Evaluation of carbapenemase screening and confirmation tests with Enterobacteriaceae and development of a practical diagnostic algorithm

Comparison of Multiple Carbapenemase Tests Based on an Unbiased Colony-Selection Method

Carbapenemase-producing organisms (CPOs) present a major threat to public health, demanding precise diagnostic techniques for their detection. Discrepancies among the CPO tests have raised concerns, partly due to limitations in detecting bacterial diversity within host specimens. We explored the impact of an unbiased colony selection on carbapenemase testing and assessed its relevance to various tests. Using the FirstAll method for unbiased colony selection to reduce bias, we compared the results from different methods, namely the modified carbapenem inactivation method/EDTA-modified carbapenem inactivation method (mCIM/eCIM), the Carba5, the CPO panel, and the multiplex PCR (MPCR). We compared the FirstAll method to the conventional colony selection for MPCR with seven CPO species. In addition, we evaluated the test performance on seven CPO species using MPCR as a reference and the FirstAll method as the colony-selection method. The results revealed that the selections from the FirstAll method have improved rates of carbapenemase detection, in comparison to approximately 11.2% of the CPO isolates that were noted to be false negatives in the conventional colony-selection methods. Both the Carba5 test and the CPO panel showed suboptimal performance (sensitivity/specificity: Carba5 74.6%/89.5%, CPO panel 77.2%/74.4%) in comparison to the FirstAll method. The Carba5 test provided specific carbapenemase class assignments, but the CPO panel failed in 18.7% of the cases. The Carba5 test and the CPO panel results correlated well with ceftazidime-avibactam minimal inhibitory concentrations (MICs). The concordance for Class A/D with MICs was 94.7% for Carba5 and 92.7% for the CPO panel; whereas for Class B, it was 86.5% for Carba5 and 75.9% for the CPO panel. In conclusion, FirstAll, as the unbiased colony-selection method, was shown to impact carbapenemase testing. With FirstAll, the diagnostic performance of both the Carba5 and the CPO panel was found to be lower. Furthermore, the utilization of ceftazidime-avibactam guided by either the CPO panel or Carba5 was appropriate.

First report of a carbapenemase OXA-48-producing Hafnia alvei clinical isolate

Introduction

Carbapenems are usually used in the treatment of infections caused by cephalosporin-resistant Enterobacterales ; however, the increase in carbapenem-resistant Enterobacterales (CRE) has become one of the most important problems in public health. Hafnia alvei is associated with intestinal and extraintestinal infections, especially in patients with any chronic disease or some type of immunosupression. H. alvei is resistant to first-generation aminopenicillins and cephalosporins owing to the β-lactamase (Amp C) in their chromosome; the only carbapenem-resistant Hafnia strain described until now was due to a lack of the OmpK36 protein that plays an important role in permeability to carbapenems.

Case presentation

We present the case of a 65-year-old male diagnosed with acute lithiasic cholecystitis. Culture of the biliary prosthesis yielded a OXA-48-producing H. alvei that was identified by MALDI-TOF (matrix-assisted laser desorption/ionization-time of flight) MS. Carbapenemase production was detected by immunochromatography and confirmed by sequencing.

Conclusion

To our knowledge, this is the first report of OXA-48-producing H. alvei probably obtained by horizontal transfer from Enterobacter cloacae OXA-48 isolated in previous samples.

Performance of Phenotypic Tests to Detect β-Lactamases in a Population of β-Lactamase Coproducing Enterobacteriaceae Isolates

Objectives This study aimed to evaluate the performance of routinely used phenotypic tests to detect β-lactamase production in isolates coproducing multiple β-lactamase types.

Methods Commonly used phenotypic tests for the detection of extended spectrum β-lactamases (ESBL), AmpC β-lactamase, and carbapenemases were compared with detection and sequencing of β-lactamase genes (as the reference test) in 176 uropathogenic Enterobacteriaceae coproducing multiple β-lactamases from two hospitals in the Western Province of Sri Lanka.

Results Majority of the isolates (147/176, 83.5%) carried β-lactamase genes with (90/147, 61%) harboring multiple genes. The Clinical and Laboratory Standards Institute screening method using cefotaxime (sensitivity [Se], 97; specificity [Sp], 93; accuracy [Ac], 94) and ceftriaxone (Se, 97; Sp, 91; Ac, 93) was the most effective to detect ESBLs. The modified double disc synergy test (Se, 98; Sp, 98; Ac, 97) and combined disc test (Se, 94; Sp, 98; Ac, 96) showed good specificity for confirmation of ESBLs. Cefoxitin resistance (Se, 97; Sp, 73; Ac, 85) and the AmpC disc test (Se, 96; Sp, 82; Ac, 86) were sensitive to detect AmpC β-lactamase producers coproducing other β-lactamases but showed low specificity, probably due to coproduction of carbapenemases. Meropenem was useful to screen for New Delhi metallo β-lactamases and OXA-48-like carbapenemases (Se, 97; Sp, 96; Ac, 96). The modified carbapenem inactivation method showed excellent performance (Se, 97; Sp, 98; Ac, 97) in identifying production of both types of carbapenemases and was able to distinguish this from carbapenem resistance due to potential mutations in the porin gene.

Conclusions Microbiology laboratories that are still depend on phenotypic tests should utilize tests that are compatible with the types of β-lactamase prevalent in the region and those that are least affected by coexisting resistance mechanisms.

Detection of Extended-Spectrum β-Lactamases (ESBLs) and AmpC in Class A and Class B Carbapenemase-Producing Enterobacterales

In carbapenemase-producing Enterobacterales (CPE) additional β-lactam resistance mechanisms such as extended-spectrum-β-lactamases (ESBL) and/or AmpC-β-lactamases are generally difficult to detect by phenotypical methods. Recently, a modified version of the CLSI ESBL confirmatory combination disc diffusion (CDD) test, which involves the addition of boronic acid and EDTA on discs containing ESBL and AmpC substrates ± inhibitors, has been proposed for the detection of ESBL in class A and class B CPE. Here, the performance of the modified CDD test was evaluated using 121 genotypically characterized class A and class B CPE. Also, the effectiveness of the NG-Test CTX-M-MULTI lateral flow immunoassay was evaluated for ESBL detection. For class A CPE (n = 47), the modified CDD method exhibited an equal specificity (95.7%) and a higher sensitivity (100%) compared to the standard method (91.7%). The CTX-M-MULTI test detected ESBL in all CTX-M-type ESBL producers (n = 23), whereas it was negative for all CTX-M-type ESBL-negative isolates (n = 24). For class B CPE (n = 71), the modified method significantly improved both sensitivity (95%) and specificity (100%) in detecting ESBL compared to the standard method (17.5% sensitivity and 83.9% specificity). In comparison, the CTX-M-MULTI led to identification of ESBL in all CTX-M-ESBL-producers (n = 39) and no false-positive signal was generated with the CTX-M-type-ESBL-negative isolates (n = 30). Furthermore, the modified CDD improved the robustness of the method for AmpC detection (inconclusive results were produced in 53/57 and 10/57 cases with the standard and modified method, respectively), although the sensitivity of the test was poor (23.5%). Here, we propose a practical and cost-effective approach combining the modified CDD and the CTX-M-MULTI test for detection of ESBL and/or AmpC in class A and B CPE. IMPORTANCE Antimicrobial resistance is a growing public health threat of broad concern worldwide. Timely detection of antibiotic resistance mechanisms can help to monitor and to curb the spread of resistant bacteria within the hospital setting as well as in the environment. In this work we report an accurate and affordable method to phenotypically identify difficult-to-detect resistance determinants in highly resistant (carbapenemase-producing) bacteria. This method may be implemented in any diagnostic microbiology lab and may reduce the underreporting of relevant resistance mechanisms.

