 cfu/lungs, with a mean bacterial burden increase to 9.06 ± 0.42 after 24 h. Human-simulated plasma and ELF exposures of cefepime and zidebactam monotherapy had no activity. Human-simulated WCK 5222 plasma exposures resulted in a >1 log10 cfu/lungs reduction in bacterial burden for all isolates. Humanized WCK 5222 ELF exposures achieved a >1 log10 cfu/lungs reduction for all isolates. While statistically significant differences in bacterial burden reduction were observed between the plasma and ELF exposures for WCK 5222 in 5/8 isolates, all treatments achieved the translational kill target of a >1 log10 cfu reduction. CONCLUSIONS: Clinically achievable WCK 5222 plasma and ELF exposures produced in vivo killing of carbapenem-resistant Enterobacterales in the neutropenic murine pneumonia model that is predictive of efficacy in humans.

Activity of ß-Lactam Antibiotics against Metallo-ß-Lactamase-Producing Enterobacterales in Animal Infection Models: a Current State of Affairs.

Metallo-ß-lactamases (MBLs) result in resistance to nearly all ß-lactam antimicrobial agents, as determined by currently employed susceptibility testing methods. However, recently reported data demonstrate that variable and supraphysiologic zinc concentrations in conventional susceptibility testing media compared with physiologic (bioactive) zinc concentrations may be mediating discordant in vitro-in vivo MBL resistance. While treatment outcomes in patients appear suggestive of this discordance, these limited data are confounded by comorbidities and combination therapy. To that end, the goal of this review is to evaluate the extent of ß-lactam activity against MBL-harboring Enterobacterales in published animal infection model studies and provide contemporary considerations to facilitate the optimization of current antimicrobials and development of novel therapeutics.

In vivo activity of WCK 4282 (high-dose cefepime/tazobactam) against serine ß-lactamase-producing Enterobacterales and Pseudomonas aeruginosa in the neutropenic murine thigh infection model.

OBJECTIVES: WCK 4282, high-dose cefepime/tazobactam, possesses potent in vitro activity against Gram-negative organisms including ESBL- and cephalosporinase-harbouring strains. The purpose of this evaluation was to investigate the in vivo activity of human-simulated exposures of WCK 4282 against serine-ß-lactamase-harbouring Enterobacterales and Pseudomonas aeruginosa. METHODS: Nineteen clinical isolates were evaluated (ESBL/cephalosporinase producers, n = 8 Escherichia coli, n = 4 P. aeruginosa; KPC producers, n = 3 Klebsiella pneumoniae, n = 1 Klebsiella aerogenes; OXA-48/181 producers, n = 2 K. pneumoniae, n = 1 E. coli). WCK 4282 MICs ranged from 4 to 32 mg/L compared with 16 to >128 mg/L for cefepime. Thigh-infected neutropenic mice received cefepime, WCK 4282 or sham control over 24 h prior to harvest. Cefepime and tazobactam dosing regimens produced plasma profiles of fAUC, fT>MIC and fCmax similar to human exposure after WCK 4282 2/2 g every 8 h (1.5 h infusion). RESULTS: Bacterial burdens (log10 cfu/thigh) were 5.81 ±â€Š0.36 at 0 h and 9.29 ±â€Š0.88 at 24 h in untreated controls. WCK 4282 produced potent activity against ESBL/cephalosporinase-producing strains with WCK 4282 MIC ≤16 mg/L; mean changes in log10 cfu/thigh from 0 h were -1.70 ±â€Š0.77 and +1.86 ±â€Š2.03 log10 cfu/thigh for WCK 4282 and cefepime human-simulated regimens, respectively. WCK 4282 produced variable activity against serine-carbapenemase-harbouring isolates. For the KPC-harbouring strains, WCK 4282 produced bacteriostasis with a mean -0.1 ±â€Š0.61 log10 cfu/thigh. Against OXA-48/181-harbouring isolates, WCK 4282 produced a range of change in bacterial burden of -1.23 ±â€Š0.33 to +1.04 ±â€Š0.7 log10 cfu/thigh. CONCLUSIONS: Human-simulated exposures of WCK 4282 produced in vivo efficacy against ESBL/cephalosporinase-producing, piperacillin/tazobactam- and ceftolozane/tazobactam-non-susceptible Enterobacterales and P. aeruginosa. These findings support further development of this combination as a carbapenem-sparing agent.

