Efficacies of three drug regimens containing omadacycline to treat Mycobacteroides abscessus disease

Mycobacteroides abscessus (Mab, also known as Mycobacterium abscessus) causes opportunistic pulmonary and soft tissue infections that are difficult to cure with existing treatments. Omadacycline, a new tetracycline antibiotic, exhibits potent in vitro and in vivo activity against Mab. As regimens containing multiple antibiotics are required to produce a durable cure for Mab disease, we assessed efficacies of three three-drug combinations in a pre-clinical mouse model of pulmonary Mab disease to identify companion drugs with which omadacycline exhibits the highest efficacy. Additionally, we assessed the susceptibility of Mab recovered from mouse lungs after four weeks of exposure to the three triple-drug regimens. Among the three-drug regimens, omadacycline + imipenem + amikacin produced the largest reduction in Mab burden, whereas omadacycline + imipenem + linezolid exhibited the most effective early bactericidal activity. Omadacycline + linezolid + clofazimine, a regimen that can be administered orally, lacked early bactericidal activity but produced a gradual reduction in the lung Mab burden over time. The robust efficacy exhibited by these three regimens in the mouse model supports their further evaluation in patients with Mab lung disease. As we were unable to isolate drug-resistant Mab mutants at the completion of four weeks of treatment, these triple-drug combinations show promise of producing durable cure and minimizing selection of resistant mutants.

A Review of Omadacycline for Potential Utility in the Military Health System for the Treatment of Wound Infections

INTRODUCTION

Combat-related wound infections complicate the recovery of wounded military personnel, contributing to overall morbidity and mortality. Wound infections in combat settings present unique challenges because of the size and depth of the wounds, the need to administer emergency care in the field, and the need for subsequent treatment in military facilities. Given the increase in multidrug-resistant pathogens, a novel, broad-spectrum antibiotic is desired across this continuum of care when the standard of care fails. Omadacycline was FDA-approved in 2018 for treatment of adults with acute bacterial skin and skin structure infections (ABSSSI), as well as community-acquired bacterial pneumonia (CABP). It is a broad-spectrum antibiotic with activity against gram-positive, gram-negative, and atypical bacterial pathogens, including multidrug-resistant species. Omadacycline can overcome commonly reported tetracycline resistance mechanisms, ribosomal protection proteins, and efflux pumps, and is available in once-daily intravenous or oral formulations. In this review, we discuss the potential role of omadacycline, which is included in the Department of Defense Formulary, in the context of combat wound infections.

MATERIALS AND METHODS

A literature review was undertaken for manuscripts published before July 21, 2023. This included a series of publications found via PubMed and a bibliography made publicly available on the Paratek Pharmaceuticals, Inc. website. Publications presenting primary data published in English on omadacycline in relation to ESKAPEE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, Escherichia coli, and Enterobacter species) pathogens and Clostridioides difficile, including in vitro, in vivo, and clinical data were included.

RESULTS

Of 260 identified records, 66 were included for evidence review. Omadacycline has in vitro activity against almost all the ESKAPEE pathogens, apart from P. aeruginosa. Importantly, it has activity against the four most prevalent bacterial pathogens that cause wound infections in the military healthcare system: S. aureus, including methicillin-resistant S. aureus, A. baumannii, K. pneumoniae, and E. coli. In vivo studies in rats have shown that omadacycline is rapidly distributed in most tissues, with the highest tissue-to-blood concentration ratios in bone mineral. The clinical efficacy of omadacycline has been assessed in three separate Phase 3 studies in patients with ABSSSI (OASIS-1 and OASIS-2) and with CABP (OPTIC). Overall, omadacycline has an established safety profile in the treatment of both ABSSSI and CABP.

CONCLUSIONS

Omadacycline has broad-spectrum activity, the option to be orally administered and an established safety profile, making it a potentially attractive replacement for moxifloxacin in the military individual first aid kit, especially when accounting for the increasing resistance to fluoroquinolones. Further studies and clinical evaluation are warranted to support broader use of omadacycline to treat combat wound infections in the military healthcare system.

Evaluation of omadacycline against intracellular Mycobacterium abscessus in an infection model in human macrophages

Background

Omadacycline is an aminomethylcycline antibiotic in the tetracycline class that was approved by the US FDA in 2018 for the treatment of community-acquired bacterial pneumonia and acute bacterial skin and skin structure infections. It is available in both IV and oral formulations. Omadacycline has broad-spectrum in vitro activity and clinical efficacy against infections caused by Gram-positive and Gram-negative pathogens. Omadacycline is being evaluated in a 3 month placebo-controlled Phase 2 clinical trial of oral omadacycline versus placebo in adults with non-tuberculous mycobacteria (NTM) pulmonary disease caused by Mycobacterium abscessus (NCT04922554).

Objectives

To determine if omadacycline has intracellular antimicrobial activity against NTM, bacteria that can cause chronic lung disease, in an ex vivo model of intracellular infection.

Methods

Two strains of M. abscessus were used to infect THP-1 macrophages. Intracellular M. abscessus was then challenged with omadacycline and control antibiotics at multiples of the MIC over time to evaluate intracellular killing.

Results

At 16 ×  the MIC at 72 h, omadacycline treatment of intracellular NTM yielded a log10 reduction in cfu of 1.1 (91.74% reduction in cfu) and 1.6 (97.65% reduction in cfu) consistent with killing observed with tigecycline, whereas amikacin and clarithromycin at 16 ×  the MIC did not show any reduction in cfu against the intracellular M. abscessus.

Conclusions

Omadacycline displayed intracellular activity against M. abscessus within macrophages. The activity was similar to that of tigecycline; as expected, intracellular killing was not observed with clarithromycin and amikacin.

