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

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 modeling (MBM) and genomic studies. Two CF multidrug-resistant strains were investigated in a 168h 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=3h) 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. Both isolates showed reproducible bacterial regrowth and resistance amplification for the monotherapies by 168h. The combination performed synergistically, with minimal resistant subpopulations compared to the respective monotherapies at 168h. 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. The combination of aztreonam and tobramycin was required to suppress 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 utilized for future investigations of this promising inhaled combination.

Next generation antibiotic combinations to combat pan-drug resistant Klebsiella pneumoniae.

Antimicrobial resistance has emerged as one of the leading public health threats of the twenty-first century. Gram-negative pathogens have been a major contributor to the declining efficacy of antibiotics through both acquired resistance and tolerance. In this study, a pan-drug resistant (PDR), NDM-1 and CTX-M-15 co-producing isolate of K. pneumoniae, CDC Nevada, (Kp Nevada) was exposed to the clinical combination of aztreonam + ceftazidime/avibactam (ATM/CAZ/AVI) to overcome metallo-ß-lactamases. Unexpectedly, the ß-lactam combination resulted in long filamentous cell formation induced by PBP3 inhibition over 168 h in the hollow fiber infection model experiments with eventual reversion of the total population upon drug removal. However, the addition of imipenem to the two drug ß-lactam combination was highly synergistic with suppression of all drug resistant subpopulations over 5 days. Scanning electron microscopy and fluorescence microscopy for all imipenem combinations in time kill studies suggested a role for imipenem in suppression of long filamentous persisters, via the formation of metabolically active spheroplasts. To complement the imaging studies, salient transcriptomic changes were quantified using RT-PCR and novel cassette assay evaluated ß-lactam permeability. This showed significant upregulation of both spheroplast protein Y (SPY), a periplasmic chaperone protein that has been shown to be related to spheroplast formation, and penicillin binding proteins (PBP1, PBP2, PBP3) for all combinations involving imipenem. However, with aztreonam alone, pbp1, pbp3 and spy remained unchanged while pbp2 levels were downregulated by > 25%. Imipenem displayed 207-fold higher permeability as compared with aztreonam (mean permeability coefficient of 17,200 nm/s). Although the clinical combination of aztreonam/avibactam and ceftazidime has been proposed as an important treatment of MBL Gram-negatives, we report the first occurrence of long filamentous persister formation. To our knowledge, this is the first study that defines novel ß-lactam combinations involving imipenem via maximal suppression of filamentous persisters to combat PDR CDC Nevada K. pneumoniae.

Comprehensive stability analysis of 13 ß-lactams and ß-lactamase inhibitors in in vitro media, and novel supplement dosing strategy to mitigate thermal drug degradation.

Non-clinical antibiotic development relies on in vitro susceptibility and infection model studies. Validating the achievement of the targeted drug concentrations is essential to avoid under-estimation of drug effects and over-estimation of resistance emergence. While certain ß-lactams (e.g., imipenem) and ß-lactamase inhibitors (BLIs; clavulanic acid) are believed to be relatively unstable, limited tangible data on their stability in commonly used in vitro media are known. We aimed to determine the thermal stability of 10 ß-lactams and 3 BLIs via LC-MS/MS in cation-adjusted Mueller Hinton broth at 25 and 36°C as well as agar at 4 and 37°C, and in water at -20, 4, and 25°C. Supplement dosing algorithms were developed to achieve broth concentrations close to their target over 24 h. During incubation in broth (pH 7.25)/agar, degradation half-lives were 16.9/21.8 h for imipenem, 20.7/31.6 h for biapenem, 29.0 h for clavulanic acid (studied in broth only), 23.1/71.6 h for cefsulodin, 40.6/57.9 h for doripenem, 46.5/64.6 h for meropenem, 50.8/97.7 h for cefepime, 61.5/99.5 h for piperacillin, and >120 h for all other compounds. Broth stability decreased at higher pH. All drugs were ≥90% stable for 72 h in agar at 4°C. Degradation half-lives in water at 25°C were >200 h for all drugs except imipenem (14.7 h, at 1,000 mg/L) and doripenem (59.5 h). One imipenem supplement dose allowed concentrations to stay within ±31% of their target concentration. This study provides comprehensive stability data on ß-lactams and BLIs in relevant in vitro media using LC-MS/MS. Future studies are warranted applying these data to antimicrobial susceptibility testing and assessing the impact of ß-lactamase-related degradation.

