Evaluation of the Carba NP test for carbapenemase detection in Enterobacteriaceae, Pseudomonas spp. and Acinetobacter spp., and its practical use in the routine work of a national reference laboratory for susceptibility testing

Chemical sensors for the early diagnosis of bacterial resistance to β-lactam antibiotics

β-Lactamases are bacterial enzymes that inactivate β-lactam antibiotics and, as such, are the most prevalent cause of antibiotic resistance in Gram-negative bacteria. The ever-increasing production and worldwide dissemination of bacterial strains producing carbapenemases is currently a global health concern. These enzymes catalyze the hydrolysis of carbapenems - the β-lactam antibiotics with the broadest spectrum of activity that are often considered as drugs of last resort. The incidence of carbapenem-resistant pathogens such as Pseudomonas aeruginosa, Acinetobacter baumannii and carbapenemase or extended spectrum beta-lactamase (ESBL)-producing Enterobacterales, which are frequent in clinical settings, is worrisome since, in some cases, no therapies are available. These include all metallo-β-lactamases (VIM, IMP, NDM, SMP, and L1), and serine-carbapenemases of classes A (KPC, SME, IMI, and GES), and of classes D (OXA-23, OXA-24/40, OXA-48 and OXA-58). Consequently, the early diagnosis of bacterial strains harboring carbapenemases is a pivotal task in clinical microbiology in order to track antibiotic bacterial resistance and to improve the worldwide management of infectious diseases. Recent research efforts on the development of chromogenic and fluorescent chemical sensors for the specific and sensitive detection and quantification of β-lactamase production in multidrug-resistant pathogens are summarized herein. Studies to circumvent the main limitations of the phenotypic and molecular methods are discussed. Recently reported chromogenic and fluorogenic cephalosporin- and carbapenem-based β-lactamase substrates will be reviewed as alternative options to the currently available nitrocefin and related compounds, a chromogenic cephalosporin-based reagent widely used in clinical microbiology laboratories. The scope of these new chemical sensors, along with the synthetic approaches to synthesize them, is also summarized.

Reliability of a Screening Method Using Antibiotic Disks to Detect Carbapenemases in Glucose-Nonfermenting Gram-Negative Microorganisms From Clinical Samples of a Regional Hospital in Southeastern Spain

BACKGROUND

Infections by glucose-nonfermenting gram-negative bacilli (NFGNB) pose a major public health problem due to multiresistance to beta-lactam antibiotics, especially plasmid-borne carbapenemases. Their detection by microbiology laboratories is challenging, and there is a need for easy-to-use and reliable diagnostic techniques. Our objective was to evaluate an in-house screening method to presumptively detect carbapenemases in NFGNB in a simple and clinically useful manner.

METHODS

The study included 175 NFGNB isolates from urinary, respiratory, and rectal samples. In a triple assay, isolates were incubated at 37°C for 24 h on three solid-culture media: MacConkey II Agar, 5% Sheep Blood Columbia Agar and Mueller Hinton II Agar; meropenem (MEM) and cefepime (FEP) disks were employed for screening. Studies were then performed on the inhibition halo diameter, scanning effects, and the appearance of mutant colonies, which were compared with those observed using the colorimetric Neo-Rapid CARB Kit and immunochromatography (NG5-Test Carba and K-Set for OXA-23). Receiver operating characteristic curves were constructed for these data.

RESULTS

Carbapenemases were expressed by 79/175 (45.1%): 19 Pseudomonas aeruginosa and 60 Acinetobacter baumannii. Optimal inhibition halo diameter cutoffs to detect this resistance on 5% sheep blood agar were as follows: 6 mm (MEM) and 6.5 mm (FEP) for P. aeruginosa (in the absence of scanning effects and mutations) and 10.5 mm (MEM) and 16 mm (FEP) for A. baumannii (even in the presence of scanning effects).

CONCLUSION

The combined utilization of MEM and FEP antibiotic disks in 5% sheep blood agar, measuring their inhibition haloes, offers an effective method to predict the presence of carbapenemases as resistance mechanism in P. aeruginosa and A. baumannii.

