Synergistic effects of inhaled aztreonam plus tobramycin on hypermutable cystic fibrosis Pseudomonas aeruginosa isolates in a dynamic biofilm model evaluated by mechanism-based modelling and whole genome sequencing.

OBJECTIVE: Hypermutable Pseudomonas aeruginosa strains are highly prevalent in chronic lung infections of patients with cystic fibrosis (CF). Acute exacerbations of these infections have limited treatment options. This study aimed to investigate inhaled aztreonam and tobramycin against clinical hypermutable P. aeruginosa strains using the CDC dynamic in vitro biofilm reactor (CBR), mechanism-based mathematical modelling (MBM) and genomic studies. METHODS: Two CF multidrug-resistant strains were investigated in a 168 h CBR (n = 2 biological replicates). Regimens were inhaled aztreonam (75 mg 8-hourly) and tobramycin (300 mg 12-hourly) in monotherapies and combination. The simulated pharmacokinetic profiles of aztreonam and tobramycin (t1/2 = 3 h) were based on published lung fluid concentrations in patients with CF. Total viable and resistant counts were determined for planktonic and biofilm bacteria. MBM of total and resistant bacterial counts and whole genome sequencing were completed. RESULTS: Both isolates showed reproducible bacterial regrowth and resistance amplification for the monotherapies by 168 h. The combination performed synergistically, with minimal resistant subpopulations compared to the respective monotherapies at 168 h. Mechanistic synergy appropriately described the antibacterial effects of the combination regimen in the MBM. Genomic analysis of colonies recovered from monotherapy regimens indicated noncanonical resistance mechanisms were likely responsible for treatment failure. CONCLUSION: The combination of aztreonam and tobramycin was required to suppress the regrowth and resistance of planktonic and biofilm bacteria in all biological replicates of both hypermutable multidrug-resistant P. aeruginosa CF isolates. The developed MBM could be utilised for future investigations of this promising inhaled combination.

Providing insight into the mechanism of action of cationic lipidated oligomers using metabolomics.

The increasing resistance of clinically relevant microbes against current commercially available antimicrobials underpins the urgent need for alternative and novel treatment strategies. Cationic lipidated oligomers (CLOs) are innovative alternatives to antimicrobial peptides and have reported antimicrobial potential. An understanding of their antimicrobial mechanism of action is required to rationally design future treatment strategies for CLOs, either in monotherapy or synergistic combinations. In the present study, metabolomics was used to investigate the potential metabolic pathways involved in the mechanisms of antibacterial activity of one CLO, C12-o-(BG-D)-10, which we have previously shown to be effective against methicillin-resistant Staphylococcus aureus (MRSA) ATCC 43300. The metabolomes of MRSA ATCC 43300 at 1, 3, and 6 h following treatment with C12-o-(BG-D)-10 (48 µg/mL, i.e., 3× MIC) were compared to those of the untreated controls. Our findings reveal that the studied CLO, C12-o-(BG-D)-10, disorganized the bacterial membrane as the first step toward its antimicrobial effect, as evidenced by marked perturbations in the bacterial membrane lipids and peptidoglycan biosynthesis observed at early time points, i.e., 1 and 3 h. Central carbon metabolism and the biosynthesis of DNA, RNA, and arginine were also vigorously perturbed, mainly at early time points. Moreover, bacterial cells were under osmotic and oxidative stress across all time points, as evident by perturbations of trehalose biosynthesis and pentose phosphate shunt. Overall, this metabolomics study has, for the first time, revealed that the antimicrobial action of C12-o-(BG-D)-10 may potentially stem from the dysregulation of multiple metabolic pathways.IMPORTANCEAntimicrobial resistance poses a significant challenge to healthcare systems worldwide. Novel anti-infective therapeutics are urgently needed to combat drug-resistant microorganisms. Cationic lipidated oligomers (CLOs) show promise as new antibacterial agents against Gram-positive pathogens like methicillin-resistant Staphylococcus aureus (MRSA). Understanding their molecular mechanism(s) of antimicrobial action may help design synergistic CLO treatments along with monotherapy. Here, we describe the first metabolomics study to investigate the killing mechanism(s) of CLOs against MRSA. The results of our study indicate that the CLO, C12-o-(BG-D)-10, had a notable impact on the biosynthesis and organization of the bacterial cell envelope. C12-o-(BG-D)-10 also inhibits arginine, histidine, central carbon metabolism, and trehalose production, adding to its antibacterial characteristics. This work illuminates the unique mechanism of action of C12-o-(BG-D)-10 and opens an avenue to design innovative antibacterial oligomers/polymers for future clinical applications.