Evaluation of the EasyScreen™ ESBL/CPO Detection Kit for the Detection of ß-Lactam Resistance Genes

Early detection of multidrug resistant bacteria is of paramount importance for implementing appropriate infection control strategies and proper antibacterial therapies. We have evaluated a novel real-time PCR assay using fluorescent probes and 3base^® technology, the EasyScreen^TM ESBL/CPO Detection Kit (Genetic Signatures, Newtown, Australia), for the detection of 15 β-lactamase genes (bla_VIM, bla_NDM, bla_IMP, bla_OXA-48, bla_KPC, bla_OXA-23, bla_OXA-51, bla_SME,bla_IMI, bla_GES,bla_TEM,bla_SHV, bla_CTX-M,bla_CMY, bla_DHA) and colistin resistance mcr-1 gene from 341 bacterial isolates (219 Enterobacterales, 66 P. aeruginosa and 56 A. baumannii) that were grown on Mueller–Hinton (MH) agar plates. One colony was suspended in provided extraction buffer, which lyses and converts the nucleic acids into a 3base^®-DNA form (cytosines are converted into uracil, and subsequently thymine during PCR). The converted bacterial DNA is then added to the 6 PCR mixes, with primers for three targets plus one internal control. The EasyScreen^TM ESBL/CPO Detection Kit was able to detect the 5-major (NDM, VIM, IMP, KPC, OXA-48) and 2-minor (IMI, Sme) carbapenemases and their variants irrespective of the species expressing them with nearly 100% sensitivity and specificity. With cephalosporinases CMY (82% of sensitivity) and DHA (87% of sensitivity) detection of chromosomally encoded variants was less efficient. Similarly, the chromosomally encoded OXA-51 variants were not consistently detected in A. baumannii. Despite being capable of efficiently detecting bla_CTX-M-, bla_TEM-, bla_SHV- and bla_GES-like genes, the EasyScreen™ ESBL/CPO Detection Kit was not able to distinguish between penicillinases and ESBL-variants of TEM and SHV and between GES-ESBLs and GES-carbapenemases. As GES enzymes are still rare, their detection as an ESBL or a carbapenemase remains important. Detection of mcr-1 was efficient, but none of the other mcr-alleles were detected in the 341 bacterial isolates tested. The EasyScreen^TM ESBL/CPO Detection Kit is adapted for the detection of the most prevalent carbapenemases encountered in Gram-negatives isolated worldwide.

Coupling Machine Learning and High Throughput Multiplex Digital PCR Enables Accurate Detection of Carbapenem-Resistant Genes in Clinical Isolates

Rapid and accurate identification of patients colonised with carbapenemase-producing organisms (CPOs) is essential to adopt prompt prevention measures to reduce the risk of transmission. Recent studies have demonstrated the ability to combine machine learning (ML) algorithms with real-time digital PCR (dPCR) instruments to increase classification accuracy of multiplex PCR assays when using synthetic DNA templates. We sought to determine if this novel methodology could be applied to improve identification of the five major carbapenem-resistant genes in clinical CPO-isolates, which would represent a leap forward in the use of PCR-based data-driven diagnostics for clinical applications. We collected 253 clinical isolates (including 221 CPO-positive samples) and developed a novel 5-plex PCR assay for detection of bla_IMP, bla_KPC, bla_NDM, bla_OXA-48, and bla_VIM. Combining the recently reported ML method “Amplification and Melting Curve Analysis” (AMCA) with the abovementioned multiplex assay, we assessed the performance of the AMCA methodology in detecting these genes. The improved classification accuracy of AMCA relies on the usage of real-time data from a single-fluorescent channel and benefits from the kinetic/thermodynamic information encoded in the thousands of amplification events produced by high throughput real-time dPCR. The 5-plex showed a lower limit of detection of 10 DNA copies per reaction for each primer set and no cross-reactivity with other carbapenemase genes. The AMCA classifier demonstrated excellent predictive performance with 99.6% (CI 97.8–99.9%) accuracy (only one misclassified sample out of the 253, with a total of 160,041 positive amplification events), which represents a 7.9% increase (p-value <0.05) compared to conventional melting curve analysis. This work demonstrates the use of the AMCA method to increase the throughput and performance of state-of-the-art molecular diagnostic platforms, without hardware modifications and additional costs, thus potentially providing substantial clinical utility on screening patients for CPO carriage.

A pentaplex real-time PCR assay for rapid identification of major beta-lactamase genes KPC, NDM, CTX, CMY, and OXA-48 directly from bacteria in blood

Introduction. Antibiotic resistance, particularly in cases of sepsis, has emerged as a growing global public health concern and economic burden. Current methods of blood culture and antimicrobial susceptibility testing of agents involved in sepsis can take as long as 3-5 days. It is vital to rapidly identify which antimicrobials can be used to effectively treat sepsis cases on an individual basis. Here, we present a pentaplex, real-time PCR-based assay that can quickly identify the most common beta-lactamase genes (Klebsiella pneumoniae carbapenemase (KPC); New Delhi metallo-beta-lactamase (NDM); cefotaximase-Munich (CTX-M); cephamycin AmpC beta-lactamases (CMY); and Oxacillinase-48 (OXA-48)) from pathogens derived directly from the blood of patients presenting with bacterial septicemia.Aim. To develop an assay which can rapidly identify the most common beta-lactamase genes in Carbapenem-resistant Enterobacteriaceae bacteria (CREs) from the United States.Hypothesis/Gap Statement. Septicemia caused by carbapenem-resistant bacteria has a death rate of 40-60 %. Rapid diagnosis of antibiotic susceptibility directly from bacteria in blood by identification of beta-lactamase genes will greatly improve survival rates. In this work, we develop an assay capable of concurrently identifying the five most common beta-lactamase and carbapenemase genes.Methodology. Primers and probes were created which can identify all subtypes of Klebsiella pneumoniae carbapenemase (KPC); New Delhi metallo-beta-lactamase (NDM); cefotaximase-Munich (CTX); cephamycin AmpC beta-lactamase (CMY); and oxacillinase-48 (OXA-48). The assay was validated using 13 isolates containing various PCR targets from the Centre for Disease Control Antimicrobial Resistance Isolate Bank Enterobacterales Carbapenemase Diversity Panel. Blood obtained from volunteers was spiked with CREs and bacteria were separated, lysed, and subjected to analysis via the pentaplex assay.Results. This pentaplex assay successfully identified beta-lactamase genes derived from bacteria separated from blood at concentrations of 4-8 c.f.u. ml-1.Conclusion. This assay will improve patient outcomes by supplying physicians with critical drug resistance information within 2 h of septicemia onset, allowing them to prescribe effective antimicrobials corresponding to the resistance gene(s) present in the pathogen. In addition, information supplied by this assay will lessen the inappropriate use of broad-spectrum antimicrobials and prevent the evolution of further antibiotic resistance.

Systematic Comparison of Three Commercially Available Combination Disc Tests and the Zinc-Supplemented Carbapenem Inactivation Method (zCIM) for Carbapenemase Detection in Enterobacterales Isolates

Detection of carbapenemases in Enterobacterales is crucial for patient treatment and infection control. Among others, combination disc tests (CDTs) with different inhibitors (e.g., EDTA) and variations of the carbapenem inactivation method (CIM) are recommended by EUCAST or the CLSI and are used by many laboratories as they are relatively inexpensive. In this study, we compare three commercially available CDTs, faropenem disc testing (FAR), and the zinc-supplemented CIM (zCIM) test for the detection of carbapenemase-producing Enterobacterales (CPE). The Rosco KPC/MBL and OXA-48 Confirm kit (ROS-CDT), the Liofilchem KPC&MBL&OXA-48 disc kit (LIO-CDT), Mastdiscs Combi Carba plus (MAST-CDT), FAR, and zCIM were challenged with 106 molecularly characterized CPE and 47 non-CPE isolates. The sensitivities/specificities were 86% (confidence interval [CI], 78 to 92%)/98% (CI, 89 to 100%) for MAST-CDT and ROS-CDT, 96% (CI, 91 to 99%)/87% (CI, 74 to 95%) for LIO-CDT, and 99% (CI, 95 to 100%)/81% (CI, 67 to 91%) for FAR compared to 98% (CI, 93 to 100%)/100% (CI, 92 to 100%) for zCIM. The CDTs showed great performance differences depending on the carbapenemase class, with MAST-CDT and LIO-CDT best detecting class B, ROS-CDT best detecting class A, and LIO-CDT best detecting class D carbapenemases. The overall performance of commercially available CDTs was good but varied greatly for different carbapenemases and between manufacturers, compared with FAR and zCIM, which performed well for all carbapenemase types. For reliable carbapenemase detection, CDTs should preferably not be used as the sole test but can be part of a diagnostic strategy when combined with other assays (e.g., CIM-based, immunochromatographic, or molecular tests).

