Evaluation of Molecular Assays for Rapid Detection of Methicillin-Resistant Staphylococcus aureus

Abstract

The diagnostic sensitivities of the BD GeneOhm and Cepheid Xpert assays were compared using culture on log-serial dilutions of well-characterized methicillin-resistant Staphylococcus aureus (MRSA) and non-MRSA strains and on nasal and groin swabs from patients with histories of MRSA carriage. The sensitivities of GeneOhm and Xpert were high at 10 3 -CFU/ml MRSA concentrations (92.3% and 96.3%, respectively) although decreased considerably (<35%) at a 1-log-lower concentration. Unexpectedly, both assays also detected select coagulase-negative staphylococci, which requires further evaluation.

Detection of Methicillin-Resistant Staphylococcus aureus by a Duplex Droplet Digital PCR Assay

“…No nonstaphylococcal Gram-positive or Gram-negative bacterial species were detected by either the mecA or SA primerprobe sets with this assay. Previous studies have employed methicillin-resistant CoNS (MRCoNS) and methicillin-sensitive CoNS (MSCoNS) strains to evaluate false-positive detection with inhouse real-time PCR targeting the orfX-SCCmec junction (23), as well as the GeneXpert and GeneOhm assays (24,25,26). In our case, we lost no sensitivity or specificity for our assay when MRSA cultures were spiked with either MSSA or MSCoNS.…”

“…The Cepheid GeneXpert detected 610 CFU/ml, corresponding to 58 CFU/swab, compared to 750 CFU/ml and 40 CFU/ml with the direct and enrichment cultures (27). Subsequent studies have reported the LoD for MRSA in the GeneXpert assay to be 109.4 CFU/assay (24) and 3,300 CFU/ml and 250 CFU/swab (26). In comparison, our assays, both qPCR and ddPCR, detected MRSA at 4 ϫ 10 3 CFU/ml, equivalent to 3 ϫ 10 2 CFU/swab and 6 CFU/reaction mixture in a background of 10 5 CFU/ml of S. epidermidis.…”

Searching Biomarkers in the Sequenced Genomes of Staphylococcus for their Rapid Identification

“…In general, other highly conserved genes become helpful, which requires additional time and money. In most of the molecular approaches used for identifying Staphylococcus species, 27 genes have been widely used either individually or in combination [1,[17][18][19][20][22][23][24]. Of these 27 genes, only gyrA is among those which are common to all the genomes.…”

“…Here, S. aureus ATCC25923 act as a positive control, whereas S. epidermidis ATCC12228 is used as a negative control [5]. Identification of genetically diverse isolates of methicillin-resistant S. aureus (MRSA) has been successfully done using orfX-staphylococcal cassette chromosome mec-(SCCmec) based assays carrying blaZ, ccr, mecA, mecI, and mecR1 genes [1,[22][23][24][25]. A few more genes used for identifying S. epidermidis include: sodA, rpoB, tuf, gap, dnaJ, hsp40, and tRNA intergenic spacer [20].…”

Impacto de una técnica automatizada rápida en la identificación de SAMR/ERV en pacientes trasladados desde otros centros hospitalarios

“…Permite obtener resultados oportunos, en el plazo de una hora, luego de ser cargado con las muestras clínicas 8 . Ha sido validado en distintos escenarios clínicos, tanto para SARM 5,9,10 como para ERV 7,11 . Las ventajas comparativas de estas técnicas son su rapidez en los resultados, el ser operador En todos ellos se obtuvo muestras por hisopado nasofaríngeo e hisopado rectal y se indicó desde la admisión a la unidad, medidas de precaución adicional de contacto, las que se mantuvieron hasta disponer de resultados de cultivos negativos.…”