Washing whole and cut produce by dipping or submerging in chlorinated water has a sanitizing effect, although reduction in microbial populations is minimal and is usually less than 100-fold. A study was undertaken to evaluate the efficacy of a spray application of chlorine in killing Salmonella, Escherichia coli O157:H7, Listeria monocytogenes, yeasts and molds, and total aerobic mesophilic microorganisms on whole apples, tomatoes, and lettuce leaves. Inoculated produce was treated (sprayed and then soaked) with water (control) or solutions containing 200 or 2,000 ppm of chlorine for 0, 1, 3, 5, or 10 min, rinsed with sterile water, and analyzed for populations (CFU/cm2) of target microorganisms. Compared to the control treatment, further reductions in numbers of pathogens of 0.35 to 2.30 log CFU/cm2 were achieved by treatment with chlorine. Chlorine was generally more effective at 2,000 ppm than at 200 ppm. Inactivation of microorganisms occurred essentially within 1 min after application of chlorine. These reductions are significant relative to populations of pathogenic microorganisms that may be present on produce. Spray application of chlorine to raw produce at food service or household levels may be a suitable, and more convenient, alternative to treatment by dipping or submersion.

Colonization of the ceca and contamination on carcasses of chickens by Campylobacter spp. was investigated. Samples were taken on the farm and after transport and holding. In the first set of experiments, 20 chickens, obtained from each of 10 broiler farms, were collected from houses containing 6- to 7-wk-old birds. Half of the birds were slaughtered at the farm; the other half were transported (10 birds per chicken coop) to a holding facility and killed within 16 to 18 h. The levels of Campylobacter spp. on the carcass and in the ceca were assessed. Ceca from birds in 9 of the 10 farms sampled were positive for Campylobacter spp. Colonization levels ranged from 10(4.11) to 10(7.28) cfu Campylobacter spp./g cecal matter, except on one farm, where the organism was not isolated. The mean count on the farm was 10(5.44) cfu Campylobacter spp./g cecal material, and after transport the mean was 10(6.15) cfu/g. Significant increases (P = .0085) in levels of Campylobacter spp. on the chicken carcasses occurred after transport. Levels of Campylobacter spp. enumerated from unprocessed chicken carcasses after transport averaged 10(7.11) per carcass, up from an average of 10(3.66) cfu per carcass of the farm. To further verify this observation, field trials were conducted to assess levels on carcasses before and after commercial transport. Employing five farms and 200 6-wk-old chickens, the above observations were confirmed: prior to transport 12.1% of the chickens harbored an average of 10(2.71) cfu per carcass, but after transport 56.0% of the chicken exteriors harbored an average of 10(5.15) cfu per carcass. The results of this study indicate that transport and holding prior to processing contributes to the Campylobacter spp. of > 10(4) cfu normally found on processed poultry carcasses.

The survival of unheated and heat-stressed (52؇C, 30 min) cells of Escherichia coli O157:H7 inoculated into tryptic soy broth (TSB) adjusted to various pHs (6.0, 5.4, and 4.8) with lactic acid and various water activities (a w s) (0.99, 0.95, and 0.90) with NaCl and incubated at 5, 20, 30, and 37؇C was studied. The performance of tryptic soy agar (TSA), modified sorbitol MacConkey agar (MSMA), and modified eosin methylene blue agar in supporting colony development of incubated cells was determined. Unheated cells of E. coli O157:H7 grew to population densities of 10 8 to 10 9 CFU ml ؊1 in TSB (pHs 6.0 and 5.4) at an a w of 0.99. Regardless of the pH and a w of TSB, survival of E. coli O157:H7 was better at 5؇C than at 20 or 30؇C. At 30؇C, inactivation or inhibition of growth was enhanced by reduction of the a w and pH. A decrease in the a w (0.99 to 0.90) of TSB in which the cells were heated at 52؇C for 30 min resulted in a 1.5-log 10 reduction in the number of E. coli O157:H7 cells recovered on TSA; pH did not significantly affect the viability of cells. Recovery was significantly reduced on MSMA when cells were heated in TSB with reduced pH or a w for an increased length of time. With the exception of TSB (a w , 0.90) incubated at 37؇C, heat-stressed cells survived for 24 h in recovery broth. TSB (a w , 0.99) at pH 6.0 or 5.4 supported growth of E. coli O157:H7 cells at 20 or 37؇C, but higher numbers of heated cells survived at 5 or 20؇C than at 37؇C. The ability of unheated and heat-stressed E. coli O157:H7 cells to survive or grow as affected by the a w of processed salami was investigated. Decreases of about 1 to 2 log 10 CFU g ؊1 occurred soon after inoculation of salami (pHs 4.86 and 4.63 at a w s of 0.95 and 0.90, respectively). Regardless of the physiological condition of the cells before inoculation into processed salami at an a w of either 0.95 or 0.90, decreases in populations occurred during storage at 5 or 20؇C for 32 days. If present at <100 CFU g ؊1 , E. coli O157:H7 would unlikely survive storage at 5؇C for 32 days. However, contamination of salami with E. coli O157:H7 at 10 4 to 10 5 CFU g ؊1 after processing would pose a health risk to consumers for more than 32 days if storage were at 5؇C. Regardless of the treatment conditions, performance of the media tested for the recovery of E. coli O157:H7 cells followed the order TSA > modified eosin methylene blue agar > MSMA.

