Activities of NXL104 combinations with ceftazidime and aztreonam against carbapenemase-Producing Enterobacteriaceae

In vitro activity of ceftazidime/avibactam against isolates of Pseudomonas aeruginosa collected in European countries: INFORM global surveillance 2012-15

Objectives

The activity of ceftazidime/avibactam was assessed against 5716 Pseudomonas aeruginosa isolates collected from 96 medical centres in 18 European countries as part of the International Network for Optimal Resistance Monitoring (INFORM) global surveillance programme from 2012 to 2015. Activity was analysed against subsets of isolates based on resistance phenotypes and β-lactamase content.

Methods

Antimicrobial susceptibility testing was performed by broth microdilution and β-lactamase genes were detected by PCR screening and sequencing.

Results

Ceftazidime/avibactam was highly active in vitro against the overall collection of P. aeruginosa isolates and colistin-resistant isolates (92.4% and 92.9% susceptible, respectively). Although activity was slightly reduced against MBL-negative subsets of ceftazidime-non-susceptible (79.6% susceptible), meropenem-non-susceptible (85.1% susceptible) and MDR (81.6% susceptible) P. aeruginosa, ceftazidime/avibactam remained the second most active entity, after colistin, compared with all other comparator agents tested. At the country level, susceptibility to ceftazidime/avibactam ranged from 74.6% to 99.6%, with decreased susceptibilities only observed in countries where MBLs are more frequently encountered, such as the Czech Republic, Greece, Romania and Russia. Ceftazidime/avibactam was also active in vitro against 87.6% of meropenem-non-susceptible isolates in which no acquired β-lactamases were detected by molecular methods; these isolates were assumed to hyperproduce the chromosomally encoded AmpC in combination with alterations in OprD or drug efflux. As expected, ceftazidime/avibactam was not active against isolates carrying MBLs.

Conclusions

The data show that ceftazidime/avibactam is highly potent in vitro against clinical isolates of P. aeruginosa collected in European countries, including isolates that exhibit resistance to ceftazidime, meropenem and colistin and combined resistance to agents from multiple drug classes.

Therapeutic Efficacy of LN-1-255 in Combination with Imipenem in Severe Infection Caused by Carbapenem-Resistant Acinetobacter baumannii

The carbapenem-hydrolyzing class D β-lactamases (CHDLs) are the main mechanism of carbapenem resistance in Acinetobacter baumannii CHDLs are not effectively inactivated by clinically available β-lactam-type inhibitors. We have previously described the in vitro efficacy of the inhibitor LN-1-255 in combination with carbapenems. The aim of this study was to compare the efficacy of LN-1-255 with that of imipenem in murine pneumonia using A. baumannii strains carrying their most extended carbapenemases, OXA-23 and OXA-24/40. The bla _OXA-23 and bla _OXA-24/40 genes were cloned into the carbapenem-susceptible A. baumannii ATCC 17978 strain. Clinical isolates Ab1 and JC12/04, producing the enzymes OXA-23 and OXA-24/40, respectively, were used in the study. Pharmacokinetic (PK) parameters were determined. An experimental pneumonia model was used to evaluate the efficacy of the combined imipenem-LN-1-255 therapy. MICs of imipenem decreased between 32- and 128-fold in the presence of LN-1-255. Intramuscular treatment with imipenem-LN-1-255 (30/50 mg/kg) decreased the bacterial burden by (i) 4 and 1.7 log₁₀ CFU/g lung in the infection with the ATCC 17978-OXA-23 and Ab1 strains, respectively, and by (ii) 2.5 and 4.5 log₁₀ CFU/g lung in the infection produced by the ATCC 17978-OXA-24/40 and the JC12/04 strains, respectively. In all assays, combined therapy offered higher protection against pneumonia than that provided by monotherapy. No toxicity was observed in treated mice. Imipenem treatment combined with LN-1-255 treatment significantly reduced the severity of infection by carbapenem-resistant A. baumannii strains carrying CHDLs. Preclinical assays demonstrated the potential of LN-1-255 and imipenem therapy as a new antibacterial treatment.

In Vitro Antimicrobial Susceptibility Differences Between Carbapenem-Resistant KPC-2-Producing and NDM-1-Producing Klebsiella pneumoniae in a Teaching Hospital in Northeast China

Carbapenem-resistant Klebsiella pneumoniae (CRKP) has become a serious challenge for clinical treatment and public health. We found that both KPC-2-producing K. pneumoniae (KPC-KP) and NDM-1-producing K. pneumoniae (NDM-KP) are epidemic in a teaching hospital in Northeast China. The main aim of the present study was to compare antimicrobial susceptibility differences between KPC-KP and NDM-KP and elucidate complex resistant genotypes of the KPC-KP and NDM-KP by PCR and sequencing. Among 82 CRKP isolated between January 2015 and December 2016, 59 isolates were KPC-KP and 23 isolates were NDM-KP. All 59 KPC-KP had no susceptibility to gentamicin, tobramycin, levofloxacin, and ciprofloxacin, had very low susceptibility to amikacin (3.39%) and fosfomycin (8.47%), whereas the susceptibility of NDM-KP to the above antibiotics was 21.74%, 13.04%, 17.39%, 17.39%, 69.57%, and 73.91%, respectively. Although the susceptibility of NDM-KP to tigecycline (95.65%) and polymyxin B (73.91%) was higher than that of KPC-KP (84.75% and 69.49%, respectively), the difference was not statistically significant. The MIC₉₀ of KPC-KP and NDM-KP to aztreonam-avibactam were 4 and 2 μg/mL, respectively. All 82 CRKP carried 2 or 3 Extended Spectrum Beta-Lactamase (ESBL) genes, and 79/82 CRKP carried the AmpC gene bla_FOX. The aminoglycoside resistance gene rmtB was detected in 96.61% of KPC-KP and in 21.74% of NDM-KP. It seems that KPC-KP was more resistant to antibiotics than NDM-KP in this study, so that available therapeutic regimens against KPC-KP are very limited. Aztreonam-avibactam may be a promising and valuable option against both KPC-KP and NDM-KP.

Current status of countermeasures for infectious diseases and resistant microbes in the field of urology

A worldwide increase in antimicrobial-resistant microbes due to the improper use of antimicrobial agents, along with a lack of progress in developing new antimicrobials, is becoming a societal problem. Although carbapenem-resistant Enterobacteriaceae, which are resistant to carbapenem antimicrobials, first appeared in 1993, treatment options remain limited. Mechanisms behind antimicrobial resistance involve changes to microbial outer membranes, drug efflux pump abnormalities, β-lactamase production and the creation of biofilms around cell bodies. Genetic information related to these forms of antimicrobial resistance exists on chromosomes and plasmids, and when located on the latter can easily be transmitted to other strains, no matter the species, which creates a risk of antimicrobial resistance spreading exceptionally rapidly. To prevent the spread of antimicrobial resistance, the World Health Organization in 2015 published an action plan on antimicrobial resistance, based on which World Health Organization member countries have laid out specific policies and targets. Urinary tract infections are a type of healthcare-associated infection, and the sexually transmitted disease pathogen, Neisseria gonorrhoeae, has been included in a list of microbes that pose a risk to human health published by the US Centers for Disease Control and Prevention. Urologists face numerous problems when attempting to use antimicrobials properly, which is one method of dealing with antimicrobial resistance. Therefore, this article describes the current state of resistant microbes associated with urinary tract infections and countermeasures for antimicrobial resistance, including new antimicrobials.