Improved characterization of aminoglycoside penetration into human lung epithelial lining fluid via population pharmacokinetics.

Aminoglycosides are important treatment options for serious lung infections, but modeling analyses to quantify their human lung epithelial lining fluid (ELF) penetration are lacking. We estimated the extent and rate of penetration for five aminoglycosides via population pharmacokinetics from eight published studies. The area under the curve in ELF vs plasma ranged from 50% to 100% and equilibration half-lives from 0.61 to 5.80 h, indicating extensive system hysteresis. Aminoglycoside ELF peak concentrations were blunted, but overall exposures were moderately high.

Distinguishing Inducible and Non-Inducible Resistance to Colistin in Pseudomonas aeruginosa by Quantitative and Systems Pharmacology Modeling at Low and Standard Inocula.

Colistin is a polymyxin and peptide antibiotic that can yield rapid bacterial killing, but also leads to resistance emergence. We aimed to develop a novel experimental and Quantitative and Systems Pharmacology approach to distinguish between inducible and non-inducible resistance. Viable count profiles for the total and less susceptible populations of Pseudomonas aeruginosa ATCC 27853 from static and dynamic in vitro infection models were simultaneously modeled. We studied low and normal initial inocula to distinguish between inducible and non-inducible resistance. A novel cutoff filter approach allowed us to describe the eradication and inter-conversion of bacterial populations. At all inocula, 4.84 mg/L of colistin (sulfate) yielded ≥4 log10 killing, followed by >4 log10 regrowth. A pre-existing, less susceptible population was present at standard but not at low inocula. Formation of a non-pre-existing, less susceptible population was most pronounced at intermediate colistin (sulfate) concentrations (0.9 to 5 mg/L). Both less susceptible populations inter-converted with the susceptible population. Simultaneously modeling of the total and less susceptible populations at low and standard inocula enabled us to identify the de novo formation of an inducible, less susceptible population. Inducible resistance at intermediate colistin concentrations highlights the importance of rapidly achieving efficacious polymyxin concentrations by front-loaded dosage regimens.

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.

Ceftolozane/tazobactam plus tobramycin against free-floating and biofilm bacteria of hypermutable Pseudomonas aeruginosa epidemic strains: Resistance mechanisms and synergistic activity.

OBJECTIVE: Acute exacerbations of biofilm-associated Pseudomonas aeruginosa infections in cystic fibrosis (CF) have limited treatment options. Ceftolozane/tazobactam (alone and with a second antibiotic) has not yet been investigated against hypermutable clinical P. aeruginosa isolates in biofilm growth. This study aimed to evaluate, using an in vitro dynamic biofilm model, ceftolozane/tazobactam alone and in combination with tobramycin at simulated representative lung fluid pharmacokinetics against free-floating (planktonic) and biofilm states of two hypermutable P. aeruginosa epidemic strains (LES-1 and CC274) from adolescents with CF. METHODS: Regimens were intravenous ceftolozane/tazobactam 4.5 g/day continuous infusion, inhaled tobramycin 300 mg 12-hourly, intravenous tobramycin 10 mg/kg 24-hourly, and both ceftolozane/tazobactam-tobramycin combinations. The isolates were susceptible to both antibiotics. Total and less-susceptible free-floating and biofilm bacteria were quantified over 120-168 h. Ceftolozane/tazobactam resistance mechanisms were investigated by whole-genome sequencing. Mechanism-based modelling of bacterial viable counts was performed. RESULTS: Monotherapies of ceftolozane/tazobactam and tobramycin did not sufficiently suppress emergence of less-susceptible subpopulations, although inhaled tobramycin was more effective than intravenous tobramycin. Ceftolozane/tazobactam resistance development was associated with classical (AmpC overexpression plus structural modification) and novel (CpxR mutations) mechanisms depending on the strain. Against both isolates, combination regimens demonstrated synergy and completely suppressed the emergence of ceftolozane/tazobactam and tobramycin less-susceptible free-floating and biofilm bacterial subpopulations. CONCLUSION: Mechanism-based modelling incorporating subpopulation and mechanistic synergy well described the antibacterial effects of all regimens against free-floating and biofilm bacterial states. These findings support further investigation of ceftolozane/tazobactam in combination with tobramycin against biofilm-associated P. aeruginosa infections in adolescents with CF.

