The antibiotic pipeline for multi-drug resistant gram negative bacteria: what can we expect?

Effect of Nk-lysin peptides on bacterial growth, MIC, antimicrobial resistance, and viral activities

NK-lysins from chicken, bovine and human are used as antiviral and antibacterial agents. Gram-negative and gram-positive microorganisms, including Streptococcus pyogenes, Streptococcus mutans, Escherichia coli, Pseudomonas aeruginosa, Klebsiella oxytoca, Shigella sonnei, Klebsiella pneumoniae and Salmonella typhimurium, are susceptible to NK-lysin treatment. The presence of dominant TEM-1 gene was noted in all untreated and treated bacteria, while TOHO-1 gene was absent in all bacteria. Importantly, β-lactamase genes CTX-M-1, CTX-M-8, and CTX-M-9 genes were detected in untreated bacterial strains; however, none of these were found in any bacterial strains following treatment with NK-lysin peptides. NK-lysin peptides are also used to test for inhibition of infectivity, which ranged from 50 to 90% depending on NK-lysin species. Chicken, bo vine and human NK-lysin peptides are demonstrated herein to have antibacterial activity and antiviral activity against Rotavirus (strain SA-11). On the basis of the comparison between these peptides, potent antiviral activity of bovine NK-lysin against Rotavirus (strain SA-11) is particularly evident, inhibiting infection by up to 90%. However, growth was also significantly inhibited by chicken and human NK-lysin peptides, restricted by 80 and 50%, respectively. This study provided a novel treatment using NK-lysin peptides to inhibit expression of β-lactamase genes in β-lactam antibiotic-resistant bacterial infections.

Synthesis and antibacterial effects of silver nanoparticles (AgNPs) against multi-drug resistant bacteria

BACKGROUND

The emergence of the global problem of multi-drug resistant bacteria (MDR) is closely related to the improper use of antibiotics, which gives birth to an urgent need for antimicrobial innovation in the medical and health field. Silver nanoparticles (AgNPs) show significant antibacterial potential because of their unique physical and chemical properties. By accurately regulating the morphology, size and surface properties of AgNPs, the antibacterial properties of AgNPs can be effectively enhanced and become a next generation antibacterial material with great development potential.

OBJECTIVE

The detection of the inhibitory effect of AgNPs on MDR provides more possibilities for the research and development of new antimicrobial agents.

METHODS

Promote the formation of AgNPs by redox reaction; determine the minimum inhibitory concentration (MIC) of AgNPs to bacteria by broth microdilution method; evaluate the killing efficacy of AgNPs against multi-drug-resistant bacteria by plate counting; evaluate the inhibitory effect of AgNPs on biofilm construction by crystal violet staining; study the drug resistance of bacteria by gradually increasing the concentration of AgNPs; and detect the toxicity of AgNPs to cells by CCK-8 method.

RESULTS

AgNPs has a significant bactericidal effect on a variety of drug-resistant bacteria. After exposure to AgNPs solution for 12 hours, the number of E. coli decreased sharply, and S. aureus was basically eliminated after 16 hours. In particular, AgNPs showed stronger inhibition against Gram-negative bacteria. In addition, AgNPs can effectively hinder the formation of bacterial biofilm, and its inhibitory effect increases with the increase of AgNPs solution concentration. When AgNPs is used for a long time, the development of bacterial resistance to it is slow. From the point of view of safety, AgNPs has no harmful effects on organisms and has biosafety.

CONCLUSION

AgNPs can inhibit MDR, and the bacteriostatic ability of Gram-negative bacteria is higher than that of Gram-positive bacteria. It can also inhibit the formation of bacterial biofilm, avoid drug resistance and reduce cytotoxicity.

Oral administration of a 2-aminopyrimidine robenidine analogue (NCL195) significantly reduces Staphylococcus aureus infection and reduces Escherichia coli infection in combination with sub-inhibitory colistin concentrations in a bioluminescent mouse model

We have previously reported promising in vivo activity of the first-generation 2-aminopyramidine robenidine analogue NCL195 against Gram-positive bacteria (GPB) when administered via the systemic route. In this study, we examined the efficacy of oral treatment with NCL195 (± low-dose colistin) in comparison to oral moxifloxacin in bioluminescent Staphylococcus aureus and Escherichia coli peritonitis-sepsis models. Four oral doses of 50 mg/kg NCL195, commencing immediately post-infection, were administered at 4 h intervals in the S. aureus peritonitis-sepsis model. We used a combination of four oral doses of 50 mg/kg NCL195 and four intraperitoneal doses of colistin at 0.125 mg/kg, 0.25 mg/kg, or 0.5 mg/kg in the E. coli peritonitis-sepsis model. Subsequently, the dose rates of four intraperitoneal doses of colistin were increased to 0.5 mg/kg, 1 mg/kg, or 2 mg/kg at 4 h intervals to treat a colistin-resistant E. coli infection. In the S. aureus infection model, oral treatment of mice with NCL195 resulted in significantly reduced S. aureus infection loads (P < 0.01) and longer survival times (P < 0.001) than vehicle-only treated mice. In the E. coli infection model, co-administration of NCL195 and graded doses of colistin resulted in a dose-dependent significant reduction in colistin-susceptible (P < 0.01) or colistin-resistant (P < 0.05) E. coli loads compared to treatment with colistin alone at similar concentrations. Our results confirm that NCL195 is a potential candidate for further preclinical development as a specific treatment for multidrug-resistant infections, either as a stand-alone antibiotic for GPB or in combination with sub-inhibitory concentrations of colistin for Gram-negative bacteria.

Propranolol restores susceptibility of XDR Gram-negative pathogens to meropenem and Meropenem combination has been evaluated with either tigecycline or amikacin

BACKGROUND

Infection with extensive-drug-resistant (XDR) carbapenem-resistant (CR) Gram-negative bacteria (GNB) are viewed as a serious threat to human health because of the limited therapeutic options. This imposes the urgent need to find agents that could be used as adjuvants or combined with carbapenems to enhance or restore the susceptibility of XDR CR- GNB. Therefore, this study aimed to examine the effect of propranolol (PR) in combination with Meropenem (MEM) on the susceptibility profile of XDR CR-GNB recovered from severely infected patients as well as to evaluate combining MEM with either tigecycline (TGC) or amikacin (AK).

METHODS

A total of 59 non-duplicate CR- GNB were investigated for carbapenemase production by the major phenotypic methods. Molecular identification of five major carbapenemase-coding genes was carried out using polymerase chain reactions (PCR). Antimicrobial susceptibility tests were carried out using standard methods. Phenotypic and genotypic relatedness was carried out using the heatmap and ERIC PCR analysis. PR, 0.5 -1 mg/mL against the resulting non-clonal XDR CR-GNB pathogens were evaluated by calculating the MIC decrease factor (MDF). A combination of MEM with either AK or TGC was performed using the checkerboard assay.

RESULTS

A total of 21 (35.6%) and 38 (64.4%) CR-GNB isolates were identified as enterobacterial isolates (including 16 (27.1%) Klebsiella Pneumoniae and 5 (8.5%) Escherichia coli) and non-fermentative bacilli (including, 23 (39%), Acinetobacter baumannii, and 15 (25.4%) Pseudomonas aeruginosa). The heatmap and ERIC PCR analysis resulted in non-clonal 28 XDR CR isolates. PR, at a concentration of 0.5 mg /ml, decreased MICs values of the tested XDR CR isolates (28; 100%) and restored susceptibility of only 4 (14.3%) isolates. However, PR (1 mg/mL) when combined with MEM has completely (28; 100%) restored the susceptibility of the tested XDR CR- GNB to MEM. The MEM + AK and MEM + TGC combination showed mostly additive effects (92.8% and 71.4%, respectively).

CONCLUSION

PR at a concentration of 1 mg/mL restored the susceptibility of XDR CR- GNB to MEM which is considered a promising result that should be clinically investigated to reveal its suitability for clinical use in patients suffering from these life-threatening pathogens.

