bWe developed a multiplex SYBR green real-time PCR for the BD Max instrument (BD Diagnostics, Sparks, MD) to detect a panel of carbapenemases. The assay was evaluated with 152 consecutive isolates sent to the German National Reference Laboratory, and 65/65 of the carbapenemase-positive and 87/87 of the carbapenemase-negative strains were identified correctly. R apid detection and differentiation of carbapenemases are important for epidemiological investigations and infection control measures, thereby contributing to the prevention of global spread and optimization of antimicrobial therapy (1). Phenotypebased techniques can be used to identify carbapenemases (2-7), yet the specificity and sensitivity of those procedures vary. Other assays use matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF) (8), enzymatic measurements like the Carba NP test (9), and spectrophotometry (10). However, phenotypic and functional assays are often followed by molecular detection of the encoding carbapenemase genes. Molecular analysis is laborious, but fully automated PCR platforms might circumvent this restriction. Multiplexing allows detection in an economically reasonable manner (11).In our study, SYBR green real-time PCR on the BD Max system (BD Diagnostics, Sparks, MD) combined with melt curve analysis was developed to detect frequent carbapenemases in cultured isolates. Primers were mixed in two multiplex PCRs (master mix 1 [MM1] and MM2) that were selected on differences in the melting points of the amplicons. Panel 1 (MM1) amplified IMP-1, IMP-2, GES, KPC, VIM-2, and 16S rRNA as an internal amplification control. Panel 2 (MM2) detected OXA-23-like, VIM-1, OXA-48-like, and NDM (see Table S1 in the supplemental material). One to 2 colonies of a suspect isolate were added to 0.5 ml of 10 mM Tris-1 mM EDTA (pH 8.0) containing 0.1-mm glass beads (BioSpec, Bartlesville, OK). The sample was vortexed and incubated at 95°C for 10 min, and the cleared supernatant was directly used for the PCR. Each single reaction consisted of forward and reverse primers for each of the carbapenemases (final concentration, 0.25 M), a primer for 16S rRNA (only MM1, 0.05 M), 6.25 l of 2ϫ ABsolute SYBR green mix No Rox (Thermo Scientific, Schwerte, Germany), and PCR-grade water up to 10 l. Then 2.5 l of the strain lysate was combined with 10 l of the respective master mix and pipetted manually into a microfluidic BD Max PCR cartridge. The PCR was run in the PCR-only mode at 95°C for 15 min for 30 PCR cycles (98°C, 30 s; 56°C, 20 s; 72°C, 51.1 s) followed by melt curve analysis from 60°C to 100°C in 0.2°C steps.Using plasmids encoding the various carbapenemases, we observed clearly distinct melting temperatures ( Fig. 1A and B). Only IMP-1 and IMP-2 could not be differentiated. Melting temperatures were consistent and highly reproducible (Fig. 1C). The strains harboring a carbapenemase gene could be identified by comparison to the reference temperatures obtained with plasmids (an example is shown in Fig. 1D). Even the co...

We evaluated the fully automated molecular BD MAX Cdiff assay (BD Diagnostics) and the Xpert C. difficile test (Cepheid) for rapid detection of Clostridium difficile infection. Culture was done on chromogenic agar followed by matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry identification and toxin detection. Repeat testing was required for 1.8% and 6.0% of the BD MAX and Xpert tests, respectively. Sensitivities, specificities, positive predictive values (PPV), and negative predictive values (NPV) were 90.5%, 97.9%, 89.3%, and 98.1%, respectively, for BD MAX and 97.3%, 97.9%, 90.0%, and 99.5%, respectively, for Xpert. Clostridium difficile is the most important cause of hospitalacquired diarrhea. To implement timely infection control measures and appropriate treatment, rapid identification of toxigenic C. difficile is necessary (1). However, laboratory diagnostics remain challenging, as rapid test procedures relying on enzyme immunoassays (EIAs) show limited sensitivity (2), whereas the more-sensitive toxigenic culture and cytotoxicity assays are demanding and time-consuming. Two-step algorithms consisting of sensitive detection of glutamate dehydrogenase followed by a confirmatory toxin test have been proposed (2-4), yet the actual sensitivity has been questioned (5). Nucleic acid amplification techniques have been developed to combine low turnaround times with high sensitivity (6), but these assays require specific infrastructure. More recently, fully automated PCR assays that combine nucleic acid extraction, amplification, and detection have been developed. The Xpert C. difficile assay (Cepheid, Sunnyvale, CA) has high sensitivity and specificity and allows for accurate and rapid detection of Clostridium difficile infection (CDI). Recently, the BD MAX platform (BD Diagnostics, Franklin Lakes, NJ) has been made available; this allows for processing up to 24 samples in a fully automated PCR system. Clinical evaluation of the BD MAX Cdiff assay, based on detection of tcdB, has been published only for comparison with the BD GeneOhm assay (7).This study was conducted between April and July 2012 at the 2,000-bed tertiary care University Hospital Heidelberg. From 333 individual patients, 448 stool specimens, mostly (94.9%) soft or liquid, were examined. Samples were analyzed upon delivery or after overnight storage at 4°C. Specimens were analyzed by the BD MAX Cdiff assay and the Xpert C. difficile test. The standard technique used by the microbiology laboratory as the routine assay was the toxin A/B EIA (miniVIDAS; bioMérieux, Marcy l'Etoile, France). For the BD MAX Cdiff assay, stool samples were vortexed for 15 s and a 10-l loop was used to inoculate the sample tube. The Xpert C. difficile test and the miniVIDAS assay were done strictly in accordance with the manufacturers' protocols. As the reference method (8), stool samples were streaked onto chromID C. difficile agar plates (bioMérieux), incubated anaerobically at 35°C, and read after 24 and 48 h (9, 10). Suspicious col...

