Antimicrobial activity of cefepime-tazobactam combination against extended spectrum beta-lactamase and/or AmpC beta-lactamase- producing gram-negative bacilli.

BACKGROUND: The problem of resistance to beta-lactam antibiotics, which is caused by ESBL and AmpC ß-lactamases, is getting worse globally. Infections caused by bacterial isolates harboring these enzymes are difficult to treat with carbapenems being the sole effective treatment option for such infections. The objective of this study was to determine the frequency of ESBLs and AmpC-producing Gram-negative bacilli isolated from clinical specimens and to evaluate the sensitivity of cefepime-tazobactam combination against them. METHODS: This is an observational cross-sectional study carried out on 100 Gram-negative bacilli at Theodor Bilharz Research Institute Hospital during the period from February 2015 to January 2016. ESBL production was screened by using the disc diffusion test followed by confirmation by the combined disc confirmatory test, the screening for AmpC production was conducted using the cefoxitin disc test, which was subsequently confirmed by the AmpC disc test. Isolates confirmed positive for ESBL and/ or AmpC production were investigated for their susceptibility to antibiotics. RESULTS: Among 100 Gram-negative bacilli, 44 isolates were confirmed as ESBL producers by the combined disc confirmatory test out of 56 isolates that tested positive for ESBL production through the disc diffusion test. The presence of AmpC production was assessed using the cefoxitin disc test, 32 isolates were screened to be AmpC producers, and the AmpC disc test confirmed AmpC production in 9 isolates of them. Using the Mast® D68C set, 32 isolates were ESBL producers, 3 were AmpC producers, and 4 isolates were ESBL/AmpC co-producers. The highest sensitivity was to cefepime-tazobactam (91.48%) followed by the carbapenems. CONCLUSION: Cefepime-tazobactam showed remarkable activity against ESBL and/or AmpC-producing Gram-negative bacilli and may be considered as a therapeutic alternative to carbapenems.

Lessons learned from an external quality assurance program in applying CLSI interpretive criteria for reporting piperacillin/tazobactam susceptibility.

We evaluated the performance of automated susceptibility testing for piperacillin/tazobactam (PTZ) MICs against the reference microbroth dilution method. The Minimum Inhibitory Concentration of PTZ against a clinical isolate of Klebsiella pneumoniae was determined by reference broth micro-dilution method in 10 replicates which yielded a modal MIC of 16 mg/L (susceptible dose-dependent). Out of 434 laboratories who obtained MIC of 16 mg/L correctly, only 301 interpreted the result as susceptible dose dependent as per 2022 revised CLSI criteria. Educating the clinical laboratories in validating AST methods as per latest CLSI guidelines is of utmost important.

Early treatment response to piperacillin/tazobactam in patients with bloodstream infections caused by non-ESBL ampicillin/sulbactam-resistant Escherichia coli: a binational cohort study.

PURPOSE: This study aimed to compare treatment outcomes for bloodstream infections (BSI) caused by a piperacillin/tazobactam (PIP/TAZ)-susceptible E. coli among three patient groups: BSI caused by ampicillin/sulbactam (AMP/SLB)-resistant isolates treated with PIP/TAZ, BSI caused by AMP/SLB-sensitive isolates treated with PIP/TAZ, and BSI caused by AMP/SLB-resistant isolates treated with another monotherapy. METHODS: This retrospective study was conducted in two academic centres in Europe. Adult patients with E. coli BSI were screened from 2014 to 2020. Inclusion criteria were non-ESBL BSI and initial monotherapy for ≥ 72 h. To reduce the expected bias between the patient groups, propensity score matching was performed. The primary outcome was early treatment response after 72 h and required absence of SOFA score increase in ICU/IMC patients, as well as resolution of fever, leukocytosis, and bacteraemia. RESULTS: Of the 1707 patients screened, 315 (18.5%) were included in the final analysis. Urinary tract infection was the most common source of BSI (54.9%). Monotherapies other than PIP/TAZ were cephalosporins (48.6%), carbapenems (34.3%), and quinolones (17.1%). Enhanced early treatment response rate was detected (p = 0.04) in patients with BSI caused by AMP/SLB-resistant isolates treated with another monotherapy (74.3%) compared to those treated with PIP/TAZ (57.1%), and was mainly driven by the use of cephalosporins and quinolones (p ≤ 0.03). Clinical success, 28-day mortality, and rate of relapsing BSI did not significantly differ between the groups. CONCLUSIONS: Our study suggests that initial use of PIP/TAZ may be associated with reduced early treatment response in E. coli BSI caused by AMP/SLB-resistant isolates compared to alternative monotherapies.

