Pharmacogenetic variability and the probability of site of action target attainment during tuberculosis meningitis treatment: a physiologically based pharmacokinetic modeling and simulations study

Objective and methodsOur objective was to investigate the role of patient pharmacogenetic variability in determining site of action target attainment during tuberculous meningitis (TBM) treatment. Rifampin and isoniazid PBPK model that included SLCO1B1 and NAT2 effects on exposures respectively were obtained from literature, modified, and validated using available cerebrospinal-fluid (CSF) concentrations. Population simulations of isoniazid and rifampin concentrations in brain interstitial fluid and probability of target attainment according to genotypes and M. tuberculosis MIC levels, under standard and intensified dosing, were conducted.ResultsThe rifampin and isoniazid model predicted steady-state drug concentration within brain interstitial fluid matched with the observed CSF concentrations. At MIC level of 0.25 mg/L, 57% and 23% of the patients with wild type and heterozygous SLCO1B1 genotype respectively attained the target in CNS with rifampin standard dosing, improving to 98% and 91% respectively with 35 mg/kg dosing. At MIC level of 0.25 mg/L, 33% of fast acetylators attained the target in CNS with isoniazid standard dosing, improving to 90% with 7.5 mg/kg dosing.ConclusionIn this study, the combined effects of pharmacogenetic and M. tuberculosis MIC variability were potent determinants of target attainment in CNS. The potential for genotype-guided dosing during TBM treatment should be further explored in prospective clinical studies.Pharmacolog

Molecular evolution of Klebsiella pneumoniae ST278 harboring blaNDM-7 involved in nosocomial transmission

During 2013, ST278 Klebsiella pneumoniae with blaNDM-7 was isolated from the urine (KpN01) and rectum (KpN02) of a patient in Calgary, Canada. The same strain (KpN04) was subsequently isolated from another patient in the same unit. Interestingly, a carbapenem-susceptible ST278 (KpN06) was obtained one month later from the blood of the second patient. Next generation sequencing (NGS) revealed that the loss of carbapenem-resistance in KpN06 was due to a 5-kb deletion on the blaNDM-7-harboring IncX3 plasmid. In addition, an IncFIB plasmid in KpN06 had a 27 kb deletion that removed genes encoding for heavy metal resistance. Phylogenetic analysis showed that the ST278 K. pneumoniae from patient 2 were likely descendants of KpN02 and that KpN06 was a close progenitor of an environmental ST278. It is unclear whether KpN06 lost the blaNDM-7 gene in vivo. This study detailed the remarkable plasticity and speed of evolutionary changes in multidrug resistance K. pneumoniae demonstrating the highly recombinant nature of this species. It also highlights the ability of NGS to clarify molecular micro-evolutionary events within antibiotic-resistant organisms.This work was supported in part by a research grant from the Calgary Laboratory Services (#10009392) and grants from the National Institutes of Health (1R01AI090155 to B.N.K, and R21AI117338 to L.C).http://jid.oxfordjournals.org2017-06-30hb2016Medical Microbiolog

Molecular characterization by using next generation sequencing of plasmids containing blaNDM-7 in Enterobacteriaceae from Calgary, Canada

Enterobacteriaceae with blaNDM-7 is relatively uncommon and had previously been described in Europe, India, USA and Japan. This study describes the characteristics of Enterobacteriaceae [Klebsiella pneumoniae (n=2), Escherichia coli (n=2), Serratia marcescens (n=1), Enterobacter hormaechei (n=1)] with blaNDM-7 obtained in 4 patients from Calgary, Canada during 2013-4. The 46,161 bp IncX3 plasmids with blaNDM-7 are highly similar to other blaNDM-harboring IncX3 plasmids and interestingly, showed identical structures within the different isolates. This finding may indicate horizontal transmission within our health region or may indicate contact with individuals from endemic areas within the hospital setting. Patients infected or colonized with bacteria containing blaNDM-7 IncX3 plasmids will generate infection control challenges. Epidemiological and molecular studies are required to better understand the dynamics of transmission, risk factors and reservoirs for bacteria harboring blaNDM-7. To the best of our knowledge, this is the first report of S. marcescens, and E. hormaechei with blaNDM-7.Calgary Laboratory Services (#10006465) and in part by a grant (to B.N.K.) from the National Institutes of Health (1R01AI090155).http://aac.asm.org2016-09-30hb201

Relebactam is a potent inhibitor of the kpc-2 -lactamase and restores imipenem susceptibility in kpc-producing enterobacteriaceae

