Global Dissemination of blaKPC into Bacterial Species beyond Klebsiella pneumoniae and In Vitro Susceptibility to Ceftazidime-Avibactam and Aztreonam-Avibactam

Past, present, and future perspectives on aztreonam and avibactam

INTRODUCTION

Aztreonam is a monobactam antibiotic approved in 1986 to treat infections caused by aerobic Gram-negative bacteria, but, together with cephalosporins, lost clinical utility due to the emergence of extended-spectrum β-lactamases (ESBLs) and novel (serine) carbapenemases. Avibactam was the first in a novel non-β-lactam β-lactamase inhibitor class to effectively inhibit these enzymes. It has been approved in combination with ceftazidime to treat Gram-negative infections caused by bacteria that produce AmpC, ESBLs and serine carbapenemases, and with aztreonam to treat patients infected with metallo-β-lactamase-producing enteric bacteria. Combinations of avibactam with ceftazidime and/or aztreonam have been used successfully to treat enteric pathogens producing multiple classes of β-lactamases.

AREAS COVERED

Development of aztreonam, avibactam, and avibactam combinations are placed into a historical perspective, based on both preclinical and clinical data. A search of MEDLINE (Ovid) was used to identify relevant literature.

EXPERT OPINION

Avibactam combined with ceftazidime and aztreonam in either dual or triple combinations provides the opportunity to treat previously untreatable Gram-negative infections that produce multiple β-lactamases. Aztreonam combinations should be particularly attractive, due to stability to metallo-β-lactamase hydrolysis and its safety advantage in treating penicillin-allergic patients. Other inhibitor combinations in development may challenge these combinations.

Carbapenem-Resistant Pseudomonas aeruginosa's Resistome: Pan-Genomic Plasticity, the Impact of Transposable Elements and Jumping Genes

Pseudomonas aeruginosa, a Gram-negative, motile bacterium, may cause significant infections in both community and hospital settings, leading to substantial morbidity and mortality. This opportunistic pathogen can thrive in various environments, making it a public health concern worldwide. P. aeruginosa's genomic pool is highly dynamic and diverse, with a pan-genome size ranging from 5.5 to 7.76 Mbp. This versatility arises from its ability to acquire genes through horizontal gene transfer (HGT) via different genetic elements (GEs), such as mobile genetic elements (MGEs). These MGEs, collectively known as the mobilome, facilitate the spread of genes encoding resistance to antimicrobials (ARGs), resistance to heavy metals (HMRGs), virulence (VGs), and metabolic functions (MGs). Of particular concern are the acquired carbapenemase genes (ACGs) and other β-lactamase genes, such as classes A, B [metallo-β-lactamases (MBLs)], and D carbapenemases, which can lead to increased antimicrobial resistance. This review emphasizes the importance of the mobilome in understanding antimicrobial resistance in P. aeruginosa.

Global phylogeography and genetic characterization of carbapenem and ceftazidime-avibactam resistant KPC-33-producing Pseudomonas aeruginosa

Ceftazidime-avibactam (CZA) is currently one of the last resorts used to treat infections caused by carbapenem-resistant Enterobacteriaceae and Pseudomonas aeruginosa. However, KPC variants have become the main mechanism mediating CZA resistance in KPC-producing gram-negative bacteria after increasing the application of CZA. Our previous study revealed that CZA-resistant KPC-33 had emerged in carbapenem-resistant P. aeruginosa (CRPA) and had resulted in death due to hypervirulence and extensive drug resistance; however, the evolutionary path of KPC-33-producing CRPA has not been investigated. Here, we observed the emergence of blaKPC-33 in CRPA under drug pressure, leading to resistance to CZA. We further elucidated the pathway of resistance development due to blaKPC mutations in P. aeruginosa. Three KPC-producing P. aeruginosa (KPC-PA) strains (including one blaKPC-33-positive strain and two blaKPC-2-positive strains) were successively isolated from a hospitalized patient. The blaKPC-33-positive CZA-resistant strain SRPA0656 (CZA MIC >128 μg/mL, imipenem MIC = 32 μg/mL) was isolated after the blaKPC-2-positive P. aeruginosa SRP2863 (CZA MIC = 1 μg/mL, imipenem MIC >128 μg/mL) was treated with CZA. The subsequent use of carbapenems to treat the infection led to the re-emergence of the KPC-2-producing strain SRPA3703. Additionally, we collected four other KPC-33-producing P. aeruginosa strains. Antimicrobial susceptibility testing revealed that all the KPC-33-bearing P. aeruginosa strains in this study were multidrug-resistant but susceptible to colistin and amikacin. Whole-genome sequencing indicated that blaKPC-33 was located on two Tn4401-like transposons contained in the plasmids and that most of these plasmids could be transferred into P. aeruginosa PAO1Rif isolates. Growth rate determination demonstrated that the relative growth rate of P. aeruginosa harboring blaKPC-33 was faster than that of P. aeruginosa harboring blaKPC-2 in the logarithmic phase. Global phylogenetic analysis revealed that most KPC-PA strains were isolated from China and the USA. MLST revealed that the most common ST in KPC-PA was ST463, which was detected only in China, and that all the strains carried blaKPC-2 or its derivatives. These results indicated that the use of CZA for the treatment of KPC-2-producing P. aeruginosa may have contributed to the evolution of KPC-33. The widespread dissemination of KPC-PA (especially the ST463) and Tn4401 transposons may increase the spread of CRPA isolates carrying blaKPC-33. Close attention to the development of resistance to CZA during clinical treatment of CRPA infection and monitoring CZA-resistant strains is necessary to prevent further spread.

Antimicrobial Resistance Profiles of Pseudomonas aeruginosa in the Arabian Gulf Region Over a 12-Year Period (2010-2021)

OBJECTIVES

To evaluate literature from a 12-year period (2010-2021) on the antimicrobial resistance profile of Pseudomonas aeruginosa from the Arabian Gulf countries (Bahrain, Kuwait, Oman, Qatar, Saudi Arabia, and the United Arab Emirates).

METHODS

An electronic literature search was conducted for articles on antimicrobial resistance in P. aeruginosa and associated phenotypes, covering the period of 1st January 2010 to 1st December 2021.

RESULTS

Antimicrobial resistance in the Arabian Gulf was highest to meropenem (10.3-45.7%) and lowest to colistin (0.0-0.8%), among the agents tested. Annual data showed that ceftazidime resistance (Kuwait), piperacillin-tazobactam non-susceptibility (Qatar), and aztreonam, imipenem, and meropenem resistance (Saudi Arabia) increased by 12-17%. Multiple mechanisms of carbapenem resistance were identified and multiple clones were detected, including high-risk clones such as ST235. The most common carbapenemases detected were the VIM-type metallo-β-lactamases.

CONCLUSIONS

Among P. aeruginosa in the Arabian Gulf countries, resistance to meropenem was higher than to the other agents tested, and meropenem resistance increased in Saudi Arabia during the study period. Resistance to colistin, a classic antibiotic used to treat Pseudomonas spp. infections, remained low. The VIM-type β-lactamase genes were dominant. We recommend local and regional antimicrobial resistance surveillance programs to detect the emergence of resistance genes and to monitor antimicrobial resistance trends in P. aeruginosa.

Genomic and Phenotypic Analysis of bla KPC-2 Associated Carbapenem Resistance in Klebsiella aerogenes: Insights into Clonal Spread and Resistance Mechanisms Across Hospital Departments in Beijing

Purpose

This study conducted an phenotypic and whole-genome sequencing analysis with Klebsiella aerogenes to elucidate its clinical epidemiological characteristics, antimicrobial resistance (AMR) phenotype, biofilm formation ability and hemolytic activity testing, AMR genes and phylogenetic relationships, so as to provide a further understanding of the intra-hospital strain transmission.

Methods

Samples were collected from a hospital in Beijing between 2020 and 2022. All strains underwent bacterial identification, antimicrobial susceptibility testing (AST) using the VITEK-2 compact system. Biofilm formation ability and hemolytic activity were tested. Second-generation sequencing was applied to all strains, with those carrying the bla KPC gene were selected for third-generation sequencing. Whole-genome analysis identified resistance genes, plasmid types, MLST typing, and phylogenetic relationships. Plasmids were assembled to detect plasmid structures and AMR gene location.

Results

Among the 42 K. aerogenes isolates, 21 were carbapenem-resistant K. aerogenes (CRKA). All strains exhibited strong biofilm formation and no hemolytic activity. Most were sourced from sputum (83.3%). CRKA demonstrated extensive resistance to antibiotics, particularly β-lactamase inhibitors and Cefotetan. This resistance pattern was closely associated with the presence of an IncFII(pHN7A8) plasmid, which carried multiple resistance genes, including bla KPC-2, bla CTX-M-65, bla TEM-1, rmtB and a large number of mobile elements. The majority of CRKA strains clustered within the same branch of the phylogenetic tree, exhibiting minimal single nucleotide polymorphism (0-13 SNPs) differences, and they shared the same sequence type (ST292), resistance genes, and plasmids, originating from different departments, suggesting clonal transmission among the hospital.

Conclusion

Our research reveals that the clonal transmission of CRKA occurs across various departments within the hospital. The widespread resistance observed in CRKA, attributed to the presence of bla KPC and ESBLs genes, underscores the need for heightened vigilance to prevent the further dissemination of CRKA within the hospital and, potentially, throughout the wider community.

Effect of ceftazidime-avibactam combined with different antimicrobials against carbapenem-resistant Klebsiella pneumoniae

This study aimed to assess the in vitro efficacy of ceftazidime-avibactam (CZA) in combination with various antimicrobial agents against carbapenem-resistant Klebsiella pneumoniae (CRKP). We selected 59 clinical CRKP isolates containing distinct drug resistance mechanisms. The minimum inhibitory concentrations (MICs) of meropenem (MEM), colistin (COL), eravacycline (ERA), amikacin (AK), fosfomycin (FOS), and aztreonam (ATM), both individually and in combination with CZA, were tested using the checkerboard method. The interactions of antimicrobial agent combinations were assessed by fractional inhibitory concentration index (FICI) and susceptible breakpoint index (SBPI). The time-kill curve assay was employed to dynamically evaluate the effects of these drugs alone and in combination format. In the checkerboard assay, the combination of CZA+MEM showed the highest level of synergistic effect against both KPC-producing and carbapenemase-non-producing isolates, with synergy rates of 91.3% and 100%, respectively. Following closely was the combination of FOS+CZA . For metallo-beta-lactamases (MBLs) producing strains, ATM+CZA displayed complete synergy, while the combination of MEM+CZA showed a synergy rate of only 57.14% for NDM-producing strains and 91.67% for IMP-producing strains. In the time-kill assay, MEM+CZA also demonstrated significant synergistic effects against the two KPC-2-producing isolates (Y070 and L70), the two carbapenemase-non-producing isolates (Y083 and L093), and the NDM-1-producing strain L13, with reductions in log10 CFU/mL exceeding 10 compared to the control. Against the IMP-producing strain Y047, ATM+CZA exhibited the highest synergistic effect, resulting in a log10 CFU/mL reduction of 10.43 compared to the control. The combination of CZA and MEM exhibited good synergistic effects against KPC-producing and non-enzyme-producing strains, followed by the FOS+CZA combination. Among MBL-producing strains, ATM+CZA demonstrated the most pronounced synergistic effect. However, the combinations of CZA with ERA, AK, and COL show irrelevant effects against the tested clinical isolates.

