Table 2.

Number of E. coli O157 CFU in rumen fluid of hay-fed heifers after oral dose

Heifera	E. coli O157:H7 CFU/ml of rumen fluid after oral doseb
	1 h	4 h	Day 1	Day 2	Day 3	Day 7
V1	8.60 × 105	5.10 × 103	1.55 × 103	3.10 × 101	N	N
V2	2.47 × 105	3.70 × 104	7.90 × 102	1.00 × 102	N	N
V3	1.13 × 106	2.70 × 104	1.12 × 103	5.00 × 101	5.00 × 101	W+M+
V4	7.50 × 105	2.56 × 104	4.00 × 102	1.80 × 102	1.60 × 102	W+M+
V5	2.43 × 106	9.50 × 103	2.60 × 102	3.00 × 101	W+M+	N
V6	4.40 × 105	2.80 × 104	1.30 × 103	2.00 × 101	W+M+	W+M+
V7	1.75 × 106	4.40 × 103	7.10 × 102	7.00 × 101	N	N
V8	9.40 × 106	3.50 × 104	2.60 × 102	2.00 × 101	9.00 × 101	W+M+

^aEight 15-month-old Charolais heifers were challenged with an oral dose of 10¹⁰ CFU containing equal numbers of the parental strain and the sdiA mutant. Samples were taken (hour or day) postdose.

^bN, sample was negative by both direct and enrichment culture methods; W+M+, sample was positive only by enrichment culture and contained both the parental and the mutant strains. Bacterial culture data on grain-fed heifer have been previously published.