Evaluation of phenotypic detection of carbapenemase-producing Pseudomonas spp. from clinical isolates

Carbapenems are considered last-resort antibiotics for the treatment of infections caused by multidrug-resistant Gram-negative bacteria. Although the main mechanism of carbapenem-resistance in Pseudomonas aeruginosa is the loss of OprD porin, carbapenemases continue to be a problem worldwide. The aim of this study was to evaluate the performance of phenotypic tests (Carba NP, Blue Carba, and mCIM/eCIM) for detection of carbapenemase-producing Pseudomonas spp. in Brazil. One hundred twenty-seven Pseudomonas spp. clinical isolates from different Brazilian states were submitted to phenotypic and molecular carbapenemase detection. A total of 90 carbapenemase-producing P. aeruginosa and 5 Pseudomonas putida (35, blaVIM-2; 17, blaSPM-1; 2, blaIMP-10; 1, blaVIM-24; 1, blaNDM-1; 39, blaKPC-2). The phenotypic Carba NP, Blue Carba, and mCIM/eCIM showed sensitivity of 94.7%, 93.6%, and 93.6%, and specificity of 90.6%, 100%, and 96.8%, respectively. However, only the Carba NP presented the highest sensitivity and showed the ability in differentiating the carbapenemases between class A and class B using EDTA. Blue Carba failed to detect most of the class B carbapenemases, having the worst performance using EDTA. Our results show changes in the epidemiology of the spread of carbapenemases and the importance of their detection by phenotypic and genotypic tests. Such, it is essential to use analytical tools that faithfully detect bacterial resistance in vitro in a simple, sensitive, rapid, and cost-effective way. Much effort must be done to improve the current tests and for the development of new ones.

Rapid detection of KPC-producing Enterobacterales by using a modified Carba NP test with imipenem/relebactam

INTRODUCTION

Here, we propose a novel modified Carba NP test for detecting KPC-producing Enterobacterales using imipenem/relebactam.

MATERIAL AND METHODS

The test performance was evaluated in a random selection of 160 previously molecularly characterized clinical isolates carrying the 110 bla_KPC, 1 bla_GES, 12 bla_VIM, 4 bla_IMP, 3 bla_NDM and 42 bla_OXA-48-like genes. The proposed method relies on the detection of imipenem hydrolysis in an imipenem/relebactam antibiotic solution and subsequent visual interpretation by color change.

RESULTS

All class A producing Enterobacterales (111/111) were detected using imipenem/relebactam as no visual appreciation of color change was perceived due to a nule hydrolysis of imipenem in the antibiotic solution. Overall, the assay showed 100% sensitivity (111/111) and specificity (69/69) for detecting class A KPC-producing Enterobacterales.

DISCUSSION

The biochemical assay provides very reliable results for detecting KPC-producing Enterobacterales, with a turnaround time of less than 1 hour, minimum handling and no specialized equipment required.

Combating the menace of antimicrobial resistance in Africa: a review on stewardship, surveillance and diagnostic strategies

The emergence of antibiotic-resistant pathogens has threatened not only our ability to deal with common infectious diseases but also the management of life-threatening complications. Antimicrobial resistance (AMR) remains a significant threat in both industrialized and developing countries alike. In Africa, though, poor clinical care, indiscriminate antibiotic use, lack of robust AMR surveillance programs, lack of proper regulations and the burden of communicable diseases are factors aggravating the problem of AMR. In order to effectively address the challenge of AMR, antimicrobial stewardship programs, solid AMR surveillance systems to monitor the trend of resistance, as well as robust, affordable and rapid diagnostic tools which generate data that informs decision-making, have been demonstrated to be effective. However, we have identified a significant knowledge gap in the area of the application of fast and affordable diagnostic tools, surveillance, and stewardship programs in Africa. Therefore, we set out to provide up-to-date information in these areas. We discussed available hospital-based stewardship initiatives in addition to the role of governmental and non-governmental organizations. Finally, we have reviewed the application of various phenotypic and molecular AMR detection tools in both research and routine laboratory settings in Africa, deployment challenges and the efficiency of these methods.

Phenotypic and genotypic detection methods for antimicrobial resistance in ESKAPE pathogens (Review)

Antimicrobial resistance (AMR) represents a growing public health problem worldwide. Infections with such bacteria lead to longer hospitalization times, higher healthcare costs and greater morbidity and mortality. Thus, there is a greater need for rapid detection methods in order to limit their spread. The ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacter spp.) are a series of epidemiologically-important microorganisms of great concern due to their high levels of resistance. This review aimed to update the background information on the ESKAPE pathogens as well as to provide a summary of the numerous phenotypic and molecular methods used to detect their AMR mechanisms. While they are usually linked to hospital acquired infections, AMR is also spreading in the veterinary and the environmental sectors. Yet, the epidemiological loop closes with patients which, when infected with such pathogens, often lack therapeutic options. Thus, it was aimed to give the article a One Health perspective.