In Vitro Activities of Aztreonam-Avibactam, Eravacycline, Cefoselis, and Other Comparators against Clinical Enterobacterales Isolates: a Multicenter Study in China, 2019

Aztreonam-avibactam, eravacycline, and cefoselis are three novel antimicrobial agents for the treatment of serious infections caused by Gram-negative bacteria. We evaluated the in vitro activities of the above-mentioned three antimicrobial agents against clinical Enterobacterales isolates. A total of 1,202 Enterobacterales isolates, including 10 genera or species, were collected from 26 hospitals that cover seven regions of China. The susceptibilities of the 30 antimicrobial agents were interpreted based on the combination of U.S. Food and Drug Administration and Clinical and Laboratory Standards Institute guidelines. The results indicated that all Enterobacterales isolates showed high susceptibility to aztreonam-avibactam (98.25%), eravacycline (85.69%), and cefoselis (62.73%). The first two antimicrobial agents also demonstrated potent activities against multidrug-resistant and carbapenem-resistant Enterobacterales independent of antimicrobial resistance mechanisms. The rates of susceptibility to aztreonam-avibactam, eravacycline, and cefoselis were lowest in Morganella spp. (84.42%), Proteus spp. (33.65%), and Escherichia coli (40.14%), respectively. In general, the lower rates of susceptibility to eravacycline and cefoselis were in the older inpatient group. The strains isolated from urinary tract exhibited the lowest rate of susceptibility (78.97%) to eravacycline, and the lowest rate of susceptibility (45.83%) to cefoselis was observed in nervous system specimens. The strains isolated from intensive care unit (ICU) wards showed significantly reduced susceptibility to cefoselis compared with those isolated from non-ICU wards. The MIC values of aztreonam-avibactam and ceftazidime-avibactam have poor consistency (weighted kappa = 0.243), as did eravacycline and tigecycline (weighted kappa = 0.478). Cefoselis and cefepime showed highly similar activities against Enterobacterales (weighted kappa = 0.801). Our results support the clinical development of aztreonam-avibactam, eravacycline, and cefoselis to treat infections caused by Enterobacterales. IMPORTANCE Infections caused by multidrug-resistant (MDR) Enterobacterales, especially carbapenem-resistant Enterobacterales (CRE), have been a challenging clinical problem due to the limited therapeutic options. Therefore, the need to develop novel antimicrobial agents and evaluate their activities against Enterobacterales in vitro is urgent. Our results show that the novel antimicrobial agents aztreonam-avibactam and eravacycline retain activities against MDR and CRE isolates, including carbapenemase producers and non-carbapenemase producers. Further analysis combined with clinical information on the strains tested revealed that no significant differences were observed in susceptibility rates of strains with different demographic parameters to aztreonam-avibactam. Age, specimen source, and department were associated with the susceptibility of strains to eravacycline and cefoselis (P ≤ 0.01). Compared with ceftazidime-avibactam, aztreonam-avibactam has its advantages and limitations against Enterobacterales. The potent activity of eravacycline against Enterobacterales was higher than that of tigecycline. Cefoselis and cefepime showed a highly consistent activity against Enterobacterales.

Off-label use versus formal recommendations of conventional and novel antibiotics for the treatment of infections caused by multidrug-resistant bacteria

The infections caused by multidrug- and extensively drug-resistant (MDR, XDR) bacteria, including Gram-positive cocci (GPC, including methicillin-resistant Staphylococcus aureus, MDR-Streptococcus pneumoniae and vancomycin-resistant enterococci) and Gram-negative bacilli (GNB, including carbapenem-resistant [CR] Enterobacterales, CR-Pseudomonas aeruginosa and XDR/CR-Acinetobacter baumannii complex) can be quite challenging for physicians with respect to treatment decisions. Apart from complicated urinary tract and intra-abdominal infections (cUTIs, cIAIs), bloodstream infections and pneumonia, these difficult-to-treat bacteria also cause infections at miscellaneous sites (bones, joints, native/prosthetic valves and skin structures, etc.). Antibiotics like dalbavancin, oritavancin, telavancin and daptomycin are currently approved for the treatment of acute bacterial skin and skin structural infections (ABSSSIs) caused by GPC. Additionally, ceftaroline, linezolid and tigecycline have been formally approved for the treatment of community-acquired pneumonia and ABSSSI. Cefiderocol and meropenem-vaborbactam are currently approved for the treatment of cUTIs caused by XDR-GNB. The spectra of ceftazidime-avibactam and imipenem/cilastatin-relebactam are broader than that of ceftolozane-tazobactam, but these three antibiotics are currently approved for the treatment of hospital-acquired pneumonia, cIAIs and cUTIs caused by MDR-GNB. Clinical investigations of other novel antibiotics (including cefepime-zidebactam, aztreonam-avibactam and sulbactam-durlobactam) for the treatment of various infections are ongoing. Nevertheless, evidence for adequate antibiotic regimens against osteomyelitis, arthritis and infective endocarditis due to several GPC and MDR-GNB is still mostly lacking. A comprehensive review of PubMed publications was undertaken and the formal indications and off-label use of important conventional and novel antibiotics against MDR/XDR-GPC and GNB isolates cultured from miscellaneous sites are presented in this paper.

Investigating forthcoming strategies to tackle deadly superbugs: current status and future vision

INTRODUCTION

Superbugs are microorganisms that cause disease and have increased resistance to the treatments typically used against infections. Recently, antibiotic resistance development has been more rapid than the pace at which antibiotics are manufactured, leading to refractory infections of pathogenic bacteria. Scientists are concerned that a particularly virulent and lethal "superbug" will one day join the ranks of existing bacteria that cause incurable diseases, resulting in a global health disaster on the scale of the Black Death.

AREAS COVERED

Therefore, this study highlights the current developments in the management of antibiotic-resistant bacteria and recommends strategies for further regulating antibiotic-resistant microorganisms associated with the healthcare system. This review also addresses the origins, prevalence, and pathogenicity of superbugs, and the design of antibacterial against these growing multidrug-resistant organisms from a medical perspective.

EXPERT OPINION

It is recommended that antimicrobial resistance (AMR) should be addressed by limiting human-to-human transmission of resistant strains, lowering the use of broad-spectrum antibiotics, and developing novel antimicrobials. Using the risk-factor domains framework from this study would assure that not only clinical but also community and hospital-specific factors are covered, lowering the chance of confounders. Extensive subjective research is necessary to fully understand the underlying factors and uncover previously unexplored areas.

Recent Developments to Cope the Antibacterial Resistance via β-Lactamase Inhibition

Antibacterial resistance towards the β-lactam (BL) drugs is now ubiquitous, and there is a major global health concern associated with the emergence of new β-lactamases (BLAs) as the primary cause of resistance. In addition to the development of new antibacterial drugs, β-lactamase inhibition is an alternative modality that can be implemented to tackle this resistance channel. This strategy has successfully revitalized the efficacy of a number of otherwise obsolete BLs since the discovery of the first β-lactamase inhibitor (BLI), clavulanic acid. Over the years, β-lactamase inhibition research has grown, leading to the introduction of new synthetic inhibitors, and a few are currently in clinical trials. Of note, the 1, 6-diazabicyclo [3,2,1]octan-7-one (DBO) scaffold gained the attention of researchers around the world, which finally culminated in the approval of two BLIs, avibactam and relebactam, which can successfully inhibit Ambler class A, C, and D β-lactamases. Boronic acids have shown promise in coping with Ambler class B β-lactamases in recent research, in addition to classes A, C, and D with the clinical use of vaborbactam. This review focuses on the further developments in the synthetic strategies using DBO as well as boronic acid derivatives. In addition, various other potential serine- and metallo- β-lactamases inhibitors that have been developed in last few years are discussed briefly as well. Furthermore, binding interactions of the representative inhibitors have been discussed based on the crystal structure data of inhibitor-enzyme complex, published in the literature.

Successful prolonged treatment of a carbapenem-resistant Acinetobacter baumannii hip infection with cefiderocol: A case report

We report a 50-year-old Caucasian male with a complicated past medical history who developed extensive polymicrobial osteomyelitis, including a carbapenem-resistant Acinetobacter baumannii (CRAB). In order to streamline therapy, the patient received compassionate use cefiderocol for 6 weeks which was well tolerated. In addition, the patient's infection was considered cured at end of treatment. Few cases on the use of prolonged cefiderocol for treatment of osteomyelitis due to CRAB have been published. Our patient did not report adverse reactions, nor did he develop laboratory abnormalities which were assessed throughout and at the end of the 6-week course.