Identifying and mathematically modeling the time-course of extracellular metabolic markers associated with resistance to ceftolozane/tazobactam in Pseudomonas aeruginosa.

Extracellular bacterial metabolites have potential as markers of bacterial growth and resistance emergence but have not been evaluated in dynamic in vitro studies. We investigated the dynamic metabolomic footprint of a multidrug-resistant hypermutable Pseudomonas aeruginosa isolate exposed to ceftolozane/tazobactam as continuous infusion (4.5 g/day, 9 g/day) in a hollow-fiber infection model over 7-9 days in biological replicates (n = 5). Bacterial samples were collected at 0, 7, 23, 47, 71, 95, 143, 167, 191, and 215 h, the supernatant quenched, and extracellular metabolites extracted. Metabolites were analyzed via untargeted metabolomics, including hierarchical clustering and correlation with quantified total and resistant bacterial populations. The time-courses of five (of 1,921 detected) metabolites from enriched pathways were mathematically modeled. Absorbed L-arginine and secreted L-ornithine were highly correlated with the total bacterial population (r -0.79 and 0.82, respectively, P<0.0001). Ribose-5-phosphate, sedoheptulose-7-phosphate, and trehalose-6-phosphate correlated with the resistant subpopulation (0.64, 0.64, and 0.67, respectively, P<0.0001) and were likely secreted due to resistant growth overcoming oxidative and osmotic stress induced by ceftolozane/tazobactam. Using pharmacokinetic/pharmacodynamic-based transduction models, these metabolites were successfully modeled based on the total or resistant bacterial populations. The models well described the abundance of each metabolite across the differing time-course profiles of biological replicates, based on bacterial killing and, importantly, resistant regrowth. These proof-of-concept studies suggest that further exploration is warranted to determine the generalizability of these findings. The metabolites modeled here are not exclusive to bacteria. Future studies may use this approach to identify bacteria-specific metabolites correlating with resistance, which would ultimately be extremely useful for clinical translation.

Ceftolozane-Tazobactam against Pseudomonas aeruginosa Cystic Fibrosis Clinical Isolates in the Hollow-Fiber Infection Model: Challenges Imposed by Hypermutability and Heteroresistance.

Pseudomonas aeruginosa remains a challenge in chronic respiratory infections in cystic fibrosis (CF). Ceftolozane-tazobactam has not yet been evaluated against multidrug-resistant hypermutable P. aeruginosa isolates in the hollow-fiber infection model (HFIM). Isolates CW41, CW35, and CW44 (ceftolozane-tazobactam MICs of 4, 4, and 2 mg/L, respectively) from adults with CF were exposed to simulated representative epithelial lining fluid pharmacokinetics of ceftolozane-tazobactam in the HFIM. Regimens were continuous infusion (CI; 4.5 g/day to 9 g/day, all isolates) and 1-h infusions (1.5 g every 8 hours and 3 g every 8 hours, CW41). Whole-genome sequencing and mechanism-based modeling were performed for CW41. CW41 (in four of five biological replicates) and CW44 harbored preexisting resistant subpopulations; CW35 did not. For replicates 1 to 4 of CW41 and CW44, 9 g/day CI decreased bacterial counts to <3 log10 CFU/mL for 24 to 48 h, followed by regrowth and resistance amplification. Replicate 5 of CW41 had no preexisting subpopulations and was suppressed below ~3 log10 CFU/mL for 120 h by 9 g/day CI, followed by resistant regrowth. Both CI regimens reduced CW35 bacterial counts to <1 log10 CFU/mL by 120 h without regrowth. These results corresponded with the presence or absence of preexisting resistant subpopulations and resistance-associated mutations at baseline. Mutations in ampC, algO, and mexY were identified following CW41 exposure to ceftolozane-tazobactam at 167 to 215 h. Mechanism-based modeling well described total and resistant bacterial counts. The findings highlight the impact of heteroresistance and baseline mutations on the effect of ceftolozane-tazobactam and limitations of MIC to predict bacterial outcomes. The resistance amplification in two of three isolates supports current guidelines that ceftolozane-tazobactam should be utilized together with another antibiotic against P. aeruginosa in CF.

Development of a sustained release implant of benzathine penicillin G for secondary prophylaxis of rheumatic heart disease.