Evaluation of the Synergy of Ceftazidime-Avibactam in Combination with Meropenem, Amikacin, Aztreonam, Colistin, or Fosfomycin against Well-Characterized Multidrug-Resistant Klebsiella pneumoniae and Pseudomonas aeruginosa

Multidrug-resistant (MDR) Gram-negative organisms are a major health concern due to lack of effective therapy. Emergence of resistance to newer agents like ceftazidime-avibactam (CZA) further magnifies the problem. In this context, combination therapy of CZA with other antimicrobials may have potential in treating these pathogens. Unfortunately, there are limited data regarding these combinations. Therefore, the objective of this study was to evaluate CZA in combination with amikacin (AMK), aztreonam (AZT), colistin (COL), fosfomycin (FOS), and meropenem (MEM) against 21 carbapenem-resistant Klebsiella pneumoniae and 21 MDR Pseudomonas aeruginosa strains. The potential for synergy was evaluated via MIC combination evaluation and time-kill assays. All strains were further characterized by whole-genome sequencing, quantitative real-time PCR, and SDS-PAGE analysis to determine potential mechanisms of resistance. Compared to CZA alone, we observed a 4-fold decrease in CZA MICs for a majority of K. pneumoniae strains and at least a 2-fold decrease for most P. aeruginosa isolates in the majority of combinations tested. In both P. aeruginosa and K. pneumoniae strains, CZA in combination with AMK or AZT was synergistic (≥2.15-log10 CFU/ml decrease). CZA-MEM was effective against P. aeruginosa and CZA-FOS was effective against K. pneumoniae Time-kill analysis also revealed that the synergy of CZA with MEM or AZT may be due to the previously reported restoration of MEM or AZT activity against these organisms. Our findings show that CZA in combination with these antibiotics has potential for therapeutic options in difficult to treat pathogens. Further evaluation of these combinations is warranted.

IID572: A New Potentially Best-In-Class β-Lactamase Inhibitor

Resistance in Gram-negative bacteria to β-lactam drugs is mediated primarily by the expression of β-lactamases, and co-dosing of β-lactams with a β-lactamase inhibitor (BLI) is a clinically proven strategy to address resistance. New β-lactamases that are not impacted by existing BLIs are spreading and creating the need for development of novel broader spectrum BLIs. IID572 is a novel broad spectrum BLI of the diazabicyclooctane (DBO) class that is able to restore the antibacterial activity of piperacillin against piperacillin/tazobactam-resistant clinical isolates. IID572 is differentiated from other DBOs by its broad inhibition of β-lactamases and the lack of intrinsic antibacterial activity.

Defining the Role of Novel β-Lactam Agents That Target Carbapenem-Resistant Gram-Negative Organisms

With the current carbapenem-resistant organism crisis, conventional approaches to optimizing pharmacokinetic-pharmacodynamic parameters are frequently inadequate, and traditional salvage agents (eg, colistin, tigecycline, etc) confer high toxicity and/or have low efficacy. However, several β-lactam agents with activity against carbapenem-resistant organisms were approved recently by the US Food and Drug Administration, and more are anticipated to be approved in the near future. The primary goal of this review is to assist infectious disease practitioners with preferentially selecting 1 agent over another when treating patients infected with a carbapenem-resistant organism. However, resistance to some of these antibiotics has already developed. Antibiotic stewardship programs can ensure that they are reserved for situations in which other options are lacking and are paramount for the survival of these agents.

Antibacterials in the pipeline and perspectives for the near future

Antimicrobial resistance is a global threat to the management of infections in our patients. Sound stewardship of antibacterial agents at our disposal must be accompanied by a concerted effort to develop new agents to bolster our armamentarium. This review will cover the latest antibiotics that have come through the pipeline and the role they can play in the management of infections that are increasingly difficult to treat due to resistance mechanisms.

Influence of substrates and inhibitors on the structure of Klebsiella pneumoniae carbapenemase-2

The hydrolysis of last resort carbapenem antibiotics by Klebsiella pneumoniae carbapenemase-2 (KPC-2) presents a significant danger to global health. Combined with horizontal gene transfer, the emergence KPC-2 threatens to quickly expand carbapenemase activity to ever increasing numbers of pathogens. Our understanding of KPC-2 has greatly increased over the past decade thanks, in great part, to 20 crystal structures solved by groups around the world. These include apo KPC-2 structures, along with structures featuring a library of 10 different inhibitors representing diverse structural and functional classes. Herein we focus on cataloging the available KPC-2 structures and presenting a discussion of key aspects of each structure and important relationships between structures. Although the available structures do not provide information on dynamic motions with KPC-2, and the family of structures indicates small conformational changes across a wide array of bound inhibitors, substrates, and products, the structures provide a strong foundation for additional studies in the coming years to discover new KPC-2 inhibitors.

Impact statement

The work herein is important to the field as it provides a clear and succinct accounting of available KPC-2 structures. The work advances the field by collecting and analyzing differences and similarities across the available structures. This work features new analyses and interpretations of the existing structures which will impact the field in a positive way by making structural insights more widely available among the beta-lactamase community.

Evaluating the Efficacies of Carbapenem/β-Lactamase Inhibitors Against Carbapenem-Resistant Gram-Negative Bacteria in vitro and in vivo

Background

Carbapenem-resistant Gram-negative bacteria are a major clinical concern as they cause virtually untreatable infections since carbapenems are among the last-resort antimicrobial agents. β-Lactamases implicated in carbapenem resistance include KPC, NDM, and OXA-type carbapenemases. Antimicrobial combination therapy is the current treatment approach against carbapenem resistance in order to limit the excessive use of colistin; however, its advantages over monotherapy remain debatable. An alternative treatment strategy would be the use of carbapenem/β-lactamase inhibitor (βLI) combinations. In this study, we assessed the in vitro and in vivo phenotypic and molecular efficacies of three βLIs when combined with different carbapenems against carbapenem-resistant Gram-negative clinical isolates. The chosen βLIs were (1) Avibactam, against OXA-type carbapenemases, (2) calcium-EDTA, against NDM-1, and (3) Relebactam, against KPC-2.

Methods

Six Acinetobacter baumannii clinical isolates were screened for bla _OXA-23-like, bla _OXA-24/40, bla _OXA-51-like, bla _OXA-58, and bla _OXA-143-like, and eight Enterobacteriaceae clinical isolates were screened for bla _OXA-48, bla _NDM-1, and bla _KPC-2. The minimal inhibitory concentrations of Imipenem (IPM), Ertapenem (ETP), and Meropenem (MEM) with corresponding βLIs for each isolate were determined. The efficacy of the most suitable in vitro treatment option against each of bla _OXA-48, bla _NDM-1, and bla _KPC-2 was assessed via survival studies in a BALB/c murine infection model. Finally, RT-qPCR was performed to assess the molecular response of the genes of resistance to the carbapenem/βLI combinations used under both in vitro and in vivo settings.

Results

Combining MEM, IPM, and ETP with the corresponding βLIs restored the isolates' susceptibilities to those antimicrobial agents in 66.7%, 57.1%, and 30.8% of the samples, respectively. Survival studies in mice revealed 100% survival rates when MEM was combined with either Avibactam or Relebactam against bla _OXA-48 and bla _KPC-2, respectively. RT-qPCR demonstrated the consistent overexpression of bla _OXA-48 upon treatment, without hindering Avibactam's activity, while bla _NDM-1 and bla _KPC-2 experienced variable expression levels upon treatment under in vitro and in vivo settings despite their effective phenotypic results.

Conclusion

New carbapenem/βLI combinations may be viable alternatives to antimicrobial combination therapy as they displayed high efficacy in vitro and in vivo. Meropenem/Avibactam and Meropenem/Relebactam should be tested on larger sample sizes with different carbapenemases before progressing further in its preclinical development.

Activity of ceftazidime/avibactam against problem Enterobacteriaceae and Pseudomonas aeruginosa in the UK, 2015-16

Background

Ceftazidime/avibactam combines an established oxyimino-cephalosporin with the first diazabicyclooctane β-lactamase inhibitor to enter clinical use. We reviewed its activity against Gram-negative isolates, predominantly from the UK, referred for resistance investigation in the first year of routine testing, beginning in July 2015.

Methods

Isolates were as received from referring laboratories; there is a bias to submit those with suspected carbapenem resistance. Identification was by MALDI-TOF mass spectroscopy, and susceptibility testing by BSAC agar dilution. Carbapenemase genes were sought by PCR; other resistance mechanisms were inferred using genetic data and interpretive reading.

