Efficacy of humanized carbapenem and ceftazidime regimens against Enterobacteriaceae producing OXA-48 carbapenemase in a murine infection model

OXA-48-like carbapenemases in Proteus mirabilis - novel genetic environments and a challenge for detection

OXA-48-like enzymes represent the most frequently detected carbapenemases in Enterobacterales in Western Europe, North Africa and the Middle East. In contrast to other species, the presence of OXA-48-like in Proteus mirabilis leads to an unusually susceptible phenotype with low MICs for carbapenems and piperacillin-tazobactam, which is easily missed in the diagnostic laboratory. So far, there is little data available on the genetic environments of the corresponding genes, blaOXA-48-like, in P. mirabilis. In this study susceptibility phenotypes and genomic data of 13 OXA-48-like-producing P. mirabilis were investigated (OXA-48, n = 9; OXA-181, n = 3; OXA-162, n = 1). Ten isolates were susceptible to meropenem and ertapenem and three isolates were susceptible to piperacillin-tazobactam. The gene blaOXA-48 was chromosomally located in 7/9 isolates. Thereof, in three isolates blaOXA-48 was inserted into a P. mirabilis genomic island. Of the three isolates harbouring blaOXA-181 one was located on an IncX3 plasmid and two were located on a novel MOBF plasmid, pOXA-P12, within the new transposon Tn7713. In 5/6 isolates with plasmidic location of blaOXA-48-like, the plasmids could conjugate to E. coli recipients in vitro. Vice versa, blaOXA-48-carrying plasmids could conjugate from other Enterobacterales into a P. mirabilis recipient. These data show a high diversity of blaOXA-48-like genetic environments compared to other Enterobacterales, where genetic environments are quite homogenous. Given the difficult-to-detect phenotype of OXA-48-like-producing P. mirabilis and the location of blaOXA-48-like on mobile genetic elements, it is likely that OXA-48-like-producing P. mirabilis can disseminate, escape most surveillance systems, and contribute to a hidden spread of OXA-48-like.

Phenotypes, genotypes and breakpoints: an assessment of β-lactam/β-lactamase inhibitor combinations against OXA-48

BACKGROUND

Two of the three recently approved β-lactam agent (BL)/β-lactamase inhibitor (BLI) combinations have higher CLSI susceptibility breakpoints (ceftazidime/avibactam 8 mg/L; meropenem/vaborbactam 4 mg/L) compared with the BL alone (ceftazidime 4 mg/L; meropenem 1 mg/L). This can lead to a therapeutic grey area on susceptibility reports depending on resistance mechanism. For instance, a meropenem-resistant OXA-48 isolate (MIC 4 mg/L) may appear as meropenem/vaborbactam-susceptible (MIC 4 mg/L) despite vaborbactam's lack of OXA-48 inhibitory activity.

METHODS

OXA-48-positive (n = 51) and OXA-48-negative (KPC, n = 5; Klebsiella pneumoniae wild-type, n = 1) Enterobacterales were utilized. Susceptibility tests (broth microdilution) were conducted with ceftazidime/avibactam, imipenem/relebactam and meropenem/vaborbactam, as well as their respective BL partner. Antimicrobial activity of all six agents was evaluated in the murine neutropenic thigh model using clinically relevant exposures. Efficacy was assessed as the change in bacterial growth at 24 h, compared with 0 h controls.

RESULTS

On average, the three BL/BLI agents resulted in robust bacteria killing among OXA-48-negative isolates. Among OXA-48-positive isolates, poor in vivo activity with imipenem/relebactam was concordant with its resistant phenotypic profile. Variable meropenem/vaborbactam activity was observed among isolates with a 'susceptible' MIC of 4 mg/L. Only 30% (7/23) of isolates at meropenem/vaborbactam MICs of 2 and 4 mg/L met the ≥1-log bacterial reduction threshold predictive of clinical efficacy in serious infections. In contrast, ceftazidime/avibactam resulted in marked bacterial density reduction across the range of MICs, and 96% (49/51) of isolates exceeded the ≥1-log bacterial reduction threshold.

CONCLUSIONS

Data demonstrate that current imipenem/relebactam and ceftazidime/avibactam CLSI breakpoints are appropriate. Data also suggest that higher meropenem/vaborbactam breakpoints relative to meropenem can translate to potentially poor clinical outcomes in patients infected with OXA-48-harbouring isolates.

Phenotypes, genotypes and breakpoints: an assessment of β-lactam/ β-lactamase inhibitor combinations against OXA-48

BACKGROUND

Two out of the three recently approved β-lactam (BL)/β-lactamase inhibitors (BLIs) have higher CLSI susceptibility breakpoints (ceftazidime/avibactam 8 mg/L; meropenem/vaborbactam 4 mg/L) compared with the BL alone (ceftazidime 4 mg/L; meropenem 1 mg/L). This can lead to a therapeutic grey area on susceptibility reports depending on resistance mechanism. For instance, a meropenem-resistant OXA-48 isolate (MIC 4 mg/L) may appear as meropenem/vaborbactam-susceptible (MIC 4 mg/L) despite vaborbactam's lack of OXA-48 inhibitory activity.

METHODS

OXA-48-positive (n = 51) and OXA-48-negative (KPC, n = 5; Klebsiella pneumoniae WT, n = 1) Enterobacterales were utilized. Susceptibility tests (broth microdilution) were conducted with ceftazidime/avibactam, imipenem/relebactam and meropenem/vaborbactam, as well as their respective BL partner. Antimicrobial activity of all six agents was evaluated in the murine neutropenic thigh model using clinically relevant exposures. Efficacy was assessed as the change in bacterial growth at 24 h, compared with 0 h controls.

RESULTS

On average, the three BL/BLI agents resulted in robust bacteria killing among OXA-48-negative isolates. Among OXA-48-positive isolates, poor in vivo activity with imipenem/relebactam was concordant with its resistant phenotypic profile. Variable meropenem/vaborbactam activity was observed among isolates with a 'susceptible' MIC of 4 mg/L. Only 30% (7/23) of isolates at meropenem/vaborbactam MICs of 2 and 4 mg/L met the ≥1 log bacterial reduction threshold predictive of clinical efficacy in serious infections. In contrast, ceftazidime/avibactam resulted in marked bacterial density reduction across the range of MICs and 73% (37/51) of isolates exceeded the ≥1 log bacterial reduction threshold.

