Reduction of Escherichia coli O157:H7 and Salmonella on laboratory-inoculated alfalfa seed with commercial citrus-related products

Alfalfa sprouts contaminated with the bacterial pathogens Escherichia coli O157:H7 and Salmonella have been the source of numerous outbreaks of foodborne illness in the United States and in other countries. The seed used for sprouting appears to be the primary source of these pathogens. The aim of this study was to determine whether the efficacy of commercial citrus-related products for sanitizing sprouting seed is similar to that of high levels of chlorine. Five products (Citrex, Pangermex, Citricidal, Citrobio, and Environné) were tested at concentrations of up to 20,000 ppm in sterile tap water and compared with buffered chlorine (at 16,000 ppm). Alfalfa seeds were inoculated with four-strain cocktails of Salmonella and E. coli O157:H7 to give final initial concentrations of ca. 9.0 and 7.0 CFU/g, respectively. Treatments (10 min) with Citrex, Pangermex, and Citricidal at 20,000 ppm and chlorine at 16,000 ppm produced similar log reductions for alfalfa seed inoculated with four-strain cocktails of E. coli O157:H7 and Salmonella (3.42 to 3.46 log CFU/g and 3.56 to 3.74 log CFU/g, respectively), and all four treatments were significantly (P<0.05) more effective than the control treatment (a buffer wash). Citrobio at 20,000 ppm was as effective as the other three products and chlorine against Salmonella but not against E. coli O157:H7. Environné was not more effective (producing reductions of 2.2 to 2.9 log CFU/g) than the control treatment (which produced reductions of 2.1 to 2.3 log CFU/g) against either pathogen. None of the treatments reduced seed germination. In vitro assays, as well as transmission electron microscopy, confirmed the antibacterial nature of the products that were effective against the two pathogens and indicated that they were bactericidal. When used at 20,000 ppm, the effective citrus-related products may be viable alternatives to chlorine for the sanitization of sprouting seed pending regulatory approval.     

Irradiation to kill Escherichia coli O157:H7 and Salmonella on ready-to-eat radish and mung bean sprouts

A study was carried out to evaluate the effectiveness of ionizing radiation in eliminating Escherichia coli O157:H7 and Salmonella on commercial ready-to-eat radish and mung bean sprouts and to assess the chemical and physical quality of these sprouts. The use of ionizing radiation was investigated as a means of reducing or totally inactivating these pathogens, if present, on the sprouts. Treatment of mung bean and radish sprouts with a dose of 1.5 and 2.0 kGy, respectively, significantly reduced E. coli O157:H7 and Salmonella to nondetectable limits. The total vitamin C content was gradually reduced with the increase in irradiation dose (P < 0.0001). However, the effect of storage interval on the loss of vitamin C was nonsignificant for radish sprouts and significant for mung bean sprouts (P < 0.04). The color, firmness, and overall visual quality of the tested sprouts were acceptable when effective doses were applied to both radish and mung bean sprouts. Therefore, ionizing radiation could be useful in reducing the population of pathogens on sprouts and yet retain acceptable quality parameters.     

Hot water treatments to inactivate Escherichia coli O157:H7 and Salmonella in mung bean seeds

The majority of the seed sprout-related outbreaks have been associated with Escherichia coli O157:H7 and Salmonella. Therefore, an effective method is needed to inactivate these organisms on the seeds before they are sprouted. This study was conducted to assess the effectiveness of various hot water treatments to inactivate E. coli O157:H7 and Salmonella populations on mung beans seeds intended for sprout production and to determine the effect of these treatments on seed germination after the seeds were dipped in chilled water for 30 s. Mung bean seed inoculated with four-strain cocktails of E. coli O157:H7 and Salmonella were soaked into hot water at 80 and 90 degrees C with shaking for various periods and then dipped in chilled water for 30 s. The treated seeds were then assessed for the efficacy of the treatment for reducing populations of the pathogens and the effects of the treatment on germination. After inoculation and air drying, 6.08 +/- 0.34 log CFU/g E. coli O157:H7 and 5.34 +/- 0.29 log CFU/g Salmonella were detected on the seeds. After hot water treatment at 90 degrees C for 90 s followed by dipping in chilled water for 30 s, no viable pathogens were found and no survivors were found in the enrichment medium and during the sprouting process. The germination yield of the seed was not affected significantly. Therefore, hot water treatment followed by dipping in chilled water for 30 s could be an effective seed decontamination method for mung bean seeds intended for sprout production.     