Role of new antibiotics in extended-spectrum β-lactamase-, AmpC- infections

PURPOSE OF REVIEW

Extended-spectrum β-lactamases (ESBL)- and ampicillinase class C (AmpC)-producing Enterobacterales represent one of the major public threats of the current era. As a consequence, during the last decades there have been great efforts to develop new therapeutic agents against these microorganisms. The aim of this review is to summarize the clinical features associated with novel antibiotics with activity against ESBL- and AmpC-producing isolates.

RECENT FINDINGS

There a number of therapeutic agents with activity against ESBL and AmpC than have been introduced and approved over the past few years. Ceftazidime-avibactam and ceftolozane-tazobactam are both carbapenem sparing agents that appear interesting alternatives for treatment of serious Gram-negative infections. Other new β-lactams/ β-lactamase inhibitors (e.g. cefepime-enmetazobactam; ceftaroline fosamil-avibactam; aztreonam-avibactam and cefepime-zidebactam) as well as eravacycline, omadacycline, and plazomicin are also promising agents for treatment of ESBL- and AmpC- infections, but further clinical data are needed to establish their efficacy in comparison to carbapenems. The role of carbapenems/ β-lactamase inhibitors remains to be clarified.

SUMMARY

New therapeutic agents against ESBL- and AmpC-producing Enterobacterales have distinctive specificities and limitations that require further investigations. Future randomized clinical trials are required to define the best strategy for their use in patients with serious infections due to ESBL- and/or AmpC- infections.

Clinical Pharmacokinetics and Pharmacodynamics of Imipenem-Cilastatin/Relebactam Combination Therapy

On 16 July, 2019, the US Food and Drug Administration approved imipenem-cilastatin/relebactam (Recarbrio™) for the treatment of adults with complicated urinary tract infections and complicated intra-abdominal infections. This decision was based on substantial clinical and pre-clinical data, including rigorous pharmacokinetic and pharmacodynamic work, and is an important step forward in the management of these debilitating conditions. This article provides an overview of the body of research associated with imipenem-cilastatin/relebactam, beginning with an examination of the fundamental underpinnings of the pharmacokinetic/pharmacodynamic index. This is followed by the pharmacokinetic/pharmacodynamic work that led to the approval of this novel drug combination, including data derived from checkerboard and hollow fiber infection studies, as well as large, multi-center, phase III clinical trials known as RESTORE-IMI 1 and RESTORE-IMI 2. The article also explores how this important new antibiotic may be used to treat other infections in the years to come, including hospital-acquired bacterial pneumonia and ventilator-associated pneumonia attributed to imipenem-non-susceptible pathogens and certain atypical mycobacterial infections.

Substituted-Amidine Functionalized Monocyclic β-Lactams: Synthesis and In Vitro Antibacterial Profile

Background. Owing to the intrinsic stability against common β-lactamases and metallo-lactamases, monobactams gathered special attention in antibiotic drug development. However, so far, aztreonam is the only monobactam approved by FDA for clinical use. We designed new derivatives of aztreonam to enhance its antibacterial efficacy. Methods. We synthesized a series of monocyclic β-lactams by modifying mainly at the C3 position of azetidinone ring. NH2 group at C3 of azetidinone was attached to thiazole and thiadiazole which in turn was linked to nitrogenous heterocyclic rings via amidine moieties. We then investigated the in vitro antibacterial activities of synthesized compounds against ten bacterial strains of clinical interest in comparison to aztreonam and ceftazidime. Results. All compounds showed improved antibacterial activities against tested strains compared to reference drugs. Compounds 14d and 14e were most potent and showed the highest potency against all bacterial strains, with MIC values ranging from 0.25 µg/mL to 8 µg/mL, as compared to aztreonam (MIC 16 µg/mL to >64 µg/mL) and ceftazidime (MIC >64 µg/mL). These compounds (14d and 14e) may be valuable lead targets against multidrug-resistant Gram-negative bacteria.

In vitro Activity of Meropenem-Vaborbactam versus Other Antibiotics Against Carbapenem-Resistant Escherichia coli from Southeastern China

Purpose

This study aimed to evaluate the in vitro activity of meropenem-vaborbactam (MVB) against a collection of carbapenem-resistant Escherichia coli (CREC) isolates and to compare the activity with other antibiotics with regard to different separation sites, carbapenem-resistant mechanisms, and sequence types (STs).

Methods

A total of 58 CREC strains were used as the experimental strains from the First Affiliated Hospital of Wenzhou Medical University in southeastern China. The minimum inhibitory concentrations of MVB, ceftazidime-avibactam, and tigecycline against all the experimental strains were determined by the microdilution broth method.

Results

MVB exhibited higher antimicrobial activity (83% susceptibility) than that of other antibiotics, except for colistin and tigecycline. The susceptibility of CREC strains towards MVB varied with regard to carbapenem-resistant mechanisms and STs, especially in Klebsiella pneumoniae carbapenemase (KPC)-positive isolates and ST8 isolates.

Conclusion

MVB exhibited considerably high activity against KPC-producing and ST8 CREC isolates. It has the great potential to be an alternative for the treatment of infections caused by CREC after determining the type of carbapenemase, the susceptibility to MVB and/or STs.

Synergistic Activity and Biofilm Formation Effect of Colistin Combined with PFK-158 Against Colistin-Resistant Gram-Negative Bacteria

Purpose

The emergence of colistin resistance among Gram-negative bacteria (GNB) poses a serious public health threat. Therefore, it is necessary to enhance the antibacterial activity of colistin through the combination with other drugs. In this study, we demonstrated the synergistic activity and the possible synergy mechanism of colistin with PFK-158 against colistin-resistant GNB, including non-fermenting bacteria and Enterobacteriaceae.

Patients and Methods

Thirty-one colistin-resistant GNB, including Pseudomonas aeruginosa (n = 9), Acinetobacter baumannii (n = 5), Escherichia coli (n = 8) and Klebsiella pneumoniae (n = 9), were collected as the experimental strains and the minimum inhibitory concentrations (MICs) of colistin, other routine antimicrobial agents and PFK-158 against all strains were determined by the broth microdilution method. The synergistic activity of colistin with PFK-158 was assessed by the checkerboard assay and time-kill assay. The biofilm formation assay and scanning electron microscopy were used to demonstrate the biofilm formation effect of colistin with PFK-158 against colistin-resistant GNB.

Results

The results of the checkerboard assay showed that when colistin was used in combination with PFK-158, synergistic activity was observed against the 31 colistin-resistant GNB. The time-kill assay presented a significant killing activity of colistin with PFK-158 against the 9 colistin-resistant GNB selected randomly, including Pseudomonas aeruginosa (n = 6), Acinetobacter baumannii (n = 1), Escherichia coli (n = 1), and Klebsiella pneumoniae (n = 1). The biofilm formation assay and scanning electron microscopjihy showed that colistin with PFK-158 can effectively suppress the formation of biofilm and reduce the cell arrangement density of biofilm against most experimental strains.

Conclusion

The results of the performed experiments suggest that the combination of colistin and PFK-158 may be a potential new choice as a new antibiofilm group for the treatment of infections caused by the colistin-resistant GNB.

Curbing gastrointestinal infections by defensin fragment modifications without harming commensal microbiota

The occurrence and spread of multidrug-resistant pathogens, especially bacteria from the ESKAPE panel, increases the risk to succumb to untreatable infections. We developed a novel antimicrobial peptide, Pam-3, with antibacterial and antibiofilm properties to counter this threat. The peptide is based on an eight-amino acid carboxyl-terminal fragment of human β-defensin 1. Pam-3 exhibited prominent antimicrobial activity against multidrug-resistant ESKAPE pathogens and additionally eradicated already established biofilms in vitro, primarily by disrupting membrane integrity of its target cell. Importantly, prolonged exposure did not result in drug-resistance to Pam-3. In mouse models, Pam-3 selectively reduced acute intestinal Salmonella and established Citrobacter infections, without compromising the core microbiota, hence displaying an added benefit to traditional broad-spectrum antibiotics. In conclusion, our data support the development of defensin-derived antimicrobial agents as a novel approach to fight multidrug-resistant bacteria, where Pam-3 appears as a particularly promising microbiota-preserving candidate.