Results

Susceptibility rates to ceftazidime/avibactam exceeded 95% for: (i) Enterobacteriaceae with KPC, GES or other Class A carbapenemases; (ii) Enterobacteriaceae with OXA-48-like enzymes; and (iii) for ESBL or AmpC producers, even when these had impermeability-mediated ertapenem resistance. Almost all isolates with metallo-carbapenemases were resistant. Potentiation of ceftazidime by avibactam was seen for 87% of ceftazidime-resistant Enterobacteriaceae with 'unassigned' ceftazidime resistance mechanisms, including two widely referred groups of Klebsiella pneumoniae where no synergy was seen between cephalosporins and established β-lactamase inhibitors. Potentiation here may be a diazabicyclooctane/cephalosporin enhancer effect. Activity was seen against Pseudomonas aeruginosa with derepressed AmpC, but not for those with efflux-mediated resistance.

Conclusions

Of the available β-lactams or inhibitor combinations, ceftazidime/avibactam has the widest activity spectrum against problem Enterobacteriaceae, covering all major types except metallo-carbapenemase producers; against P. aeruginosa it has a slightly narrower spectrum than ceftolozane/tazobactam, which also covers efflux-type resistance.

Treatment of infections caused by multidrug-resistant Gram-negative bacteria: report of the British Society for Antimicrobial Chemotherapy/Healthcare Infection Society/British Infection Association Joint Working Party

The Working Party makes more than 100 tabulated recommendations in antimicrobial prescribing for the treatment of infections caused by multidrug-resistant (MDR) Gram-negative bacteria (GNB) and suggest further research, and algorithms for hospital and community antimicrobial usage in urinary infection. The international definition of MDR is complex, unsatisfactory and hinders the setting and monitoring of improvement programmes. We give a new definition of multiresistance. The background information on the mechanisms, global spread and UK prevalence of antibiotic prescribing and resistance has been systematically reviewed. The treatment options available in hospitals using intravenous antibiotics and in primary care using oral agents have been reviewed, ending with a consideration of antibiotic stewardship and recommendations. The guidance has been derived from current peer-reviewed publications and expert opinion with open consultation. Methods for systematic review were NICE compliant and in accordance with the SIGN 50 Handbook; critical appraisal was applied using AGREE II. Published guidelines were used as part of the evidence base and to support expert consensus. The guidance includes recommendations for stakeholders (including prescribers) and antibiotic-specific recommendations. The clinical efficacy of different agents is critically reviewed. We found there are very few good-quality comparative randomized clinical trials to support treatment regimens, particularly for licensed older agents. Susceptibility testing of MDR GNB causing infection to guide treatment needs critical enhancements. Meropenem- or imipenem-resistant Enterobacteriaceae should have their carbapenem MICs tested urgently, and any carbapenemase class should be identified: mandatory reporting of these isolates from all anatomical sites and specimens would improve risk assessments. Broth microdilution methods should be adopted for colistin susceptibility testing. Antimicrobial stewardship programmes should be instituted in all care settings, based on resistance rates and audit of compliance with guidelines, but should be augmented by improved surveillance of outcome in Gram-negative bacteraemia, and feedback to prescribers. Local and national surveillance of antibiotic use, resistance and outcomes should be supported and antibiotic prescribing guidelines should be informed by these data. The diagnosis and treatment of both presumptive and confirmed cases of infection by GNB should be improved. This guidance, with infection control to arrest increases in MDR, should be used to improve the outcome of infections with such strains. Anticipated users include medical, scientific, nursing, antimicrobial pharmacy and paramedical staff where they can be adapted for local use.

In Vitro Activity of Ceftazidime-Avibactam against Clinical Isolates of Enterobacteriaceae and Pseudomonas aeruginosa Collected in Latin American Countries: Results from the INFORM Global Surveillance Program, 2012 to 2015

The International Network for Optimal Resistance Monitoring (INFORM) global surveillance program collected clinical isolates of Enterobacteriaceae (n = 7,665) and Pseudomonas aeruginosa (n = 1,794) from 26 medical centers in six Latin American countries from 2012 to 2015. The in vitro activity of ceftazidime-avibactam and comparators was determined for the isolates using the Clinical and Laboratory Standards Institute (CLSI) reference broth microdilution method. Enterobacteriaceae were highly susceptible (99.7%) to ceftazidime-avibactam, including 99.9% of metallo-β-lactamase (MBL)-negative isolates; 87.4% of all P. aeruginosa isolates and 92.8% of MBL-negative isolates were susceptible to ceftazidime-avibactam. Susceptibility to ceftazidime-avibactam ranged from 99.4% to 100% for Enterobacteriaceae and from 79.1% to 94.7% for P. aeruginosa when isolates were analyzed by country of origin. Ceftazidime-avibactam inhibited 99.6% to 100% of Enterobacteriaceae isolates that carried serine β-lactamases, including extended-spectrum β-lactamases (ESBLs), AmpC cephalosporinases, and carbapenemases (KPC and OXA-48-like) as well as 99.7%, 99.6%, 99.5%, and 99.2% of MBL-negative isolates demonstrating ceftazidime-nonsusceptible, multidrug-resistant (MDR), meropenem-nonsusceptible, and colistin-resistant phenotypes, respectively. Among carbapenem-nonsusceptible isolates of P. aeruginosa (n = 750), 14.7% carried MBLs with or without additional acquired serine β-lactamases, while in the majority of isolates (70.0%), no acquired β-lactamase was identified. Ceftazidime-avibactam inhibited 89.5% of carbapenem-nonsusceptible P. aeruginosa isolates in which no acquired β-lactamase was detected. Overall, clinical isolates of Enterobacteriaceae collected in Latin America from 2012 to 2015 were highly susceptible to ceftazidime-avibactam, including isolates that exhibited resistance to ceftazidime, meropenem, colistin, or an MDR phenotype. Country-specific variations were noted in the susceptibility of P. aeruginosa isolates to ceftazidime-avibactam.

Pharmacodynamic modelling of β-lactam/β-lactamase inhibitor checkerboard data: illustration with aztreonam-avibactam

OBJECTIVES

Checkerboard experiments followed by fractional inhibitory concentration (FIC) index determinations are commonly used to assess in vitro pharmacodynamic interactions between combined antibiotics, but FIC index cannot be determined in case of antibiotic/non-active compound combinations. The aim of this study was to use a simple modelling approach to quantify the in vitro activity of aztreonam-avibactam, a new β-lactam-β-lactamase inhibitor combination.

METHODS

MIC checkerboard experiments were performed with 12 Enterobacteriaceae with diverse β-lactamases profiles. Aztreonam MICs in the absence and presence of avibactam at different concentrations (ranging from 0.0625 to 4 mg/L) were determined. Aztreonam MIC versus avibactam concentrations were fitted by an inhibitory E_max model with a baseline effect parameter.

RESULTS

A concentration-dependent relationship was observed with a steep initial reduction of aztreonam MIC at low avibactam concentrations and reaching a maximum at higher avibactam concentrations that was adequately fitted by the model. Maximum avibactam effect was characterized by the ratio of aztreonam MICs in the absence of avibactam (MIC₀) and when avibactam concentration tends toward infinity (MIC_∞), and this ratio ranged between 90 and 10 068 depending on the strain. Avibactam potency was characterized by avibactam concentrations corresponding to 50% of the maximum effect (IC₅₀ values between 0.00022 and 0.053 mg/L).

CONCLUSIONS

An inhibitory E_max model with a baseline effect could quantify maximum avibactam effect and potency among various strains. This simple modelling approach can be used to compare the activity of other combinations of antibiotics with non-antibiotic drugs when FIC index is inappropriate.

