A Full MALDI-Based Approach to Detect Plasmid-Encoded KPC-Producing Klebsiella pneumoniae

A side-by-side comparison of the new VITEK MS PRIME and the MALDI Biotyper sirius in the clinical microbiology laboratory

PURPOSE

This study aims to evaluate the performance of two latest generation matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) systems in routine laboratory settings, focusing on turnaround time (TAT), time to results (TTR), hands-on time, and identification rate.

METHODS

We conducted a time and motion study on three workflow scenarios to simulate different laboratory settings. Overall, 618 bacterial isolates from a tertiary hospital's laboratory were processed using the VITEK MS PRIME (bioMérieux) and the MALDI Biotyper sirius (Bruker Daltonics) and their corresponding databases VITEK IVD Database 3.2 and MBT reference library 12.

RESULTS

The target preparation process showed no significant difference in TAT, but the Biotyper workflow had a shorter hands-on time by 3 to 6 min. In the measurement process, TTR was three to five times shorter for the Biotyper sirius while hands-on time was significantly shorter for VITEK MS PRIME (approximately 1.5 min per target). The identification rate without retesting was 97.9% for VITEK MS PRIME and 98.9% for Biotyper sirius. Both systems achieved 100% agreement at genus and 96.2% at species level.

CONCLUSION

Both systems exhibited excellent identification rates for routine bacterial isolates. Due to its high speed, the Biotyper sirius is suited for laboratories with high sample throughput and a workflow designed for processing larger batches. The VITEK MS PRIME, with its "load and go" system accommodating up to 16 targets, reduces hands-on time, making it a reasonable choice for laboratories with fewer identifications overall but a higher number of targets and a workflow designed for parallel processing on different workstations.

Poor Sensitivity of the MALDI Biotyper® MBT Subtyping Module for Detection of Klebsiella pneumoniae Carbapenemase (KPC) in Klebsiella Species

Rapid detection of Klebsiella pneumoniae carbapenemase (KPC) in the Klebsiella species is desirable. The MALDI Biotyper® MBT Subtyping Module (Bruker Daltonics) uses an algorithm that detects a peak at ~11,109 m/z corresponding to a protein encoded by the p019 gene to detect KPC simultaneously with organism identification by a matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-ToF MS). Here, the subtyping module was evaluated using 795 clinical Klebsiella isolates, with whole genome sequences used to assess for blaKPC and p019. For the isolates identified as KPC positive by sequencing, the overall sensitivity of the MALDI-ToF MS subtyping module was 239/574 (42%) with 100% specificity. For the isolates harboring p019, the subtyping module showed a sensitivity of 97% (239/246) and a specificity of 100%. The subtyping module had poor sensitivity for the detection of blaKPC-positive Klebsiella isolates, albeit exhibiting excellent specificity. The poor sensitivity was a result of p019 being present in only 43% of the blaKPC-positive Klebsiella isolates.

MALDI-TOF MS-Based Approaches for Direct Identification of Gram-Negative Bacteria and BlaKPC-Carrying Plasmid Detection from Blood Cultures: A Three-Year Single-Centre Study and Proposal of a Diagnostic Algorithm