Therapeutic strategies against autophagic escape by pathogenic bacteria

Growing multidrug-resistant (MDR) strains of various infectious bacterial species are hindering research aiming to eliminate such infections. During a bacterial infection, the host response eliminates the pathogen via fusion of the endocytic vesicles with lysosomes, called xenophagy. However, MDR bacteria have evolved strategies to escape xenophagy. In this review, we propose novel therapeutics for overcoming such escape, including chimeric antibiotics, nanoformulations for the induction of autophagy in infected cells, and small interfering (si)RNA-mediated silencing of genes to inhibit the host-pathogen interaction. We also discuss the role of combinations of antibiotics showing synergy, the administrative routes of differentially capped nanoparticles (NPs), and the use of different types of nanoformulations for eliminating pathogenic bacteria from the host.

Treatment of extended-spectrum β-lactamases infections: what is the current role of new β-lactams/β-lactamase inhibitors?

PURPOSE OF REVIEW

The widespread diffusion of extended-spectrum β-lactamases (ESBLs)-producing Enterobacteriales currently represents a major threat for public health worldwide. Carbapenems are currently considered the first-line choice for serious ESBL infections. However, the dramatic global increase in ESBL prevalence has led to a significant overuse of carbapenems that has promoted the selection and spread of carbapenemases, which might further prejudicated our ability to treat infections due to multidrug-resistant pathogens. Therefore, strategies to limit the use of carbapenems should be implemented.

RECENT FINDINGS

Although piperacillin-tazobactam should no longer be considered an alternative to carbapenems for definitive treatment of bloodstream infections due to ESBL-producing strains, it might still represent an alternative for step-down therapy or for low-to-moderate severity infection originating from urinary or biliary sources and when piperacillin-tazobactam minimum inhibitory concentration of 4 mg/l or less. Ceftazidime-avibactam and ceftolozane-tazobactam are both carbapenem sparing agents that appear interesting alternatives for treatment of serious ESBL infections. New β-lactams/β-lactamase inhibitors (BL/BLI), including cefepime-enmetazobactam, ceftaroline fosamil-avibactam, aztreonam-avibactam and cefepime-zidebactam, are also promising agents for treatment of ESBL infections, but further clinical data are needed to establish their efficacy relative to carbapenems. The role of carbapenems/β-lactamase inhibitors remain to be clarified.

SUMMARY

New BL/BLI have distinctive specificities and limitations that require further investigations. Future randomized clinical trials are required to define the best strategy for their administering for ESBL infections.

The role of new β-lactamase inhibitors in gram-negative infections

PURPOSE OF REVIEW

In recent years, traditional β-lactams have dramatically reduced their effectiveness against gram-negative bacteria mainly because of their ability to express multiple β-lactamase or carabapenemases that are not hydrolyzed by the old β-lactam inhibitors (BLIs) such as clavulanic acid, tazobactam, and sulbactam. New BLIs molecules have been developed to face the need of compounds that are active against multidrug or pandrug resistant gram-negative pathogens. The aim of this review is to summarize the new generation of BLIs and β-lactams combinations.

RECENT FINDINGS

A number of new molecules with activity against Ambler class A (e.g., extended-spectrum β-lactamases, serine carbapenemases), class C (e.g., AmpC), or class D (e.g., oxacillinase-48) have been recently approved in combination with old β-lactams for the treatment of multidrug-resistant bacteria, and other agents are under investigation. These new compounds include diazabicyclooctanones non-β-lactam inhibitors (e.g., avibactam, relebactam, nacubactam) and boronic acid inhibitors (e.g., vaborbactam).

SUMMARY

Newly approved and investigational new BLIs are expected to offer many advantages for the management of patients with multidrug-resistant gram-negative pathogens. Promising characteristics of new compounds include high activity against multi drug resistance gram-negative bacteria and a favorable safety profile.

In Vitro Activity of Ceftazidime-Avibactam Alone and in Combination with Amikacin Against Colistin-Resistant Gram-Negative Pathogens

Aims: Colistin became the critical treatment option for multidrug-resistant Gram-negative bacteria (GNB); however, resistance to colistin is increasingly being reported among clinical isolates. New therapy strategies should be considered nowadays. The aim of this study was to investigate the in vitro activity of a novel β-lactam/β-lactamases inhibitor ceftazidime-avibactam (CZA) alone and in combination with amikacin against colistin-resistant Gram-negative pathogens. Results: Among all the colistin-resistant GNB strains, 30.4% (21/69) were resistant to CZA, which was similar to the resistance rate of 25.4% (35/138) in colistin-susceptible strains (p > 0.05), displaying a relatively lower resistance rate compared with other antimicrobial agents (except amikacin). A majority of CZA-resistant GNB isolates (33/56) produced NDM carbapenemase. The fractional inhibitory concentration index method revealed synergistic (47.6%, 10/21) or additive (52.4%, 11/21) effects of CZA in combination with amikacin against colistin- and CZA-resistant GNB isolates, wherein the synergistic activity was found against all tested Klebsiella pneumoniae isolates (four) and Pseudomonas aeruginosa isolates (two). The time-killing curve assay verified the synergistic activity of CZA and amikacin in K. pneumoniae (FK2778) and P. aeruginosa (TL2294). The susceptible breakpoint index values showed that CZA in combination with amikacin reduced the MIC to less than the susceptibility breakpoint among 71.4% (15/21) of all tested strains. Conclusion: CZA may be a new alternative for colistin-resistant Gram-negative infections and pending clinical studies combining CZA with amikacin should be considered against these pathogens, particularly for K. pneumoniae and P. aeruginosa.

Innovaciones en la terapia antimicrobiana

La resistencia microbiana ha llevado a la búsqueda de innovadoras alternativas para su contención y dentro de las más promisorias están el uso de péptidos sintéticos, no sólo por sus características intrínsecas antimicrobianas, sino por  las interacciones sinérgicas y antagónicas que presenta con otros mediadores inmunológicos. Estas propiedades han permitido crear péptidos sintéticos reguladores de defensa innata que representan un nuevo enfoque inmunomodulador para el tratamiento de infecciones; sin embargo, sólo los diseñados con alto score antimicrobiano, han demostrado eficacia en estudios clínicos de Fase 3. Debido a su amplio espectro de actividad, un único péptido puede actuar contra bacterias Gram negativas, Gram positivas, hongos, e incluso virus y parásitos, aumentando el interés por investigar estas dinámicas moléculas.  Por otra parte, se encuentra el sistema CRISPR, para la edición de genomas bacterianos, permitirá reducir su actividad virulenta y diseñar antimicrobianos basados en nucleasas CRISPR-Cas 9 programables contra dianas específicas, las que representan un promisorio camino en el estudio de nuevas alternativas con alto potencial para eliminar la resistencia a antibióticos de bacterias altamente patógenas. Asimismo, se aborda la terapia con fagos, referida a la accion de virus que infectan bacterias, usados solos o en cocteles para aumentar el espectro de acción de estos, aprovechando su abundacia en la naturaleza, ya que se ha considerado que cada bacteria tiene un virus específico que podría emplearse como potente agente antibacteriano. Finalmente,  mientras se usen como principal medio de contención solo tratamientos convencionales antimicrobianos, incluso de manera oportuna y acertada, la microevolución en las bacterias se asegurará de seguir su curs

Fragmentation of Human Neutrophil α-Defensin 4 to Combat Multidrug Resistant Bacteria

The occurrence and spread of multidrug-resistant bacteria is a prominent health concern. To curb this urgent threat, new innovative strategies pursuing novel antimicrobial agents are of the utmost importance. Here, we unleashed the antimicrobial activity of human neutrophil peptide-4 (HNP-4) by tryptic digestion. We identified a single 11 amino acid long fragment (HNP-4_{1 - 11}) with remarkable antimicrobial potential, exceeding that of the full length peptide on both mass and molar levels. Importantly, HNP-4_{1 - 11} was equally bactericidal against multidrug-resistant and non-resistant strains; a potency that was further enhanced by N- and C-terminus modifications (acetylation and amidation, respectively). These observations, combined with negligible cytotoxicity not exceeding that of the full length peptide, presents proteolytic digestion of innate host-defense-peptides as a novel strategy to overcome the current health crisis related to antibiotic-resistant bacteria.

