Table 2.

The number of E. coli O157:H7-positive samples and concentration ranges by steer after oral challenge

Group no.	Steer no.	E. coli O157:H7 challenge strain	Detection of E. coli O157:H7a				Range of CFU/ml of generic E. coli
			No. of positive samplesb	Day p.i. of first positive sample	Range of CFU/ml	No. of days p.i. to maximum CFU count
1	1	FRIK 47	1	2	1.1 × 101	2	1.0 × 103–5.8 × 104
	2	FRIK 47	0	NA	NA	NA	3.0 × 103–4.4 × 104
	3	FRIK 47	9	2	1.0 × 101–1.1 × 104	8	3.0 × 103–7.2 × 104
	4	FRIK 47	13	2	0.5 × 101–1.6 × 104	10	4.0 × 103–1.4 × 105
	5	FRIK 47	8	2	0.1 × 101–1.1 × 105	16	3.0 × 103–3.0 × 105
	6	FRIK 47	0	NA	NA	NA	1.0 × 103–9.0 × 104
2	7	FRIK 47	9	2	0.1 × 101–1.1 × 105	8	4.0 × 103–4.1 × 105
	8	FRIK 47	10	2	0.2 × 101–3.2 × 104	12	2.0 × 103–3.9 × 105
	9	FRIK 47	11	2	0.2 × 101–1.0 × 104	8	1.0 × 103–3.0 × 106
	10	FRIK 47	13	4	0.1 × 101–2.7 × 104	18	1.0 × 103–1.3 × 106
	11	FRIK 47	9	2	11–5.4 × 104	22	1.0 × 103–1.6 × 105
	12	FRIK 47	8	12	0.5 × 101–1.7 × 104	28	1.0 × 103–7.1 × 104
3	13	FRIK 1641	10	2	2.4 × 101–1.1 × 105	10	2.0 × 103–1.2 × 105
	14	FRIK 1641	5	22	5.4 × 101–1.1 × 105	26	1.0 × 103–9.6 × 105
	15	FRIK 1641	7	16	0.2 × 101–6.7 × 104	20	7.5 × 103–4.9 × 105
	16	FRIK 1641	0	NA	NA	NA	2.0 × 103–1.9 × 105
	17	FRIK 1641	7	2	0.2 × 101–4.5 × 103	6	3.0 × 103–1.2 × 105
	18	FRIK 1641	9	12	0.2 × 101–1.4 × 104	18	1.0 × 103–6.9 × 105
4	19	FRIK 2533	3	26	0.8 × 101–1.6 × 103	30	1.7 × 104–1.2 × 105
	20	FRIK 2533	1	30	4.7 × 102	30	1.0 × 103–7.0 × 104
	21	FRIK 2533	4	24	5.6 × 102–1.1 × 105	28	1.0 × 103–2.5 × 106
	22	FRIK 2533	1	2	1.8 × 101	2	1.0 × 103–1.3 × 106
	23	FRIK 2533	3	2	0.1 × 101–0.4 × 101	2	5.5 × 103–2.0 × 105
	24	FRIK 2533	2	24	0.6 × 101–9.0 × 102	30	1.7 × 104–9.7 × 105

^aEach steer was orally challenged with 10⁶ CFU of one of three E. coli O157:H7 strains, followed by collection of RAMS on alternate days over 30 days. NA, not available; p.i., postinoculation.

^bOver the 30-day trial period, 15 RAMS were collected from each steer.