Sustained Bactericidal Activity Research Articles

Cefepime-taniborbactam demonstrates potent in vitro activity vs Enterobacterales with blaOXA-48.

Taniborbactam (formerly VNRX-5133) is a novel, investigational boronic acid β-lactamase inhibitor. The combination of cefepime (FEP) with taniborbactam is active against Enterobacterales carrying class A, B, C, and/or D enzymes. We assessed the activity of FEP-taniborbactam against Enterobacterales clinical strains carrying blaOXA-48 (N = 50, 100%), of which 78% harbored at least one extended-spectrum β-lactamase (ESBL). CLSI-based agar dilution susceptibility testing was conducted using FEP-taniborbactam and comparators FEP, meropenem-vaborbactam (MVB), and ceftazidime-avibactam (CZA). The addition of taniborbactam lowered FEP MICs to the provisionally susceptible range of ≤16 µg/mL; the MIC90 value decreased from ≥64 µg/mL for FEP to 4 µg/mL for FEP-taniborbactam. Notably, FEP-taniborbactam MIC50/MIC90 values (0.5/4 µg/mL) were lower than those for MVB (1/16 µg/mL) and comparable to those for CZA (0.5/1 µg/mL). Time-kill assays with E. coli clinical strains DOV (blaOXA-48, blaCTX-M-15, blaTEM-1, and blaOXA-1) and MLI (blaOXA-48, blaVEB, blaTEM-1, and blaCMY-2) revealed that FEP-taniborbactam at concentrations 1×, 2×, and 4× MIC displayed time-dependent reductions in the number of CFU/mL from 0 to 6 h, and at 4× MIC demonstrated bactericidal activity (3 log10 reduction in CFU/mL at 24 h). Therefore, taniborbactam in combination with FEP was highly active against this diverse panel of Enterobacterales with blaOXA-48 and represents a potential addition to our antibiotic arsenal.IMPORTANCEOXA-48-like β-lactamases are class D carbapenemases widespread in Klebsiella pneumoniae and other Enterobacterales and are associated with carbapenem treatment failures. As up to 80% of OXA-48-like positive isolates coproduce extended-spectrum β-lactamases, a combination of β-lactams with broad-spectrum β-lactamase inhibitors is required to counteract all OXA-48-producing strains effectively. Herein, we evaluated the activity of cefepime-taniborbactam against 50 clinical strains producing OXA-48. We report that adding taniborbactam shifted the minimum inhibitory concentration (MIC) toward cefepime's susceptible range, restoring its antimicrobial activity. Notably, cefepime-taniborbactam MIC50/MIC90 values (0.5/4 µg/mL) were comparable to ceftazidime-avibactam (0.5/1 µg/mL). Finally, time-kill assays revealed sustained bactericidal activity of cefepime-taniborbactam for up to 24 h. In conclusion, cefepime-taniborbactam will be a welcome addition to the antibiotic arsenal to combat Enterobacterales producing OXA-48.

Potent synergy and sustained bactericidal activity of polymyxins combined with Gram-positive only class of antibiotics versus four Gram-negative bacteria

BackgroundGram-negative bacteria (GNB) are becoming increasingly resistant to a wide variety of antibiotics. There are currently limited treatments for GNB, and the combination of antibiotics with complementary mechanisms has been reported to be a feasible strategy for treating GNB infection. The inability to cross the GNB outer membrane (OM) is an important reason that a broad spectrum of Gram-positive only class of antibiotics (GPOAs) is lacking. Polymyxins may help GPOAs to permeate by disrupting OM of GNB.ObjectiveTo identify what kind of GPOAs can be aided to broaden their anti-GNB spectrum by polymyxins, we systematically investigated the synergy of eight GPOAs in combination with colistin (COL) and polymyxin B (PMB) against GNB in vitro.MethodsThe synergistic effect of COL or PMB and GPOAs combinations against GNB reference strains and clinical isolates were determined by checkerboard tests. The killing kinetics of the combinations were assessed using time-kill assays.ResultsIn the checkerboard tests, polymyxins-GPOAs combinations exert synergistic effects characterized by species and strain specificity. The synergistic interactions on P. aeruginosa strains are significantly lower than those on strains of A. baumannii, K. pneumoniae and E. coli. Among all the combinations, COL has shown the best synergistic effect in combination with dalbavancin (DAL) or oritavancin (ORI) versus almost all of the strains tested, with FICIs from 0.16 to 0.50 and 0.13 to < 0.28, respectively. In addition, the time-kill assays demonstrated that COL/DAL and COL/ORI had sustained bactericidal activity.ConclusionsOur results indicated that polymyxins could help GPOAs to permeate the OM of specific GNB, thus showed synergistic effects and bactericidal effects in the in vitro assays. In vivo combination studies should be further conducted to validate the results of this study.

Simulated drug disposition in critically ill patients to evaluate effective PK/PD targets for combating Pseudomonas aeruginosa resistance to meropenem.