IMPORTANCE

Our study confirmed the efficacy of the combination CZA+MEM against KPC-producing and non-carbapenemase-producing strains. For metalloenzyme-producing strains, CZA+ATM demonstrated the most significant synergy. Additionally, CZA exhibited a notable synergy effect when combined with FOS. These combination therapies present promising new options for the treatment of CRKP infection.

Genomic insights into the expansion of carbapenem-resistant Klebsiella pneumoniae within Portuguese hospitals

Carbapenem-resistant Klebsiella pneumoniae (CR-KP) are a public health concern, causing infections with a high mortality rate, limited therapeutic options and challenging infection control strategies. In Portugal, the CR-KP rate has increased sharply, but the factors associated with this increase are poorly explored. In order to address this question, phylogenetic and resistome analysis were used to compare the draft genomes of 200 CR-KP isolates collected in 2017-2019 from five hospitals in the Lisbon region, Portugal. Most CR-KP belonged to sequence type (ST) 13 (29%), ST17 (15%), ST348 (13%), ST231 (12%) and ST147 (7%). Carbapenem resistance was conferred mostly by the presence of KPC-3 (74%) or OXA-181 (18%), which were associated with IncF/IncN and IncX plasmids, respectively. Almost all isolates were multi-drug resistant, harbouring resistance determinants to aminoglycosides, beta-lactams, trimethoprim, fosfomycin, quinolones and sulphonamides. In addition, 11% of isolates were resistant to colistin. Colonizing and infecting isolates were highly related, and most colonized patients (89%) reported a previous hospitalization. Moreover, among the 171 events of cross-dissemination identified by core genome multi-locus sequence typing data analysis (fewer than five allelic differences), 41 occurred between different hospitals and 130 occurred within the same hospital. The results suggest that CR-KP dissemination in the Lisbon region results from acquisition of carbapenemases in mobile genetic elements, influx of CR-KP into the hospitals by colonized ambulatory patients, and transmission of CR-KP within and between hospitals. Prudent use of carbapenems, patient screening at hospital entry, and improvement of infection control are needed to decrease the burden of CR-KP infection in Portugal.

Prevalence and characteristics of ESBL-producing Escherichia coli in clinically healthy pigs: implications for antibiotic resistance spread in livestock

AIM

This study aimed to compare and characterize the resistance profile and the presence of extended-spectrum beta-lactamase (ESBL) related genes in Escherichia coli isolated from healthy finishing pigs fed with or without antibiotics in their diets.

METHODS AND RESULTS

A total of 27 ceftiofur-resistant E. coli isolates were obtained from 96 healthy pigs. The antibiotic resistance profile was tested, and all 27 isolates were classified as multidrug-resistant (MDR). A high proportion of isolates were resistant to cephalosporins, ampicillin, ciprofloxacin, and tetracyclines. The ESBL production was observed in 85% of isolates by double-disc synergy test. The MDR-E. coli isolates harbored ESBL genes, such as blaTEM, blaCTX-M-1, blaCTX-M-2, and blaCTX-M-8,25. In addition, other antibiotics resistance genes (ARGs) were also detected, such as sul2, ant(3″)-I, tetA, and mcr-1. The mobilization of the blaCTX-M gene was confirmed for nine E. coli isolates by conjugation assays. The presence of blaCTX-M on mobile genetic elements in these isolates was demonstrated by Southern blot hybridization, and the resistance to cephalosporins was confirmed in the transconjugants. Our results indicate the prevalence of CTX-M-producing E. coli strains harboring mobile genetic elements in the normal microbiota of healthy pigs.

CONCLUSIONS

These findings highlight the significance of ESBL genes as a global health concern in livestock and the potential spread of antimicrobial resistance to other members of the gastrointestinal tract microbiota.

Role of β-Lactamase Inhibitors as Potentiators in Antimicrobial Chemotherapy Targeting Gram-Negative Bacteria

Since the discovery of penicillin, β-lactam antibiotics have commonly been used to treat bacterial infections. Unfortunately, at the same time, pathogens can develop resistance to β-lactam antibiotics such as penicillins, cephalosporins, monobactams, and carbapenems by producing β-lactamases. Therefore, a combination of β-lactam antibiotics with β-lactamase inhibitors has been a promising approach to controlling β-lactam-resistant bacteria. The discovery of novel β-lactamase inhibitors (BLIs) is essential for effectively treating antibiotic-resistant bacterial infections. Therefore, this review discusses the development of innovative inhibitors meant to enhance the activity of β-lactam antibiotics. Specifically, this review describes the classification and characteristics of different classes of β-lactamases and the synergistic mechanisms of β-lactams and BLIs. In addition, we introduce potential sources of compounds for use as novel BLIs. This provides insights into overcoming current challenges in β-lactamase-producing bacteria and designing effective treatment options in combination with BLIs.

In vitro activity of aztreonam-avibactam and comparators against Metallo-β-Lactamase-producing Enterobacterales from ATLAS Global Surveillance Program, 2016-2020

OBJECTIVES

Metallo-β-lactamase (MBL)-producing Enterobacterales are a major challenge worldwide due to limited treatment options. Aztreonam-avibactam (ATM-AVI), which is under clinical development, has shown activity against MBL-positive isolates. This study evaluated the prevalence of MBL producers and the nature of enzymes among a global collection of clinical isolates of Enterobacterales from the Antimicrobial Testing Leadership and Surveillance program (ATLAS) surveillance program (2016-2020), and the antimicrobial activity of ATM-AVI and comparators against this collection.

METHODS

Non-duplicate clinical isolates of Enterobacterales (N = 106 686) collected across 63 countries were analysed. Antimicrobial susceptibility was performed using broth microdilution. Minimum inhibitory concentrations (MICs) were interpreted using Clinical and Laboratory Standards Institute and European Committee on Antimicrobial Susceptibility Testing breakpoints. Provisional pharmacokinetic/pharmacodynamic breakpoint of ≤8 mg/L was considered for ATM-AVI. β-lactamase genes were characterized by polymerase chain reaction and sequencing. The Cochran Armitage Trend test was used to determine significant trends in percentage of isolates over time.

RESULTS

Overall, MBL-positive isolates were 1.6% of total Enterobacterales isolates globally, with a significant increasing trend observed over time, globally and across regions (P < 0.05). New Delhi MBL (NDM) was the most common MBL (83.3%). ATM-AVI demonstrated potent activity against MBL-positive isolates (MIC ≤8 mg/L: 99.4% isolates inhibited; MIC90, 1 mg/L). Consistent activity was also noted across different regions. Potent activity was demonstrated against different NDM variants and MBL-positive isolates co-carrying other carbapenemases (98.1% and 99.7% isolates inhibited at ≤8 mg/L, respectively). About 0.6% MBL-positive isolates (10/1707) had MICs >8 mg/L for ATM-AVI.

CONCLUSION

ATM-AVI demonstrated potent activity against MBL-positive isolates, including NDM variants and MBL-positive isolates co-carrying other carbapenemases, and may represent a good option for treating infections caused by MBL-positive Enterobacterales.

Inter-plasmid transfer of antibiotic resistance genes accelerates antibiotic resistance in bacterial pathogens

Antimicrobial resistance is a major threat for public health. Plasmids play a critical role in the spread of antimicrobial resistance via horizontal gene transfer between bacterial species. However, it remains unclear how plasmids originally recruit and assemble various antibiotic resistance genes (ARGs). Here, we track ARG recruitment and assembly in clinically relevant plasmids by combining a systematic analysis of 2420 complete plasmid genomes and experimental validation. Results showed that ARG transfer across plasmids is prevalent, and 87% ARGs were observed to potentially transfer among various plasmids among 8229 plasmid-borne ARGs. Interestingly, recruitment and assembly of ARGs occur mostly among compatible plasmids within the same bacterial cell, with over 88% of ARG transfers occurring between compatible plasmids. Integron and insertion sequences drive the ongoing ARG acquisition by plasmids, especially in which IS26 facilitates 63.1% of ARG transfer events among plasmids. In vitro experiment validated the important role of IS26 involved in transferring gentamicin resistance gene aacC1 between compatible plasmids. Network analysis showed four beta-lactam genes (blaTEM-1, blaNDM-4, blaKPC-2, and blaSHV-1) shuffling among 1029 plasmids and 45 clinical pathogens, suggesting that clinically alarming ARGs transferred accelerate the propagation of antibiotic resistance in clinical pathogens. ARGs in plasmids are also able to transmit across clinical and environmental boundaries, in terms of the high-sequence similarities of plasmid-borne ARGs between clinical and environmental plasmids. This study demonstrated that inter-plasmid ARG transfer is a universal mechanism for plasmid to recruit various ARGs, thus advancing our understanding of the emergence of multidrug-resistant plasmids.

Klebsiella pneumoniae carbapenemase variants: the new threat to global public health

Klebsiella pneumoniae carbapenemase (KPC) variants, which refer to the substitution, insertion, or deletion of amino acid sequence compared to wild blaKPC type, have reduced utility of ceftazidime-avibactam (CZA), a pioneer antimicrobial agent in treating carbapenem-resistant Enterobacterales infections. So far, more than 150 blaKPC variants have been reported worldwide, and most of the new variants were discovered in the past 3 years, which calls for public alarm. The KPC variant protein enhances the affinity to ceftazidime and weakens the affinity to avibactam by changing the KPC structure, thereby mediating bacterial resistance to CZA. At present, there are still no guidelines or expert consensus to make recommendations for the diagnosis and treatment of infections caused by KPC variants. In addition, meropenem-vaborbactam, imipenem-relebactam, and other new β-lactam-β-lactamase inhibitor combinations have little discussion on KPC variants. This review aims to discuss the clinical characteristics, risk factors, epidemiological characteristics, antimicrobial susceptibility profiles, methods for detecting blaKPC variants, treatment options, and future perspectives of blaKPC variants worldwide to alert this new great public health threat.