BACKGROUND: Regular intramuscular (i.m.) benzathine penicillin G (BPG) injections have been the cornerstone of rheumatic heart disease (RHD) secondary prophylaxis since the 1950s. Patient adherence to IM BPG is poor, largely due to pain, the need for regular injections every 3-4 weeks and health sector delivery challenges in resource-limited settings. There is an urgent need for new approaches for secondary prophylaxis, such as an implant which could provide sustained penicillin concentrations for more than 6 months. METHODS: In this study we developed and evaluated a slow release implant with potential for substantially extended treatment. The side wall of a solid drug rich core was coated with polycaprolactone which acts as an impermeable barrier. The exposed surfaces at the ends of the implant defined the release surface area, and the in vitro release rate of drug was proportional to the exposed surface area across implants of differing diameter. The in vivo pharmacokinetics and tolerability of the implants were evaluated in a sheep model over 9 weeks after subcutaneous implantation. RESULTS: The absolute release rates obtained for the poorly water-soluble benzathine salt were dependent on the exposed surface area demonstrating the impermeability of the wall of the implant. The implants were well-tolerated after subcutaneous implantation in a sheep model, without adverse effects at the implantation site. Gross structural integrity was maintained over the course of the study, with erosion limited to the dual-exposed ends. Steady release of penicillin G was observed over the 9 weeks and resulted in approximately constant plasma concentrations close to accepted target concentrations. CONCLUSION: In principle, a long acting BPG implant is feasible as an alternative to i.m. injections for secondary prophylaxis of RHD. However, large implant size is currently a significant impediment to clinical utility and acceptability.

Penicillin G concentrations required for prophylaxis against Group A Streptococcus infection evaluated using a hollow fibre model and mathematical modelling.

BACKGROUND: Acute rheumatic fever (ARF), an autoimmune reaction to Group A Streptococcus (Streptococcus pyogenes; Strep A) infection, can cause rheumatic heart disease (RHD). New formulations of long-acting penicillins are being developed for secondary prophylaxis of ARF and RHD. OBJECTIVES: To evaluate the penicillin G concentrations required to suppress growth of Strep A. METHODS: Broth microdilution MIC and MBC for Strep A strains M75611024, M1T15448 and M18MGAS8232 were determined. All strains were studied in a hollow fibre model (initial inoculum 4 log10 cfu/mL). Constant penicillin G concentrations of 0.008, 0.016 and 0.05 mg/L were examined against all strains, plus 0.012 mg/L against M18MGAS8232. Viable counts were determined over 144 h. Subsequently, all penicillin G-treated cartridges were emptied, reinoculated with 5 log10 cfu/mL and counts determined over a further 144 h. Mathematical modelling was performed. RESULTS: MIC and MBC were 0.008 mg/L for all strains; small subpopulations of M75611024 and M1T15448, but not M18MGAS8232, grew at 1× MIC. Following the first inoculation, 0.008 mg/L achieved limited killing and/or stasis against M75611024 and M1T15448, with subsequent growth to ∼6 log10 cfu/mL. Following both inocula, concentrations ≥0.016 mg/L suppressed M75611024 and M1T15448 to <1 log10 cfu/mL from 6 h onwards with eradication. Concentrations ≥0.008 mg/L suppressed M18MGAS8232 to <1 log10 cfu/mL from 24 h onwards with eradication after both inoculations. Mathematical modelling well described all strains using a single set of parameter estimates, except for different maximum bacterial concentrations and proportions of bacteria growing at 1× MIC. CONCLUSIONS: In the absence of validated animal and human challenge models, the study provides guidance on penicillin G target concentrations for development of new penicillin formulations.

Effect of Different Piperacillin-Tazobactam Dosage Regimens on Synergy of the Combination with Tobramycin against Pseudomonas aeruginosa for the Pharmacokinetics of Critically Ill Patients in a Dynamic Infection Model.

We evaluated piperacillin-tazobactam and tobramycin regimens against Pseudomonas aeruginosa isolates from critically ill patients. Static-concentration time-kill studies (SCTK) assessed piperacillin-tazobactam and tobramycin monotherapies and combinations against four isolates over 72 h. A 120 h-dynamic in vitro infection model (IVM) investigated isolates Pa1281 (MICpiperacillin 4 mg/L, MICtobramycin 0.5 mg/L) and CR380 (MICpiperacillin 32 mg/L, MICtobramycin 1 mg/L), simulating the pharmacokinetics of: (A) tobramycin 7 mg/kg q24 h (0.5 h-infusions, t1/2 = 3.1 h); (B) piperacillin 4 g q4 h (0.5 h-infusions, t1/2 = 1.5 h); (C) piperacillin 24 g/day, continuous infusion; A + B; A + C. Total and less-susceptible bacteria were determined. SCTK demonstrated synergy of the combination for all isolates. In the IVM, regimens A and B provided initial killing, followed by extensive regrowth by 72 h for both isolates. C provided >4 log10 CFU/mL killing, followed by regrowth close to initial inoculum by 96 h for Pa1281, and suppressed growth to <4 log10 CFU/mL for CR380. A and A + B initially suppressed counts of both isolates to <1 log10 CFU/mL, before regrowth to control or starting inoculum and resistance emergence by 72 h. Overall, the combination including intermittent piperacillin-tazobactam did not provide a benefit over tobramycin monotherapy. A + C, the combination regimen with continuous infusion of piperacillin-tazobactam, provided synergistic killing (counts <1 log10 CFU/mL) of Pa1281 and CR380, and suppressed regrowth to <2 and <4 log10 CFU/mL, respectively, and resistance emergence over 120 h. The shape of the concentration-time curve was important for synergy of the combination.

