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.

Assessing the impact of meropenem exposure on ceftolozane/tazobactam-resistance development in Pseudomonas aeruginosa using in vitro serial passage.

BACKGROUND: Patients infected with difficult-to-treat Pseudomonas aeruginosa are likely to receive meropenem (MEM) empirically before escalation to ceftolozane/tazobactam (C/T). We assessed whether pre-exposure to MEM affected C/T resistance development on C/T exposure. MATERIALS AND METHODS: Nine clinical P. aeruginosa isolates were exposed to MEM 16 mg/L for 72 h. Then, isolates were serially passaged in the presence of C/T (concentration of 10 mg/L) for 72 h as two groups: an MEM-exposed group inoculated with MEM pre-exposed isolates and a non-MEM control group. At 24 h intervals, samples were plated on drug-free and drug-containing agar (C/T concentration 16/8 mg/L) and incubated to quantify bacterial densities (log10 cfu/mL). Growth on C/T agar indicated resistance development, and resistant population was calculated by dividing the cfu/mL on C/T plates by the cfu/mL on drug-free agar. RESULTS: At 72 h, resistant populations were detected in 6/9 isolates. In five isolates, MEM exposure significantly increased the prevalence of ceftolozane/tazobactam-resistance development; the percentages of resistance population were 100%, 100%, 53.5%, 31% and 3% for the MEM-exposed versus 0%, 0%, 2%, 0.35% and ≤0.0003% in the unexposed groups. One isolate had a similar resistant population at 72 h between the two groups. The remaining isolates showed no development of resistance, regardless of previous MEM exposure. CONCLUSIONS: MEM exposure may pre-dispose to C/T resistance development and thus limit the therapeutic utility of this ß-lactam/ß-lactamase inhibitor. Resistance may be a result of stress exposure or molecular-level mutations conferring cross-resistance. Further in vivo studies are needed to assess clinical implications of these findings.

Validation of a Stenotrophomonas maltophilia bloodstream infection prediction score in the hematologic malignancy population.

Stenotrophomonas maltophilia (SM) bloodstream infections (BSIs) contribute to significant mortality in hematologic malignancy (HM) and hematopoietic stem cell transplantation (HSCT) patients. A risk score to predict SM BSI could reduce time to appropriate antimicrobial therapy (TTAT) and improve patient outcomes. A single center cohort study of hospitalized adults with HM/HSCT was conducted. Patients had ≥ 1 blood culture with a Gram-negative (GN) organism. A StenoSCORE was calculated for each patient. The StenoSCORE2 was developed using risk factors for SM BSI identified via logistic regression. Receiver operating characteristic (ROC) curves were plotted. Sensitivity and specificity for the StenoSCORE and StenoSCORE2 were calculated. Thirty-six SM patients and 534 non-SM patients were assessed. A StenoSCORE ≥ 33 points was 80% sensitive, 68% specific, and accurately classified 69% of GN BSIs. StenoSCORE2 variables included acute leukemia, prolonged neutropenia, mucositis, ICU admission, recent meropenem and/or cefepime exposure. The StenoSCORE2 performed better than the StenoSCORE (ROC AUC 0.84 vs. 0.77). A StenoSCORE2 ≥ 4 points was 86% sensitive, 76% specific, and accurately classified 77% of GN BSIs. TTAT was significantly longer for patients with SM BSI compared with non-SM BSI (45.16 h vs. 0.57 h; p < 0.0001). In-hospital and 28-day mortality were significantly higher for patients with SM BSI compared to non-SM BSI (58.3% vs. 18.5% and 66.7% vs. 26.4%; p-value < 0.0001). The StenoSCORE and StenoSCORE2 performed well in predicting SM BSIs in patients with HM/HSCT and GN BSI. Clinical studies evaluating whether StenoSCORE and/or StenoSCORE2 implementation improves TTAT and clinical outcomes are warranted.

Assessing the in vivo impact of novel ß-lactamase inhibitors on the efficacy of their partner ß-lactams against serine carbapenemase-producing Pseudomonas aeruginosa using human-simulated exposures.