Novel Rapid Test for Detecting Carbapenemase

We developed a carbapenemase test based on the ability of imipenem to inhibit noncarbapenemase β-lactamases. The test uses bacterial isolates with a fluorescent β-lactamase substrate, producing objective results with 100% sensitivity and specificity in 10 minutes. The assay is inexpensive and consists of only 1 mixing step.

Performance Evaluation of the Newly Developed In Vitro Rapid Diagnostic Test for Detecting OXA-48-Like, KPC-, NDM-, VIM- and IMP-Type Carbapenemases: The RESIST-5 O.K.N.V.I. Multiplex Lateral Flow Assay

The objective of this study was to evaluate the performance of the RESIST-5 O.K.N.V.I. assay for identifying these five common domestic carbapenemases among a large number of clinical isolates in South Korea. A total of 268 non-duplicated clinical isolates of gram-negative bacilli were included in this study as follows: 258 carbapenemase-producing (CP) strains (OXA-48-like, KPC, NDM, VIM, IMP, GES, OXA-23 and two or more carbapenemase producers) and 10 non-CP carbapenem-resistant Enterobacterales (non-CP CREs). Overall sensitivity and specificity were 98.4% and 100%, respectively. In addition, all non-targeted carbapenemase producers including GES and OXA-23 producers and non-CP CREs were correctly identified as negative results. There were only four discrepant cases in which three VIM carbapenemase producers and one NDM carbapenemase producer were not detected. The RESIST-5 O.K.N.V.I. assay as an in vitro diagnostic test for detecting five common carbapenemases provided rapid and accurate results in a short time, indicating that this method could provide an innovative solution for early detection, resulting in appropriate antimicrobial treatment in the clinical field.

Emerging Options for the Diagnosis of Bacterial Infections and the Characterization of Antimicrobial Resistance

Precise and rapid identification and characterization of pathogens and antimicrobial resistance patterns are critical for the adequate treatment of infections, which represent an increasing problem in intensive care medicine. The current situation remains far from satisfactory in terms of turnaround times and overall efficacy. Application of an ineffective antimicrobial agent or the unnecessary use of broad-spectrum antibiotics worsens the patient prognosis and further accelerates the generation of resistant mutants. Here, we provide an overview that includes an evaluation and comparison of existing tools used to diagnose bacterial infections, together with a consideration of the underlying molecular principles and technologies. Special emphasis is placed on emerging developments that may lead to significant improvements in point of care detection and diagnosis of multi-resistant pathogens, and new directions that may be used to guide antibiotic therapy.

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.

Antibiotic Resistance Patterns of Pseudomonas spp. Isolated From Raw Milk Revealed by Whole Genome Sequencing

Psychrotrophic bacteria in raw milk are most well known for their spoilage potential and the economic losses they cause to the dairy industry. Food-related psychrotrophic bacteria are increasingly reported to have antibiotic resistance features. The aim of this study was to evaluate the resistance patterns of Pseudomonas spp. isolated from bulk-tank milk. In total, we investigated the antibiotic susceptibility profiles of 86 Pseudomonas spp. isolates from raw milk. All strains were tested against 15 antimicrobial agents. Pseudomonas isolates were most highly resistant to imipenem (95.3%), followed by trimethoprim-sulfamethoxazole (69.8%), aztreonam (60.5%), chloramphenicol (45.3%), and meropenem (27.9%). Their multiple antibiotic resistance (MAR) index values ranged from 0.0 to 0.8. Whole-genome sequencing revealed the presence of intrinsic resistance determinants, such as BcI, ampC-09, blaCTX-M, oprD, sul1, dfrE, catA1, catB3, catI, floR, and cmlV. Moreover, resistance-nodulation-cell division (RND) and ATP-binding cassette (ABC) antibiotic efflux pumps were also found. This study provides further knowledge of the antibiotic resistance patterns of Pseudomonas spp. in milk, which may advance our understanding of resistance in Pseudomonas and suggests that antibiotic resistance of Pseudomonas spp. in raw milk should be a concern.

Tentative breakpoints and areas of technical uncertainty for early reading automated disc diffusion for Enterobacterales

BACKGROUND

Disc diffusion is a reliable, accurate and cost-efficient procedure for antimicrobial susceptibility testing (AST) but requires long (18-24 h) incubation times. Reading of disc diffusion after short incubation times (6-8 h) by automated systems is feasible but should be categorized with time-adapted breakpoints to reduce errors.

OBJECTIVES

This study systematically compared early readings (6 and 8 h) of disc diffusion using an automated system with that of the standard 18 h EUCAST method. Time-adapted tentative breakpoints were proposed to discriminate susceptible from resistant isolates and areas of technical uncertainty were defined to minimize the risk of errors.

METHODS

A total of 1106 Enterobacterales isolates with a wide variety of resistance mechanisms and resistance profiles were included. All isolates were analysed for susceptibility to amoxicillin/clavulanic acid, ceftriaxone, cefepime, meropenem, ciprofloxacin and gentamicin using the automated WASPLabTM system. Part of the collection (515 isolates) was also analysed for susceptibility to an additional 10 antibiotics.

RESULTS

Separation between WT and non-WT populations was poorer at early incubation times than following standard incubation. Editing of rapid automated AST results after 6 and 8 h incubation with time-adapted breakpoints resulted in 84.0% and 88.5% interpretable results with assignment to the resistant or susceptible category. Major error and very major error rates for the 6 h readings were only 0.4% and 0.3%, virtually identical to those of 18 h AST reading.

CONCLUSIONS

Time-adapted clinical breakpoints in disc diffusion testing for Enterobacterales allow for accurate automated AST interpretation after shortened incubation times for a large number of antibiotics, with the additional possibility of subsequent confirmation after 18 h incubation.

Phenotypic and genotypic characterization of carbapenem resistance mechanisms in Klebsiella pneumoniae from blood culture specimens: A study from North India

BACKGROUND:

Emergence of carbapenem resistance among Enterobacteriaceae in different geographical regions is of great concern as these bacteria are easily transmissible among patients. Carbapenem-resistance in Enterobacteriaceae is due to production of carbapenemases of various classes and hyper production of the ESBLs (Extended spectrum beta lactamases) and Amp C beta lactamases with reduced cell wall permeability mechanisms. Phenotypic detection and differentiation is important for proper infection control and appropriate patient management. This study was done to know the prescence of various beta lactamases and carbapenemases with other mechanisms of resistance in Klebsiella pneumoniae isolates.

MATERIALS AND METHODS:

50 non-duplicate carbapenem resistant isolates of Klebsiella pneumoniae from blood culture specimens were included and various mechanisms of resistance were studied based on phenotypic and genotypic methods.

RESULTS:

Out of 50 isolates, 39 (78%) of K. pneumoniae isolates were Extended Spectrum Beta Lactamase (ESBL) producers based on CLSI guidelines. All 50 showed positive Modified Hodge Test (MHT) and 32 showed Metallo Beta Lactamase (MBL) by Combined Disc Test (CDT). Four isolates showed AmpC production with porin loss. None of the isolates showed Class A KPC production by CDT. In our study all the 10 isolates evaluated by genotypic technique produced CTX-M group 1 enzyme by multiplex PCR. Seven out of 10 strains which showed positive MBL results were positive for NDM.