Why Molnupiravir Fails in Hospitalized Patients.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of coronavirus disease 2019 (COVID-19), has radically altered daily life. Effective antiviral therapies to combat COVID-19, especially severe disease, remain scarce. Molnupiravir is an antiviral that has shown clinical efficacy against mild-to-moderate COVID-19 but failed to provide benefit to hospitalized patients with severe disease. Here, we explained the mechanism behind the failure of molnupiravir in hospitalized patients and identified alternative dosing strategies that would improve therapeutic outcomes in all patients with COVID-19. We showed that delaying therapy initiation markedly decreased the antiviral effect of molnupiravir, and these results were directly related to intracellular drug triphosphate pools and intracellular viral burden at the start of therapy. The adverse influence of therapeutic delay could be overcome by increasing drug exposure, which increased intracellular molnupiravir triphosphate concentrations that inhibited viral replication. These findings illustrated that molnupiravir must be administered as early as possible following COVID-19 symptom onset to maximize therapeutic efficacy. Higher doses may be effective in patients hospitalized with severe disease, but the safety of high-dose molnupiravir regimens is unknown. Our findings could be extended to design effective regimens with nucleoside analogs for other RNA viruses, especially those with pandemic potential. IMPORTANCE In this study, we showed that early intervention with molnupiravir resulted in a greater antiviral effect, and we explained the mechanism behind this phenomenon. Our results predicted and explained the failure of molnupiravir in hospitalized patients and highlighted the utility of preclinical pharmacodynamic studies to design optimal antiviral regimens for the treatment of viral diseases. This contrasts with the procedure that was implemented early in the pandemic in which clinical studies were conducted in the absence of preclinical experimentation. These findings are significant and demonstrated the importance of experimental approaches in antiviral development for treatments against COVID-19 as well as other viral diseases.

Mechanistic Insights to Combating NDM- and CTX-M-Coproducing Klebsiella pneumoniae by Targeting Cell Wall Synthesis and Outer Membrane Integrity.

Metallo-ß-lactamase (MBL)-producing Gram-negative bacteria cause infections associated with high rates of morbidity and mortality. Currently, a leading regimen to treat infections caused by MBL-producing bacteria is aztreonam combined with ceftazidime-avibactam. The purpose of the present study was to evaluate and rationally optimize the combination of aztreonam and ceftazidime-avibactam with and without polymyxin B against a clinical Klebsiella pneumoniae isolate producing NDM-1 and CTX-M by use of the hollow fiber infection model (HFIM). A novel de-escalation approach to polymyxin B dosing was also explored, whereby a standard 0-h loading dose was followed by maintenance doses that were 50% of the typical clinical regimen. In the HFIM, the addition of polymyxin B to aztreonam plus ceftazidime-avibactam significantly improved bacterial killing, leading to eradication, including for the novel de-escalation dosing strategy. Serial samples from the growth control and monotherapies were explored in a Galleria mellonella virulence model to assess virulence changes. Weibull regression showed that low-level ceftazidime resistance and treatment with monotherapy resulted in increased G. mellonella mortality (P < 0.05). A neutropenic rabbit pneumonia model demonstrated that aztreonam plus ceftazidime-avibactam with or without polymyxin B resulted in similar bacterial killing, and these combination therapies were statistically significantly better than monotherapies (P < 0.05). However, only the polymyxin B-containing combination therapy produced a statistically significant decrease in lung weights (P < 0.05), indicating a decreased inflammatory process. Altogether, adding polymyxin B to the combination of aztreonam plus ceftazidime-avibactam for NDM- and CTX-M-producing K. pneumoniae improved bacterial killing effects, reduced lung inflammation, suppressed resistance amplification, and limited virulence changes.