Susceptibility of ceftolozane/tazobactam against multidrug-resistant and carbapenem-resistant Pseudomonas aeruginosa.

Ceftolozane (CTLZ) is a novel cephalosporin antibiotic that exhibits broad-spectrum activity against gram-negative pathogens, including Pseudomonas aeruginosa, especially when combined with tazobactam (TAZ). We examined the minimum inhibitory concentration (MIC) of CTLZ/TAZ for 21 multidrug-resistant P. aeruginosa (MDRP) and eight carbapenem-resistant P. aeruginosa (CRPA) strains isolated at Okayama University Hospital, Japan. Consequently, 81% (17/21) of the MDRP strains and 25% (2/8) of the CRPA strains were resistant to CTLZ/TAZ (MIC >8 µg/mL). All 18 blaIMP-positive strains showed resistance to CTLZ/TAZ, whereas the drug retained in vitro susceptibility in 54.5% (6/11 strains) of blaIMP-negative strains.

Comparative in vitro antipseudomonal activity of ceftolozane/tazobactam against Pseudomonas aeruginosa isolates from children with cystic fibrosis.

This study evaluated the in vitro activity of Ceftolozane/tazobactam (C/T) vs 10 comparator agents against Pseudomonas aeruginosa isolates obtained from clinical respiratory samples from pediatric patients with cystic fibrosis at three hospitals during 2015 to 2020. Antimicrobial susceptibility testing was performed using microbroth dilution technique with custom prepared Sensititre® MIC plates. MICs were determined via Sensititre Vizion® system and results were interpreted using current CLSI and EUCAST (2022) breakpoint criteria. C/T was the most potent agent as compared with other antipseudomonal drugs against 291 isolates with MIC50 = 1 µg/mL and MIC90 = 2 µg/mL with percent susceptibility as 95.2%. C/T remained active against majority of ß-lactam non-susceptible isolates; percent susceptibility ranging from 61.2% to 80% including 65.9% ceftazidime non-susceptible isolates. C/T had high activity against P. aeruginosa from 3 geographically diverse pediatric medical centers. Study results suggest that C/T may be used as a potential therapeutic option for treating pediatric patients with CF.

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.

Activity of Ceftolozane-Tazobactam Against Gram-Negative Isolates from Australia and New Zealand as part of the PACTS Surveillance 2016-2018.

OBJECTIVES: Ceftolozane-tazobactam (C-T) is an anti-pseudomonal cephalosporin combined with a well-described ß-lactamase inhibitor. Ceftolozane-tazobactam has enhanced activity against Pseudomonas aeruginosa, and activity against Enterobacterales isolates that produce extended-spectrum ß-lactamases (ESBLs) or AmpC cephalosporinases. In this study, we analysed the susceptibility of Gram-negative isolates to C-T and comparators collected in Australia and New Zealand from 2016 to 2018 as part of the Program to Assess Ceftolozane-Tazobactam Susceptibility (PACTS) surveillance. METHODS: A total of 1693 nonduplicate Enterobacterales and 435 P. aeruginosa isolates were collected prospectively from hospitalized patients in six medical centres in Australia and two in New Zealand. Susceptibilities (S) to C-T and comparators were determined using broth microdilution. EUCAST breakpoints were used. Isolates with multi-drug resistant (MDR), extensively drug resistant (XDR), extended-spectrum ß-lactamase non-carbapenem resistant (ESBL, non-CRE) phenotype, and CRE were analysed. RESULTS: For P. aeruginosa, 97.5% were S to C-T while 89.9% were S to meropenem. According to EUCAST criteria, 86.4% were susceptible-increased exposure to piperacillin-tazobactam. MDR and XDR P. aeruginosa isolates had 76.7% and 65.4% S to C-T, respectively; 34.9% and 19.2% S to meropenem, respectively; and 23.3% and 15.4% were susceptible-increased exposure to piperacillin-tazobactam, respectively. Meropenem (99.8% S), amikacin (99.1% S), and C-T (96.5% S) were the most active against Enterobacterales. Susceptibilities to C-T were 94.3% for ESBL, non-CRE phenotype, and 78.4% for MDR isolates. Only three CRE and five XDR isolates were identified. CONCLUSIONS: These in vitro data indicate that C-T is a potent antimicrobial with activity against MDR and XDR P. aeruginosa, as well as ESBL, non-CRE phenotype isolates and MDR Enterobacterales.

