Aminoglycoside Concentrations Research Articles

Optimizing aminoglycoside selection for KPC-producing Klebsiella pneumoniae with the aminoglycoside-modifying enzyme (AME) gene aac(6')-Ib.

KPC-producing Klebsiella pneumoniae (KPC-Kp) isolates commonly co-harbour the aminoglycoside-modifying enzyme (AME) gene aac(6')-Ib, which encodes an AME that can confer resistance to some of the commercially available aminoglycosides. We sought to determine the influence of AAC(6')-Ib in KPC-Kp on the pharmacodynamic activity of aminoglycosides. Six KPC-Kp clinical isolates, three with and three without aac(6')-Ib, were analysed. Using these isolates, the bacterial killing of amikacin, gentamicin and tobramycin was assessed in static time-kill experiments. The pharmacodynamic activity of the aminoglycosides was then assessed in a dynamic one-compartment infection model over 72 h using simulated human pharmacokinetics of once-daily dosing with amikacin (15 mg/kg), gentamicin (5 mg/kg) and tobramycin (5 mg/kg). At clinically relevant aminoglycoside concentrations in time-kill experiments and the dynamic one-compartment model, gentamicin was more active than amikacin or tobramycin against the isolates harbouring aac(6')-Ib. Amikacin, gentamicin and tobramycin all showed progressively reduced bacterial killing with exposure to repeated doses against most isolates in the dynamic one-compartment model. MIC values were generally not a good predictor of gentamicin pharmacodynamic activity against KPC-Kp, but were more reliable for amikacin and tobramycin. Gentamicin may be preferred over amikacin or tobramycin for treatment of KPC-Kp infections. However, gentamicin MICs are not a consistent predictor of its pharmacodynamic activity and unexpected treatment failures are possible.

Is serum gentamicin concentration modified with autologous cell-saved blood transfusion after total knee arthroplasty using tranexamic acid? A randomised control trial

BackgroundSelf-transfusion has been proven as an effective management of blood loss after total knee arthroplasty (TKA). Considering that the high local concentration of antibiotic from bone cement is delivered intravenously through the self-transfusion process, systematic toxicity has never been evaluated. In addition, the effectiveness of self-transfusion with the routine concomitant use of other modern blood-salvage strategies, like tranexamic acid, should also be assessed. Therefore, we performed a randomised study to assess: 1) the safety of self-transfusion in TKA by comparing the gentamicin concentrations resulting from the use or not of autologous blood transfusion; 2) the efficacy of self-transfusion in TKA, with the concomitant administration of tranexamic acid. HypothesisSelf-transfusion in TKA elevates the serum gentamicin concentration and the potential risk of nephrotoxicity. MethodsThe serum concentration of aminoglycosides was measured in two groups of 20 patients each, after TKA, according to the use of self-transfusion. Hemoglobin, renal function and calculated blood loss were compared at several points in time between groups. ResultsThe only time where there was a statistically significant difference in serum gentamicin, was at 48h postoperatively between groups [0.3 ug/mL±0.21, range: 0.15 to 0.72 vs. 0.14ug/mL±0.1, range: 0 to 0.35 (p=0.02)]. There were no significant differences in total blood loss [1341mL±501, range: 830 to 2230 vs. 1263mL±459 range: 840 to 2480 (p=0.67)] and need of allogeneic blood transfusion [3 units vs. 2 units] between groups. ConclusionThe use of autologous blood transfusion was found to be safe, in terms of nephrotoxicity of aminoglycosides after TKA, but it seemed to be ineffective as a blood salvage strategy, when used concomitantly with the administration of tranexamic acid. Level of evidenceII; low-powered randomised study. ClinicalTrials.gov registration numberNCT04505748.