OBJECTIVES: To evaluate the efficacy of human-simulated regimens (HSRs) of ceftazidime, ceftazidime/avibactam, imipenem, imipenem/relebactam, meropenem and meropenem/vaborbactam in a murine thigh infection model against serine carbapenemase-producing Pseudomonas aeruginosa. METHODS: Nine P. aeruginosa clinical isolates harbouring GES-5 (n = 1), GES-20 (n = 1), GES-5/20 (n = 1), GES-19, GES-20 (n = 3) and KPC (n = 3) were evaluated. Six mice were administered HSRs of ceftazidime 2 g q8h (2 h infusion), ceftazidime/avibactam 2.5 g q8h (2 h infusion), meropenem 2 g q8h (3 h infusion), imipenem 0.5 g q6h (0.5 h infusion), imipenem/relebactam 1.25 g q6h (0.5 h infusion) and meropenem/vaborbactam 4 g q8h (3 h infusion). Change in bacterial burden relative to baseline and the percent of isolates meeting the 1 log10 kill endpoint were assessed. RESULTS: The addition of avibactam to ceftazidime increased the percentage of isolates meeting 1 log10 kill from 33% to 100% of GES- or KPC-harbouring isolates. Imipenem/relebactam HSR produced ≥1 log10 of kill against 83% and 100% of GES- and KPC-harbouring isolates, respectively, while imipenem alone failed to reach 1 log10 kill for any isolates. Vaborbactam resulted in variable restoration of meropenem activity as 1 log10 kill was achieved in only 33% and 66% of GES- and KPC-harbouring isolates, respectively, compared with no isolates for meropenem alone. CONCLUSIONS: Ceftazidime/avibactam and imipenem/relebactam were active against 100% and 89% of KPC- or GES-harbouring isolates tested in vivo. The activity of meropenem/vaborbactam was variable, suggesting this may be an inferior treatment option in this setting. Further studies to evaluate clinical outcomes in GES- and KPC-producing P. aeruginosa are warranted given their increasing prevalence worldwide.

In vitro activity of cefiderocol against a global collection of carbapenem-resistant Pseudomonas aeruginosa with a high level of carbapenemase diversity.

OBJECTIVES: To determine the in vitro activity of cefiderocol in a global collection of carbapenem-resistant Pseudomonas aeruginosa including >200 carbapenemase-producing isolates. METHODS: Isolates (n = 806) from the ERACE-PA Surveillance Program were assessed. Broth microdilution MICs were determined for cefiderocol (iron-depleted CAMHB) and comparators (CAMHB). Susceptibility was interpreted by CLSI and EUCAST breakpoints and reported as percent of isolates. The MIC distribution of cefiderocol in the entire cohort and by carbapenemase status was assessed. RESULTS: In the entire cohort, cefiderocol was the most active agent (CLSI 98% susceptible; EUCAST 95% susceptible; MIC50/90, 0.25/2 mg/L). Amikacin (urinary only breakpoint) was the second most active, with 70% of isolates testing as susceptible. The percentage of isolates susceptible to all other agents was low (<50%) including meropenem/vaborbactam, imipenem/relebactam, piperacillin/tazobactam and levofloxacin. Cefiderocol maintained significant activity against the most commonly encountered carbapenemases including VIM- (CLSI 97% susceptible; EUCAST 92% susceptible) and GES (CLSI 100% susceptible; EUCAST 97% susceptible)-harbouring isolates. The cefiderocol MIC distribution was similar regardless of carbapenemase status, with MIC50/90 values of 0.5/4 mg/L, 0.5/2 mg/L and 0.25/1 mg/L for MBL, serine carbapenemase and molecular carbapenemase-negative isolates, respectively. CONCLUSIONS: Cefiderocol displayed potent in vitro activity in this global cohort of carbapenem-resistant P. aeruginosa including >200 carbapenemase-harbouring isolates. Cefiderocol was highly active against MBL-producing isolates, where treatment options are limited. These data can help guide empirical therapy guidelines based on local prevalence of carbapenemase-producing P. aeruginosa or in response to rapid molecular diagnostics.

In vitro synergy of the combination of sulbactam-durlobactam and cefepime at clinically relevant concentrations against A. baumannii, P. aeruginosa and Enterobacterales.

BACKGROUND: Sulbactam-durlobactam is a potent combination active against Acinetobacter baumannii; however, it lacks activity against other nosocomial pathogens. Cefepime is a common first-line therapy for hospital/ventilator-associated pneumonia caused by Gram-negative pathogens including Pseudomonas aeruginosa and Enterobacterales. With increasing resistance to cefepime, and the significant proportion of polymicrobial nosocomial infections, effective therapy for infections caused by Acinetobacter baumannii, P. aeruginosa and Enterobacterales is needed. This study investigated the in vitro synergy of sulbactam-durlobactam plus cefepime against relevant pathogens. METHODS: Static time-kills assays were performed in duplicate against 14 cefepime-resistant isolates (A. baumannii, n = 4; P. aeruginosa, n = 4; Escherichia coli, n = 3; Klebsiella pneumoniae, n = 3). One WT K. pneumoniae isolate was included. Antibiotic concentrations simulated the free-steady state average concentration of clinically administered doses in patients. RESULTS: Sulbactam-durlobactam alone showed significant activity against A. baumannii consistent with the MIC values. Sulbactam-durlobactam plus cefepime showed synergy against one A. baumannii isolate with an elevated MIC to sulbactam-durlobactam (32 mg/L). Against all P. aeruginosa isolates, synergy was observed with sulbactam-durlobactam plus cefepime. For the Enterobacterales, one E. coli isolate demonstrated synergy while the others were indifferent due to significant kill from sulbactam-durlobactam alone. The combination of sulbactam-durlobactam plus cefepime showed synergy against one of the K. pneumoniae and additive effects against the other two K. pneumoniae tested. No antagonism was observed in any isolates including the WT strain. CONCLUSIONS: Synergy and no antagonism was observed with a combination of sulbactam-durlobactam and cefepime; further in vivo pharmacokinetic/pharmacodynamics data and clinical correlation are necessary to support our findings.