Bacterial infections, including those caused by Pseudomonas aeruginosa, often lead to sepsis, necessitating effective antibiotic treatment like carbapenems. The key pharmacokinetic/pharmacodynamic (PK/PD) index correlated to carbapenem efficacy is the fraction time of unbound plasma concentration above the minimum inhibitory concentration (MIC) of the pathogen (%fT > MIC). While multiple targets exist, determining the most effective one for critically ill patients remains a matter of debate. This study evaluated meropenem's bactericidal potency and its ability to combat drug resistance in Pseudomonas aeruginosa under three representative PK/PD targets: 40% fT > MIC, 100% fT > MIC, and 100% fT > 4× MIC. The hollow fiber infection model (HFIM) was constructed, validated, and subsequently inoculated with a substantial Pseudomonas aeruginosa load (1 × 108 CFU/mL). Different meropenem regimens were administered to achieve the specified PK/PD targets. At specified intervals, samples were collected from the HFIM system and subjected to centrifugation. The resulting supernatant was utilized to determine drug concentrations, while the precipitates were used to track changes in both total and drug-resistant bacterial populations over time by the spread plate method. The HFIM accurately reproduced meropenem's pharmacokinetics in critically ill patients. All three PK/PD target groups exhibited a rapid bactericidal response within 6 h of the initial treatment. However, the 40% fT > MIC and 100% fT > MIC groups subsequently showed bacterial resurgence and resistance, whereas the 100% fT > 4× MIC group displayed sustained bactericidal activity with no evidence of drug resistance. The HFIM system revealed that maintaining 100% fT > 4× MIC offers a desirable microbiological response for critically ill patients, demonstrating strong bactericidal capacity and effective prevention of drug resistance.

Preparation of photothermal responsive, antibacterial hydrogel by using PVA-Alg and silver nanofibers as building blocks.

Introduction: Photothermal responsive, antimicrobial hydrogels are very attractive and have great potential in the field of tissue engineering. The defective wound environment and metabolic abnormalities in diabetic skin would lead to bacterial infections. Therefore, multifunctional composites with antimicrobial properties are urgently needed to improve the current therapeutic outcomes of diabetic wounds. We prepared an injectable hydrogel loaded with silver nanofibers for efficient and sustained bactericidal activity. Methods: To construct this hydrogel with good antimicrobial activity, homogeneous silver nanofibers were first prepared by solvothermal method and then dispersed in PVA-lg solution. After homogeneous mixing and gelation, injectable hydrogels (Ag@H) wrapped with silver nanofibers were obtained. Results: By virtue of Ag nanofibers, Ag@H exhibited good photothermal conversion efficiency and good antibacterial activity against drug-resistant bacteria, while the in vivo antibacterial also showed excellent performance. The results of antibacterial experiments showed that Ag@H had significant bactericidal effects on MRSA and E. coli with 88.4% and 90.3% inhibition rates, respectively. Discussion: The above results indicate that Ag@H with photothermal reactivity and antibacterial activity is very promising for biomedical applications, such as wound healing and tissue engineering.

Evaluation of Omadacycline Alone and in Combination with Rifampin against Staphylococcus aureus and Staphylococcus epidermidis in an In Vitro Pharmacokinetic/Pharmacodynamic Biofilm Model.

Biofilm-associated infections lead to substantial morbidity. Omadacycline (OMC) is a novel aminomethylcycline with potent in vitro activity against Staphylococcus aureus and Staphylococcus epidermidis, but data surrounding its use in biofilm-associated infections are lacking. We investigated the activity of OMC alone and in combination with rifampin (RIF) against 20 clinical strains of staphylococci in multiple in vitro biofilm analyses, including an in vitro pharmacokinetic/pharmacodynamic (PK/PD) CDC biofilm reactor (CBR) model (simulating human exposures). The observed MICs for OMC demonstrated potent activity against the evaluated strains (0.125 to 1 mg/L), with an increase of MICs generally observed in the presence of biofilm (0.25 to >64 mg/L). Furthermore, RIF was shown to reduce OMC biofilm MICs (bMICs) in 90% of strains, and OMC plus RIF combination in biofilm time-kill analyses (TKAs) exhibited synergistic activity in most of the strains. Within the PK/PD CBR model, OMC monotherapy primarily displayed bacteriostatic activity, while RIF monotherapy generally exhibited initial bacterial eradication, followed by rapid regrowth likely due to the emergence of RIF resistance (RIF bMIC, >64 mg/L). However, the combination of OMC plus RIF produced rapid and sustained bactericidal activity in nearly all the strains (3.76 to 4.03 log10 CFU/cm2 reductions from starting inoculum in strains in which bactericidal activity was reached). Furthermore, OMC was shown to prevent the emergence of RIF resistance. Our data provide preliminary evidence that OMC in combination with RIF could be a viable option for biofilm-associated infections with S. aureus and S. epidermidis. Further research involving OMC in biofilm-associated infections is warranted.