CONCLUSIONS:

Carbapenems are often considered last resort antibiotics in the treatment of infections due to multidrug-resistant organisms. It is therefore mandatory to maintain the clinical efficacy of carbapenems by early detection of various enzymes. For routine clinical laboratories both phenotypic and genotypic tests need to be followed to detect various mechanisms of carbapenem resistance and this is of epidemiological relevance also.

The effect of varying multidrug-resistence (MDR) definitions on rates of MDR gram-negative rods

Background

A multitude of definitions determining multidrug resistance (MDR) of Gram-negative organisms exist worldwide. The definitions differ depending on their purpose and on the issueing country or organization. The MDR definitions of the European Centre for Disease Prevention and Control (ECDC) were primarily chosen to harmonize epidemiological surveillance. The German Commission of Hospital Hygiene and Infection Prevention (KRINKO) issued a national guideline which is mainly used to guide infection prevention and control (IPC) measures. The Swiss University Hospital Zurich (UHZ) - in absentia of national guidelines - developed its own definition for IPC purposes. In this study we aimed to determine the effects of different definitions of multidrug-resistance on rates of Gram-negative multidrug-resistant organisms (GN-MDRO).

Methods

MDR definitions of the ECDC, the German KRINKO and the Swiss University Hospital Zurich were applied on a dataset comprising isolates of Escherichia coli, Klebsiella pneumoniae, Enterobacter sp., Pseudomonas aeruginosa, and Acinetobacter baumannii complex. Rates of GN-MDRO were compared and the percentage of patients with a GN-MDRO was calculated.

Results

In total 11'407 isolates from a 35 month period were included. For Enterobacterales and P. aeruginosa, highest MDR-rates resulted from applying the 'ECDC-MDR' definition. 'ECDC-MDR' rates were up to four times higher compared to 'KRINKO-3/4MRGN' rates, and up to six times higher compared to UHZ rates. Lowest rates were observed when applying the 'KRINKO-4MRGN' definitions. Comparing the 'KRINKO-3/4MRGN' with the UHZ definitions did not show uniform trends, but yielded higher rates for E. coli and lower rates for P. aeruginosa. On the patient level, the percentages of GN-MDRO carriers were 2.1, 5.5, 6.6, and 18.2% when applying the 'KRINKO-4MRGN', 'UHZ-MDR', 'KRINKO-3/4MRGN', and the 'ECDC-MDR' definition, respectively.

Conclusions

Different MDR-definitions lead to considerable variation in rates of GN-MDRO. Differences arise from the number of antibiotic categories required to be resistant, the categories and drugs considered relevant, and the antibiotic panel tested. MDR definitions should be chosen carefully depending on their purpose and local resistance rates, as definitions guiding isolation precautions have direct effects on costs and patient care.

The Global Ascendency of OXA-48-Type Carbapenemases

Surveillance studies have shown that OXA-48-like carbapenemases are the most common carbapenemases in Enterobacterales in certain regions of the world and are being introduced on a regular basis into regions of nonendemicity, where they are responsible for nosocomial outbreaks. OXA-48, OXA-181, OXA-232, OXA-204, OXA-162, and OXA-244, in that order, are the most common enzymes identified among the OXA-48-like carbapenemase group. OXA-48 is associated with different Tn1999 variants on IncL plasmids and is endemic in North Africa and the Middle East. OXA-162 and OXA-244 are derivatives of OXA-48 and are present in Europe. OXA-181 and OXA-232 are associated with ISEcp1, Tn2013 on ColE2, and IncX3 types of plasmids and are endemic in the Indian subcontinent (e.g., India, Bangladesh, Pakistan, and Sri Lanka) and certain sub-Saharan African countries. Overall, clonal dissemination plays a minor role in the spread of OXA-48-like carbapenemases, but certain high-risk clones (e.g., Klebsiella pneumoniae sequence type 147 [ST147], ST307, ST15, and ST14 and Escherichia coli ST38 and ST410) have been associated with the global dispersion of OXA-48, OXA-181, OXA-232, and OXA-204. Chromosomal integration of bla _OXA-48 within Tn6237 occurred among E. coli ST38 isolates, especially in the United Kingdom. The detection of Enterobacterales with OXA-48-like enzymes using phenotypic methods has improved recently but remains challenging for clinical laboratories in regions of nonendemicity. Identification of the specific type of OXA-48-like enzyme requires sequencing of the corresponding genes. Bacteria (especially K. pneumoniae and E. coli) with bla _OXA-48, bla _OXA-181, and bla _OXA-232 are emerging in different parts of the world and are most likely underreported due to problems with the laboratory detection of these enzymes. The medical community should be aware of the looming threat that is posed by bacteria with OXA-48-like carbapenemases.

Detection of NDM-19, a novel variant of the New Delhi metallo-β-lactamase with increased carbapenemase activity under zinc-limited conditions, in Switzerland

A novel New Delhi metallo-β-lactamase (NDM) variant, NDM-19, was identified in a carbapenem-resistant E. coli strain isolated from a subcutaneous infection of a laparotomy scar from an Egyptian patient in a Swiss hospital. NDM-19 is a derivative of NDM-7, from which it differs by a single amino acid substitution (Ala233Val). Under zinc-limiting growth conditions, E. coli DH5α transformants producing NDM-19 displayed reduced susceptibility towards expanded-spectrum cephalosporins and carbapenems as compared to transformants producing NDM-1 or NDM-7.

New Delhi Metallo-β-lactamase and other mechanisms of carbapenemases among Enterobacteriaceae in rural South India

OBJECTIVES

The emergence and dissemination of carbapenem-resistant Enterobacteriaceae (CRE) is an important public health problem. This study aimed to understand the prevalence and mechanisms of carbapenem resistance in clinically important members of Enterobacteriaceae in rural South India.

METHODS

Routine clinical isolates of Escherichia coli and Klebsiella spp. were tested for Ertapenem (ETP) non-susceptibility by the disk diffusion method over a 3-year period (2012-2014). The ETP non-susceptible isolates were preserved, and tested for the MIC of carbapenems and the carriage of major carbapenemase-encoding genes. Representative genes were sequenced and selective isolates were tested for the production of carbapenemase by carbapenem inactivation method.

RESULTS

A total of 444 ETP non-susceptible isolates were identified in increasing incidence over the study period. Among them, MIC₅₀ and MIC₉₀ of carbapenems (excluding ETP) were 0.25-0.5μg/mL and 8-16μg/mL, respectively, and the prevalence of non-ETP carbapenem resistance was estimated as 3%. Among the 177 tested isolates, 65 (37%) had one or more carbapenemase-encoding genes with a predominance of New Delhi Metallo-β-lactamase (NDM; 32 of 65; 49.2%).

CONCLUSIONS

This study documented the MIC range for carbapenems, prevalence and mechanisms of carbapenem resistance among Enterobacteriaceae in rural South India. It substantiated NDM as a leading mechanism of carbapenem resistance and highlighted the importance of MIC testing in patient management.

Genetic Study of Extended Spectrum Beta-Lactamase and Carbapenemase Producing Escherichia Coli Causing Sepsis among Egyptian Children

Background:

Treatment failure of sepsis caused by Escherichia coli (E. Coli) is a leading cause of death of infants and children in intensive care units.

Objective:

To detect the prevalence of Extended-Spectrum Beta-Lactamase (ESBL) and carbapenemase-genes between E. coli isolates from infants and children with septicemia and to identify their antibiotic sensitivity pattern.

Methods:

This is a cross-sectional study performed on 88 patients with sepsis. The isolated E. coli were identified by Gram stain and biochemically by the Microscan automated system. ESBL and carbapenemase producing E. coli were isolated on double disk diffusion and EDTA double disk, respectively. Polymerase chain reaction for ESBL and carbapenemase producing E. coli genes were performed. Bacterial susceptibility to antibiotics was tested. The initial results were measured through the 30-days of hospital admission. IRB approved the study.