In Vivo Activity of WCK 4282 (High-Dose Cefepime/Tazobactam) against Serine-ß-Lactamase-Producing Enterobacterales and Pseudomonas aeruginosa in the Neutropenic Murine Lung Infection Model.

WCK 4282 (cefepime 2 g-tazobactam 2 g) maximizes systemic exposure of tazobactam and restores cefepime activity against various extended-spectrum ß-lactamase (ESBL)- and cephalosporinase-producing strains in vitro We describe clinical WCK 4282 exposure efficacies against various serine ß-lactamase-producing Enterobacterales and Pseudomonas aeruginosa isolates in a murine pneumonia model. Clinical cefepime-resistant isolates (17 Enterobacterales and 2 P. aeruginosa) were utilized. Isolates expressed ESBLs, cephalosporinases, and/or serine carbapenemases (KPC and OXA-48-like). WCK 4282 MICs were 4 to 32 µg/ml. For in vivo experiments, lungs of neutropenic mice were inoculated using standard inoculum (107 log10 CFU/ml). Serine carbapenemase-producing isolates were also assessed using a low inoculum (1:5 dilution). Treatment mice received a human-simulated regimen (HSR) of cefepime, meropenem (control for serine carbapenemase expression with low inoculum experiments), or WCK 4282 human-simulated regimens. Efficacy was assessed as change in log10 CFU/lungs at 24 h compared with 0-h controls. At standard inoculum, the mean 0-h bacterial burden was 6.65 ± 0.23 log10 CFU/lungs, and it increased at 24 h by 2.48 ± 0.60 log10 CFU/lungs among untreated controls. Initial bacterial burdens of lower inocula ranged from 5.81 ± 0.12 to 6.39 ± 0.13 log10 CFU/lungs. At standard and/or low inocula, cefepime and meropenem provided minimal activity. WCK 4282 produced a >1 log10 reduction against 9/9 ESBL-/cephalosporinase-producing strains. WCK 4282 provided variable activity among mice infected with standard or lower inocula of OXA-48-like-producers. WCK 4282 exposures provided 0.53 ± 1.07 log10 CFU/lungs growth against KPC producers at a standard inoculum versus bacteriostasis (-0.15 ± 0.54 change in log10 CFU/lungs) at a low inoculum. WCK 4282 produced potent in vivo activity against ESBL- and cephalosporinase-producing Enterobacterales and P. aeruginosa isolates and potential activity against OXA-48-like-producing Enterobacterales isolates in a neutropenic pneumonia model.

The paradoxical in vivo activity of ß-lactams against metallo-ß-lactamase-producing Enterobacterales is not restricted to carbapenems.