CONCLUSIONS

Data demonstrate that current imipenem/relebactam and ceftazidime/avibactam CLSI breakpoints are appropriate. Data also suggest that higher meropenem/vaborbactam breakpoints relative to meropenem can translate to potentially poor clinical outcomes in patients infected with OXA-48-harbouring isolates.

OXA-48-Like β-Lactamases: Global Epidemiology, Treatment Options, and Development Pipeline

Modern medicine is threatened by the rising tide of antimicrobial resistance, especially among Gram-negative bacteria, where resistance to β-lactams is most often mediated by β-lactamases. The penicillin and cephalosporin ascendancies were, in their turn, ended by the proliferation of TEM penicillinases and CTX-M extended-spectrum β-lactamases. These class A β-lactamases have long been considered the most important. For carbapenems, however, the threat is increasingly from the insidious rise of a class D carbapenemase, OXA-48, and its close relatives. Over the past 20 years, OXA-48 and "OXA-48-like" enzymes have proliferated to become the most prevalent enterobacterial carbapenemases across much of Europe, Northern Africa, and the Middle East. OXA-48-like enzymes are notoriously difficult to detect because they often cause only low-level in vitro resistance to carbapenems, meaning that the true burden is likely underestimated. Despite this, they are associated with carbapenem treatment failures. A highly conserved incompatibility complex IncL plasmid scaffold often carries bla_OXA-48 and may carry other antimicrobial resistance genes, leaving limited treatment options. High conjugation efficiency means that this plasmid is sometimes carried by multiple Enterobacterales in a single patient. Producers evade most β-lactam-β-lactamase inhibitor combinations, though promising agents have recently been licensed, notably ceftazidime-avibactam and cefiderocol. The molecular machinery enabling global spread, current treatment options, and the development pipeline of potential new therapies for Enterobacterales that produce OXA-48-like β-lactamases form the focus of this review.

Detection of expanded-spectrum cephalosporin hydrolysis by lateral flow immunoassay

Early detection of expanded-spectrum cephalosporin (ESC) resistance is essential not only for an effective therapy but also for the prompt implementation of infection control measures to prevent dissemination in the hospital. We have developed and validated a lateral flow immunoassay (LFIA), called LFIA-CTX test, for the detection of ESC (cefotaxime) hydrolytic activity based on structural discrimination between the intact antibiotic and its hydrolysed product. A single bacterial colony was suspended in an extraction buffer containing cefotaxime. After a 30-min incubation, the solution is loaded on the LFIA for reading within 10 min. A total of 348 well-characterized Gram-negative isolates were tested. Among them, the 38 isolates that did not express any cefotaxime-hydrolysing β-lactamase gave negative results. Of the 310 isolates expressing at least one cefotaxime-hydrolysing β-lactamase, all were tested positive, except three OXA-48-like producers, which were repeatedly detected negative. Therefore, the sensitivity was 99.1% and the specificity was 100%. The LFIA-CTX test is efficient, fast, low-cost and easy to implement in the workflow of a routine microbiology laboratory.

In Vitro Synergism of Azithromycin Combination with Antibiotics against OXA-48-Producing Klebsiella pneumoniae Clinical Isolates

Carbapenem-resistant Klebsiella pneumoniae has globally emerged as an urgent threat leading to the limitation for treatment. K. pneumoniae carrying blaOXA-48, which plays a broad magnitude of carbapenem susceptibility, is widely concerned. This study aimed to characterize related carbapenem resistance mechanisms and forage for new antibiotic combinations to combat blaOXA-48-carrying K. pneumoniae. Among nine isolates, there were two major clones and a singleton identified by ERIC-PCR. Most isolates were resistant to ertapenem (MIC range: 2->256 mg/L), but two isolates were susceptible to imipenem and meropenem (MIC range: 0.5-1 mg/L). All blaOXA-48-carrying plasmids conferred carbapenem resistance in Escherichia coli transformants. Two ertapenem-susceptible isolates carried both outer membrane proteins (OMPs), OmpK35 and OmpK36. Lack of at least an OMP was present in imipenem-resistant isolates. We evaluated the in vitro activity of an overlooked antibiotic, azithromycin, in combination with other antibiotics. Remarkably, azithromycin exhibited synergism with colistin and fosfomycin by 88.89% and 77.78%, respectively. Bacterial regrowth occurred after exposure to colistin or azithromycin alone. Interestingly, most isolates were killed, reaching synergism by this combination. In conclusion, the combination of azithromycin and colistin may be an alternative strategy in dealing with blaOXA-48-carrying K. pneumoniae infection during a recent shortage of newly effective antibiotic development.

Efficacy of human-simulated exposures of meropenem/vaborbactam and meropenem against OXA-48 β-lactamase-producing Enterobacterales in the neutropenic murine thigh infection model

OBJECTIVES

Despite vaborbactam lacking inhibitory activity against OXA-48, approximately a third of OXA-48-harbouring Enterobacterales test susceptible to meropenem/vaborbactam due to its higher breakpoint than meropenem alone. The present study evaluated the efficacy of human-simulated exposures of meropenem/vaborbactam against OXA-48-harbouring Enterobacterales in the neutropenic murine thigh model.

METHODS

Twenty-six isolates [OXA-48 (n = 24) and KPC (n = 2)] were evaluated. MICs were conducted in triplicate per CLSI. Mice received human-simulated regimens of meropenem/vaborbactam, meropenem or vehicle for 24 h. Mice were inoculated with ∼1 × 107 cfu/mL in each thigh 2 h prior to dosing and both thighs were harvested at 24 h. Efficacy was assessed using mean log10 cfu/thigh at 24 h and the achievement of 1 log10 reduction relative to 0 h control as an established surrogate marker predictive of success for serious infections.