Efficacy of Omadacycline-Containing Regimen in a Mouse Model of Pulmonary Mycobacteroides abscessus Disease

Mycobacteroides abscessus is an opportunistic pathogen in people with structural lung conditions such as bronchiectasis, chronic obstructive pulmonary disease, and cystic fibrosis. Pulmonary M. abscessus infection causes progressive symptomatic and functional decline as well as diminished lung function and is often incurable with existing antibiotics. We investigated the efficacy of a new tetracycline, omadacycline, in combination with existing antibiotics recommended to treat this indication, in a mouse model of M. abscessus lung disease. Amikacin, azithromycin, bedaquiline, biapenem, cefoxitin, clofazimine, imipenem, linezolid, and rifabutin were selected as companions to omadacycline. M. abscessus burden in the lungs of mice over a 4-week treatment duration was considered the endpoint. Omadacycline in combination with linezolid, imipenem, cefoxitin, biapenem, or rifabutin exhibited early bactericidal activity compared to any single drug. Using three M. abscessus isolates, we also determined the in vitro frequency of spontaneous resistance against omadacycline to be between 1.9 × 10-10 and 6.2 × 10-10 and the frequency of persistence against omadacycline to be between 5.3 × 10-6 and 1.3 × 10-5. Based on these findings, the combination of omadacycline and select drugs that are included in the recent treatment guidelines may exhibit improved potency to treat M. abscessus lung disease. IMPORTANCE M. abscessus disease incidence is increasing in the United States. This disease is difficult to cure with existing antibiotics. In this study, we describe the efficacy of a new tetracycline antibiotic, omadacycline, in combination with an existing antibiotic to treat this disease. A mouse model of M. abscessus lung disease was used to assess the efficacies of these experimental treatment regimens. Omadacycline in combination with select existing antibiotics exhibited bactericidal activity during the early phase of treatment.

Omadacycline and Clostridioides difficile: A Systematic Review of Preclinical and Clinical Evidence

OBJECTIVE

The objective of this systematic review is to summarize in vitro, preclinical, and human data related to omadacycline and Clostridioides difficile infection (CDI).

DATA SOURCES

PubMed and Google Scholar were searched for "omadacycline" AND ("Clostridium difficile" OR "C difficile" OR "Clostridioides difficile") for any studies published before February 15, 2022. The US Food and Drug Administration (FDA) Adverse Events Reporting System (AERS) was searched for omadacycline (for reports including "C. difficile" or "CDI" or "gastrointestinal infection"). The publications list publicly available at Paratek Pharmaceuticals, Inc. Web site was reviewed.

STUDY SELECTION AND DATA EXTRACTION

Publications presenting primary data on omadacycline and C. difficile published in English were included.

DATA SYNTHESIS

Preclinical and clinical evidence was extracted from 14 studies. No case reports in indexed literature and no reports on FDA AERS were found. Omadacycline has potent in vitro activity against many C. difficile clinical strains and diverse ribotypes. In phase 3 studies, there were no reports of CDI in patients who received omadacycline for either community-acquired bacterial pneumonia or acute bacterial skin and skin structure infection.

RELEVANCE TO PATIENT CARE AND CLINICAL PRACTICE

Omadacycline should be considered a low-risk antibiotic regarding its propensity to cause CDI.

CONCLUSIONS

Reducing the burden of CDI on patients and the health care system should be a priority. Patients with appropriate indications who are at heightened risk of CDI may be suitable candidates for omadacycline therapy. In these patients, omadacycline may be preferable to antibiotics with a high CDI risk.

Sub-growth-inhibitory concentrations of omadacycline inhibit Staphylococcus aureus haemolytic activity in vitro

Objectives

To evaluate the effect of sub-growth-inhibitory concentrations of omadacycline on Staphylococcus aureus ATCC 10832 haemolytic activity in vitro.

Methods

Following determination of the MICs of omadacycline and comparator antibiotics, the strain was grown in the presence of individual antibiotics and the percentage of haemolysis assayed; ‘washout’ experiments were performed with omadacycline only.

Results

Omadacycline inhibited S. aureus haemolytic activity in vitro at sub-growth-inhibitory concentrations. Inhibition was maintained at least 4 h after removal of extracellular drug.

Conclusions

Omadacycline’s in vitro potency and suppression of virulence factors might contribute to its efficacy in the treatment of acute bacterial skin and skin structure infections and community-acquired bacterial pneumonia caused by virulent strains of S. aureus. This finding could be relevant for other organisms and virulence factors that depend on new protein synthesis.

1208. Omadacycline In Vitro Activity Against Bacillus Anthracis

Background

Bacillus anthracis, the etiological agent of anthrax, is one of the agents most likely to be used in a biologic attack. Omadacycline previously has demonstrated potent in vitro and in vivo activity against B. anthracis. This project evaluated the in vitro activity of omadacycline against a larger set of B. anthracis strains across two laboratories.

Methods

Methods: Antibiotic susceptibility testing followed Clinical Laboratory Standard Institute methods against a collection of 53 B. anthracis strains at the University of Florida (UF) and 50 B. anthracis strains at MRIGlobal, representing human and animal isolates from North America, Africa, Europe, Asia, and Australia. Minimum inhibitory concentrations (MICs) for omadacycline and comparators at both sites (doxycycline, ciprofloxacin, levofloxacin, moxifloxacin) were determined by broth microdilution.

Results

Results: In the UF study, omadacycline demonstrated an MIC50 of 0.015 mg/L and an MIC90 of 0.03 mg/L against B. anthracis. Omadacycline MIC values were equal to or lower than doxycycline. In the MRIGlobal study, omadacycline demonstrated an MIC50 of 0.06 mg/L and an MIC90 of 0.06 mg/L (Table 1). All comparator MIC values were within ranges previously observed against these strains. Against a ciprofloxacin-resistant strain (MIC = 2 mg/L), omadacycline had an MIC value of 0.015 mg/L; against a doxycycline-resistant strain (MIC = 4 mg/L), omadacycline had an MIC value of 0.06 mg/L. Reproducibility was observed between the 2 laboratories for omadacycline in vitro activity against B. anthracis (Table 2).