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.

Comparison of Different Labeling Techniques for the LC-MS Profiling of Human Milk Oligosaccharides.

Human milk oligosaccharides (HMOs) exhibit various biological activities for infants, such as serving as prebiotics, blocking pathogens, and aiding in brain development. HMOs are a complex mixture of hetero-oligosaccharides that are generally highly branched, containing multiple structural isomers and no intrinsic chromophores, presenting a challenge to both their resolution and quantitative detection. While liquid chromatography-mass spectrometry (LC-MS) has become the primary strategy for analysis of various compounds, the very polar and chromophore-free properties of native glycans hinder their separation in LC and ionization in MS. Various labeling approaches have been developed to achieve separation of glycans with higher resolution and greater sensitivity of detection. Here, we compared five commonly used labeling techniques [by 2-aminobenzamide, 2-aminopyridine, 2-aminobenzoic acid (2-AA), 2,6-diaminopyridine, and 1-phenyl-3-methyl-5-pyrazolone] for analyzing HMOs specifically under hydrophilic-interaction chromatography-mass spectrometry (HILIC-MS) conditions. The 2-AA labeling showed the most consistent deprotonated molecular ions, the enhanced sensitivity with the least structural selectivity, and the sequencing-informative tandem MS fragmentation spectra for the widest range of HMOs; therefore, this labeling technique was selected for further optimization under the porous graphitized carbon chromatography-mass spectrometry (PGC-MS) conditions. The combination strategy of 2-AA labeling and PGC-MS techniques provided online decontamination (removal of excess 2-AA, salts, and lactose) and resolute detection of many HMOs, enabling us to characterize the profiles of complicated HMO mixtures comprehensively in a simple protocol.

Generating Genotype-Specific Aminoglycoside Combinations with Ceftazidime/Avibactam for KPC-Producing Klebsiella pneumoniae.

Antibiotic combinations, including ceftazidime/avibactam (CAZ/AVI), are frequently employed to combat KPC-producing Klebsiella pneumoniae (KPC-Kp), though such combinations have not been rationally optimized. Clinical KPC-Kp isolates with common genes encoding aminoglycoside-modifying enzymes (AMEs), aac(6')-Ib' or aac(6')-Ib, were used in static time-kill assays (n = 4 isolates) and the hollow-fiber infection model (HFIM; n = 2 isolates) to evaluate the activity of gentamicin, amikacin, and CAZ/AVI alone and in combinations. A short course, one-time aminoglycoside dose was also evaluated. Gentamicin plus CAZ/AVI was then tested in a mouse pneumonia model. Synergy with CAZ/AVI was more common with amikacin for aac(6')-Ib'-containing KPC-Kp but more common with gentamicin for aac(6')-Ib-containing isolates in time-kill assays. In the HFIM, although the isolates were aminoglycoside-susceptible at baseline, aminoglycoside monotherapies displayed variable initial killing, followed by regrowth and resistance emergence. CAZ/AVI combined with amikacin or gentamicin resulted in undetectable counts 50 h sooner than CAZ/AVI monotherapy against KPC-Kp with aac(6')-Ib'. CAZ/AVI monotherapy failed to eradicate KPC-Kp with aac(6')-Ib and a combination with gentamicin led to undetectable counts 70 h sooner than with amikacin. A one-time aminoglycoside dose with CAZ/AVI provided similar killing to aminoglycosides dosed for 7 days. In the mouse pneumonia model (n = 1 isolate), gentamicin and CAZ/AVI achieved a 6.0-log10 CFU/lung reduction at 24 h, which was significantly greater than either monotherapy (P < 0.005). Aminoglycosides in combination with CAZ/AVI were promising for KPC-Kp infections; this was true even for a one-time aminoglycoside dose. Selecting aminoglycosides based on AME genes or susceptibilities can improve the pharmacodynamic activity of the combination.