Antimicrobial Activities of Aztreonam-Avibactam and Comparator Agents against Enterobacterales Analyzed by ICU and Non-ICU Wards, Infection Sources, and Geographic Regions: ATLAS Program 2016-2020

Increasing antimicrobial resistance among multidrug-resistant (MDR), extended-spectrum β-lactamase (ESBL)- and carbapenemase-producing Enterobacterales (CPE), in particular metallo-β-lactamase (MBL)-positive strains, has led to limited treatment options in these isolates. This study evaluated the activity of aztreonam-avibactam (ATM-AVI) and comparator antimicrobials against Enterobacterales isolates and key resistance phenotypes stratified by wards, infection sources and geographic regions as part of the ATLAS program between 2016 and 2020. Minimum inhibitory concentrations (MICs) were determined per Clinical and Laboratory Standards Institute (CLSI) guidelines. The susceptibility of antimicrobials were interpreted using CLSI and European Committee on Antimicrobial Susceptibility Testing (EUCAST) breakpoints. A tentative pharmacokinetic/pharmacodynamic breakpoint of 8 µg/mL was considered for ATM-AVI activity. ATM-AVI inhibited ≥99.2% of Enterobacterales isolates across wards and ≥99.7% isolates across infection sources globally and in all regions at ≤8 µg/mL. For resistance phenotypes, ATM-AVI demonstrated sustained activity across wards and infection sources by inhibiting ≥98.5% and ≥99.1% of multidrug-resistant (MDR) isolates, ≥98.6% and ≥99.1% of ESBL-positive isolates, ≥96.8% and ≥90.9% of carbapenem-resistant (CR) isolates, and ≥96.8% and ≥97.4% of MBL-positive isolates, respectively, at ≤8 µg/mL globally and across regions. Overall, our study demonstrated that ATM-AVI represents an important therapeutic option for infections caused by Enterobacterales, including key resistance phenotypes across different wards and infection sources.

Genotypic detection of β-lactamase-producing Escherichia coli isolates obtained from Seven Crater Lakes of San Pablo, Laguna, Philippines

The extended-spectrum β-lactamase (ESBL)-producing Escherichia coli is becoming a global public health concern. More comprehensive surveillance of β-lactam resistance in E. coli would improve monitoring strategies and control resistance transmission in contaminated environments. This study investigated the prevalence of β-lactamase genes in E. coli isolated from the Seven Crater Lakes in San Pablo, Laguna, Philippines. Water samples from lakes were collected for the isolation of E. coli (n = 846) and molecular characterization by detecting the presence of the uidA gene. The isolates were then tested for the presence of β-lactamase genes using PCR. Among the screened genes, blaAmpC was the most dominant (91%). Other β-lactamase genes such as blaTEM, blaSHV, and blaCTXM were also detected with percentage occurrence of 34, 5, and 1%, respectively. Multiple genes within individual isolates were also observed, wherein blaTEM/AmpC was the most prevalent gene combination. Moreover, a significant negative correlation between blaAmpC with blaSHV and blaCTXM was depicted in this study. Overall, these findings demonstrate the presence of β-lactamase genes in E. coli in the Seven Crater Lakes of San Pablo and can be used in developing effective strategies to control antibiotic resistance in environmental waters.

In vitro activity of imipenem/relebactam against non-Morganellaceae Enterobacterales and Pseudomonas aeruginosa in the Asia-Pacific region: SMART 2017-2020

OBJECTIVES

To describe the in vitro activity of imipenem/relebactam (IMR) against non-Morganellaceae Enterobacterales (NME) and Pseudomonas aeruginosa, including piperacillin/tazobactam-nonsusceptible and meropenem-nonsusceptible isolates, infecting hospitalized patients in the Asia-Pacific region.

METHODS

From 2017 to 2020, 49 clinical laboratories in nine countries in the Asia-Pacific region participated in the SMART global surveillance program and contributed 26 783 NME and 6383 P. aeruginosa. Minimum inhibitory concentrations (MICs) were determined using CLSI broth microdilution and interpreted using CLSI M100 (2021) breakpoints. β-Lactamase genes were identified in selected isolate subsets (2017-2020) and oprD was sequenced in molecularly characterized P. aeruginosa collected in 2020.

RESULTS

Amikacin (97.9% susceptible), IMR (95.8%), meropenem (95.4%), and imipenem (92.6%) were the most active agents against NME. Among piperacillin/tazobactam-nonsusceptible NME (n=4070), 76.1% were IMR-susceptible (range by country, 97.5% [New Zealand] to 50.6% [Vietnam]); 22.4% of meropenem-nonsusceptible NME (n=1225) were IMR-susceptible (range by country, 68.8% [South Korea] to 7.6% [Thailand]). A total of 2.7% of NME carried a metallo-β-lactamase (MBL), 0.9% an OXA-48-like carbapenemase (MBL-negative), and 0.7% a KPC (MBL-negative). Amikacin (94.0% susceptible) and IMR (90.3%) were the most active agents against P. aeruginosa; 71.2% of isolates were imipenem-susceptible. Relebactam increased susceptibility to imipenem by 25.6% (from 40.5% to 66.1%) in piperacillin/tazobactam-nonsusceptible and by 44.8% (from 7.1% to 51.9%) in meropenem-nonsusceptible P. aeruginosa. Only 4.3% of P. aeruginosa were MBL-positive. A total of 70.3% (90/128) of IMR-nonsusceptible P. aeruginosa were oprD-deficient.

CONCLUSION

In 2017-2020, 96% of NME and 90% of P. aeruginosa from the Asia-Pacific region were IMR-susceptible. IMR percent susceptible rates were higher in countries with lower MBL carriage.

Rationale and evidence for the use of new beta-lactam/beta-lactamase inhibitor combinations and cefiderocol in critically ill patients

BACKGROUND

Healthcare-associated infections involving Gram-negative bacteria (GNB) with difficult-to-treat resistance (DTR) phenotype are associated with impaired patient-centered outcomes and poses daily therapeutic challenges in most of intensive care units worldwide. Over the recent years, four innovative β-lactam/β-lactamase inhibitor (BL/BLI) combinations (ceftolozane-tazobactam, ceftazidime-avibactam, imipenem-relebactam and meropenem-vaborbactam) and a new siderophore cephalosporin (cefiderocol) have been approved for the treatment of certain DTR-GNB infections. The literature addressing their microbiological spectrum, pharmacokinetics, clinical efficacy and safety was exhaustively audited by our group to support the recent guidelines of the French Intensive Care Society on their utilization in critically ill patients. This narrative review summarizes the available evidence and unanswered questions on these issues.

METHODS

A systematic search for English-language publications in PUBMED and the Cochrane Library database from inception to November 15, 2022.

RESULTS

These drugs have demonstrated relevant clinical success rates and a reduced renal risk in most of severe infections for whom polymyxin- and/or aminoglycoside-based regimen were historically used as last-resort strategies-namely, ceftazidime-avibactam for infections due to Klebsiella pneumoniae carbapenemase (KPC)- or OXA-48-like-producing Enterobacterales, meropenem-vaborbactam for KPC-producing Enterobacterales, ceftazidime-avibactam/aztreonam combination or cefiderocol for metallo-β-lactamase (MBL)-producing Enterobacterales, and ceftolozane-tazobactam, ceftazidime-avibactam and imipenem-relebactam for non-MBL-producing DTR Pseudomonas aeruginosa. However, limited clinical evidence exists in critically ill patients. Extended-infusion scheme (except for imipenem-relebactam) may be indicated for DTR-GNB with high minimal inhibitory concentrations and/or in case of augmented renal clearance. The potential benefit of combining these agents with other antimicrobials remains under-investigated, notably for the most severe presentations. Other important knowledge gaps include pharmacokinetic information in particular situations (e.g., pneumonia, other deep-seated infections, and renal replacement therapy), the hazard of treatment-emergent resistance and possible preventive measures, the safety of high-dose regimen, the potential usefulness of rapid molecular diagnostic tools to rationalize their empirical utilization, and optimal treatment durations. Comparative clinical, ecological, and medico-economic data are needed for infections in whom two or more of these agents exhibit in vitro activity against the causative pathogen.

CONCLUSIONS

New BL/BLI combinations and cefiderocol represent long-awaited options for improving the management of DTR-GNB infections. Several research axes must be explored to better define the positioning and appropriate administration scheme of these drugs in critically ill patients.

Novel Beta Lactam Antibiotics for the Treatment of Multidrug-Resistant Gram-Negative Infections in Children: A Narrative Review

Infections due to carbapenem-resistant Enterobacterales (CRE) are increasingly prevalent in children and are associated with poor clinical outcomes, especially in critically ill patients. Novel beta lactam antibiotics, including ceftolozane-tazobactam, ceftazidime-avibactam, meropenem-vaborbactam, imipenem-cilastatin-relebactam, and cefiderocol, have been released in recent years to face the emerging challenge of multidrug-resistant (MDR) Gram-negative bacteria. Nonetheless, several novel agents lack pediatric indications approved by the Food and Drug Administration (FDA) and the European Medicine Agency (EMA), leading to uncertain pediatric-specific treatment strategies and uncertain dosing regimens in the pediatric population. In this narrative review we have summarized the available clinical and pharmacological data, current limitations and future prospects of novel beta lactam antibiotics in the pediatric population.