The rapid identification of pathogens of bloodstream infections (BSIs) and the detection of antibiotic resistance markers are critically important for optimizing antibiotic therapy and infection control. The purpose of this study was to evaluate two approaches based on MALDI-TOF MS technology for direct identification of Gram-negative bacteria and automatic detection of Klebsiella pneumoniae carbapenemase (KPC) producers using the Bruker MBT Subtyping IVD Module in a large routine laboratory over a three-year period. MALDI-TOF MS analysis was performed directly from blood culture (BC) bottles following bacterial pellet recovery by Rapid MBT Sepsityper® Kit and on blood agar 4-h subcultures. Automated detection of blaKPC-carrying pKpQIL-plasmid by Bruker MBT Subtyping Module was evaluated in BCs tested positive to K. pneumoniae or E. coli. The results were compared with those obtained with conventional reference methods. Among the 2858 (93.4%) monomicrobial BCs, the overall species identification rates of the Rapid Sepsityper and the short-term subculture protocols were 84.5% (n = 2416) and 90.8% (n = 2595), respectively (p < 0.01). Excellent specificity for KPC-producers identification were observed for both MALDI-TOF MS protocols. The pKpQIL plasmid-related peak was detected in overall 91 of the 120 (75.8%) KPC-producing isolates. Notably, 14 out of the 17 (82.3%) K. pneumoniae isolates carrying blaKPC variants associated with ceftazidime/avibactam resistance and tested negative by the immunocromatography assay, were correctly identified as KPC-producers by MALDI-TOF MS. In conclusion, combination of both Rapid Sepsityper and short-term subculture protocols may represent an optimal solution to promptly identify more than 95% of Gram-negative bacteria causing BSIs. MALDI Biotyper® platform enabled a reliable and robust automated detection of KPC producers in parallel with species identification. However, integration of molecular or immunocromatographic assays are recommended according to local epidemiology.

Clinical Performance of the Osmotic Shock-MALDI MS Method to Detect Klebsiella pneumoniae Carbapenemase in Clinical Isolates

The World Health Organization recently highlighted the serious worldwide problem of the emergence of antibiotic-resistant or antibiotic multidrug-resistant bacteria. Carbapenem-resistant Enterobacterales, including carbapenemase-producing Enterobacterales (CPE), are major antibiotic-resistant bacteria that can be identified by various methods, including antibiotic susceptibility testing, PCR, and immunologic assays.

“Omic” Approaches to Bacteria and Antibiotic Resistance Identification

The quick and accurate identification of microorganisms and the study of resistance to antibiotics is crucial in the economic and industrial fields along with medicine. One of the fastest-growing identification methods is the spectrometric approach consisting in the matrix-assisted laser ionization/desorption using a time-of-flight analyzer (MALDI-TOF MS), which has many advantages over conventional methods for the determination of microorganisms presented. Thanks to the use of a multiomic approach in the MALDI-TOF MS analysis, it is possible to obtain a broad spectrum of data allowing the identification of microorganisms, understanding their interactions and the analysis of antibiotic resistance mechanisms. In addition, the literature data indicate the possibility of a significant reduction in the time of the sample preparation and analysis time, which will enable a faster initiation of the treatment of patients. However, it is still necessary to improve the process of identifying and supplementing the existing databases along with creating new ones. This review summarizes the use of “-omics” approaches in the MALDI TOF MS analysis, including in bacterial identification and antibiotic resistance mechanisms analysis.

Rapid Identification of Methicillin-Resistant Staphylococcus aureus Using MALDI-TOF MS and Machine Learning from over 20,000 Clinical Isolates

Rapidly identifying methicillin-resistant Staphylococcus aureus (MRSA) with high integration in the current workflow is critical in clinical practices. We proposed a matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI–TOF MS)-based machine learning model for rapid MRSA prediction. The model was evaluated on a prospective test and four external clinical sites. For the data set comprising 20,359 clinical isolates, the area under the receiver operating curve of the classification model was 0.78 to 0.88. These results were further interpreted using shapely additive explanations and presented using the pseudogel method. The important MRSA feature, m/z 6,590 to 6,599, was identified as a UPF0337 protein SACOL1680 with a lower binding affinity or no docking results compared with UPF0337 protein SA1452, which is mainly detected in methicillin-susceptible S. aureus. Our MALDI–TOF MS-based machine learning model for rapid MRSA identification can be easily integrated into the current clinical workflows and can further support physicians in prescribing proper antibiotic treatments.