Activity of novel ß-lactam/ß-lactamase inhibitor combinations against serine carbapenemase-producing carbapenem-resistant Pseudomonas aeruginosa.

BACKGROUND: Antimicrobial resistance in Pseudomonas aeruginosa is complex and multifaceted. While the novel ß-lactamase inhibitors (BLIs) avibactam, relebactam and vaborbactam inhibit serine-based ß-lactamases, the comparative potency of the novel ß-lactam (BL)/BLI combinations against serine carbapenemase-producing P. aeruginosa is unknown. OBJECTIVES: To compare the in vitro activity of ceftazidime/avibactam, ceftazidime, imipenem/relebactam, imipenem, meropenem/vaborbactam and meropenem against serine ß-lactamase-producing P. aeruginosa. METHODS: Carbapenem-resistant P. aeruginosa were collated through the Enhancing Rational Antimicrobials against Carbapenem-resistant P. aeruginosa (ERACE-PA) Global Surveillance. Isolates positive for serine-based carbapenemases were assessed. MICs were determined by broth microdilution to each novel BL/BLI and BL alone. RESULTS: GES was the most common carbapenemase identified (n = 59) followed by KPC (n = 8). Ceftazidime/avibactam had MIC50/MIC90 values of 4/8 mg/L and 91% of isolates were susceptible. Conversely, ceftazidime alone was active against only 3% of isolates. The MIC50/MIC90 of imipenem/relebactam were 16/>16 mg/L and 13% of all isolates were defined as susceptible. Of the KPC-producing isolates, 38% were susceptible to imipenem/relebactam, compared with 0% to imipenem. The meropenem/vaborbactam MIC50/MIC90 were >16/>16 mg/L, and 6% of isolates were susceptible, which was similar to meropenem alone (MIC50/90, >8/>8 mg/L; 3% susceptible) suggesting the addition of vaborbactam cannot overcome co-expressed, non-enzymatic resistance mechanisms. CONCLUSIONS: Among the novel BL/BLIs, ceftazidime/avibactam displayed better in vitro activity and thus is a rational treatment option for serine carbapenemase-harbouring P. aeruginosa. While imipenem/relebactam displayed some activity, particularly against isolates with blaKPC, meropenem/vaborbactam exhibited poor activity, with MICs similar to meropenem alone.

Cefepime in vivo activity against carbapenem-resistant Enterobacterales that test as cefepime susceptible or susceptible-dose dependent in vitro: implications for clinical microbiology laboratory and clinicians.

BACKGROUND: Carbapenem-resistant Enterobacterales (CRE) are a public health concern. Among these isolates, there are reports of isolates that test as cefepime susceptible or susceptible-dose dependent (SDD) in vitro despite presence of a carbapenemase. This study aimed to evaluate the pharmacokinetic/pharmacodynamic profile of cefepime against carbapenemase-producing (CP-CRE) and non-producing (non-CP-CRE) isolates with a range of cefepime MICs. METHODS: Reference broth microdilution and modified carbapenem inactivation method (mCIM) were performed on genotypically characterized clinical CRE isolates. Ultimately, CP-CRE (n = 21; blaKPC) and non-CP-CRE (n = 19) isolates with a distribution of cefepime MICs (≤0.5 to >256 mg/L) were utilized in the murine thigh infection model. Mice were treated with cefepime human-simulated regimens (HSRs) representative of a standard dose (1 g q12h 0.5 h infusion) or the SDD dose (2 g q8h 0.5 h infusion). Efficacy was assessed as the change in bacterial growth at 24 h compared with 0 h control, where ≥1 log bacterial reduction is considered translational value for clinical efficacy. RESULTS: Among both cohorts of CRE isolates, i.e. CP-CRE and non-CP-CRE, that tested as SDD to cefepime in vitro, 1 log bacterial reduction was not attainable with cefepime. Further blunting of cefepime efficacy was observed among CP-CRE isolates compared with non-CP-CRE across both susceptible and SDD categories. CONCLUSIONS: Data indicate to avoid cefepime for the treatment of serious infections caused by CRE isolates that test as cefepime susceptible or SDD. Data also provide evidence that isolates with the same antibiotic MIC may have different pharmacokinetic/pharmacodynamic profiles due to their antimicrobial resistance mechanism.