Conventional and Real-Time PCR Targeting blaOXA Genes as Reliable Methods for a Rapid Detection of Carbapenem-Resistant Acinetobacter baumannii Clinical Strains

Multidrug-resistant Acinetobacter baumannii, particularly those producing carbapenemases, are spread worldwide. A reliable detection of carbapenemases is essential to choose the appropriate antimicrobial therapy and, consequently, prevent the dissemination of carbapenem-resistant strains. The aim of this study is to examine the molecular basis of the carbapenem resistance mechanism and estimation of conventional PCR and real-time PCR usefulness for the detection of oxacillinases when compared to phenotypic carbapenemases detection. The following methods were evaluated: the CarbAcineto NP test, Carbapenem Inactivation Method, CPO panels of semiautomated antimicrobial susceptibility testing method on the BD Phoenix™ M50 system, conventional Polymerase Chain Reaction and real-time PCR. The eazyplex^® SuperBug complete A assay was used as the reference method. Among the tested strains, 39 (67.2%) carried the bla_OXA-40 gene, while the bla_OXA-23 gene was noted amongst 19 (32.8%) isolates. The diagnostic sensitivities of the studied assays were as follows: CarbAcineto NP—65.5%; CIM—100%; CPO—100%; conventional PCR—100%; real-time PCR—100%.

Comparative study of phenotypic-based detection assays for carbapenemase-producing Acinetobacter baumannii with a proposed algorithm in resource-limited settings

The increasing incidence of carbapenem resistance in Acinetobacter baumannii is a critical concern worldwide owing to the limitations of therapeutic alternatives. The most important carbapenem resistance mechanism for A. baumannii is the enzymatic hydrolysis mediated by carbapenemases, mostly OXA-type carbapenemases (class D) and, to a lesser extent, metallo-β-lactamases (class B). Therefore, early and accurate detection of carbapenemase-producing A. baumannii is required to achieve the therapeutic efficacy of such infections. Many methods for carbapenemase detection have been proposed as effective tests for A. baumannii; however, none of them are officially recommended. In this study, three carbapenemase detection methods, namely, CarbaAcineto NP test, modified carbapenem inactivation method (mCIM), and simplified carbapenem inactivation method (sCIM) were evaluated for phenotypic detection of clinically isolated A. baumannii. The MICs of imipenem, meropenem, and doripenem were determined for 123 clinically isolated A. baumannii strains before performing three phenotypic detections. The overall sensitivity and specificity values were 89.09%/100% for the carbAcineto NP test, 71.82%/100% for sCIM, and 32.73%/33.13% for mCIM. CarbAcineto NP test and sCIM performed excellently (100% sensitivity) when both Class B and Class D carbapenemases were present in the same isolate. Based on the results, the combined detection method of sCIM and CarbAcineto NP test was proposed to detect carbapenemase-producing A. baumannii rather than a single assay, significantly increasing the sensitivity of detection to 98.18%. The proposed algorithm was more reliable and cost-effective than the CarbAcineto NP test alone. It can be easily applied in routine microbiology laboratories for developing countries with limited resources.

Diagnostic Accuracy and Agreement between Four Phenotypic Carbapenemase Detection Tests among Enterobacterales

Introduction:

Carbapenem-resistant Enterobacterales (CREs) are becoming increasingly popular as a cause of hospital-acquired infections that are difficult to treat and are frequently reported as causes of outbreaks in various hospitals. Conventional culturing techniques take at least 2 days to report a case as carbapenem resistant, and it is therefore important to detect such resistance mechanisms as early as possible.

Methods:

This study aimed to compare the diagnostic performance of Carba NP, modified Hodge test (MHT), ethylenediaminetetraacetic acid (EDTA) disk synergy test (DST), and the modified carbapenem inactivation method (mCIM). This study was done at Microbiology Laboratory, Aga Khan University Hospital, Karachi. It was an observational study. Carba NP, MHT, EDTA DST, and the mCIM were performed on consecutive isolates of Enterobacterales. Sensitivity, specificity, and agreement between the four tests were calculated.