IMPORTANCE Over 20,000 clinical MSSA and MRSA isolates were collected to build a machine learning (ML) model to identify MSSA/MRSA and their markers. This model was tested across four external clinical sites to ensure the model’s usability. We report the first discovery and validation of MRSA markers on the largest scale of clinical MSSA and MRSA isolates collected to date, covering five different clinical sites. Our developed approach for the rapid identification of MSSA and MRSA can be highly integrated into the current workflows.

Methodology Establishment and Application of VITEK Mass Spectrometry to Detect Carbapenemase-Producing Klebsiella pneumoniae

The ability of VITEK mass spectrometry (MS) in detection of bacterial resistance is currently under exploration and evaluation. In this study, we developed and validated a VITEK MS method to rapidly test carbapenemase-producing Klebsiella pneumoniae (CPKP). Solvents, antibiotic concentrations, crystal conditions and times, centrifugation speeds, and other factors were optimized to design a rapid sample pretreatment process for CPKP detection by VITEK MS. The related parameters of the mass spectrum were adjusted on the instrument to establish an CPKP detection mode. 133 clinically isolated strains of CPKP in the microbiology laboratory at the Shenzhen People’s Hospital from 2004 to 2017 were selected for accuracy evaluation. The fresh suspected strains from the microbiology laboratory in 2020 were used to complete the clinical verification. Two antibiotics, meropenem (MEM) and imipenem (IPM), were used as substrates. These two substrates were incubated with suspected CPKP, and the results were obtained by VITEK MS detection. Using this method, different types of CPKP showed different detection results and all the CPKP strains producing KPC-2 and IMP-4 carbapenemase were detected by VITEK MS. Thus, VITEK MS can be used for rapid detection of CPKP, especially for some common types of CPKP. This method provides high accuracy and speed of detection. Combined with its cost advantages, it can be intensely valuable in clinical microbiology laboratories after the standard operating procedures are determined.

Classical and Molecular Techniques to Diagnose HAP/VAP

Nosocomial pneumonia, including hospital-acquired pneumonia (HAP) and ventilator-associated pneumonia (VAP), are the most common nosocomial infections occurring in critically ill patients requiring intensive care. However, challenges exist in making a timely and accurate diagnosis of HAP and VAP. Under diagnosis of HAP and VAP can result in greater mortality risk, especially if accompanied by delays in the administration of appropriate antimicrobial treatment. Over diagnosis of HAP and VAP results in the unnecessary administration of broad spectrum antibiotics that can lead to further escalation of antibiotic resistance. Optimal diagnosis and management of HAP and VAP require a systematic approach that combines clinical and radiographic assessments along with proper microbiologic techniques. The use of more invasive sampling methods (bronchoalveolar lavage and protected specimen brush) may enhance specimen collection resulting in more specific diagnoses to limit unnecessary antibiotic exposure. Molecular techniques, currently in use and investigational technique, may improve the diagnosis of HAP and VAP by allowing more rapid identification of offending pathogens, if present, thus increasing both appropriate antibiotic treatment and avoiding unnecessary drug exposure.

Carbapenemase Producing Klebsiella pneumoniae (KPC): What Is the Best MALDI-TOF MS Detection Method