Loss of U1498 methylation in 16S rRNA by RsmE methyltransferase associates its role with aminoglycoside resistance in mycobacteria

ObjectivesModulation of methylation pattern through mutations in ribosomal methyltransferases is a key mechanism of bacterial drug resistance. However, RsmG (GidB), which specifically methylates G527 in 16S rRNA, remains the only conserved methyltransferase known to be associated with low-level drug resistance in mycobacterial isolates. The mycobacterial RsmE homologue methylates U1498 in 16S rRNA in a highly specific manner. U1498 lies in the vicinity of the binding site for various aminoglycosides in the ribosome. However, the association of methylation at U1498 with altered drug response remains poorly understood. MethodsA deletion mutant of the RsmE homologue in Mycobacterium smegmatis was generated by a suicidal vector strategy and drug susceptibility assays were performed on wild-type, knockout and complemented strains with varying concentrations of ribosomal- and non-ribosomal-targeting drugs. ResultsDeletion of the RsmE homologue of M. smegmatis led to an at least two-fold increase in the minimum inhibitory concentrations (MICs) of aminoglycosides that bind in the decoding centre proximal to U1498 in the 30S subunit. The change in MICs was highly specific and reproducible and did not show any cross-resistance to other drug classes. Surprisingly, Rv2372c, the RsmE homologue of Mycobacterium tuberculosis, has the largest number of mutations among conserved ribosomal methyltransferases, after gidB, highlighting the role of mutations in RsmE methyltransferase as a key emerging mechanism of resistance in clinical strains. ConclusionWe present the first evidence of an association of methylation of U1498 in 16S rRNA with development of low-level resistance in mycobacteria that must be tackled in a timely manner.

Potentiating aminoglycoside antibiotics to reduce their toxic side effects.

The lack of new antibiotics necessitates the improvement of existing ones, many of which are limited by toxic side effects. Aminoglycosides, antibiotics with excellent activity and low bacterial resistance, are hampered by dose-dependent toxic effects in patients (nephrotoxicity, ototoxicity). High antibiotic concentrations are often required to treat dormant, non-dividing bacteria, though previous studies show that aminoglycosides can be activated against such bacteria by specific metabolites. Here, we employed this mechanism to greatly boost the activity of low concentrations of aminoglycosides against prevalent Gram-negative pathogens (Escherichia coli, Salmonella enterica, and Klebsiella pneumoniae), suggesting that less toxic drug concentrations might be used effectively in patients. We go on to show that this effect improved treatment of biofilms, did not increase aminoglycoside resistance, and was due to the generation of proton-motive force (PMF). By single-cell microscopy, we demonstrate that stationary-phase cells, while non-dividing, actively maintain a growth-arrested state that is not reversed by metabolite addition. Surprisingly, within starved populations, we observed rare cells (3%) that divided without added nutrients. Additionally, we discovered that mannitol could directly protect human kidney cells from aminoglycoside cytotoxicity, independent of the metabolite’s effect on bacteria. This work forwards a mechanism-based strategy to improve existing antibiotics by mitigating their toxic side effects.

Inhibition of biofilm and virulence properties of Pseudomonas aeruginosa by sub-inhibitory concentrations of aminoglycosides

Aminoglycosides are a commonly used class of antibiotics; however, their application has been discontinued due to the emergence of multi-drug resistance bacterial strains. In the present study, the subinhibitory concentrations (sub-MIC) of several aminoglycosides were determined and tested as an antibiofilm and for their anti-virulence properties against Pseudomonas aeruginosa PAO1, which is an opportunistic foodborne pathogen. P. aeruginosa PAO1 exhibits multiple mechanisms of resistance, including the formation of biofilm and production of several virulence factors, against aminoglycoside antibiotics. The sub-MIC of these antibiotics exhibited biofilm inhibition of P. aeruginosa in alkaline TSB (pH 7.9). Moreover, various concentrations of these aminoglycosides also eradicate the mature biofilm of P. aeruginosa. In the presence of sub-MIC of aminoglycosides, the morphological changes of P. aeruginosa were found to change from rod-shaped to the filamentous, elongated, and streptococcal forms. Similar growth conditions and sub-MIC of aminoglycosides were also found to attenuate several virulence properties of P. aeruginosa PAO1. Molecular docking studies demonstrate that these aminoglycosides possess strong binding properties with the LasR protein, which is a well-characterized quorum-sensing receptor of P. aeruginosa. The present study suggests a new approach to revitalize aminoglycosides as antibiofilm and antivirulence drugs to treat infections caused by pathogenic bacteria.