Table 1. MIC Concentration Summary for Omadacycline and Comparators Against B. anthracis Strains

Conclusion

Based on the in vitro activity in both studies, omadacycline has the potential to be effective in treating anthrax infection. Reproducibility of omadacycline in vitro activity against B. anthracis was observed at 2 independent study sites.

Disclosures

Alisa W. Serio, PhD, Paratek Pharmaceuticals, Inc. (Employee, Shareholder) Diane M. Anastasiou, BA, Paratek Pharmaceuticals, Inc. (Consultant)

1687. Omadacycline in Female Adults With Acute Pyelonephritis: Results from a Randomized, Double-Blind, Adaptive Phase 2 Study

Background

Omadacycline (OMC) is a novel intravenous (IV) and oral aminomethylcycline, approved in the USA for community-acquired bacterial pneumonia and acute bacterial skin and skin structure infections in adults. We present data from a randomized, adaptive dose–response phase 2 study of OMC in adult females with acute pyelonephritis (AP).

Methods

Females aged ≥ 18 y with acute uncomplicated pyelonephritis were initially randomized to 1 of 4 once-daily regimens of OMC vs once-daily standard regimen of IV-to-oral levofloxacin (LEV) (total therapy: 7–10 days) (NCT03757234); the randomization algorithm was subsequently adapted by the data monitoring committee (DMC; blinded to the investigators) following interim analyses of efficacy in the microbiological-intent-to-treat (micro-ITT) population (Table 1). Efficacy was assessed for noninferiority according to investigator’s assessment of clinical response (IACR) and microbiological response at post-therapy evaluation (PTE; Day 21) and end of therapy (EOT). Treatment-emergent adverse events (TEAEs) were assessed. Results were reviewed by the DMC.

Table 1

Results

201 patients were randomized. Baseline characteristics were similar across groups (Table 2). Among patients with an identified pathogen, the most common species was E. coli. For IACR at both EOT and PTE, no OMC group met noninferiority to LEV (Figure 1), as the lower limit of the 95% CI for the treatment difference exceeded −10% (range −12.4% to −34.8%). Responses at PTE were consistent with those at EOT. Microbiological responses in each OMC group were generally lower than LEV. OMC was well tolerated; 36.2% and 32.4% of OMC- and LEV-treated patients had ≥ 1 TEAE. The most frequently reported TEAEs (≥ 5%) in the OMC the LEV groups, respectively, were headache (10.2% vs 6.8%), asymptomatic bacteriuria (6.3% vs 1.4%), diarrhea (2.4% vs 6.8%), and nausea (5.5% vs 6.8%).

Table 2

Figure

Conclusion

In this adaptive, phase 2 study, clinical success was high for both groups, although no OMC group met criteria for noninferiority to levofloxacin in AP, potentially due to pharmacokinetic/pharmacodynamic drivers of efficacy for AP. Omadacycline was well tolerated, with a safety profile consistent with its current labeling. Further evaluation is warranted to further understand the outcomes of this study.

Disclosures

J. Scott Overcash, MD, FACEP, Paratek Pharmaceuticals, Inc. (Scientific Research Study Investigator) Evan Tzanis, BS, Paratek Pharmaceuticals, Inc. (Employee, Shareholder) Amy Manley, BS, Paratek Pharmaceuticals, Inc. (Employee) Courtney Kirsch, BS, Paratek Pharmaceuticals, Inc. (Employee) Alisa W. Serio, PhD, Paratek Pharmaceuticals, Inc. (Employee, Shareholder) Tiffany White, PhD, ContraFact Corporation (Consultant, (ended Feb 2020))Facile Therapeutics (Consultant)Paratek Pharmaceuticals, Inc. (Employee) Kelly Wright, PharmD, Paratek Pharmaceuticals, Inc. (Employee, Shareholder) Surya Chitra, PhD, Paratek Pharmaceuticals, Inc. (Consultant) Paul B. Eckburg, MD, AN2 Therapeutics (Consultant)Bugworks Research (Consultant)Curza (Advisor or Review Panel member)Paratek Pharmaceuticals, Inc. (Consultant)SNIPR Biome (Consultant)Spero Therapeutics (Consultant)

1202. Subinhibitory Concentrations of Omadacycline Inhibit Staphylococcus aureus Hemolytic Activity in Vitro

Background

In animal models of Staphylococcus aureus infection, α-hemolysin has been shown to be a key virulence factor. Treatment of S. aureus with subinhibitory levels of protein synthesis inhibitors can decrease α-hemolysin expression. Omadacycline, a novel aminomethylcycline antibiotic in the tetracycline class of bacterial protein biosynthesis inhibitors, is approved in the United States for treatment of community-acquired bacterial pneumonia (CABP) and acute bacterial skin and skin structure infections (ABSSSI) in adults. This study was performed to determine the durability of inhibition and effect of subinhibitory concentrations of omadacycline on S. aureus hemolytic activity.

Methods

All experiments used the methicillin-sensitive S. aureus strain Wood 46 (ATCC 10832), a laboratory strain known to secrete high levels of α-hemolysin. Minimum inhibitory concentrations (MICs) of omadacycline and comparator antibiotics (tetracycline, cephalothin, clindamycin, vancomycin, linezolid) were determined. Growth of S. aureus with all antibiotics was determined and the percentage of hemolysis assayed. “Washout” experiments were performed with omadacycline only.

Results

S. aureus cultures treated with 1/2 or 1/4 the MIC of omadacycline for 4 hours showed hemolysis units/10⁸ CFU of 47% and 59% of vehicle-treated cultures, respectively (Fig. 1A, 1B). In washout experiments, treatment with as little as 1/4 the MIC of omadacycline for 1 hour decreased the hemolysis units/10⁸ CFU by 60% for 4 hours following removal of the drug (Table 1).

Figure 1

Table 1

Conclusion

Omadacycline inhibited S. aureus hemolytic activity in vitro at subinhibitory concentrations and inhibition was maintained for ≥ 4 hours after removal of extracellular drug (Fig. 2). The suppression of virulence factors throughout the approved omadacycline dosing interval, in addition to the in vitro potency of omadacycline, may contribute to the efficacy of omadacycline for ABSSSI and CABP due to virulent S. aureus. This finding may apply to other organisms and other virulence factors that require new protein synthesis to establish disease.