Comparison of In Vitro Activity of Ceftazidime-Avibactam and Imipenem-Relebactam against Clinical Isolates of Pseudomonas aeruginosa

The role of novel β-lactam/β-lactamase inhibitor combinations in ceftazidime-nonsusceptible (CAZ-NS) and imipenem-nonsusceptible (IPM-NS) Pseudomonas aeruginosa has not been fully elucidated. This study evaluated the in vitro activity of novel β-lactam/β-lactamase inhibitor combinations against Pseudomonas aeruginosa clinical isolates, determined how avibactam restored ceftazidime activity, and compared the activity of ceftazidime-avibactam (CZA) and imipenem-relebactam (IMR) against KPC-producing P. aeruginosa. Similar high susceptibility rates for CZA, IMR, and ceftolozane-tazobactam (88.9% to 89.8%) were found for 596 P. aeruginosa clinical isolates from 11 hospitals in China, and a higher susceptibility rate to ceftazidime than imipenem was observed (73.5% versus 63.1%). For CAZ-NS and IPM-NS isolates, susceptibility rates for CZA, ceftolozane-tazobactam, and IMR were 61.5% (75/122), 54.9% (67/122), and 51.6% (63/122), respectively. For CAZ-NS, IPM-NS but CZA-susceptible isolates, 34.7% (26/75) harbored acquired β-lactamases with KPC-2 predominant (n = 19), and 45.3% (34/75) presented overexpression of chromosomal β-lactamase ampC. Among 22 isolates carrying KPC-2 carbapenemase alone, susceptibility rates to CZA and IMR were 86.4% (19/22) and 9.1% (2/22), respectively. Notably, 95% (19/20) of IMR-nonsusceptible isolates had an inactivating mutation of oprD gene. In conclusion, CZA, ceftolozane-tazobactam, and IMR exhibit high activity against P. aeruginosa, and CZA is more active than IMR against CAZ-NS and IPM-NS isolates as well as KPC-producing P. aeruginosa. Avibactam overcomes ceftazidime resistance engendered by KPC-2 enzyme and overexpressed AmpC. IMPORTANCE The emergence of antimicrobial resistance poses a particular challenge globally, and the concept of P. aeruginosa with "difficult-to-treat" resistance (DTR-P. aeruginosa) was proposed. Here, P. aeruginosa clinical isolates were highly susceptible to three β-lactamase inhibitor combinations, CZA, IMR, and ceftolozane-tazobactam. The combination of KPC-2 enzyme and nonfunctional porin OprD contributed to IMR resistance in P. aeruginosa, and CZA was more active than IMR in fighting against KPC-2-producing P. aeruginosa. CZA also showed good activity against CAZ-NS and IPM-NS P. aeruginosa, primarily by inhibiting KPC-2 enzyme and overproduced AmpC, supporting the clinical use of CZA in the treatment of infections caused by DTR-P. aeruginosa.

Risk factors and outcomes of inpatients with carbapenem-resistant Pseudomonas aeruginosa bloodstream infections in China: a 9-year trend and multicenter cohort study

Objective

Bacteremia caused by carbapenem-resistant Pseudomonas aeruginosa (CRPA) has high mortality, threatening the healthcare quality worldwide. Analysis is required to update the epidemiological data of CRPA bloodstream infections (BSI) and evaluate the prevalent strains in China. Moreover, it is necessary to clarify the risk factors associated with the development and mortality of CRPA bacteremia.

Methods

This is a 9-year multicenter retrospective study, enrolling 137 patients with CRPA BSI and 137 carbapenem-susceptible P. aeruginosa (CSPA) BSI during January 2012 and December 2020. Antimicrobials susceptibility between the two groups were compared. Risk factors of CRPA BSI were identified by binary logistic regression for development and cox regression for mortality. The Kaplan-Meier method was used to compare time to mortality. CRPA and difficult-to-treat resistant P. aeruginosa (DTRPA) detection rate was analyzed year-by-year in ZYH.

Results

A total of 7,384 P. aeruginosa clinical samples were cultured in ZYH during 9  years, and notable increase of CRPA and DTRPA detection rate in P. aeruginosa BSI was identified (from 17 to 60%; from 2.1 to 25%). Multivariate analysis revealed that prior ICU hospitalization, immunosuppressive therapy and exposure to carbapenems were independent risk factors for development of CRPA BSI. The 30-day crude mortality of 137 CRPA BSI was 39%. A total of 46 DTRPA were identified, and the 30-day mortality for patients infected by DTRPA was 50%. The 30-day crude mortality of CRPA BSI was independently associated with multiple organ failure and higher Pitt bacteremia score, whereas receipt appropriate therapy improved prognosis.

Conclusion

A significant increase in the detection rate of CRPA and DTRPA in P. aeruginosa BSI was identified. Strict policies for carbapenems usage, cautious decisions regarding the usage of immunosuppressive agent and standard care for patients with prior ICU hospitalization are necessary for CRPA BSI management.

Worldwide Dissemination of blaKPC Gene by Novel Mobilization Platforms in Pseudomonas aeruginosa: A Systematic Review

The dissemination of blaKPC-harboring Pseudomonas aeruginosa (KPC-Pa) is considered a serious public health problem. This study provides an overview of the epidemiology of these isolates to try to elucidate novel mobilization platforms that could contribute to their worldwide spread. A systematic review in PubMed and EMBASE was performed to find articles published up to June 2022. In addition, a search algorithm using NCBI databases was developed to identify sequences that contain possible mobilization platforms. After that, the sequences were filtered and pair-aligned to describe the blaKPC genetic environment. We found 691 KPC-Pa isolates belonging to 41 different sequence types and recovered from 14 countries. Although the blaKPC gene is still mobilized by the transposon Tn4401, the non-Tn4401 elements (NTEKPC) were the most frequent. Our analysis allowed us to identify 25 different NTEKPC, mainly belonging to the NTEKPC-I, and a new type (proposed as IVa) was also observed. This is the first systematic review that consolidates information about the behavior of the blaKPC acquisition in P. aeruginosa and the genetic platforms implied in its successful worldwide spread. Our results show high NTEKPC prevalence in P. aeruginosa and an accelerated dynamic of unrelated clones. All information collected in this review was used to build an interactive online map.

In vitro activity of imipenem/relebactam against piperacillin/tazobactam-resistant and meropenem-resistant non-Morganellaceae Enterobacterales and Pseudomonas aeruginosa collected from patients with bloodstream, intra-abdominal and urinary tract infections in Western Europe: SMART 2018-2020

Introduction. Piperacillin/tazobactam and carbapenems are important agents for the treatment of serious Gram-negative infections in hospitalized patients. Resistance to both agents is a significant concern in clinical isolates of Enterobacterales and Pseudomonas aeruginosa; new agents with improved activity are needed.Gap Statement. Publication of current, region-specific data describing the in vitro activity of newer agents such as imipenem/relebactam (IMR) against piperacillin/tazobactam-resistant and carbapenem-resistant Enterobacterales and P. aeruginosa are needed to support their clinical use.Aim. To describe the in vitro activity of IMR against non-Morganellaceae Enterobacterales (NME) and P. aeruginosa isolated from bloodstream, intra-abdominal and urinary tract infection samples by hospital laboratories in Western Europe with a focus on the activity of IMR against piperacillin/tazobactam-resistant and meropenem-resistant isolates.Methodology. From 2018 to 2020, 29 hospital laboratories in six countries in Western Europe participated in the SMART global surveillance programme and contributed 9487 NME and 1004 P. aeruginosa isolates. MICs were determined by CLSI broth microdilution testing and interpreted by EUCAST (2021) breakpoints. β-Lactamase genes were identified in selected isolate subsets (2018-2020) and oprD sequenced in molecularly characterized P. aeruginosa (2020).Results. IMR (99.4 % susceptible), amikacin (98.0 %), meropenem (97.7 %) and imipenem (97.6 %) were the most active agents against NME; 83.1 % of NME were piperacillin/tazobactam-susceptible. Relebactam increased imipenem susceptibility of NME from Italy by 8.3 %, from Portugal by 2.9 %, and from France, Germany, Spain and the UK by <1 %. In total, 96.4 % of piperacillin/tazobactam-resistant (n=1601) and 73.7 % of meropenem-resistant (n=152) NME were IMR-susceptible. Also, 0.4 % of NME were MBL-positive, 0.9 % OXA-48-like-positive (MBL-negative) and 1.5 % KPC-positive (MBL-negative). Amikacin (95.4 % susceptible) and IMR (94.1 %) were the most active agents against P. aeruginosa; 81.7 % of isolates were imipenem-susceptible and 79.6 % were piperacillin/tazobactam-susceptible. Relebactam increased susceptibility to imipenem by 12.5 % overall (range by country, 4.3-17.5 %); and by 30.7 % in piperacillin/tazobactam-resistant and 24.3 % in meropenem-resistant P. aeruginosa. In total, 1.6 % of P. aeruginosa isolates were MBL-positive. Seven of eight molecularly characterized IMR-resistant P. aeruginosa isolates from 2020 were oprD-deficient.Conclusion. IMR may be a potential treatment option for bloodstream, intra-abdominal and urinary tract infections caused by NME and P. aeruginosa in Western Europe, including infections caused by piperacillin/tazobactam-resistant and meropenem-resistant isolates.

In vitro activity of imipenem/relebactam against piperacillin/tazobactam-resistant and meropenem-resistant non-Morganellaceae Enterobacterales and Pseudomonas aeruginosa collected from patients with lower respiratory tract infections in Western Europe: SMART 2018-20

Objectives

To describe the in vitro activity of imipenem/relebactam against non-Morganellaceae Enterobacterales (NME) and Pseudomonas aeruginosa recently isolated from lower respiratory tract infection samples by hospital laboratories in Western Europe.

Methods

From 2018 to 2020, 29 hospital laboratories in six countries in Western Europe participated in the SMART global surveillance programme and contributed 4414 NME and 1995 P. aeruginosa isolates. MICs were determined using the CLSI broth microdilution method and interpreted by EUCAST (2021) breakpoints. β-Lactamase genes were identified in selected isolate subsets (2018-20) and oprD sequenced in molecularly characterized P. aeruginosa (2020).

Results

Imipenem/relebactam (99.1% susceptible), amikacin (97.2%), meropenem (96.1%) and imipenem (95.9%) were the most active agents tested against NME; by country, relebactam increased imipenem susceptibility from <1% (France, Germany, UK) to 11.0% (Italy). A total of 96.0% of piperacillin/tazobactam-resistant (n = 990) and 81.1% of meropenem-resistant (n = 106) NME were imipenem/relebactam-susceptible. Only 0.5% of NME were MBL positive, 0.9% were OXA-48-like-positive (MBL negative) and 2.8% were KPC positive (MBL negative). Amikacin (91.5% susceptible) and imipenem/relebactam (91.4%) were the most active agents against P. aeruginosa; 72.3% of isolates were imipenem-susceptible. Relebactam increased susceptibility to imipenem by 34.4% (range by country, 39.1%-73.5%) in piperacillin/tazobactam-resistant and by 37.4% (3.1%-40.5%) in meropenem-resistant P. aeruginosa. Only 1.8% of P. aeruginosa isolates were MBL positive. Among molecularly characterized imipenem/relebactam-resistant P. aeruginosa isolates from 2020, 90.9% (30/33) were oprD deficient.