Results:

Of 207 Enterobacterales isolated, 127 were resistant to carbapenems. One hundred and fourteen of these were tested by a polymerase chain reaction, and the sensitivities of the Carba NP, MHT, EDTA DST, and the mCIM were found to be 94.34%, 75.47%, 79.25%, and 98.11%, respectively.

Conclusions:

Due to increased rates of carbapenem resistance, there is a need to employ mechanisms in hospitals that can identify such organisms as early as possible, both from clinical and epidemiological standpoints. The Carba NP test is a rapid, cost–effective, and reliable method and mCIM is more accurate but time consuming and both can be safely used for the screening of CREs.

An Application of Imipenem Discs or P. aeruginosa ATCC 27853 Reference Strain Increases Sensitivity of Carbapenem Inactivation Method for Non-Fermenting Gram-Negative Bacteria

Non-fermenting Gram-negative rods are one of the most commonly isolated bacteria from human infections. These microorganisms are typically opportunistic pathogens that pose a serious threat to public health due to possibility of transmission in the human population. Resistance to beta-lactams, due to carbapenemases synthesis, is one of the most important antimicrobial resistance mechanisms amongst them. The aim of this study was to evaluate the usefulness of the Carbapenem Inactivation Method (CIM), and its modifications, for the detection of carbapenemase activity amongst non-fermenting Gram-negative rods. This research involved 81 strains of Gram-negative rods. Of the tested strains, 55 (67.9%) synthesized carbapenemases. For non-fermenting rods, 100% sensitivity and specificity was obtained in the version of the CIM test using imipenem discs and E. coli ATCC 25922 strain. The CIM test allows for differentiation of carbapenems resistance mechanisms resulting from carbapenemase synthesis from other resistance types. It is a reliable diagnostic method for the detection of carbapenemase activity amongst non-fermenting Gram-negative rods. Application of imipenem discs and P. aeruginosa ATCC 27853 reference strain increases CIM results sensitivity, while imipenem discs and E. coli ATCC 25922 strain use maintains full precision of the test for non-fermenting rods.

Rapid detection of KPC-producing Enterobacterales by using a modified Carba NP test with imipenem/relebactam

INTRODUCTION

Here, we propose a novel modified Carba NP test for detecting KPC-producing Enterobacterales using imipenem/relebactam.

MATERIAL AND METHODS

The test performance was evaluated in a random selection of 160 previously molecularly characterized clinical isolates carrying the 110 blaKPC, 1 blaGES, 12 blaVIM, 4 blaIMP, 3 blaNDM and 42 blaOXA-48-like genes. The proposed method relies on the detection of imipenem hydrolysis in an imipenem/relebactam antibiotic solution and subsequent visual interpretation by color change.

RESULTS

All class A producing Enterobacterales (111/111) were detected using imipenem/relebactam as no visual appreciation of color change was perceived due to a nule hydrolysis of imipenem in the antibiotic solution. Overall, the assay showed 100% sensitivity (111/111) and specificity (69/69) for detecting class A KPC-producing Enterobacterales.

DISCUSSION

The biochemical assay provides very reliable results for detecting KPC-producing Enterobacterales, with a turnaround time of less than 1 hour, minimum handling and no specialized equipment required.

Analysis of blaCHDL Genes and Insertion Sequences Related to Carbapenem Resistance in Acinetobacter baumannii Clinical Strains Isolated in Warsaw, Poland