Figure 2

Disclosures

Alisa W. Serio, PhD, Paratek Pharmaceuticals, Inc. (Employee, Shareholder) S. Ken Tanaka, PhD, Paratek Pharmaceuticals, Inc. (Employee, Shareholder) Kelly Wright, PharmD, Paratek Pharmaceuticals, Inc. (Employee, Shareholder) Lynne Garrity-Ryan, PhD, Paratek Pharmaceuticals, Inc. (Employee, Shareholder)

1688. Omadacycline in Female Adults With Cystitis: Results From a Randomized, Double-Blinded, Adaptive Phase 2 Study

Background

In a previous phase 1b study, ≥ 90% of patients with cystitis treated with omadacycline (OMC), a novel intravenous (IV) and oral aminomethylcycline, achieved clinical success. We assessed the safety and efficacy of OMC vs nitrofurantoin (NIT) for treatment of cystitis in a randomized, adaptive phase 2 study.

Methods

Females ≥18 years with uncomplicated symptomatic cystitis were randomized to oral dose regimens of OMC or NIT for 7 days (NCT03425396; Table 1). Efficacy was assessed for noninferiority by investigator’s assessment of clinical response (IACR) at post-treatment evaluation (PTE; primary endpoint; Day 14). Other endpoints included IACR, microbiologic response, and composite clinical and microbiologic response at end of treatment (EOT) and PTE. Treatment-emergent adverse events (TEAEs) were assessed. Results were reviewed by a data monitoring committee.

Table 1

Results

Of 225 patients enrolled, 93.8% completed the study. Baseline (BL) characteristics were similar across groups, except Group 4, which was added late in the study based on blinded review of tolerability. (Table 2). Most patients had moderate BL symptoms of urinary tract infection. Among those with an identified pathogen, the most common species was E. coli. BL minimum inhibitory concentrations (MICs) against E. coli were 0.5 to 8 µg/mL for OMC and < 2 to 64 µg/mL for NIT. Clinical success rates for the intent-to-treat (ITT) population at PTE were high for all groups (OMC 78–88%; NIT 91%; Figure). Microbiologic response rates were higher with NIT vs OMC at PTE (Figure). Noninferiority of OMC to NIT was not met, as the lower limit of the 95% CI for treatment difference exceeded −10% (range −16.8% to −44.1%). OMC was generally well tolerated, with gastrointestinal disorders as the most frequent TEAEs (OMC 22%; NIT 14.8%).

Table 2

Figure

Conclusion

In this phase 2 study, clinical success rates were high in the OMC and NIT groups, although no OMC group met noninferiority criteria. Microbiological responses with all doses of OMC were generally lower than in the NIT group, potentially influenced by the higher BL MICs observed in this study compared with the previous phase 1b study. OMC was well tolerated, with a safety profile consistent with its current labeling. Further analyses are needed to fully understand study outcomes.

Disclosures

J. Scott Overcash, MD, FACEP, Paratek Pharmaceuticals, Inc. (Scientific Research Study Investigator) Evan Tzanis, BS, Paratek Pharmaceuticals, Inc. (Employee, Shareholder) Amy Manley, BS, Paratek Pharmaceuticals, Inc. (Employee) Alissa Sirbu, BSN, Paratek Pharmaceuticals, Inc. (Employee) Alisa W. Serio, PhD, Paratek Pharmaceuticals, Inc. (Employee, Shareholder) Tiffany White, PhD, ContraFact Corporation (Consultant, (ended Feb 2020))Facile Therapeutics (Consultant)Paratek Pharmaceuticals, Inc. (Employee) Kelly Wright, PharmD, Paratek Pharmaceuticals, Inc. (Employee, Shareholder) Surya Chitra, PhD, Paratek Pharmaceuticals, Inc. (Consultant) Paul B. Eckburg, MD, AN2 Therapeutics (Consultant)Bugworks Research (Consultant)Curza (Advisor or Review Panel member)Paratek Pharmaceuticals, Inc. (Consultant)SNIPR Biome (Consultant)Spero Therapeutics (Consultant)

Activity of plazomicin compared with other aminoglycosides against isolates from European and adjacent countries, including Enterobacteriaceae molecularly characterized for aminoglycoside-modifying enzymes and other resistance mechanisms

Background

Plazomicin is a next-generation aminoglycoside that was developed to overcome common aminoglycoside-resistance mechanisms.

Objectives

We evaluated the activity of plazomicin and comparators against clinical isolates collected from 26 European and adjacent countries during 2014 and 2015 as part of the Antimicrobial Longitudinal Evaluation and Resistance Trends (ALERT) global surveillance programme.

Methods

All 4680 isolates collected from 45 hospitals were tested for susceptibility to antimicrobials using the reference broth microdilution method. Selected isolates were screened for genes encoding carbapenemases, aminoglycoside-modifying enzymes (AMEs) and 16S rRNA methyltransferases.

Results

Plazomicin (MIC50/90 0.5/2 mg/L) inhibited 95.8% of Enterobacteriaceae at ≤2 mg/L, including carbapenem-resistant Enterobacteriaceae (MIC50/90 0.25/128 mg/L). Plazomicin was more active compared with other aminoglycosides against isolates carrying blaKPC (MIC50/90 0.25/2 mg/L), isolates carrying blaOXA-48-like (MIC50/90 0.25/16 mg/L) and carbapenemase-negative isolates (MIC50/90 0.25/1 mg/L). Approximately 60% of the isolates harbouring blaVIM and blaNDM-1 carried 16S rRNA methyltransferases (mainly rmtB and armA). AME genes were detected among 728 isolates and 99.0% of these were inhibited by plazomicin at ≤2 mg/L. Plazomicin activity against Pseudomonas aeruginosa (MIC50/90 4/8 mg/L) was similar to amikacin activity (MIC50/90 2/16 mg/L). Plazomicin demonstrated activity against CoNS (MIC50/90 0.12/0.25 mg/L) and Staphylococcus aureus (MIC50/90 0.5/1 mg/L). Plazomicin activity was limited against Acinetobacter spp. (MIC50/90 8/>128 mg/L), Enterococcus spp. (MIC50/90 32/128 mg/L) and Streptococcus pneumoniae (MIC50/90 32/64 mg/L).