Reduction of Salmonella spp. and strains of Escherichia coli O157:H7 by gamma radiation of inoculated sprouts

There have been several recent outbreaks of salmonellosis and infections with Escherichia coli O157:H7 linked to the consumption of raw sprouts. Use of ionizing radiation was investigated as a means to reduce or to totally inactivate these pathogens, if present, on the sprouts. The radiation D value, which is the amount of irradiation in kilograys for a 1-log reduction in cell numbers, for these pathogens was established using a minimum of five doses at 19 +/- 1 degrees C. Before inoculation, the sprouts were irradiated to 6 kGy to remove the background microflora. The sprouts were inoculated either with Salmonella spp. cocktails made with either meat or vegetable isolates or with E. coli O157:H7 cocktails made with either meat or vegetable isolates. The radiation D values for the Salmonella spp. cocktails on sprouts were 0.54 and 0.46 kGy, respectively, for the meat and vegetable isolates. The radiation D values for the E. coli O157:H7 cocktails on sprouts were 0.34 and 0.30 kGy, respectively, for the meat and vegetable isolates. Salmonella was not detected by enrichment culture on sprouts grown from alfalfa seeds naturally contaminated with Salmonella after the sprouts were irradiated to a dose of 0.5 kGy or greater. Ionizing radiation is a process that can be used to reduce the population of pathogens on sprouts.     

Survival of Salmonella spp. and Escherichia coli O157:H7 on fresh and frozen strawberries

For maximum shelf life, fresh strawberries are harvested directly without washing into retail containers. Frozen berries are usually hulled in the field and washed prior to freezing, sometimes with the addition of sucrose. To determine survival of potential bacterial contaminants, cut or intact surfaces of fresh strawberries were spot inoculated with five- or six-strain cocktails of Salmonella or Escherichia coli O157:H7 (log 7.0 CFU/sample). Inoculated strawberries were dried for 1 h at 24 degrees C and were stored in closed containers at 5 or 24 degrees C. Sliced strawberries with or without added 20% sucrose were inoculated with one of two strains of E. coli O157:H7 and frozen at -20 degrees C. An initial population reduction of approximately 0.5-log cycles was observed on intact but not cut berries after the 1-h drying period. During storage at 24 degrees C for up to 48 h, populations of Salmonella and E. coli O157:H7 did not decline further. When strawberries were stored at 5 degrees C for up to 7 days, populations of both pathogens remained constant on cut surfaces but decreased by 1 - to 2-log cycles on intact surfaces. After 30 days of frozen storage, the population of E. coli O157:H7 had declined by 0.7- to 2.2-log cycles (with and without sucrose, respectively). Results of this study indicate that E. coli O157:H7 and Salmonella are capable of survival but not growth on the surface of fresh strawberries throughout the expected shelf life of the fruit and can survive in frozen strawberries for periods of greater than 1 month.     

Reduction of Escherichia coli O157:H7 and Salmonella typhimurium in artificially contaminated alfalfa seeds and mung beans by fumigation with ammonia.

Sprouts eaten raw are increasingly perceived as hazardous foods because they have been vehicles in outbreaks of foodborne disease, often involving Escherichia coli O157:H7 and Salmonella Typhimurium. Although the source of these pathogens has not been established, it is known that the seeds usually are already contaminated at the time sprouting begins. Earlier studies had shown that ammonia was lethal to these same pathogens in manure, so it seemed reasonable to determine whether ammonia was effective against them when associated with seeds to be used for sprouting. Experimentally contaminated (10(8) to 10(9) CFU/g) and dried seeds, intended for sprouting, were sealed in glass jars in which 180 or 300 mg of ammonia/liter of air space was generated by action of ammonium sulfate and sodium hydroxide. Samples were taken after intervals up to 22 h at 20 degrees C. Destruction of approximately 2 to 3 logs was observed with both bacteria associated with alfalfa seeds, versus 5 to 6 logs with mung beans. Greater kills are apparently associated with lower initial bacterial loads. Germination of these seeds was unaffected by the treatment. It appears that this simple treatment could contribute significantly to the safety of sprout production from alfalfa seeds and mung beans.     

