Comparison of the BD Max methicillin-resistant Staphylococcus aureus (MRSA) assay and the BD GeneOhm MRSA achromopeptidase assay with direct- and enriched-culture techniques using clinical specimens for detection of MRSA

Novel strategies for rapid identification and susceptibility testing of MRSA

INTRODUCTION

Methicillin-resistant Staphylococcus aureus (MRSA) is associated with adverse clinical outcomes and increased morbidity, mortality, length of hospital stay, and health-care costs. Rapid diagnosis of MRSA infections has been associated with positive impact on clinical outcomes.

AREAS COVERED

We searched relevant papers in PubMed for the last 10 years. In major papers, we scanned the bibliographies to ensure that important articles were included. This review describes screening and diagnostic test methods for MRSA and their analytical performances with a focus on rapid molecular-based assays including those that are on the horizon. Future novel technologies will allow more rapid detection of phenotypic resistance. In the case of whole-genome sequencing, detection of mutations may predict resistance, transmission, and virulence.

EXPERT OPINION

Currently there are many diagnostic options for the detection of MRSA in surveillance and clinical samples. In general, these are highly accurate and have resulted in improvements in targeted management and reduction in hospital or intensive care unit length of stay for both MSSA and MRSA. Impact on mortality has been variable. Promising novel technologies will not only accurately identify pathogens and detect their resistance markers but will allow discovery of virulence determinants that might further affect patient management.

Analysis of Clinical Isolates of Extended-Spectrum β-Lactamase-Producing Bacteria with Primer and Probe Sets Developed to Detect blaCTX-M, blaTEM, and blaSHV Using a Fully Automated Gene Detection System

In this study, we evaluated extended-spectrum β-lactamase (ESBL)-producing bacteria with the newly developed primer and probe sets to detect bla_CTX-M, bla_TEM, and bla_SHV using BD MAX^TM, a fully automated multiplex polymerase chain reaction assay system. In 36 isolates confirmed by whole-genome sequencing to have bla_CTX-M, bla_TEM, or bla_SHV, the developed primer and probe sets accurately detected each gene without being influenced by the presence of other β-lactamase genes. In nine control strains that do not harbor either bla_CTX-M, bla_TEM, or bla_SHV no cross-reaction was observed. In 191 strains phenotypically determined to be ESBL-producers by conventional antimicrobial susceptibility tests, 189 strains were blaC_TX-M-, bla_TEM-, or bla_SHV-positive as assessed by BD MAX^TM using the developed primer and probe sets, and two strains were negative for these genes. Whole-genome sequencing revealed that these two strains were phenotypically false-positive ESBL-producers. The accuracy of the primer and probe sets seems to be satisfactory, and they may be applicable to detect CTX-M-type ESBL-producing bacteria.

Evolving Rapid Methicillin-resistant Staphylococcus aureus Detection: Cover All the Bases

The dissemination of methicillin-resistant (MR) Staphylococcus aureus (SA) in community and health-care settings is of great concern and associated with high mortality and morbidity. Rapid detection of MRSA with short turnaround time can minimize the time to initiate appropriate therapy and further promote infection control. Early detection of MRSA directly from clinical samples is complicated by the frequent association of MRSA with methicillin-susceptible SA (MSSA) and coagulase-negative Staphylococcus (CoNS) species. Infection associated with true MRSA or MSSA is differentiated from CoNS, requires target specific primers for the presence of SA and mec A or nuc or fem A gene for confirmation of MR. Recently, livestock-associated MRSA carrying mec C variant complicates the epidemiology of MRSA further. Several commercial rapid molecular kits are available with a different combination of these targets for the detection of MRSA or MSSA. The claimed sensitivity and specificity of the currently available commercial kits is varying, because of the different target combination used for detection of SA and MR.

Evaluation of the automated Becton Dickinson MAX real-time PCR platform for detection of Pneumocystis jirovecii

AIM

We evaluated the performance of the automated quantitative BD MAX (Becton Dickinson) real-time PCR platform for detecting Pneumocystis jirovecii.