In Vitro Activity of Eravacycline against Gram-Positive Bacteria Isolated in Clinical Laboratories Worldwide from 2013 to 2017

Eravacycline is a novel, fully synthetic fluorocycline antibiotic being developed for the treatment of serious infections, including those caused by resistant Gram-positive pathogens. Here, we evaluated the in vitro activities of eravacycline and comparator antimicrobial agents against a recent global collection of frequently encountered clinical isolates of Gram-positive bacteria. The CLSI broth microdilution method was used to determine in vitro MIC data for isolates of Enterococcus spp. (n = 2,807), Staphylococcus spp. (n = 4,331), and Streptococcus spp. (n = 3,373) isolated primarily from respiratory, intra-abdominal, urinary, and skin specimens by clinical laboratories in 37 countries on three continents from 2013 to 2017. Susceptibilities were interpreted using both CLSI and EUCAST breakpoints. There were no substantive differences (a >1-doubling-dilution increase or decrease) in eravacycline MIC₉₀ values for different species/organism groups over time or by region. Eravacycline showed MIC₅₀ and MIC₉₀ results of 0.06 and 0.12 μg/ml, respectively, when tested against Staphylococcus aureus, regardless of methicillin susceptibility. The MIC₉₀ values of eravacycline for Staphylococcus epidermidis and Staphylococcus haemolyticus were equal (0.5 μg/ml). The eravacycline MIC₉₀s for Enterococcus faecalis and Enterococcus faecium were 0.06 μg/ml and were within 1 doubling dilution regardless of the vancomycin susceptibility profile. Eravacycline exhibited MIC₉₀ results of ≤0.06 μg/ml when tested against Streptococcus pneumoniae and beta-hemolytic and viridans group streptococcal isolates. In this surveillance study, eravacycline demonstrated potent in vitro activity against frequently isolated clinical isolates of Gram-positive bacteria (Enterococcus, Staphylococcus, and Streptococcus spp.), including isolates collected over a 5-year period (2013 to 2017), underscoring its potential benefit in the treatment of infections caused by common Gram-positive pathogens.

In Vitro Activity of Eravacycline against Gram-Negative Bacilli Isolated in Clinical Laboratories Worldwide from 2013 to 2017

Eravacycline is a novel, fully synthetic fluorocycline antibiotic developed for the treatment of serious infections, including those caused by multidrug-resistant (MDR) pathogens. Here, we evaluated the in vitro activities of eravacycline and comparator antimicrobial agents against a global collection of frequently encountered clinical isolates of Gram-negative bacilli. The CLSI broth microdilution method was used to determine MIC data for isolates of Enterobacterales (n = 13,983), Acinetobacter baumannii (n = 2,097), Pseudomonas aeruginosa (n = 1,647), and Stenotrophomonas maltophilia (n = 1,210) isolated primarily from respiratory, intra-abdominal, and urinary specimens by clinical laboratories in 36 countries from 2013 to 2017. Susceptibilities were interpreted using both CLSI and EUCAST breakpoints. Multidrug-resistant (MDR) isolates were defined by resistance to agents from ≥3 different antimicrobial classes. The MIC₉₀s ranged from 0.25 to 1 μg/ml for Enterobacteriaceae and were 1 μg/ml for A. baumannii and 2 μg/ml for S. maltophilia, Proteus mirabilis, and Serratia marcescens Eravacycline's potency was up to 4-fold greater than that of tigecycline against genera/species of Enterobacterales, A. baumannii, and S. maltophilia The MIC₉₀s for five of six individual genera/species of Enterobacterales and A. baumannii were within 2-fold of the MIC₉₀s for their respective subsets of MDR isolates, while the MDR subpopulation of Klebsiella spp. demonstrated 4-fold higher MIC₉₀s. Eravacycline demonstrated potent in vitro activity against the majority of clinical isolates of Gram-negative bacilli, including MDR isolates, collected over a 5-year period. This study further underscores the potential benefit of eravacycline in the treatment of infections caused by MDR Gram-negative pathogens.

Design, synthesis and biological evaluation of novel DNA gyrase inhibitors and their siderophore mimic conjugates

Bacterial DNA gyrase is an important target for the development of novel antibacterial drugs, which are urgently needed because of high level of antibiotic resistance worldwide. We designed and synthesized new 4,5,6,7-tetrahydrobenzo[d]thiazole-based DNA gyrase B inhibitors and their conjugates with siderophore mimics, which were introduced to increase the uptake of inhibitors into the bacterial cytoplasm. The most potent conjugate 34 had an IC₅₀ of 58 nM against Escherichia coli DNA gyrase and displayed MIC of 14 µg/mL against E. coli ΔtolC strain. Only minor improvements in the antibacterial activities against wild-type E. coli in low-iron conditions were seen for DNA gyrase inhibitor - siderophore mimic conjugates.

New Drugs for Multidrug-Resistant Gram-Negative Organisms: Time for Stewardship

A gradual rise in drug-resistant trends among Gram-negative organisms, especially carbapenem-resistant (CR) Enterobacteriaceae (CRE), CR-Pseudomonas aeruginosa, and extensively-drug-resistant (XDR) Acinetobacter baumannii, poses an enormous threat to healthcare systems worldwide. In the last decade, many pharmaceutical companies have devoted enormous resources to the development of new potent antibiotics against XDR Gram-negative pathogens, particularly CRE. Some of these novel antibiotics against CRE strains are β-lactam/β-lactamase-inhibitor combination agents, while others belong to the non-β-lactam class. Most of these antibiotics display good in vitro activity against the producers of Ambler class A, C, and D β-lactamase, although avibactam and vaborbactam are not active in vitro against metallo-β-lactamase (MβL) enzymes. Nevertheless, in vitro efficacy against the producers of some or all class B enzymes (New Delhi MβL, Verona integron-encoded MβL, etc) has been shown with cefepime-zidebactam, aztreonam-avibactam, VNRX-5133, cefiderocol, plazomicin, and eravacycline. As of Feburary 2019, drugs approved for treatment of some CRE-related infections by the US Food and Drug Administration included ceftazidime-avibactam, meropenem-vaborbactam, plazomicin, and eravacycline. Although active against extended-spectrum and AmpC β-lactamase-producing Enterobacteriaceae, delafloxacin does not show in vitro activity against CRE. Murepavadin is shown to be specifically active against CR- and colistin-resistant P. aeruginosa strains. Despite successful development of novel antibiotics, strict implementation of an antibiotic stewardship policy in combination with the use of well-established phenotypic tests and novel multiplex PCR methods for detection of the most commonly encountered β-lactamases/carbapenemases in hospitals is important for prescribing effective antibiotics against CRE and decreasing the resistance burden due to CRE.

Optimizing therapy in carbapenem-resistant Enterobacteriaceae infections

PURPOSE OF REVIEW

In the absence of randomized clinical trial data, questions remain regarding the optimal treatment of carbapenem-resistant Enterobacteriaceae (CRE) infections. CRE have historically been susceptible to polymyxins, tigecycline or aminoglycosides (mostly gentamicin), and these antibiotics have long been considered the drugs of choice for CRE infections, although varying rates of resistance to all have been reported. This review looks at data from clinical studies assessing the outcomes of CRE infections treated with different antibiotic regimens.

RECENT FINDINGS

The recently approved fixed-dose combination agent, ceftazidime-avibactam (CAZ-AVI), is active against KPC and OXA-48-producing Enterobacteriaceae. The limited clinical data available on CAZ-AVI indicate that it is associated with survival benefits relative to other commonly used regimens, although development of resistance is a concern. New drugs active against CRE isolates (including the recently approved meropenem-vaborbactam) are in different stages of development.

