Foodborne Gastroenteritis Caused by Escherichia coli
643
Stx2 strains.
74 Of the 51 positive colonies, 5 were Stx1, 34 were Stx2, and 12 were Stx1 and Stx2. The
eight meat, poultry, and seafood products gave the following positive results: 63% of 8 veal, 48% of
21 lamb, 23% of 60 beef, 18% of 51 pork, 12% of 33 chicken, 10% of 62 fish, 7% of 15 turkey, and
4.5% of 44 shellfish.
74
In their baseline studies of bacteria in or on beef and poultry carcasses and ground beef, the U.S. Department of Agriculture (USDA) findings are as follows: no E. coli O157:H7 was found in 563 samples
of ground beef;
85 none on 1297 broiler carcasses;
86 and none on the carcasses of 2112 cows and bulls.
87
From steer and heifer carcasses, 4 of 2081 contained this organism at a maximum level of 0.93 most
probable number (MPN)/cm
2 .
88 Biotype 1 was found on 96% of these carcasses at numbers <10/cm
2 .
When added to radish seeds and incubated at 18–25
◦ C for 7 days, the organism was found in inner
tissues and stomata of cotyledons as well as on the outer surfaces.
39 It could not be removed by
immersion in 0.1% HgCl 2 .
Immediately following the Pacific Northwest outbreak in 1993, the Food Safety and Inspection
Service (FSIS) of the USDA undertook a multistate study of the prevalence and incidence of EC
O157:H7 in both beef and dairy herds. The largest number per gram found was 15, and the average
was around 4 cfu/g of fresh beef. Between 1994 and September 1998, the USDA in a nationwide
survey found EC O157:H7 in 23 of 23,900 ground beef samples, about 1/1000 samples. The incidence
and prevalencee of E. coli 0157:H7 and generic strains on meats and poultry are listed in Chapters 4,
5, 6, and 9.
In a risk assessment study of E. coli O157:H7 in hamburger, the three highest ranked predictive
factors relative to the probability of illness by this organism from hamburgers were concentration of
the organism in animal feces, host susceptibility, and carcass contamination.
11
Prevalence in Dairy Cattle
Because more foodborne outbreaks of EHEC syndromes have been linked to beef than to any other
single food source, it is widely believed that dairy herds are the primary reservoirs of these organisms.
Whether this is true or not, dairy herds have been the subject of most studies. Overall, weaned calves
have a higher prevalence of EHEC strains in their feces than either calves or adult cattle, and this is
not surprising when one considers that the rumen biota of weaned calves is not as well established as
for adult cattle. For example, of 1266 fecal samples from calves, heifers, and cows, only 18 (1.42%)
were positive for EC O157:H7.
93 Only 1 of 662 cow samples was positive, whereas 5 of 210 calf and
12 of 394 heifer feces samples were positive.
Overall, these bacteria have been isolated from 0.3 to 2.2% of fecal samples collected from healthy
calves or cattle in the United States, Canada, the United Kingdom, Germany, and Spain.
19 Of 23 raw
milk samples examined from two farms, only 1 was positive for EC O157:H7. Using DNA probes,
28 different EHEC strains were found by these investigators with 8% from adult cows and 19% from
heifers and calves.
93 Overall, EHEC strains were found on 80% of the farms examined. In another
study of dairy herd fecal samples from 14 states in 1993, 31 of 965 (3.2%) were positive for EC
O157:H7.
97 Of these 31, 16 were positive by direct plating with numbers of 10
3 –10
5 cfu/g, whereas
the other 15 were positive by enrichment only. Regarding toxin types, 19 of the 31 isolates produced
Stx1 and Stx2, whereas 12 produced Stx2 only.
97
In a study of experimentally infected calves and adult cattle, Cray and Moon
17 found that calves
shed inoculated EC O157:H7 longer than adult cows, that the inoculated organisms were restricted to
the gastrointestinal tract, and that most cattle infected with EC O157:H7 remain clinically normal. The
infectious dose of in-vitro-grown EC O157:H7 for adult cattle was believed to be ≥10
7 cfu.
17 In an
earlier study in Germany, 10.8% of 1387 isolates from 259 healthy adult cattle hybridized with DNA
643
Stx2 strains.