Pharmacodynamic evaluation of intermittent versus extended and continuous infusions of piperacillin/tazobactam in a hollow-fibre infection model against Escherichia coli clinical isolates.

OBJECTIVES: To compare the bacterial killing and emergence of resistance of intermittent versus prolonged (extended and continuous infusions) infusion dosing regimens of piperacillin/tazobactam against two Escherichia coli clinical isolates in a dynamic hollow-fibre infection model (HFIM). METHODS: Three piperacillin/tazobactam dosing regimens (4/0.5 g 8 hourly as 0.5 and 4 h infusions and 12/1.5 g/24 h continuous infusion) against a ceftriaxone-susceptible, non-ESBL-producing E. coli 44 (Ec44, MIC 2 mg/L) and six piperacillin/tazobactam dosing regimens (4/0.5 g 8 hourly as 0.5 and 4 h infusions and 12/1.5 g/24 h continuous infusion; 4/0.5 g 6 hourly as 0.5 and 3 h infusions and 16/2 g/24 h continuous infusion) were simulated against a ceftriaxone-resistant, AmpC- and ESBL-producing E. coli 50 (Ec50, MIC 8 mg/L) in a HFIM over 7 days (initial inoculum ∼107 cfu/mL). Total and less-susceptible subpopulations and MICs were determined. RESULTS: All simulated dosing regimens against Ec44 exhibited 4 log10 of bacterial killing over 8 h without regrowth and resistance emergence throughout the experiment. For Ec50, there was the initial bacterial killing of 4 log10 followed by regrowth to 1011 cfu/mL within 24 h against all simulated dosing regimens, and the MICs for resistant subpopulations exceeded 256 mg/L at 72 h. CONCLUSIONS: Our study suggests that, for critically ill patients, conventional intermittent infusion, or prolonged infusions of piperacillin/tazobactam may suppress resistant subpopulations of non-ESBL-producing E. coli clinical isolates. However, intermittent, or prolonged infusions may not suppress the resistant subpopulations of AmpC- and ESBL-producing E. coli clinical isolates. More studies are required to confirm these findings.

Crystal structures of the molecular class A ß-lactamase TEM-171 and its complexes with tazobactam.

The resistance of bacteria to ß-lactam antibiotics is primarily caused by the production of ß-lactamases. Here, novel crystal structures of the native ß-lactamase TEM-171 and two complexes with the widely used inhibitor tazobactam are presented, alongside complementary data from UV spectroscopy and fluorescence quenching. The six chemically identical ß-lactamase molecules in the crystallographic asymmetric unit displayed different degrees of disorder. The tazobactam intermediate was covalently bound to the catalytic Ser70 in the trans-enamine configuration. While the conformation of tazobactam in the first complex resembled that in published ß-lactamase-tazobactam structures, in the second complex, which was obtained after longer soaking of the native crystals in the inhibitor solution, a new and previously unreported tazobactam conformation was observed. It is proposed that the two complexes correspond to different stages along the deacylation path of the acyl-enzyme intermediate. The results provide a novel structural basis for the rational design of new ß-lactamase inhibitors.

Pharmacodynamic evaluation of piperacillin/tazobactam versus meropenem against extended-spectrum ß-lactamase-producing and non-producing Escherichia coli clinical isolates in a hollow-fibre infection model.