SUMMARY

CAZ-AVI and meropenem-vaborbactam seem destined to become the backbone of target therapy for high-risk patients with severe infections caused by susceptible CRE strains. However, empirical therapy should be based on risk factors to be defined in the near future, whereas the necessity of combinations with CAZ-AVI requires further studies. Polymyxins are still important options for low-risk patients with susceptible CRE infections, but also for high-risk patients in regions where metallo-β-lactamase-producing CRE predominate because CAZ-AVI and meropenem-vaborbactam are both ineffective against these strains.

Proline-rich antimicrobial peptides show a long-lasting post-antibiotic effect on Enterobacteriaceae and Pseudomonas aeruginosa

Background

Proline-rich antimicrobial peptides (PrAMPs) represent a promising class of potential therapeutics to treat multiresistant infections. They inhibit bacterial protein translation at the 70S ribosome by either blocking the peptide-exit tunnel (oncocin type) or trapping release factors (apidaecin type).

Objectives

Besides direct concentration-dependent antibacterial effects, the post-antibiotic effect (PAE) is the second most important criterion of antimicrobial pharmacodynamics to be determined in vitro. Here, PAEs of 10 PrAMPs and three antibiotics against three Escherichia coli strains, Klebsiella pneumoniae ATCC 10031 and Pseudomonas aeruginosa ATCC 27853 were studied after 1 h of exposure.

Methods

A robust high-throughput screening to determine PAEs was established, i.e. liquid handling by a 96-channel pipetting system and continuous incubation and absorbance measurement in a microplate reader.

Results

Prolonged PAEs (≥4 h) were detected for all peptides at their MIC values against all strains; PAEs were even >10 h for Api88, Api137, Bac7(1-60) and A3-APO. The PAEs increased further at 4 × MIC. Aminoglycosides gentamicin and kanamycin usually showed lower PAEs (≤4 h) at MIC, but PAEs increased to > 10 h at 4 × MIC. Bacteriostatic chloramphenicol exhibited the shortest PAEs (<4 h).

Conclusions

The PAEs of PrAMPs studied against Enterobacteriaceae and P. aeruginosa for the first time were typically 4-fold stronger than for conventional antibiotics. Together with their fast and irreversible uptake by bacteria, the observed prolonged PAE of PrAMPs helps to explain their high in vivo efficacy despite unfavourable pharmacokinetics.

A critical review of HPLC-based analytical methods for quantification of Linezolid

Linezolid is a synthetic antimicrobial agent belonging to the oxazolidinone class. Since its approval in the year 2000 until now, linezolid remains the main representative drug for the oxazolidinone class of drugs, which is used in therapy due to its unique mode of action, which involves inhibition of protein synthesis. As linezolid holds great importance in antimicrobial therapy, it is necessary to compile the various analytical methods that have been reported in the literature for its analysis. Analytical techniques used for pharmaceutical analyses and therapeutic drug monitoring play an important role in comprehending the aspects regarding bioavailability, bioequivalence, and therapeutic monitoring during patient follow-ups. Even though linezolid has had the approval for clinical use for more than 18 years now, most of the analytical methods for its determination reported in the scientific literature are the ones which utilize HPLC. Therefore, the present review provides a summary of the HPLC-based methods used in the determination and quantification of linezolid in different matrices since the time of its discovery.

β-Lactamases and β-Lactamase Inhibitors in the 21st Century

The β-lactams retain a central place in the antibacterial armamentarium. In Gram-negative bacteria, β-lactamase enzymes that hydrolyze the amide bond of the four-membered β-lactam ring are the primary resistance mechanism, with multiple enzymes disseminating on mobile genetic elements across opportunistic pathogens such as Enterobacteriaceae (e.g., Escherichia coli) and non-fermenting organisms (e.g., Pseudomonas aeruginosa). β-Lactamases divide into four classes; the active-site serine β-lactamases (classes A, C and D) and the zinc-dependent or metallo-β-lactamases (MBLs; class B). Here we review recent advances in mechanistic understanding of each class, focusing upon how growing numbers of crystal structures, in particular for β-lactam complexes, and methods such as neutron diffraction and molecular simulations, have improved understanding of the biochemistry of β-lactam breakdown. A second focus is β-lactamase interactions with carbapenems, as carbapenem-resistant bacteria are of grave clinical concern and carbapenem-hydrolyzing enzymes such as KPC (class A) NDM (class B) and OXA-48 (class D) are proliferating worldwide. An overview is provided of the changing landscape of β-lactamase inhibitors, exemplified by the introduction to the clinic of combinations of β-lactams with diazabicyclooctanone and cyclic boronate serine β-lactamase inhibitors, and of progress and strategies toward clinically useful MBL inhibitors. Despite the long history of β-lactamase research, we contend that issues including continuing unresolved questions around mechanism; opportunities afforded by new technologies such as serial femtosecond crystallography; the need for new inhibitors, particularly for MBLs; the likely impact of new β-lactam:inhibitor combinations and the continuing clinical importance of β-lactams mean that this remains a rewarding research area.

The Anthelmintic Drug Niclosamide Synergizes with Colistin and Reverses Colistin Resistance in Gram-Negative Bacilli

There is an urgent need for new therapies to overcome antimicrobial resistance especially in Gram-negative bacilli (GNB). Repurposing old U.S. Food and Drug Administration-approved drugs as complementary agents to existing antibiotics in a synergistic combination presents an attractive strategy. Here, we demonstrate that the anthelmintic drug niclosamide selectively synergized with the lipopeptide antibiotic colistin against colistin-susceptible but more importantly against colistin-resistant GNB, including clinical isolates that harbor the mcr-1 gene. Breakpoints for colistin susceptibility in resistant Gram-negative bacilli were reached in the presence of 1 μg/ml (3 μM) niclosamide. Reversal of colistin resistance was also observed in combinations of niclosamide and polymyxin B. Enhanced bacterial killing was evident for the combination, in comparison to colistin monotherapy, against resistant Pseudomonas aeruginosa, Acinetobacter baumannii, Klebsiella pneumoniae, Escherichia coli, and Enterobacter cloacae Accumulating evidence in the literature, along with our results, strongly suggests the potential for the combination of niclosamide and colistin to treat colistin-resistant Gram-negative bacillary infections. Our finding is significant since colistin is an antibiotic of last resort for multidrug-resistant Gram-negative bacterial infections that are nonresponsive to conventional treatments. With the recent global dissemination of plasmid-encoded colistin resistance, the addition of niclosamide to colistin therapy may hold the key to overcome colistin resistance.

In-Vitro Evaluation of Different Antimicrobial Combinations with and without Colistin Against Carbapenem-Resistant Acinetobacter Baumannii

Carbapenem-resistant Acinetobacter baumannii (CR-Ab) infections are associated with high morbidity and mortality. The aim of the study was to evaluate the in-vitro activity of different antimicrobial combinations (with and without colistin, COL) against clinical isolates of CR-Ab collected from patients with CR-Ab infection, including unconventional combinations such as COL + VANcomycin (VAN) and COL + rifampin (RIF). CR-Ab strains were collected from hospitalized patients at Sapienza University of Rome. Antimicrobial susceptibility patterns were determined throughout MIC50/90s whereas the synergistic activity was evaluated by qualitative (i.e., checkerboard) and quantitative (i.e., killing studies) methods. All the strains were found oxacillinase (OXA) producers and tigecycline (TIG) sensitive whereas 2 strains were resistant to COL. Application of the checkerboard method indicated complete synergism in COL combinations at different extension: 21.4%, 57.1%, 42.8%, 35.7% for COL + meropenem (MEM), COL + RIF, COL + VAN and COL + TIG, respectively, with the non-conventional combinations COL + VAN and COL + RIF exhibiting the highest rate of synergism. Regarding COL-free combination, complete synergism was observed in 35.7% of the strains for MEM + TIG. Killing studies showed that the combinations COL + MEM, COL + TIG and MEM + TIG were bactericidal and synergistic against both colistin-sensitive and low colistin-resistant strains whereas only the combinations COL + VAN and COL + RIF showed an early and durable bactericidal activity against all the tested strains, with absence of growth at 24 h. This study demonstrated that COL-based combinations lead to a high level of synergic and bactericidal activity, especially COL + VAN and COL + RIF, even in the presence of high level of COL resistance.