The imipenem-relebactam combination is in development as a potential treatment regimen for infections caused by Enterobacteriaceae possessing complex -lactamase backgrounds. Relebactam is a -lactamase inhibitor that possesses the diazabicyclooctane core, as in avibactam; however, the R1 side chain of relebactam also includes a piperidine ring, whereas that of avibactam is a carboxyamide. Here, we investigated the inactivation of the Klebsiella pneumoniae carbapenemase KPC-2, the most widespread class A carbapenemase, by relebactam and performed susceptibility testing with imipenem-relebactam using KPC-producing clinical isolates of Enterobacteriaceae. MIC measurements using agar dilution methods revealed that all 101 clinical isolates of KPC-producing Enterobacteriaceae (K. pneumoniae, Klebsiella oxytoca, Enterobacter cloacae, Enterobacter aerogenes, Citrobacter freundii, Citrobacter koseri, and Escherichia coli) were highly susceptible to imipenem-relebactam (MICs 2 mg/liter). Relebactam inhibited KPC-2 with a second-order onset of acylation rate constant (k2/K) value of 24,750 M1 s1 and demonstrated a slow off-rate constant (koff) of 0.0002 s1. Biochemical analysis using time-based mass spectrometry to map intermediates revealed that the KPC-2–relebactam acyl-enzyme complex was stable for up to 24 h. Importantly, desulfation of relebactam was not observed using mass spectrometry. Desulfation and subsequent deacylation have been observed during the reaction of KPC-2 with avibactam. Upon molecular dynamics simulations of relebactam in the KPC-2 active site, we found that the positioning of active-site water molecules is less favorable for desulfation in the KPC-2 active site than it is in the KPC-2–avibactam complex. In the acyl complexes, the water molecules are within 2.5 to 3 Å of the avibactam sulfate; however, they are more than 5 to 6 Å from the relebactam sulfate. As a result, we propose that the KPC-2–relebactam acyl complex is more stable than the KPC-2–avibactam complex. The clinical implications of this difference are not currently known

Nacubactam enhances meropenem activity against carbapenem-resistant klebsiella pneumoniae producing KPC

Carbapenem-resistant Enterobacteriaceae (CRE) are resistant to most antibiotics, making CRE infections extremely difficult to treat with available agents. Klebsiella pneumoniae carbapenemases (KPC-2 and KPC-3) are predominant carbapenemases in CRE in the United States. Nacubactam is a bridged diazabicyclooctane (DBO) -lactamase inhibitor that inactivates class A and C -lactamases and exhibits intrinsic antibiotic and -lactam “enhancer” activity against Enterobacteriaceae. In this study, we examined a collection of meropenem-resistant K. pneumoniae isolates carrying blaKPC-2 or blaKPC-3; meropenem-nacubactam restored susceptibility. Upon testing isogenic Escherichia coli strains producing KPC-2 variants with single-residue substitutions at important Ambler class A positions (K73, S130, R164, E166, N170, D179, K234, E276, etc.), the K234R variant increased the meropenem-nacubactam MIC compared to that for the strain producing KPC-2, without increasing the meropenem MIC. Correspondingly, nacubactam inhibited KPC-2 (apparent Ki [Kiapp] 31 3 M) more efficiently than the K234R variant (Kiapp 270 27 M) and displayed a faster acylation rate (k2/K), which was 5,815 582 M1 s1 for KPC-2 versus 247 25 M1 s1 for the K234R variant. Unlike avibactam, timed mass spectrometry revealed an intact sulfate on nacubactam and a novel peak (337 Da) with the K234R variant. Molecular modeling of the K234R variant showed significant catalytic residue (i.e., S70, K73, and S130) rearrangements that likely interfere with nacubactam binding and acylation. Nacubactam’s aminoethoxy tail formed unproductive interactions with the K234R variant’s active site. Molecular modeling and docking observations were consistent with the results of biochemical analyses. Overall, the meropenem-nacubactam combination is effective against carbapenem-resistant K. pneumoniae. Moreover, our data suggest that -lactamase inhibition by nacubactam proceeds through an alternative mechanism compared to that for avibactam

OqxAB, a quinolone and olaquindox efflux pump, is widely distributed among multidrug-resistant Klebsiella pneumoniae isolates of human origin