Inactivation of Escherichia coli O157:H7 and Salmonella spp. on alfalfa seeds by caprylic acid and monocaprylin

Alfalfa and other seed sprouts have been implicated in several Escherichia coli O157:H7 and Salmonella spp. human illness outbreaks in the U.S. Continuing food safety issues with alfalfa seeds necessitate the need for discovery and use of novel and effective antimicrobials. The potential use of caprylic acid (CA) and monocaprylin (MC) for reducing E. coli O157:H7 and Salmonella spp. populations on alfalfa seeds was evaluated. The effectiveness of three concentrations of CA and MC (25, 50, and 75 mM) to reduce E. coli O157:H7 and Salmonella spp. populations in 0.1% peptone water and on alfalfa seeds was evaluated. Surviving populations of E. coli O157:H7 and Salmonella spp. were enumerated by direct plating on tryptic soy agar (TSA). Non-inoculated alfalfa seeds were soaked for up to 120 min to evaluate the effect of CA and MC solutions on seed germination rate. For planktonic cells, the efficacy of the treatments was: 75 MC > 50 MC > 25 MC > 75 CA > 50 CA > 25 CA. Both E. coli O157:H7 and Salmonella spp. were reduced to below the detection limit (0.6 log CFU/ml) within 10 min of exposure to 75 MC from initial populations of 7.65 ± 0.10 log CFU/ml and 7.71 ± 0.11 log CFU/ml, respectively. Maximum reductions of 1.56 ± 0.25 and 2.56 ± 0.17 log CFU/g for E. coli O157:H7 and Salmonella spp., respectively, were achieved on inoculated alfalfa seeds (from initial populations of 4.74 ± 0.62 log CFU/g and 5.27 ± 0.20 log CFU/g, respectively) when treated with 75 MC for 90 min. Germination rates of CA or MC treated seeds ranged from 84% to 99%. The germination rates of CA or MC soaked seeds and water soaked seeds (control) were similar (P > 0.05) for soaking times of ≤ 90 min. Monocaprylin (75 mM) can be used to reduce E. coli O157:H7 and Salmonella spp. on alfalfa seeds without compromising seed viability.     

Inactivation kinetics of inoculated Escherichia coli O157:H7 and Salmonella enterica on lettuce by chlorine dioxide gas

The purpose of this investigation was to study inactivation kinetics of inoculated Escherichia coli O157:H7 and Salmonella enterica on lettuce leaves by ClO(2) gas at different concentrations (0.5, 1.0, 1.5, 3.0, and 5.0 mg l(-1)) for 10 min and to determine the effect of ClO(2) gas on the quality and shelf life of lettuce during storage at 4 degrees C for 7 days. One hundred microliters of each targeted organism was separately spot-inoculated onto the surface (5 cm(2)) of lettuce (approximately 8-9 log CFU ml(-1)), air-dried, and treated with ClO(2) gas at 22 degrees C and 90-95% relative humidity for 10 min. Surviving bacterial populations on lettuce were determined using a membrane transferring method, which included a non-selective medium followed by a selective medium. The inactivation kinetics of E. coli O157:H7 and S. enterica was determined using first-order kinetics to establish D-values and z-values. The D-values of E. coli and S. enterica were 2.9+/-0.1 and 3.8+/-0.5 min, respectively, at 5.0 mg l(-1) ClO(2) gas. The z-values of E. coli and S. enterica were 16.2+/-2.4 and 21.4+/-0.5 mg l(-1), respectively. A 5 log CFU reduction (recommended by the United States Food and Drug Administration) for E. coli and S. enterica could be achieved with 5.0 mg l(-1) ClO(2) gas for 14.5 and 19.0 min, respectively. Treatment with ClO(2) gas significantly reduced inherent microflora on lettuce and microbial counts remained significantly (p<0.05) lower than the uninoculated control during storage at 4 degrees C for 7 days. However, treatment with ClO(2) gas had a significantly (p<0.05) negative impact on visual leaf quality. These results showed that treatment with ClO(2) gas significantly reduced selected pathogens and inherent microorganisms on lettuce; however, the processing conditions would likely need to be altered for consumer acceptance.     

Reduction of Listeria monocytogenes, Salmonella spp., and Escherichia coli O157:H7 During Processing of Country-cured Hams

ABSTRACT: The country-cured ham process, including curing, equalization, cold-smoked or nonsmoked, and aging up to 6 mo, was validated and showed its effectiveness in achieving a 6-log reduction of Listeria monocytogenes, Salmonella spp., and Escherichia coli O157:H7. The viable counts of L. monocytogenes populations decreased to below detection levels after 206 d, Salmonella populations required 122 d, and E. coli O157:H7 required 66 d. However, L. monocytogenes -inoculated hams were positive and Salmonella spp-inoculated and E. coli O157:H7-inoculated hams were negative following enrichment procedures at the end of the aging process. Therefore, the survival of L. monocytogenes on country-cured ham represents a risk.     

Fate of Escherichia coli O157:H7 and Salmonella Enteritidis on currency.