Combating Multidrug-Resistant Bacteria by Integrating a Novel Target Site Penetration and Receptor Binding Assay Platform Into Translational Modeling.

Multidrug-resistant bacteria are causing a serious global health crisis. A dramatic decline in antibiotic discovery and development investment by pharmaceutical industry over the last decades has slowed the adoption of new technologies. It is imperative that we create new mechanistic insights based on latest technologies, and use translational strategies to optimize patient therapy. Although drug development has relied on minimal inhibitory concentration testing and established in vitro and mouse infection models, the limited understanding of outer membrane permeability in Gram-negative bacteria presents major challenges. Our team has developed a platform using the latest technologies to characterize target site penetration and receptor binding in intact bacteria that inform translational modeling and guide new discovery. Enhanced assays can quantify the outer membrane permeability of ß-lactam antibiotics and ß-lactamase inhibitors using multiplex liquid chromatography tandem mass spectrometry. While ß-lactam antibiotics are known to bind to multiple different penicillin-binding proteins (PBPs), their binding profiles are almost always studied in lysed bacteria. Novel assays for PBP binding in the periplasm of intact bacteria were developed and proteins identified via proteomics. To characterize bacterial morphology changes in response to PBP binding, high-throughput flow cytometry and time-lapse confocal microscopy with fluorescent probes provide unprecedented mechanistic insights. Moreover, novel assays to quantify cytosolic receptor binding and intracellular drug concentrations inform target site occupancy. These mechanistic data are integrated by quantitative and systems pharmacology modeling to maximize bacterial killing and minimize resistance in in vitro and mouse infection models. This translational approach holds promise to identify antibiotic combination dosing strategies for patients with serious infections.

First Penicillin-Binding Protein Occupancy Patterns for 15 ß-Lactams and ß-Lactamase Inhibitors in Mycobacterium abscessus.

Mycobacterium abscessus causes serious infections that often require over 18 months of antibiotic combination therapy. There is no standard regimen for the treatment of M. abscessus infections, and the multitude of combinations that have been used clinically have had low success rates and high rates of toxicities. With ß-lactam antibiotics being safe, double ß-lactam and ß-lactam/ß-lactamase inhibitor combinations are of interest for improving the treatment of M. abscessus infections and minimizing toxicity. However, a mechanistic approach for building these combinations is lacking since little is known about which penicillin-binding protein (PBP) target receptors are inactivated by different ß-lactams in M. abscessus We determined the preferred PBP targets of 13 ß-lactams and 2 ß-lactamase inhibitors in two M. abscessus strains and identified PBP sequences by proteomics. The Bocillin FL binding assay was used to determine the ß-lactam concentrations that half-maximally inhibited Bocillin binding (50% inhibitory concentrations [IC50s]). Principal component analysis identified four clusters of PBP occupancy patterns. Carbapenems inactivated all PBPs at low concentrations (0.016 to 0.5 mg/liter) (cluster 1). Cephalosporins (cluster 2) inactivated PonA2, PonA1, and PbpA at low (0.031 to 1 mg/liter) (ceftriaxone and cefotaxime) or intermediate (0.35 to 16 mg/liter) (ceftazidime and cefoxitin) concentrations. Sulbactam, aztreonam, carumonam, mecillinam, and avibactam (cluster 3) inactivated the same PBPs as cephalosporins but required higher concentrations. Other penicillins (cluster 4) specifically targeted PbpA at 2 to 16 mg/liter. Carbapenems, ceftriaxone, and cefotaxime were the most promising ß-lactams since they inactivated most or all PBPs at clinically relevant concentrations. These first PBP occupancy patterns in M. abscessus provide a mechanistic foundation for selecting and optimizing safe and effective combination therapies with ß-lactams.

