Rapid MRSA PCR on respiratory specimens from ventilated patients with suspected pneumonia: a tool to facilitate antimicrobial stewardship.

Methicillin-resistant Staphylococcus aureus (MRSA) is an important cause of pneumonia in ventilated patients. Our objective was to evaluate the GeneXpert MRSA/SA SSTI Assay (Xpert MRSA/SA) (Cepheid, Sunnyvale, CA) for use in lower respiratory tract (LRT) specimens for rapid MRSA detection and to determine the potentially saved antibiotic-days if a culture-based identification method was replaced by this assay. Remnant LRT samples from ventilated patients submitted to the microbiology laboratory for routine culture were tested using conventional culture and Xpert MRSA/SA. One hundred of 310 LRT specimens met the inclusion criteria. Ten samples were positive for MRSA by Xpert MRSA/SA, while six were positive by routine culture methods. Xpert MRSA/SA correctly identified 5/6 positive and 89/94 negative MRSA specimens, for a sensitivity of 83.3%, specificity of 94.7%, positive predictive value of 45.6%, and negative predictive value of 98.9%. The assay also correctly detected 3/3 positive and 90/97 negative methicillin-susceptible S. aureus (MSSA) specimens, for a sensitivity of 100%, specificity of 92.8%, positive predictive value of 30%, and negative predictive value of 100%. A total of 748 vancomycin and 305 linezolid antibiotic-days were associated with the enrolled specimens. Vancomycin and linezolid utilization could decrease by 68.4% and 83%, respectively, if discontinued 1 day after negative polymerase chain reaction (PCR) results. The Xpert MRSA/SA SSTI rapid MRSA PCR assay performed well in respiratory samples from ventilated patients with suspected pneumonia and has the potential to facilitate stewardship efforts such as reducing empiric vancomycin and linezolid therapy.

Comparison and optimization of two MALDI-TOF MS platforms for the identification of medically relevant yeast species.

The rapid identification of yeast is essential for the optimization of antifungal therapy. The objective of our study was to evaluate two matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) platforms, the bioMérieux VITEK MS (IVD Knowledgebase v.2.0) and Bruker Biotyper (software version 3.1), for the rapid identification of medically relevant yeast. One hundred and seventeen isolates, representing six genera and 18 species, were analyzed using multiple direct smear methods to optimize identification. Sequence analysis was the gold standard for comparison. Isolates were analyzed with VITEK MS using the direct smear method +/- a 25 % formic acid on-plate extraction. For Biotyper, isolates were analyzed using direct smear without formic acid, and with 25 % and 100 % formic acid on-plate extractions. When all methods were included, VITEK MS correctly identified 113 (96.6 %) isolates after 24 h with one misidentification, and Biotyper correctly identified 77 (65.8 %) isolates using a threshold of ≥2.0 with no misidentifications. Using a revised threshold of ≥1.7, Biotyper correctly identified 103 (88.0 %) isolates, with 3 (2.6 %) misidentifications. For both platforms, the number of identifications was significantly increased using a formic acid overlay (VITEK MS, p < 0.01; Biotyper, p < 0.001), and reducing the Biotyper threshold from ≥2.0 to ≥1.7 significantly increased the rate of identification (p < 0.001). The data in this study demonstrate that the direct smear method with on-plate formic acid extraction can be used for yeast identification on both MS platforms, and more isolates are identified using the VITEK MS system (p < 0.01).