The fate of foodborne pathogens Escherichia coli O157:H7 and Salmonella Enteritidis on coin surfaces was determined at room temperature (25 degrees C). A five-strain mixture of E. coli O157:H7 or Salmonella Enteritidis of approximately 5 x 10(4) CFU was applied to the surfaces of sterile U.S. coins (pennies, nickels, dimes, and quarters) and to the surfaces of two control substrata (Teflon and glass coverslips). During storage at room temperature, E. coli O157:H7 survived for 7, 9, and 11 days on the surfaces of pennies, nickels, and dimes and quarters, respectively. However, the pathogen died off within 4 to 7 days on both the Teflon and glass surfaces. Salmonella Enteritidis survived for 1, 2, 4, and 9 days on the surfaces of pennies, nickels, quarters, and dimes, respectively. Unlike E. coli O157:H7, survival of Salmonella Enteritidis was greatest on both Teflon and glass coverslips, with more than 100 cells per substratum detected at the 17th day of storage. Results indicate that coins could serve as potential vehicles for transmitting both E. coli O157:H7 and Salmonella Enteritidis.     

Spatial distribution of Salmonella, Escherichia coli O157:H7, and other bacterial populations in commercial and laboratory-scale sprouting mung bean beds

The reliability of testing spent irrigation water to assess the microbiological status of sprouting mung bean beds has been investigated. In commercial trials, the distribution of opportunistic contaminants within 32 bean sprout beds (25 kg of mung beans per bin) was assessed 48 h after germination. The prevalence of generic Escherichia coli, thermotolerant coliforms, and Aeromonas in sprouts (n = 288) was 5, 11, and 39%, respectively, and 57, 70, and 79% in the corresponding spent irrigation water samples (n = 96). Contamination was heterogeneously distributed within the seedbed. In laboratory trials, beans inoculated with a five-strain cocktail of either Salmonella or E. coli O157:H7 (10(3) to 10(4) CFU/g) were introduced (1 g/500 g of noninoculated seeds) at defined locations (top, middle, or base), and the beans were then sprouted for 48 h. When seeds inoculated with pathogens were introduced at the base or top of the seedbed, the pathogens were typically restricted to these sites and resulted in 44% of the spent irrigation water samples returning false-negative results. Introducing inoculated beans into the middle or at the presoak stage enhanced the distribution of both pathogens within the subsequent sprout bed and resulted in comparable levels recovered in spent irrigation water. The study demonstrated that even though screening a single sample of spent irrigation water is more reliable than testing sprouts directly, it does not provide an accurate assessment of the microbiological status of sprouting mung bean beds. Such limitations may be addressed by ensuring that bean batches are mixed prior to use and by taking spent irrigation water samples from multiple sites at the latter stages of the sprouting process.     

Survival of Salmonella and Escherichia coli O157:H7 in chorizos

Mexican-style raw meat sausages (chorizos) are not regulated in California when they are produced in small ethnic food markets. These sausages are sold uncooked, but their formulation imparts a color that may lead the consumer to assume that they are already cooked, and thus the chorizos may sometimes be eaten without proper cooking. If pathogens are present in such cases, illness may result. Survival of Salmonella and Escherichia coli O157:H7 in chorizos was evaluated under different storage conditions selected based on an initial survey of uninspected chorizos in California. Chorizos were formulated with five different initial water activity (aw) values (0.85, 0.90, 0.93, 0.95, and 0.97), stored under four conditions (refrigeration at 6 to 8 degrees C, room temperature at 24 to 26 degrees C, under a hood at 24 to 26 degrees C with forced air circulation, and incubation at 30 to 31 degrees C with convective air circulation), and sampled after 1, 2, 4, and 7 days. The initial pH was 4.8 and remained near 5.0 from day 1 of the sampling period. Two separate studies of packs inoculated with five-strain cocktails of Salmonella and of E. coli O157:H7 were performed twice for each initial aw. The three lowest aw values (0.85, 0.90, and 0.93) and the incubation and hood storage conditions were more effective (P < or = 0.05) at reducing the target pathogen levels in chorizos than were the two highest aw values (0.95 and 0.97) and the refrigeration storage condition, regardless of storage time. These results provide a scientific basis for guidelines given to producers of uninspected chorizo and should reduce the probability of foodborne illness associated with these products.     

