642 Modern Food Microbiology differences in thermal D values between different meat products, and the D60◦ C values (minutes) and products are noted below:2 0.45–0.47 0.37–0.55 0.38–0.55 0.55–0.58 Beef Pork sausage Chicken Turkey The D values increased with increasing fat content, and this is a well-established phenomenon (see Chapter 17) These findings support a previous study where D and z values for high-fat and lean beef were as follows:51 30.5% fat 2.0% fat D = 0.45 minute D = 0.30 minute z = 8.37◦ F z = 8.30◦ F In another study, an inoculum of ∼103 /g of strain O157:H7 in low-fat ground beef was destroyed when cooked to internal temperatures of 66◦ , 68◦ , or 72◦ C.25 A recent study on the thermal properties of EC O157:H7 in apple juice revealed that a 4-D process could be achieved by heating at 60◦ C for ∼1.6 minutes.78 This is based on D values at 52◦ C obtained from 20 separate trials that ranged from 9.5 to 30 minutes with a mean of 18 minutes and a z of 4.8◦ C Although EC O157:H7 cells became more heat sensitive in apple juice when l-malic acid was increased from 0.2 to 0.8%, or when pH was reduced from 4.4 to 3.6, benzoic acid at 1,000 ppm was the most effective additive in increasing heat sensitivity.78 The fate of EC O157:H7 along with Listeria monocytogenes and Salmonella Typhimurium in beef jerky was studied, and neither could be found in finished and dried products after 10 hours with inocula of ∼107 /g or after storage for weeks.36 Regarding radiation resistance of EHEC strains, there is no apparent basis for them to differ greatly from other enteric bacteria Using chicken and an EC O157:H7 strain, the D value at 5◦ C was 0.27 kGy, whereas at -5◦ C, D was 0.42 kGy.82 Employing a nonpathogenic strain of E coli, Fielding et al.26 found radiation D to be ∼0.34 kGy in broth with a pH around 7.0, but the D was 0.24 kGy when cells were grown at pH 4.0 prior to irradiation See Chapter 15 for more on irradiation of foods In apple juice, nonacid adapted strains had a range of 0.12–0.21 kGy but when acid-adapted, the values increased to 0.22–0.31 kGy.7 In regard to survival in ovine and bovine manure, E coli O157:H7 was found to survive in the former for 100 days at 4◦ or 10◦ C, and survival was unaffected by the possession of stx genes.45 Prevalence in Foods Overall, the incidence and prevalence of EHEC strains in meat, milk, poultry, and seafood products are highly variable Considerably more positives are found when DNA probes are used to detect for EHEC strains than when EC O157:H7 is tested alone The first published study on the prevalence in meats of EHEC strains was that of Doyle and Schoeni,22 who tested for EC O157:H7 and found this strain in 3.7% of 164 beef, 1.5% of 264 pork, 1.5% of 263 poultry, and 2.0% of 205 lamb samples In Thailand, EC O157:H7 was recovered from 9% of retail beef, 8–28% of slaughterhouse beef, and 11–84% of cattle fecal specimens.79 Although EC O157:H7 could not be recovered from sausage in the United Kingdom, a DNA probe gave positive results on 25% of 184 samples for other EHEC strains.77 None were found in 112 samples from 71 chickens.77 In a study of foods in the Seattle area following the 1993 outbreak, 17.3% of 294 foods were positive for colonies that contained Stx1 and/or Foodborne Gastroenteritis Caused by Escherichia coli 643 Stx2 strains.74 Of the 51 positive colonies, 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 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, of 2081 contained this organism at a maximum level of 0.93 most probable number (MPN)/cm2 88 Biotype was found on 96% of these carcasses at numbers 104 /g Human Disease Syndromes/Prevalence The prototype strain for the syndromes below is EC O157:H7 The H7 type was initially isolated in 1944 from a human diarrheal specimen, whereas the O157 type was first isolated and named in 1972 from diarrheal swine feces.66 However, the first O157:H7 strain was recovered in 1975 from a patient with bloody diarrhea Stx-producing strains of E coli were identified in 1977 in the United States61 and Canada44 Following its original isolation in 1975, the next recorded isolation of EC O157:H7 was in 1978, when it was recovered from diarrheal stools in Canada HUS and HC are caused by Stx-producing strains of E coli It has been estimated that from to 7% of infections by EC O157:H7 will develop HUS.31 HUS consists of hemolytic anemia, thrombocytopenia, and acute renal failure Although not directly linked to EHEC strains until 1985, HUS was first described in 1955 In a German study on the duration of shedding of EC O157:H7 in 53 children, the 28 children who had HC diarrhea shed the organism between