Conclusions

Plazomicin demonstrated activity against Enterobacteriaceae isolates tested in this study, including isolates carrying AMEs and a high percentage of the carbapenem-non-susceptible isolates. Plazomicin displayed activity against staphylococci.

Optimization and Mechanistic Characterization of Pyridopyrimidine Inhibitors of Bacterial Biotin Carboxylase

A major challenge for new antibiotic discovery is predicting the physicochemical properties that enable small molecules to permeate Gram-negative bacterial membranes. We have applied physicochemical lessons from previous work to redesign and improve the antibacterial potency of pyridopyrimidine inhibitors of biotin carboxylase (BC) by up to 64-fold and 16-fold against Escherichia coli and Pseudomonas aeruginosa, respectively. Antibacterial and enzyme potency assessments in the presence of an outer membrane-permeabilizing agent or in efflux-compromised strains indicate that penetration and efflux properties of many redesigned BC inhibitors could be improved to various extents. Spontaneous resistance to the improved pyridopyrimidine inhibitors in P. aeruginosa occurs at very low frequencies between 10^-8 and 10^-9. However, resistant isolates had alarmingly high minimum inhibitory concentration shifts (16- to >128-fold) compared to the parent strain. Whole-genome sequencing of resistant isolates revealed that either BC target mutations or efflux pump overexpression can lead to the development of high-level resistance.

Plazomicin Is Active Against Metallo-β-Lactamase-Producing Enterobacteriaceae

Plazomicin is an aminoglycoside that was approved in June 2018 by the US Food and Drug Administration for the treatment of complicated urinary tract infections, including pyelonephritis, due to Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae, and Proteus mirabilis. Plazomicin was engineered to overcome the most common aminoglycoside resistance mechanism, inactivation by aminoglycoside-modifying enzymes, but is not active against the less common 16S ribosomal RNA methyltransferases (16S-RMTase), which confer target site modification. As an aminoglycoside, plazomicin maintains activity against Enterobacteriaceae that express resistance mechanisms to other antibiotic classes, including metallo-β-lactamases. Therefore, in the absence of a 16S-RMTase, plazomicin is active against metallo-β-lactamase-producing Enterobacteriaceae.

In vitro activity of Plazomicin against Enterobacteriaceae isolates carrying genes encoding aminoglycoside-modifying enzymes most common in US Census divisions

Aminoglycoside-nonsusceptible isolates of Escherichia coli, Klebsiella, Proteus, and Enterobacter species (480/3675) from US hospitals collected during 2014-2015 were screened for 16S rRNA methyltransferase and aminoglycoside-modifying enzyme (AME) genes. Only 5 isolates had high aminoglycoside MICs and carried 16S rRNA methyltransferases. AME genes were observed among 89.7% (426/475) of isolates and the most common genes were aac(3)-IIa (n = 270) and aac(6')-Ib (n = 269). Among other genes, ant(2″)-Ia, aac(3)-Iva, and aph(3')-VIa were observed among 36, 23, and 3 isolates, respectively. Forty-nine (10.3%) isolates yielded negative results for the investigated AME genes. Plazomicin (MIC_50/90, 0.5/1 μg/ml) inhibited 99.3% of the AME-carrying isolates at its susceptible breakpoint while amikacin, gentamicin, and tobramycin inhibited 90.1%, 20.9%, and 18.3%, respectively. Plazomicin was approved by the US Food and Drug Administration in June 2018 for the treatment of complicated urinary tract infections when limited treatment options are available. This agent displayed activity against isolates carrying AMEs that were resistance to other aminoglycosides and comparator agents.

1964. Microbiological Outcomes With Plazomicin (PLZ) vs. Colistin (CST) in Patients With Bloodstream Infections (BSI) Caused by Carbapenem-Resistant Enterobacteriaceae (CRE) in the CARE Study

Background

PLZ is a next-generation aminoglycoside with structural modifications that protect it from aminoglycoside-modifying enzymes (AMEs) and in vitro activity against multidrug-resistant (MDR) Enterobacteriaceae, including aminoglycoside- and carbapenem-resistant strains. In the CARE study, PLZ was associated with improvement in 28-day all-cause mortality vs. CST in patients with CRE BSI. We report the microbiological outcomes in the CARE study by pathogen and key resistance mechanism.

Methods

CARE was a multinational, open-label trial that enrolled BSI patients with documented or presumed CRE into two cohorts. Patients in the randomized cohort received PLZ (15 mg/kg q24h IV) or CST (300-mg load [CST base activity] then 5 mg/kg/day IV) plus adjunctive tigecycline or meropenem. Patients in the observational cohort received PLZ plus investigator’s choice of adjunctive agent. Treatment duration was 7–14 days. Isolate identification and susceptibility testing were conducted by a central laboratory. Whole-genome sequencing was used to identify AME and carbapenemase genes. Microbiological outcomes were assessed in patients with confirmed CRE who received ≥1 dose of study drug (mMITT population).

Results

Of 45 BSI patients enrolled, 43 had confirmed CRE (mMITT), including Klebsiella pneumoniae (n = 42) and Enterobacter aerogenes (n = 1). Against CRE, PLZ MICs ranged from 0.12 to >128 µg/mL; 25/28 (89.3%) isolates from PLZ-treated patients had a PLZ MIC ≤4 µg/mL, while 3 had a PLZ MIC ≥128 µg/mL and a confirmed 16S ribosomal methyltransferase gene. CST MICs ranged from 0.25 to >128 µg/mL; 6/16 (37.5%) isolates from CST-treated patients had an MIC >2 µg/mL. There were 47 distinct Enterobacteriaceae pathogens isolated from 43 patients, and of these, AME genes were detected in 43/47 (91.5%), most commonly aac(6’)-Ib (n = 29). Carbapenemase genes were detected in 45/47 (95.7%) isolates, most commonly bla_KPC (n = 33). PLZ demonstrated higher microbiological eradication rates than CST against CRE, including AME- and carbapenemase-producing isolates (table).