Simulated Intravenous versus Inhaled Tobramycin with or without Intravenous Ceftazidime Evaluated against Hypermutable Pseudomonas aeruginosa via a Dynamic Biofilm Model and Mechanism-Based Modeling.

Acute exacerbations of chronic respiratory infections in patients with cystic fibrosis are highly challenging due to hypermutable Pseudomonas aeruginosa, biofilm formation and resistance emergence. We aimed to systematically evaluate the effects of intravenous versus inhaled tobramycin (TOB) with and without intravenous ceftazidime (CAZ). Two hypermutable P. aeruginosa isolates, CW30 (MICCAZ, 0.5 mg/liter; MICTOB, 2 mg/liter) and CW8 (MICCAZ, 2 mg/liter; MICTOB, 8 mg/liter), were investigated for 120 h in dynamic in vitro biofilm studies. Treatments were intravenous ceftazidime, 9 g/day (33% lung fluid penetration); intravenous tobramycin, 10 mg/kg of body every 24 h (50% lung fluid penetration); inhaled tobramycin, 300 mg every 12 h; and both ceftazidime-tobramycin combinations. Total and less susceptible planktonic and biofilm bacteria were quantified over 120 h. Mechanism-based modeling was performed. All monotherapies were ineffective for both isolates, with regrowth of planktonic (≥4.7 log10 CFU/ml) and biofilm (>3.8 log10 CFU/cm2) bacteria and resistance amplification by 120 h. Both combination treatments demonstrated synergistic or enhanced bacterial killing of planktonic and biofilm bacteria. With the combination simulating tobramycin inhalation, planktonic bacterial counts of the two isolates at 120 h were 0.47% and 36% of those for the combination with intravenous tobramycin; for biofilm bacteria the corresponding values were 8.2% and 13%. Combination regimens achieved substantial suppression of resistance of planktonic and biofilm bacteria compared to each antibiotic in monotherapy for both isolates. Mechanism-based modeling well described all planktonic and biofilm counts and indicated synergy of the combination regimens despite reduced activity of tobramycin in biofilm. Combination regimens of inhaled tobramycin with ceftazidime hold promise to treat acute exacerbations caused by hypermutable P. aeruginosa strains and warrant further investigation.

Pharmacodynamics of ceftazidime plus tobramycin combination dosage regimens against hypermutable Pseudomonas aeruginosa isolates at simulated epithelial lining fluid concentrations in a dynamic in vitro infection model.

OBJECTIVES: Hypermutable Pseudomonas aeruginosa strains are a major challenge in cystic fibrosis. We investigated bacterial killing and resistance emergence for approved ceftazidime and tobramycin regimens, alone and in combination. METHODS: Pseudomonas aeruginosa PAOΔmutS and six hypermutable clinical isolates were examined using 48-h static concentration time-kill (SCTK) studies (inoculum ~107.5 CFU/mL); four strains were also studied in a dynamic in vitro model (IVM) (inoculum ~108 CFU/mL). The IVM simulated concentration-time profiles in epithelial lining fluid following intravenous administration of ceftazidime (3 g/day and 9 g/day continuous infusion), tobramycin (5 mg/kg and 10 mg/kg via 30-min infusion 24-hourly; half-life 3.5 h), and their combinations. Time courses of total and less-susceptible populations were determined. RESULTS: Ceftazidime plus tobramycin demonstrated synergistic killing in SCTK studies for all strains, although to a lesser extent for ceftazidime-resistant strains. In the IVM, ceftazidime and tobramycin monotherapies provided ≤5.4 and ≤3.4 log10 initial killing, respectively; however, re-growth with resistance occurred by 72 h. Against strains susceptible to one or both antibiotics, high-dose combination regimens provided >6 log10 initial killing, which was generally synergistic from 8-24 h, and marked suppression of re-growth and resistance at 72 h. The time course of bacterial density in the IVM was well described by mechanism-based models, enabling Monte Carlo simulations (MCSs) to predict likely effectiveness of the combination in patients. CONCLUSION: Results of the IVM and MCS suggested antibacterial effect depends both on the strain's susceptibility and hypermutability. Further investigation of the combination against hypermutable P. aeruginosa strains is warranted.