RESULTS

Meropenem/vaborbactam MICs ranged from 1 to 64 mg/L. The mean inoculum at 0 h was 5.77 ± 0.26 compared with 8.26 ± 1.53 for controls at 24 h. As anticipated for KPCs, meropenem/vaborbactam resulted in enhanced mean ± SD change in bacterial density (-1.10 ± 0.26), compared with meropenem (1.45 ± 0.88). Vaborbactam did not enhance mean ± SD change against OXA-48 isolates compared with meropenem (-0.44 ± 1.29 and -0.43 ± 1.36, respectively). For OXA-48-harbouring isolates with meropenem/vaborbactam MICs ≥16 (n = 5), 8 (n = 5), 4 (n = 9) and ≤2 (n = 5) mg/L, 0%, 0%, 44% and 60% of isolates achieved the target reduction ≥1 log10 with either agent, respectively.

CONCLUSIONS

These data highlight that meropenem/vaborbactam and meropenem humanized exposures in vivo resulted in similar, albeit poor, activity against OXA-48-producing Enterobacterales despite susceptible MICs per EUCAST and CLSI interpretation. As a result, caution is warranted when treating meropenem/vaborbactam-susceptible Enterobacterales without a genotypic profile.

Carbapenem-Resistant Enterobacterales, Carbapenem Resistant Organisms, Carbapenemase-Producing Enterobacterales, and Carbapenemase-Producing Organisms: Terminology Past its "Sell-By Date" in an Era of New Antibiotics and Regional Carbapenemase Epidemiology

Carbapenem resistance in Gram-negative bacteria is a public health concern. Consequently, numerous government and agency reports discuss carbapenem-resistant Enterobacterales (CRE) and carbapenem-resistant organisms (CROs). Unfortunately, these terms are fuzzy. Do they include (1) Proteeae with inherent imipenem resistance; (2) porin-deficient Enterobacterales resistant to ertapenem but not other carbapenems; (3) Enterobacterales with OXA-48-like enzymes that remain "carbapenem susceptible" at breakpoint; and (4) Pseudomonas aeruginosa that merely lack porin OprD? Counting CPE or CPOs is better but still insufficient, because different carbapenemases have differing treatment implications, particularly for new β-lactam/β-lactamase inhibitor combinations. At the least, it is essential for authors, journals, and regulatory agencies to specify the carbapenemases meant. The future may demand even greater precision, for mutations can alter hydrolytic activity, and the ability to confer resistance, within carbapenemase families.

Cefepime/tazobactam compared with other tazobactam combinations against problem Gram-negative bacteria

OBJECTIVES

Piperacillin/tazobactam has long been a broad-spectrum 'workhorse' antibiotic; however, it is compromised by resistance. One response is to re-partner tazobactam with cefepime, which is easier to protect, being less β-lactamase labile, and to use a high-dose and prolonged infusion. On this basis, Wockhardt are developing cefepime/tazobactam (WCK 4282) as a 2+2 g q8h combination with a 90-min infusion.

METHODS

The activity of cc cefepime/tazobactam was assessed, with other tazobactam combinations as comparators, against 1632 Enterobacterales, 745 Pseudomonas aeruginosa and 450 other non-fermenters, as submitted to the UK National Reference Laboratory. These were categorised by carbapenemase-gene detection and interpretive reading of phenotypes, with MICs determined by British Society for Antimicrobial Chemotherapy agar dilution.

RESULTS

Although higher breakpoints may be justifiable, based on the pharmacodynamics, the results were reviewed against current cefepime criteria. On this basis, cefepime/tazobactam was broadly active against Enterobacterales with AmpC enzymes and extended-spectrum β-lactamases (ESBLs), even when they had ertapenem resistance, suggesting porin loss. At 8+8 mg/L, activity extended to > 90% of Enterobacterales with OXA-48 and KPC carbapenemases, although the MICs for KPC producers belonging to the international Klebsiella pneumoniae ST258 lineage were higher; metallo-β-lactamase producers remained resistant. Cefepime/tazobactam was less active than ceftolozane/tazobactam against Pseudomonas aeruginosa with AmpC de-repression or high-level efflux but achieved wider antipseudomonal coverage than piperacillin/tazobactam. Activity against other non-fermenters was species-specific.

CONCLUSION

Overall, cefepime/tazobactam had a spectrum exceeding those of piperacillin/tazobactam and ceftolozane/tazobactam and resembling or exceeding that of carbapenems. Used as a 'new-combination of old-agents' it has genuine potential to be 'carbapenem-sparing'.

Detection of various beta-Lactamases in Escherichia coli and Klebsiella sp.: A study from Tertiary Care Centre of North India

Objective

The emergence of carbapenem-resistant Escherichia coli and Klebsiella species is a global threat. We aimed to compare two phenotypic methods and evaluate the genotypic method for the detection of beta-lactamases produced by E. coli and Klebsiella spp.

Materials and Methods

One hundred and twenty-six E. coli and Klebsiella isolates were examined for phenotypic production of beta-lactamases by using disc diffusion, combined disc test (CDT) and modified carbapenem inactivation method (mCIM). All strains were also studied for the presence of various genes by polymerase chain reaction.

Results

Out of 126 isolates, 96% of the isolates were extended-spectrum β-lactamase (ESBL) producers based on the presence of various ESBL genes. CDT method showed higher number of total (89%) carbapenemases in comparison to mCIM (81%). Among carbapenemases none of the isolates were Klebsiella pneumoniae carbapenemase producer by CDT, while 69% isolates were metallo-beta-lactamase (MBL) producers. Another method, mCIM/ethylene diamine tetraacetic acid mCIM showed 100% agreement for MBL detection. As regards, AmpC and class D carbapenemases; 0.04% and 16% positivity was detected, respectively, based on CDT method. Molecular analysis revealed 91% of the isolates harbouring carbapenemase genes. blaNDMwas the most common gene detected followed byblaOXA-48. Nine of the blaNDM-positive isolates also possessed blaOXA-48gene.

Conclusion

Our finding shows high percentages of ESBL and carbapenemases in E. coli and Klebsiella spp. Among phenotypic methods, CDT seems to be a better choice as prevalence of carbapenemases shows lots of variation in our country. For Class B enzymes, both CDT and mCIM/eCIM can be used in the routine laboratories.

