FIG. 1.

Amplification data obtained with the Xpert MRSA kit for two of the four MRSA isolates used in LoD assays (A and B), two replicates of S. aureus ATCC 25923 (C and D), and two replicates of an MRSA isolate (tested at 10⁶ CFU/ml) recovered from a specimen yielding a kit-negative result (E and F). All isolates demonstrated kit-negative results with appropriate amplification of the internal control. The amplification plots in panels A and B demonstrate an exponential rise in fluorescence emission that is consistent with amplification of the MRSA target, suggesting false-negative kit results. The amplification data shown in panel C are representative of results obtained with most replicates of S. aureus ATCC 25923, but on some occasions this MSSA isolate yielded a plot suggestive of MRSA target amplification (panel D). The data shown in panels E and F were obtained from an MRSA isolate tested at a bacterial concentration of 10⁶ CFU/ml on two separate occasions. While both replicates yielded kit-negative results, one replicate demonstrated evidence of MRSA target amplification (panel F).