Exploring the Relationship between FEV1 Loss and Recovery and Aminoglycoside Pharmacokinetics in Adult Patients with Cystic Fibrosis: Implications for Clinical Dosing Strategies.

Systemic aminoglycosides remain a cornerstone of treatment for cystic fibrosis (CF) pulmonary exacerbations (PEx); however, the impact of aminoglycoside pharmacokinetics (PK) on outcomes is not well defined in adult CF patients. Our objective was to assess the impact of increasing PK exposures on the clinical outcomes of PEx treatment in adult CF patients receiving high-dose and standard-dose extended-interval aminoglycosides. We conducted a retrospective study of adult CF patients treated with an intravenous aminoglycoside for a PEx. Serum amikacin, gentamicin, and tobramycin levels and forced expiratory volume over 1 second (FEV1 ) data were used to evaluate exposure-response relationships. PK parameters were estimated using a Bayesian approach to obtain area under the curve (AUC)0-24 hr , maximum concentration (Cmax0-24 hr ), and minimum concentration (Cmin0-24 hr ) estimates. The primary efficacy end point was a 90% recovery of baseline FEV1 by 30days posttreatment. Toxicity included signs or symptoms of ototoxicity, vestibular toxicity, or renal toxicity. Multivariate linear mixed-effects models of FEV1 were used for exposure-response analysis. The study included 51 patients who contributed 188 FEV1 observations. There were 3.0±1.7 (mean±SD) aminoglycoside concentrations per patient. The mean AUC0-24 hr , Cmax0-24 hr , and Cmin0-24 hr across all agents and patients were 156±96mg*hr/L, 29.9±12.7mg/L, and 0.35±0.66mg/L, respectively. A total of 42 amikacin-, gentamicin-, or tobramycin-treated patients contributed to the efficacy analysis, of whom 85.7% experienced recovery posttreatment. Of the 51 included patients, 6 (11.8%) experienced seven toxicity events. In exploratory exposure-response analyses, neither AUC0-24 hr nor Cmax0-24 hr was associated with FEV1 values after adjusting for clinical covariates and baseline FEV1 . Increasing aminoglycoside AUC0-24 hr and Cmax0-24 hr were not associated with FEV1 during PEx treatment. Although individualizing aminoglycoside dosing in adult CF patients is necessary to minimize toxicity risk, more work is needed to define optimally safe and effective dosing strategies for this population.

Comparison of the Effect of Phenylalanine Arginine Beta Naphthylamide (PAβN) and Curcumin on Minimum Inhibitory Concentration of Aminoglycosides on Pseudomonas aeruginosa Clinical Isolates

Background and Objective: Efflux pump inhibitors (EPIs) can block efflux pumps and are helpful in potentiating the activity of aminoglycosides against Pseudomonas aeruginosa. The present study compared the effects of phenylalanine-arginine beta naphthylamide (PAβN) and curcumin on aminoglycoside minimum inhibitory concentration (MIC) on Pseudomonas aeruginosa clinical isolates. Materials and Methods: For this descriptive-analytical study, 100 clinical isolates of Pseudomonas aeruginosa were collected and identified by differential diagnostic tests. The MICs of amikacin, gentamicin, and tobramycin were evaluated before and after adding EPIs using a micro-broth dilution test. Results: The bacteria were isolated from different types of samples, including urine (26 isolates), sputum (37 isolates), ulcers (20 isolates), catheters (eight isolates), blood (five isolates), feces (two isolates), and eyes (two isolates). Overall, 60 of the isolates were obtained from males (mean age = 47.85), and 40 from females (mean age = 44.76). In the MIC test, 11 (25.5), 15 (34.8), and 18 (41.8) isolates were resistant to amikacin, gentamicin, and tobramycin, respectively. Significant reductions in the MICs of amikacin, gentamicin, and tobramycin were observed after adding curcumin in 54-100 of aminoglycoside-resistant isolates, while fewer changes in the MICs of aminoglycosides were seen against these clinical isolates after adding PAβN (36-55). Conclusion: Curcumin and PAβN can potentiate the effect of aminoglycosides on clinical isolates of Pseudomonas aeruginosa and change their susceptibility pattern due to efflux pump inhibition. However, our outcomes detected that curcumin was more effective than the PAβN against the aminoglycoside-resistant isolates of P. aeruginosa.