BACKGROUND: Using murine models of infection, we previously reported the potent in vivo activity of carbapenems against MBL-producing Enterobacterales despite the observed resistance in vitro. In the current study, we examined the in vivo activity of a cefepime human-simulated regimen against MBL-producing Enterobacterales in a murine thigh infection model. METHODS: A population of clinical isolates and isogenic engineered MBL-producing Enterobacterales transformants expressing MBLs but no detectable cefepime-hydrolysing serine ß-lactamases were utilized. KPC-producing isolates were included as positive controls. Cefepime, piperacillin/tazobactam and meropenem MICs were determined using broth microdilution in conventional CAMHB and EDTA-supplemented (zinc-limited) broth. In vivo efficacy of a cefepime human-simulated regimen (2 g q8h as a 2 h infusion) was determined in the neutropenic murine thigh infection model against the test strains. Efficacy was measured as the change in log10 cfu/thigh at 24 h compared with 0 h controls. RESULTS: MBL-producing Enterobacterales strains were found to be cefepime, piperacillin/tazobactam and meropenem non-susceptible in conventional broth. Supplementation with EDTA at a concentration of 300 mg/L resulted in multi-fold reduction in the MICs and restoration of susceptibility. In accordance with the MICs generated in zinc-limited broth, administration of a cefepime human-simulated regimen was associated with substantial bacterial reductions among mice infected with MBL-producing Enterobacterales. Absence of MIC reduction in zinc-limited broth and lack of efficacy among mice infected with KPC-producing isolates were observed. CONCLUSIONS: For MBL-producing Enterobacterales, susceptibility testing with Mueller-Hinton broth, a zinc-rich testing medium, is flawed since it does not recapitulate the host environment, in which zinc concentrations are low.

In vivo pharmacodynamics of new-generation ß-lactamase inhibitor taniborbactam (formerly VNRX-5133) in combination with cefepime against serine-ß-lactamase-producing Gram-negative bacteria.

OBJECTIVES: Cefepime/taniborbactam is a cephalosporin/cyclic boronate ß-lactamase inhibitor combination under development for the treatment of infections due to MDR Enterobacterales and Pseudomonas aeruginosa. Using a neutropenic murine thigh infection model, we aimed to determine the pharmacokinetic/pharmacodynamic index, relative to taniborbactam exposure, that correlated most closely with the efficacy of the cefepime/taniborbactam combination and the magnitude of index required for efficacy against serine-ß-lactamase-producing strains. METHODS: Twenty-six clinical Enterobacterales (expressing ESBLs, plasmid-mediated AmpC and/or carbapenemases of classes A or D; cefepime/taniborbactam combination MICs 0.06-16 mg/L) and 11 clinical P. aeruginosa (AmpC overproducing or KPC expressing; cefepime/taniborbactam combination MICs 1-16 mg/L) were evaluated. A cefepime human-simulated regimen (HSR) equivalent to a clinical dose of 2 g q8h as a 2 h infusion was given in combination with taniborbactam for 24 h. For a subset of P. aeruginosa isolates, a sub-therapeutic cefepime exposure was utilized. RESULTS: Dose-fractionation studies revealed that dosing frequency had no impact on taniborbactam potentiation of cefepime activity. Relative to the initial bacterial burden, the median taniborbactam fAUC0-24/MIC associated with 1 log kill in combination with the cefepime HSR for Enterobacterales and P. aeruginosa isolates was 2.62 and 0.46, respectively. In combination with sub-therapeutic cefepime, the median taniborbactam fAUC0-24/MIC associated with 1 and 2 log kill against AmpC-overproducing P. aeruginosa was 2.00 and 3.30, respectively, relative to the bacterial burden in the cefepime-treated groups. The taniborbactam HSR (equivalent to 0.5 g q8h as a 2 h infusion) was adequate to attain ≥1 log reduction against all test isolates. CONCLUSIONS: Our data show that the cefepime/taniborbactam combination (2 g/0.5 g q8h as a 2 h infusion) exerts potent in vivo activity against cefepime-resistant isolates, including serine-carbapenemase producers.

In vivo activity of human-simulated regimens of imipenem alone and in combination with relebactam against Pseudomonas aeruginosa in the murine thigh infection model.