Klebsiella pneumoniae carbapenemase (KPC)-producing bacteria is a group of highly dangerous antibiotic resistant Gram-negative Enterobacteriaceae. They cause infections associated with significant morbidity and mortality. Therefore, the rapid detection of KPC-producing bacteria plays a key role in clinical microbiology. Matrix assisted laser desorption/ionization time-of- flight (MALDI-TOF) is a rapidly evolving technology that finds application in various clinical, scientific, and industrial disciplines. In the present study, we demonstrated three different procedures of carbapenemase-producing K. pneumoniae (KPC) detection. The most basic model of MALDI-TOF instrument MS Microflex LT was used, operating in the linear ion-positive mode, commonly used in modern clinical laboratories. The first procedure was based on indirect monitoring of carbapenemase production with direct detection of hydrolyzed carbapenem antibiotic degradation products in the mass spectrum. The second procedure was based on direct detection of bla_KPC accompanying peak with an 11,109 Da in the mass spectrum of carbapenemase-producing K. pneumoniae (KPC), which represents the cleaved protein (pKpQIL_p019) expressed by pKpQIL plasmid. In addition, several unique peaks were detected in the carbapenemase-producing K. pneumoniae (KPC) mass spectrum. The third procedure was the identification of carbapenemase-producing K. pneumoniae (KPC) based on the protein fingerprint using local database created from the whole mass spectra. By comparing detection procedures, we determined that the third procedure was very fast and relatively easy. However, it requires previous verification of carbapenemase-producing K. pneumoniae (KPC) using other methods as genetic bla_KPC identification, detection of carbapenem degradation products, and accompanying peak with 11,109 Da, which represents cleaved pKpQIL_p019 protein expressed by pKpQIL plasmid. Detection of carbapenemase-producing K. pneumoniae using MALDI-TOF provides fast and accurate results that may help to reduce morbidity and mortality in hospital setting when applied in diagnostic situations.

Detection of Multidrug-Resistant Enterobacterales-From ESBLs to Carbapenemases

Multidrug-resistant Enterobacterales (MDRE) are an emerging threat to global health, leading to rising health care costs, morbidity and mortality. Multidrug-resistance is commonly caused by different β-lactamases (e.g., ESBLs and carbapenemases), sometimes in combination with other resistance mechanisms (e.g., porin loss, efflux). The continuous spread of MDRE among patients in hospital settings and the healthy population require adjustments in healthcare management and routine diagnostics. Rapid and reliable detection of MDRE infections as well as gastrointestinal colonization is key to guide therapy and infection control measures. However, proper implementation of these strategies requires diagnostic methods with short time-to-result, high sensitivity and specificity. Therefore, research on new techniques and improvement of already established protocols is inevitable. In this review, current methods for detection of MDRE are summarized with focus on culture based and molecular techniques, which are useful for the clinical microbiology laboratory.

Occurrence of the p019 Gene in the blaKPC-Harboring Plasmids: Adverse Clinical Impact for Direct Tracking of KPC-Producing Klebsiella pneumoniae by Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry

Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) has recently been used for the direct detection of KPC-producing isolates by analysis of the 11,109 Da mass peak representing the P019 protein. In this study, we evaluate the presence of the 11,109 Da mass peak in a collection of 435 unduplicated Klebsiella pneumoniae clinical isolates. The prevalence of the P019 peak in the bla_KPC K. pneumoniae isolates was 49.2% (32/65). The 11,109 Da mass peak was not observed in any of the other carbapenemase (319) or noncarbapenemase producers (116). Computational analysis of the presence of the p019 gene was performed in the aforementioned carbapenemase-producing K. pneumoniae isolates fully characterized by whole-genome sequencing (WGS) and in a further collection of 1,649 K. pneumoniae genomes included in EuSCAPE. Herein, we have demonstrated that the p019 gene is not exclusively linked to the pKpQil plasmid but that it is present in the following plasmids: IncFIB(K)/IncFII(K)/ColRNAI, IncFIB(pQil), IncFIB(pQil)/ColRNAI, IncFIB(pQil)/IncFII(K), IncFIB(K)/IncFII(K), and IncX3. In addition, we have proven the independent movement of the Tn4401 and the ISKpn31, of which the p019 gene is a component. The absence of the p019 gene was obvious in Col440I, Col(pHAD28), IncFIB(K)/IncX3/IncFII(K), and IncFIB(K)/IncFII(K) plasmids. In addition, we also observed another plasmid in which neither Tn4401 nor ISKpn31 was found, IncP6. In the EuSCAPE, the occurrence of p019 varied from 0% to 100% among the different geographical locations. The adverse clinical impact of the diminished prevalence of the p019 gene within the plasmid encoding KPC-producing Klebsiella pneumoniae puts forward the need for reconsideration when applying this technique in a clinical setting.

