An international, prospective, multicenter evaluation of the combination of AdvanDx Staphylococcus QuickFISH BC with mecA XpressFISH for detection of methicillin-resistant Staphylococcus aureus isolates from positive blood cultures.

Sepsis caused by Staphylococcus aureus is a major health problem worldwide. Better outcomes are achieved when rapid diagnosis and determination of methicillin susceptibility enable early optimization of antimicrobial therapy. Eight large clinical laboratories, seven from the United States and one from Scotland, evaluated the combination of the Staphylococcus QuickFISH BC and the new mecA XpressFISH assay (both AdvanDx, Woburn, MA, USA) for the detection of methicillin-resistant S. aureus in positive blood cultures. Blood cultures flagged as positive by automated blood culture instruments and demonstrating only Gram-positive cocci in clusters on Gram stain were tested by QuickFISH, a 20-min assay. If only S. aureus was detected, mecA XpressFISH testing followed. The recovered S. aureus isolates were tested by cefoxitin disk diffusion as the reference method. The QuickFISH assay results were concordant with the routine phenotypic testing methods of the testing laboratories in 1,211/1,221 (99.1%) samples and detected 488/491 S. aureus organisms (sensitivity, 99.4%; specificity, 99.6%). Approximately 60% of the samples (730) contained coagulase-negative staphylococci or nonstaphylococci as assessed by the QuickFISH assay and were not tested further. The 458 compliant samples positive exclusively for S. aureus by the QuickFISH assay were tested by the mecA XpressFISH assay, which detected 209 of 211 methicillin-resistant S. aureus organisms (sensitivity, 99.1%; specificity, 99.6%). The mecA XpressFISH assay also showed high reproducibility, with 534/540 tests performed by 6 operators over 5 days achieving reproducible results (98.9% agreement). The combination of the Staphylococcus QuickFISH BC and mecA XpressFISH assays is sensitive, specific, and reproducible for the detection of methicillin-resistant S. aureus and yields complete results in 2 h after the blood culture turns positive.

Evaluation of the Biofire FilmArray meningitis/encephalitis assay for the detection of Cryptococcus neoformans/gattii.

OBJECTIVES: Cryptococcal meningitis (CM) remains an important cause of morbidity and mortality among immunocompromised patients. Laboratory diagnostics for CM includes antigen detection, staining and culture. Data on the performance of the Biofire® FilmArray® meningitis/encephalitis (ME) panel for detecting Cryptococcus neoformans/gattii is limited, with several reports describing false negativity for this target. METHODS: A retrospective analysis of 1384 physician-ordered ME panel tests ordered between January 2017 to October 2018 was performed. ME panel results were compared to cerebrospinal fluid (CSF) cryptococcal antigen (CrAg) and CSF culture testing and clinical significance of cryptococcal detection was determined. RESULTS: There were 34 patients positive for cryptococcal detection by either ME panel, CSF CrAg or CSF culture in 2.7% of CSF specimens tested (38/1384). Of the 34 patients positive for cryptococcal detection, 85.3% were human immunodeficiency virus positive (29/34). The ME panel detected 32/38 (84.2%) cryptococcal-positive specimens, culture detected 28/38 (73.7%) and CSF CrAg was positive in 37/38 specimens (97.4%). The ME panel had a sensitivity and specificity of 96.4% (95% CI 81.7-99.9%) and 99.6% (95% CI 99.2-99.9%) compared with culture, and 83.8% (95% CI 68.0-93.8%) and 99.9% (95% CI 99.6-100.0%) compared to CSF CrAg testing, respectively. CrAg titres were lower among ME panel-negative, culture-negative specimens compared with ME panel-positive, culture-negative specimens (reciprocal median end-point titres of 128 ± 60 vs. 1920 ± 1730, p 0.04). All five CrAg-positive, ME panel- and culture-negative specimens were obtained from previously treated CM patients. DISCUSSION: The ME panel had high correlation with CSF culture and a somewhat lower correlation with CSF CrAg testing. The potential utility of using negative ME panel test results to predict culture sterility among patients undergoing treatment for CM warrants further study.

Emergence of dalbavancin non-susceptible, vancomycin-intermediate Staphylococcus aureus (VISA) after treatment of MRSA central line-associated bloodstream infection with a dalbavancin- and vancomycin-containing regimen.

OBJECTIVES: Dalbavancin is a long-acting lipoglycopeptide with activity against gram-positives, including methicillin-resistant Staphylococcus aureus (MRSA). The potential for lipoglycopeptides, with half-lives greater than 1 week, to select for resistance is unknown. Here we explore a case of MRSA central line-associated bloodstream infection in which dalbavancin and vancomycin non-susceptibility emerged in a urine isolate collected after the patient was treated with vancomycin and dalbavancin sequentially. METHODS: Isolates from blood and urine underwent susceptibility testing, and whole genome sequencing (WGS). The blood isolate was subjected to successive passage in vitro in the presence of escalating dalbavancin concentrations and the emergent isolate was subjected to repeat susceptibility testing and WGS. RESULTS: The blood isolate was fully susceptible to vancomycin; however, MICs of the urine isolate to dalbavancin, vancomycin, telavancin, and daptomycin were at least fourfold higher than the blood-derived strain. Both strains were indistinguishable by spa and variable number tandem repeat (VNTR) typing, and WGS revealed only seven variants, indicating clonality. Four variants affected genes, including a 3bp in-frame deletion in yvqF, a gene which has been implicated in glycopeptide resistance. Vancomycin and dalbavancin non-susceptibility emerged in the blood isolate after successive passage in vitro in the presence of dalbavancin, and WGS identified a single non-synonymous variant in yvqF. CONCLUSIONS: This is the first case in which VISA has emerged in the context of a dalbavancin-containing regimen. The selection for cross-resistance to vancomycin in vitro by dalbavancin exposure alone is troubling. Clinicians should be aware of the possibility for emergence of dalbavancin non-susceptibility and glycopeptide cross-resistance arising following therapy.