In vitro evaluation of double carbapenem and colistin combinations against OXA-48, NDM carbapenemase-producing colistin-resistant Klebsiella pneumoniae strains

BACKGROUND

Treatment of pandrug-resistant isolates often necessitates combination therapy. Checkerboard synergy and time-killing assay tests were performed to evaluate the benefits of a triple combination with meropenem, ertapenem, and colistin against 10 colistin-resistant K. pneumoniae clinical isolates harboring different β-lactamases. (bla_OXA-48, bla_NDM).

MATERIALS AND METHODS

In this study, ertapenem and meropenem (ERT/MEM), meropenem and colistin (MEM/COL), ertapenem, meropenem and colistin (ERT/MEM/COL) combinations were tested using checkerboard techniques and time-kill assays of each antibiotic alone and in combination against 10 colistin-resistant clinical K. pneumoniae isolates. An analysis of K. pneumoniae isolate B6 using a scanning electron microscope revealed morphologic changes in the cell surface after treatment with each antibiotic both alone and in combination. The whole genome of K. pneumoniae KPNB1 was sequenced using an Ion Torrent PGM sequencer.

RESULTS

According to the checkboard results, synergistic combinations were observed with ertapenem/meropenem (5/10 isolates), meropenem/colistin (7/10) and ertapenem/meropenem/colistin (9/10); no antagonism was observed for all combinations. For the time-kill assay results; synergism and bactericidal effects were observed with meropenem/colistin (10/10) and with ertapenem/meropenem/colistin (10/10) combinations, and an indifference effect was observed with the ertapenem and meropenem (10/10) combination. Strain number 1 was found 100% identical to Klebsiella pneumoniae subsp. pneumoniae HS11286 according to the outcomes of complete genome sequence analysis, and the strain carried the genes bla_OXA-181, bla_CTXM-15, blaNDM, arr-3, aac (6')-Ib-cr, rmtF, and catB1.

CONCLUSION

Using double carbapenem antibiotics with colistin could be a potential alternative to treat colistin and carbapenem-resistant K. pneumoniae. The present study is the first Turkish report of OXA-181-type carbapenemase causing colistin resistance.

Antimicrobial activity of cephalosporin-beta-lactamase inhibitor combinations against drug-susceptible and drug-resistant Pseudomonas aeruginosa strains

Objectives

We conducted this study to test the susceptibility of P. aeruginosa to the routinely used drugs and to the two recently available antimicrobial agents, ceftazidime-avibactam and ceftolozane-tazobactam.

Methods

We isolated the non-replicate strains of P. aeruginosa from inpatients between December 2018 and April 2019. The VITEK® MS system was used for phenotypic identification and VITEK 2 for initial antimicrobial susceptibility testing. We supplemented these tests with determination of the minimum inhibitory concentration (MIC) of four antimicrobials; imipenem, meropenem, ceftazidime-avibactam and ceftolozane-tazobactam. The standards of the Clinical and Laboratory Standards Institute were followed.

Results

A total of 67 strains of P. aeruginosa, including 38 multidrug-resistant strains, were obtained from various specimens. Susceptibility to various tested aminoglycosides and fluoroquinolones was maintained in 49.3–56.7% and 40.0–43.3% of the total isolates. Amongst β-lactams, the strains were susceptible to the following agents in an ascending order: ceftazidime (32.8%), cefepime (37.3%), imipenem (36.0%), piperacillin-tazobactam (39.0%), meropenem (44.8%), ceftazidime-avibactam (61.2%) and ceftolozane-tazobactam (62.7%). The susceptibility rates of the multidrug-resistant strains to both ceftazidime-avibactam and ceftolozane-tazobactam were less than 35%. High levels of resistance to the new agents (MIC > 256 ug/ml) were detected in 21 and 22 isolates.

Conclusion

Our study shows limitation in the empirical use of ceftazidime-avibactam and ceftolozane-tazobactam as therapeutics in serious infections. Moreover, our data highlights the need for prompt antimicrobial susceptibility testing to guide their clinical usage.

Precision medicine for the diagnosis and treatment of carbapenem-resistant Enterobacterales: time to think from a different perspective

INTRODUCTION

Carbapenem-resistant Enterobacterales (CRE) represent a global public health problem. Precision medicine (PM) is a multicomponent medical approach that should be used to individualize the management of patients infected with CRE.

AREAS COVERED

Here, we differentiate carbapenem-producing CRE (CP-CRE) from non-CP-CRE and the importance of this distinction in clinical practice. The current phenotypic CRE-case definition and its implications are also discussed. Additionally, we summarize data regarding phenotypic and molecular diagnostic tools and available antibiotics. In order to review the most relevant data, a comprehensive literature search of peer-reviewed articles in PubMed and abstracts presented at high-impact conferences was performed.

EXPERT OPINION

PM in CRE infections entails a multi-step process that includes applying the current phenotypic definition, utilization of the right phenotypic or molecular testing methods, and thorough evaluation of risk factors, source of infection, and comorbidities. A powerful armamentarium is available to treat CRE infections, including recently approved agents. Randomized controlled trials targeting specific pathogens instead of site of infections may be appropriate to fill in the current gaps. In light of the diverse enzymology behind CP-CRE, PM should be employed to provide the best therapy based on the underlying resistance mechanism.