Study on carbapenemase-producing bacteria by matrix-assisted laser desorption/ionization approach

The development of new techniques for the detection of carbapenemase activity is of great importance since the increased incident of resistance against carbapenems represents a serious threat to global public health. In this context, the matrix-assisted laser desorption/ionization approach already demonstrated to be a reliable tool for rapid carbapenemase detection. As a newly developed test, there is still a lack of in-depth analysis of its robustness and possible wider application. The main goal of this study was to evaluate the potential for using the design MBT STAR-Carba assay as the pre-characterization method for Enterobacterales and P. aeruginosa strains in terms of the produced classes of carbapenemases using modified procedure parameters—various suspension densities and incubation times. Moreover, its usefulness for the in-depth analysis and characterization of metallo-β-lactamases (MBL) was tested by applying inhibition assays. In this study, the designed assay proved to be a sensitive tool for the detection of carbapenemase hydrolytic activity, which can be successfully used to partially classify the class of carbapenemase present. Additionally, the use of defined high concentration suspensions would allow to shorten the incubation time to 1 minute for certain strains. Considering that the assay was also suitable to investigate the effect of different inhibitors on the MBL activity, it demonstrates far higher discriminatory potential than only a rapid routine carbapenemase detection tool and could be used as a susceptibility assay.

Interhospital dissemination of KPC-3 producing-Klebsiella pneumoniae ST512. Detection by MALDI-TOF

INTRODUCTION/OBJECTIVE

To describe an outbreak of KPC-3-producing Klebsiella pneumoniae (KPN) and determine the diagnostic efficacy of MALDI-TOF in its detection.

METHODS

Retrospective study of the KPC-3-KPN isolated in 2 hospitals in Ciudad Real. The peak at 11,109kDa±15 was sought in the KPN spectra provided by MALDI-TOF.

RESULTS

We isolated 156 KPN strains that carried the bla_KPC-3 gene, with a unique profile belonging to ST512 (31 strains studied). There was 25% of infected patients, 84% were nosocomial or related to health care and 93% had some underlying disease (31% of exitus in the first month). The detection of the peak showed 90% sensitivity and 100% specificity.

CONCLUSIONS

We detected the clonal spread of a KPN ST512 strain producing KPC-3 in 3 hospitals in Ciudad Real. In addition, we show the profitability of MALDI-TOF in the early detection of KPC-KPN.

Helix Matrix Transformation Combined With Convolutional Neural Network Algorithm for Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry-Based Bacterial Identification

Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) analysis is a rapid and reliable method for bacterial identification. Classification algorithms, as a critical part of the MALDI-TOF MS analysis approach, have been developed using both traditional algorithms and machine learning algorithms. In this study, a method that combined helix matrix transformation with a convolutional neural network (CNN) algorithm was presented for bacterial identification. A total of 14 bacterial species including 58 strains were selected to create an in-house MALDI-TOF MS spectrum dataset. The 1D array-type MALDI-TOF MS spectrum data were transformed through a helix matrix transformation into matrix-type data, which was fitted during the CNN training. Through the parameter optimization, the threshold for binarization was set as 16 and the final size of a matrix-type data was set as 25 × 25 to obtain a clean dataset with a small size. A CNN model with three convolutional layers was well trained using the dataset to predict bacterial species. The filter sizes for the three convolutional layers were 4, 8, and 16. The kernel size was three and the activation function was the rectified linear unit (ReLU). A back propagation neural network (BPNN) model was created without helix matrix transformation and a convolution layer to demonstrate whether the helix matrix transformation combined with CNN algorithm works better. The areas under the receiver operating characteristic (ROC) curve of the CNN and BPNN models were 0.98 and 0.87, respectively. The accuracies of the CNN and BPNN models were 97.78 ± 0.08 and 86.50 ± 0.01, respectively, with a significant statistical difference (p < 0.001). The results suggested that helix matrix transformation combined with the CNN algorithm enabled the feature extraction of the bacterial MALDI-TOF MS spectrum, which might be a proposed solution to identify bacterial species.