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.

ObjectivesThis 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.MethodsSeven 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).ResultsIn 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.ConclusionsThe 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.

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

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

1263. Assessment of Cefepime (FEP)-Taniborbactam (TAN) Human Exposures to Suppress the Emergence of Resistance among Serine (SBL)- and Metallo-β-Lactamase (MBL)-Producing Gram-Negative Bacteria (GNB) in a Hollow Fiber Infection Model (HFIM)

BackgroundFEP-TAN (FTB) efficacy and safety are currently being evaluated in a Phase 3 trial (NCT03840148). TAN, a boronic acid-based β-lactamase inhibitor, restores susceptibility to FEP when resistance is driven by SBL or MBL (ie, NDM, VIM). This in vitro study assessed whether clinical FTB exposures suppress treatment-emergent resistance in pathogenic Enterobacterales and Pseudomonas aeruginosa.MethodsBioreactors (C2011, FiberCell) were inoculated with clinical GNB strains (N=6) using highly concentrated log phase cultures (> 108 CFU). Syringe pumps supplied humanized exposures of FEP (2 g), FTB (2 g/0.5 g), ceftazidime-avibactam (CZA, 2 g/0.5 g), each as 2 h infusions q8h, or meropenem-vaborbactam (MEV, 2 g/2 g q8h, 3 h infusion) for 7 days. Exposures were confirmed by UPLC-MS/MS for all agents. Subpopulations with elevated FTB MICs (4x) were monitored with drug-supplemented agar. CZA or MEV served as positive or negative controls for selected strains. Samples, serially removed from bioreactors, were saline-washed prior to quantitative culture to prevent drug carryover.ResultsAll strains grew rapidly in the presence of FEP (Figure 1), consistent with resistance by broth microdilution (BMD, Table 1). With the addition of TAN, there was extensive killing of the total bacterial populations by FTB, and subpopulations with elevated FTB MICs were never recovered. Like FTB against Klebsiella pneumoniae (KP) BAA-1705, CZA initially decreased the inoculum to the lower limit of detection, but unlike FTB, allowed regrowth to 3.7 log10 CFU/mL by day 7. The first dose of FTB was bactericidal against VIM+ and NDM+ KP strains while regrowth occurred prior to 8 h of MEV and CZA challenge, respectively. Notably, early failure of MEV is discordant with susceptibility by BMD (MIC= 4 µg/mL). By day 7, FTB sterilized an OXA-48+ KP strain that when challenged by MEV, grew to 9.8 log10 CFU/ml at 24 h.Figure 1. Bacterial burdens observed in the HFIM when treated with FEP alone or FEP+TAN (FTB) Table 1. Characterization of strains assessed in the HFIM; minimum inhibitory concentration (MIC) values for treatments not assessed are included in parentheses. ConclusionIn a 7-day HFIM with humanized exposures and high initial inoculums, FTB provided sustained bactericidal activity against multidrug-resistant Enterobacterales and P. aeruginosa strains harboring a diversity of β-lactamases and suppressed growth of resistant subpopulations. These data are crucial to inform understanding of the potential role for FTB in GNB infections and future clinical studies.DisclosuresLindsay M. Avery, PharmD, Venatorx Pharmaceuticals (Employee, Shareholder) Salvador Vernacchio, BS, Venatorx Pharmaceuticals (Employee, Shareholder) Lisa McLaughlin, BS, Venatorx Pharmaceuticals (Employee, Shareholder) Luigi Xerri, PhD, Venatorx Pharmaceuticals (Employee, Shareholder) Greg Moeck, PhD, Venatorx Pharmaceuticals (Employee, Shareholder) Daniel Pevear, PhD, Venatorx Pharmaceuticals (Employee, Shareholder)

Highly Sustained Release of Bactericides from Complex Coacervates.

Materials for preventing harmful bacterial contamination attract widespread interest in areas that include healthcare, home/personal care products, and crop protection. One approach to achieving this functionality is through the sustained release of antibacterial compounds. To this end, we show how putty-like complex coacervates, formed through the association of poly(allylamine hydrochloride) (PAH) with pentavalent tripolyphosphate (TPP) ions, can provide a sustained antibacterial effect by slowly releasing bactericides. Using triclosan (TC) as a model bactericide, we demonstrate that, through their dispersion in the parent PAH solution with nonionic surfactants, hydrophobic biocides can be efficiently and predictably encapsulated within PAH/TPP coacervates. Once encapsulated, the bactericide can be released over multiple months, and the release rates can be readily tuned by varying the bactericide and surfactant compositions used during encapsulation. Through this release, the PAH/TPP coacervates provide sustained bactericidal activity against model Gram-positive and Gram-negative bacteria (Staphylococcus aureus and Escherichia coli) grown under a nutrient-rich condition over at least two weeks. Thereafter, though some partial activity persists after one month, the release slows down and the bactericide-eluting coacervates lose their efficacy. Overall, we show that bactericide release from easy-to-prepare complex coacervates can provide a pathway to sustained disinfection.