Detection of high level aminoglycoside resistance genes among clinical isolates of Enterococcus species

BackgroundEnterococci are intrinsically resistant to clinically achievable concentrations of aminoglycosides. However, high-level resistance to aminoglycosides (HLAR) is primarily due to the acquisition of genes encoding aminoglycoside-modifying enzymes (AMEs). Aminoglycosides along with cell wall inhibitors are given clinically for treating enterococcal infections. The current study was conducted to investigate the rate of HLAR and to determine aminoglycoside resistance encoding genes profile in enterococcal isolates from different clinical specimens.ResultsFrom 120 Enterococcus species, 50 (41.7%) enterococcal isolates were proven to have HLAR, 78% (39/50) have high-level gentamicin resistance (HLGR), and 74% (37/50) were high-level streptomycin-resistant (HLSR). HLGR isolates carried aminoglycoside modifying gene aac (6′)-Ie-aph (2′)-Ia in 26/39 (66.7%) of isolates, whereas 32/37 (86.5%) of HLSR carried aph (3′)-IIIa gene and were observed in E. faecalis, E. faecium, E. gallinarum, and E. casseliflavus. The aph (2′)-Ib, aph (2′)-Ic, and aph (2′)-Id that encode HLGR could not be detected.ConclusionsThe high detection rate of HLAR among the studied Enterococcus species and the coexistence of HLGR and HLSR strains provide crucial insights to the necessity of routine testing for HLAR in the microbiology lab. The main AME genes among HLGR and HLSR enterococci were aac (6′)-Ie-aph (2″)-Ia and aph (3′)-IIIa, respectively.

13-(2-Methylbenzyl) Berberine Is a More Potent Inhibitor of MexXY-Dependent Aminoglycoside Resistance than Berberine.

We previously showed that berberine attenuates MexXY efflux-dependent aminoglycoside resistance in Pseudomonas aeruginosa. Here, we aimed to synthesize berberine derivatives with higher MexXY inhibitory activities. We synthesized 11 berberine derivatives, of which 13-(2-methylbenzyl) berberine (13-o-MBB) but not its regiomers showed the most promising MexXY inhibitory activity. 13-o-MBB reduced the minimum inhibitory concentrations (MICs) of various aminoglycosides 4- to 128 fold for a highly multidrug resistant P. aeruginosa strain. Moreover, 13-o-MBB significantly reduced the MICs of gentamicin and amikacin in Achromobacter xylosoxidans and Burkholderia cepacia. The fractional inhibitory concentration indices indicated that 13-o-MBB acted synergistically with aminoglycosides in only MexXY-positive P. aeruginosa strains. Time-kill curves showed that 13-o-MBB or higher concentrations of berberine increased the bactericidal activity of gentamicin by inhibiting MexXY in P. aeruginosa. Our findings indicate that 13-o-MBB inhibits MexXY-dependent aminoglycoside drug resistance more strongly than berberine and that 13-o-MBB is a useful inhibitor of aminoglycoside drug resistance due to MexXY.

Antimicrobial biopolymer formation from sodium alginate and algae extract using aminoglycosides.

Antimicrobial biopolymers provide a biodegradable, sustainable, safe, and cheap approach to drug delivery and wound dressing to control bacterial infection and improve wound healing respectively. Here, we report a one-step method of making antimicrobial alginate polymer from sodium alginate and aqueous extract of Wakame using antibiotic aminoglycosides. Thin layer chromatography of commercially available sodium alginate and Wakame extract showed similar oligosaccharide profiles. Screening of six aminoglycosides showed that kanamycin disulfate and neomycin sulfate produces the highest amount of biopolymer; however, kanamycin disulfate produces the most malleable and form fitting biopolymer. Image texture analysis of biopolymers showed similar quantification parameters for all the six aminoglycosides. Weight of alginate polymer as a function of aminoglycoside concentration follows a growth model of prion protein, consistent with the aggregating nature of both processes. Slow release of antibiotics and the resulting zone of inhibition against E. coli DH5α were observed by agar well diffusion assay. Inexpensive method of production and slow release of antibiotics will enable diverse applications of antimicrobial alginate biopolymer reported in this paper.