Raw ground beef patties inoculated with stationary-phase cells of Escherichia coli 0157:H7, salmonellae, or Campylobacterjejuni were subjected to gamma irradiation (60Co) treatment, with doses ranging from 0 to 2.52 kGy. The influence of two levels of fat (8 to 14% [low fat] and 27 to 28% [high fat]) and temperature (frozen [-17 to-15°C] and refrigerated [3 to 5°C]) on the inactivation of each pathogen by irradiation was investigated. In ascending order of irradiation resistance, the D1o values ranged from 0.175 to 0.235 kGy (C. jejuni), from 0.241 to 0.307 kGy (E. coli 0157:H7), and from 0.618 to 0.800 kGy (salmonellae). Statistical analysis revealed that E. coli 0157:H7 had a significantly (P < 0.05) higher DIo value when irradiated at-17 to-15°C than when irradiated at 3 to 5°C. Regardless of the temperature during irradiation, the level of fat did not have a significant effect on the D1o value. Salmonellae behaved like E. coli 0157:H7 in low-fat beef, but temperature did not have a significant effect when the pathogen was irradiated in high-fat ground beef. Significantly higher D1o values were calculated for C. jejuni irradiated in frozen than in refrigerated low-fat beef. C. jejuni was more resistant to irradiation in low-fat beef than in high-fat beef when treatment was at-17 to-15°C. Regardless of the fat level and temperature during inactivation, these pathogens were highly sensitive to gamma irradiation. An applied dose of 2.5 kGy would be sufficient to kill 108.1 E. coli 0157:H7, 103 ' salmonellae, and 1010.6 C. jejuni, resulting in a high probability of complete inactivation of populations much higher than those occasionally present in ground beef patties. Gamma irradiation has been used as a method of preserving foods in several countries, including Belgium, France, Japan, and the Netherlands (12). The process involves exposing the food to a specific dose of ionizing irradiation from, for example, 6"Co, a radioisotope of cobalt (21). Irradiation is

The presence of psychrotrophic enterotoxigenic Bacillus cereus in ready-to-serve meats and meat products that have not been subjected to sterilization treatment is a public health concern. A study was undertaken to determine the survival, growth, and diarrheal enterotoxin production characteristics of four strains of psychrotrophic B. cereus in brain heart infusion (BHI) broth and beef gravy as affected by temperature and supplementation with nisin. A portion of unheated vegetative cells from 24-h BHI broth cultures was sensitive to nisin as evidenced by an inability to form colonies on BHI agar containing 10 g of nisin/ml. Heat-stressed cells exhibited increased sensitivity to nisin. At concentrations as low as 1 g/ml, nisin was lethal to B. cereus, the effect being more pronounced in BHI broth than in beef gravy. The inhibitory effect of nisin (1 g/ml) was greater on vegetative cells than on spores inoculated into beef gravy and was more pronounced at 8°C than at 15°C. Nisin, at a concentration of 5 or 50 g/ml, inhibited growth in gravy inoculated with vegetative cells and stored at 8 or 15°C, respectively, for 14 days. Growth of vegetative cells and spores of B. cereus after an initial period of inhibition is attributed to loss of activity of nisin. One of two test strains produced diarrheal enterotoxin in gravy stored at 8 or 15°C within 9 or 3 days, respectively. Enterotoxin production was inhibited in gravy supplemented with 1 g of nisin/ml and stored at 8°C for 14 days; 5 g of nisin/ml was required for inhibition at 15°C. Enterotoxin was not detected in gravy in which less than 5.85 log 10 CFU of B. cereus/ml had grown. Results indicate that as little as 1 g of nisin/ml may be effective in inhibiting or retarding growth of and diarrheal enterotoxin production by vegetative cells and spores of psychrotrophic B. cereus in beef gravy at 8°C, a temperature exceeding that recommended for storage or for most unpasteurized, ready-to-serve meat products.