Assessing the in vivo efficacy of rational antibiotics and combinations against difficult-to-treat Pseudomonas aeruginosa producing GES ß-lactamases.

OBJECTIVES: We evaluated the in vivo efficacy of human-simulated regimens (HSRs) of cefiderocol, ceftazidime/avibactam, meropenem and ceftazidime/avibactam/meropenem combination against Guiana-extended spectrum (GES)-producing Pseudomonas aeruginosa isolates. METHODS: Eighteen P. aeruginosa isolates producing GES-1 (n = 5), GES-5 (n = 5) or miscellaneous GESs (combinations of GES-19, GES-20 and/or GES-26; n = 8) were evaluated. In vitro MIC testing was determined using broth microdilution. In a validated murine thigh infection model, HSRs of cefiderocol 2 g q8h as a 3 h IV infusion, ceftazidime/avibactam 2.5 g q8h as a 2 h IV infusion, meropenem 2 g q8h as a 3 h IV infusion or ceftazidime/avibactam/meropenem were administered. Change in bacterial burden relative to baseline and the proportion of isolates in each genotypic group meeting 1-log10 kill endpoint were assessed. RESULTS: Modal MICs (mg/L) ranged from 0.125 to 1 for cefiderocol, 4 to >64 for ceftazidime/avibactam and 2 to >64 for meropenem. Cefiderocol produced >1-log10 of kill against all 18 tested isolates. Meropenem was active against all GES-1 isolates whereas activity against GES-5 and miscellaneous GESs was lacking, consistent with the MICs. Ceftazidime/avibactam was active against all GES-1 and GES-5 isolates and retained activity against 62.5% of miscellaneous GESs including isolates with elevated MICs. For isolates where ceftazidime/avibactam failed, the addition of meropenem restored the in vivo efficacy. CONCLUSIONS: As monotherapy, cefiderocol was active in vivo against all tested isolates. The activities of meropenem or ceftazidime/avibactam alone were variable; however, a combination of both was active against all isolates. Cefiderocol and ceftazidime/avibactam/meropenem could be valuable therapeutic options for GES-producing P. aeruginosa infections. Clinical confirmatory data are warranted.

In Vivo Pharmacodynamic Profile of EVER206, a Novel Polymyxin Antimicrobial, against Gram-Negative Bacteria in the Murine Thigh Infection Model.

The objective was to determine the magnitude of the EVER206 free-plasma area under the concentration time curve (fAUC)/MIC target associated with bacteriostasis and 1-log10 kill against clinically relevant Gram-negative bacteria in the murine thigh model. Twenty-seven clinical isolates (Pseudomonas aeruginosa, n = 10; Escherichia coli, n = 9; Klebsiella pneumoniae, n = 5; Enterobacter cloacae, n = 2; and Klebsiella aerogenes, n = 1) were tested. Mice were pretreated with cyclophosphamide (induce neutropenia) and uranyl nitrate (increase the exposure of test compound through predictable renal dysfunction). Two hours postinoculation, five doses of EVER206 were administered subcutaneously. EVER206 pharmacokinetics were determined in infected mice. Data were fit using maximum effect (Emax) models to elucidate the fAUC/MIC targets for stasis and 1-log10 bacterial kill (reported as mean [range] by species). EVER206 MICs (mg/L) ranged from 0.25 to 2 mg/L (P. aeruginosa), 0.06 to 2 mg/L (E. coli), 0.06 to 0.125 mg/L (E. cloacae), 0.06 mg/L (K. aerogenes), and 0.06 to 2 mg/L (K. pneumoniae). In vivo, the mean 0-h baseline bacterial burden was 5.57 ± 0.39 log10 CFU/thigh. Stasis was achieved in 9/10 P. aeruginosa (fAUC/MIC, 88.13 [50.33 to 129.74]), 9/9 E. coli (fAUC/MIC, 112.84 [19.19 to 279.38]), 2/2 E. cloacae (fAUC/MIC, 259.28 [124.08 to 394.47]), 0/1 K. aerogenes, and 4/5 K. pneumoniae (fAUC/MIC, 99.26 [62.3 to 144.43]) isolates tested. 1-log10 kill was achieved in 9/10 for P. aeruginosa (fAUC/MIC, 106.43 [55.22 to 152.08]), 3/9 for E. coli (fAUC/MIC, 258.96 [74.08 to 559.4]), and 1/2 for E. cloacae (fAUC/MIC, 255.33). Using the murine thigh model, the fAUC/MIC targets of EVER206 were assessed across a broad MIC distribution. Integrating these data with microbiologic and clinical exposure data will aid in determining the clinical dose of EVER206.