BACKGROUND: Imipenem/relebactam is a carbapenem/ß-lactamase inhibitor combination with in vitro activity against Pseudomonas aeruginosa and Enterobacterales, including KPC producers. OBJECTIVES: To provide translational data to support the clinical utility of the imipenem/relebactam 500/250 mg q6h regimen using a human-simulated regimen (HSR) of imipenem/relebactam, compared with imipenem alone, against a phenotypically and genotypically diverse population of P. aeruginosa. METHODS: Twenty-nine P. aeruginosa isolates, including KPC (n = 6), PDC (n = 9), PAO (n = 4), GES (n = 5) and VIM (n = 1) producers, were used for the in vivo efficacy studies. Neutropenic mice were thigh-inoculated and randomized to receive HSRs of either imipenem 500 mg q6h, imipenem 1 g q8h, imipenem/relebactam 500/250 mg q6h or saline. RESULTS: Twenty-seven of the 29 isolates examined were imipenem resistant, with 24/29 isolates showing imipenem MICs of ≥32 mg/L. The addition of relebactam decreased the MICs up to 64-fold; imipenem/relebactam MICs ranged from 0.25 to >32 mg/L. Efficacies of the imipenem monotherapies and the imipenem/relebactam therapy were comparable for the two imipenem-susceptible organisms. Among the imipenem-resistant isolates, an increased mean growth was observed in the imipenem 500 mg q6h HSR and 1 g q8h HSR treatment groups of 1.31 ±âŸ1.01 and 0.18 ±âŸ1.67 log10 cfu/thigh, respectively. In contrast, a ≥2 log reduction in bacterial density was observed in 27/29 (93%) of the imipenem-resistant isolates subjected to imipenem/relebactam 500/250 mg q6h HSR. CONCLUSIONS: The imipenem/relebactam 500/250 mg q6h HSR demonstrated superior in vivo activity compared with the conventionally employed imipenem regimens against MDR P. aeruginosa over a wide range of imipenem/relebactam MICs.

Metallo-ß-lactamase resistance in Enterobacteriaceae is an artefact of currently utilized antimicrobial susceptibility testing methods.

BACKGROUND: MBLs are a major contributor to ß-lactam resistance when tested using CAMHB. Despite in vitro resistance, positive outcomes have been reported in MBL-infected patients following carbapenem treatment. The impact of physiological zinc concentrations on this in vitro-in vivo MBL discordance warrants investigation. OBJECTIVES: To evaluate meropenem in vitro activity against MBL-producing Enterobacteriaceae in zinc-depleted broth (Chelex-CAMHB, EDTA-CAMHB) and assess meropenem efficacy in murine infection models. METHODS: Neutropenic mice received a meropenem human-simulated regimen of 2 g q8h or levofloxacin 750 mg q24h (for model validation). Zinc concentrations were determined in conventional CAMHB, zinc-depleted CAMHB and epithelial lining fluid (ELF) of lung-infected mice. RESULTS: All MBL-producing isolates (NDM, n = 25; VIM, n = 3; IMP, n = 2) examined were meropenem resistant in CAMHB and susceptible in zinc-depleted CAMHB (5- to 11-fold reduction), with zinc depletion having no impact on levofloxacin MICs. Zinc concentrations (mean ±â€¯SD) in CAMHB were 0.959 ±â€¯0.038 mg/L and in both zinc-depleted CAMHB and ELF were <0.002 mg/L. In vivo, levofloxacin displayed predictable efficacy consistent with its phenotypic profile, while meropenem produced >1 log unit bacterial killing despite in vitro resistance in conventional CAMHB. CONCLUSIONS: Results indicate that meropenem in vivo efficacy is best represented by the pharmacodynamic profile generated using MICs determined in zinc-depleted media for MBL-producing Enterobacteriaceae. These translational data suggest that the use of conventional CAMHB for MBL susceptibility testing is inappropriate in distinguishing meaningful in vivo resistance given that zinc concentrations are supraphysiological in conventional CAMHB and negligible at infection sites.

Piperacillin-Tazobactam-Resistant/Third-Generation Cephalosporin-Susceptible Escherichia coli and Klebsiella pneumoniae Isolates: Resistance Mechanisms and In vitro-In vivo Discordance.