and 62 days (median of 13), whereas the 25 who developed HUS shed organisms for 5–124 days (median of 21).42 HUS is associated more with strains that produce Stx2 alone than with those that produce Stx1, or Stx1 and Stx267 (see Chapter 22) Fifteen percent of 1275 individuals from which EHEC-positive cultures were recovered in the United Kingdom for the 3-year period 1989–1991 were reported as having developed HUS.83 Hemorrhagic colitis as a foodborne disease was first seen in 1982 in Oregon and Michigan, where in both instances victims had eaten sandwiches at a fast-food restaurant that contained undercooked ground beef.73 Of 43 patients, all had bloody diarrhea and severe abdominal cramps, with 63% experiencing nausea, 49% vomiting, but only 7% fever The mean incubation period was 3.8–3.9 days, and symptoms lasted for to more than days.73 From other outbreaks, the time of onset of symptoms ranged between 3.1 and days The recovery of the etiological agent from stools requires examination of specimens within several days after symptoms Stools tend to be negative for or more days after onset of illness.94 The bloody red stool is the telltale symptom for this syndrome and it reflects involvement of the etiological agent in the colon Fever is rare, and the infectious dose is believed to be as low as 10 cfu Many of the reported outbreaks and cases of HC associated with food and water are summarized in Table 27–2 Although most were caused by E coli O157:H7, the 1993 outbreaks in New Hampshire and Rhode Island that were traced to raw salads were caused by serotype O6:NM (NM = nonmotile) The first established foodborne outbreak of an Stx-producer other than E coli O157:H7 in the United States was serotype O104:H21, which was traced to contaminated pasteurized milk in 1994.13 Serotype 0111:NM was traced to semidry fermented sausage in South Australia in 1995, and in 1992 the same serotype was the first ever Stx-producing strain associated with HUS in Italy when nine cases with one death occurred.10 Table 27–2 Some of the Reported Foodborne and Waterborne Outbreaks Caused by Stx-Producing Strains of E coli Year Vehicle 1982 1982 1983 1983 1984 1985 1985 1986 1986 1987 1987 1987 1988 1988 1989 1990 1990 1991 1992 1993 Hamburger meat Hamburger meat Hamburger meat Hamburger meat Seafood Newberg Cold sandwiches/other∗ Raw potatoes Raw milk Hamburger meat Frozen beef patties Turkey rolls Ground beef/other∗ Roast beef Cooked frozen patties Water School lunch Roast beef Apple cider Unknown† Hamburger meat 1993 1993 1993 1994 1994 1994 1994 1995 1995 1996 1996 1996 Home-cooked burgers Garden salad‡ Tabouleh salad‡ Hamburgers Hamburgers (rare) Dry-cured salami Contaminated pasteurized milk Semidry fermented sausage† Salad bar lettuce Butcher shop foods White radish sprouts Apple cider (unpasteurized) 1997 1997 1998 1998 1998 1998 1998 1998 1998 1999 1999 2001 2002 2002a 2002 Alfalfa sprouts Ground beef Drinking water Water park play pool Fruit salads Cake Coleslaw Fresh cheese Coleslaw Well water Salad bar salads Raw goat’s milk Ground beef Locally produced apple juice Cotton candy, ice cream ∗ Also person-to-person † EC O111:NM The 23 victims had ‡ EC O6:NM.EC O104:H21 a Sorbitol-positive 0157:H-strains HUS Cases/Deaths Location 26/0 21/0 19/0 34/4 42/0 73/19 24/0 46/0 37/2 15/2 26/0 51/4 61/0 32/0 243/4 10/0 70/0 23/0 9/1 732/3 Oregon Michigan Alberta, Canada Nebraska Maine Ontario, Canada United Kingdom Ontario, Canada Washington Alberta, Canada United Kingdom Utah Wisconsin Minnesota Cabool, Missouri Montana North Dakota Massachusetts Italy Washington, Idaho, California, Nevada California Rhode Island New Hampshire New Jersey Virginia Washington, California Montana S Australia Montana Scotland Japan California, Colorado, Washington, British Columbia Michigan, Virginia Colorado Wyoming Georgia Wisconsin California Indiana Wisconsin North Carolina New York state Texas Canada Colorado + others Germany N Wales 10/0 47/– 121/0 46/0 20/0 23/0 17/0 23/1 >100/– ca 500 9492/3 28 108/0 15 114 26/1 47 20 33 55 142 775 58 28/5 64 24 ... Home-cooked burgers Garden salad‡ Tabouleh salad‡ Hamburgers Hamburgers (rare) Dry-cured salami Contaminated pasteurized milk Semidry fermented sausage† Salad bar lettuce Butcher shop foods White... isolates produced Stx1 and Stx2, whereas 12 produced Stx2 only.97 In a study of experimentally infected calves and adult cattle, Cray and Moon17 found that calves shed inoculated EC O157:H7 longer... for adult cattle was believed to be ≥107 cfu.17 In an earlier study in Germany, 10.8% of 1387 isolates from 259 healthy adult cattle hybridized with DNA 644 Modern Food Microbiology Figure 27–2