In Vitro Activity of Ceftazidime-Avibactam and Aztreonam-Avibactam against OXA-48-Carrying Enterobacteriaceae Isolated as Part of the International Network for Optimal Resistance Monitoring (INFORM) Global Surveillance Program from 2012 to 2015

Enterobacteriaceae producing the Ambler class D OXA-48 carbapenemase, combined with additional resistance mechanisms, such as permeability defects or cocarriage of class A, B, or C β-lactamases, can become highly resistant to most β-lactams currently in use, including carbapenems. A total of 45,872 Enterobacteriaceae clinical isolates collected in 39 countries as part of the International Network for Optimal Resistance Monitoring (INFORM) global surveillance study in 2012 to 2015 were tested for susceptibility to β-lactams and comparator agents using the Clinical and Laboratory Standards Institute broth microdilution methodology and screened for the presence of β-lactamases. The bla _OXA-48 and bla _OXA-48-like genes were detected in 333 isolates across 14 species of Enterobacteriaceae collected in 20 countries across the globe. Few agents tested were effective in vitro against the overall collection of OXA-48-producers (n = 265), with tigecycline (MIC₉₀, 2 µg/ml; 92.5% susceptible), ceftazidime-avibactam (MIC₉₀, 4 µg/ml; 92.5% susceptible), and aztreonam-avibactam (MIC₉₀, 0.5 µg/ml; 99.6% of isolates with MIC ≤8 µg/ml) demonstrating the greatest activity. Similarly, colistin (MIC₉₀, 1 µg/ml; 94.2% susceptible), tigecycline (MIC₉₀, 2 µg/ml; 92.6% susceptible), ceftazidime-avibactam (MIC₉₀, >128 µg/ml; 89.7% susceptible), and aztreonam-avibactam (MIC₉₀, 4 µg/ml; 100% of isolates with MIC ≤8 µg/ml) were most active against OXA-48-like-positive isolates (n = 68). The in vitro activity of ceftazidime-avibactam was improved against the subset of metallo-β-lactamase (MBL)-negative, OXA-48- and OXA-48-like-positive isolates (99.2% and 100% susceptible, respectively). The data reported here support the continued investigation of ceftazidime-avibactam and aztreonam-avibactam for the treatment of infections caused by carbapenem-resistant Enterobacteriaceae carrying OXA-48 and OXA-48-like β-lactamases in combination with serine- or metallo-β-lactamases.

In Vitro Activities of Ceftaroline/Avibactam, Ceftazidime/Avibactam, and Other Comparators Against Pathogens From Various Complicated Infections in China

Background

We conducted a national antimicrobial surveillance study of both gram-positive and gram-negative organisms isolated from hospitalized patients. This report presents data on antimicrobial susceptibility among 4998 organisms collected in China between 2012 and 2014.

Method

The minimum inhibitory concentrations (MICs) and susceptibilities of ceftaroline/avibactam (CPA), ceftazidime/avibactam (CZA) and a range of comparative agents were determined according to guidelines established by the Clinical and Laboratory Standards Institute (CLSI).

Results

The highest overall susceptibility levels for all Enterobacteriaceae during the study period were observed for CPA, CZA, doripenem (DOR), meropenem (MEM), and amikacin (AMK), which were all >90%. However, both CPT and CAZ alone and in combination with avibactam showed low activities for Acinetobacter spp., whereas CPA and CZA exhibited MIC90 values for Pseudomonas aeruginosa that were reduced by 4- and 8-fold, respectively, compared with those of CPT and CAZ. High susceptibilities of Acinetobacter spp. and P. aeruginosa to colistin and P. aeruginosa to AMK were observed. For the gram-positive strains, no significant activity changes were seen for Enterococcus, Staphylococcus, and viridans group streptococci to CPT or CAZ alone or in combination with avibactam, whereas Streptococcus pneumoniae and β-hemolytic Streptococcus showed almost 100% susceptibility to both CPT and CPA.

Conclusion

The addition of 4 mg/L avibactam greatly increased the activities of CPT and CAZ against most Enterobacteriaceae and P. aeruginosa isolates, whereas no significant changes were observed in Acinetobacter spp. or any of the gram-positive strains.

The 2018 Garrod Lecture: Preparing for the Black Swans of resistance

The need for governments to encourage antibiotic development is widely agreed, with 'market entry rewards' being suggested. Unless these are to be spread widely-which is unlikely given the $1 billion sums proposed-we should be wary, for this approach is likely to evolve into one of picking, or commissioning, a few 'winners' based on extrapolation of current resistance trends. The hazard to this is that whilst the evolution of resistance has predictable components, notably mutation, it also has completely unpredictable ones, contingent upon 'Black Swan' events. These include the escape of 'new' resistance genes from environmental bacteria and the recruitment of these genes by promiscuous mobile elements and epidemic strains. Such events can change the resistance landscape rapidly and unexpectedly, as with the rise of Escherichia coli ST131 with CTX-M ESBLs and the emergence of 'impossible' VRE. Given such unpredictability, we simply cannot say with any certainty, for example, which of the four current approaches to combating MBLs offers the best prospect of sustainable prizeworthy success. Only time will tell, though it is encouraging that multiple potential approaches to overcoming these problematic enzymes are being pursued. Rather than seeking to pick winners, governments should aim to reduce development barriers, as with recent relaxation of trial regulations. In particular, once β-lactamase inhibitors have been successfully trialled with one partner drug, there is scope to facilitate licensing them for partnering with other established β-lactams, thereby insuring against new emerging resistance.

Virtual Screening and Experimental Testing of B1 Metallo-β-lactamase Inhibitors

The global rise of metallo-β-lactamases (MBLs) is problematic due to their ability to inactivate most β-lactam antibiotics. MBL inhibitors that could be coadministered with and restore the efficacy of β-lactams are highly sought after. In this study, we employ virtual screening of candidate MBL inhibitors without thiols or carboxylates to avoid off-target effects using the Avalanche software package, followed by experimental validation of the selected compounds. As target enzymes, we chose the clinically relevant B1 MBLs NDM-1, IMP-1, and VIM-2. Among 32 compounds selected from an approximately 1.5 million compound library, 6 exhibited IC₅₀ values less than 40 μM against NDM-1 and/or IMP-1. The most potent inhibitors of NDM-1, IMP-1, and VIM-2 had IC₅₀ values of 19 ± 2, 14 ± 1, and 50 ± 20 μM, respectively. While chemically diverse, the most potent inhibitors all contain combinations of hydroxyl, ketone, ester, amide, or sulfonyl groups. Docking studies suggest that these electron-dense moieties are involved in Zn(II) coordination and interaction with protein residues. These novel scaffolds could serve as the basis for further development of MBL inhibitors. A procedure for renaming NDM-1 residues to conform to the class B β-lactamase (BBL) numbering scheme is also included.

Production of β-Lactamase Inhibitors by Streptomyces Species

β-Lactamase inhibitors have emerged as an effective alternative to reduce the effects of resistance against β-lactam antibiotics. The Streptomyces genus is known for being an exceptional natural source of antimicrobials and β-lactamase inhibitors such as clavulanic acid, which is largely applied in clinical practice. To protect against the increasing prevalence of multidrug-resistant bacterial strains, new antibiotics and β-lactamase inhibitors need to be discovered and developed. This review will cover an update about the main β-lactamase inhibitors producers belonging to the Streptomyces genus; advanced methods, such as genetic and metabolic engineering, to enhance inhibitor production compared with wild-type strains; and fermentation and purification processes. Moreover, clinical practice and commercial issues are discussed. The commitment of companies and governments to develop innovative strategies and methods to improve the access to new, efficient, and potentially cost-effective microbial products to combat the antimicrobial resistance is also highlighted.