FX11 limits Mycobacterium tuberculosis growth and potentiates bactericidal activity of isoniazid through host-directed activity.

ABSTRACTLactate dehydrogenase A (LDHA) mediates interconversion of pyruvate and lactate, and increased lactate turnover is exhibited by malignant and infected immune cells. Hypoxic lung granuloma in Mycobacterium tuberculosis-infected animals present elevated levels of Ldha and lactate. Such alterations in the metabolic milieu could influence the outcome of host-M. tuberculosis interactions. Given the central role of LDHA for tumorigenicity, targeting lactate metabolism is a promising approach for cancer therapy. Here, we sought to determine the importance of LDHA for tuberculosis (TB) disease progression and its potential as a target for host-directed therapy. To this end, we orally administered FX11, a known small-molecule NADH-competitive LDHA inhibitor, to M. tuberculosis-infected C57BL/6J mice and Nos2−/− mice with hypoxic necrotizing lung TB lesions. FX11 did not inhibit M. tuberculosis growth in aerobic/hypoxic liquid culture, but modestly reduced the pulmonary bacterial burden in C57BL/6J mice. Intriguingly, FX11 administration limited M. tuberculosis replication and onset of necrotic lung lesions in Nos2−/− mice. In this model, isoniazid (INH) monotherapy has been known to exhibit biphasic killing kinetics owing to the probable selection of an INH-tolerant bacterial subpopulation. However, adjunct FX11 treatment corrected this adverse effect and resulted in sustained bactericidal activity of INH against M. tuberculosis. As a limitation, LDHA inhibition as an underlying cause of FX11-mediated effect could not be established as the on-target effect of FX11 in vivo was unconfirmed. Nevertheless, this proof-of-concept study encourages further investigation on the underlying mechanisms of LDHA inhibition and its significance in TB pathogenesis.

Highly Dual Antifouling and Antibacterial Ultrafiltration Membranes Modified with Silane Coupling Agent and Capsaicin-Mimic Moieties.

Dual antifouling and antibacterial polysulfone(PSf)/polyethersulfone(PES) hybrid membranes were developed by the synergy of capsaicin-mimic N-(5-methyl acrylamide-2,3,4 hydroxy benzyl) acrylamide (AMTHBA) and vinyl triethylene (b-methoxy ethoxy) silane (VTMES). First, AMTHBA as a natural antimicrobial agent was incorporated into a casting solution via “microwave-assistance (MWA) in situ polymerization-blending” process to construct a hydroxyl-rich environment. Then, VTMES crosslinked to a hydroxyl-rich polymer matrix via hydrolytic condensation, and the influence of VTMES content on the hybrid membrane properties was systematically investigated. When the VTMES added amount was 1.0 wt %, the hybrid membrane achieved an optimal separation performance including a steady-state humic acid (HA) (5 mg/L) permeation flux of 326 L·m−2·h−1 and a rejection percentage of 97%. The antibacterial tests revealed that the hybrid membranes exhibited sustained bactericidal activity and effective inhibition of bacterial adhesion. Besides, the dual-functional membranes were clean as new after two-cycles filtration (with a cleaning efficiency of ~90%), indicating that the network silicone film on the surface benefits the foulant repellence. Hopefully, the dual-functional membranes constructed in this study can be applicable to the pretreatment stage of water treatment.

1539. Dalbavancin, Vancomycin, and Daptomycin Alone and in Combination with Cefazolin Against Vancomycin Intermediate-Resistant (VISA) and Daptomycin Non-Susceptible (DNS) Staphylococcus aureus

BackgroundGlycopeptides and lipopeptides, more specifically vancomycin (VAN) and daptomycin (DAP) have been principally utilized in treating MRSA infections. Due to continued use, MRSA strains have developed resistance to these antibiotics including vancomycin intermediate susceptible Staphylococcus aureus (VISA) and daptomycin non-susceptible strains (DNS). Lipoglycopeptides; notably dalbavancin (DAL), have been employed due to their ease of administration and enhanced activity against highly resistant S. aureus. As previously demonstrated, the use of β-lactams, specifically cefazolin (CFZ) in combination with anti-MRSA drug therapy has been effective in eradicating S. aureus complicated by increased resistance. The objective of this study was to evaluate the activity of DAL, VAN, and DAP, alone and in combination with CFZ in a pharmacokinetic/pharmacodynamic (PK/PD) model.MethodsThe well-characterized DNS-VISA strain, D712, was evaluated in eight different regimens in duplicate via a one-compartment 7-day PK/PD model. The experimental regimens were as follows: D712 growth control, DAL 1500 mg given on day 1, VAN 2 g given every 12 hours, DAP 10 mg/kg once-daily, CFZ 2 g given every 8 hours and DAL, DAP, and VAN in combination with CFZ.ResultsThe combinations of DAL+CFZ, VAN+CFZ, and DAP+CFZ demonstrated a significant log10 CFU/mL reduction (more than 5 log 10 CFU/mL and up to detection limit), compared with each drug used as monotherapy (P < 0.001). Neither DAP nor VAN demonstrated sustained bactericidal activity, (represented by a >3-log10 CFU/mL reduction from baseline) and resulted in significant regrowth, when administered alone. However, the DAP +CFZ, and VAN+CFZ combination models demonstrated bactericidal activity at 4 hours and 24 hours, respectively. While DAL alone did demonstrate bactericidal activity, the DAL+CFZ combination was more rapidly bactericidal, achieving a > 3-log reduction from baseline in 8 hours vs. 48 hours (P < 0.05).ConclusionThe combination of DAL, VAN, or DAP with CFZ demonstrated significantly improved activity against this multiple drug-resistant S. aureus strain. Further research is warranted, both in vivo and in vitro, to explore the synergistic capabilities of anti-MRSA drug therapy in combination with β-lactams.Disclosures All authors: No reported disclosures.