Conclusions

Imipenem/relebactam appears to be a potential treatment option for lower respiratory tract infections caused by piperacillin/tazobactam- and meropenem-resistant NME and P. aeruginosa in Western Europe.

New antibiotics for Gram-negative pneumonia

Pneumonia is frequently encountered in clinical practice, and Gram-negative bacilli constitute a significant proportion of its aetiology, especially when it is acquired in a hospital setting. With the alarming global rise in multidrug resistance in Gram-negative bacilli, antibiotic therapy for treating patients with pneumonia is challenging and must be guided by in vitro susceptibility results. In this review, we provide an overview of antibiotics newly approved for the treatment of pneumonia caused by Gram-negative bacilli. Ceftazidime-avibactam, imipenem-relebactam and meropenem-vaborbactam have potent activity against some of the carbapenem-resistant Enterobacterales, especially Klebsiella pneumoniae carbapenemase producers. Several novel antibiotics have potent activity against multidrug-resistant Pseudomonas aeruginosa, such as ceftazidime-avibactam, ceftolozane-tazobactam, imipenem-relabactam and cefiderocol. Cefiderocol may also play an important role in the management of pneumonia caused by Acinetobacter baumannii, along with plazomicin and eravacycline.

Exploring the Antibiotic Resistance Profile of Clinical Klebsiella pneumoniae Isolates in Portugal

While antibiotic resistance is rising to dangerously high levels, resistance mechanisms are spreading globally among diverse bacterial species. The emergence of antibiotic-resistant Klebsiella pneumoniae, mainly due to the production of antibiotic-inactivating enzymes, is currently responsible for most treatment failures, threatening the effectiveness of classes of antibiotics used for decades. This study assessed the presence of genetic determinants of β-lactam resistance in 102 multi-drug resistant (MDR) K. pneumoniae isolates from patients admitted to two central hospitals in northern Portugal from 2010 to 2020. Antimicrobial susceptibility testing revealed a high rate (>90%) of resistance to most β-lactam antibiotics, except for carbapenems and cephamycins, which showed antimicrobial susceptibility rates in the range of 23.5−34.3% and 40.2−68.6%, respectively. A diverse pool of β-lactam resistance genetic determinants, including carbapenemases- (i.e., blaKPC-like and blaOXA-48-like), extended-spectrum β-lactamases (ESBL; i.e., blaTEM-like, blaCTX-M-like and blaSHV-like), and AmpC β-lactamases-coding genes (i.e., blaCMY-2-like and blaDHA-like) were found in most K. pneumoniae isolates. blaKPC-like (72.5%) and ESBL genes (37.3−74.5%) were the most detected, with approximately 80% of K. pneumoniae isolates presenting two or more resistance genes. As the optimal treatment of β-lactamase-producing K. pneumoniae infections remains problematic, the high co-occurrence of multiple β-lactam resistance genes must be seen as a serious warning of the problem of antimicrobial resistance.

Clinical carbapenem-resistant Klebsiella pneumoniae isolates simultaneously harboring blaNDM-1, blaOXA types and qnrS genes from the Kingdom of Bahrain: Resistance profile and genetic environment

The prevalence of Carbapenem-resistant Klebsiella pneumoniae (CRKP) is currently increasing worldwide, prompting WHO to classify it as an urgent public health threat. CRKP is considered a difficult to treat organism owing to limited therapeutic options. In this study, a total of 24 CRKP clinical isolates were randomly collected from Salmaniya Medical Complex, Bahrain. Bacterial identification and antibiotic susceptibility testing were performed, on MALDI-TOF and VITEK-2 compact, respectively. The isolates were screened for carbapenem resistance markers (bla_NDM,bla_OXA-23,bla_OXA-48 and bla_OXA-51) and plasmid-mediated quinolone resistance genes (qnrA, qnrB, and qnrS) by monoplex PCR. On the other hand, only colistin-resistant isolates (n=12) were screened for MCR-1, MCR-2 and MCR-3 genes by monoplex PCR. Moreover, the Genetic environment of bla_NDM, integrons analysis, and molecular characterization of plasmids was also performed. Antibiotic susceptibility revealed that all the isolates (100%) were resistant to ceftolozane/tazobactam, piperacillin/tazobactam, 96% resistant to ceftazidime, trimethoprim/sulfamethoxazole, 92% resistant to meropenem, gentamicin and cefepime, 88% resistant to ciprofloxacin, imipenem, and 37% resistant to amikacin. Ceftazidime/avibactam showed the least resistance (12%). 75% (n=12/16) were resistant to colistin and 44% (n=7/16) showed intermediate susceptibility to tigecycline. The detection of resistant determinants showed that the majority (95.8%) of CRKP harbored bla_NDM-1, followed by bla_OXA-48 (91.6%) bla_OXA-51 (45.8%), and bla_OXA-23 (41.6%). Sequencing of the bla_NDM amplicons revealed the presence of bla_NDM-1. Alarmingly, 100% of isolates showed the presence of qnrS. These predominant genes were distributed in various combinations wherein the majority were bla_NDM-1 + bla_OXA-51+ qnrS + bla_OXA-48 (n =10, 41.7%), bla_NDM-1 + bla_OXA-23+ qnrS + bla_OXA-48 (n=8, 33.3%), among others. In conclusion, the resistance rate to most antibiotics is very high in our region, including colistin and tigecycline, and the genetic environment of CRKP is complex with the carriage of multiple resistance markers. Resistance to ceftazidime/avibactam is uncommon and hence can be used as a valuable option for empirical therapy. Molecular data on resistance markers and the genetic environment of CRKP is lacking from this geographical region; this would be the first report addressing the subject matter. Surveillance and strict infection control strategies should be reinforced in clinical settings to curb the emergence and spread of such isolates.

Description of Oscheius cyrus n. sp. (Nematoda: Rhabditidae) as new entomopathogenic nematode from Iran

A new species of the genus Oscheius, Oscheius cyrus n. sp., collected in the moist soils taken from forest heights in the north of Iran, is recorded. A comprehensive description, comprising molecular (internal transcribed spacer (ITS), 18S, and 28S rDNA genes) information, morphometrics data, light microscope and scanning electron microscope images, is supplied. The species resembles Oscheius myriophilus. However, the highest ranges for female body length, female tail, infective juvenile tail length, median bulb, absence of epiptygma and lateral field incisures number vary. The new species was distinguished from Oscheius insectivorus by the general lip region. The male was not found. Molecular analysis showed that the new species has the most similarity to O. myriophilus both in the ITS and 18S regions. Morphological and molecular data confirmed its belonging to the Insectivora-group. Furthermore, the species of Ochrobactrum pseudogrignonense was reported as a dominant associated bacterium of the new Oscheius species. Finally, the mortality of the host after seven days varied from 20% to 82.5%, depending on nematodes' concentration.

Ceftazidime/Avibactam in Ventilator-Associated Pneumonia Due to Difficult-to-Treat Non-Fermenter Gram-Negative Bacteria in COVID-19 Patients: A Case Series and Review of the Literature

Ventilator-associated pneumonia (VAP) in critically ill patients with COVID-19 represents a very huge global threat due to a higher incidence rate compared to non-COVID-19 patients and almost 50% of the 30-day mortality rate. Pseudomonas aeruginosa was the first pathogen involved but uncommon non-fermenter gram-negative organisms such as Burkholderia cepacea and Stenotrophomonas maltophilia have emerged as other potential etiological causes. Against carbapenem-resistant gram-negative microorganisms, Ceftazidime/avibactam (CZA) is considered a first-line option, even more so in case of a ceftolozane/tazobactam resistance or shortage. The aim of this report was to describe our experience with CZA in a case series of COVID-19 patients hospitalized in the ICU with VAP due to difficult-to-treat (DTT) P. aeruginosa, Burkholderia cepacea, and Stenotrophomonas maltophilia and to compare it with data published in the literature. A total of 23 patients were treated from February 2020 to March 2022: 19/23 (82%) VAPs were caused by Pseudomonas spp. (16/19 DTT), 2 by Burkholderia cepacea, and 6 by Stenotrophomonas maltophilia; 12/23 (52.1%) were polymicrobial. Septic shock was diagnosed in 65.2% of the patients and VAP occurred after a median of 29 days from ICU admission. CZA was prescribed as a combination regimen in 86% of the cases, with either fosfomycin or inhaled amikacin or cotrimoxazole. Microbiological eradication was achieved in 52.3% of the cases and the 30-day overall mortality rate was 14/23 (60.8%). Despite the high mortality of critically ill COVID-19 patients, CZA, especially in combination therapy, could represent a valid treatment option for VAP due to DTT non-fermenter gram-negative bacteria, including uncommon pathogens such as Burkholderia cepacea and Stenotrophomonas maltophilia.

Co-resistance to ceftazidime-avibactam and cefiderocol in clinical isolates producing KPC variants

Cefiderocol (FDC) and ceftazidime-avibactam (CZA) are among the latest generation of commercialized antibiotics against carbapenem-resistant Gram negatives. However, emergence of CZA resistance is being increasingly reported, involving different KPC variants in Enterobacterales. By analyzing two CZA-resistant KPC-3 clinical variants, KPC-41 and KPC-50, we showed that KPC-41, and to a lesser extent KPC-50, may also have an impact on susceptibility to FDC leading to a cross-resistance. This feature highlights that a susceptibility testing to FDC is mandatory prior any clinical use of FDC for treating infections due to KPC producers.

Comparison of Antibiotic Susceptibility of Carbapanem-Resistant Enterobactericeae Species with Two Different Panels (Phoenix BD)

Objective: The aim of this study; The aim of this study is to compare the antibiotic susceptibility of carbapanem-resistant Enterobactericeae strains isolated in the microbiology laboratory of our hospital with two different panels and to evaluate the performance of the CPO test. Material & Method: The samples sent to the microbiology laboratory of our hospital between 01.01.2020 - 31.12.2020 were evaluated. Specimens with growth were loaded onto the BD Phoenix 100 automated system BD Phoenix NMIC 433 panel, and 50 isolates of Enterobacteriaceae that resulted in carbapenem resistant were studied with the BD Phoenix NMIC 505 CPO panel. 50 carbapenem-resistant Enterobacteriaceae isolates were classified according to Ambler class A, B, and D by the CPO panel. Results: Of the isolates, 28 (56%) were isolated from male patients and 22 (44%) from female patients. Of the carbapenem-resistant Enterobacteriaceae isolates, 43 (86%) were identified as Klebsiella pneumoniae and 4 (8%) were Escherichia coli. When the evaluation of antibiotic susceptibility rates of the CPO panel and NMIC 433 panel of carbapenem-resistant Enterobacteriaceae isolates were examined; Antibiotic susceptibility results of 50 Enterobacteriaceae isolates studied in both panels were found to be the same. When the antibiotics that can be studied in the CPO panel were examined, it was observed that the most effective antibiotic was ceftazidime-avibactam. When the results were examined, it was observed that 46 (92%) isolates were susceptible to ceftazidime-avibactam. The number of bacteria producing class B carbapenemase was 4 (8%) and the number of bacteria producing class D carbapenemase was 42 (84%). Conclusion: It should be noted that ceftazidime avibactam can be used as a treatment option in carbapenem-resistant species. Further work on the CPO panel will help identify the contribution of the CPO panel to the routine workflow.