BACKGROUND: Urosepsis caused by extended-spectrum ß-lactamase (ESBL)-producing Escherichia coli is increasing worldwide. Carbapenems are commonly recommended for the treatment of ESBL infections; however, to minimize the emergence of carbapenem resistance, interest in alternative treatments has heightened. OBJECTIVES: This study compared pharmacodynamics of piperacillin/tazobactam versus meropenem against ESBL-producing and non-producing E. coli clinical isolates. METHODS: E. coli isolates, obtained from national reference laboratory in Bangladesh, were characterized by phenotypic tests, WGS, susceptibility tests and mutant frequency analysis. Three ESBL-producing and two non-producing E. coli were exposed to piperacillin/tazobactam (4.5 g, every 6 h and every 8 h, 30 min infusion) and meropenem (1 g, every 8 h, 30 min infusion) in a hollow-fibre infection model over 7 days. RESULTS: Piperacillin/tazobactam regimens attained ∼4-5 log10 cfu/mL bacterial killing within 24 h and prevented resistance emergence over the experiment against ESBL-producing and non-producing E. coli. However, compared with 8 hourly meropenem, the 6 hourly piperacillin/tazobactam attained ∼1 log10 lower bacterial kill against one of three ESBL-producing E. coli (CTAP#173) but comparable killing for the other two ESBL-producing (CTAP#168 and CTAP#169) and two non-producing E. coli (CTAP#179 and CTAP#180). The 6 hourly piperacillin/tazobactam regimen attained ∼1 log10 greater bacterial kill compared with the 8 hourly regimen against CTAP#168 and CTAP#179 at 24 h. CONCLUSIONS: Our study suggests piperacillin/tazobactam may be a potential alternative to carbapenems to treat urosepsis caused by ESBL-producing E. coli, although clinical trials with robust design are needed to confirm non-inferiority of outcome.

Exposure-Efficacy Analyses Support Optimal Dosing Regimens of Ceftolozane/Tazobactam in Participants with Hospital-Acquired/Ventilator-Associated Bacterial Pneumonia in ASPECT-NP.

An exposure-efficacy analysis of the phase 3 ASPECT-NP trial was performed to evaluate the relationship between plasma exposure of ceftolozane and tazobactam and efficacy endpoints (primary: 28-day all-cause mortality; key secondary: clinical cure at test-of-cure visit) in adult participants with hospital-acquired or ventilator-associated bacterial pneumonia (HABP/VABP). Participants (N = 231) from the ceftolozane/tazobactam treatment group in the intention-to-treat population who had pharmacokinetic data available and relevant baseline lower respiratory tract (LRT) pathogen(s) susceptibility data were included. Population pharmacokinetic models were used to predict individual ceftolozane and tazobactam plasma exposure measures (percentage of the interdose interval with free drug concentrations above the MIC [%ƒT>MIC] and %ƒT above a threshold [%ƒT>CT = 1 µg/mL], respectively) associated with the last dose using the highest ceftolozane/tazobactam MIC for the relevant baseline LRT pathogens. Efficacy measures were comparable between the baseline LRT pathogens and across MIC cutoffs (1-8 µg/mL). Most participants (82%) had 99% ƒT>MIC for ceftolozane; 9% (N = 21/231) had 0% ƒT>MIC due to high MICs of the LRT pathogen (64-256 µg/mL). The %ƒT>MIC for ceftolozane exceeded 73% for all participants with baseline LRT pathogen(s) MIC ≤4 µg/mL. All 231 participants achieved the tazobactam pharmacokinetic/pharmacodynamic target of >20% ƒT>CT where CT = 1 µg/mL. For either efficacy endpoint, median ceftolozane %ƒT>MIC was 99% in participants achieving efficacy. No exposure-efficacy trend was observed for ceftolozane or tazobactam. These results further support the recommended ceftolozane/tazobactam dosing regimens evaluated in ASPECT-NP for patients with HABP/VABP.

In vitro study of elution kinetics and biological activity of piperacillin/tazobactam and gentamicin in acrylic bone cement.