Evaluation of Activity and Emergence of Resistance of Polymyxin B and ZTI-01 (Fosfomycin for Injection) against KPC-Producing Klebsiella pneumoniae.

ABSTRACTZTI-01 (fosfomycin for injection) is a broad-spectrum antibiotic with a novel mechanism of action and is currently under development in the United States for treatment of complicated urinary tract infections. Globally, fosfomycin and polymyxin B are increasingly being used to treat multidrug-resistant Gram-negative infections. The objectives were to evaluate the pharmacodynamic activity of polymyxin B and fosfomycin alone and in combination against KPC-producing Klebsiella pneumoniae and to assess the rate and extent of emergence of resistance to different antibiotic regimens. Two clinical isolates, BRKP26 (MIC of polymyxin B[MICPMB], 0.5 mg/liter; MIC of fosfomycin [MICFOF], 32 mg/liter) and BRKP67 (MICPMB, 8 mg/liter; MICFOF, 32 mg/liter) at an initial inoculum of 107 CFU/ml, were evaluated over 168 h in a hollow-fiber infection model simulating clinically relevant polymyxin B (2.5-mg/kg loading dose as a 2 h-infusion followed by 1.5-mg/kg dose every 12 h [q12h] as a 1-h infusion) and fosfomycin (6 g q6h as a 1-h or 3-h infusion) regimens alone and in combination. Population analysis profiles (PAPs) and MIC testing were performed to assess emergence of resistance. Polymyxin B or fosfomycin monotherapy was ineffective and selected for resistance by 24 h. Polymyxin B plus a fosfomycin 1-h infusion demonstrated sustained bactericidal activity by 4 h, with undetectable colony counts beyond 144 h. Polymyxin B plus a fosfomycin 3-h infusion demonstrated bactericidal activity at 4 h, followed by regrowth similar to that of the control by 144 h. PAPs revealed resistant subpopulations by 120 h. The combination of polymyxin B and a fosfomycin 1-h infusion is a promising treatment option for KPC-producing K. pneumoniae and suppresses the emergence of resistance. Further evaluation of novel dosing strategies is warranted to optimize therapy.

Antibacterial activity of human simulated epithelial lining fluid concentrations of amikacin inhale alone and in combination with meropenem against Acinetobacter baumannii

Background: Acinetobacter baumannii(ACBN) is a MDR organism causing pneumonia in ventilated patients. High MICs often result in insufficient lung exposures, thus poor outcomes have been observed with parenteral antimicrobials. Amikacin Inhale(AMK-I), is a drug–device combination of amikacin and a Pulmonary Drug Delivery System device. We aimed to describe the pharmacodynamic profile of human simulated epithelial lining fluid(ELF) exposures of AMK-I and intravenous meropenem alone and in combination against ACBN with variable susceptibility profiles.Methods: AMK-I ELF exposures and the ELF profile of meropenem achieved after intravenous administration were evaluated in an in vitro pharmacodynamic model. Nine ACBN with amikacin/meropenem MICs of 2–512/2 to >64 mg/L were utilized. MICs were repeated post exposure to assess the development of resistance.Results: AMK-I monotherapy rapidly achieved and sustained bactericidal activity for isolates with amikacin MIC ≤128 mg/L. For isolates with MICs of 256 and 512 mg/L initial reductions in bacterial density were observed followed by regrowth. The combination produced similar bactericidal activity against ACBN with amikacin MICs of ≤128. While the combination regimen produced initial reductions and prolonged the duration of activity against organisms with MICs of 256 and 512 mg/L, regrowth and MIC elevations were noted during the 72-h exposure period.Conclusion: The combination achieved rapid and sustained efficacy when amikacin MICs were ≤128 mg/L and prolonged the duration of activity compared to monotherapy for organisms with MICs 256 mg/L and 512 mg/L. These data support the utility of AMK-I as an adjunct for the treatment of pneumonia caused by A. baumannii with MICs above current susceptibility break-points.