MATERIALS & METHODS

A total of 34 retrospective and 137 prospective samples were included.

RESULTS

Retrospectively, all (100%) positive samples were correctly detected by this platform compared with a nested PCR. Among prospective samples, the overall sensitivity, specificity, positive likelihood ratio and negative likelihood ratio were 92.6%, 94.5%, 17.0 and 0.1, respectively. All bronchoalveolar lavage fluid (BALF)/bronchial washing samples were correctly identified by this platform. Samples from patients with colonization had significantly higher median amplification cycle threshold values than patients with P. jirovecii pneumonia.

CONCLUSION

The quantitative BD MAX real-time PCR is a rapid and highly sensitive modality for detecting P. jirovecii, especially in samples from bronchoalveolar lavage fluid/bronchial washing fluid.

Development of a Real-Time PCR Protocol Requiring Minimal Handling for Detection of Vancomycin-Resistant Enterococci with the Fully Automated BD Max System

Vancomycin-resistant enterococci (VRE) are an important cause of health care-associated infections, resulting in significant mortality and a significant economic burden in hospitals. Active surveillance for at-risk populations contributes to the prevention of infections with VRE. The availability of a combination of automation and molecular detection procedures for rapid screening would be beneficial. Here, we report on the development of a laboratory-developed PCR for detection of VRE which runs on the fully automated Becton Dickinson (BD) Max platform, which combines DNA extraction, PCR setup, and real-time PCR amplification. We evaluated two protocols: one using a liquid master mix and the other employing commercially ordered dry-down reagents. The BD Max VRE PCR was evaluated in two rounds with 86 and 61 rectal elution swab (eSwab) samples, and the results were compared to the culture results. The sensitivities of the different PCR formats were 84 to 100% for vanA and 83.7 to 100% for vanB; specificities were 96.8 to 100% for vanA and 81.8 to 97% for vanB The use of dry-down reagents and the ExK DNA-2 kit for extraction showed that the samples were less inhibited (3.3%) than they were by the use of the liquid master mix (14.8%). Adoption of a cutoff threshold cycle of 35 for discrimination of vanB-positive samples allowed an increase of specificity to 87.9%. The performance of the BD Max VRE assay equaled that of the BD GeneOhm VanR assay, which was run in parallel. The use of dry-down reagents simplifies the assay and omits any need to handle liquid PCR reagents.

The use of molecular methods for the detection and identification of methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is a major pathogen in many hospitals and long-term care facilities as well as in the community. To limit the spread of MRSA, early detection and proper treatment are essential. Because conventional culture as gold standard is time consuming, new techniques such as PCR-based and hybridization assays have emerged for the rapid detection of MRSA. This review will focus on the currently available molecular-based assays and on their utility and performance for detection of S. aureus, of its virulence factors and of the markers for acquired resistance.

Development and Validation of a Laboratory-Developed Multiplex Real-Time PCR Assay on the BD Max System for Detection of Herpes Simplex Virus and Varicella-Zoster Virus DNA in Various Clinical Specimens

A multiplex real-time PCR (quantitative PCR [qPCR]) assay detecting herpes simplex virus (HSV) and varicella-zoster virus (VZV) DNA together with an internal control was developed on the BD Max platform combining automated DNA extraction and an open amplification procedure. Its performance was compared to those of PCR assays routinely used in the laboratory, namely, a laboratory-developed test for HSV DNA on the LightCycler instrument and a test using a commercial master mix for VZV DNA on the ABI7500fast system. Using a pool of negative cerebrospinal fluid (CSF) samples spiked with either calibrated controls for HSV-1 and VZV or dilutions of a clinical strain that was previously quantified for HSV-2, the empirical limit of detection of the BD Max assay was 195.65, 91.80, and 414.07 copies/ml for HSV-1, HSV-2, and VZV, respectively. All the samples from HSV and VZV DNA quality control panels (Quality Control for Molecular Diagnostics [QCMD], 2013, Glasgow, United Kingdom) were correctly identified by the BD Max assay. From 180 clinical specimens of various origins, 2 CSF samples were found invalid by the BD Max assay due to the absence of detection of the internal control; a concordance of 100% was observed between the BD Max assay and the corresponding routine tests. The BD Max assay detected the PCR signal 3 to 4 cycles earlier than did the routine methods. With results available within 2 h on a wide range of specimens, this sensitive and fully automated PCR assay exhibited the qualities required for detecting simultaneously HSV and VZV DNA on a routine basis.