Standards of aminoglycoside therapeutic drug monitoring in a South African private hospital: perspectives and implications.

Therapeutic drug monitoring (TDM) is essential to ensure that aminoglycoside peak concentrations are high enough for effective antimicrobial treatment and trough levels are low enough to minimise toxicity. Inappropriate utilisation of TDM may lead to suboptimal therapy, toxicity and waste of resources. This study aimed to investigate the standard of aminoglycoside TDM performed in adult hospitalised patients. An observational, descriptive, cross-sectional study. A 221-bed private hospital. All patients, older than 18 years, on intravenous aminoglycosides for more than 48 hours were included. None, was observational. A computerised database and patient files were used to obtain the information required for this study. Descriptive statistical analysis was used. Aminoglycoside blood levels and estimated glomerular filtration rate (eGFR) in the patients. One hundred and three (103) patients were included: 65 on gentamicin and 38 on amikacin. Blood levels were performed in only 19 gentamicin (29.23%) and 22 amikacin (57.89%) patients. Trough levels were taken more than 2 hours before the next dose in 12 gentamicin (63.16%) and 12 amikacin (54.54%) patients. The majority of patients (96.92% on gentamicin and 84.21% on amikacin) received once daily doses. TDM was performed in all patients with an estimated glomerular filtration rate (eGFR) lower than 60 mL/min/1.73m2 and in 23.31% of gentamicin patients and 56.76% of amikacin patients with an eGFR higher than 60 mg/min/1.73m2. Incorrect sampling times and unnecessary levels taken in patients with normal renal function indicate a need for aminoglycoside treatment guidelines in the private hospital. None.

Can Aminoglycosides Be Used as a New Treatment for Helicobacter pylori? In vitro Activity of Recently Isolated Helicobacter pylori.

BackgroundSmectite can serve as a drug delivery system and gentamicin-intercalated smectite hybrids are expected to supersede the standard therapy for Helicobacter pylori eradication. The aim of this study was to confirm whether the minimum inhibitory concentration (MIC) of aminoglycosides applied as smectite hybrids remained low against recently isolated H. pylori strains.Materials and MethodsA total of 140 strains were collected for a minimum period of 3 years. Antimicrobial susceptibility tests were performed, and the MICs of eight antibiotics (amoxicillin, clarithromycin, metronidazole, tetracycline, levofloxacin, gentamicin, netilmicin, and tobramycin) were determined by using the Epsilometer test and following the European Committee on Antimicrobial Susceptibility Testing recommendations.ResultsThe resistance rate of clarithromycin was high, up to 30.7%, although it is a major antimicrobial agent used in standard therapy. The MIC50 and MIC90 of gentamicin (0.25 mg/L and 0.75 mg/L) and netilmicin (0.19 mg/L and 0.75 mg/L) were lower than other alternative therapies for H. pylori eradication. In clarithromycin-resistant strains, the MIC50 was 0.25 mg/L and the MIC90 was 1 mg/L for gentamicin; for netilmicin, the values were 0.25 mg/L and 0.75 mg/L, respectively.ConclusionThrough the use of gentamicin and netilmicin, which have low MICs for H. pylori, aminoglycoside-intercalated smectite hybrids are expected to emerge as a new standard therapy for H. pylori eradication.

2449. Validation of In Vitro Activity of Aminoglycosides Against Recently Isolated Helicobacter pylori for Commercialization of Gentamicin-Intercalated Smectite Hybrid as a New Therapeutic Agent