Conclusion

The results provide evidence of the efficacy of PLZ-based therapy for patients with BSI due to MDR Enterobacteriaceae, including AME- and carbapenemase-producing organisms.

Disclosures

A. W. Serio, Achaogen, Inc.: Employee and Shareholder, Salary. A. Smith, Achaogen, Inc.: Employee and Shareholder, Salary. K. M. Krause, Achaogen, Inc.: Employee, Salary. I. Galani, Achaogen, Inc.: Scientific Advisor, Research funding and honoraria. MSD: Scientific Advisor, Honoraria. A. C. Gales, MSD: Consultant and Speaker, Consulting fee. Pfizer: Consultant and Speaker, Consulting fee. BD: Consultant, Consulting fee. Bayer: Consultant, Consulting fee. A. Jubb, Achaogen, Inc.: Employee and Shareholder, Salary. L. E. Connolly, Achaogen, Inc.: Consultant, Consulting fee.

1345. Comparative Activity of Plazomicin and Other Aminoglycosides Against Enterobacteriaceae Isolates From Various Infection Sources From Hospitalized Patients in the United States

Background

Plazomicin is a next-generation aminoglycoside that is currently under review at the United States Food and Drug Administration for complicated urinary tract infections (cUTIs), including acute pyelonephritis, and bloodstream infections (BSIs) due to certain Enterobacteriaceae (ENT) in patients who have limited or no alternative treatment options. We evaluated the activity of plazomicin and aminoglycosides against ENT isolates collected in US hospitals during 2014 to 2017 by site of infection.

Methods

A total of 8,510 ENT isolates were collected from BSIs (2,133), pneumonia in hospitalized patients (PIHP; 1,826), skin and skin structure infections (SSSIs; 1,155), intra-abdominal infections (IAIs; 731), UTIs (2,508), and other or unknown infection sites (others; 157) in 71 US hospitals during 2014 to 2017. Isolates were susceptibility (S) tested by reference broth microdilution methods and results were interpreted using CLSI breakpoints.

Results

Plazomicin (MIC50/90 ranges, 0.25–0.5/1–2 µg/mL) inhibited 98.8–99.9% of the ENT isolates at ≤4 µg/mL across all infection types (figure). At ≤4 µg/mL, plazomicin inhibited 93.8–100% of the carbapenem-resistant ENT (CRE) isolates stratified by infection type. The S rates for amikacin ranged from 98.7% to 99.7% against ENT isolates overall. However, amikacin S rates for CRE ranged from 53.1% for UTI to 100% for IAI isolates. Gentamicin (89.2–93.6%S) and tobramycin (88.8–94.3%S) were slightly less active than plazomicin and amikacin against the ENT isolates stratified by infection source. Gentamicin S rates against CRE isolates ranged from 43.8% to 66.7% while tobramycin inhibited &lt;45% of the CRE isolates from the different infection sources.

Conclusion

The activity of plazomicin and amikacin was similar against ENT isolates from US hospitals and did not vary by infection type; however, amikacin activity against CRE isolates varied by infection source while plazomicin remained active against CRE isolates regardless of infection source. These results highlight the potential role of plazomicin for treating serious infections caused by CRE. This project was partially funded under BARDA Contract No. HHSO100201000046C.

Disclosures

M. Castanheira, Achaogen: Research Contractor, Research support. J. M. Streit, Achaogen: Research Contractor, Research support. A. W. Serio, Achaogen: Employee, Salary. K. M. Krause, Achaogen: Employee, Salary. R. K. Flamm, Achaogen: Research Contractor, Research support.

2060. Comparison of Plazomicin MIC Test Strip and Broth Microdilution MIC Results for 125 Enterobacteriaceae

Background

Plazomicin (PLZ) is a next-generation aminoglycoside with in vitro activity against MDR Enterobactericeae, including CRE. PLZ is currently under review at the FDA for the treatment of complicated urinary tract infections, including pyelonephritis, and bloodstream infections due to certain Enterobacteriaceae in patients who have limited or no alternative treatment option. This study was performed to evaluate the performance of a newly developed gradient strip, the plazomicin MIC Test Strip (MTS) from Liofilchem, Roseto degli Abruzzi, Italy compared with the broth microdilution method against relevant Enterobacteriaceae.

Methods

The study isolates included 125 Enterobacteriaceae (12 species as shown in the table), which were chosen to include a range of plazomicin MICs and isolates with known resistant mechanisms. Each isolate was tested for PLZ MIC by broth microdilution (BMD; LSI prepared frozen panels) and by PLZ MTS on 100 mm Mueller Hinton agar (MHA) plates (Becton Dickinson, Sparks, MD) and a subset of 20 strains was also tested on MHA plates from two additional manufacturers (Hardy, Santa Maria, CA and Remel, Lenexa, KA). Quality control (QC) strains (E. coli ATCC 25922 and P. aeruginosa ATCC 27853) were tested on each day of testing and results compared with CLSI expected ranges.

Results

As shown in the table, PLZ MTS and BMD results were within ± one doubling dilution (essential agreement) for 99.2% of all study isolates. The category agreement rate was 91.2% (based on proposed susceptible/intermediate/resistant breakpoints of ≤4/8/≥16 µg/mL) and there were no very major or major errors observed. The QC results were within CLSI published ranges. PLZ results for MTS tested on Remel and Hardy MHA for the subset of 20 isolates were similar to BD MHA results (equivalent or 1 dilution lower).

Conclusion

This initial evaluation of the plazomicin MTS showed good correlation to BMD MIC. Further testing with additional isolates and media at multiple test sites is warranted.