Novel Cassette Assay To Quantify the Outer Membrane Permeability of Five ß-Lactams Simultaneously in Carbapenem-Resistant Klebsiella pneumoniae and Enterobacter cloacae.

Poor penetration through the outer membrane (OM) of Gram-negative bacteria is a major barrier of antibiotic development. While ß-lactam antibiotics are commonly used against Klebsiella pneumoniae and Enterobacter cloacae, there are limited data on OM permeability especially in K. pneumoniae Here, we developed a novel cassette assay, which can simultaneously quantify the OM permeability to five ß-lactams in carbapenem-resistant K. pneumoniae and E. cloacae Both clinical isolates harbored a blaKPC-2 and several other ß-lactamases. The OM permeability of each antibiotic was studied separately ("discrete assay") and simultaneously ("cassette assay") by determining the degradation of extracellular ß-lactam concentrations via multiplex liquid chromatography-tandem mass spectrometry analyses. Our K. pneumoniae isolate was polymyxin resistant, whereas the E. cloacae was polymyxin susceptible. Imipenem penetrated the OM at least 7-fold faster than meropenem for both isolates. Imipenem penetrated E. cloacae at least 258-fold faster and K. pneumoniae 150-fold faster compared to aztreonam, cefepime, and ceftazidime. For our ß-lactams, OM permeability was substantially higher in the E. cloacae compared to the K. pneumoniae isolate (except for aztreonam). This correlated with a higher OmpC porin production in E. cloacae, as determined by proteomics. The cassette and discrete assays showed comparable results, suggesting limited or no competition during influx through OM porins. This cassette assay allowed us, for the first time, to efficiently quantify the OM permeability of multiple ß-lactams in carbapenem-resistant K. pneumoniae and E. cloacae Characterizing the OM permeability presents a critical contribution to combating the antimicrobial resistance crisis and enables us to rationally optimize the use of ß-lactam antibiotics.IMPORTANCE Antimicrobial resistance is causing a global human health crisis and is affecting all antibiotic classes. While ß-lactams have been commonly used against susceptible isolates of Klebsiella pneumoniae and Enterobacter cloacae, carbapenem-resistant isolates are spreading worldwide and pose substantial clinical challenges. Rapid penetration of ß-lactams leads to high drug concentrations at their periplasmic target sites, allowing ß-lactams to more completely inactivate their target receptors. Despite this, there are limited tangible data on the permeability of ß-lactams through the outer membranes of many Gram-negative pathogens. This study presents a novel, cassette assay, which can simultaneously characterize the permeability of five ß-lactams in multidrug-resistant clinical isolates. We show that carbapenems, and especially imipenem, penetrate the outer membrane of K. pneumoniae and E. cloacae substantially faster than noncarbapenem ß-lactams. The ability to efficiently characterize the outer membrane permeability is critical to optimize the use of ß-lactams and combat carbapenem-resistant isolates.

Glycosaminoglycanomic profiling of human milk in different stages of lactation by liquid chromatography-tandem mass spectrometry.

Glycans in human milk serve several important biological functions that promote infant health. As kind of important glycans, glycosaminoglycans (GAGs) are a complex family of polyanionic carbohydrate, participating in a variety of critical physiological and pathological processes. In this study, the content and the detailed composition of human milk GAGs from Chinese mothers in different stages of lactation, based on a liquid chromatography-tandem mass spectrometry approach was investigated. The results showed that the GAG fraction in the human milk samples was very complex as it was composed of heparan sulfate, chondroitin sulfate, and hyaluronic acid. With lactation extending, the total amount of GAGs in human milk decreased. This study provided an important guide for the demands of GAGs during different stages of lactation. The results were also beneficial for studies on the composition and functional properties of infant formula.

Low anticoagulant heparin oligosaccharides as inhibitors of BACE-1, the Alzheimer's ß-secretase.