In Vitro Activity of Ceftazidime-Avibactam against Clinical Isolates of Enterobacteriaceae and Pseudomonas aeruginosa Collected in Asia-Pacific Countries: Results from the INFORM Global Surveillance Program, 2012 to 2015

The in vitro activities of ceftazidime-avibactam and comparators against 9,149 isolates of Enterobacteriaceae and 2,038 isolates of Pseudomonas aeruginosa collected by 42 medical centers in nine countries in the Asia-Pacific region from 2012 to 2015 were determined as part of the International Network for Optimal Resistance Monitoring (INFORM) global surveillance program. Antimicrobial susceptibility testing was conducted by Clinical and Laboratory Standards Institute (CLSI) broth microdilution, and isolate subset analysis was performed on the basis of the resistant phenotypes and β-lactamase content. Ceftazidime-avibactam demonstrated potent in vitro activity (MIC, ≤8 μg/ml) against all Enterobacteriaceae tested (99.0% susceptible) and was the most active against isolates that were metallo-β-lactamase (MBL) negative (99.8% susceptible). Against P. aeruginosa, 92.6% of all isolates and 96.1% of MBL-negative isolates were susceptible to ceftazidime-avibactam (MIC, ≤8 μg/ml). The rates of susceptibility to ceftazidime-avibactam ranged from 97.0% (Philippines) to 100% (Hong Kong, South Korea) for Enterobacteriaceae and from 83.1% (Thailand) to 100% (Hong Kong) among P. aeruginosa isolates, with lower susceptibilities being observed in countries where MBLs were more frequently encountered (Philippines, Thailand). Ceftazidime-avibactam inhibited 97.2 to 100% of Enterobacteriaceae isolates, per country, that carried serine β-lactamases, including extended-spectrum β-lactamases, AmpC cephalosporinases, and carbapenemases (KPC, GES, OXA-48-like). It also inhibited 91.3% of P. aeruginosa isolates that were carbapenem nonsusceptible in which no acquired β-lactamase was detected. Among MBL-negative Enterobacteriaceae isolates that were ceftazidime nonsusceptible, meropenem nonsusceptible, colistin resistant, and multidrug resistant, ceftazidime-avibactam inhibited 96.1, 87.7, 100, and 98.8% of isolates, respectively, and among MBL-negative P. aeruginosa isolates that were ceftazidime nonsusceptible, meropenem nonsusceptible, colistin resistant, and multidrug resistant, ceftazidime-avibactam inhibited 79.6, 83.6, 83.3, and 68.2% of isolates, respectively. Overall, clinical isolates of Enterobacteriaceae and P. aeruginosa collected in nine Asia-Pacific countries from 2012 to 2015 were highly susceptible to ceftazidime-avibactam.

Avibactam Pharmacokinetic/Pharmacodynamic Targets

Avibactam is a novel non-β-lactam β-lactamase inhibitor that has been approved in the United States and Europe for use in combination with ceftazidime. Combinations of avibactam with aztreonam or ceftaroline fosamil have also been clinically evaluated. Until recently, there has been very little precedence of which pharmacokinetic/pharmacodynamic (PK/PD) indices and magnitudes are appropriate to use for β-lactamase inhibitors in population PK modeling for analyzing potential doses and susceptibility breakpoints. For avibactam, several preclinical studies using different in vitro and in vivo models have been conducted to identify the PK/PD index of avibactam and the magnitude of exposure necessary for effect in combination with ceftazidime, aztreonam, or ceftaroline fosamil. The PD driver of avibactam critical for restoring the activity of all three partner β-lactams was found to be time dependent rather than concentration dependent and was defined as the time that the concentration of avibactam exceeded a critical concentration threshold (%fT>C_T). The magnitude of the C_T and the time that this threshold needed to be exceeded to elicit particular PD endpoints varied depending on the model and the partner β-lactam. This review describes the preclinical studies used to determine the avibactam PK/PD target in combination with its β-lactam partners.

Novel Imidazole Aldoximes with Broad-Spectrum Antimicrobial Potency against Multidrug Resistant Gram-Negative Bacteria

In the search for a new class of potential antimicrobial agents, five novel N-substituted imidazole 2-aldoximes and their six quaternary salts were evaluated. The antimicrobial activity was assessed against a panel of representative Gram-positive and Gram-negative bacteria, including multidrug resistant bacteria. All compounds demonstrated potent in vitro activity against the tested microorganisms, with MIC values ranging from 6.25 to 50.0 μg/mL. Among the tested compounds, two quaternary compounds (N-but-3-enyl- and meta- (10) or para- N-chlorobenzyl (11) imidazolium 2-aldoximes) displayed the most potent and broad-spectrum activity against both Gram-positive and Gram-negative bacterial strains. The broth microdilution assay was also used to investigate the antiresistance efficacy of the both most active compounds against a set of Enterobacteriaceae isolates carried a multiple extended-spectrum β-lactamases (ESBLs) in comparison to eight clinically relevant antibiotics. N-but-3-enyl-N-meta-chlorobenzyl imidazolium 2-aldoxime was found to possess promising antiresistance efficacy against a wide range of β-lactamases producing strains (MIC 2.0 to 16.0 μg/mL). Best results for that compound were obtained against Escherichia coli and Enterobacter cloacae producing multiple β-lactamases form A and C molecular classes, which were 32- and 128-fold more potent than ceftazidime and cefotaxime, respectively. To visualize the results, principal component analysis was used as an additional classification tool. The mixture of ceftazidime and compound 10 (3 μg:2 μg) showed a strong activity and lower the necessary amount (up to 40-fold) of 10 against five of ESBL-producing isolates (MIC ≤ 1 µg/mL).

Ceftazidime-Avibactam: A Review in the Treatment of Serious Gram-Negative Bacterial Infections

Ceftazidime-avibactam (Zavicefta®) is an intravenously administered combination of the third-generation cephalosporin ceftazidime and the novel, non-β-lactam β-lactamase inhibitor avibactam. In the EU, ceftazidime-avibactam is approved for the treatment of adults with complicated urinary tract infections (cUTIs) [including pyelonephritis], complicated intra-abdominal infections (cIAIs), hospital-acquired pneumonia (HAP) [including ventilator-associated pneumonia (VAP)], and other infections caused by aerobic Gram-negative organisms in patients with limited treatment options. This article discusses the in vitro activity and pharmacological properties of ceftazidime-avibactam, and reviews data on the agent's clinical efficacy and tolerability relating to use in these indications, with a focus on the EU label. Ceftazidime-avibactam has excellent in vitro activity against many important Gram-negative pathogens, including many extended-spectrum β-lactamase-, AmpC-, Klebsiella pneumoniae carbapenemase- and OXA-48-producing Enterobacteriaceae and drug-resistant Pseudomonas aeruginosa isolates; it is not active against metallo-β-lactamase-producing strains. The clinical efficacy of ceftazidime-avibactam in the treatment of cUTI, cIAI and HAP (including VAP) in adults was demonstrated in pivotal phase III non-inferiority trials with carbapenem comparators. Ceftazidime-avibactam treatment was associated with high response rates at the test-of-cure visit in patients with infections caused by ceftazidime-susceptible and -nonsusceptible Gram-negative pathogens. Ceftazidime-avibactam was generally well tolerated, with a safety and tolerability profile consistent with that of ceftazidime alone and that was generally typical of the injectable cephalosporins. Thus, ceftazidime-avibactam represents a valuable new treatment option for these serious and difficult-to-treat infections.

Treatment of Infections Caused by Extended-Spectrum-Beta-Lactamase-, AmpC-, and Carbapenemase-Producing Enterobacteriaceae

Therapy of invasive infections due to multidrug-resistant Enterobacteriaceae (MDR-E) is challenging, and some of the few active drugs are not available in many countries. For extended-spectrum β-lactamase and AmpC producers, carbapenems are the drugs of choice, but alternatives are needed because the rate of carbapenem resistance is rising. Potential active drugs include classic and newer β-lactam-β-lactamase inhibitor combinations, cephamycins, temocillin, aminoglycosides, tigecycline, fosfomycin, and, rarely, fluoroquinolones or trimethoprim-sulfamethoxazole. These drugs might be considered in some specific situations. AmpC producers are resistant to cephamycins, but cefepime is an option. In the case of carbapenemase-producing Enterobacteriaceae (CPE), only some "second-line" drugs, such as polymyxins, tigecycline, aminoglycosides, and fosfomycin, may be active; double carbapenems can also be considered in specific situations. Combination therapy is associated with better outcomes for high-risk patients, such as those in septic shock or with pneumonia. Ceftazidime-avibactam was recently approved and is active against KPC and OXA-48 producers; the available experience is scarce but promising, although development of resistance is a concern. New drugs active against some CPE isolates are in different stages of development, including meropenem-vaborbactam, imipenem-relebactam, plazomicin, cefiderocol, eravacycline, and aztreonam-avibactam. Overall, therapy of MDR-E infection must be individualized according to the susceptibility profile, type, and severity of infection and the features of the patient.