Direct detection of intact Klebsiella pneumoniae carbapenemase variants from cell lysates: Identification, characterization and clinical implications

Introduction

Carbapenemase-producing organisms (CPOs) are a growing threat to human health. Among the enzymes conferring antibiotic resistance produced by these organisms, Klebsiella pneumoniae carbapenemase (KPC) is considered to be a growing global health threat. Reliable and specific detection of this antibiotic resistance-causing enzyme is critical both for effective therapy and to mitigate further spread.

Objectives

The objective of this study is to develop an intact protein mass spectrometry-based method for detection and differentiation of clinically-relevant KPC variants directly from bacterial cell lysates. The method should be specific for any variant expressed in multiple bacterial species, limit false positive results and be rapid in nature to directly influence clinical outcomes.

Methods

Lysates obtained directly from bacterial colonies were used for intact protein detection using liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). Bottom-up and top-down proteomic methods were used to characterize the KPC protein targets of interest. Comparisons between KPC-producing and KPC-non-producing isolates from a wide variety of species were also performed.

Results

Characterization of the mature KPC protein revealed an unexpected signal peptide cleavage site preceding an AXA signal peptide motif, modifying the molecular weight (MW) of the mature protein. Taking the additional AXA residues into account allowed for direct detection of the intact protein using top-down proteomic methods. Further validation was performed by transforming a KPC-harboring plasmid into a negative control strain, followed by MS detection of the KPC variant from the transformed cell line. Application of this approach to clearly identify clinically-relevant variants among several species is presented for KPC-2, KPC-3, KPC-4 and KPC-5.

Conclusion

Direct detection of these enzymes contributes to the understanding of occurrence and spread of these antibiotic-resistant organisms. The ability to detect intact KPC variants via a simple LC-MS/MS approach could have a direct and positive impact on clinical therapy, by providing both direction for epidemiological tracking and appropriate therapy.

Direct detection of intact Klebsiella pneumoniae carbapenemases produced by Enterobacterales using MALDI-TOF MS

Objectives

A MALDI-TOF MS-based identification method for KPC-producing Enterobacterales was developed.

Methods

The molecular mass of the intact KPC-2 polypeptide was estimated for blaKPC-2 transformants using MALDI Microflex and the exact mass was confirmed by LC and a high-resolution MS/MS system. A total of 1181 clinical Enterobacterales strains, including 369 KPC producers and 812 KPC non-producers, were used to set up the methodology and the results were compared with those from PCR analyses. For external validation, a total of 458 Enterobacterales clinical isolates from a general hospital between December 2018 and April 2019 were used.

Results

The exact molecular mass of the intact KPC-2 protein was 28 718.13 Da and KPC peaks were observed at m/z 28 708.87–28 728.34 using MALDI Microflex. Most of the KPC-2 (99.1%, 335/338) and KPC-3 (100%, 6/6) producers presented a clear peak via this method, while 12.0% (3/25) of the KPC-4 producers had a peak of weak intensity associated with low levels of gene expression. It took less than 20 min for the entire assay to be performed with colonies on an agar plate. External validation showed that the analytical sensitivity and specificity of the method compared with PCR were 100% (59/59) and 99.50% (397/399), respectively.

Conclusions

The MALDI-TOF MS-based method for directly detecting the intact KPC protein is applicable to routine tests in clinical microbiology laboratories, supported by its speed, low cost and excellent sensitivity and specificity.