Acinetobacter baumannii is an important cause of nosocomial infections worldwide. The elucidation of the carbapenem resistance mechanisms of hospital strains is necessary for the effective treatment and prevention of resistance gene transmission. The main mechanism of carbapenem resistance in A. baumannii is carbapenemases, whose expressions are affected by the presence of insertion sequences (ISs) upstream of bla_CHDL genes. In this study, 61 imipenem-nonsusceptible A. baumannii isolates were characterized using phenotypic (drug-susceptibility profile using CarbaAcineto NP) and molecular methods. Pulsed field gel electrophoresis (PFGE) and multi-locus sequence typing (MLST) methods were utilized for the genotyping. The majority of isolates (59/61) carried one of the following acquired bla_CHDL genes: bla_OXA-24-like (39/59), ISAba1-bla_OXA-23-like (14/59) or ISAba3-bla_OXA-58-like (6/59). Whole genome sequence analysis of 15 selected isolates identified the following intrinsic bla_OXA-66 (OXA-51-like; n = 15) and acquired class D β-lactamases (CHDLs): ISAba1-bla_OXA-23 (OXA-23-like; n = 7), ISAba3-bla_OXA-58-ISAba3 (OXA-58-like; n = 2) and bla_OXA-72 (OXA-24-like; n = 6). The isolates were classified into 21 pulsotypes using PFGE, and the representative 15 isolates were found to belong to sequence type ST2 of the Pasteur MLST scheme from the global IC2 clone. The Oxford MLST scheme revealed the diversity among these studied isolates, and identified five sequence types (ST195, ST208, ST208/ST1806, ST348 and ST425). CHDL-type carbapenemases and insertion elements upstream of the bla_CHDL genes were found to be widespread among Polish A. baumannii clinical isolates, and this contributed to their carbapenem resistance.

Development of a new spectrophotometric assay for rapid detection and differentiation of KPC, MBL and OXA-48 carbapenemase-producing Klebsiella pneumoniae clinical isolates

The increased prevalence of carbapenemase-producing Enterobacteriaceae (CPE) has made essential the design of quicker tests for CPE detection. In the present study, a simple and rapid assay was developed based on measurement of the hydrolytic activity of imipenem at a final concentration of 65 µg/mL (100 µM) through ultraviolet-visible (UV-Vis) spectrophotometry. All measurements were conducted at 297 nm. A total of 83 carbapenem-non-susceptible CPE, consisting of Klebsiella pneumoniae clinical isolates and genotypically characterised as KPC-, VIM-, NDM- or OXA-48-producers, were tested. For comparison, 30 carbapenem-non-susceptible clinical isolates, consisting of Escherichia coli and K. pneumoniae and genotypically confirmed as non-CPE, were also examined. The spectrophotometric assay enabled efficient discrimination of CPE from non-CPE isolates even in 45 min (P < 0.0001). Moreover, the presence of phenylboronic acid (PBA) or ethylene diamine tetra-acetic acid (EDTA) in the reaction mixture was able to inhibit the hydrolytic capacity of KPC- or metallo-β-lactamase (MBL)-producers, respectively, while the hydrolytic activity of OXA-48-producing strains was not affected by the presence of these inhibitors (P < 0.001). The newly developed assay presented 100% sensitivity and specificity to detect and differentiate KPC-, MBL- and OXA-48-producers compared with genotypic characterisation. Thus, the proposed spectrophotometric method can be considered as an easy, fast, accurate and cost-effective diagnostic tool for screening carbapenem-non-susceptible K. pneumoniae isolates in the clinical laboratory.

Carba NP test for the detection of carbapenemase-producing Pseudomonas aeruginosa

INTRODUCTION

The Carba NP test is a biochemical chromogenic assay developed to detect carbapenemase activity. Variable performance has been reported according to the type of carbapenemase and bacterial species involved. We aimed to describe the benefit of the Carba NP test and its commercial version, the RAPIDEC® CARBA NP, to detect carbapenemase-producing Pseudomonas aeruginosa.

METHODS

PubMed and ScienceDirect databases were searched. The following data was collected from each included study: research protocol, molecular profile of the tested strains, and sensitivity and specificity of the test used to detect carbapenemase-producing P. aeruginosa.

RESULTS

Thirty-four studies were included. The most frequently tested strains were metallo-beta-lactamase producers. The pooled sensitivity to detect carbapenemase-producing P. aeruginosa with the original Carba NP test, the Clinical and Laboratory Standards Institute (CLSI) Carba NP test, and the RAPIDEC® CARBA NP was 92%, 95%, and 96%, respectively. The pooled specificity was 99% with the original and the CLSI Carba NP tests, and 92% with the RAPIDEC® CARBA NP. Several studies evaluated modified versions of the Carba NP test to detect carbapenemase-producing P. aeruginosa, with reported sensitivity and specificity exceeding 90% in most cases.

CONCLUSION

The Carba NP test allows for fast screening and easy handling as well as optimal performance to detect carbapenemase-producing P. aeruginosa. These findings should be confirmed by further studies including a larger cohort of isolates and various types of carbapenemases, mainly non-metallo-beta-lactamases.