WCK 4234, a novel diazabicyclooctane potentiating carbapenems against Enterobacteriaceae, Pseudomonas and Acinetobacter with class A, C and D β-lactamases

Background

Several diazabicyclooctanes (DBOs) are under development as inhibitors of class A and C β-lactamases. Inhibition of OXA (class D) carbapenemases is variable, with those of Acinetobacter spp. remaining notably resistant. We describe a novel DBO, WCK 4234 (Wockhardt), with distinctive activity against OXA carbapenemases.

Methods

MICs of imipenem and meropenem were determined by CLSI agar dilution with WCK 4234 added at 4 or 8 mg/L. Test organisms were clinical Enterobacteriaceae, Acinetobacter baumannii and Pseudomonas aeruginosa with carbapenemases or carbapenem resistance via porin loss plus AmpC or ESBL activity. AmpC mutants were also tested.

Results

WCK 4234, which lacked direct antibacterial activity, strongly potentiated imipenem and meropenem against Enterobacteriaceae with OXA-48/OXA-181 or KPC enzymes, or with combinations of impermeability and AmpC or ESBL activity, with MICs reduced to ≤2 mg/L in almost all cases. Carbapenems likewise were potentiated against P. aeruginosa ( n  =   2) with OXA-181 enzyme, with MICs reduced from 64-128 to 2-8 mg/L and against A. baumannii with OXA carbapenemases, particularly OXA-23 or hyperproduced OXA-51, with MICs reduced to ≤2 mg/L for 9/10 acinetobacters with OXA-23 enzyme. Carbapenems were not potentiated against Enterobacteriaceae or non-fermenters with metallo-β-lactamases.

Conclusions

WCK 4234 distinctively overcame resistance mediated by OXA-type carbapenemases, including those of A. baumannii . It behaved similarly to other DBOs against strains with KPC carbapenemases or combinations of impermeability and ESBL or AmpC activity.

Recent advances in the understanding and management of Klebsiella pneumoniae

Klebsiella pneumoniae, a gram-negative bacillus of the Enterobacteriaceae family, is a component of the normal human microbiota and a common cause of community- and healthcare-associated infections. The increasing prevalence of antimicrobial resistance among K. pneumoniae isolates, particularly among those causing healthcare-associated infections, is an important public health concern. Infections caused by these multidrug-resistant organisms, for which safe and effective antimicrobial therapy options are extremely limited, are associated with poor outcomes for patients. The optimal approach to the treatment of infections caused by these multidrug-resistant strains remains undefined, and treatment decisions for an individual patient should be based on a number of organism- (for example, minimum inhibitory concentration) and patient-specific (for example, site of infection) factors. The emergence of pandrug-resistant strains of K. pneumoniae highlights the critical need for consistent implementation of effective strategies for prevention of transmission and infection and for the development of new antimicrobials with activity against these emerging pathogens.

In Vitro Activity of Aztreonam-Avibactam against Enterobacteriaceae and Pseudomonas aeruginosa Isolated by Clinical Laboratories in 40 Countries from 2012 to 2015

The combination of the monobactam aztreonam and the non-β-lactam β-lactamase inhibitor avibactam is currently in clinical development for the treatment of serious infections caused by metallo-β-lactamase (MBL)-producing Enterobacteriaceae, a difficult-to-treat subtype of carbapenem-resistant Enterobacteriaceae for which therapeutic options are currently very limited. The present study tested clinically significant isolates of Enterobacteriaceae (n = 51,352) and Pseudomonas aeruginosa (n = 11,842) collected from hospitalized patients in 208 medical center laboratories from 40 countries from 2012 to 2015 for in vitro susceptibility to aztreonam-avibactam, aztreonam, and comparator antimicrobial agents using a standard broth microdilution methodology. Avibactam was tested at a fixed concentration of 4 μg/ml in combination with 2-fold dilutions of aztreonam. The MIC90s of aztreonam-avibactam and aztreonam were 0.12 and 64 μg/ml, respectively, for all Enterobacteriaceae isolates; >99.9% of all isolates and 99.8% of meropenem-nonsusceptible isolates (n = 1,498) were inhibited by aztreonam-avibactam at a concentration of ≤8 μg/ml. PCR and DNA sequencing identified 267 Enterobacteriaceae isolates positive for MBL genes (NDM, VIM, IMP); all Enterobacteriaceae carrying MBLs demonstrated aztreonam-avibactam MICs of ≤8 μg/ml and a MIC90 of 1 μg/ml. Against all P. aeruginosa isolates tested, the MIC90 of both aztreonam-avibactam and aztreonam was 32 μg/ml; against MBL-positive P. aeruginosa isolates (n = 452), MIC90 values for aztreonam-avibactam and aztreonam were 32 and 64 μg/ml, respectively. The current study demonstrated that aztreonam-avibactam possesses potent in vitro activity against a recent, sizeable global collection of Enterobacteriaceae clinical isolates, including isolates that were meropenem nonsusceptible, and against MBL-positive isolates of Enterobacteriaceae, for which there are few treatment options.

Identifying Spectra of Activity and Therapeutic Niches for Ceftazidime-Avibactam and Imipenem-Relebactam against Carbapenem-Resistant Enterobacteriaceae

We determined imipenem, imipenem-relebactam, ceftazidime, and ceftazidime-avibactam MICs against 100 CRE isolates that underwent whole-genome sequencing. Klebsiella pneumoniae carbapenemases (KPCs) were the most common carbapenemases. Forty-six isolates carried extended-spectrum β-lactamases (ESBLs). With the addition of relebactam, imipenem susceptibility increased from 8% to 88%. With the addition of avibactam, ceftazidime susceptibility increased from 0% to 85%. Neither imipenem-relebactam nor ceftazidime-avibactam was active against metallo-β-lactamase (MBL) producers. Ceftazidime-avibactam (but not imipenem-relebactam) was active against OXA-48-like producers, including a strain not harboring any ESBL. Major OmpK36 porin mutations were independently associated with higher imipenem-relebactam MICs (P < 0.0001) and showed a trend toward independent association with higher ceftazidime-avibactam MICs (P = 0.07). The presence of variant KPC-3 was associated with ceftazidime-avibactam resistance (P < 0.0001). In conclusion, imipenem-relebactam and ceftazidime-avibactam had overlapping spectra of activity and niches in which each was superior. Major OmpK36 mutations in KPC-K. pneumoniae may provide a foundation for stepwise emergence of imipenem-relebactam and ceftazidime-avibactam resistance.

Burkholderia cenocepacia Infections in Cystic Fibrosis Patients: Drug Resistance and Therapeutic Approaches

Burkholderia cenocepacia is an opportunistic pathogen particularly dangerous for cystic fibrosis (CF) patients. It can cause a severe decline in CF lung function possibly developing into a life-threatening systemic infection known as cepacia syndrome. Antibiotic resistance and presence of numerous virulence determinants in the genome make B. cenocepacia extremely difficult to treat. Better understanding of its resistance profiles and mechanisms is crucial to improve management of these infections. Here, we present the clinical distribution of B. cenocepacia described in the last 6 years and methods for identification and classification of epidemic strains. We also detail new antibiotics, clinical trials, and alternative approaches reported in the literature in the last 5 years to tackle B. cenocepacia resistance issue. All together these findings point out the urgent need of new and alternative therapies to improve CF patients’ life expectancy.

New β-Lactamase Inhibitors in the Clinic

Given the serious medical burden of β-lactamases, many approaches are being used identify candidate agents for β-lactamase inhibition. Here, we review two β-lactam-β-lactamase inhibitor (BL-BLI) combinations, ceftolozane-tazobactam and ceftazidime-avibactam that recently entered the clinic. In addition, we focus on BL-BLI combinations in preclinical development that have demonstrated activity in clinical isolates via susceptibility testing and/or in in vivo models of infection. We highlight only the BLIs that are able to reduce the Clinical Laboratory Standards Institute (CLSI) breakpoints for the BL partner into the susceptible range. Our analysis includes the primary literature, meeting abstracts, as well as the patent literature.