Genomic Epidemiology of Carbapenem- and Colistin-Resistant Klebsiella pneumoniae Isolates From Serbia: Predominance of ST101 Strains Carrying a Novel OXA-48 Plasmid

Klebsiella pneumoniae is a major cause of severe healthcare-associated infections and often shows MDR phenotypes. Carbapenem resistance is frequent, and colistin represents a key molecule to treat infections caused by such isolates. Here we evaluated the antimicrobial resistance (AMR) mechanisms and the genomic epidemiology of clinical K. pneumoniae isolates from Serbia. Consecutive non-replicate K. pneumoniae clinical isolates (n = 2,298) were collected from seven hospitals located in five Serbian cities and tested for carbapenem resistance by disk diffusion. Isolates resistant to at least one carbapenem (n = 426) were further tested for colistin resistance with Etest or Vitek2. Broth microdilution (BMD) was performed to confirm the colistin resistance phenotype, and colistin-resistant isolates (N = 45, 10.6%) were characterized by Vitek2 and whole genome sequencing. Three different clonal groups (CGs) were observed: CG101 (ST101, N = 38), CG258 (ST437, N = 4; ST340, N = 1; ST258, N = 1) and CG17 (ST336, N = 1). mcr genes, encoding for acquired colistin resistance, were not observed, while all the genomes presented mutations previously associated with colistin resistance. In particular, all strains had a mutated MgrB, with MgrB^C28S being the prevalent mutation and associated with ST101. Isolates belonging to ST101 harbored the carbapenemase OXA-48, which is generally encoded by an IncL/M plasmid that was no detected in our isolates. MinION sequencing was performed on a representative ST101 strain, and the obtained long reads were assembled together with the Illumina high quality reads to decipher the bla _{OXA- 48} genetic background. The bla _{OXA- 48} gene was located in a novel IncFIA-IncR hybrid plasmid, also containing the extended spectrum β-lactamase-encoding gene bla _CTX-M-15 and several other AMR genes. Non-ST101 isolates presented different MgrB alterations (C28S, C28Y, K2^∗, K3^∗, Q30^∗, adenine deletion leading to frameshift and premature termination, IS5-mediated inactivation) and expressed different carbapenemases: OXA-48 (ST437 and ST336), NDM-1 (ST437 and ST340) and KPC-2 (ST258). Our study reports the clonal expansion of the newly emerging ST101 clone in Serbia. This high-risk clone appears adept at acquiring resistance, and efforts should be made to contain the spread of such clone.

In vitro efficacy of imipenem-relebactam and cefepime-AAI101 against a global collection of ESBL-positive and carbapenemase-producing Enterobacteriaceae

OBJECTIVES

To evaluate the potential clinical in vitro efficacy of novel β-lactam/β-lactamase-inhibitor combinations - including imipenem-relebactam (IPM-REL) and cefepime-AAI101 (enmetazobactam) (FEP-AAI) - against contemporary multidrug-resistant (MDR) Enterobacteriaceae.

METHODS

Agar-based MIC screening against MDR Enterobacteriaceae (n = 264) was used to evaluate the in vitro efficacy of IPM-REL and FEP-AAI, to compare the results with established combinations, and to investigate alternative β-lactam partners for relebactam (REL) and enmetazobactam (AAI). The inhibition activities of REL, AAI and the comparators avibactam (AVI) and tazobactam, against isolated recombinant β-lactamases covering representatives from all four Ambler classes of β-lactamases, were tested using a fluorescence-based assay.

RESULTS

Using recombinant proteins, all four inhibitors were highly active against the tested class A serine β-lactamases (SBLs). REL and AVI showed moderate activity against the Class C AmpC from Pseudomonas aeruginosa and the Class D OXA-10/-48 SBLs, but outperformed tazobactam and AAI. All tested inhibitors lacked activity against Class B metallo-β-lactamases (MBLs). In the presence of REL and IPM, but not AAI, susceptibility increased against Klebsiella pnuemoniae carbapenemase (KPC)-positive and OXA-48-positive isolates. Both aztreonam-AVI and ceftolozane-tazobactam were more effective than IPM-REL. In all the tested combinations, AAI was a more effective inhibitor of class A β-lactamases (ESBLs) than the established inhibitors.

CONCLUSION

The results lead to the proposal of alternative combination therapies involving REL and AAI to potentiate the use of β-lactams against clinical Gram-negative isolates expressing a variety of lactamases. They highlight the potential of novel combinations for combating strains not covered by existing therapies.

High-Level Carbapenem Resistance in OXA-232-Producing Raoultella ornithinolytica Triggered by Ertapenem Therapy

OXA-232 is an OXA-48-group class D β-lactamase that hydrolyzes expanded-spectrum cephalosporins and carbapenems at low levels. Clinical strains producing OXA-232 are sometimes susceptible to carbapenems, making it difficult to identify them in the clinical microbiology laboratory. We describe the development of carbapenem resistance in sequential clinical isolates of Raoultella ornithinolytica carrying bla _OXA-232 in a hospitalized patient, where the ertapenem MIC increased from 0.5 μg/ml to 512 μg/ml and the meropenem MIC increased from 0.125 μg/ml to 32 μg/ml during the course of ertapenem therapy. Whole-genome sequencing (WGS) analysis identified loss-of-function mutations in ompC and ompF in carbapenem-resistant isolates that were not present in the initial carbapenem-susceptible isolate. Complementation of a carbapenem-resistant isolate with an intact ompF gene resulted in 16- to 32-fold reductions in carbapenem MICs, whereas complementation with intact ompC resulted in a 2-fold reduction in carbapenem MICs. Additionally, bla _OXA-232 expression increased 2.9-fold in a carbapenem-resistant isolate. Rapid development of high-level carbapenem resistance in initially carbapenem-susceptible OXA-232-producing R. ornithinolytica under selective pressure from carbapenem therapy highlights the diagnostic challenges in detecting Enterobacteriaceae strains producing this inefficient carbapenemase.

Analysis of the Degradation of Broad-Spectrum Cephalosporins by OXA-48-Producing Enterobacteriaceae Using MALDI-TOF MS

The objective of the study was to evaluate the activity of OXA-48 against different broad-spectrum cephalosporins and to identify the reaction products by MALDI-TOF MS. The action of OXA-48 on cefotaxime, ceftazidime, and ceftriaxone was assessed by this method, using an Escherichia coli J53 transconjugant carrying only the ~62 Kb IncL plasmid containing the bla_OXA-48 gene, and the same strain without any plasmid was included as a negative control. In addition, a collection of 17 clinical OXA-48-producing Enterobacteriaceae, which were susceptible to broad-spectrum cephalosporins, was evaluated. MALDI-TOF MS-based analysis of the E. coli transconjugant carrying the bla_OXA-48-harboring plasmid, and also the clinical isolates, showed degradation of cefotaxime into two inactive compounds-decarboxylated and deacetylated cefotaxime (~370 Da) and deacetyl cefotaxime (~414 Da), both with the hydrolyzed beta-lactam ring. Reaction products were not obtained when the experiment was performed with ceftriaxone or ceftazidime. From a clinical point of view, our study supports the idea that the efficacy of cefotaxime against OXA-48-producing Enterobacteriaceae is doubtful, in contrast to ceftazidime and ceftriaxone which could be valid choices for treating infections caused by these bacteria. However, further clinical studies confirming this hypothesis are required.