Rates of thermal inactivation of five strains of Escherichia coli O157:H7 isolated from ground beef implicated in outbreaks of hemorrhagic colitis and five strains isolated from bovine feces were determined. Ground beef (22% fat, 10 g), inoculated with individual test strains at populations ranging from 6.85 to 7.40 log10 CFU g-1 of beef, was formed into patties (0.3 cm thick and 8.0 cm in diameter) and sealed in polyethylene bags. For each strain and treatment temperature (54.4, 58.9, 62.8, 65.6, or 68.3 degrees C), 6 bags were simultaneously immersed into a recirculating water bath. Viable cells in patties heated for various lengths of time were enumerated by plating diluted samples on sorbitol MacConkey agar supplemented with 4-methylumbelliferyl-beta-D-glucuronide (MSMA) and modified eosin methylene blue (MEMB) agar. Regardless of strain or treatment temperature, higher numbers of E. coli O157:H7 cells were generally recovered on MEMB agar than on MSMA, indicating the inferiority of MSMA as a recovery medium for quantitative determination of E. coli O157:H7 cells in heat-processed ground beef. Significantly (P < or = 0.05) higher D values when enumeration was done using MEMB agar compared with MSMA. Mean D values for combined strain data at 54.4, 58.9, 62.8, and 65.6 degrees C from cultures on MEMB agar were 123.90, 6.47, 0.62, and 0.20 min, respectively, whereas D values of 25.5, 5.21, and 0.18 min were obtained at the same temperatures from cultures on MSMA. Results suggest that cooking ground beef patties to an internal temperature of 68.3 degrees C for 40 s will inactivate at least 99.99% of E. coli O157:H7 cells; z values of 4.0 and 5.1 degrees C were calculated from mean D values obtained from MEMB agar and MSMA, respectively, as recovery media. Differences in D values existed among strains but rates of thermal inactivation do not appear to be correlated with the sources of the isolates.

In late 1995, fecal coliforms were detected in iced tea obtained from several restaurants in the U.S. On the basis of fecal coliform results, the news media inaccurately and sensationally accused the tea industry of marketing tea containing feces. We analyzed 11 iced-tea samples obtained from fast-food restaurants and 25 dry leaf-tea samples purchased from retail grocers for the presence of coliforms and fecal coliforms. All samples of iced tea contained coliforms and fecal coliforms; most probable numbers of coliforms in iced tea ranged from 210 to &gt; 1,100/ml, whereas those of fecal coliforms were 15 to &gt;1,100/ml. Twenty-three of twenty-five leaf-tea samples contained coliforms and fecal coliforms; ranges for positive samples were 3 to 1,100/g and 3 to 460/g, respectively. Two Klebsiella species and three Enterobacter species were isolated from iced tea. Only Klebsiella pneumoniae (93.8% of isolates) and Enterobacter cloacae (6.2%) were isolated from leaf tea. Escherichia coli was not isolated from any of the iced-tea or leaf-tea samples analyzed. The D55°c values of two isolates of K. pneumoniae and three isolates of E. cloacae from leaf tea, when heated in steeped tea, ranged from 3.75 to 5.08 min. Initial populations of up to 5.70 log CFU/ml were reduced to &lt;10 CFU/ml within 5 min at 65°C. While 23 of 25 (92%) of the leaf-tea samples analyzed contained fecal coliforms, as defined by standard methodology, there is no evidence that leaf tea represents a health hazard. The expected presence in leaf tea of Klebsiella and Enterobacter species, which test positive for the fecal coliform group, should not automatically be construed as indicators of fecal contamination nor as an imminent threat to human health. The presence of coliforms and fecal coliforms in iced tea indicates post-steeping contamination caused by poor sanitation practices in restaurants at which the iced tea was purchased.

The influence of two levels of fat (11.l to 13.9% [low-fat] and 27.1 to 27.9% [high-fat]) and temperature (frozen [−17 to −15°C] and refrigerated [3 to 5°C]) on gamma irradiation (60CO) inactivation of Listeria monocytogenes and Staphylococcus aureus in raw ground beef patties was investigated. Ground beef patties inoculated with stationary growth phase cells of five-strain mixtures of L. monocytogenes or S. aureus were treated with seven mean gamma irradiation doses up to 2.062 or 2.147 kGy, respectively. D10 values ranged from 0.507 to 0.610 kGy and 0.435 to 0.453 kGy for L. monocytogenes and S. aureus, respectively. Neither the fat content of beef nor the temperature during irradiation treatment influenced inactivation rates of the two pathogens. Regression coefficients were high for all treatment conditions, the lowest being 0.984 for L. monocytogenes and 0.990 for S. aureus in high-fat frozen beef. Based on the highest D10 value obtained, a dose of 2.50 kGy would theoretically kill 4.10 log10 L. monocytogenes and 5.12 log10 S. aureus per gram of ground beef. The fact that this investigation was done under commercial processing and irradiation treatment conditions, to the extent possible, makes the significance of the results more meaningful to the beef industry.