In vivo efficacy & resistance prevention of cefiderocol in combination with ceftazidime/avibactam, ampicillin/sulbactam or meropenem using human-simulated regimens versus Acinetobacter baumannii.

OBJECTIVE: Evaluate the in vivo efficacy and resistance prevention of cefiderocol in combination with ceftazidime/avibactam, ampicillin/sulbactam and meropenem using human-simulated regimens (HSR) in the murine infection model. METHODS: In total, 15 clinical A. baumannii were assessed: cefiderocol MICs, 2 mg/L (previously developed resistance on therapy), n = 3; 8 mg/L, n = 2; ≥32 mg/L, n = 10 (including VEB and PER-harbouring isolates). Mice received inactive control, cefiderocol, cefiderocol + ceftazidime/avibactam (C-CZA), cefiderocol + ampicillin/sulbactam (C-SAM) or cefiderocol + meropenem (C-MEM) HSRs. The mean change in log10 cfu/thigh compared with starting inoculum was assessed. Resistance development on treatment was a >4-fold increase in MIC relative control animals. In vitro activities of combinations were assessed by disc stacking. RESULTS: Against cefiderocol-non-susceptible isolates, combinations produced significant kill with C-CZA -3.75 ±â€Š0.37 reduction in log10 cfu/thigh, C-SAM produced -3.55 ±â€Š0.50 and C-MEM produced -2.18 ±â€Š1.75 relative to baseline. Elevated MICs in cefiderocol treated animals occurred in three out of three isolates with MICs of 2 mg/L. Of these isolates, one developed elevated MICs with C-MEM compared with none treated with C-CZA or C-SAM. Disc stacking with C-CZA or C-SAM returned all isolates to at least the CLSI intermediate breakpoint, which may correlate with in vivo efficacy. CONCLUSIONS: Against cefiderocol-non-susceptible isolates, cefiderocol + ceftazidime/avibactam or ampicillin/sulbactam HSR produced in vivo kill against all 12 cefiderocol-non-susceptible isolates. Cefiderocol with ceftazidime/avibactam or ampicillin/sulbactam prevented the development of resistance during treatment against cefiderocol-high-end-susceptible isolates with a propensity for resistance on therapy. These data support the clinical evaluation of cefiderocol with ceftazidime/avibactam or ampicillin/sulbactam against A. baumannii, including multi-drug-resistant isolates.

Directed carbapenemase testing is no longer just for Enterobacterales: cost, labor, and workflow assessment of expanding carbapenemase testing to carbapenem-resistant P. aeruginosa.

Molecular carbapenem-resistance testing, such as for the presence of carbapenemases genes, is commonly implemented for the detection of carbapenemase-producing Enterobacterales. Carbapenemase-producing P. aeruginosa is also associated with significant morbidity and mortality, although; prevalence may be underappreciated in the United States due to a lack of carbapenemase testing. The present study sought to compare hands-on time, cost and workflow implementation of carbapenemase gene testing in Enterobacterales and P. aeruginosa isolates versus sending out isolates to a public health laboratory (PHL) for testing to assess if in-house can provide actionable results. The time to carbapenemase gene results were compared. Differences in cost for infection prevention measures were extrapolated from the time of positive carbapenemase gene detection in-house versus PHL. The median time to perform carbapenemase gene testing was 7.5 min (range 5-14) versus 10 min (range 8-22) for preparation to send isolates to the PHL. In-house testing produced same day results compared with a median of 6 days (range 3-14) to receive results from PHL. Cost of in-house testing and send outs were similar ($46.92 versus $40.53, respectively). If contact precautions for patients are implemented until carbapenemase genes are ruled out, in-house testing can save an estimated $76,836.60 annually. Extension of in-house carbapenemase testing to include P. aeruginosa provides actionable results 3-14 days earlier than PHL Standard Pathway testing, facilitating guided therapeutic decisions and infection prevention measures. Supplemental phenotypic algorithms can be implemented to curb the cost of P. aeruginosa carbapenemases testing by identifying isolates most likely to harbour carbapenemases.

Phenotypes, genotypes and breakpoints: an assessment of ß-lactam/ß-lactamase inhibitor combinations against OXA-48.