Overcoming the rising incidence and evolving mechanisms of antibiotic resistance by novel drug delivery approaches - An overview

Antimicrobial resistance is a normal evolutionary process for microorganisms. Antibiotics exerted accelerated selective pressure that hasten bacterial resistance through mutation, and acquisition external genes. These genes often carry multiple antibiotic resistant determinants allowing the recipient microbe an instant "super-bug" status. The extent of Antimicrobial Resistance (AMR) has reached a level of global crisis, existing antimicrobials are no long effective in treating infections caused by AMR pathogens. The great majority of clinically available antimicrobial agents are administered through oral and intra-venous routes. Overcoming antibacterial resistance by novel drug delivery approach offered new hopes, particularly in the treatment of AMR pathogens in sites less assessible through systemic circulation such as the lung and skin. In the current review, we will revisit the mechanism and incidence of important AMR pathogens. Finally, we will discuss novel drug delivery approaches including novel local antibiotic delivery systems, hybrid antibiotics, and nanoparticle-based antibiotic delivery systems.

Review of Ceftazidime-Avibactam for the Treatment of Infections Caused by Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic Gram-negative pathogen that causes a range of serious infections that are often challenging to treat, as this pathogen can express multiple resistance mechanisms, including multidrug-resistant (MDR) and extensively drug-resistant (XDR) phenotypes. Ceftazidime–avibactam is a combination antimicrobial agent comprising ceftazidime, a third-generation semisynthetic cephalosporin, and avibactam, a novel non-β-lactam β-lactamase inhibitor. This review explores the potential role of ceftazidime–avibactam for the treatment of P. aeruginosa infections. Ceftazidime–avibactam has good in vitro activity against P. aeruginosa relative to comparator β-lactam agents and fluoroquinolones, comparable to amikacin and ceftolozane–tazobactam. In Phase 3 clinical trials, ceftazidime–avibactam has generally demonstrated similar clinical and microbiological outcomes to comparators in patients with complicated intra-abdominal infections, complicated urinary tract infections or hospital-acquired/ventilator-associated pneumonia caused by P. aeruginosa. Although real-world data are limited, favourable outcomes with ceftazidime–avibactam treatment have been reported in some patients with MDR and XDR P. aeruginosa infections. Thus, ceftazidime–avibactam may have a potentially important role in the management of serious and complicated P. aeruginosa infections, including those caused by MDR and XDR strains.

Ceftazidime-avibactam: are we safe from class A carbapenemase producers' infections?

Recently, new combinations of β-lactams and β-lactamase inhibitors became available, including ceftazidime-avibactam, and increased the ability to treat infections caused by carbapenem-resistant Enterobacterales (CRE). Despite the reduced time of clinical use, isolates expressing resistance to ceftazidime-avibactam have been reported, even during treatment or in patients with no previous contact with this drug. Here, we detailed review data on global ceftazidime-avibactam susceptibility, the mechanisms involved in resistance, and the molecular epidemiology of resistant isolates. Ceftazidime-avibactam susceptibility remains high (≥ 98.4%) among Enterobacterales worldwide, being lower among extended-spectrum β-lactamase (ESBL) producers and CRE. Alterations in class A β-lactamases are the major mechanism involved in ceftazidime-avibactam resistance, and mutations are mainly, but not exclusively, located in the Ω loop of these enzymes. Modifications in Klebsiella pneumoniae carbapenemase (KPC) 3 and KPC-2 have been observed by many authors, generating variants with different mutations, insertions, and/or deletions. Among these, the most commonly described is Asp179Tyr, both in KPC-3 (KPC-31 variant) and in KPC-2 (KPC-33 variant). Changes in membrane permeability and overexpression of efflux systems may also be associated with ceftazidime-avibactam resistance. Although several clones have been reported, ST258 with Asp179Tyr deserves special attention. Surveillance studies and rationale use are essential to retaining the activity of this and other antimicrobials against class A CRE.

Evaluation of SuperCAZ/AVI® Medium for Screening Ceftazidime-avibactam Resistant Gram-negative Isolates

The industrial version of SuperCAZ/AVI® medium developed for screening CAZ/AVI resistant Gram-negative isolates has been evaluated here using a collection of 87 well-characterized clinical isolates of worldwide origin. In addition, testing was performed by spiking stools with a series of resistant and susceptible isolates. In those conditions, the SuperCAZ/AVI® medium exhibited a sensitivity and specificity of 100 %, down to the lower limit of detection of 10¹ to 10² CFU/ml. The SuperCAZ/AVI® medium is a sensitive and specific screening medium for detection of CZA-resistant bacteria regardless of their resistance mechanisms.

Epidemiology of Carbapenem Resistance Determinants Identified in Meropenem-Nonsusceptible Enterobacterales Collected as Part of a Global Surveillance Program, 2012 to 2017

To estimate the incidence of carbapenem-resistant Enterobacterales (CRE), a global collection of 81,781 surveillance isolates of Enterobacterales collected from patients in 39 countries in five geographic regions from 2012 to 2017 was studied. Overall, 3.3% of isolates were meropenem-nonsusceptible (MIC ≥2 μg/ml), ranging from 1.4% (North America) to 5.3% (Latin America) of isolates by region. Klebsiella pneumoniae accounted for the largest number of meropenem-nonsusceptible isolates (76.7%). The majority of meropenem-nonsusceptible Enterobacterales carried KPC-type carbapenemases (47.4%), metallo-β-lactamases (MBLs; 20.6%) or OXA-48-like β-lactamases (19.0%). Forty-three carbapenemase sequence variants (8 KPC-type, 4 GES-type, 7 OXA-48-like, 5 NDM-type, 7 IMP-type, and 12 VIM-type) were detected, with KPC-2, KPC-3, OXA-48, NDM-1, IMP-4, and VIM-1 identified as the most common variants of each carbapenemase type. The resistance mechanisms responsible for meropenem-nonsusceptibility varied by region. A total of 67.3% of all carbapenemase-positive isolates identified carried at least one additional plasmid-mediated or intrinsic chromosomally encoded extended-spectrum β-lactamase, AmpC β-lactamase, or carbapenemase. The overall percentage of meropenem-nonsusceptible Enterobacterales increased from 2.7% in 2012 to 2014 to 3.8% in 2015 to 2017. This increase could be attributed to the increasing proportion of carbapenemase-positive isolates that was observed, most notably among isolates carrying NDM-type MBLs in Asia/South Pacific, Europe, and Latin America; OXA-48-like carbapenemases in Europe, Middle East/Africa, and Asia/South Pacific; VIM-type MBLs in Europe; and KPC-type carbapenemases in Latin America. Ongoing CRE surveillance combined with a global antimicrobial stewardship strategy, sensitive clinical laboratory detection methods, and adherence to infection control practices will be needed to interrupt the spread of CRE.

In vitro activity of cefiderocol and comparators against isolates of Gram-negative pathogens from a range of infection sources: SIDERO-WT-2014-2018 studies in France

Objectives

Over recent years, France has experienced an increase of infections caused by carbapenem-resistant Gram-negative (GN) pathogens. Cefiderocol is approved in Europe for the treatment of aerobic GN infections in adults with limited treatment options. This study evaluated the in vitro activity of cefiderocol and comparators against GN clinical isolates from France.

Methods

MICs were determined by broth microdilution, according to International Organization for Standardization guidelines. Cefiderocol was tested using iron-depleted CAMHB. Susceptibility rates were based on EUCAST breakpoints. In the absence of a species-specific breakpoint, pharmacokinetic/pharmacodynamic breakpoints were used.

Results

Of 2027 isolates, 1344 (66.3%) were Enterobacterales and 683 (33.7%) were non-fermenters. The most common pathogen was Pseudomonas aeruginosa (16.8%), followed by Escherichia coli (16.0%), Klebsiella pneumoniae (13.1%), Acinetobacter baumannii (7.9%) and Stenotrophomonas maltophilia (5.1%). Isolates represented a range of infection sources including nosocomial pneumonia (33.6%), complicated urinary tract infection (24.3%), bloodstream infection (13.1%) and complicated intra-abdominal infection (18.0%). In total, 135/2027 (6.7%) isolates were meropenem resistant (MIC >8 mg/L); 133/135 (98.5%) were non-fermenters. Overall, 1330/1344 (99.0%) Enterobacterales and 681/683 (99.7%) non-fermenters were cefiderocol susceptible, including 100% of meropenem-resistant S. maltophilia (n = 98) and P. aeruginosa (n = 18) isolates. Susceptibility to cefiderocol was significantly higher (P < 0.01) in nosocomial pneumonia isolates (681/682 [99.9%]) than susceptibility to meropenem (586/682 [85.9%]), ceftolozane/tazobactam (593/682 [87.0%]), ceftazidime/avibactam (612/682 [89.7%]) and colistin (538/682 [78.9%]).

Conclusions

Cefiderocol demonstrated high in vitro susceptibility rates against a wide range of Gram-negative pathogens, including meropenem-resistant strains, and was significantly more active than comparators against pneumonia isolates.

Resistance to ceftazidime/avibactam in infections and colonisations by KPC-producing Enterobacterales: a systematic review of observational clinical studies

OBJECTIVES

Ceftazidime/avibactam (CAZ-AVI), approved in 2015, is an important first-line option for Klebsiella pneumoniae carbapenemase-producing Enterobacterales (KPC-E). Although still uncommon, resistance to CAZ-AVI has emerged and may represent a serious cause of concern.

METHODS

We performed a systematic literature review of clinical and microbiological features of infections and colonisations by CAZ-AVI-resistant KPC-E, focused on the in vivo emergence of CAZ-AVI resistance in different clinical scenarios.