Use of antibiotics among livestock contributes to the selection and dissemination of multidrug resistant (MDR) bacteria. Olaquindox and carbadox are quinoxaline derivatives with antibacterial properties that prevent dysentery and enhance weight gain in suckling pigs. Resistance to quinoxalines is mediated by the efflux pump OqxAB, which also extrudes antibiotics such as chloramphenicol and fluoroquinolones. The gene encoding this efflux pump, oqxAB, was initially detected within plasmid pOLA52, which was found in Escherichia coli isolated from swine manure. Dissemination of oqxAB has been noted in Salmonella species, and the original genetic reservoir of oqxAB was traced to the chromosome of Klebsiella pneumoniae. Surprisingly, OqxAB has been reported only in clinical isolates of K. pneumoniae from China, South Korea, and Spain

ARGONAUT-I: Activity of cefiderocol (s-649266), a siderophore cephalosporin, against gram-negative bacteria, including carbapenem-resistant nonfermenters and enterobacteriaceae with defined extended-spectrum β-lactamases and carbapenemases

The activity of the siderophore cephalosporin cefiderocol is targeted against carbapenem-resistant Gram-negative bacteria. In this study, the activity of cefiderocol against characterized carbapenem-resistant Acinetobacter baumannii complex, Stenotrophomonas maltophilia, Pseudomonas aeruginosa, and Enterobacteriaceae strains was determined by microdilution in iron-depleted Mueller-Hinton broth. The MIC90s against A. baumannii, S. maltophilia, and P. aeruginosa were 1, 0.25, and 0.5 mg/ liter, respectively. Against Enterobacteriaceae, the MIC90 was 1 mg/liter for the group harboring OXA-48-like, 2 mg/liter for the group harboring KPC-3, and 8 mg/liter for the group harboring TEM/SHV ESBL, NDM, and KPC-2

Emergence of resistance to colistin during the treatment of bloodstream infection caused by Klebsiella pneumoniae carbapenemase-producing Klebsiella pneumoniae

We report the emergence of colistin resistance in Klebsiella pneumoniae carbapenemase (KPC)-producing Klebsiella pneumoniae after 8 days of colistin-based therapy, resulting in relapse of bloodstream infection and death. Disruption of the mgrB gene by insertion of a mobile genetic element was found to be the mechanism, which was replicated in vitro after exposure to subinhibitory concentrations of colistin and meropenem

A γ-lactam siderophore antibiotic effective against multidrug-resistant Pseudomonas aeruginosa, Klebsiella pneumoniae, and Acinetobacter spp.

Serious infections caused by multidrug-resistant (MDR) organisms (Klebsiella pneumoniae, Pseudomonas aeruginosa, Acinetobacter baumannii) present a critical need for innovative drug development. Herein, we describe the preclinical evaluation of YU253911, 2, a novel γ-lactam siderophore antibiotic with potent antimicrobial activity against MDR Gram-negative pathogens. Penicillin-binding protein (PBP) 3 was shown to be a target of 2 using a binding assay with purified P. aeruginosa PBP3. The specific binding interactions with P. aeruginosa were further characterized with a high-resolution (2.0 Å) X-ray structure of the compound's acylation product in P. aeruginosa PBP3. Compound 2 was shown to have a concentration >1 μg/ml at the 6 h time point when administered intravenously or subcutaneously in mice. Employing a meropenem resistant strain of P. aeruginosa, 2 was shown to have dose-dependent efficacy at 50 and 100 mg/kg q6h dosing in a mouse thigh infection model. Lastly, we showed that a novel γ-lactam and β-lactamase inhibitor (BLI) combination can effectively lower minimum inhibitory concentrations (MICs) against carbapenem resistant Acinetobacter spp. that demonstrated decreased susceptibility to 2 alone

Sequential, Multiple-Assignment, Randomized Trials for COMparing Personalized Antibiotic StrategieS (SMART-COMPASS)

Patient management is not based on a single decision. Rather, it is dynamic: Based on a sequence of decisions, with therapeutic adjustments made over time. Adjustments are personalized: Tailored to individual patients as new information becomes available. However, strategies allowing for such adjustments are infrequently studied. Traditional antibiotic trials are often nonpragmatic, comparing drugs for definitive therapy when drug susceptibilities are known. COMparing Personalized Antibiotic StrategieS (COMPASS) is a trial design that compares strategies consistent with clinical practice. Strategies are decision rules that guide empiric and definitive therapy decisions. Sequential, multiple-assignment, randomized (SMART) COMPASS allows evaluation when there are multiple, definitive therapy options. SMART COMPASS is pragmatic, mirroring clinical, antibiotic-treatment decision-making and addressing the most relevant issue for treating patients: Identification of the patient-management strategy that optimizes the ultimate patient outcomes. SMART COMPASS is valuable in the setting of antibiotic resistance, when therapeutic adjustments may be necessary due to resistance