Cefepime loaded O-carboxymethyl chitosan microspheres with sustained bactericidal activity and enhanced biocompatibility

Cefepime (CFP) is a frequently used antibiotic for prevention of post-surgery infection. Systemic delivery of CFP in a bulk dose usually shows effective therapeutic effects, while cytotoxicity can also be generated. To avoid the drawback of systemic delivery of antibiotic, local and controlled administration of drug is being employed to prolong therapeutic effects and reduce cytotoxicity by sustaining drug release and minimizing drug exposure. In this work, CFP loaded polymer O-carboxymethyl chitosan (OCMC) microspheres (CFP-OCMC-MPs) were fabricated and their antimicrobial activity against Staphylococcus aureus as well as biocompatibility were evaluated. The microspheres possessed the spherical surface with diameter approximately 7 μm. Fourier transforms infrared spectral and wide-angle X-ray diffraction analysis showed that CFP was steadily incorporated. The drug loading content and encapsulation efficiency of the microspheres were 21.4 ± 0.5% and 42.3 ± 0.7%, respectively. The drug release profiles were found to be biphasic with an initial burst release followed by a gradual release phase, following the Higuchi model. In addition, the CFP-OCMC-MPs were able to kill all the bacteria cultured in suspension within 24 h and exhibited long-lasting bactericidal activity as demonstrated by inhibition zone study. Compared to CFP, CFP-OCMC-MPs showed a milder toxicity toward osteoblast-like cells over an 8 day period. All these results suggest that CFP-OCMC-MPs are endowed with sustained treatment of bacterial infection and enhanced biocompatibility.

Combinatorial pharmacodynamics of polymyxin B and tigecycline against heteroresistant Acinetobacter baumannii

The prevalence of heteroresistant Acinetobacter baumannii is increasing. Infections due to these resistant pathogens pose a global treatment challenge. Here, the pharmacodynamic activities of polymyxin B (PMB) (2–20 mg/L) and tigecycline (0.15–4 mg/L) were evaluated as monotherapy and in combination using a 4 × 4 concentration array against two carbapenem-resistant and polymyxin-heteroresistant A. baumannii isolates. Time Kill Experiments was employed at starting inocula of 106 and 108 CFU/mL over 48 h. Clinically relevant combinations of PMB (2 mg/L) and tigecycline (0.90 mg/L) resulted in greater reductions in the bacterial population compared with polymyxin alone by 8 h (ATCC 19606, −6.38 vs. −3.43 log10 CFU/mL; FADDI AB115, −1.38 vs. 2.08 log10 CFU/mL). At 10× the clinically achievable concentration (PMB 20 mg/L in combination with tigecycline 0.90 mg/L), there was bactericidal activity against FADDI AB115 by 4 h that was sustained until 32 h, and against ATCC 19606 that was sustained for 48 h. These studies show that aggressive polymyxin-based dosing in combination with clinically achievable tigecycline concentrations results in early synergistic activity that is not sustained beyond 8 h, whereas combinations with higher tigecycline concentrations result in sustained bactericidal activity against both isolates at both inocula. These results indicate a need for optimised front-loaded polymyxin-based combination regimens that utilise high polymyxin doses at the onset of treatment to achieve good pharmacodynamic activity whilst minimising adverse events.

Evaluation of High-Dose Daptomycin Versus Vancomycin Alone or Combined with Clarithromycin or Rifampin Against Staphylococcus aureus and S. epidermidis in a Novel In Vitro PK/PD Model of Bacterial Biofilm.

IntroductionMedical device infections are associated with significant morbidity and mortality. These difficult-to-treat infections often result in antibiotic failure and resistance. Combination therapy is often required, however, the most optimal combination is unknown. We evaluated the in vitro activity of daptomycin (DAP) or vancomycin (VAN) alone and in combination with rifampin (RIF) or clarithromycin (CLA) against strains of Staphylococcus aureus and S. epidermidis grown in biofilm on 3 prosthetic device materials.MethodsOne methicillin-resistant S. aureus (MRSA R5266), one heteroresistant vancomycin-intermediate S. aureus (hVISA R3640), and one methicillin-resistant S. epidermidis (MRSE R461) strain was evaluated in a CDC biofilm reactor with titanium, Teflon®, and steel coupons. Regimens simulated included DAP 10 mg/kg/day, and VAN 1 g q12h alone or in combination with RIF 600 mg q24h or CLA 250 mg q12h. Additional regimens including DAP 12 mg/kg/day or VAN ± RIF 450 mg q12h were evaluated against the hVISA strain.ResultsDAP + RIF or VAN + RIF demonstrated enhanced activity against R3640 in embedded biofilm (EB) cells in all materials versus DAP or VAN alone (P ≤ 0.040). Only DAP + RIF demonstrated sustained bactericidal activity (≥3.80 log10 CFU/cm2 reduction from baseline) against EB and planktonic cells of R5266 and EB cells of R461 in all 3 materials. Of interest, CLA did not appear to enhance DAP or VAN killing activities, and the addition of RIF prevented the emergence of resistance to DAP or VAN in all organisms.ConclusionUsing an in vitro bacterial biofilm model containing three common prosthetic device materials, DAP + RIF and VAN + RIF were the most effective regimens. DAP + RIF displayed the greatest activity and represents a promising combination to evaluate for treatment of biofilm-associated staphylococcal infections.Electronic supplementary materialThe online version of this article (doi:10.1007/s40121-014-0055-5) contains supplementary material, which is available to authorized users.

