Table 3.

mRV-PCR and culture method results for tap water samples seeded with B. atrophaeus spores.

Sample volume (L)	Step where spores were seeded1	Number of spores expected in each analysis (13 mL)2	mRV-PCR method		Culture method	Results agree?
			Delta Ct	Present/Absent	Membrane filtration (cfu/13 mL)
100	Concentrate	55	14.77	Present	46	Yes
100	Concentrate	29	16.19	Present	23	Yes
100	Concentrate	14	17.31	Present	6	Yes
100	Concentrate	6	15.97	Present	3	Yes
100	Concentrate	3	14.63	Present	<3	No
100	Concentrate	NS	0.00	Absent	<3	Yes
50 + sediment3	Concentrate	25	15.22	Present	>1	Yes
10	Retentate	3700	22.55	Present	2600	Yes
10	Retentate	380	17.36	Present	350	Yes
10	Retentate	25	25.47	Present	28	Yes
10	Retentate	37	22.87	Present	29	Yes
10	Retentate	6	24.82	Present	2	Yes
10	Retentate	<6	18.25	Present	<1	No
100	Retentate	3800	28.77	Present	3100	Yes
100	Retentate	470	16.36	Present	340	Yes
100	Retentate	18	14.44	Present	51	Yes
100	Retentate	31	22.29	Present	50	Yes
100	Retentate	18	15.81	Present	5	Yes
100	Retentate	<6	0.00	Absent	1	No
100	Sample	600	27.60	Present	200	Yes
100	Sample	650	28.91	Present	390	Yes
100	Sample	350	24.98	Present	230	Yes
100	Sample	NS	0.00	Absent	<1	Yes
100	Sample	8	10.83	Present	19	Yes
100	Sample	120	13.81	Present	33	Yes
100	Sample	1200	12.37	Present	270	Yes

Acronyms: mg/L, millligrams per liter; Ct, cycle threshold; cfu/mL, colony forming units per milliliter; <, less than; NS, not seeded.

¹Concentrate, spores were seeded after concentration by ultrafiltration and centrifugation; Retentate, spores were seeded after concentration by ultrafiltration and before centrifugation; Sample, spores were seeded before concentration by ultrafiltration and centrifugation.

²The seeded, concentrated sample was split equally between the mRV-PCR and culture method. This value represents the expected number of spores to be present for each analysis, based on the concentration of spores seeded into the sample.

³A 50-L tap water sample amended with 13.4 g of river sediment.