We previously reported the detection of Escherichia coli and Klebsiella pneumoniae that displayed in vitro piperacillin-tazobactam (TZP) resistance but were susceptible to third-generation cephalosporins (TZP-R/Ceph3-S). In this study, we assessed the phenotypic and genotypic profiles of 12 clinical non-clonal TZP-R/Ceph3-S E. coli and K. pneumoniae isolates derived from bloodstream infections. Whole-genome sequencing revealed that most of the TZP-R/Ceph3-S E. coli and K. pneumoniae isolates examined harbored blaTEM-1 and blaSHV-1 genes, respectively, but none harbored extended-spectrum ß-lactamase, AmpC ß-lactamase or carbapenemase genes. Increasing the tazobactam concentration from 4 mg/L to 16 mg/L restored TZP in vitro susceptibility among E. coli isolates expressing TEM-1, but had minimal impact on the susceptibility of K. pneumoniae to TZP. Real-time qPCR analysis showed that blaTEM-1 expression was amplified in TZP-R E. coli upon incubation with sub-inhibitory TZP concentrations. Using an immunocompetent murine septicemia model, the efficacy of TZP against TZP-R/Ceph3-S isolates was assessed using TZP doses that mimicked human plasma exposures following intravenous (IV) administration of TZP 4.5 g q6h over 0.5 h for 24 h. Efficacy was assessed by survival through 96 h. There was high mortality in untreated control mice for all tested isolates. Compared with controls, TZP human-simulated exposure significantly improved survival for all TZP-R/Ceph3-S E. coli and K. pneumoniae isolates examined (P < 0.05). Thus, TZP was associated with remarkable in vivo activity against TZP-R/Ceph3-S E. coli and K. pneumoniae despite the observed resistance in vitro.

In vivo studies on antibiotic combination for the treatment of carbapenem-resistant Gram-negative bacteria: a systematic review and meta-analysis protocol.

OBJECTIVE: There is poor evidence to determine the superiority of combination regimens versus monotherapy against infections due to carbapenem-resistant (CR) Gram-negative bacteria. In vivo models can simulate the pathophysiology of infections in humans and assess antibiotic efficacy. We aim to investigate in vivo effects of antibiotic combination on mortality and disease burden for infections due to CR Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacteriaceae and provide an unbiased overview of existing knowledge. The results of the study can help prioritising future research on the most promising therapies against CR bacteria. METHODS AND ANALYSIS: This protocol was formulated using the Systematic Review Protocol for Animal Intervention Studies (SYRCLE) Checklist. Publications will be collected from PubMed, Scopus, Embase and Web of Science. Quality checklists adapted by Collaborative Approach to Meta-Analysis and Review of Animal Data from Experimental Studies and SYRCLE's risk of bias tool will be used. If the meta-analysis seems feasible, the ES and the 95% CI will be analysed. The heterogeneity between studies will be assessed by I2 test. Subgroup meta-analysis will be performed when possible to assess the impact of the studies on efficacy of the treatments. Funnel plotting will be used to evaluate the risk of publication bias. DISSEMINATION: This systematic review and meta-analysis is part of a wider research collaboration project, the COmbination tHErapy to treat sepsis due to carbapenem-Resistant bacteria in adult and paediatric population: EvideNCE and common practice (COHERENCE) study that includes also the analyses of in vitro and human studies. Data will be presented at international conferences and the results will be published in peer-reviewed journals. PROSPERO REGISTRATION NUMBER: CRD42019128104(available at: https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42019128104).

Synergistic Activity of Exebacase (CF-301) in Addition to Daptomycin against Staphylococcus aureus in a Neutropenic Murine Thigh Infection Model.

We evaluated the efficacy of escalating doses of exebacase administered with subtherapeutic daptomycin exposures against 8 Staphylococcus aureus isolates in a neutropenic murine thigh infection model. Daptomycin alone resulted in mean growth of 0.39 ± 1.19 log10 CFU/thigh. When administered with daptomycin, exebacase resulted in a mean log10 CFU/thigh reduction of -1.03 ± 0.72 (range, -0.77 ± 0.98 to -1.20 ± 0.59) across evaluated doses (15 to 90 mg/kg), indicative of potential in vivo synergy.