Phenotypic and genotypic characterization of carbapenem-resistant Acinetobacter baumannii isolates from Egypt

Background

Antibiotic use is largely under-regulated in Egypt leading to the emergence of resistant isolates. Carbapenems are last resort agents to treat Acinetobacter baumannii infections resistant to other classes of antibiotics. However, carbapenem-resistant isolates are emerging at an alarming rate. This study aimed at phenotypically and molecularly characterizing seventy four carbapenem-unsusceptible A. baumannii isolates from Egypt to detect the different enzymes responsible for carbapenem resistance.

Methods

Carbapenemase production was assessed by a number of phenotypic methods: modified Hodge test (MHT), carbapenem inactivation method (CIM), combined disc test (CDT), CarbAcineto NP test and boronic acid disc test. Polymerase chain reaction (PCR) was used to screen the isolates for the presence of some genes responsible for resistance to carbapenems, as well as some insertion sequences.

Results

PCR amplification of class D carbapenemases revealed the prevalence of bla_OXA-51 and bla_OXA-23 in 100% of the isolates and of bla_OXA-58 in only one isolate (1.4%). bla_VIM and bla_NDM-1 belonging to class B metallo-β-lactamases were present in 100 and 12.1% of the isolates, respectively. The prevalence of ISAba1, ISAba2 and ISAba3 was 100, 2.7 and 4.1%, respectively. None of the tested isolates carried bla_OXA-40, bla_IMP, bla_SIM, bla_SPM, bla_GIM or the class A bla_KPC. Taking PCR as the gold standard method for the detection of different carbapenemases, the sensitivities of the MHT, CIM, CDT, CarbAcineto NP test and boronic acid disc/imipenem or meropenem test for this particular collection of isolates were 78.4, 68.9, 79.7, 95.9, and 56.8% or 70.3%, respectively.

Conclusions

The widespread detection of carbapenem-resistant A. baumannii (CR-AB) has become a real threat to the efficacy of treatment regimens. Among the studied cohort of CR-AB clinical isolates, bla_OXA-51, bla_OXA-23 and bla_VIM were the most prevalent, followed by bla_NDM-1 and bla_OXA-58. The genotypic detection of carbapenemases among CR-AB clinical isolates using PCR was most conclusive, followed closely by the phenotypic testing using CarbAcineto NP test.

Reduced Incubation Time of the Modified Carbapenem Inactivation Test and Performance of Carbapenem Inactivation in a Set of Carbapenemase-Producing Enterobacteriaceae with a High Proportion of bla IMP Isolates

Accurate and timely identification of carbapenemase-producing Enterobacteriaceae (CPE) is critical for microbiology laboratories in order to facilitate infection prevention, reduce the spread of multiresistant Gram-negative bacilli, and reduce delays to effective antibiotic therapy. We undertook a study to compare the carbapenem inactivation method (CIM) against the modified carbapenem inactivation method (mCIM) on a broad range of CPE isolates from Australia, including a high proportion of bla _IMP isolates. Furthermore, we evaluated the performance of the mCIM with a reduced incubation time using automated incubation and digital plate reading in order to better facilitate quick confirmation of carbapenemases. The overall sensitivity of the mCIM was 98.2%, compared to 95.6% for the CIM. The minimum incubation time for the mCIM while maintaining its sensitivity was 12 hours. Both the CIM and mCIM perform well on a broad range of CPE isolates seen in Australia.

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.

Performance evaluation of the MALDI Biotyper Selective Testing of Antibiotic Resistance-β-Lactamase (MBT STAR-BL) assay for the detection of IMP metallo-β-lactamase activity in Enterobacteriaceae

The MALDI Biotyper Selective Testing of Antibiotic Resistance-β-Lactamase (MBT STAR-BL) assay enables rapid detection of β-lactamase activity using matrix-assisted laser desorption ionization-time-of-flight mass spectrometry. The assay is based on analysis of bacterially induced hydrolysis of β-lactam antibiotics. We investigated the performance of the MBT STAR-BL assay for detecting IMP metallo-β-lactamase (MBL) activity in Enterobacteriaceae. A total of 145 strains (30 Escherichia coli, 43 Klebsiella pneumoniae, and 72 Enterobacter cloacae complex) were evaluated using meropenem hydrolysis assays. The MBT STAR-BL correctly identified all 48 IMP MBL producers as positive, even those exhibiting a low minimal inhibitory concentration (MIC) (1 μg/mL) for meropenem. Conversely, all non-IMP MBL producers, including strains with higher MICs (4 or 8 μg/mL), were correctly identified as negative. The MBT STAR-BL is a rapid, accurate, and reliable system for detecting IMP MBL activity in Enterobacteriaceae.