Comparative Evaluation of Two PCR-Based Methods for Detection of Methicillin-Resistant Staphylococcus aureus (MRSA): Xpert MRSA Gen 3 and BD-Max MRSA XT

We compared two walk-away molecular diagnostic assays, the GeneXpert MRSA Gen 3 assay and the BD-Max MRSA XT assay. A total of 119 prospective swabs and 36 culture-positive samples were tested. Xpert MRSA Gen 3 had sensitivity of 95.7% and specificity of 100% versus 87.5% and 97.1% for BD-Max. The difference in agreement with the enriched culture results was significantly in favor of the Xpert assay (P < 0.02, McNemar nonparametric text).

Active Surveillance of Methicillin-Resistant Staphylococcus aureus Using a Fully Automated Molecular Test in an Emergency Medical Center

The prevention and control of methicillin-resistant Staphylococcus aureus (MRSA) are important, particularly in emergency units. The active surveillance of MRSA was prospectively performed at the emergency medical center of Nagasaki University Hospital. After obtaining nasal swab specimens, a fully automated molecular test (FAMT) and a culture-screening method were utilized for MRSA detection. A total of 150 patients were enrolled in the study, and 366 nasal swab specimens were obtained. MRSA was detected by culture in 11 (7.3%) patients including one new acquisition and by the FAMT in 34 (22.7%) patients including 13 new acquisitions. The sensitivity, specificity, positive predictive value, and negative predictive value of the FAMT at the patient level were 86.7, 85.2, 39.4, and 98.3%, respectively, when compared with the culture-based results. An FAMT can effectively detect MRSA colonization, which may remain undetected with the conventional method, and it may be useful in detecting newly acquired MRSAs.

Evaluation of the BD Max MRSA XT assay for use with different swab types

We evaluated the performance of the BD Max MRSA XT assay for use with different swab types. The 90% detection rates (95% confidence intervals) were 387 (97 to 1,551), 877 (238 to 3,230), 986 (183 to 5,287), 1,292 (328 to 5,078), 2,400 (426 to 13,518), and 5,848 (622 to 55,021) CFU/swab for Liquid Stuart, Liquid Amies, dry, Amies Gel without charcoal, ESwab collection, and Amies gel with charcoal swabs (Becton Dickinson), respectively. Amies Gel without charcoal, ESwab collection, and Amies gel with charcoal swabs had a tendency to be less sensitive, but none of the differences was statistically significant.

Validation of the FluoroType® MRSA assay for the rapid identification of methicillin-resistant Staphylococcus aureus directly from patient material

We performed the first evaluation study of the new HyBeacon based FluoroType(®) MRSA assay for the detection of MRSA directly from 617 patient specimens. Using culture as the reference method sensitivity and specificity were higher than 95%. Results were available within 2.5h, including DNA extraction.

Dual-site sampling improved detection rates for MRSA colonization in patients with cutaneous abscesses

Extranasal sites are common reservoirs of Staphylococcus aureus colonization and may be relevant for methicillin-resistant S. aureus (MRSA) screening and infection control strategies. The objective here was to determine whether inguinal specimens could also be screened using Xpert SA Nasal Complete assay for MRSA. Results were compared to broth enrichment culture. Among 162 consented adults seeking care in the emergency department for cutaneous abscesses, inguinal specimens were found positive for MRSA more often than nares specimens, 24% and 26% by PCR or culture, respectively, compared to 19% each by PCR or culture. Overall, 6% of adults colonized with MRSA would have been missed by nares screening alone. Compared to culture, Xpert SA Nasal Complete assay demonstrated sensitivity and specificity of 89% and 97%, respectively, for detecting nares and/or inguinal MRSA colonization. In conclusion, inguinal specimens were a more common reservoir for MRSA than nares specimens in this population of patients.