Results:

Of 88 patients with sepsis, 49 and 30 strains were ESBL producing and carbapenemase producing E. coli; respectively. Neither risk factors for infection nor clinical picture can differentiate between ESBL and carbapenemase producing E. coli. The most frequently detected gene of ESBL producing E. coli was SHV, it was more sensitive to Piperacillin/Tazobactam (90%) and cefepime (86.7%) while for carbapenemase-producing E. coli; IMP was the most frequent, its sensitivity was high to Piperacillin/Tazobactam and Ciprofloxacin (52.6% each).

Conclusion:

The commonest gene of ESBL producing E. coli is SHV whereas for carbapenemase-producing E. coli is IMP. Piperacillin/Tazobactam is the candidate drug to start in children with septicemia and suspected ESBL or carbapenemase-producing E. coli infection.

Rapid detection of the commonly encountered carbapenemases (New Delhi metallo-β-lactamase, OXA-48/181) directly from various clinical samples using multiplex real-time polymerase chain reaction assay

Background

Resistance due to New Delhi metallo-β-lactamase (NDM) and OXA-48/181 continues to emerge as a threat which is associated with nosocomial outbreaks and is a serious healthcare concern. Phenotypic detection being laborious and time-consuming requires rapid detection of NDM and OXA-48/181, which is achieved through real-time polymerase chain reaction (RT-PCR).

Materials and Methods

In this study, RT-PCR assay was developed to simultaneously detect NDM and OXA-48/181. The assay was validated on 102 non-duplicate, phenotypically characterised clinical samples.

Results

The assay showed a sensitivity and specificity of 97% and 100% for the detection of carbapenemases in comparison to conventional PCR. The in-house developed multiplex RT-PCR would help to rule-in the presence of NDM and OXA-48/181.

Conclusions

Rapid detection of these carbapenemases would be assist in better patient management, in terms of accurate antimicrobial treatment, help in cohorting infected from uninfected patient to prevent spread.

Performance evaluation of the PANA RealTyper™ CRE Kit for detecting carbapenemase genes in Gram-negative bacilli

OBJECTIVES

The spread of carbapenemase-producing organisms has been continuously reported over the past decade. Rapid and accurate detection of carbapenemase production is essential for adequate infection control and appropriate antimicrobial treatment in the clinical setting. In this study, the performance of the newly developed PANA RealTyper™ CRE Kit (PANAGENE, Daejeon, South Korea) for the detection of six common carbapenemase genes (bla_KPC, bla_GES, bla_IMP, bla_NDM, bla_VIM and bla_OXA-48-like) was evaluated.

METHODS

A total of 479 non-duplicate clinical isolates of Gram-negative bacilli, including 391 carbapenemase-producers and 88 non-producers, were tested. Conventional PCR and sequencing were performed as reference methods for performance evaluation of the PANA RealTyper™ CRE Kit.

RESULTS

The PANA RealTyper™ CRE Kit showed a reliable performance for the detection of carbapenemase-producing organisms compared with the monoplex PCR system, with sensitivity and specificity values both >95%, with only a few discrepant results for six types of carbapenemase genes.

CONCLUSION

This kit is rapid and accurate for simultaneously detecting various carbapenemase genes in a single reaction and could contribute to early decisions for appropriate antimicrobial treatment in the clinical setting.

NDM Metallo-β-Lactamases and Their Bacterial Producers in Health Care Settings

New Delhi metallo-β-lactamase (NDM) is a metallo-β-lactamase able to hydrolyze almost all β-lactams. Twenty-four NDM variants have been identified in >60 species of 11 bacterial families, and several variants have enhanced carbapenemase activity. Klebsiella pneumoniae and Escherichia coli are the predominant carriers of bla _NDM, with certain sequence types (STs) (for K. pneumoniae, ST11, ST14, ST15, or ST147; for E. coli, ST167, ST410, or ST617) being the most prevalent. NDM-positive strains have been identified worldwide, with the highest prevalence in the Indian subcontinent, the Middle East, and the Balkans. Most bla _NDM-carrying plasmids belong to limited replicon types (IncX3, IncFII, or IncC). Commonly used phenotypic tests cannot specifically identify NDM. Lateral flow immunoassays specifically detect NDM, and molecular approaches remain the reference methods for detecting bla _NDM Polymyxins combined with other agents remain the mainstream options of antimicrobial treatment. Compounds able to inhibit NDM have been found, but none have been approved for clinical use. Outbreaks caused by NDM-positive strains have been reported worldwide, attributable to sources such as contaminated devices. Evidence-based guidelines on prevention and control of carbapenem-resistant Gram-negative bacteria are available, although none are specific for NDM-positive strains. NDM will remain a severe challenge in health care settings, and more studies on appropriate countermeasures are required.

Prospective evaluation of a screening algorithm for carbapenemase-producing Enterobacteriaceae

BACKGROUND

Carbapenemase-producing Enterobacteriaceae (CPE) have become a major public health issue. The objective of the present study was to prospectively assess the analytical performance of a CPE detection algorithm based on phenotypic tests (the screening test) and MALDI-ToF hydrolysis (the confirmatory test).

METHODS

Over a 6-month period and based on a disk diffusion method, 74 carbapenem-resistant strains were included in this study.

RESULTS

Of the collected isolates, 54 turned out to be negative after phenotypic tests. Hence, 20 strains (including all of the CPEs) were checked with the confirmation test. Seven strains were positive. After molecular biology assessments in a reference center, three of the seven were found to be false positives. The algorithm had a negative predictive value and a sensitivity of 100%, a specificity of 77%, and a positive predictive value of 20%.

CONCLUSION

The algorithm has a 24-hour turnaround time and helps to avoid using expensive molecular biology tests; we consider that it can be used on a routine basis for screening clinical strains.

The emergence of carbapenem-resistant Klebsiella pneumoniae isolates producing OXA-48 and NDM in the Southern (Asir) province, Saudi Arabia

OBJECTIVES

To identify the prevalence of carbapenem-resistant Klebsiella pneumoniae (CRKP) and the most common types of cabapenemases among CRKP in the Southern (Asir) province hospitals, Saudi Arabia. Methods: The cross-sectional study was conducted between late April and September in 2015. A total of 54 Klebsiella pneumoniae (K. pneumoniae) isolates with reduced sensitivity to carbapenems were obtained from various clinical specimens of the 2 largest hospitals in the Southern province. Minimum inhibitory concentrations (MICs) of carbapenems were confirmed using E-test. Molecular detection of the most common carbapenemase genes (blaIMP, bla-carbapenem-hydrolyzing oxacillinase [OXA-48], blaVIM, bla-New Delhi metallo-ß-lactamas [NDM], and blaKPC) was performed using multiplex-polymerase chain reaction. Results: The current study found that increasing age and intensive care unit admission were associated with CRKP isolation. The major type of carbapenemases was OXA-48 with 81.5% (n=44) and it seems to reach an endemic level. New Delhi metallo-ß-lactamas (NDM) was the second most frequent carbapenemase by 7.4% (n=4) of isolates while Verona integron-encoded metallo-ß-lactamase (VIM) was reported only in one isolate. Conclusion: Saudi Arabia receives large numbers of visitors and migrant workers from OXA-48 and NDM endemic countries such as Turkey, India, and Pakistan every year.

Current antimicrobial susceptibility testing for beta-lactamase-producing Enterobacteriaceae in clinical settings

The worldwide prevalence of beta-lactamase-producing Enterobacteriaceae (BL-E) is increasing. Bacterial infections involving ESBLs can be more difficult to treat because of antibiotic resistance, as there are fewer effective antibiotics left to be used. Moreover, treatment failure is often observed. Thus, quick and accurate identification of β-lactamases is imperative to minimize it. This review article describes most commonly used phenotypic techniques and molecular methods for the detection of ESBLs, acquired AmpC β-lactamases, and carbapenemases produced by Enterobacteriaceae. Phenotypic detection tests remain useful and relevant in clinical laboratories while molecular diagnostic methods are less affordable, more technically demanding, and not standardized. Molecular methods could be used to speed up results of bacterial antibiotic resistance or to clarify the results of phenotypic β-lactamases confirmation tests.