Searching for the Optimal Treatment of Ceftriaxone-Resistant Streptococcus pneumoniae in Community-Acquired Pneumonia

Ceftriaxone-resistant Streptococcus pneumoniae (CRSP) (minimal inhibitory concentration > 1 mcg/mL) is a growing major concern in the optimal selection of empirical antimicrobial treatment of community-acquired pneumonia (CAP). It has been estimated that up to 37.9% of S. pneumoniae are resistant to ceftriaxone in the United States in 2012,1 with a mean of 19.2% in Europe including greater than 25% in Eastern Europe (Bulgaria, Romania, and Turkey) in 20112 and 18.5% in China in 2011.3 This high rate of CRSP has been in part correlated with the introduction of the PCV7 in 2001 and of PCV13 in 2010 and the selection of serotypes 19A, 6C, and 22F.4,5 The increasing use of antimicrobials in humans and in food-producing animals among others is expected to contribute to the rising rate of CRSP.6 Mutation of cell wall penicillin-binding protein (PBP), particularly PBP1a, PBP2x, and PBP2b, was associated with CRSP.7 Because S. pneumoniae is the most common etiologic agent of CAP, physicians should optimize the empirical therapy of CAP in areas with a high rate of CRSP. Wenzler et al8 examined in this issue the clinical outcomes of patients with CRSP (minimal inhibitory concentration > 1 mcg/mL) versus ceftriaxone-susceptible S. pneumoniae in adult patients with pneumonia and respiratory culture positive for S. pneumoniae. Regardless of the sample size limitation, this study has striking findings. None of the patients with CRSP infection had 90 days of previous exposure of ceftriaxone. Time to clinical cure was longer in patients with CRSP (4 [1–5] vs 8 [3–12] days, P = 0.51), and length of stay was longer for patients with CRSP (17 [9–23] vs 9 [7–13] days, P = 0.46). The empirical treatment was changed in 50% of the patients with CRSP infection versus 0% in those with ceftriaxone-susceptible pneumoniae infection. A 50% of patients with CRSP infection were treated with fluoroquinolones, and 70% were treated with either vancomycin or linezolid. Among other findings, 70% of the patients with CRSP infection had pneumonia severity index of IV or greater. Overall, both groups had similar clinical outcomes although these outcomes may not have been similar if patients with CRSP infection were treated with ceftriaxone according to CAP treatment guidelines. Large prospective studies are needed to validate the optimal treatment of CRSP CAP. Current options for the treatment of CRSP CAP are fluoroquinolones, vancomycin, linezolid, and ceftaroline. Ceftaroline is the first of the growing group of active cephalosporins against methicillin-resistant Staphylococcus aureus and it also has activity against CRSP. Ceftaroline showed sustained bactericidal activity against CRSP in a pharmacokinetics and pharmakodynamics model study.9 This ceftaroline activity was validated in a rabbit model at a simulated human dose of 20 mg/kg by reducing 6 log units of CRSP in the lungs.10 Furthermore, a second analysis of studies focus 1 and 2 revealed that patients with S. pneumoniae CAP treated with ceftaroline had more favorable outcome than patients treated with ceftriaxone (odds ratio, 2.6; 95% confidence interval, 1.11–6.17; P = 0.0286).11 An approach in the empirical therapy of CRSP CAP could be a similar strategy used for bacterial meningitis by adding vancomycin to ceftriaxone treatment. Current Infectious Diseases Society of America guidelines do not recommend the use of vancomycin in cases with severe CAP nor CRSP. Vancomycin has a limited bactericidal activity when compared with β-lactams. Although levofloxacin and moxifloxacin have effective activity against CRSP, fluoroquinolones use has been reported to trigger higher rates of multiple drug resistance Pseudomonas, methicillin-resistant Staphylococcus aureus, and Clostridium difficile infections.12 In contrast to linezolid, ceftaroline has a spectrum similar to ceftriaxone covering gram-negative rods, including those etiologic organisms of CAP such as Klebsiella spp., Haemophilus spp., and Moraxella. In summary, physicians should consider antimicrobials with activity against CRSP in patients with CAP residing in areas with substantial prevalence of CRSP, in particular, those from the US southern states, having history of previous antibiotic therapy, and being immunocompromised.1,6 This concern is critical in patients with advanced comorbidities and increased risk for poor outcomes. Current data support more the use of ceftaroline treatment in cases with suspected CRSP pneumonia. Physicians should be cautious to use fluoroquinolones treatment of CRSP infection given the risk for antimicrobial resistance. Other treatment options include vancomycin although it has limited bactericidal activity compared with β-lactams and linezolid, which has the advantage of 100% of intestinal absorption that makes it a candidate for oral therapy.