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.

We evaluated the new, fully automated molecular BD Max methicillin-resistant Staphylococcus aureus (MRSA) assay for detection of methicillin-resistant S. aureus in a low-prevalence (4.1%) setting. Sensitivity, specificity, and positive and negative predictive values were 93.9%, 99.2%, 83.8%, and 99.7%, respectively. The assay reported fewer unresolved results than the BD GeneOhm MRSA ACP assay. M olecular tests for the rapid detection of methicillin-resistantStaphylococcus aureus (MRSA) (10) are used in routine screening programs (6,24,25). Despite intrinsic limitations due to SCCmec variability (4,14,22,23), they are considered an important cornerstone in preventing spread of MRSA in health care facilities (2,7,12). Implementation of MRSA screening programs in hospitals demands greater automation to manage the increased volume of tests (24,25). The BD Max system (Becton, Dickinson Diagnostics, Sparks, MD) is a new, fully automated assay system for commercial and user-developed in vitro molecular diagnostic tests. It combines cell lysis, nucleic acid extraction, PCR setup, amplification, and detection in a single machine, thereby facilitating use of molecular tests. The aim of this study was to evaluate the BD Max MRSA assay, compared with the widely used BD GeneOhm MRSA achromopeptidase (ACP) assay (5,11,17,18,20), using direct and enriched culture as the reference method for detection of MRSA.The study was conducted at the 2,000-bed tertiary care University Hospital Heidelberg from October 2011 to January 2012. Screening swabs (BBL CultureSwab, liquid Stuart; BD) collected from patients admitted to intermediate and intensive care units, from patients admitted from external hospitals, and from surgical patients with wound infections were used. The primary specimen was nasal (91.2%; n ϭ 734) as approved for the test, but perianal (3.7%; n ϭ 30), wound (3.2%; n ϭ 26), and some other swabs were also included. Eight hundred five swabs from 690 individual patients were analyzed by using the BD GeneOhm MRSA ACP assay, BD Max MRSA test, and direct and enrichment culture. Swabs were first placed in 600 l BD GeneOhm MRSA ACP sample buffer and vortexed for 1 min. Ninety microliters was used for the BD GeneOhm MRSA ACP assay run on a SmartCycler II PCR system (Cepheid, Sunnyvale, CA). For the new BD Max MRSA assay, 200 l of the ACP sample buffer was inoculated into the BD Max sample buffer tube. Tubes were loaded into a rack containing the BD Max MRSA unitized reagent strips, extraction and master mix reagents. The BD Max executes the entire test in a fully automated mode. Each day an external positive control (90 l of the hydrated BD GeneOhm MRSA positive control) was included. A negative water control was tested on a weekly basis. Unresolved samples from both molecular tests were reanalyzed once from the sample buffer tube. From the remaining ACP sample buffer, 100 l was removed and directly streaked onto cefoxitin-containing BBL CHROMagar MRSA agar plates (BD), which were inspected after 24 h and 48 h. Moreover, 100 l ...