RESULTS

Twenty-three papers were retrieved accounting for 42 patients and 57 isolates, mostly belonging to K. pneumoniae ST258 harbouring D179Y substitution in the KPC enzyme. The USA, Greece and Italy accounted for 80% of cases. In one-third of isolates resistance was not associated with previous CAZ-AVI exposure. Moreover, 20% of the strains were colistin-resistant and 80% were extended-spectrum β-lactamase (ESBL)-producers. The majority of infected patients had severe underlying diseases (39% cancer, 22% solid-organ transplantation) and 37% died. The abdomen, lung and blood were the most involved infection sites. Infections by CAZ-AVI-resistant strains were mainly treated with combination therapy (85% of cases), with meropenem being the most common (65%) followed by tigecycline (30%), gentamicin (25%), colistin (25%) and fosfomycin (10%). Despite the emergence of resistance, 35% of patients received CAZ-AVI.

CONCLUSION

Taken together, these data highlight the need for prompt susceptibility testing including CAZ-AVI for Enterobacterales, at least in critical areas. Resistance to CAZ-AVI is an urgent issue to monitor in order to improve both empirical and targeted CAZ-AVI use as well as the management of patients with infections caused by CAZ-AVI-resistant strains.

Nosocomial Pneumonia in the Era of Multidrug-Resistance: Updates in Diagnosis and Management

Nosocomial pneumonia (NP), including hospital-acquired pneumonia in non-intubated patients and ventilator-associated pneumonia, is one of the most frequent hospital-acquired infections, especially in the intensive care unit. NP has a significant impact on morbidity, mortality and health care costs, especially when the implicated pathogens are multidrug-resistant ones. This narrative review aims to critically review what is new in the field of NP, specifically, diagnosis and antibiotic treatment. Regarding novel imaging modalities, the current role of lung ultrasound and low radiation computed tomography are discussed, while regarding etiological diagnosis, recent developments in rapid microbiological confirmation, such as syndromic rapid multiplex Polymerase Chain Reaction panels are presented and compared with conventional cultures. Additionally, the volatile compounds/electronic nose, a promising diagnostic tool for the future is briefly presented. With respect to NP management, antibiotics approved for the indication of NP during the last decade are discussed, namely, ceftobiprole medocaril, telavancin, ceftolozane/tazobactam, ceftazidime/avibactam, and meropenem/vaborbactam.

Mobile Carbapenemase Genes in Pseudomonas aeruginosa

Carbapenem-resistant Pseudomonas aeruginosa is one of the major concerns in clinical settings impelling a great challenge to antimicrobial therapy for patients with infections caused by the pathogen. While membrane permeability, together with derepression of the intrinsic beta-lactamase gene, is the global prevailing mechanism of carbapenem resistance in P. aeruginosa, the acquired genes for carbapenemases need special attention because horizontal gene transfer through mobile genetic elements, such as integrons, transposons, plasmids, and integrative and conjugative elements, could accelerate the dissemination of the carbapenem-resistant P. aeruginosa. This review aimed to illustrate epidemiologically the carbapenem resistance in P. aeruginosa, including the resistance rates worldwide and the carbapenemase-encoding genes along with the mobile genetic elements responsible for the horizontal dissemination of the drug resistance determinants. Moreover, the modular mobile elements including the carbapenemase-encoding gene, also known as the P. aeruginosa resistance islands, are scrutinized mostly for their structures.

Antimicrobial susceptibility pattern of carbapenemase-producing Gram-negative nosocomial bacteria at Al Zahra hospital, Isfahan, Iran

BACKGROUND AND OBJECTIVES

Bacterial antibiotic resistance is one of the most important threats for public health around the world. Carbapenemase-producing Gram-negative bacteria have resistance to most antibiotics including carbapenems complicating the treatment of infections. The aim of this study was to determine the antimicrobial susceptibility pattern of carbapenemase-producing nosocomial Gram-negative pathogens at a referral teaching hospital to reveal the best options for treatment of related infections.

MATERIALS AND METHODS

Gram-negative bacteria, isolated from hospitalized patients with nosocomial infections, underwent meropenem susceptibility test by disk diffusion method. Meropenem-resistant strains were evaluated for the presence of carbapenemase using Modified Hodge test (MHT). Finally, the antibiotic susceptibility test was performed to determine the sensitivity of each carbapenemase-positive strain against various antimicrobial agents according to the guidelines of Clinical and Laboratory Standards Institute (CLSI).

RESULTS

Over the study period, 155 carbapenemase-positive isolates were detected. Pneumonia was the most frequent related nosocomial infection (67.1%) followed by UTI (23.2%). Acinetobacter baumannii (53.5%) and Klebsiella pneumoniae (40%) were the most frequently isolated pathogens. The pathogens had high rate of resistance to all antibiotics. Colistin had the most in vitro effect against all pathogens. Also, K. pneumoniae had a co-trimoxazole sensitivity rate equal to colistin (30.6%).

CONCLUSION

Carbapenemase-positive Gram-negative bacteria causing nosocomial infections are common in our hospital and have high rate of resistance to most antibiotics. Improvement in the pattern of antibiotic use and infection control measures are necessary to overcome this resistance.

The safety and efficacy of relebactam/imipenem/cilastatin in Japanese patients with complicated intra-abdominal infection or complicated urinary tract infection: A multicenter, open-label, noncomparative phase 3 study

INTRODUCTION

Relebactam, a novel class A/C β-lactamase inhibitor developed as a fixed-dose combination with imipenem/cilastatin, restores imipenem activity against imipenem-nonsusceptible gram-negative pathogens.

METHODS

This phase 3, multicenter, open-label, noncomparative study (NCT03293485) evaluated relebactam/imipenem/cilastatin (250 mg/500 mg/500 mg) dosed every 6 h for 5-14 days in Japanese patients with complicated intra-abdominal infections (cIAIs) or complicated urinary tract infections (cUTIs), including those with secondary sepsis. Sepsis was defined as an infection-induced systemic inflammatory response syndrome, with a documented positive blood culture; patients meeting these protocol-defined criteria were evaluated for efficacy against sepsis.

RESULTS

Of 83 patients enrolled, 81 patients (cIAI, n = 37; cUTI, n = 44) received ≥1 dose of study treatment. Escherichia coli was the most common baseline pathogen isolated in both patients with cIAI and cUTI. Adverse events (AEs) were reported in 74.1% (n = 60/81) of patients, and drug-related AEs occurred in 18.5% (n = 15/81). The most common AEs were diarrhea and nausea (8.6%). Serious AEs occurred in nine patients, including one death, but none were considered treatment related. The primary efficacy endpoint for patients with cIAI was clinical response at end of treatment (EOT) in the microbiologically evaluable (ME) population, and for patients with cUTI was microbiological response at EOT in the ME population. The proportion of cIAI and cUTI patients achieving favorable responses were 85.7% (n = 24/28) and 100.0% (n = 39/39), respectively. All patients with sepsis (cIAI, n = 1; cUTI, n = 5) achieved a favorable composite clinical and microbiological response at EOT.

CONCLUSIONS

A favorable safety and efficacy profile for relebactam/imipenem/cilastatin was observed in Japanese patients with cIAI and cUTI.

Carbapenemases: Transforming Acinetobacter baumannii into a Yet More Dangerous Menace

Acinetobacter baumannii is a common cause of serious nosocomial infections. Although community-acquired infections are observed, the vast majority occur in people with preexisting comorbidities. A. baumannii emerged as a problematic pathogen in the 1980s when an increase in virulence, difficulty in treatment due to drug resistance, and opportunities for infection turned it into one of the most important threats to human health. Some of the clinical manifestations of A. baumannii nosocomial infection are pneumonia; bloodstream infections; lower respiratory tract, urinary tract, and wound infections; burn infections; skin and soft tissue infections (including necrotizing fasciitis); meningitis; osteomyelitis; and endocarditis. A. baumannii has an extraordinary genetic plasticity that results in a high capacity to acquire antimicrobial resistance traits. In particular, acquisition of resistance to carbapenems, which are among the antimicrobials of last resort for treatment of multidrug infections, is increasing among A. baumannii strains compounding the problem of nosocomial infections caused by this pathogen. It is not uncommon to find multidrug-resistant (MDR, resistance to at least three classes of antimicrobials), extensively drug-resistant (XDR, MDR plus resistance to carbapenems), and pan-drug-resistant (PDR, XDR plus resistance to polymyxins) nosocomial isolates that are hard to treat with the currently available drugs. In this article we review the acquired resistance to carbapenems by A. baumannii. We describe the enzymes within the OXA, NDM, VIM, IMP, and KPC groups of carbapenemases and the coding genes found in A. baumannii clinical isolates.

In vitro selection of aztreonam/avibactam resistance in dual-carbapenemase-producing Klebsiella pneumoniae

OBJECTIVES

To examine the in vitro selection of aztreonam/avibactam resistance among MBL-producing Klebsiella pneumoniae and to understand the mechanism of increased resistance.

METHODS

The MICs of aztreonam were determined with and without avibactam (4 mg/L) using a broth microdilution method. Single-step and multi-step mutant selection was conducted on five MBL-producing K. pneumoniae strains, including two dual carbapenemase producers. Genomic sequencing and gene cloning were performed to investigate the mechanism of increased resistance.

RESULTS

We examined the MICs for 68 MBL-producing K. pneumoniae isolates, including 13 dual carbapenemase producers. Compared with aztreonam alone, the addition of avibactam (4 mg/L) reduced the MICs for all isolates by >128-fold, with MIC50 and MIC90 values of 0.25 and 1 mg/L, respectively. One NDM-1-, OXA-48-, CTX-M-15- and CMY-16-positive ST101 K. pneumoniae strain was selected to be resistant to aztreonam/avibactam, with a >16-fold increase in MIC (>128 mg/L). WGS revealed that the resistant mutants lost the blaNDM-1 gene, but acquired amino acid substitutions in CMY-16 (Tyr150Ser and Asn346His). Construction of blaCMY-16 mutants confirmed that the substitutions (Tyr150Ser and Asn346His) were primarily responsible for the decreased susceptibility to aztreonam/avibactam. In addition, transfer of blaCMY-16 mutant (Tyr150Ser and Asn346His) plasmid constructs into certain clinical carbapenemase-producing isolates demonstrated >64-fold increased MICs of aztreonam/avibactam and aztreonam/avibactam/ceftazidime.

CONCLUSIONS

Aztreonam in combination with avibactam showed potent in vitro activity against MBL-producing K. pneumoniae. However, our study suggested the likelihood of aztreonam/avibactam resistance among MBL- and AmpC-co-producing strains and clinical practice should beware of the possibility of the emerging resistance.