BackgroundThe eradication rate of Helicobacter pylori as a standard therapy based on amoxicillin and clarithromycin, exhibits a decreasing trend. Alternative approaches have been explored, but there is still controversy in the regimen change and these do not provide a satisfactory substitute to the existing standard therapy. Thus, a novel and efficient H. pylori eradication regimen should be developed. Smectite can serve as a drug delivery system and gentamicin-intercalated smectite hybrids (S-GEN) are expected to supersede the standard therapy for H. pylori eradication. In the previous study, we synthesized S-GEN complexes as a novel therapeutic agent. In a murine model, S-GEN released gentamicin to the gastric wall stably and the therapeutic effect was not inferior to the conventional standard therapy. The aim of this study was to confirm whether the minimum inhibitory concentration (MIC) of aminoglycosides applied as smectite hybrids remained low against recently isolated H. pylori strains.MethodsThe H. pylori strains were collected via endoscopic biopsy from 1,422 patients at Gangnam Severance Hospital in Seoul, Korea, between March 2015 and February 2018. Antimicrobial susceptibility tests were performed, and the MICs of eight antibiotics (amoxicillin, clarithromycin, metronidazole, tetracycline, levofloxacin, gentamicin, netilmicin, and tobramycin) were determined by using the Epsilometer test and following the European Committee on Antimicrobial Susceptibility Testing recommendations.ResultsFinally, 140 H. pylori strains were analyzed in this study. The resistance rate to clarithromycin was 30.7%, although it is a major antimicrobial agent used in standard therapy. The MIC50 and MIC90 of gentamicin (MIC50 0.25 mg/L, MIC90 0.75 mg/L) and netilmicin (MIC50 0.19 mg/L, MIC90 0.75 mg/L) were lower than that of metronidazole, tetracycline and levofloxacin, which are alternative therapies for H. pylori eradication. In clarithromycin-resistant strains, the MIC50 was 0.25 mg/L and the MIC90 was 1 mg/L for gentamicin; for netilmicin, the values were 0.25 mg/L and 0.75 mg/L, respectively.ConclusionThrough the use of gentamicin and netilmicin, which have low MICs for H. pylori, aminoglycoside-intercalated smectite hybrids are expected to emerge as a new standard therapy for H. pylori eradication.Disclosures All authors: No reported disclosures.

RETRACTED: Effects of prophage regions in a plasmid carrying a carbapenemase gene on survival against antibiotic stress

We investigated the evolutionary importance of cryptic prophage elements in a blaNDM-1-bearing plasmid by exploring the effect of prophage regions on survival against antibiotic stress. While analysing a plasmid harboring an NDM-1-encoding gene in Klebsiella pneumoniae from South Korea, we found a prophage region within the plasmid. We constructed single-prophage knockout (KO) mutants by gene replacement. The intact plasmid and plasmids with deleted prophages were conjugated into Escherichia coli DH5α. Growth rate and antibiotic susceptibility were determined, and survival rates of strains were evaluated in the presence of antibiotics, such as imipenem, amikacin, gentamicin, cefotaxime, and piperacillin/tazobactam. A transcriptional response of sigma factor-coding genes (rpoS and rpoE) and reactive oxygen species (ROS)-related genes from different operons (soxS, fumC, oxyR, and katE) to a sub-inhibitory concentration of aminoglycosides was monitored by quantitative real-time polymerase chain reaction (qRT-PCR). The prophage region consists of four cryptic prophages of 16,795 bp and 19 coding DNA sequences. An Escherichia coli transconjugant carrying the plasmid with intact prophages showed increased survival during treatment with various antibiotics, including imipenem and amikacin; however, transconjugants carrying this plasmid with a single-prophage KO did not. mRNA expression analyses revealed that sigma factor proteins (rpoB and rpoE) were highly upregulated by antibiotics. We propose that cryptic prophages in the antibiotic resistance plasmid may contribute to adaptation of the bacterial host to antibiotic stress. We are concerned that the combination of prophages with a drug resistance plasmid helps drug-resistant bacteria in a hostile environment and accelerates their dissemination.

Association between gentamicin resistance and stress tolerance in water isolates of Ralstonia pickettii and R. mannitolilytica.