Comparison of ESwab with traditional swabs for detection of methicillin-resistant Staphylococcus aureus using two different walk-away commercial real-time PCR methods

The ESwab system (Copan Diagnostics) was evaluated as a nasopharyngeal specimen collection device to be used for methicillin-resistant Staphylococcus aureus (MRSA) detection by the GeneXpert and BD Max MRSA assays. Different MRSA strains and dilutions of each strain were tested in triplicate. ESwabs proved to be a suitable collection system for the two assays tested.

Rapid methods for detection of MRSA in clinical specimens

Antimicrobial susceptibility test methods such as disk diffusion, broth microdilution, and oxacillin screen plate require 24 h of incubation after having the organism growing in pure culture. Rapid and accurate identification of MRSA isolates is essential not only for patient care, but also for effective infection control programs to limit the spread of MRSA. In the last few years, several commercial rapid tests for detection of MRSA directly from nasal swabs and blood cultures have been developed for use in clinical laboratories. Real-time PCR and other molecular tests are gaining popularity as MRSA screening tests to identify patients who are candidates for contact precaution at the time of admission decreasing the risk for nosocomial transmission. These new methodologies have the advantage of a lower turnaround time than that of traditional culture and susceptibility testing and they are capable of detecting MRSA directly from nasal or wound swabs allowing rapid identification of colonized or infected patients. In addition, molecular methods able to detect and differentiate S. aureus and MRSA (SA/MRSA) directly from blood cultures are becoming a useful tool for rapid detection of bacteremia caused by MSSA and MRSA. This review focuses on the procedures for performing testing using rapid methods currently available for detection of MRSA directly from clinical specimens.

Detection and clinical relevance of Staphylococcus aureus nasal carriage: an update

Staphylococcus aureus nasal carriage is a well-defined risk factor of infection with this bacterium. The increased risk of S. aureus infection in nasal carriers is supported by the fact that the strains isolated from both colonization and infection sites are indistinguishable in most of the cases. Persistent nasal carriage seems to be associated with an increased risk of infection and this status could be defined now in clinical routine by using one or two quantitative nasal samples. There is evidence for supporting the detection of nasal carriage of S. aureus in patients undergoing cardiac surgery and in those undergoing hemodialysis in order to implement decolonization measures. More studies are needed to determine which carriers have the highest risk of infection and why decolonization strategies failed to reduce S. aureus infection in some other groups of patients.

Development and evaluation of a real-time PCR assay for detection of Pneumocystis jirovecii on the fully automated BD MAX platform

Pneumocystis jirovecii is an opportunistic pathogen in immunocompromised and AIDS patients. Detection by quantitative PCR is faster and more sensitive than microscopic diagnosis yet requires specific infrastructure. We adapted a real-time PCR amplifying the major surface glycoprotein (MSG) target from Pneumocystis jirovecii for use on the new BD MAX platform. The assay allowed fully automated DNA extraction and multiplex real-time PCR. The BD MAX assay was evaluated against manual DNA extraction and conventional real-time PCR. The BD MAX was used in the research mode running a multiplex PCR (MSG, internal control, and sample process control). The assay had a detection limit of 10 copies of an MSG-encoding plasmid per PCR that equated to 500 copies/ml in respiratory specimens. We observed accurate quantification of MSG targets over a 7- to 8-log range. Prealiquoting and sealing of the complete PCR reagents in conical tubes allowed easy and convenient handling of the BD MAX PCR. In a retrospective analysis of 54 positive samples, the BD MAX assay showed good quantitative correlation with the reference PCR method (R(2) = 0.82). Cross-contamination was not observed. Prospectively, 278 respiratory samples were analyzed by both molecular assays. The positivity rate overall was 18.3%. The BD MAX assay identified 46 positive samples, compared to 40 by the reference PCR. The BD MAX assay required liquefaction of highly viscous samples with dithiothreitol as the only manual step, thus offering advantages for timely availability of molecular-based detection assays.