BACKGROUND: Antibiotics differ in their elution characteristics from bone cement. But no such data is available on piperacillin and tazobactam. Therefore, we performed an in vitro observational study to examine (1) in vitro elution characteristics of piperacillin and tazobactam from bone cement, (2) their biological activity using minimum inhibitory concentration and (3) elution characteristics and biological activity when combined with gentamicin in bone cement. HYPOTHESIS: The null hypothesis was that piperacillin and tazobactam after elution from bone cement can achieve concentrations higher than minimum inhibitory concentration. MATERIAL AND METHODS: Forty milligrams bone cement was mixed with the following combination of antibiotics: without any antibiotic (sample A, control), 4g/0.50g piperacillin/tazobactam (sample B), 6g/0.75g piperacillin/tazobactam (sample C), 8g/1.0g piperacillin/tazobactam (sample D) and 4g/0.50g piperacillin/tazobactam and 400mg gentamicin (sample E). Samples were analysed on reverse-phase ultra-high-performance liquid chromatography. Antibacterial activity in the elute were tested against standard American Type Culture Collection (ATCC) strains. RESULTS: Detectable drug elution for piperacillin and tazobactam was seen till 21days. Peak drug levels for all formulations were seen at 48hours (140.8 & 297.5µg/mL for samples B of piperacillin and tazobactam respectively). About 0.83-1.24% of piperacillin and 23.17-29.17% of tazobactam were released from the samples. Gentamicin improved elution of piperacillin and tazobactam: 140.8 vs. 919.9µg/mL (p=0.000) for samples B & E of piperacillin respectively and 297.5 & 1138.4µg/mL (p=0.001) for samples B & E of tazobactam respectively at 2days. Sample E showed complete inhibition of tested microorganisms, while B sample was microbiologically less active compared to E on day 5. CONCLUSIONS: Piperacillin and tazobactam eluted successfully from bone cement and also retained antimicrobial activity after elution. Maximum elution was seen up to day 2 after which it reduced drastically. Antimicrobial action was seen up to 7days. LEVEL OF EVIDENCE: III; comparative study.

Short-Term Effects of Appropriate Empirical Antimicrobial Treatment with Ceftolozane/Tazobactam in a Swine Model of Nosocomial Pneumonia.

The rising frequency of multidrug-resistant and extensively drug-resistant (MDR/XDR) pathogens is making more frequent the inappropriate empirical antimicrobial therapy (IEAT) in nosocomial pneumonia, which is associated with increased mortality. We aim to determine the short-term benefits of appropriate empirical antimicrobial treatment (AEAT) with ceftolozane/tazobactam (C/T) compared with IEAT with piperacillin/tazobactam (TZP) in MDR Pseudomonas aeruginosa pneumonia. Twenty-one pigs with pneumonia caused by an XDR P. aeruginosa strain (susceptible to C/T but resistant to TZP) were ventilated for up to 72 h. Twenty-four hours after bacterial challenge, animals were randomized to receive 2-day treatment with either intravenous saline (untreated) or 25 to 50 mg of C/T per kg body weight (AEAT) or 200 to 225 mg of TZP per kg (IEAT) every 8 h. The primary outcome was the P. aeruginosa burden in lung tissue and the histopathology injury. P. aeruginosa burden in tracheal secretions and bronchoalveolar lavage (BAL) fluid, the development of antibiotic resistance, and inflammatory markers were secondary outcomes. Overall, P. aeruginosa lung burden was 5.30 (range, 4.00 to 6.30), 4.04 (3.64 to 4.51), and 4.04 (3.05 to 4.88) log10CFU/g in the untreated, AEAT, and IEAT groups, respectively (P = 0.299), without histopathological differences (P = 0.556). In contrast, in tracheal secretions (P < 0.001) and BAL fluid (P = 0.002), bactericidal efficacy was higher in the AEAT group. An increased MIC to TZP was found in 3 animals, while resistance to C/T did not develop. Interleukin-1ß (IL-1ß) was significantly downregulated by AEAT in comparison to other groups (P = 0.031). In a mechanically ventilated swine model of XDR P. aeruginosa pneumonia, appropriate initial treatment with C/T decreased respiratory secretions' bacterial burden, prevented development of resistance, achieved the pharmacodynamic target, and may have reduced systemic inflammation. However, after only 2 days of treatment, P. aeruginosa tissue concentrations were moderately affected.