Heparin (HP) is a promising agent for anti-Alzheimer's disease (AD), but its anticoagulant activity limits its applications. So a low anticoagulant heparin (LAH) with anti-AD effect is needed. A novel LAH and heparan sulfate (HS) were purified from crude porcine intestinal heparin. Their structures were characterized by nuclear magnetic resonance and liquid chromatography-mass spectrometry. LAH had a relatively high degree of sulfation, but lower than that of HP. 3-O-Sulfated-containing glucosamine residues further confirmed the low anticoagulant activity of LAH. Sixteen oligosaccharides of LAH and HS were prepared and assigned. Evaluation of anti-BACE-1 activities suggested that their potencies were positively correlated with degree of sulfation and polymerization of oligosaccharides. Besides, LAH-derived hexa- to dodecasaccharides was promised to be administrated in vitro as BACE-1 inhibitors. This study presented ideal BACE-1 inhibitors, LAH-derived oligosaccharides, with virtually no anticoagulant activities, which were promised to be excellent leads for treatment of AD.

In Vivo Anti-Cancer Mechanism of Low-Molecular-Weight Fucosylated Chondroitin Sulfate (LFCS) from Sea Cucumber Cucumaria frondosa.

The low-molecular-weight fucosylated chondroitin sulfate (LFCS) was prepared from native fucosylated chondroitin sulfate (FCS), which was extracted and isolated from sea cucumber Cucumaria frondosa, and the anti-cancer mechanism of LFCS on mouse Lewis lung carcinoma (LLC) was investigated. The results showed that LFCS remarkably inhibited LLC growth and metastasis in a dose-dependent manner. LFCS induced cell cycle arrest by increasing p53/p21 expression and apoptosis through activation of caspase-3 activity in LLC cells. Meanwhile, LFCS suppressed the expression of vascular endothelial growth factor (VEGF), increased the expression of tissue inhibitor of metalloproteinase-1 (TIMP-1) and downregulated the matrix metalloproteinases (MMPs) level. Furthermore, LFCS significantly suppressed the activation of ERK1/2/p38 MAPK/NF-κB pathway, which played a prime role in expression of MMPs. All of these data indicate LFCS may be used as anti-cancer drug candidates and deserve further study.

Extraction, Isolation, Structural Characterization and Anti-Tumor Properties of an Apigalacturonan-Rich Polysaccharide from the Sea Grass Zostera caespitosa Miki.

An apigalacturonan (AGA)-rich polysaccharide, ZCMP, was isolated from the sea grass Zostera caespitosa Miki. The depolymerized fragments derived from ZCMP were obtained by either acidic degradation or pectinase degradation, and their structures were characterized by electrospray ionization collision-induced-dissociation mass spectrometry (ESI-CID-MS2) and nuclear magnetic resonance (NMR) spectroscopy. The average molecular weight of ZCMP was 77.2 kD and it consisted of galacturonic acid (GalA), apiosefuranose (Api), galactose (Gal), rhamnose (Rha), arabinose (Ara), xylose (Xyl), and mannose (Man), at a molar ratio of 51.4꞉15.5꞉6.0꞉11.8꞉4.2꞉4.4꞉4.2. There were two regions of AGA (70%) and rhamnogalacturonan-I (RG-Ι, 30%) in ZCMP. AGA was composed of an α-1,4-D-galactopyranosyluronan backbone mainly substituted at the O-3 position by single Api residues. RG-Ι possessed a backbone of repeating disaccharide units of →4GalAα1,2Rhaα1→, with a few α-L-arabinose and ß-D-galactose residues as side chains. The anti-angiogenesis assay showed that ZCMP inhibited the migratory activity of human umbilical vein endothelial cell (HUVECs), with no influence on endothelial cells growth. ZCMP also promoted macrophage phagocytosis. These findings of the present study demonstrated the potential anti-tumor activity of ZCMP through anti-angiogenic and immunoregulatory pathways.