BACKGROUND: Two of the three recently approved ß-lactam agent (BL)/ß-lactamase inhibitor (BLI) combinations have higher CLSI susceptibility breakpoints (ceftazidime/avibactam 8 mg/L; meropenem/vaborbactam 4 mg/L) compared with the BL alone (ceftazidime 4 mg/L; meropenem 1 mg/L). This can lead to a therapeutic grey area on susceptibility reports depending on resistance mechanism. For instance, a meropenem-resistant OXA-48 isolate (MIC 4 mg/L) may appear as meropenem/vaborbactam-susceptible (MIC 4 mg/L) despite vaborbactam's lack of OXA-48 inhibitory activity. METHODS: OXA-48-positive (n = 51) and OXA-48-negative (KPC, n = 5; Klebsiella pneumoniae wild-type, n = 1) Enterobacterales were utilized. Susceptibility tests (broth microdilution) were conducted with ceftazidime/avibactam, imipenem/relebactam and meropenem/vaborbactam, as well as their respective BL partner. Antimicrobial activity of all six agents was evaluated in the murine neutropenic thigh model using clinically relevant exposures. Efficacy was assessed as the change in bacterial growth at 24 h, compared with 0 h controls. RESULTS: On average, the three BL/BLI agents resulted in robust bacteria killing among OXA-48-negative isolates. Among OXA-48-positive isolates, poor in vivo activity with imipenem/relebactam was concordant with its resistant phenotypic profile. Variable meropenem/vaborbactam activity was observed among isolates with a 'susceptible' MIC of 4 mg/L. Only 30% (7/23) of isolates at meropenem/vaborbactam MICs of 2 and 4 mg/L met the ≥1-log bacterial reduction threshold predictive of clinical efficacy in serious infections. In contrast, ceftazidime/avibactam resulted in marked bacterial density reduction across the range of MICs, and 96% (49/51) of isolates exceeded the ≥1-log bacterial reduction threshold. CONCLUSIONS: Data demonstrate that current imipenem/relebactam and ceftazidime/avibactam CLSI breakpoints are appropriate. Data also suggest that higher meropenem/vaborbactam breakpoints relative to meropenem can translate to potentially poor clinical outcomes in patients infected with OXA-48-harbouring isolates.

Piperacillin/Tazobactam Dose Optimization in the Setting of Piperacillin/Tazobactam-susceptible, Carbapenem-resistant Pseudomonas aeruginosa: Time to Reconsider Susceptible Dose Dependent.

PURPOSE: This study evaluates the in vitro potency of piperacillin/tazobactam among a global collection of carbapenem-resistant Pseudomonas aeruginosa (CR-PA) and assesses the adequacy of the Clinical and Laboratory Standards Institute (CLSI) P aeruginosa breakpoint dose in the setting of CR-PA using Monte Carlo simulation. METHODS: Isolates were collected during the Enhancing Rational Antimicrobials Against Carbapenem-Resistant P aeruginosa (ERACE-PA) Global Surveillance Program. Piperacillin/tazobactam MICs were determined using broth microdilution per CLSI standards. A 5000-patient Monte Carlo simulation was performed using various piperacillin/tazobactam dosing regimens to determine the probability of target attainment (PTA) for 50% free time above the MIC. The MIC distribution of piperacillin/tazobactam-susceptible CR-PA was used to calculate cumulative fraction of response (CFR). Optimal PTA and CFR were defined as 90% target achievement. FINDINGS: A total of 28% of tested CR-PA were piperacillin/tazobactam susceptible. Of these, 71% had MICs of 8 to 16/4 mg/L. Doses of 3.375 g q6h as 0.5-hour infusion (current breakpoint dose) had adequate PTA at MIC of 8/4 mg/L (CFR, 81%); however, extended infusion of 3 or 4 hours improved PTA at 16/4 mg/L (CFR, >90%). Doses of 4.5 g q8h as a 4-hour infusion and 4.5 g q6h as a 3-hour infusion both provide >90% PTA at an MIC of 16 mg/L (CFRs, 97 and 100%, respectively), favoring susceptible dose dependent interpretive criteria with these regimens. IMPLICATIONS: Although susceptible, piperacillin/ tazobactam has reduced potency in CR-PA. If piperacillin/tazobactam is used for susceptible CR-PA, high-doses (4.5 g q6h) and extended infusion (3 hours or continuous infusion) are needed to optimize exposure.

Phenotypic and genotypic profile of ceftolozane/tazobactam-non-susceptible, carbapenem-resistant Pseudomonas aeruginosa.