Epidemiology of β-Lactamase-Producing Pathogens

β-Lactam antibiotics have been widely used as therapeutic agents for the past 70 years, resulting in emergence of an abundance of β-lactam-inactivating β-lactamases. Although penicillinases in Staphylococcus aureus challenged the initial uses of penicillin, β-lactamases are most important in Gram-negative bacteria, particularly in enteric and nonfermentative pathogens, where collectively they confer resistance to all β-lactam-containing antibiotics. Critical β-lactamases are those enzymes whose genes are encoded on mobile elements that are transferable among species. Major β-lactamase families include plasmid-mediated extended-spectrum β-lactamases (ESBLs), AmpC cephalosporinases, and carbapenemases now appearing globally, with geographic preferences for specific variants. CTX-M enzymes include the most common ESBLs that are prevalent in all areas of the world. In contrast, KPC serine carbapenemases are present more frequently in the Americas, the Mediterranean countries, and China, whereas NDM metallo-β-lactamases are more prevalent in the Indian subcontinent and Eastern Europe. As selective pressure from β-lactam use continues, multiple β-lactamases per organism are increasingly common, including pathogens carrying three different carbapenemase genes. These organisms may be spread throughout health care facilities as well as in the community, warranting close attention to increased infection control measures and stewardship of the β-lactam-containing drugs in an effort to control selection of even more deleterious pathogens.

In vitro activity of imipenem-relebactam against resistant phenotypes of Enterobacteriaceae and Pseudomonas aeruginosa isolated from intraabdominal and urinary tract infection samples - SMART Surveillance Europe 2015-2017

Introduction. Infections attributable to carbapenem-resistant Gram-negative bacilli are increasing globally. New antimicrobial agents are urgently needed to treat patients with these infections.Aim. To describe susceptibility to the novel carbapenem-β-lactamase inhibitor combination imipenem-relebactam and comparators of clinical isolates of non-Proteeae Enterobacteriaceae (NPE) and Pseudomonas aeruginosa from intraabdominal infections (IAIs) and urinary tract infections (UTIs).Methods. Broth microdilution MICs were determined for isolates collected in 22 European countries in 2015-2017 and interpreted using EUCAST breakpoints; imipenem-relebactam MICs were interpreted using imipenem breakpoints.Results. For NPE, 98.4 % of isolates from IAIs (n=10,465) and 98.5 % of UTI isolates (n=7,446) were susceptible to imipenem-relebactam, as were 42.4 % of imipenem-nonsusceptible (n=474), 98.6 % of Klebsiella pneumoniae carbapenemase (KPC)-positive (n=138), and 93.9 % of multidrug-resistant (MDR) isolates (n=4,424) from IAIs and UTIs combined. Molecular analysis demonstrated that two-thirds of imipenem-nonsusceptible isolates rendered susceptible by relebactam carried KPCs; 96 % (261/271) of imipenem-nonsusceptible isolates of NPE that remained nonsusceptible in the presence of relebactam carried metallo-β-lactamase (MBL)-type and/or OXA-48-like carbapenemases. Among P. aeruginosa, 94.4 % of IAI (n=1,245) and 93.0 % of UTI isolates (n=714) were susceptible to imipenem-relebactam, as were 74.4 % of imipenem-nonsusceptible (n=469) and 79.8 % of MDR isolates (n=595) from IAIs and UTIs combined. Among the 120 isolates of P. aeruginosa that remained nonsusceptible to imipenem upon addition of relebactam, 72 % carried MBLs. The distribution of NPE and P. aeruginosa carrying carbapenemases varied substantially across Europe, as did resistance to imipenem and imipenem-relebactam.Conclusions. Continued surveillance of antimicrobial resistance and resistance mechanisms, including the study of imipenem-relebactam as it approaches regulatory approval, appears warranted.

CG258 Klebsiella pneumoniae isolates without β-lactam resistance at the onset of the carbapenem-resistant Enterobacteriaceae epidemic in New York City

Objectives

To examine the epidemiology of β-lactam resistance in 'clonal group 258' (CG258), a successful KPC clonal group, over 14 years.

Methods

Isolates were collected from 1999 to 2013 for a study of antibiotic resistance in Enterobacteriaceae in New York City; 515 bloodstream isolates had antibiotic susceptibility data available and 436 were available for a CG258 PCR assay. The 56 resulting CG258 isolates were characterized by MLST, capsular type and ESBL and KPC carriage. KPC-positive isolates were assessed for common KPC plasmid types, KPC subtype and Tn4401 isoform.

Results

RT-PCR revealed 56 isolates were CG258. Seventeen of the 56 CG258 isolates were phenotypically susceptible to all carbapenems (all KPC negative). Five out of 17 susceptible isolates were of the cps-2 (wzi154) capsule type; none was cps-1 (wzi29). Nineteen out of 28 KPC-2 isolates were cps-1 (wzi29) and 8/10 KPC-3 isolates carried cps-2 (wzi154); however, cps-2 (wzi154) predominated among KPC-2-positive isolates in 2003 and 2004. KPC-2 was first detected in 2003 and KPC-3 was first detected in 2006. KPC-harbouring plasmids pKpQIL (all Tn4401a) and pBK30683 (all Tn4401d) were detected in 16/38 and 6/38 carbapenem-resistant isolates, respectively.

Discussion

CG258-lineage Klebsiella pneumoniae isolates were completely absent in 1999, but common in 2003. Twenty-one percent of CG258 isolates were susceptible to carbapenems in addition to lacking both common ESBL and blaKPC-mediated resistance. The cps-2 (wzi154) capsule type was common in both these susceptible isolates and in early KPC-2-harbouring isolates, suggesting it was the initial capsule type in CG258. Carbapenem-resistant isolates carried common KPC-harbouring plasmids with the same KPC and Tn4401 isoforms, suggesting frequent clonal spread.

Interplay between β-lactamases and new β-lactamase inhibitors

Resistance to β-lactam antibiotics in Gram-negative bacteria is commonly associated with production of β-lactamases, including extended-spectrum β-lactamases (ESBLs) and carbapenemases belonging to different molecular classes: those with a catalytically active serine and those with at least one active-site Zn²⁺ to facilitate hydrolysis. To counteract the hydrolytic activity of these enzymes, combinations of a β-lactam with a β-lactamase inhibitor (BLI) have been clinically successful. However, some β-lactam-BLI combinations have lost their effectiveness against prevalent Gram-negative pathogens that produce ESBLs, carbapenemases or multiple β-lactamases in the same organism. In this Review, descriptions are provided for medically relevant β-lactamase families and various BLI combinations that have been developed or are under development. Recently approved inhibitor combinations include the inhibitors avibactam and vaborbactam of the diazabicyclooctanone and boronic acid inhibitor classes, respectively, as new scaffolds for future inhibitor design.

Colistin-sparing approaches with newer antimicrobials to treat carbapenem-resistant organisms: Current evidence and future prospects

Antimicrobial resistance is on the rise across the globe. Increasing incidence of infections due to carbapenem resistance organisms is becoming difficult to treat, due to the limited availability of therapeutic agents. Very few agents such as colistin, fosfomycin, tigecycline and minocycline are widely used, despite its toxicity. However, with the availability of novel antimicrobials, beta-lactam/beta-lactamase inhibitor-based and non-beta-lactam-based agents could be of great relief. This review covers three important aspects which include (i) current management of carbapenem-resistant infections, (ii) determination of specific types of carbapenemases produced by multidrug-resistant and extensively drug-resistant Gram-negative pathogens and (iii) the currently available novel beta-lactam/beta-lactamase inhibitors and non-beta-lactam-based agents' laboratory findings, clinical outcome and implications.

Recognizing and Overcoming Resistance to New Beta-Lactam/Beta-Lactamase Inhibitor Combinations

PURPOSE OF REVIEW

To describe the mechanisms and clinical relevance of emergent resistance to three recently introduced beta-lactamase inhibitor combinations (BLICs) active against resistant Gram-negative organisms: ceftolozane-tazobactam, ceftazidime-avibactam, and meropenem-vaborbactam.

RECENT FINDINGS

Despite their recent introduction into practice, clinical reports of resistance to BLICs among typically susceptible organisms have already emerged, in some cases associated with therapeutic failure. The resistance mechanisms vary by agent, including mutations in beta-lactamase active sites, upregulation of efflux pumps, and alterations in the structure or expression of porin channels. These changes may confer cross-resistance or, rarely, increased susceptibility to related agents. Clinicians need to be aware of the potential for initial or emergent resistance to BLICs and ensure appropriate antimicrobial susceptibility testing is performed. Dose optimization and novel combinations of agents may play a role in preventing and managing resistance. Recently approved BLICs have provided important new therapeutic options against resistant Gram-negative organisms, but are already coming up against emergent resistance. Awareness of the potential for resistance, early detection, and dose optimization may be important in preserving the utility of these agents.

Plasmid evolution in carbapenemase-producing Enterobacteriaceae: a review

Carbapenem-resistant Enterobacteriaceae (CRE) have been listed by the WHO as high-priority pathogens owing to their high association with mortalities and morbidities. Resistance to multiple β-lactams complicates effective clinical management of CRE infections. Using plasmid typing methods, a wide distribution of plasmid replicon groups has been reported in CREs around the world, including IncF, N, X, A/C, L/M, R, P, H, I, and W. We performed a literature search for English research papers, published between 2013 and 2018, reporting on plasmid-mediated carbapenem resistance. A rise in both carbapenemase types and associated plasmid replicon groups was seen, with China, Canada, and the United States recording a higher increase than other countries. bla_KPC was the most prevalent, except in Angola and the Czech Republic, where OXA-181 (n = 50, 88%) and OXA-48-like (n = 24, 44%) carbapenemases were most prevalent, respectively; bla_KPC-2/3 accounted for 70% (n = 956) of all reported carbapenemases. IncF plasmids were found to be responsible for disseminating different antibiotic resistance genes worldwide, accounting for almost 40% (n = 254) of plasmid-borne carbapenemases. bla_CTX-M , bla_TEM , bla_SHV , bla_OXA-1/9 , qnr, and aac-(6')-lb were mostly detected concurrently with carbapenemases. Most reported plasmids were conjugative but not present in multiple countries or species, suggesting limited interspecies and interboundary transmission of a common plasmid. A major limitation to effective characterization of plasmid evolution was the use of PCR-based instead of whole-plasmid sequencing-based plasmid typing.