Members of the species Ralstonia pickettii and R. mannitolilytica, although ubiquitous and lacking major virulence factors, have been associated with nosocomial outbreaks. Tolerance to metals, antibiotics, and disinfectants may represent an advantage for their ubiquity and opportunistic pathogenic potential. In this study, we compared five strains that differed on the origin (hospital effluent, tap water, mineral water) and in the susceptibility to aminoglycosides, regarding their tolerance to metals and disinfection. The growth kinetics and biofilm formation capacity were tested in four R. pickettii strains and one R. mannitolilytica at sub-inhibitory concentrations of aminoglycosides or arsenite. The survival to UV radiation, chlorine, or hydrogen peroxide was also compared in aminoglycoside resistant and susceptible strains. Aminoglycoside-resistant strains presented a higher tolerance to arsenite than the susceptible ones and either aminoglycosides or arsenite was observed to stimulate the biofilm formation. Sub-inhibitory concentrations of the aminoglycoside gentamicin or arsenite significantly decreased the growth rate and yield, but only arsenite caused a significant increase of the lag phase. Hydrogen peroxide presented higher disinfection effectiveness against aminoglycoside susceptible than against resistant strains, an effect that was not observed for UV or chlorine. Although this conclusion needs validation based on a larger number of isolates, including clinical, the results suggest that aminoglycoside resistance may be associated with traits that influence Ralstonia spp. fitness in the environment.

Measurement of Skeletal Muscle Area Improves Estimation of Aminoglycoside Clearance across Body Size.

A consistent approach to the dosing of aminoglycosides across the modern body size distribution has been elusive. We evaluated whether radiologically derived measures of body composition could explain more of the interpatient variability in aminoglycoside pharmacokinetics (PK) than standard body size metrics. This retrospective study included adult patients treated with gentamicin or tobramycin with at least three drug concentrations and computed tomography (CT) imaging available. Aminoglycoside volume and clearance (CL) estimates were computed using a two-compartment model by Bayesian analysis. Morphomic data were extracted from CT images using a custom algorithm. Bivariable and multivariable linear regression were used to assess relationships between PK parameters and covariates. A total of 335 patients were included with a median (minimum, maximum) of 4 (3, 16) aminoglycoside concentrations per patient. The median (minimum, maximum) age, height, and weight of included patients were 57 (21, 93) years, 170 (145, 203) centimeters, and 81 (42, 187) kilograms. Both standard and morphomic measures poorly explained variability in volume (R2 < 0.06). Skeletal muscle area and volume explained more of the interpatient variability in CL than weight or sex. Higher precision was observed using a modified Cockcroft-Gault equation with skeletal muscle area at L3 (R2= 0.38) or L4 (R2= 0.37) than the standard Cockcroft-Gault equation using lean (R2= 0.23), adjusted (R2= 0.23), or total (R2= 0.22) body weights. These results highlight that skeletal muscle measurements from CT images obtained in the course of care can improve the precision of aminoglycoside CL estimation over current body size scalars.

Individualising Therapy to Minimize Bacterial Multidrug Resistance

The scourge of antibiotic resistance threatens modern healthcare delivery. A contributing factor to this significant issue may be antibiotic dosing, whereby standard antibiotic regimens are unable to suppress the emergence of antibiotic resistance. This article aims to review the role of pharmacokinetic and pharmacodynamic (PK/PD) measures for optimising antibiotic therapy to minimise resistance emergence. It also seeks to describe the utility of combination antibiotic therapy for suppression of resistance and summarise the role of biomarkers in individualising antibiotic therapy. Scientific journals indexed in PubMed and Web of Science were searched to identify relevant articles and summarise existing evidence. Studies suggest that optimising antibiotic dosing to attain defined PK/PD ratios may limit the emergence of resistance. A maximum aminoglycoside concentration to minimum inhibitory concentration (MIC) ratio of > 20, a fluoroquinolone area under the concentration-time curve to MIC ratio of > 285 and a β-lactam trough concentration of > 6 × MIC are likely required for resistance suppression. In vitro studies demonstrate a clear advantage for some antibiotic combinations. However, clinical evidence is limited, suggesting that the use of combination regimens should be assessed on an individual patient basis. Biomarkers, such as procalcitonin, may help to individualise and reduce the duration of antibiotic treatment, which may minimise antibiotic resistance emergence during therapy. Future studies should translate laboratory-based studies into clinical trials and validate the appropriate clinical PK/PD predictors required for resistance suppression in vivo. Other adjunct strategies, such as biomarker-guided therapy or the use of antibiotic combinations require further investigation.

Aminoglycoside Concentrations Required for Synergy with Carbapenems against Pseudomonas aeruginosa Determined via Mechanistic Studies and Modeling.