OBJECTIVES: To evaluate the genotypic and ceftazidime/avibactam-susceptibility profiles amongst ceftolozane/tazobactam-non-susceptible (NS), MBL-negative Pseudomonas aeruginosa in a global surveillance programme. METHODS: Isolates were collected as part of the ERACE-PA Global Surveillance programme. Carbapenem-resistant P. aeruginosa deemed clinically relevant by the submitting laboratories were included. Broth microdilution MICs were conducted per CLSI standards to ceftolozane/tazobactam, ceftazidime/avibactam, ceftazidime and cefepime. Genotypic carbapenemases were detected using CarbaR and CarbaR NxG (research use only). Isolates negative for carbapenemases by PCR were assessed via WGS. Isolates were included in the analysis if they were ceftolozane/tazobactam-NS and lacked detection of known MBLs. RESULTS: Of the 807 isolates collected in the ERACE-PA programme, 126 (16%) were ceftolozane/tazobactam-NS and lacked MBLs. Cross-resistance to ceftazidime and cefepime was common, with only 5% and 16% testing susceptible, respectively. Ceftazidime/avibactam retained in vitro activity, with 65% of isolates testing susceptible. GES was the most common enzymology, detected in 57 (45%) isolates, and 89% remained susceptible to ceftazidime/avibactam. Seven isolates harboured KPC and all tested susceptible to ceftazidime/avibactam. In the remaining 62 isolates, WGS revealed various ESBLs or OXA ß-lactamases. While 39% remained susceptible to ceftazidime/avibactam, marked variability was observed among the diverse resistance mechanisms. CONCLUSIONS: Ceftazidime/avibactam remained active in vitro against the majority of ceftolozane/tazobactam-NS, MBL-negative P. aeruginosa. Ceftazidime/avibactam was highly active against isolates harbouring GES and KPC ß-lactamases. These data highlight the potential clinical utility of genotypic profiling as well as the need to test multiple novel agents when carbapenem-resistant P. aeruginosa are encountered.

Carbapenem-resistant Pseudomonas aeruginosa: an assessment of frequency of isolation from ICU versus non-ICU, phenotypic and genotypic profiles in a multinational population of hospitalized patients.

BACKGROUND: Historically, multi-drug resistant organisms have been associated with the ICU setting. The present study sought to define the frequency of isolation from ICU versus non-ICU, phenotypic and genotypic profiles of carbapenem-resistant Pseudomonas aeruginosa (CR-PA) from a global cohort. METHODS: Multicenter surveillance study (17 centers from 12 countries) including 672 CR-PA isolates from 2019 to 2021. Phenotypic carbapenemase testing was assessed. Genotypic carbapenemase testing was conducted (CarbaR and CarbaR NxG) to detect ß-lactamases. Broth microdilution MICs were established for ceftazidime, cefepime, ceftolozane/tazobactam, and ceftazidime/avibactam. RESULTS: 59% of CR-PA were isolated from patients outside the ICU. The most common source in ICU and non-ICU patients was respiratory (55% and 30%, respectively). In the ICU, 35% of isolates were phenotypically carbapenemase-positive versus 29% for non-ICU. VIM was the most common carbapenemase (54% and 44%, respectively) followed by GES (27% and 28%, respectively). Susceptibility to ceftazidime or cefepime were relatively low in ICU (39% and 41% of isolates, respectively) and non-ICU (47% and 52% of isolates, respectively). Ceftolozane/tazobactam and ceftazidime/avibactam were more active with 56% and 66% of isolates susceptible in the ICU while 65% and 76% in non-ICU, respectively. When carbapenemase-negative, 86% and 88% of ICU isolates were susceptible to ceftolozane/tazobactam and ceftazidime/avibactam. Similarly, in the carbapenemase-negative, non-ICU isolates 88% and 92% of isolates were susceptible, respectively. CONCLUSION: Although multidrug resistant pathogens are often regarded as a challenge in the ICU population, the majority of CR-PA were isolated from non-ICU patients. Implementing phenotypic/genotypic testing will assist in guiding treatment. Carbapenem-resistance in P. aeruginosa should be regarded as a surrogate for MDR and this phenotype is increasingly prevalent outside the ICU.

In vivo translational assessment of the GES genotype on the killing profile of ceftazidime, ceftazidime/avibactam and meropenem against Pseudomonas aeruginosa.