Disclosures

All authors: No reported disclosures.

Plazomicin Retains Antibiotic Activity against Most Aminoglycoside Modifying Enzymes

Plazomicin is a next-generation, semisynthetic aminoglycoside antibiotic currently under development for the treatment of infections due to multidrug-resistant Enterobacteriaceae. The compound was designed by chemical modification of the natural product sisomicin to provide protection from common aminoglycoside modifying enzymes that chemically alter these drugs via N-acetylation, O-adenylylation, or O-phosphorylation. In this study, plazomicin was profiled against a panel of isogenic strains of Escherichia coli individually expressing twenty-one aminoglycoside resistance enzymes. Plazomicin retained antibacterial activity against 15 of the 17 modifying enzyme-expressing strains tested. Expression of only two of the modifying enzymes, aac(2')-Ia and aph(2″)-IVa, decreased plazomicin potency. On the other hand, expression of 16S rRNA ribosomal methyltransferases results in a complete lack of plazomicin potency. In vitro enzymatic assessment confirmed that AAC(2')-Ia and APH(2'')-IVa (aminoglycoside acetyltransferase, AAC; aminoglycoside phosphotransferase, APH) were able to utilize plazomicin as a substrate. AAC(2')-Ia and APH(2'')-IVa are limited in their distribution to Providencia stuartii and Enterococci, respectively. These data demonstrate that plazomicin is not modified by a broad spectrum of common aminoglycoside modifying enzymes including those commonly found in Enterobacteriaceae. However, plazomicin is inactive in the presence of 16S rRNA ribosomal methyltransferases, which should be monitored in future surveillance programs.

Antimicrobial activity of plazomicin against Enterobacteriaceae-producing carbapenemases from 50 Brazilian medical centers

Plazomicin is a next-generation aminoglycoside with activity against Enterobacteriaceae, including carbapenemase-producing Enterobacteriaceae (CPE). The aim of this study was to evaluate the activity of plazomicin against CPE (Klebsiella spp., Escherichia coli, Serratia spp., Enterobacter spp., Citrobacter spp., Morganella spp., Proteus spp., Providencia spp.) from different Brazilian hospitals. A total of 4000 carbapenem-resistant Enterobacteriaceae isolates were collected from clinical samples in 50 Brazilian hospitals during 2013-2015. Of these, 499 carbapenem-resistant isolates (CLSI criteria) were selected for further evaluation via broth microdilution to assess for the activity of plazomicin, colistin, tigecycline, meropenem, amikacin, and gentamicin. Additionally, the isolates were assessed for the presence of carbapenemase genes (bla_KPC, bla_NDM, bla_OXA-48-like, bla_IMP, bla_BKC, bla_GES, and bla_VIM) by polymerase chain reaction (PCR). When PCR was positive to bla_OXA-48-like, bla_IMP, bla_GES, and bla_VIM, the carbapenemase genes were sequenced. bla_KPC was the most prevalent carbapenemase gene found (n=397), followed by bla_NDM (n=81), bla_OXA-48 (n=12), and bla_IMP-1 (n=3). Other genes were identified in only 1 isolate each: bla_BKC-1, bla_GES-16, bla_GES-1, bla_OXA-370, and bla_VIM-1. One isolate had 2 carbapenemase genes (bla_KPC and bla_NDM). Thirty-three percent of the isolates were nonsusceptible to colistin, 24% to tigecycline, 97% to meropenem, 51% to amikacin, and 81% to gentamicin (via EUCAST criteria). The plazomicin MIC_50/90 was 0.5/64mg/L, with 85% of MICs ≤2mg/L and 87% of MICs ≤4mg/L. Elevated MICs to plazomicin were not associated with a specific carbapenemase or bacterial species. The MICs of plazomicin against CPE were lower than those of other aminoglycosides. Plazomicin is a promising drug for the treatment of CPE infections.

Activity of Plazomicin against Enterobacteriaceae Isolates Collected in the United States Including Isolates Carrying Aminoglycoside-Modifying Enzymes Detected by Whole Genome Sequencing

Background

Plazomicin (PLZ) is a next-generation aminoglycoside (AMG) stable against aminoglycoside-modifying enzymes (AME) that completed Phase 3 studies for complicated urinary tract infections and serious infections due to carbapenem-resistant Enterobacteriaceae (ENT). We evaluated the activity of PLZ and AMGs against ENT collected in US hospitals during 2016.

Methods

A total of 2,097 ENT were susceptibility (S) tested by CLSI reference broth microdilution methods. E. coli, Klebsiella spp. Enterobacter spp., and P. mirabilis isolates displaying non-S MICs (CLSI criteria) for gentamicin (GEN), amikacin (AMK), and/or tobramycin (TOB) were submitted to WGS, de novo assembly and screening for AME genes.

Results

Against ENT, PLZ was more active than all 3 clinically available AMGs (Table). PLZ and AMK activities were stable regardless of the infection type; however, differences were observed for GEN and TOB. Bloodstream isolates displayed higher GEN MICs when compared with the other infection sites. TOB activity varied 4-fold, being higher for bloodstream and pneumonia infections and lower for skin/soft tissue and other/unknown specimens. Against 198 isolates carrying 1 or more AME-encoding genes detected among 208 AMG-non-S isolates, the activity of PLZ was 8- to 16-fold greater when compared with the activity of AMK and at least 16-fold higher than the activity of GEN or TOB.

Conclusion

PLZ was active against ENT isolates from US hospitals regardless of infection type. PLZ displayed activity against isolates carrying AME genes that represent 12.0% of selected species. AME-carrying isolates were considerably more resistant to AMK, GEN, and TOB, highlighting the potential value of PLZ to treat infections caused by these organisms.

This project has been funded under BARDA Contract No. HHSO100201000046C.