Determinants of Mortality in Patients with Nosocomial Acinetobacter baumannii Bacteremia in Southwest China: A Five-Year Case-Control Study

Purpose

This study was aimed to identify the determinants of in-hospital mortality in Acinetobacter baumannii (A. baumannii) bacteremia and to assess impact of carbapenem resistance on mortality.

Methods

A five-year case-control study was conducted from January 2011 to December 2015 in a tertiary teaching hospital with 3200 beds, Southwest China. Clinical outcomes and potential determinants of mortality in patients with nosocomial A. baumannii bacteremia and carbapenem-resistant A. baumannii (CRAB) bacteremia were evaluated using Cox and logistic regression analyses.

Results

A total of 118 patients with nosocomial A. baumannii bacteremia were included. Seventy-one percent (84/118) of them had carbapenem-resistant A. baumannii (CRAB) bacteremia. The in-hospital mortality of nosocomial A. baumannii bacteremia was 21.2%, and the attributable in-hospital mortality rate due to CRAB was 21.5%. Significant difference of 30-day in-hospital mortality in the Kaplan-Meier curves was found between CRAB and CSAB groups (log-rank test, P=0.025). The Cox regression analysis showed that patients with CRAB bacteremia had 2.72 times higher risk for 30-day in-hospital mortality than did those with carbapenem-susceptible A. baumannii (CSAB) bacteremia (95% confidence intervals (CIs) 1.14-6.61, P=0.016). The logistic regression analysis reported that mechanical ventilation and respiratory tract as origin of bacteremia were independent predictors of mortality among patients with nosocomial A. baumannii bacteremia and CRAB bacteremia, while high APACHE II score on the day of bacteremia and multiple organ dysfunction syndromes (MODS) during hospitalization were independent predictors of mortality among patients with nosocomial A. baumannii bacteremia but not CRAB bacteremia.

Conclusion

It was the severity of illness (high APACHE II score and MODS) not carbapenem resistance that highlighted the mortality of patients with nosocomial A. baumannii bacteremia. The impact of mechanical ventilation on mortality suggested that respiratory dysfunction might prime the poor outcome. Protection of respiratory function during the progression of nosocomial A. baumannii bacteremia should be given more importance. Early identification and intervention of patients with nosocomial A. baumannii bacteremia in critical ill conditions were advocated.

New Bugs and New Drugs: Updates in Clinical Microbiology

BACKGROUND

The landscape of clinical microbiology laboratories is changing. As new technologies are introduced, we are better able to detect and identify pathogens and to recognize and characterize emerging antimicrobial resistance mechanisms.

CONTENT

In this review, a selected cross-section of current hot topics in clinical microbiology is discussed. These topics include (a) diagnostics for urinary tract and sexually transmitted infections; (b) phenotypic and genotypic methods of detecting carbapenem resistance and discussion of newly approved anti-infective agents for these multi-drug resistant organisms; and (c) the significance, epidemiology, and identification of the emerging pathogens Mycobacterium chimaera and Candida auris.

SUMMARY

Communication between clinical microbiologists and their clinical colleagues is imperative to convey the significance of emerging pathogens and resistance determinants, as well as the performance characteristics of new diagnostic methods. Additionally, as antimicrobial resistance is surging, it is important to comprehensively evaluate the resistance profiles of clinical isolates to facilitate antimicrobial stewardship and inform infection prevention measures. Although antimicrobial resistance is a global public health crisis, it is encouraging that new anti-infective agents are in the pipeline and being approved for use in patients.