Evaluation of Meropenem-Ciprofloxacin Combination Dosage Regimens for the Pharmacokinetics of Critically Ill Patients With Augmented Renal Clearance.

Augmented renal clearance (ARC, creatinine clearance > 130 mL/minute) makes difficult achievement of effective concentrations of renally cleared antibiotics in critically ill patients. This study examined the synergistic killing and resistance suppression for meropenem-ciprofloxacin combination dosage regimens against Pseudomonas aeruginosa isolates within the context of ARC. Clinically relevant meropenem and ciprofloxacin concentrations, alone and in combinations, were studied against three clinical isolates with a range of susceptibilities to each of the antibiotics. Isolate Pa1280 was susceptible to both meropenem and ciprofloxacin, Pa1284 had intermediate susceptibility to meropenem and was susceptible to ciprofloxacin, and CR380 was resistant to meropenem and had intermediate susceptibility to ciprofloxacin. Initially, isolates were studied in 72-hour static-concentration time-kill (SCTK) studies. Subsequently, the pharmacokinetic profiles expected in patients with ARC receiving dosage regimens, including at the highest approved daily doses (meropenem 6 g daily divided and administered as 0.5-hour infusions every 8 hours, or as a continuous infusion; ciprofloxacin 0.4 g as 1-hour infusions every 8 hours), were examined in a dynamic hollow-fiber infection model (HFIM) over 7-10 days. In both SCTK and HFIM, combination regimens were generally synergistic and suppressed growth of less-susceptible subpopulations, these effects being smaller for isolate CR380. The time-courses of total and less-susceptible bacterial populations in the HFIM were well-described by mechanism-based models, which enabled conduct of Monte Carlo simulations to predict likely effectiveness of approved dosage regimens at different creatinine clearances. Optimized meropenem-ciprofloxacin combination dosage regimens may be a viable consideration for P. aeruginosa infections in critically ill patients with ARC.

Clinically Relevant Epithelial Lining Fluid Concentrations of Meropenem with Ciprofloxacin Provide Synergistic Killing and Resistance Suppression of Hypermutable Pseudomonas aeruginosa in a Dynamic Biofilm Model.

Treatment of exacerbations of chronic Pseudomonas aeruginosa infections in patients with cystic fibrosis (CF) is highly challenging due to hypermutability, biofilm formation, and an increased risk of resistance emergence. We evaluated the impact of ciprofloxacin and meropenem as monotherapy and in combination in the dynamic in vitro CDC biofilm reactor (CBR). Two hypermutable P. aeruginosa strains, PAOΔmutS (MIC of ciprofloxacin [MICciprofloxacin], 0.25 mg/liter; MICmeropenem, 2 mg/liter) and CW44 (MICciprofloxacin, 0.5 mg/liter; MICmeropenem, 4 mg/liter), were investigated for 120 h. Concentration-time profiles achievable in epithelial lining fluid (ELF) following FDA-approved doses were simulated in the CBR. Treatments were ciprofloxacin at 0.4 g every 8 h as 1-h infusions (80% ELF penetration), meropenem at 6 g/day as a continuous infusion (CI) (30% and 60% ELF penetration), and their combinations. Counts of total and less-susceptible planktonic and biofilm bacteria and MICs were determined. Antibiotic concentrations were quantified by an ultrahigh-performance liquid chromatography photodiode array (UHPLC-PDA) assay. For both strains, all monotherapies failed, with substantial regrowth and resistance of planktonic (≥8 log10 CFU/ml) and biofilm (>8 log10 CFU/cm2) bacteria at 120 h (MICciprofloxacin, up to 8 mg/liter; MICmeropenem, up to 64 mg/liter). Both combination treatments demonstrated synergistic bacterial killing of planktonic and biofilm bacteria of both strains from ∼48 h onwards and suppressed regrowth to ≤4 log10 CFU/ml and ≤6 log10 CFU/cm2 at 120 h. Overall, both combination treatments suppressed the amplification of resistance of planktonic bacteria for both strains and of biofilm bacteria for CW44. The combination with meropenem at 60% ELF penetration also suppressed the amplification of resistance of biofilm bacteria for PAOΔmutS Thus, combination treatment demonstrated synergistic bacterial killing and resistance suppression against difficult-to-treat hypermutable P. aeruginosa strains.