Rectal screening for carbapenemase-producing Enterobacteriaceae: a proposed workflow

OBJECTIVES

Active screening is a crucial element for the prevention of carbapenemase-producing Enterobacteriaceae (CPE) transmission in healthcare settings. Here we propose a culture-based protocol for rectal swab CPE screening that combines CPE detection with identification of the carbapenemase type.

METHODS

The workflow integrates an automatic digital analysis of selective chromogenic media (WASPLab®; Copan), with subsequent rapid tests for the confirmation of carbapenemase production [i.e. detection of Klebsiella pneumoniae carbapenemase (KPC)-specific peak by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF/MS) or a multiplex immunochromatographic assay identifying the five commonest carbapenemase types]. To evaluate the performance of this protocol in depth, data for 21 162 rectal swabs submitted for CPE screening to the Microbiology Unit of S. Orsola-Malpighi Hospital (Bologna, Italy) were analysed.

RESULTS

Considering its ability to correctly segregate plates with/without Enterobacteriaceae, WASPLab Image Analysis Software showed globally a sensitivity and specificity of 100% and 79.4%, respectively. Of the plates with bacterial growth (n = 901), 693 (76.9%) were found to be positive for CPE by MALDI-TOF/MS (KPC-specific peak for K. pneumoniae) or by immunochromatographic assay. Only 2.8% (16/570) of KPC-positive K. pneumoniae strains were missed by the specific MALDI-TOF/MS algorithm, being detected by the immunochromatographic assay. The mean turnaround time needed from sample arrival to the final report ranged between 18 and 24 h, representing a significant time saving compared with manual reading.

CONCLUSION

This workflow proved to be fast and reliable, being particularly suitable for areas endemic for KPC-producing K. pneumoniae and for high-throughput laboratories.

Detection of carbapenemase producers by matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF MS)

Matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF MS) has been recently applied in detection of carbapenemase-producing Gram-negative isolates. In the present study, we review the latest developments in this field.

Performance Evaluation of the MBT STAR®-Carba IVD Assay for the Detection of Carbapenemases With MALDI-TOF MS

Objectives: The increasing rate of carbapenem resistance in Gram-negative bacteria is a major public health problem and rapid detection is essential for infection management. We evaluated the performances of the MBT STAR^®-Carba IVD assay (Bruker Daltonics) to detect carbapenemase-producing organisms (CPO) from bacterial colonies and directly from positive blood culture bottles with MALDI-TOF MS. Methods: We analyzed 130 strains with a reduced susceptibility to at least one carbapenem including 109 CPO (6 KPC, 27 NDM, 21 VIM, 1 IMP, 41 OXA-48-like, 8 OXA-23, 2 OXA-24/-40, and 2 OXA-58) and 21 non-CPO. The assay on colonies was performed with all 130 strains while the assay on spiked blood cultures was performed with 45 strains. Samples were prepared with the MBT STAR^®-CARBA IVD kit and imipenem hydrolysis by the potential carbapenemase was analyzed with the MBT STAR^®-BL module (Bruker Daltonics) on MALDI-TOF MS. Results: Performed on colonies, the assay detected all carbapenemase-producing Enterobacteriaceae (n = 78), Pseudomonas spp. (n = 19) and Acinetobacter spp. (n = 12). All 21 tested non-CPO remained negative resulting in sensitivity and specificity of 100%. Performed on positive blood cultures, the assay detected all carbapenemase-producing Enterobacteriaceae (n = 23) and Pseudomonas spp. (n = 4) but missed 9/12 carbapenemase-producing Acinetobacter spp. However, a prolonged imipenem-incubation time of the strain pellet improved carbapenemase detection. Non-CPO from positive blood culture bottles remained negative (n = 5) with the assay with the exception of one Klebsiella pneumoniae isolate. Conclusion: The MBT STAR^®-Carba IVD assay is a highly reliable method for the detection of carbapenemase activity in Gram-negative bacteria. However, time-consuming sample preparation steps and reagent costs need to be considered before implementation in a routine clinical microbiology laboratory.