This study aimed to systematically identify the aminoglycoside concentrations required for synergy with a carbapenem and characterize the permeabilizing effect of aminoglycosides on the outer membrane of Pseudomonas aeruginosa Monotherapies and combinations of four aminoglycosides and three carbapenems were studied for activity against P. aeruginosa strain AH298-GFP in 48-h static-concentration time-kill studies (SCTK) (inoculum: 107.6 CFU/ml). The outer membrane-permeabilizing effect of tobramycin alone and in combination with imipenem was characterized via electron microscopy, confocal imaging, and the nitrocefin assay. A mechanism-based model (MBM) was developed to simultaneously describe the time course of bacterial killing and prevention of regrowth by imipenem combined with each of the four aminoglycosides. Notably, 0.25 mg/liter of tobramycin, which was inactive in monotherapy, achieved synergy (i.e., ≥2-log10 more killing than the most active monotherapy at 24 h) combined with imipenem. Electron micrographs, confocal image analyses, and the nitrocefin uptake data showed distinct outer membrane damage by tobramycin, which was more extensive for the combination with imipenem. The MBM indicated that aminoglycosides enhanced the imipenem target site concentration up to 4.27-fold. Tobramycin was the most potent aminoglycoside to permeabilize the outer membrane; tobramycin (0.216 mg/liter), gentamicin (0.739 mg/liter), amikacin (1.70 mg/liter), or streptomycin (5.19 mg/liter) was required for half-maximal permeabilization. In summary, our SCTK, mechanistic studies and MBM indicated that tobramycin was highly synergistic and displayed the maximum outer membrane disruption potential among the tested aminoglycosides. These findings support the optimization of highly promising antibiotic combination dosage regimens for critically ill patients.

A structural basis for the antibiotic resistance conferred by an N1-methylation of A1408 in 16S rRNA.

The aminoglycoside resistance conferred by an N1-methylation of A1408 in 16S rRNA by a novel plasmid-mediated methyltransferase NpmA can be a future health threat. In the present study, we have determined crystal structures of the bacterial ribosomal decoding A site with an A1408m1A antibiotic-resistance mutation both in the presence and absence of aminoglycosides. G418 and paromomycin both possessing a 6′-OH group specifically bind to the mutant A site and disturb its function as a molecular switch in the decoding process. On the other hand, binding of gentamicin with a 6′-NH3+ group to the mutant A site could not be observed in the present crystal structure. These observations agree with the minimum inhibitory concentration of aminoglycosides against Escherichia coli. In addition, one of our crystal structures suggests a possible conformational change of A1408 during the N1-methylation reaction by NpmA. The structural information obtained explains how bacteria acquire resistance against aminoglycosides along with a minimum of fitness cost by the N1-methylation of A1408 and provides novel information for designing the next-generation aminoglycoside.

Chemical profile and antimicrobial activity of Secondatia floribunda A. DC (Apocynaceae)

ObjectiveTo establish the chemical profile, and to evaluate the antibacterial and modulatory activity of the ethanolic extracts of the stalk's inner bark and heartwood of Secondatia floribunda. MethodsQuantification of total phenols and flavonoids was determined by the Folin-Ciocalteu method and aluminum chloride, respectively. Phenolic compounds were identified and quantified by HPLC-DAD (High Performance Liquid Chromatography-Diodearray Detector) and the Infrared Spectroscopy was performed using the measure by Attenuated Total Reflectance with Fourier Transform (ATR-FTIR). Antibacterial assays for determination of the Minimum Inhibitory Concentration (MIC) and modification of aminoglycosides were performed by microdilution. ResultsInfrared spectra showed similar characteristics, having among its main absorption bands hydroxyl group (OH). The antibacterial activity showed clinically significant results for the strains of Staphylococcus aureus and Escherichia coli. In modulation assay, synergic and antagonistic effect for both extracts was observed. Heartwood extract in combination with antibiotics showed a significant MIC reduction at 19.8% (P < 0.000 1)-79.3% (P < 0.01). ConclusionsThis study is the first report of chemical and biological information of Secondatia floribunda suggesting that it is clinically relevant source of a new antibacterial therapy, especially due to the presence of significant levels of phenolic compounds.