644 Modern Food Microbiology
Figure 27–2 The effect of hay on the total numbers of colonic E. coli in cattle that had been consuming the
90% grain diet. (A) Cattle were switched from 90% grain to hay on day 0. (B) The numbers of E. coli were
able to survive acid shock (pH 2.0, Luria broth, 1 hour). The bars indicate standard deviations of the mean (three
animals, one replicate per animal, two independent experiments). The dotted lines show the detection limit of
the enumerations. Source: Reprinted with permission from Diez-Gonzalez et al.,
21 copyright c
1998, American
Association for the Advancement of Science.
probes for Stx1 and Stx2.
58 Hybridization to Stx1 alone occurred with 15.8% of the SLT positives,
whereas 38.6% hybridized to Stx2 alone.
A number of studies have addressed the general microbial ecology of E. coli O157:H7 in the
intestines and feces of bovines relative to animal rations. In one study, with cattle on high roughage for
4 days, there was a significantly lower number of E. coli O157:H7/g of feces but after 48 hours of fasting,
they had significantly higher numbers.
41 The high-roughage ration consisted of 50% unprocessed
alfalfa hay and 50% corn silage (monensin was absent). In another study, the presence of E. coli
O157:H7 was significantly associated with corn silage feeding.
33 These investigators found E. coli
O157:H7 to be higher in herds that were fed monensin and other additives and suggested that this
ionophore could be a factor in the prevalence of this organism in cattle feces. In yet another study,
cattle fed mostly grain had lower colonic pH and more acid-resistant E. coli than those fed only
hay.
21 The grain-fed cattle had about 10
6 -fold more acid-resistant E. coli than those fed hay, and the
Figure 27–2 The effect of hay on the total numbers of colonic E. coli in cattle that had been consuming the
90% grain diet. (A) Cattle were switched from 90% grain to hay on day 0. (B) The numbers of E. coli were
able to survive acid shock (pH 2.0, Luria broth, 1 hour). The bars indicate standard deviations of the mean (three
animals, one replicate per animal, two independent experiments). The dotted lines show the detection limit of
the enumerations. Source: Reprinted with permission from Diez-Gonzalez et al.,
21 copyright c
1998, American
Association for the Advancement of Science.
probes for Stx1 and Stx2.
58 Hybridization to Stx1 alone occurred with 15.8% of the SLT positives,
whereas 38.6% hybridized to Stx2 alone.
A number of studies have addressed the general microbial ecology of E. coli O157:H7 in the
intestines and feces of bovines relative to animal rations. In one study, with cattle on high roughage for
4 days, there was a significantly lower number of E. coli O157:H7/g of feces but after 48 hours of fasting,
they had significantly higher numbers.
41 The high-roughage ration consisted of 50% unprocessed
alfalfa hay and 50% corn silage (monensin was absent). In another study, the presence of E. coli
O157:H7 was significantly associated with corn silage feeding.
33 These investigators found E. coli
O157:H7 to be higher in herds that were fed monensin and other additives and suggested that this
ionophore could be a factor in the prevalence of this organism in cattle feces. In yet another study,
cattle fed mostly grain had lower colonic pH and more acid-resistant E. coli than those fed only
hay.
21 The grain-fed cattle had about 10
6 -fold more acid-resistant E. coli than those fed hay, and the