In Vitro Discordance with In Vivo Activity: Humanized Exposures of Ceftazidime-Avibactam, Aztreonam, and Tigecycline Alone and in Combination against New Delhi Metallo-β-Lactamase-Producing Klebsiella pneumoniae in a Murine Lung Infection Model

The management of infections with New Delhi metallo-beta-lactamase-1 (NDM)-producing bacteria remains clinically challenging given the multidrug resistant (MDR) phenotype associated with these bacteria. Despite resistance in vitro, ceftazidime-avibactam previously demonstrated in vivo activity against NDM-positive Enterobacteriaceae Herein, we observed in vitro synergy with ceftazidime-avibactam and aztreonam against an MDR Klebsiella pneumoniae harboring NDM. In vivo, humanized doses of ceftazidime-avibactam monotherapy resulted in >2 log10 CFU bacterial reduction; therefore, no in vivo synergy was observed.

Novel Beta-Lactamase Inhibitors: Unlocking Their Potential in Therapy

Carbapenem-resistant Enterobacteriaceae are amongst the most feared pathogens due to severely limited treatment options. In response to this threat, three novel β-lactamase inhibitors have been developed in an attempt to reinvigorate and sustain our current antimicrobial therapies. Avibactam, vaborbactam, and relebactam are inhibitor agents with high affinity to Ambler class A and C β-lactamases and favorable outcomes in current clinical trials. However, although they do possess key similarities, these agents have unique differences which may have important clinical implications. The microbiologic spectrum, pharmacokinetics, and key clinical trials for each of these novel agents are reviewed. A proposed role in therapy and potential novel combinations are examined.

Ceftazidime-avibactam: novel antimicrobial combination for the treatment of complicated urinary tract infections

Ceftazidime-avibactam is a combination of a third-generation cephalosporin and a novel non-beta-lactam beta-lactamase inhibitor. This combination was recently recommended for the treatment of complicated urinary tract infections, including acute pyelonephritis, in adults with limited or no alternative treatment options. The current review is aimed to determine activity, efficacy and safety of ceftazidime-avibactam in the treatment of patients with complicated urinary tract infections.

Impact of defined cell envelope mutations in Escherichia coli on the in vitro antibacterial activity of avibactam/β-lactam combinations

Avibactam is a novel non-β-lactam β-lactamase inhibitor being developed in combination with ceftazidime, ceftaroline and aztreonam for the treatment of infections caused by Gram-negative bacteria. Avibactam protects the antibacterial activity of these antibiotics by inhibiting Ambler classes A and C and some class D β-lactamases. The Gram-negative cell envelope presents a complex barrier to hydrophilic solutes and contains multiple molecular determinants of antibiotic susceptibility and resistance. To investigate the role of some of these determinants in the activity of avibactam and its partner antibiotics in Escherichia coli, an isogenic panel with deletions in specific components of the cell envelope was constructed in an E. coli W3110 strain background. The mutant constructs were also engineered to express the β-lactamase CTX-M-15 as a tool to enable assessment of the activity of avibactam. Mutations to shorten the lipopolysaccharide (LPS), to reduce efflux from the basal (i.e. non-upregulated) level or to alter the outer membrane porin composition did not have appreciable effects on the in vitro activity of ceftazidime, ceftaroline or aztreonam alone or in combination with avibactam. In conclusion, in this susceptible strain background, none of the β-lactams nor avibactam was measurably subject to efflux based on evaluating minimum inhibitory concentrations (MICs). None of the porin single or double mutations caused a decrease in susceptibility to the test compounds, implying that the compounds do not possess a strong porin preference, but instead can pass the outer membrane through a variety of routes.

In vitro and in vivo activities of the diazabicyclooctane OP0595 against AmpC-derepressed Pseudomonas aeruginosa

Pseudomonas aeruginosa is a common cause for healthcare-associated infections, which have been historically treated by antipseudomonal β-lactam agents in the clinical setting. However, P. aeruginosa has evolved to overcome these β-lactam agents via multiple endogenous resistance mechanisms, including derepression of the chromosomal cephalosporinase (AmpC). In this article, we investigated the effective concentration of OP0595 for combination with piperacillin, cefepime or meropenem in in vitro susceptibility tests, and the antibacterial activity of cefepime in combination with OP0595 in both in vitro time-kill studies and in vivo murine thigh infection model study with AmpC-derepressed P. aeruginosa. The sufficient combinational concentration of OP0595 was a 4 μg ml^-1 with all these three β-lactam agents. OP0595 increased the antibacterial activity of cefepime in both in vitro and in vivo studies against all strains tested. Taken together, OP0595 is the diazabicyclooctane serine β-lactamase inhibitor with activity against AmpC-derepressed P. aeruginosa and its combinational use with a β-lactam agent will provide a new approach for the treatment of P. aeruginosa infections.

Ceftazidime-avibactam (CTZ-AVI) as a treatment for hospitalized adult patients with complicated intra-abdominal infections

Avibactam, a novel β-lactamase inhibitor, has recently been co-formulated with ceftazidime and approved for use in patients with complicated intra-abdominal and urinary tract infections, where no better treatment alternative exists. The basis for its FDA approval has been the extensive clinical experience with ceftazidime and the demonstration in vitro and in animal models that the addition of avibactam reverses resistance to ceftazidime in extended-spectrum β-lactamase and some carbapenemase-producing Enterobacteriaceae. Early clinical data are promising, with efficacy demonstrated in patients with complicated intra-abdominal and urinary tract infections. This review will summarize the in vitro, animal and clinical data available on this agent to date.

Ceftolozane/tazobactam and ceftazidime/avibactam for the treatment of complicated intra-abdominal infections

Complicated intra-abdominal infections (cIAI) represent a large proportion of all hospital admissions and are a major cause of morbidity and mortality in the intensive care unit. Rising rates of multidrug resistant organisms (MDRO), including extended-spectrum β-lactamase producing Enterobacteriaceae and carbapenem-nonsusceptible Pseudomonas spp., for which there are few remaining active antimicrobial agents, pose an increased challenge to clinicians. Patients with frequent exposures to the health care system or multiple recurrent IAIs are at increased risk for MDRO; however, treatment options have traditionally been limited, in some cases necessitating the utilization of last-line agents with unfavorable side-effect profiles. Ceftolozane/tazobactam and ceftazidime/avibactam are two new cephalosporin and β-lactamase inhibitor combinations with recent US Food and Drug Administration approvals for the treatment of cIAI in combination with metronidazole. Ceftolozane/tazobactam has demonstrated excellent in vitro activity against MDR and extensively drug-resistant Pseudomonas spp., including carbapenem-nonsusceptible strains, while ceftazidime/avibactam effectively inhibits a broad range of β-lactamases, making it an excellent option for the treatment of carbapenem-resistant Enterobacteriaceae. Both agents were shown to be noninferior to meropenem for treatment of cIAI in Phase III trials; however, reduced responses in patients with renal impairment at baseline highlight the importance of routine serum creatinine monitoring and ongoing dose adjustments. This review highlights in vitro and in vivo data of these two agents and suggests their proper place in cIAI treatment to ensure adequate therapy in our most at-risk patients while sparing unnecessary use in patients without MDRO risk factors.

Effect of β-Lactamase inhibitors on in vitro activity of β-Lactam antibiotics against Burkholderia cepacia complex species

BACKGROUND

Bacteria belonging to the Burkholderia cepacia complex (Bcc) are an important cause of chronic respiratory tract infections in cystic fibrosis patients. Intrinsic resistance to a wide range of antimicrobial agents, including a variety of β-lactam antibiotics, is frequently observed in Bcc strains. Resistance to β-lactams is most commonly mediated by efflux pumps, alterations in penicillin-binding proteins or the expression of β-lactamases. β-lactamase inhibitors are able to restore the in vitro activity of β-lactam molecules against a variety of Gram-negative species, but the effect of these inhibitors on the activity of β-lactam treatment against Bcc species is still poorly investigated.

METHODS

In the present study, the susceptibility of a panel of Bcc strains was determined towards the β-lactam antibiotics ceftazidime, meropenem, amoxicillin, cefoxitin, cefepime and aztreonam; alone or in combination with a β-lactamase inhibitor (clavulanic acid, sulbactam, tazobactam and avibactam). Consequently, β-lactamase activity was determined for active β-lactam/β-lactamase inhibitor combinations.