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.

Infections by OXA-48-like-producing Klebsiella pneumoniae non-co-producing extended-spectrum beta-lactamase: Can they be successfully treated with cephalosporins?

BACKGROUND

OXA-48 is an Ambler class D β-lactamase that hydrolyses penicillin and imipenem but has poor hydrolytic activity against cephalosporins. However, very few clinical experiences of treating extended-spectrum β-lactamase (ESBL)-negative OXA-48 producers with cephalosporins have been published.

OBJECTIVES

The aim of this study was to report clinical experience of infections due to ESBL-negative OXA-48-producing Klebsiella pneumoniae (K. pneumoniae) treated with cephalosporins.

PATIENTS AND METHODS

A retrospective study was conducted at Vall d'Hebron University Hospital, in Barcelona (Spain). It reviewed all microbiological isolates of OXA-48-producers that did not co-produce ESBL from May 2014 to May 2017, and included only clinical strains of patients treated with a cephalosporin for ≥72h.

RESULTS

From the 75 isolations of OXA-48 producers, there were 17 isolations of ESBL-negative OXA-48-producing K. pneumoniae. Three patients were treated with cephalosporins with successful outcomes: a pneumonia in a neutropenic patient treated with cefepime and amikacin; an acute focal nephritis of a renal graft treated with ceftriaxone; and an intrabdominal post-surgical infection treated with cefepime in combination with tigecycline at the beginning, and ciprofloxacin afterwards.

CONCLUSIONS

Cephalosporins could be an alternative treatment in selected patients with ESBL-negative OXA-48-producing K. pneumoniae infections, especially to avoid carbapenem use. However, it remains unknown if they should be given in combination.

Rapid detection of beta-lactamase production including carbapenemase by thin layer chromatography

OBJECTIVES

To develop a rapid and simple method that can identify the presence of β-lactamases in clinical isolates and samples, and determine their activity on different types of β-lactam antibiotics, including carbapenems, within one hour.

METHODS

In this study, we describe a thin layer chromatography-based method for rapid detection of β-lactamases including carbapenemases. The method relies on the examination of changes in the migration rate of β-lactams in chromatography, due to degradation by β-lactamase enzymes. A total of 44 isolates, 29 carbapenemase-producers and 15 non-carbapenemase-producers, were screened by this method.

RESULTS

The method has proven to be able to distinguish β-lactamases as carbapenemase or non-carbapenemase producing strains with high sensitivity in one hour.

CONCLUSIONS

The method developed, provides information about the production of β-lactamases by bacteria and β-lactam drugs inactivated by these enzymes, including carbapenems. This new method may play an important role in guiding antimicrobial treatment, especially in critically ill patients infected bacteria producing β-lactamases.

Treatment of Infections by OXA-48-Producing Enterobacteriaceae

Carbapenemase-producing Enterobacteriaceae (CPE) contribute significantly to the global public health threat of antimicrobial resistance. OXA-48 and its variants are unique carbapenemases with low-level hydrolytic activity toward carbapenems but no intrinsic activity against expanded-spectrum cephalosporins. bla _OXA-48 is typically located on a plasmid but may also be integrated chromosomally, and this gene has progressively disseminated throughout Europe and the Middle East. Despite the inability of OXA-48-like carbapenemases to hydrolyze expanded-spectrum cephalosporins, pooled isolates demonstrate high variable resistance to ceftazidime and cefepime, likely representing high rates of extended-spectrum beta-lactamase (ESBL) coproduction. In vitro data from pooled studies suggest that avibactam is the most potent beta-lactamase inhibitor when combined with ceftazidime, cefepime, aztreonam, meropenem, or imipenem. Resistance to novel avibactam combinations such as imipenem-avibactam or aztreonam-avibactam has not yet been reported in OXA-48 producers, although only a few clinical isolates have been tested. Although combination therapy is thought to improve the chances of clinical cure and survival in CPE infection, successful outcomes were seen in ∼70% of patients with infections caused by OXA-48-producing Enterobacteriaceae treated with ceftazidime-avibactam monotherapy. A carbapenem in combination with either amikacin or colistin has achieved treatment success in a few case reports. Uncertainty remains regarding the best treatment options and strategies for managing these infections. Newly available antibiotics such as ceftazidime-avibactam show promise; however, recent reports of resistance are concerning. Newer choices of antimicrobial agents will likely be required to combat this problem.

In vitro evaluation of double-carbapenem combinations against OXA-48-producing Klebsiella pneumoniae isolates using time-kill studies

Purpose. The aim of this study was to evaluate the in vitro activity of double-carbapenem combinations against OXA-48-producing Klebsiella pneumoniae clinical isolates.Methodology. Double combinations of ertapenem, meropenem and imipenem were evaluated for synergy and bactericidal activity using the time-kill methodology. All antibiotics were tested at 10 mg l^-1 and at a sub-inhibitory concentration of 0.5× minimum inhibitory concentration (MIC) for isolates with a carbapenem MIC≤8 mg l^-1. Synergy was defined as a ≥2log₁₀ colony-forming units (c.f.u.) ml^-1 decrease of viable colonies at 24 h compared to the most active carbapenem alone.Results. Ten distinct K. pneumoniae clinical isolates were tested. All carried bla _OXA-48 and bla _CTX-M-15, and exhibited an MIC range of 64-128, 4-32 and 1-32 mg l^-1 for ertapenem, meropenem and imipenem, respectively. Out of 48 isolate-combinations, synergy was observed in 9 (18.8 %) and cidal activity was observed in 13 (27.1 %). In vitro synergistic activity was noted for 5 out of 29 (17.2 %) ertapenem-, 6 out of 29 (20.7 %) meropenem- and 7 out of 38 (18.4 %) imipenem-containing combinations. No combination exhibited antagonism. Bactericidal activity was observed in 7 (24.1 %) ertapenem-, 8 (27.6 %) meropenem- and 11 (28.9 %) imipenem-containing combinations. Among the sub-inhibitory concentration combinations, three (15 %) ertapenem-, four (20 %) meropenem- and three (15 %) imipenem-containing ones showed synergistic interaction.Conclusion. Dual combinations of carbapenems, including those containing sub-inhibitory concentrations of antibiotics, were synergistic against multidrug-resistant (MDR) and extensively drug-resistant (XDR) K. pneumoniae isolates harbouring bla _OXA-48.

