TABLE 2.

Comparison of three recovery methods for detection of Bacillus anthracis from spiked swabs by real-time PCR

Recovery methoda	Average CT (mean ± SD)b at each time point for each PCR target
	1 day			7 days			28 days
	Chromosome	pXO1	pXO2	Chromosome	pXO1	pXO2	Chromosome	pXO1	pXO2
SETS	23.3 ± 0.07	22.8 ± 0.14	22.5 ± 0.14	22.9 ± 0.08	21.3 ± 0.13	21.6 ± 0.14	22.9 ± 0.20	21.6 ± 0.17	21.9 ± 0.33
Sonication	23.6 ± 0.09	22.5 ± 0.09	22.3 ± 0.08	23.3 ± 0.09	21.9 ± 0.14	21.2 ± 0.09	23.0 ± 0.12	21.2 ± 0.14	21.7 ± 0.31
Vortex	23.5 ± 0.05	22.5 ± 0.10	22.5 ± 0.09	23.6 ± 0.08	21.9 ± 0.21	22.4 ± 0.09	23.2 ± 0.15	21.7 ± 0.02	22.0 ± 0.31

^aA total of 12 nylon-flocked swabs each were spiked with 10 μl virulent B. anthracis cells at a concentration of 10⁷ CFU/ml, and the three recovery methods were compared at 1, 7, and 28 days postspiking.

^bThe eluted cell suspensions from each swab underwent automated DNA purification with the MagNA Pure Compact, followed by real-time PCR analysis. The average C_T values (mean ± standard deviation) are shown for DNA tested in triplicate using the real-time PCR assay described by Hoffmaster et al. (16).