FIG. 4.

Shedding levels over time of E. coli O157:H7 acid-resistant (□) and AS (▪) strains. Calves were inoculated with 10¹⁰ total CFU containing an equal mixture of stationary-phase-grown EK274 cells (AR) and logarithmic-grown EF501 cells (AS) on day 0. Fecal samples were cultured daily beginning 1 day postinoculation. Colony counts are displayed as the means of four calves. Bars indicate standard deviation of mean log₁₀ CFU/gram values. Asterisks indicate significant difference between shedding of acid-resistant and AS strains at P < 0.05 using repeated measures analysis of variance. Specimens containing <10³ CFU/g of feces were below the level needed for accurate enumeration.