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.

A Flow Cytometric and Computational Approaches to Carbapenems Affinity to the Different Types of Carbapenemases

The synergy of carbapenem combinations regarding Enterobacteriaceae producing different types of carbapenemases was study through different approaches: flow cytometry and computational analysis. Ten well characterized Enterobacteriaceae (KPC, verona integron-encoded metallo-β-lactamases -VIM and OXA-48-like enzymes) were selected for the study. The cells were incubated with a combination of ertapenem with imipenem, meropenem, or doripenem and killing kinetic curves performed with and without reinforcements of the drugs. A cephalosporin was also used in combination with ertapenem. A flow cytometric assay with DiBAC4-(3), a membrane potential dye, was developed in order to evaluate the cellular lesion after 2 h incubation. A chemical computational study was performed to understand the affinity of the different drugs to the different types of enzymes. Flow cytometric analysis and time-kill assays showed a synergic effect against KPC and OXA-48 producing-bacteria with all combinations; only ertapenem with imipenem was synergic against VIM producing-bacteria. A bactericidal effect was observed in OXA-48-like enzymes. Ceftazidime plus ertapenem was synergic against ESBL-negative KPC producing-bacteria. Ertapenem had the highest affinity for those enzymes according to chemical computational study. The synergic effect between ertapenem and others carbapenems against different carbapenemase-producing bacteria, representing a therapeutic choice, was described for the first time. Easier and faster laboratorial methods for carbapenemase characterization are urgently needed. The design of an ertapenem derivative with similar affinity to carbapenemases but exhibiting more stable bonds was demonstrated as highly desirable.

In vivo efficacy of humanized high dose meropenem and comparators against Pseudomonas aeruginosa isolates producing verona integron-encoded metallo-β-lactamase (VIM)

Introduction

We aimed to describe the in vivo efficacy of meropenem, in addition to cefepime and levofloxacin as comparators against VIM-producing Pseudomonas aeruginosa and compare the findings to our previous observations with Enterobacteriaceae.

Methods

Eight clinical P. aeruginosa isolates with meropenem MICs from 4 to 512 mg/L were studied in a murine neutropenic thigh infection model. Animals were treated with doses of the antibiotics to simulate the human exposure of meropenem 2 g q8 h 30-min infusion, cefepime 2 g q8 h 30-min infusion and levofloxacin 500 mg q24 h. After 24 hours, the animals were euthanized and efficacy was calculated as the change in thigh bacterial density (log₁₀ CFU) relative to the starting inoculum (0 h).

Results

As expected, levofloxacin was ineffective against all isolates due to their resistant phenotype (8 to>64 mg/L). Cefepime also showed minimal activity against all isolates consistent with its failure to achieve pharmacodynamic target exposures due to high MICs of 32 to>512 mg/L. In the presence of low MICs (4 to 16 mg/L), the fT> MIC of meropenem was sufficiently high to result in CFU reductions. However, conflicting activity was noted for isolates with MICs = 128 mg/L that possessed the same enzymatic profile, suggesting that other mechanisms of resistance are responsible for driving CFU outcomes. No activity was noted for organisms with a meropenem MIC = 512 mg/L.

Conclusion

Unlike previous observations with MBL-producing Enterobacteriaceae that showed discordance between in vitro resistance and in vivo efficacy in the murine infection model, we found that the efficacy of humanized cefepime and meropenem was generally concordant with the phenotypic profile of VIM-producing P. aeruginosa.

Global Dissemination of Carbapenemase-Producing Klebsiella pneumoniae: Epidemiology, Genetic Context, Treatment Options, and Detection Methods

The emergence of carbapenem-resistant Gram-negative pathogens poses a serious threat to public health worldwide. In particular, the increasing prevalence of carbapenem-resistant Klebsiella pneumoniae is a major source of concern. K. pneumoniae carbapenemases (KPCs) and carbapenemases of the oxacillinase-48 (OXA-48) type have been reported worldwide. New Delhi metallo-β-lactamase (NDM) carbapenemases were originally identified in Sweden in 2008 and have spread worldwide rapidly. In this review, we summarize the epidemiology of K. pneumoniae producing three carbapenemases (KPCs, NDMs, and OXA-48-like). Although the prevalence of each resistant strain varies geographically, K. pneumoniae producing KPCs, NDMs, and OXA-48-like carbapenemases have become rapidly disseminated. In addition, we used recently published molecular and genetic studies to analyze the mechanisms by which these three carbapenemases, and major K. pneumoniae clones, such as ST258 and ST11, have become globally prevalent. Because carbapenemase-producing K. pneumoniae are often resistant to most β-lactam antibiotics and many other non-β-lactam molecules, the therapeutic options available to treat infection with these strains are limited to colistin, polymyxin B, fosfomycin, tigecycline, and selected aminoglycosides. Although, combination therapy has been recommended for the treatment of severe carbapenemase-producing K. pneumoniae infections, the clinical evidence for this strategy is currently limited, and more accurate randomized controlled trials will be required to establish the most effective treatment regimen. Moreover, because rapid and accurate identification of the carbapenemase type found in K. pneumoniae may be difficult to achieve through phenotypic antibiotic susceptibility tests, novel molecular detection techniques are currently being developed.