Rapid detection of ESBL, carbapenemases, MRSA and other important resistance phenotypes within 6-8 h by automated disc diffusion antibiotic susceptibility testing

Background

In principle, automated systems allow rapid reading of disc diffusion AST (rAST) within 6-8 h.

Objectives

This study analysed whether rAST can discriminate resistance phenotypes such as ESBL, carbapenemases and MRSA/methicillin-resistant Staphylococcus epidermidis from WT populations. We describe species-drug combinations that may require clinical breakpoint adaptions for early reading due to zone diameter changes during the incubation period.

Methods

In total, 1852 clinical strains [Escherichia coli (n = 475), Klebsiella pneumoniae (n = 375), Enterobacter cloacae (n = 301), Staphylococcus aureus (n = 407) and S. epidermidis (n = 294)] were included in this study comprising WT populations and important resistance phenotypes, e.g. ESBL, carbapenemases and MRSA. We assessed (i) separation of resistance phenotypes and WT populations after 6, 8 and 12 h as compared with the 18 h standard, and (ii) diameter changes of WT populations and associated putative epidemiological cut-offs during the incubation period. Disc diffusion plates were automatically streaked, incubated and imaged using the WASPLabTM system.

Results and conclusions

We demonstrated that important resistance phenotypes could reliably be separated from WT populations at early reading times for the most prevalent bacterial pathogens encountered in the clinical laboratory. Current AST expert rules and algorithms for identification of resistance mechanisms can readily be applied for rAST, e.g. EUCAST recommended rules for detection of ESBL, AmpC, carbapenemases and MRSA/methicillin-resistant S. epidermidis. However, several species-drug combinations may require clinical breakpoint adaptations when using rAST as the diameter, and hence the epidemiological cut-off, changes during the incubation period.

A novel GoldNano Carb test for rapid phenotypic detection of carbapenemases, particularly OXA type, in Enterobacteriaceae, Pseudomonas aeruginosa and Acinetobacter spp

Objectives

To develop a simple gold nanoparticle (AuNP)-based colorimetric test, GoldNano Carb (GoldC), for detecting carbapenemase production in Gram-negative bacteria, compared with updated Carba NP (CNP) and CarbAcineto NP (CAcNP) tests by using PCR methods as gold standard.

Methods

Ninety-nine carbapenemase-producing Enterobacteriaceae (CPE), Pseudomonas spp. and Acinetobacter spp. isolates and 89 non-CPE isolates were tested by the GoldC and CNP. Additionally, the CAcNP was performed in the Acinetobacter spp. isolates. The final imipenem (imipenem/cilastatin form) concentration was 5 mg/mL for all three tests. For the GoldC, the imipenem powder was added directly to bacterial cell suspension in distilled water prior to detection of acid product by the citrate-capped AuNP solution. An AuNP change from red to purple, blue or green indicates carbapenemase activity.

Results

The GoldC detected all carbapenemase producers except one OXA-23-like producer (99.0% sensitivity), whereas 11 carbapenemase producers (10 Acinetobacter and 1 P. aeruginosa) were CNP negative (88.9% sensitivity). However, the GoldC and CNP provided 100% and 98.6% sensitivity, respectively, for the CPE and Pseudomonas spp. Both tests gave one false positive from CTX-M-1-like-producing Enterobacter spp. (98.9% specificity). The GoldC and CAcNP detected 96.7% and 93.3% of the Acinetobacter spp. isolates, respectively. Interestingly, times to positivity by the GoldC were markedly shorter than those by the CNP (76.8% versus 36.2% positive at 5 min) and CAcNP (43.3% at 5 min versus 20% within 30 min).

Conclusions

The GoldC is fast, easy, highly sensitive and inexpensive (∼$0.25 per test), suggesting that it may be suitable for routine carbapenemase detection in low-resource settings for infection control or epidemiological purposes.

Evaluation of the AID carbapenemase line probe assay for rapid detection and identification of carbapenemase genes in Gram-negative bacilli

Objectives

This study evaluated the AID carbapenemase line probe assay (LPA) for the detection and identification of carbapenem resistance genes in Enterobacteriaceae and other Gram-negative bacilli (GNB) using bacterial cultures and DNA extracts directly from patient urine samples.

Methods

The AID carbapenemase LPA detects 13 different carbapenemase genes. Test probe accuracy was verified for using clinical Enterobacteriaceae isolates harbouring bla KPC , bla VIM , bla NDM , bla GIM , bla AIM , bla SPM , bla IMP and bla OXA-48 and a well-characterized set of Escherichia coli DH5α strains transformed with the vector plasmid pUC57- kan harbouring bla BIC , bla SIM , bla DIM , bla IMI-3 , bla IMI-1 and bla NMC-A . Sensitivity and specificity was determined by testing 151 clinical GNB strains previously characterized for the production of carbapenemase activity and carbapenemase genes. Direct detection of carbapenemase genes using the LPA was determined using 299 clinical urine specimens. Analytical sensitivity for detection in urine was determined by testing serial dilutions of bla KPC and bla NDM in clinical Klebsiella pneumoniae strains.

Results

All carbapenemase gene probes showed 100% accuracy without cross-reactions. Sensitivity and specificity of the LPA using clinical isolates was 100% for each. Analytical sensitivity for detection of bla KPC and bla NDM in urine was 10 1 -10 2 cfu. The LPA detected carbapenemase genes in 20 urines, which were confirmed in 12 samples by conventional multiplex PCR. Remarkably, 0 of the 20 urines grew carbapenemase-suspicious GNB applying EUCAST recommendations.

Conclusions

The AID carbapenemase LPA is an accurate, sensitive and easy-to-use test for the detection and identification of carbapenemase genes, which can readily be implemented in any diagnostic laboratory.

Evaluation of the Amplidiag CarbaR+VRE Kit for Accurate Detection of Carbapenemase-Producing Bacteria

As carbapenemase-producing Gram-negative bacilli (CP-GNB) (Enterobacteriaceae, Pseudomonadaceae, and Acinetobacter spp.) are becoming a major public health issue, there is an urgent need for accurate and fast diagnostic tests. The Amplidiag CarbaR+VRE assay is a multiplex nucleic acid-based in vitro diagnostic test intended for the detection of CP-GNB and vancomycin-resistant enterococci (VRE) from cultured colonies. We have evaluated its ability to detect carbapenemase genes in 100 well-characterized GNB and in 200 consecutive enterobacterial isolates with reduced susceptibility to carbapenems that were referred to the French National Reference Center for carbapenem resistance. The assay has been validated on purified DNA but also directly on colonies. The Amplidiag CarbaR+VRE assay could detect all KPC, NDM, VIM, IMP, and OXA-48-like variants tested and all acquired carbapenem-hydrolyzing oxacillinases from Acinetobacter baumannii (OXA-23, OXA-24/-40, and OXA-58) as well as the overexpressed chromosomally encoded OXA-51-like β-lactamase associated with an upstream inserted ISAba1 However, as claimed by the manufacturer, other carbapenemases such as GES-like carbapenemases (GES-2, GES-5, and GES-14), GIM-1, AIM-1, SPM-1, DIM-1, OXA-198 in Pseudomonas aeruginosa, or OXA-143-like in A. baumannii were not detected. Amplidiag CarbaR+VRE's performance values were high (100% sensitivity and 99% specificity) as it could detect the five major carbapenemases-NDM, VIM, IMP, KPC, and OXA-48-as well as OXA-type carbapenemases from Acinetobacter spp. that are currently emerging also among Proteus mirabilis and other enterobacterial isolates. It can provide a result directly from colonies growing on Mueller-Hinton (MH) agar or on selective screening medium in less than 2 h. Further evaluations are now necessary to determine the performance values directly on rectal swabs.