Ceftaroline Increases Membrane Binding and Enhances the Activity of Daptomycin against Daptomycin-Nonsusceptible Vancomycin-Intermediate Staphylococcus aureus in a Pharmacokinetic/Pharmacodynamic Model

New antimicrobial agents and novel combination therapies are needed to treat serious infections caused by methicillin-resistant Staphylococcus aureus (MRSA) with reduced susceptibility to daptomycin and vancomycin. The purpose of this study was to evaluate the combination of ceftaroline plus daptomycin or vancomycin in an in vitro pharmacokinetic/pharmacodynamic model. Simulations of ceftaroline-fosamil at 600 mg per kg of body weight every 8 h (q8h) (maximum free-drug concentration in serum [fC(max)], 15.2 mg/liter; half-life [t(1/2)], 2.3 h), daptomycin at 10 mg/kg/day (fC(max), 11.3 mg/liter; t(1/2), 8 h), vancomycin at 2 g q12h (fC(max), 30 mg/liter; t(1/2), 6 h), ceftaroline plus daptomycin, and ceftaroline plus vancomycin were evaluated against a clinical, isogenic MRSA strain pair: D592 (daptomycin susceptible and heterogeneous vancomycin intermediate) and D712 (daptomycin nonsusceptible and vancomycin intermediate) in a one-compartment in vitro pharmacokinetic/pharmacodynamic model over 96 h. Therapeutic enhancement of combinations was defined as ≥2 log(10) CFU/ml reduction over the most active single agent. The effect of ceftaroline on the membrane charge, cell wall thickness, susceptibility to killing by the human cathelicidin LL37, and daptomycin binding were evaluated. Therapeutic enhancement was observed with daptomycin plus ceftaroline in both strains and vancomycin plus ceftaroline against D592. Ceftaroline exposure enhanced daptomycin-induced depolarization (81.7% versus 72.3%; P = 0.03) and killing by cathelicidin LL37 (P < 0.01) and reduced cell wall thickness (P < 0.001). Fluorescence-labeled daptomycin was bound over 7-fold more in ceftaroline-exposed cells. Whole-genome sequencing and mutation analysis of these strains indicated that change in daptomycin susceptibility is related to an fmtC (mprF) mutation. The combination of daptomycin plus ceftaroline appears to be potent, with rapid and sustained bactericidal activity against both daptomycin-susceptible and -nonsusceptible strains of MRSA.

Addition of Ceftaroline to Daptomycin after Emergence of Daptomycin-Nonsusceptible Staphylococcus aureus during Therapy Improves Antibacterial Activity

Antistaphylococcal beta-lactams enhance daptomycin activity and have been used successfully in combination for refractory methicillin-resistant Staphylococcus aureus (MRSA) infections. Ceftaroline possesses MRSA activity, but it is unknown if it improves the daptomycin potency comparably to other beta-lactams. We report a complex patient case of endocarditis who was treated with daptomycin in combination with ceftaroline, which resulted in clearance of a daptomycin-nonsusceptible strain. An in vitro pharmacokinetic/pharmacodynamic model of renal failure was used to simulate the development of daptomycin resistance and evaluate the microbiologic effects of daptomycin plus ceftaroline treatment. Combination therapy with daptomycin and ceftaroline restored daptomycin sensitivity in vivo and resulted in clearance of persistent blood cultures. Daptomycin susceptibility in vitro was increased in the presence of either ceftaroline or oxacillin. Daptomycin at 6 mg/kg of body weight every 48 h was bactericidal in the model but resulted in regrowth and daptomycin resistance (MIC, 2 to 4 μg/ml) with continued monotherapy. The addition of ceftaroline at 200 mg every 12 h after the emergence of daptomycin resistance enhanced bacterial killing. Importantly, daptomycin plus ceftaroline as the initial combination therapy produced rapid and sustained bactericidal activity and prevented daptomycin resistance. Both in vivo- and in vitro-derived daptomycin resistance resulted in bacteria with more fluid cell membranes. After ceftaroline was added in the model, fluidity was restored to the level of the initial in vivo isolate. Daptomycin-resistant isolates required high daptomycin exposures (at least 10 mg/kg) to optimize cell membrane damage with daptomycin alone. Ceftaroline combined with daptomycin was effective in eliminating daptomycin-resistant MRSA, and these results further justify the potential use of daptomycin plus beta-lactam therapy for these refractory infections.