Disclosures

M. Castanheira, Achaogen: Research Contractor, Research grant; L. M. Deshpande, Achaogen: Research Contractor, Research grant; C. M. Hubler, Achaogen: Research Contractor, Research grant; R. E. Mendes, Achaogen: Research Contractor, Research grant; A. W. Serio, Achaogen: Employee, Salary; K. M. Krause, Achaogen: Employee, Salary; R. K. Flamm, Achaogen: Research Contractor, Research grant

Aminoglycosides: An Overview

Aminoglycosides are natural or semisynthetic antibiotics derived from actinomycetes. They were among the first antibiotics to be introduced for routine clinical use and several examples have been approved for use in humans. They found widespread use as first-line agents in the early days of antimicrobial chemotherapy, but were eventually replaced in the 1980s with cephalosporins, carbapenems, and fluoroquinolones. Aminoglycosides synergize with a variety of other antibacterial classes, which, in combination with the continued increase in the rise of multidrug-resistant bacteria and the potential to improve the safety and efficacy of the class through optimized dosing regimens, has led to a renewed interest in these broad-spectrum and rapidly bactericidal antibacterials.

Expression of an epitope-tagged virulence protein in Rickettsia parkeri using transposon insertion

Despite recent advances in our ability to genetically manipulate Rickettsia, little has been done to employ genetic tools to study the expression and localization of Rickettsia virulence proteins. Using a mariner-based Himar1 transposition system, we expressed an epitope-tagged variant of the actin polymerizing protein RickA under the control of its native promoter in Rickettsia parkeri, allowing the detection of RickA using commercially-available antibodies. Native RickA and epitope-tagged RickA exhibited similar levels of expression and were specifically localized to bacteria. To further facilitate protein expression in Rickettsia, we also developed a plasmid for Rickettsia insertion and expression (pRIE), containing a variant Himar1 transposon with enhanced flexibility for gene insertion, and used it to generate R. parkeri strains expressing diverse fluorescent proteins. Expression of epitope-tagged proteins in Rickettsia will expand our ability to assess the regulation and function of important virulence factors.

Rickettsia parkeri invasion of diverse host cells involves an Arp2/3 complex, WAVE complex and Rho-family GTPase-dependent pathway

Rickettsiae are obligate intracellular pathogens that are transmitted to humans by arthropod vectors and cause diseases such as spotted fever and typhus. Although rickettsiae require the host cell actin cytoskeleton for invasion, the cytoskeletal proteins that mediate this process have not been completely described. To identify the host factors important during cell invasion by Rickettsia parkeri, a member of the spotted fever group (SFG), we performed an RNAi screen targeting 105 proteins in Drosophila melanogaster S2R+ cells. The screen identified 21 core proteins important for invasion, including the GTPases Rac1 and Rac2, the WAVE nucleation-promoting factor complex and the Arp2/3 complex. In mammalian cells, including endothelial cells, the natural targets of R. parkeri, the Arp2/3 complex was also crucial for invasion, while requirements for WAVE2 as well as Rho GTPases depended on the particular cell type. We propose that R. parkeri invades S2R+ arthropod cells through a primary pathway leading to actin nucleation, whereas invasion of mammalian endothelial cells occurs via redundant pathways that converge on the host Arp2/3 complex. Our results reveal a key role for the WAVE and Arp2/3 complexes, as well as a higher degree of variation than previously appreciated in actin nucleation pathways activated during Rickettsia invasion.

Bacillus subtilis aconitase is required for efficient late-sporulation gene expression

Bacillus subtilis aconitase, encoded by the citB gene, is homologous to the bifunctional eukaryotic protein IRP-1 (iron regulatory protein 1). Like IRP-1, B. subtilis aconitase is both an enzyme and an RNA binding protein. In an attempt to separate the two activities of aconitase, the C-terminal region of the B. subtilis citB gene product was mutagenized. The resulting strain had high catalytic activity but was defective in sporulation. The defect was at a late stage of sporulation, specifically affecting expression of sigmaK-dependent genes, many of which are important for spore coat assembly and require transcriptional activation by GerE. Accumulation of gerE mRNA and GerE protein was delayed in the aconitase mutant strain. Pure B. subtilis aconitase bound to the 3' untranslated region of gerE mRNA in in vitro gel mobility shift assays, strongly suggesting that aconitase RNA binding activity may stabilize gerE mRNA in order to allow efficient GerE synthesis and proper timing of spore coat assembly.

Expression of yeast mitochondrial aconitase in Bacillus subtilis

Expression of yeast mitochondrial aconitase (Aco1) in a Bacillus subtilis aconitase null mutant restored aconitase activity and glutamate prototrophy but only partially restored sporulation. Late sporulation gene expression in the Aco1-expressing strain was delayed.

Metabolic imbalance and sporulation in an isocitrate dehydrogenase mutant of Bacillus subtilis

A Bacillus subtilis mutant with a deletion in the citC gene, encoding isocitrate dehydrogenase, the third enzyme of the tricarboxylic acid branch of the Krebs cycle, exhibited reduced growth yield in broth medium and had greatly reduced ability to sporulate compared to the wild type due to a block at stage I, i.e., a failure to form the polar division septum. In early stationary phase, mutant cells accumulated intracellular and extracellular concentrations of citrate and isocitrate that were at least 15-fold higher than in wild-type cells. The growth and sporulation defects of the mutant could be partially bypassed by deletion of the major citrate synthase gene (citZ), by raising the pH of the medium, or by supplementation of the medium with certain divalent cations, suggesting that abnormal accumulation of citrate affects survival of stationary-phase cells and sporulation by lowering extracellular pH and chelating metal ions. While these genetic and environmental alterations were not sufficient to allow the majority of the mutant cell population to pass the stage I block (lack of asymmetric septum formation), introduction of the sof-1 mutant form of the Spo0A transcription factor, when coupled with a reduction in citrate synthesis, restored sporulation gene expression and spore formation nearly to wild-type levels. Thus, the primary factor inhibiting sporulation in a citC mutant is abnormally high accumulation of citrate, but relief of this metabolic defect is not by itself sufficient to restore competence for sporulation.