RESULTS

Clavulanic acid had no effect on minimum inhibitory concentrations, but addition of sulbactam, tazobactam or avibactam to ceftazidime, amoxicillin, cefoxitin, cefepime or aztreonam leads to increased susceptibility (at least 4-fold MIC-decrease) in some Bcc strains. The effect of β-lactamase inhibitors on β-lactamase activity is both strain- and/or antibiotic-dependent, and other mechanisms of β-lactam resistance (besides production of β-lactamases) appear to be important.

CONCLUSIONS

Considerable differences in susceptibility of Bcc strains to β-lactam antibiotics were observed. Results obtained in the present study suggest that resistance of Bcc strains against β-lactam antibiotics is mediated by both β-lactamases and non-β-lactamase-mediated resistance mechanisms.

Interaction of Avibactam with Class B Metallo-β-Lactamases

β-Lactamases are the most important mechanisms of resistance to the β-lactam antibacterials. There are two mechanistic classes of β-lactamases: the serine β-lactamases (SBLs) and the zinc-dependent metallo-β-lactamases (MBLs). Avibactam, the first clinically useful non-β-lactam β-lactamase inhibitor, is a broad-spectrum SBL inhibitor, which is used in combination with a cephalosporin antibiotic (ceftazidime). There are multiple reports on the interaction of avibactam with SBLs but few such studies with MBLs. We report biochemical and biophysical studies on the binding and reactivity of avibactam with representatives from all 3 MBL subfamilies (B1, B2, and B3). Avibactam has only limited or no activity versus MBL-mediated resistance in pathogens. Avibactam does not inhibit MBLs and binds only weakly to most of the MBLs tested; in some cases, avibactam undergoes slow hydrolysis of one of its urea N-CO bonds followed by loss of CO₂, in a process different from that observed with the SBLs studied. The results suggest that while the evolution of MBLs that more efficiently catalyze avibactam hydrolysis should be anticipated, pursuing the development of dual-action SBL and MBL inhibitors based on the diazabicyclooctane core of avibactam may be productive.

In Vitro Susceptibility of Global Surveillance Isolates of Pseudomonas aeruginosa to Ceftazidime-Avibactam (INFORM 2012 to 2014)

Broth microdilution antimicrobial susceptibility testing was performed for ceftazidime-avibactam and comparator agents against 7,062 clinical isolates of Pseudomonas aeruginosa collected from 2012 to 2014 in four geographic regions (Europe, Asia/South Pacific, Latin America, Middle East/Africa) as part of the International Network for Optimal Resistance Monitoring (INFORM) global surveillance program. The majority of isolates were susceptible to ceftazidime-avibactam, with the proportions susceptible differing marginally across the four regions (MIC90, 8 to 16 μg/ml; 88.7 to 93.2% susceptible), in contrast to lower susceptibilities to the following comparator β-lactam agents: ceftazidime (MIC90, 32 to 64 μg/ml; 71.5 to 80.8% susceptible), meropenem (MIC90, >8 μg/ml; 64.9 to 77.4% susceptible), and piperacillin-tazobactam (MIC90, >128 μg/ml; 62.3 to 71.3% susceptible). Compared to the overall population, susceptibility to ceftazidime-avibactam of isolates that were nonsusceptible to ceftazidime (n = 1,627) was reduced to between 56.8% (Middle East/Africa; MIC90, 64 μg/ml) and 68.9% (Asia/South Pacific; MIC90, 128 μg/ml), but these percentages were higher than susceptibilities to other β-lactam agents (0 to 44% susceptible, depending on region and agent; meropenem MIC90, >8 μg/ml; 26.5 to 43.9% susceptible). For this subset of isolates, susceptibilities to amikacin (MIC90, >32 μg/ml; 53.2 to 80.0% susceptible) and colistin (MIC90, 1 μg/ml; 98.5 to 99.5% susceptible) were comparable to or higher than that of ceftazidime-avibactam. A similar observation was made with isolates that were nonsusceptible to meropenem (n = 1,926), with susceptibility to ceftazidime-avibactam between 67.8% (Middle East/Africa; MIC90, 64 μg/ml) and 74.2% (Europe; MIC90, 32 μg/ml) but again with reduced susceptibility to comparators except for amikacin (MIC90, >32 μg/ml; 56.8 to 78.7% susceptible) and colistin (MIC90, 1 μg/ml; 98.9 to 99.3% susceptible). Of the 8% of isolates not susceptible to ceftazidime-avibactam, the nonsusceptibility of half could be explained by their possession of genes encoding metallo-β-lactamases. The data reported here are consistent with results from other country-specific and regional surveillance studies and show that ceftazidime-avibactam demonstrates in vitro activity against globally collected clinical isolates of P. aeruginosa, including isolates that are resistant to ceftazidime and meropenem.

Assessment of the In Vitro Activity of Ceftazidime-Avibactam against Multidrug-Resistant Klebsiella spp. Collected in the INFORM Global Surveillance Study, 2012 to 2014

Increasing resistance in Gram-negative bacilli, including Klebsiella spp., has reduced the utility of broad-spectrum cephalosporins. Avibactam, a novel non-β-lactam β-lactamase inhibitor, protects β-lactams from hydrolysis by Gram-negative bacteria that produce extended-spectrum β-lactamases (ESBLs) and serine carbapenemases, including Ambler class A and/or class C and some class D enzymes. In this analysis, we report the in vitro activity of ceftazidime-avibactam and comparators against multidrug-resistant (MDR) Klebsiella spp. from the 2012-2014 INFORM surveillance study. Isolates collected from 176 sites were sent to a central laboratory for confirmatory identification and tested for susceptibility to ceftazidime-avibactam and comparator agents, including ceftazidime alone. A total of 2,821 of 10,998 (25.7%) Klebsiella species isolates were classified as MDR, based on resistance to three or more classes of antimicrobials. Among the MDR isolates, 99.4% had an ESBL screen-positive phenotype, and 27.4% were not susceptible to meropenem as an example of a carbapenem. Ceftazidime-avibactam was highly active against MDR isolates, including ESBL-positive and serine carbapenemase-producing isolates, with MIC50/90 values of 0.5/2 μg/ml and 96.6% of all MDR isolates and ESBL-positive MDR isolates inhibited at the FDA breakpoint (MIC value of ≤8 μg/ml). Ceftazidime-avibactam did not inhibit isolates producing class B enzymes (metallo-β-lactamases) either alone or in combination with other enzymes. These in vitro results support the continued investigation of ceftazidime-avibactam for the treatment of MDR Klebsiella species infections.

New antibiotics and antimicrobial combination therapy for the treatment of gram-negative bacterial infections

PURPOSE OF REVIEW

Increasing rates of life-threatening infections due to multidrug-resistant (MDR) gram-negative bacteria, such as carbapenemase-producer strains, as well as pathogens that are resistant to all current therapeutic options, have been reported. The number of compounds that are currently being developed is still insufficient to control this global threat. We have reviewed the current available options for the treatment of MDR gram-negative infections, including combination regimens employing older antimicrobials and new compounds.

RECENT FINDINGS

A limited number of large trials have assessed the treatment options for commonly encountered resistant pathogens (e.g., Klebsiella pneumoniae, Acinetobacter baumanii, Pseudomonas aeruginosa). Antimicrobials that were used in the past, such as colistin and fosfomycin, have been recently resumed and used in association with carbapenems, tigecycline, or aminoglycosides, showing a positive impact on clinical outcomes. New compounds belonging to various antimicrobial classes (e.g. beta-lactamase inhibitors, cephalosporins, glycyclines, aminoglycosides) have been investigated.

SUMMARY

Only few new molecules have an adequate activity against MDR gram-negative pathogens, especially carbapenemase-producer strains. Among these, ceftozolane/tazobactam has been recently approved for clinical use. Other compounds, such as avibactam combinations, plazomicin, and eravacycline, have shown promising activity in phase 2 and 3 clinical trials.