Future Challenges in Pediatric and Neonatal Sepsis: Emerging Pathogens and Antimicrobial Resistance

The incidence of severe infections caused by multidrug-resistant (MDR) pathogens is currently rising worldwide, and increasing numbers of neonates and children with serious bloodstream infections due to resistant bacteria are being reported. Severe sepsis and septic shock due to gram-negative bacteria represent a significant cause of morbidity and mortality, and contribute to high health care costs. Antimicrobial resistance among Enterobacteriaceae represents a major problem in both health care-associated and community-acquired infections, with extended-spectrum β-lactamases (ESBLs) and carbapenem-resistant Enterobacteriaceae (CRE) now presenting the main threat. These infections in adult populations have been associated with poor clinical outcomes, but very limited data have been published so far about risk factors and clinical outcome of ESBL-associated and CRE sepsis in the pediatric population. The treatment of these infections in neonates and children is particularly challenging due to the limited number of available effective antimicrobials. Evidence-based use of new and older antibiotics based on both strategic and regulatory clinical trials is paramount to improve management of these severe infections in neonates and children.

Clinical relevance of in vitro synergistic activity of antibiotics for multidrug-resistant Gram-negative infections: A systematic review

OBJECTIVES

The aim of this review was to investigate the outcomes of patients infected with multidrug-resistant (MDR) or extensively drug-resistant (XDR) Gram-negative bacteria following synergy-guided antibiotic combination therapy (SGACT).

METHODS

A systematic review of PubMed and Scopus databases was performed. Published studies of any design reporting outcomes of patients with MDR Gram-negative bacteria treated with SGACT were included. Two reviewers independently assessed the relevancy and quality of the retrieved articles and extracted the available data.

RESULTS

Nineteen reports (530 patients) were included. Eleven case reports/series described 26 cases of systemic infection due to MDR Gram-negative bacteria treated with SGACT. Five deaths were reported, two of which were attributed to the infection. Six studies (including one randomised controlled trial) provided comparative data for patients treated with SGACT and those treated with unguided combination therapy (UCT) or active monotherapy. In the pooled analysis of unadjusted data from these studies (504 patients), there was no difference between SGACT and UCT or monotherapy (OR=0.47, 95% CI 0.21-1.04; I²=52%). Analysis of adjusted data showed that SGACT was significantly associated with survival (OR=0.44, 95% CI 0.20-0.98; I²=54%).

CONCLUSION

These limited but promising findings warrant further investigation of SGACT in the outcome of patients with MDR Gram-negative infections in well-designed trials.

High Potency of Melaleuca alternifolia Essential Oil against Multi-Drug Resistant Gram-Negative Bacteria and Methicillin-Resistant Staphylococcus aureus

Purpose: Herein, an extended investigation of Tea tree oil (TTO) against a number of multi-drug resistant (MDR) microorganisms in liquid and vapor phases is reported. Methods: The activity of TTO was tested against methicillin-sensitive Staphylococcus aureus (MSSA), Escherichia coli, and clinical strains of methicillin-resistant S. aureus (MRSA), extended-spectrum beta lactamases producer carbapenem-sensitive Klebsiella pneumoniae (ESBL-CS-Kp), carbapenem-resistant K. pneumoniae (CR-Kp), Acinetobacter baumannii (CR-Ab), and Pseudomonas aeruginosa (CR-Pa). Minimal inhibitory/bactericidal concentrations (MIC/MBCs) and synergistic activity between TTO and different antimicrobials were determined. In the vapor assay (VP), TTO-impregnated discs were placed on the lid of a petri dish and incubated for 24 h at 37 °C. Results: TTO showed a potent bactericidal activity against all the tested microorganisms. TTO in combination with each reference antimicrobial showed a high level of synergism at sub-inhibitory concentrations, particularly with oxacillin (OXA) against MRSA. The VP assay showed high activity of TTO against CR-Ab. Conclusion: Evaluation of in-vitro activity clearly indicated TTO as a potential effective antimicrobial treatment either alone or in association with known drugs against MDR. Therefore, TTO could represent the basis for a possible role in non-conventional regimens against S. aureus and Gram-negative MDR. TTO in VP might represent a promising option for local therapy of pneumonia caused by CR-Ab.

Synergy effect of meropenem-based combinations against Acinetobacter baumannii: a systematic review and meta-analysis

PURPOSE

The main objective of our meta-analysis was to examine the in vitro synergistic effect of meropenem-based combination therapies against Acinetobacter baumannii through a systematic review of the existing literature.

METHODS

An extensive search was performed with no restrictions on date of publication, language, and publication type. Our study evaluated the main conclusions drawn from various studies describing the synergistic activity of combination therapies in vitro.

RESULTS

In this review, 56 published studies were included. Our report included data on 20 types of antibiotics combined with meropenem in 1,228 Acinetobacter baumannii isolates. In time-kill studies, meropenem combined with polymyxin B and rifampicin showed synergy rates of 98.3% (95% CI, 83.7%-100.0%) and 89.4% (95% CI, 57.2%-100.0%), respectively, for Acinetobacter baumannii, modest synergy rates were found for meropenem combined with several antibiotics such as colistin and sulbactam, and no synergy effect was displayed in the combination of meropenem and ciprofloxacin, whereas in checkerboard method, the synergy rates of polymyxin B and rifampicin were 37.0% (95% CI, 0.00%-100.0%) and 56.3% (95% CI, 8.7%-97.8%), respectively.

CONCLUSION

We found that time-kill studies generally identified the greatest synergy, while checkerboard and Etest methods yielded relatively poor synergy rates. Further well-designed in vivo studies should be carried out to confirm these findings.

Improved Synthesis of Yt-14, A Potent Antibiotic to Multidrug-Resistant Strains

A new practical synthetic approach produced clinical drug candidate YT-14, improving the overall yield from 1.3% to 13.8%. Compared with the previous route, the new route is two steps shorter and all of the steps involve purifications without column chromatography. The advantages of this procedure include simple operating conditions and higher yields.

Efficacy of Human-Simulated Exposures of Ceftolozane-Tazobactam Alone and in Combination with Amikacin or Colistin against Multidrug-Resistant Pseudomonas aeruginosa in an In Vitro Pharmacodynamic Model

Combination therapy is an attractive option for the treatment of multidrug-resistant (MDR) Pseudomonas aeruginosa infections; however, limited data are available on combinations with ceftolozane-tazobactam (C-T). The in vitro pharmacodynamic chemostat model was employed to compare human-simulated exposures of C-T at 3 g every 8 h alone or in combination with amikacin at 25 mg/kg of body weight daily or colistin at 360 mg daily against four MDR P. aeruginosa isolates. C-T alone resulted in 24-h changes in the number of CFU of -0.02 ± 0.21, -1.81 ± 0.55, -1.44 ± 0.40, and +0.62 ± 0.05 log₁₀ CFU/ml against isolates with C-T MICs of 4, 4, 8, and 16 μg/ml, respectively. Amikacin and colistin monotherapy displayed various results. The addition of amikacin to C-T resulted in -2.00 ± 0.23 (P < 0.001, additive)-, -1.50 ± 0.83 (P = 0.687, indifferent)-, -2.84 ± 0.08 (P = 0.079, indifferent)-, and -2.67 ± 0.54 (P < 0.001, synergy)-log₁₀ CFU/ml reductions, respectively. The addition of colistin to C-T resulted in -3.02 ± 0.22 (P < 0.001, additive)-, -3.21 ± 0.24 (P > 0.05, indifferent)-, -4.6 ± 0.11 (P = 0.002, synergy)-, and -3.01 ± 0.28 (P < 0.001, synergy)-log₁₀ CFU/ml reductions, respectively, against the MDR P. aeruginosa isolates with these MICs. Greater overall reductions in bacterial burden, including additive or synergistic interactions at 24 h, with C-T plus amikacin or colistin were observed against 3 out of 4 MDR P. aeruginosa strains tested, particularly those strains that were intermediate or resistant to C-T. Further studies assessing combination regimens containing C-T against MDR P. aeruginosa are warranted.