Evaluation of the Carbapenem Detection Set™ for the detection and characterization of carbapenemase-producing Enterobacteriaceae

The objective of this study was to assess the performance of the Carbapenemase Detection Set™ (CDS; Mast Diagnostics) in association with i) the EUCAST meropenem screening cut-off and ii) the faropenem-temocillin algorithm (FTa) for the screening of carbapenemase-producing Enterobacteriaceae (CPE). A total of 200 well-characterized enterobacterial isolates with reduced susceptibility to at least one carbapenem including 63 non-CPEs and 137 CPEs belonging to different Ambler classes were initially screened for CPEs using i) the EUCAST meropenem cut-off (diameter <25 mm) and ii) the FTa. Highly suspected CPEs underwent further testing using the CDS, which is based on the inhibition zone diameters determination of combined disks (A: meropenem, B: meropenem + dipicolinic acid, C: meropenem + cloxacillin, and D: meropenem + boronic acid). With the FTa, 66.7% of the non-CPE isolates were correctly identified. Most OXA-48-like producers (90.5%) were detected with 98.6% specificity. The FTa discriminates CPE from non-CPE with 100% sensitivity, but complementary tests were still needed for 59 % (118/200) of the strains. The EUCAST cut-off led to 3 false-negative results (2 OXA-181 and 1 NMC-A producer) resulting in a sensitivity of 97.8% for the discrimination between CPE and non-CPE, and 75.5% (151/200) of the strains still required complementary test. The CDS reduced the number of isolates requiring additional tests from 59% to 22%, and from 75.5% to 38% for FTa and EUCAST cut-off, respectively. FTa possesses very good specificities for the detection and classification of Ambler class A and most class B carbapenemase-producers, except for IMP producers, which were almost not detected (10/11). In conclusion, the association of the CDS with the FTa presented only 22% of inconclusive results, while this number was 38% with the EUCAST meropenem CPE screening cut-off.

Evaluation of the CRE and ESBL ELITe MGB® kits for the accurate detection of carbapenemase- or CTX-M-producing bacteria

As carbapenemase-producing Enterobacteriaceae (CPE) and extended-spectrum β-lactamase-producing Enterobacteriaceae (ESBL-E) are becoming a major public health issue, there is an urgent need for accurate and fast diagnostic tests. The ELITe InGenius is a fully automated sample-to-result system designed for the extraction and detection by multiplex real-time polymerase chain reaction of carbapenemases KPC, NDM, VIM, IMP, and OXA-48-like variants and CTX-M group 1 and 9-producers from diverse sample matrices such as colonies, positive blood cultures, and rectal swabs. CRE and ESBL ELITe MGB® kits were evaluated on 153 cultured colonies of enterobacterial isolates with characterized β-lactamase content, on 30 spiked blood cultures, and the CRE kit was also evaluated on 53 clinical rectal swabs collected prospectively during a 3-month period and 10 spiked rectal swabs. CRE ELITe MGB® kit's performances reached 100% sensitivity and 100% specificity, while for the ESBL ELITe kit, 100% sensitivity and 96.6% specificity were observed, with a sample to result of less than 3 h and a total percentage of agreement with expected results of 99.6% (255/256).

Reducing the impact of carbapenem-resistant Enterobacteriaceae on vulnerable patient groups: what can be done?

PURPOSE OF REVIEW

Carbapenem-resistant Enterobacteriaceae (CRE) is a worldwide challenge and associated with a high mortality rate in critically ill patients. This review focused on rapid diagnosis, optimization of antimicrobial therapy, and implication of effective infection control precautions to reduce impact of CRE on vulnerable patients.

RECENT FINDINGS

Several new diagnostic assays have recently been described for the early diagnosis of CRE. Retrospective studies are supportive for colistin plus meropenem combination for the treatment of CRE infections; however, solid evidence is still lacking. Ceftazidime-avibactam may be an effective therapeutic agent for infections caused by carbapenem-hydrolyzing oxacillinase-48 and Klebsiella pneumoniae carbapenamase-producing Enterobacteriaceae, but not for New Delhi metallo-β-lactamase producers. Gastrointestinal screening may permit early identification of patients with CRE infections. There is not enough evidence to recommend selective digestive decontamination for CRE carriers.

SUMMARY

The information for rapid diagnosis of CRE is accumulating. There are new agents with high in-vitro activity against CRE, but clinical experience is limited to case reports. Active surveillance with a high rate of compliance to basic infection control precautions seems to be the best approach to reduce the impact of CRE on vulnerable patients.

Fully automated disc diffusion for rapid antibiotic susceptibility test results: a proof-of-principle study

Background

Antibiotic resistance poses a significant threat to patients suffering from infectious diseases. Early readings of antibiotic susceptibility test (AST) results could be of critical importance to ensure adequate treatment. Disc diffusion is a well-standardized, established and cost-efficient AST procedure; however, its use in the clinical laboratory is hampered by the many manual steps involved, and an incubation time of 16-18 h, which is required to achieve reliable test results.

Methods

We have evaluated a fully automated system for its potential for early reading of disc diffusion diameters after 6-12 h of incubation. We assessed availability of results, methodological precision, categorical agreement and interpretation errors as compared with an 18 h standard. In total, 1028 clinical strains (291 Escherichia coli , 272 Klebsiella pneumoniae , 176 Staphylococcus aureus and 289 Staphylococcus epidermidis ) were included in this study. Disc diffusion plates were streaked, incubated and imaged using the WASPLab TM automation system.

Results and conclusions

Our results demonstrate that: (i) early AST reading is possible for important pathogens; (ii) methodological precision is not hampered at early timepoints; and (iii) species-specific reading times must be selected. As inhibition zone diameters change over time and are phenotype/drug combination dependent, specific cut-offs and expert rules will be essential to ensure reliable interpretation and reporting of early susceptibility testing results.

Detection of carbapenemases and other mechanisms of enzymatic resistance to β-lactams in Enterobacteriaceae with diminished susceptibility to carbapenems in a tertiary care hospital

INTRODUCTION

Our objective was to characterize the enzymatic β-lactam resistance in clinical Enterobacteriaceae isolates with diminished susceptibility to carbapenems from 2013 to 2014 at Hospital Universitario Miguel Servet.

MATERIAL/METHODS

A total of 63 clinical isolates were analyzed for the presence of carbapenemases (KPC, OXA-48 and MBL), ESBLs and AmpC enzymes by combined disk methods and PCR detection of carbapenemase-encoding and beta-lactamase-encoding genes.

RESULTS

Fifteen isolates had a phenotypic test compatible with carbapenemase production; two of these were confirmed by PCR as OXA-48 producers. ESBL detection was positive in 27 isolates (43%); plasmid-mediated AmpC was detected in nine isolates (14.2%) and derepressed AmpC β-lactamase was present in 18 isolates (28%).

CONCLUSION

During the study period, the decreased susceptibility to carbapenems in Enterobacteriaceae in our area was not due to true carbapenemases but rather to β-lactamase activity (82.5% were ESBL or AmpC producers), probably in combination with decreased permeability of the outer membrane.

Multicentre evaluation of the BYG Carba v2.0 test, a simplified electrochemical assay for the rapid laboratory detection of carbapenemase-producing Enterobacteriaceae

Rapid detection of carbapenemase-producing Enterobacteriaceae (CPE) represents a major challenge for microbiology laboratories. We evaluated the BYG Carba v2.0 using a simplified protocol, which detects CPE in less than 30 minutes. This new procedure reduces the hands-on-time from 5 to one minute and only requires a limited amount of material (one to three colonies) thereby preventing the need for subculturing bacterial isolates to reach a larger amount of pure biomass. This multicentre study involved four European reference laboratories. For the 1181 isolates tested across four centres, BYG Carba v2.0 yielded overall sensitivity and specificity of 96.3% (CI95: 94.5–97.5) and 99.7% (CI95: 98.6–100) respectively. Considering only the 670 consecutive isolates tested prospectively, the BYG Carba v2.0 displayed overall positive and negative predictive values of 99.7% (CI95: 95.4–98.9) and 97.5% (CI95: 94.9–98.8). Regarding time to positivity, 85% of CPE detected were positive within ten minutes. The BYG Carba v2.0 is a new highly simplified, rapid and accurate electrochemical assay discriminating between CPE and non-CPE in less than 30 min. The real-time quantified signal allows objective and traceable interpretation of the results.