Treatment options for infections caused by carbapenem-resistant Enterobacteriaceae: can we apply "precision medicine" to antimicrobial chemotherapy?

INTRODUCTION

For the past three decades, carbapenems played a central role in our antibiotic armamentarium, trusted to effectively treat infections caused by drug-resistant bacteria. The utility of this class of antibiotics has been compromised by the emergence of resistance especially among Enterobacteriaceae.

AREAS COVERED

We review the current mainstays of pharmacotherapy against infections caused by carbapenem-resistant Enterobacteriaceae (CRE) including tigecycline, aminoglycosides, and rediscovered 'old' antibiotics such as fosfomycin and polymyxins, and discuss their efficacy and potential toxicity. We also summarize the contemporary clinical experience treating CRE infections with antibiotic combination therapy. Finally, we discuss ceftazidime/avibactam and imipenem/relebactam, containing a new generation of beta-lactamase inhibitors, which may offer alternatives to treat CRE infections. We critically evaluate the published literature, identify relevant clinical trials and review documents submitted to the United States Food and Drug Administration.

EXPERT OPINION

Defining the molecular mechanisms of resistance and applying insights about pharmacodynamic and pharmacokinetic properties of antibiotics, in order to maximize the impact of old and new therapeutic approaches should be the new paradigm in treating infections caused by CRE. A concerted effort is needed to carry out high-quality clinical trials that: i) establish the superiority of combination therapy vs. monotherapy; ii) confirm the role of novel beta-lactam/beta-lactamase inhibitor combinations as therapy against KPC- and OXA-48 producing Enterobacteriaceae; and, iii) evaluate new antibiotics active against CRE as they are introduced into the clinic.

Efficacy of humanized high-dose meropenem, cefepime, and levofloxacin against Enterobacteriaceae isolates producing Verona integron-encoded metallo-β-lactamase (VIM) in a murine thigh infection model

We aimed to describe the in vivo activity of humanized pharmacokinetic exposures of meropenem and comparators against Verona integron-encoded metallo-β-lactamase (MBL) (VIM)-producing Enterobacteriaceae in a murine model. Levofloxacin activity was predicted by its MIC, and cefepime activity displayed variability, whereas meropenem produced a >1 log CFU reduction against all isolates despite high MICs indicative of resistance. Our results suggest that despite in vitro resistance, high-dose meropenem may be a possible option against infections caused by Enterobacteriaceae producing MBL-type carbapenemases.

Carbapenemase-Producing Klebsiella pneumoniae, a Key Pathogen Set for Global Nosocomial Dominance

The management of infections due to Klebsiella pneumoniae has been complicated by the emergence of antimicrobial resistance, especially to carbapenems. Resistance to carbapenems in K. pneumoniae involves multiple mechanisms, including the production of carbapenemases (e.g., KPC, NDM, VIM, OXA-48-like), as well as alterations in outer membrane permeability mediated by the loss of porins and the upregulation of efflux systems. The latter two mechanisms are often combined with high levels of other types of β-lactamases (e.g., AmpC). K. pneumoniae sequence type 258 (ST258) emerged during the early to mid-2000s as an important human pathogen and has spread extensively throughout the world. ST258 comprises two distinct lineages, namely, clades I and II, and it seems that ST258 is a hybrid clone that was created by a large recombination event between ST11 and ST442. Incompatibility group F plasmids with blaKPC have contributed significantly to the success of ST258. The optimal treatment of infections due to carbapenemase-producing K. pneumoniae remains unknown. Some newer agents show promise for treating infections due to KPC producers; however, effective options for the treatment of NDM producers remain elusive.

Detection of OXA-48-type carbapenemase-producing Enterobacteriaceae in diagnostic laboratories can be enhanced by addition of bicarbonates to cultivation media or reaction buffers

Carbapenemase-mediated resistance to carbapenems in Enterobacteriaceae has become the main challenge in the treatment and prevention of infections recently. The partially unnoticed spread of OXA-48-type carbapenemase producers is usually assigned to low minimum inhibitory concentrations (MICs) of carbapenems that OXA-48-producing isolates often display. Therefore, there is an urgent need of specific and sensitive methods for isolation and detection of OXA-48 producers in clinical microbiology diagnostics. The influence of bicarbonates on carbapenem MICs against carbapenemase-producing Enterobacteriaceae was tested. We also checked whether the addition of bicarbonates to liquid media supplemented with meropenem may facilitate the selective enrichment of various carbapenemase producers in cultures. Furthermore, the sensitivity of carbapenemase confirmation by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-TOF MS) and spectrophotometric hydrolysis assays upon the addition of NH4HCO3 was examined. The addition of NaHCO3 significantly increased MICs of ertapenem and meropenem for OXA-48 producers. Furthermore, liquid media supplemented with NaHCO3 and meropenem were reliable for the selective enrichment of carbapenemase producers. The presence of NH4HCO3 in buffers used in the spectrophotometric and MALDI-TOF MS carbapenemase detection increased the sensitivity of that assay. Our results demonstrate that bicarbonates in media or reaction buffers can enhance the sensitivity of screening methods and diagnostic tests for carbapenemase producers.

Treating infections caused by carbapenemase-producing Enterobacteriaceae

Carbapenemase-producing Enterobacteriaceae (CPE) have spread worldwide, causing serious infections with increasing frequency. CPE are resistant to almost all available antibiotics, complicating therapy and limiting treatment options. Mortality rates associated with CPE infections are unacceptably high, indicating that the current therapeutic approaches are inadequate and must be revised. Here, we review 20 clinical studies (including those describing the largest cohorts of CPE-infected patients) that provided the necessary information regarding isolate and patient characteristics and treatment schemes, as well as a clear assessment of outcome. The data summarized here indicate that treatment with a single in vitro active agent resulted in mortality rates not significantly different from that observed in patients treated with no active therapy, whereas combination therapy with two or more in vitro active agents was superior to monotherapy, providing a clear survival benefit (mortality rate, 27.4% vs. 38.7%; p <0.001). The lowest mortality rate (18.8%) was observed in patients treated with carbapenem-containing combinations.