74 Of the 51 positive colonies, 5 were Stx1, 34 were Stx2, and 12 were Stx1 and Stx2. The
eight meat, poultry, and seafood products gave the following positive results: 63% of 8 veal, 48% of
21 lamb, 23% of 60 beef, 18% of 51 pork, 12% of 33 chicken, 10% of 62 fish, 7% of 15 turkey, and
4.5% of 44 shellfish.
74
In their baseline studies of bacteria in or on beef and poultry carcasses and ground beef, the U.S. Department of Agriculture (USDA) findings are as follows: no E. coli O157:H7 was found in 563 samples
of ground beef;
85 none on 1297 broiler carcasses;
86 and none on the carcasses of 2112 cows and bulls.
87
From steer and heifer carcasses, 4 of 2081 contained this organism at a maximum level of 0.93 most
probable number (MPN)/cm
2 .
88 Biotype 1 was found on 96% of these carcasses at numbers <10/cm
2 .
When added to radish seeds and incubated at 18–25
◦ C for 7 days, the organism was found in inner
tissues and stomata of cotyledons as well as on the outer surfaces.
39 It could not be removed by
immersion in 0.1% HgCl 2 .
Immediately following the Pacific Northwest outbreak in 1993, the Food Safety and Inspection
Service (FSIS) of the USDA undertook a multistate study of the prevalence and incidence of EC
O157:H7 in both beef and dairy herds. The largest number per gram found was 15, and the average
was around 4 cfu/g of fresh beef. Between 1994 and September 1998, the USDA in a nationwide
survey found EC O157:H7 in 23 of 23,900 ground beef samples, about 1/1000 samples. The incidence
and prevalencee of E. coli 0157:H7 and generic strains on meats and poultry are listed in Chapters 4,
5, 6, and 9.
In a risk assessment study of E. coli O157:H7 in hamburger, the three highest ranked predictive
factors relative to the probability of illness by this organism from hamburgers were concentration of
the organism in animal feces, host susceptibility, and carcass contamination.
11
Prevalence in Dairy Cattle
Because more foodborne outbreaks of EHEC syndromes have been linked to beef than to any other
single food source, it is widely believed that dairy herds are the primary reservoirs of these organisms.
Whether this is true or not, dairy herds have been the subject of most studies. Overall, weaned calves
have a higher prevalence of EHEC strains in their feces than either calves or adult cattle, and this is
not surprising when one considers that the rumen biota of weaned calves is not as well established as
for adult cattle. For example, of 1266 fecal samples from calves, heifers, and cows, only 18 (1.42%)
were positive for EC O157:H7.
93 Only 1 of 662 cow samples was positive, whereas 5 of 210 calf and
12 of 394 heifer feces samples were positive.
Overall, these bacteria have been isolated from 0.3 to 2.2% of fecal samples collected from healthy
calves or cattle in the United States, Canada, the United Kingdom, Germany, and Spain.
19 Of 23 raw
milk samples examined from two farms, only 1 was positive for EC O157:H7. Using DNA probes,
28 different EHEC strains were found by these investigators with 8% from adult cows and 19% from
heifers and calves.
93 Overall, EHEC strains were found on 80% of the farms examined. In another
study of dairy herd fecal samples from 14 states in 1993, 31 of 965 (3.2%) were positive for EC
O157:H7.
97 Of these 31, 16 were positive by direct plating with numbers of 10
3 –10
5 cfu/g, whereas
the other 15 were positive by enrichment only. Regarding toxin types, 19 of the 31 isolates produced
Stx1 and Stx2, whereas 12 produced Stx2 only.
97
In a study of experimentally infected calves and adult cattle, Cray and Moon
17 found that calves
shed inoculated EC O157:H7 longer than adult cows, that the inoculated organisms were restricted to
the gastrointestinal tract, and that most cattle infected with EC O157:H7 remain clinically normal. The
infectious dose of in-vitro-grown EC O157:H7 for adult cattle was believed to be ≥10
7 cfu.
17 In an
earlier study in Germany, 10.8% of 1387 isolates from 259 healthy adult cattle hybridized with DNA