Rapid Detection of Carbapenemase Production in Enterobacteriaceae by Use of a Modified Paper Strip Carba NP Method

Rapid and accurate detection of carbapenemase-producing Enterobacteriaceae (CPE) is important for preventing their spread in health care settings. We compared the performance of the Carba NP (CNP) test using the CLSI tube method with that using a modified paper strip method for the detection of carbapenemases in 390 Enterobacteriaceae isolates. The isolates were identified by Hong Kong's carbapenem-resistant Enterobacteriaceae surveillance program in 2016 and comprised 213 CPE and 177 carbapenemase-negative Enterobacteriaceae isolates. Molecular genotype was used as the reference. The test results were read at different time points for the CLSI method (1 min, 5 min, 1 h, and 2 h) and strip method (1 min and 5 min). The strip CNP and CLSI CNP tests correctly detect carbapenemase production in 93% and 93% of KPC producers, 100% and 38% of IMI producers, 94% and 85% of IMP producers, 98% and 90% of NDM producers, and 29% and 12% of OXA producers, respectively. Overall, the strip method has superior sensitivity to the CLSI method (86% versus 75%, respectively; P < 0.001, McNemar test). The specificity of both methods was 100%. By the CLSI method, 27%, 14%, 29%, and 6% of the CPE isolates were positive at 1 min, 5 min, 1 h, and 2 h, respectively. In contrast, by the strip method, 76% of the CPE isolates were positive at 1 min, and an additional 10% were positive at 5 min. In conclusion, the Carba NP test by use of the modified strip method has a higher sensitivity and a shorter assay time than that those by use of the CLSI tube method.

Molecular and epidemiological characterization of carbapenemase-producing Enterobacteriaceae in Norway, 2007 to 2014

The prevalence of carbapenemase-producing Enterobacteriaceae (CPE) is increasing worldwide. Here we present associated patient data and molecular, epidemiological and phenotypic characteristics of all CPE isolates in Norway from 2007 to 2014 confirmed at the Norwegian National Advisory Unit on Detection of Antimicrobial Resistance. All confirmed CPE isolates were characterized pheno- and genotypically, including by whole genome sequencing (WGS). Patient data were reviewed retrospectively. In total 59 CPE isolates were identified from 53 patients. Urine was the dominant clinical sample source (37%) and only 15% of the isolates were obtained from faecal screening. The majority of cases (62%) were directly associated with travel or hospitalization abroad, but both intra-hospital transmission and one inter-hospital outbreak were observed. The number of CPE cases/year was low (2–14 cases/year), but an increasing trend was observed. Klebsiella spp. (n = 38) and E. coli (n = 14) were the dominant species and bla_KPC (n = 20), bla_NDM (n = 19), bla_OXA-48-like (n = 12) and bla_VIM (n = 7) were the dominant carbapenemase gene families. The CPE isolates were genetically diverse except for K. pneumoniae where clonal group 258 associated with bla_KPC dominated. All isolates were multidrug-resistant and a significant proportion (21%) were resistant to colistin. Interestingly, all bla_OXA-48-like, and a large proportion of bla_NDM-positive Klebsiella spp. (89%) and E. coli (83%) isolates were susceptible in vitro to mecillinam. Thus, mecillinam could have a role in the treatment of uncomplicated urinary tract infections caused by OXA-48- or NDM-producing E. coli or K. pneumoniae. In conclusion, the impact of CPE in Norway is still limited and mainly associated with travel abroad, reflected in the diversity of clones and carbapenemase genes.

Diagnostic Evasion of Highly-Resistant Microorganisms: A Critical Factor in Nosocomial Outbreaks

Highly resistant microorganisms (HRMOs) may evade screening strategies used in routine diagnostics. Bacteria that have evolved to evade diagnostic tests may have a selective advantage in the nosocomial environment. Evasion of resistance detection can result from the following mechanisms: low-level expression of resistance genes not resulting in detectable resistance, slow growing variants, mimicry of wild-type-resistance, and resistance mechanisms that are only detected if induced by antibiotic pressure. We reviewed reports on hospital outbreaks in the Netherlands over the past 5 years. Remarkably, many outbreaks including major nation-wide outbreaks were caused by microorganisms able to evade resistance detection by diagnostic screening tests. We describe various examples of diagnostic evasion by several HRMOs and discuss this in a broad and international perspective. The epidemiology of hospital-associated bacteria may strongly be affected by diagnostic screening strategies. This may result in an increasing reservoir of resistance genes in hospital populations that is unnoticed. The resistance elements may horizontally transfer to hosts with systems for high-level expression, resulting in a clinically significant resistance problem. We advise to communicate the identification of HRMOs that evade diagnostics within national and regional networks. Such signaling networks may prevent inter-hospital outbreaks, and allow collaborative development of adapted diagnostic tests.