bWe evaluated the performance of the BD Max StaphSR assay for the direct detection of Staphylococcus aureus from blood culture medium. In a two-center trial, 155 blood cultures from the BD Bactec FX system and 212 from the bioMérieux BacT/Alert system were tested; 170 bottles yielded S. aureus, and all were identified correctly by the BD Max StaphSR assay. The assay required approximately 2.5 h, thus allowing rapid identification of blood cultures flagged positive. The BD Max StaphSR assay (BD, Quebec, Canada) is a fully automated, qualitative, in vitro diagnostic test for the direct detection of Staphylococcus aureus and methicillin-resistant S. aureus (MRSA) in patients at risk for nasal colonization. The test uses real-time PCR for the amplification of three DNA targets, i.e., SCCmec right-extremity junction (MREJ), thermostable nuclease (nuc), and methicillin resistance (mecA and mecC). Positivity for MREJ and mecA/mecC is required for the result "MRSA," and detection of nuc or MREJ without mecA/mecC is interpreted as "positive for S. aureus." The BD Max StaphSR assay was shown to have excellent sensitivity (96.4%) and specificity (93.6%), compared to combined direct and enriched cultures, for detection of S. aureus from anterior nares samples (1). In this study, we tested the performance of the StaphSR assay with a different sample type, namely, positive blood culture medium with Gram-positive cocci in clusters.Bloodstream infections often result in the need for intensive care and are associated with high mortality rates and large economic burdens (2). S. aureus is one of the main causes of bloodstream infections (3, 4). Rapid identification of positive blood cultures is a prerequisite for timely targeted treatment of patients with sepsis (5-7). Quick differentiation of S. aureus from coagulase-negative Staphylococcus (CoNS) can reduce the costs of patient care and decrease hospitalization times (8). The use of molecular assays for direct detection of S. aureus in blood culture bottles has been shown to allow rapid diagnosis of S. aureus septicemia, which might improve patient treatment (6, 9, 10). The recently introduced BD Max system allows fully automated realtime PCR, but the currently available BD Max StaphSR assay is CE marked and FDA cleared only for use with nasal swabs (11).In a first stage, we tested the use of the StaphSR assay with blood culture bottles (Bactec Plus Aerobic/F or Bactec Plus Anaerobic/F) that had been artificially inoculated with 1,000 CFU of MRSA, methicillin-susceptible S. aureus (MSSA), or methicillinresistant coagulase-negative Staphylococcus (MR-CoNS). After bottles were flagged positive, aliquots from those bottles were tested by inoculating the sample buffer tube (SBT) of the assay.The blood culture bottles were tested again after an additional 18 to 24 h of incubation, to mimic delayed analysis and to ensure that high DNA levels did not result in competition with any of the PCR target amplifications. We tested three volumes, i.e., 15, 50, and 100 l. All spiked blood cultu...

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. The BD Max MRSA XT kit (BD, Quebec, Canada) allows detection of methicillin-resistant Staphylococcus aureus (MRSA) DNA from nasal swabs in patients at risk for nasal colonization. The assay is used with the fully automated BD Max instrument (BD, Sparks, MD), which combines nucleic acid extraction, PCR setup, and PCR. The kit uses real-time PCR and fluorigenic hybridization probes to detect mecA or mecC together with staphylococcal cassette chromosome integration (SCCmec)-orfX. It is an improved MRSA assay that, by the combined detection of both targets, increases specificity (1, 2). The previous BD Max MRSA assay has been tested in clinical settings and proved to be a sensitive assay for the identification of MRSA carriers (3, 4). Rapid molecular detection of MRSA has been introduced into clinical screening programs (5, 6) and is considered an important means of early infection control to prevent the spread of MRSA (7,8). So far the assay has been approved for use only with liquid Stuart medium transport swabs (BBL CultureSwab Liquid Stuart [BD], Venturi Transystem Swab Liquid Stuart [Copan Diagnostics, Murrieta, CA]). Clearly, different swabs can affect the performance of molecular assays (9). Recent data indicate that ESwab collection systems are also compatible with the BD Max MRSA assay (10). We therefore intended to examine the analytical sensitivity of the BD Max MRSA XT assay with six different swab types that are commonly used in hospitals in Germany.We compared the following BBL CultureSwabs (BD): (i) Liquid Stuart (catalog no. 220099), (ii) Liquid Amies (220093), (iii) dry (220115), (iv) Amies gel without charcoal (22016), (v) Amies gel with charcoal (220121), and (vi) BD ESwab collection kit (220245). We evaluated the performance of the assays by mimicking the sampling process as follows: a 0.5 McFarland standard bacterial suspension was prepared from MRSA strain NCTC10442 (SCCmec type I), and then 1:4 dilutions from 6.25E4 to 2.44E2 CFU/ml were prepared. In this study, 100-l aliquots were plated on blood agar, counted after 24 h of incubation, and used for CFU calculations. A 50-l aliquot of each of five 1:4 dilutions was pipetted into an Eppendorf tube. The various swabs were placed into the Eppendorf tubes and left there until the suspension was completely absorbed. After soaking, the swabs were added back to the transport system for 20 min to allow them to be in contact with the different trans...

. 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.