Comparison of Two Phenotypic Algorithms To Detect Carbapenemase-Producing Enterobacteriaceae

A novel algorithm designed for the screening of carbapenemase-producing Enterobacteriaceae (CPE), based on faropenem and temocillin disks, was compared to that of the Committee of the Antibiogram of the French Society of Microbiology (CA-SFM), which is based on ticarcillin-clavulanate, imipenem, and temocillin disks. The two algorithms presented comparable negative predictive values (98.6% versus 97.5%) for CPE screening among carbapenem-nonsusceptible Enterobacteriaceae However, since 46.2% (n = 49) of the CPE were correctly identified as OXA-48-like producers by the faropenem/temocillin-based algorithm, it significantly decreased the number of complementary tests needed (42.2% versus 62.6% with the CA-SFM algorithm).

Advances in Rapid Identification and Susceptibility Testing of Bacteria in the Clinical Microbiology Laboratory: Implications for Patient Care and Antimicrobial Stewardship Programs

Early availability of information on bacterial pathogens and their antimicrobial susceptibility is of key importance for the management of infectious diseases patients. Currently, using traditional approaches, it usually takes at least 48 hours for identification and susceptibility testing of bacterial pathogens. Therefore, the slowness of diagnostic procedures drives prolongation of empiric, potentially inappropriate, antibacterial therapies. Over the last couple of years, the improvement of available techniques (e.g. for susceptibility testing, DNA amplification assays), and introduction of novel technologies (e.g. MALDI-TOF) has fundamentally changed approaches towards pathogen identification and characterization. Importantly, these techniques offer increased diagnostic resolution while at the same time shorten the time-to-result, and are thus of obvious importance for antimicrobial stewardship. In this review, we will discuss recent advances in medical microbiology with special emphasis on the impact of novel techniques on antimicrobial stewardship programs.

Utilizing the Carba NP test as an indicator of expression level of carbapenemase genes in Enterobacteriaceae

The Carba NP test was developed to detect carbapenemase-producing Enterobacteriaceae, and uses imipenem as the reaction substrate. In Japan, IMP-6 metallo-β-lactamase (MBL) producers, which are usually resistant to meropenem but susceptible to imipenem, and IMP-1 MBL producers, which are usually resistant to both carbapenems are prevalent. We performed the Carba NP test with IMP-6 and IMP-1 MBL producers, and both types were detected by the Carba NP test with high sensitivity. All IMP-1 MBL producers were detected by the Carba NP test, but the minimum inhibitory concentrations (MICs) of imipenem varied from 0.25 to >32μg/mL, and the time to positivity varied from 0 to 30min. Time to positivity was significantly correlated with expression levels of bla_IMP-1, but not with MICs of imipenem. These results suggested that the Carba NP test can be used as a screening assay for carbapenemase gene expression levels among producers of the same type of carbapenemase. Using this approach, it is possible to determine whether the carbapenem resistance of each carbapenemase-producing Enterobacteriaceae isolate is primarily due to carbapenemase production, or to another mechanism such as outer membrane impermeability.

Modification and evaluation of the Carba NP test by use of paper strip for simple and rapid detection of carbapenemase-producing Enterobacteriaceae

Carbapenemase-producing Enterobacteriaceae (CPE) isolates have now emerged worldwide. We therefore modified the phenotypic Carba NP test by use of a filter paper strip for easily and rapidly identifying CPE in routine laboratory. A collection of 56 CPE and carbapenemase-producing Pseudomonas spp. isolates (including 28 NDM-1, 11 IMP-14a, 1 IMP-1, 1 IMP-4, 1 IMP-9, 1 IMP-15, 4 VIM-2, 1 VIM-1, 1 IMP-14a with VIM-2, 3 OXA-48, 3 OXA-181 and 1 KPC-2 producers) and 41 non-CPE isolates (including 19 ESBL, 7 pAmpC, 3 AmpC, 9 ESBL with pAmpC and 3 non-ESBL & non-AmpC producers) as confirmed by the PCR methods were tested by the paper strip method using pharmaceutical imipenem/cilastatin as a substrate. Bacterial colonies of each isolate were applied directly on filter paper strips dropped with either imipenem-phenol red (test strip) or phenol red solution alone (control strip). The reaction was read within 5 min. This test failed to detect 3 OXA-181, 2 OXA-48 and 3 IMP-14a producers (85.7 % sensitivity), whereas no false positives were seen (100 % specificity). Further evaluation of the paper strip test in 267 CPE screening-positive isolates from three hospitals by their medical technologists showed 92.0 % sensitivity (100 % for NDM producers) and 100 % specificity compared with the PCR methods. Because of its ease, rapidness and cost effective, the paper strip test has a potential for routine CPE testing in low-resource laboratories particularly in areas with high prevalence of NDM enzymes, leading to appropriate antimicrobial therapy and infection control strategy.

Recent advances in the laboratory detection of carbapenemase-producing Enterobacteriaceae

Carbapenemase-producing Enterobacteriaceae (CPE), mainly Klebsiella pneumoniae and Escherichia coli, have been increasing rapidly on a global scale and are considered to be significant health threats. The most common carbapenemases are KPCs, NDMs, OXA-48-like, IMPs and VIMs but their distribution and prevalence differs between countries. The accurate, simple, cost effective and rapid detection of carbapenemases in clinical laboratories is an important initial step to control the spread of CPE within institutions. The diversity of carbapenemases in general, has challenged a simple approach for the detection of most types of CPE. This article summarizes the current and describes newer techniques available for the detection of carbapenemases among Enterobacteriaceae. The authors also provide a simplified approach for the accurate and rapid detection of CPEs that can easily be implemented in a clinical diagnostic laboratory.

Characterization of carbapenem-resistant Escherichia coli and Klebsiella pneumoniae from a healthcare region in Hong Kong

Carbapenem-resistant Enterobacteriaceae represents a major public health issue. This study investigated the clonality and resistance mechanisms of 92 carbapenem-resistant E. coli (n = 21) and K. pneumoniae (n = 71) isolates collected consecutively from clinical specimens and patients at high risk of carriage between 2010 and 2012 in a healthcare region in Hong Kong. Combined disk tests (CDTs) and the Carba NP test were used for phenotypic detection of carbapenemases. PCR assays were used to detect carbapenemase genes. All isolates were intermediate or resistant to at least one carbapenem. Nine (9.8 %) isolates were genotypic carbapenemase producers and included six K. pneumoniae (one ST1306/bla IMP-4, one ST889/bla IMP-4, two ST11/bla KPC-2, one ST258/bla KPC-2, one ST483/bla NDM-1) and three E. coli (one ST131/bla IMP-4, two ST744/ bla NDM-1) isolates. All nine isolates carrying carbapenemase genes could be detected by the CDTs and the Carba NP test. PCR identified bla CTX-M and bla AmpC alone or in combination in 77.8 % (7/9) and 96.4 % (80/83) of the carbapenemase-producers and non-producers, respectively. Porin loss was detected in 22.2 % (2/9) and 59.0 % (49/83) of the carbapenemase-producers and non-producers, respectively. Overall, the E. coli clones were diverse (14 different STs), but 36.6 % (26/71) of the K. pneumoniae isolates belonged to ST11. In conclusion, the prevalence of carbapenemases among carbapenem-nonsusceptible E. coli and K. pneumoniae remained low in Hong Kong. Porin loss combined with AmpC and/or CTX-M type ESBL was the major mechanism of carbapenem resistance in the study population.