Activity of TP-6076 against carbapenem-resistant Acinetobacter baumannii isolates collected from inpatients in Greek hospitals

TP-6076 is a synthetic fluorocycline antibiotic that inhibits bacterial protein synthesis. In this study, carbapenem-resistant Acinetobacter baumannii clinical isolates from 13 Greek hospitals were tested for susceptibility to TP-6076 and comparator antibiotics. Broth microdilution plates were used to determine minimum inhibitory concentrations (MICs). A total of 121 non-duplicate A. baumannii isolates were tested. The MIC₅₀ and MIC₉₀ values of TP-6076 were 0.03 mg/L and 0.06 mg/L, respectively. Tigecycline was the second most active antibiotic (MIC₉₀, 2 mg/L), followed by minocycline (MIC₉₀, 8 mg/L). TP-6076 exhibited MIC₉₀ values that were one dilution lower against tigecycline- and minocycline-susceptible isolates than against resistant isolates. There was no difference in the MIC₉₀ value for colistin-susceptible or -resistant isolates. In conclusion, TP-6076 exhibited greater antimicrobial activity in vitro against carbapenem-resistant A. baumannii than comparator antibiotics.

Antibiotic Hybrids: the Next Generation of Agents and Adjuvants against Gram-Negative Pathogens?

The global incidence of drug-resistant Gram-negative bacillary infections has been increasing, and there is a dire need to develop novel strategies to overcome this problem. Intrinsic resistance in Gram-negative bacteria, such as their protective outer membrane and constitutively overexpressed efflux pumps, is a major survival weapon that renders them refractory to current antibiotics. Several potential avenues to overcome this problem have been at the heart of antibiotic drug discovery in the past few decades. We review some of these strategies, with emphasis on antibiotic hybrids either as stand-alone antibacterial agents or as adjuvants that potentiate a primary antibiotic in Gram-negative bacteria. Antibiotic hybrid is defined in this review as a synthetic construct of two or more pharmacophores belonging to an established agent known to elicit a desired antimicrobial effect. The concepts, advances, and challenges of antibiotic hybrids are elaborated in this article. Moreover, we discuss several antibiotic hybrids that were or are in clinical evaluation. Mechanistic insights into how tobramycin-based antibiotic hybrids are able to potentiate legacy antibiotics in multidrug-resistant Gram-negative bacilli are also highlighted. Antibiotic hybrids indeed have a promising future as a therapeutic strategy to overcome drug resistance in Gram-negative pathogens and/or expand the usefulness of our current antibiotic arsenal.

Resistance Trends and Treatment Options in Gram-Negative Ventilator-Associated Pneumonia

PURPOSE OF REVIEW

Hospital-acquired and ventilator-associated pneumonia (VAP) are frequent causes of infection among critically ill patients. VAP is the most common hospital-acquired bacterial infection among mechanically ventilated patients. Unfortunately, many of the nosocomial Gram-negative bacteria that cause VAP are increasingly difficult to treat. Additionally, the evolution and dissemination of multi- and pan-drug resistant strains leave clinicians with few treatment options. VAP patients represent a dynamic population at risk for antibiotic failure and under-dosing due to altered antibiotic pharmacokinetic parameters. Since few antibiotic agents have been approved within the last 15 years, and no new agents specifically targeting VAP have been approved to date, it is anticipated that this problem will worsen. Given the public health crisis posed by resistant Gram-negative bacteria, it is essential to establish a firm understanding of the current epidemiology of VAP, the changing trends in Gram-negative resistance in VAP, and the current issues in drug development for Gram-negative bacteria that cause VAP.

RECENT FINDINGS

Rapid identification technologies and phenotypic methods, new therapeutic strategies, and novel treatment paradigms have evolved in an attempt to improve treatment outcomes for VAP; however, clinical data supporting alternative treatment strategies and adjunctive therapies remain sparse. Importantly, new classes of antimicrobials, novel virulence factor inhibitors, and beta-lactam/beta-lactamase inhibitor combinations are currently in development. Conscientious stewardship of new and emerging therapeutic agents will be needed to ensure they remain effective well into the future.

In vitro activity of eravacycline against 2213 Gram-negative and 2424 Gram-positive bacterial pathogens isolated in Canadian hospital laboratories: CANWARD surveillance study 2014-2015

Gram-negative (n=2213) and Gram-positive (n=2424) pathogens isolated from patients in 13 Canadian hospitals in 2014 and 2015 were tested for in vitro susceptibility to eravacycline and comparators using the Clinical and Laboratory Standards Institute broth microdilution method. The concentration of eravacycline inhibiting 90% of isolates (MIC₉₀) ranged from 0.5 to 2μg/mL for 9 species of Enterobacteriaceae tested (n=2067). Eravacycline activity was largely unaffected by extended-spectrum β-lactamase phenotypes in Escherichia coli (n=141) and Klebsiella pneumoniae (n=21). Eravacycline was active against Acinetobacter baumannii (n=28; MIC₉₀, 0.5μg/mL) and Stenotrophomonas maltophilia (n=118; MIC₉₀, 4μg/mL). Eravacycline MIC₉₀ for staphylococci (n=1653), enterococci (n=289), and streptococci (n=482) ranged from 0.12 to 0.25, 0.06 to 0.12, and 0.015 to 0.06μg/mL, respectively. Eravacycline's potency was equivalent to or 2- to 4-fold greater than tigecycline against Enterobacteriaceae and Gram-positive cocci tested. Eravacycline demonstrates promising activity against recent clinical Gram-negative and Gram-positive bacteria, including multidrug-resistant pathogens.

Antimicrobials for the treatment of drug-resistant Acinetobacter baumannii pneumonia in critically ill patients: a systemic review and Bayesian network meta-analysis

BACKGROUND

An optimal therapy for the treatment of pneumonia caused by drug-resistant Acinetobacter baumannii remains unclear. This study aims to compare various antimicrobial strategies and to determine the most effective therapy for pneumonia using a network meta-analysis.

METHODS

Systematic search and quality assessment were performed to select eligible studies reporting one of the following outcomes: all-cause mortality, clinical cure, and microbiological eradication. The primary outcome was all-cause mortality. A network meta-analysis was conducted with a Bayesian approach. Antimicrobial treatments were ranked based on surface under the cumulative ranking curve (SUCRA) value along with estimated median outcome rate and corresponding 95% credible intervals (CrIs). Two treatments were considered significantly different if a posterior probability of superiority (P) was greater than 97.5%.

RESULTS

Twenty-three studies evaluating 15 antimicrobial treatments were included. Intravenous colistin monotherapy (IV COL) was selected as a common comparator, serving as a bridge for developing the network. Five treatments ranked higher than IV COL (SUCRA, 57.1%; median all-cause mortality 0.45, 95% CrI 0.41-0.48) for reducing all-cause mortality: sulbactam monotherapy (SUL, 100.0%; 0.18, 0.04-0.42), high-dose SUL (HD SUL, 85.7%; 0.31, 0.07-0.71), fosfomycin plus IV COL (FOS + IV COL, 78.6%; 0.34, 0.19-0.54), inhaled COL plus IV COL (IH COL + IV COL, 71.4%; 0.39, 0.32-0.46), and high-dose tigecycline (HD TIG, 71.4%; 0.39, 0.16-0.67). Those five treatments also ranked higher than IV COL (SUCRA, 45.5%) for improving clinical cure (72.7%, 72.7%, 63.6%, 81.8%, and 90.9%, respectively). Among the five treatments, SUL (P = 98.1%) and IH COL + IV COL (P = 99.9%) were significantly superior to IV COL for patient survival and clinical cure, respectively. In terms of microbiological eradication, FOS + IV COL (P = 99.8%) and SUL (P = 98.9%) were significantly superior to IV COL.

CONCLUSIONS

This Bayesian network meta-analysis demonstrated the comparative effectiveness of fifteen antimicrobial treatments for drug-resistant A. baumannii pneumonia in critically ill patients. For survival benefit, SUL appears to be the best treatment followed by HD SUL, FOS + IV COL, IH COL + IV COL, HD TIG, and IV COL therapy, in numerical order.

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.