OBJECTIVES: To evaluate the in vivo killing profile of human-simulated exposures of ceftazidime, ceftazidime/avibactam and meropenem against GES-harbouring Pseudomonas aeruginosa in the murine thigh infection model. METHODS: Five P. aeruginosa isolates [three isogenic (GES-1, GES-5 and GES-15) and two clinical (GES-5 and GES-15)] were evaluated. MICs were determined using broth microdilution. Human-simulated regimens (HSRs) of ceftazidime 2 g IV q8h as a 2 h infusion, ceftazidime/avibactam 2.5 g IV q8h as a 2 h infusion and meropenem 2 g IV q8h as a 3 h infusion were administered. Change in bacterial burden relative to baseline was assessed. RESULTS: Modal MICs ranged from 8 to >64 mg/L for ceftazidime, from 1 to 16 mg/L for ceftazidime/avibactam and from 1 to >64 mg/L for meropenem. In vivo, for the isogenic strains, avibactam augmented ceftazidime activity against the GES-1- and GES-15-harbouring isolates. Both ceftazidime and ceftazidime/avibactam resulted in significant kill against the GES-5 isogenic isolate. The meropenem HSR produced >1 log10 kill against each isogenic isolate (MICs of 1-4 mg/L). Against the GES-5 clinical isolate, ceftazidime and ceftazidime/avibactam resulted in >1 log10 kill compared with bacterial growth with the meropenem HSR. In the clinical isolate harbouring GES-15, the elevated MICs of ceftazidime and ceftazidime/avibactam reduced the effectiveness of both compounds, while the observed reduction in meropenem MIC translated into in vivo efficacy of the HSR regimen, predictive of clinical efficacy. CONCLUSIONS: In GES-harbouring P. aeruginosa, quantitative reductions in bacterial density observed with the translational murine model suggest that the phenotypic profile of ceftazidime, ceftazidime/avibactam and meropenem is predictive of clinical efficacy when using the evaluated dosing regimens.

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.

Comparison of Zinc Concentrations in the Broth of Commercial Automated Susceptibility Testing Devices (Vitek 2, MicroScan, BD Phoenix, and Sensititre).

Up to 4-fold differences in zinc concentrations have been observed in commercial broth routinely utilized for susceptibility testing via manual broth microdilution. Herein, we report the concentration of zinc in the broth of common automated susceptibility testing (AST) platforms (Vitek, MicroScan, BD Phoenix, and Sensititre). For AST platforms with lyophilized broth contents (Vitek and MicroScan), wells were rehydrated with appropriate diluent, and contents were aliquoted out for zinc assay. Aliquots from the manufacturer-specific broth (premade cation-adjusted Mueller-Hinton broth [caMHB]) for BD Phoenix and Sensititre were also assayed by inductively coupled plasma mass spectrometry. Up to a 10-fold difference in zinc concentrations was observed across the 4 platforms (MicroScan: 0.46 mg/L; BD Phoenix: 1.16 mg/L; Vitek: 1.22 mg/L; Sensititre: 4.49 mg/L). Attention should be given to the supraphysiologic and variable zinc concentrations observed in broth used in automated platforms and the subsequent implications for susceptibility testing of metallo-ß-lactamase (MBL)-harboring isolates. This variability also hampers efforts to develop a standardized method to uniformly reduce zinc concentrations in broth and mimic physiologic zinc conditions. IMPORTANCE Growing data on the impact of extracellular zinc concentration on metallo-ß-lactamase-mediated resistance has shed light on the importance of susceptibility testing media. However, there are no studies documenting the amount of zinc in commonly utilized automated susceptibility testing (AST) platforms. This study reveals supraphysiologic zinc concentrations as well as large zinc variability among AST platforms and highlights the challenges this raises in the development of zinc-limited media.

Carbapenemase-producing Pseudomonas aeruginosa -an emerging challenge.

Carbapenem-resistant Pseudomonas aeruginosa (CR-PA) is a major healthcare-associated pathogen worldwide. In the United States, 10-30% of P. aeruginosa isolates are carbapenem-resistant, while globally the percentage varies considerably. A subset of carbapenem-resistant P. aeruginosa isolates harbour carbapenemases, although due in part to limited screening for these enzymes in clinical laboratories, the actual percentage is unknown. Carbapenemase-mediated carbapenem resistance in P. aeruginosa is a significant concern as it greatly limits the choice of anti-infective strategies, although detecting carbapenemase-producing P. aeruginosa in the clinical laboratory can be challenging. Such organisms also have been associated with nosocomial spread requiring infection prevention interventions. The carbapenemases present in P. aeruginosa vary widely by region but include the Class A beta-lactamases, KPC and GES; metallo-beta-lactamases IMP, NDM, SPM, and VIM; and the Class D, OXA-48 enzymes. Rapid confirmation and differentiation among the various classes of carbapenemases is key to the initiation of early effective therapy. This may be accomplished using either molecular genotypic methods or phenotypic methods, although both have their limitations. Prompt evidence that rules out carbapenemases guides clinicians to more optimal therapeutic selections based on local phenotypic profiling of non-carbapenemase-producing, carbapenem-resistant P. aeruginosa. This article will review the testing strategies available for optimizing therapy of P. aeruginosa infections.