Chemical and irradiation treatments for killing Escherichia coli O157:H7 on alfalfa,radish, and mung bean seeds

In this study, the effectiveness of dry-heat treatment in combination with chemical treatments (electrolyzed oxidizing [EO] water, califresh-S, 200 ppm of active chlorinated water) with and without sonication in eliminating Escherichia coli O157:H7 on laboratory-inoculated alfalfa, radish, and mung bean seeds was compared with that of dry-heat treatment in combination with irradiation treatment. The treatment of mung bean seeds with EO water in combination with sonication followed by a rinse with sterile distilled water resulted in reductions of approximately 4.0 log10 CFU of E. coli O157:H7 per g. whereas reductions of ca. 1.52 and 2.64 log10 CFU/g were obtained for radish and alfalfa seeds. The maximum reduction (3.70 log10 CFU/g) for mung bean seeds was achieved by treatment with califresh-S and chlorinated water (200 ppm) in combination with sonication and a rinse. The combination of dry heat, hot EO water treatment, and sonication was able to eliminate pathogen populations on mung bean seeds but was unable to eliminate the pathogen on radish and alfalfa seeds. Other chemical treatments used were effective in greatly reducing pathogen populations on radish and alfalfa seeds without compromising the quality of the sprouts, but these treatments did not result in the elimination of pathogens from radish and alfalfa seeds. Moreover, a combination of dry-heat and irradiation treatments was effective in eliminating E. coli O157:H7 on laboratory-inoculated alfalfa, radish, and mung bean seeds. An irradiation dose of 2.0 kGy in combination with dry heat eliminated E. coli O157:H7 completely from alfalfa and mung bean seeds, whereas a 2.5-kGy dose of irradiation was required to eliminate the pathogen completely from radish seeds. Dry heat in combination with irradiation doses of up to 2.0 kGy did not unacceptably decrease the germination percentage for alfalfa seeds or the length of alfalfa sprouts but did decrease the lengths of radish and mung bean sprouts.     

Reduction of Escherichia coli O157:H7 and Salmonella typhimurium on beef carcass surfaces using acidified sodium chlorite.

The efficacy of a phosphoric acid-activated acidified sodium chloride (PASC) spray and a citric acid-activated acidified sodium chlorite (CASC) spray applied at room temperature (22.4 to 24.7 degrees C) in combination with a water wash was compared with that of a water wash only treatment for reduction of Escherichia coli O157:H7 and Salmonella Typhimurium inoculated onto various hot-boned individual beef carcass surface regions (inside round, outside round, brisket, flank, and clod). Initial counts of 5.5 and 5.4 log CFU/cm2 were obtained after inoculation with E. coli O157:H7 and Salmonella Typhimurium, respectively. Initial numbers for both pathogens were reduced by 3.8 to 3.9 log cycles by water wash followed by PASC spray and by 4.5 to 4.6 log cycles by water wash followed by CASC spray. The sprays consisted of applying 140 ml of the appropriate sanitizing solution for 10 s at 69 kPa. Corresponding reduction values obtained by water wash alone were 2.3 log. The performance of CASC appeared to be consistently better than that of PASC. In general, no effect of the carcass surface region was observed on the log reductions for either pathogen, except for the inside round, which consistently had lower reductions. Both PASC and CASC were capable of effectively reducing pathogens spread to areas beyond the initial contaminated area of the cuts to levels close to or below the counting method detection limit (0.5 log CFU/cm2). However, 30 to 50% of the carcasses treated by these antimicrobial solutions still yielded countable colonies. Results of this study indicate that acidified sodium chlorite sprays are effective for decontaminating beef carcass surfaces.     

Thermal inactivation of Salmonella and Escherichia coli O157:H7 on alfalfa seeds

Alfalfa seeds inoculated with five strains of Salmonella or Escherichia coli O157:H7 were subjected to dry heat at 55 degrees C for up to 8 days. Five-log reductions in Salmonella or E. coli O157:H7 on seeds were observed. No pathogens were detected on the sprouted seeds, which were initially inoculated with ca. 2 log CFU/g of Salmonella or more than 8 log CFU/g of E. coli O157:H7. The percentages of germination of the alfalfa seeds did not significantly decrease after 6 days of heating at 55 degrees C. These results showed that heat treatment of alfalfa seeds at 55 degrees C for up to 6 days was effective in enhancing the safety of alfalfa sprouts without affecting germination significantly.     

Response of Salmonella and Escherichia coli O157:H7 to UV energy

To determine the efficacy of a UV light treatment at 253.7 nm (UVC light) on microbial growth, plates containing tryptic soy agar plus 50 ppm of nalidixic acid (TSAN) were inoculated with known concentrations of five-strain cocktails of Salmonella and Escherichia coli O157:H7 and subjected to different UVC treatments. The concentration of the cocktail inoculum was determined with TSAN prior to inoculation. Serial dilutions were carried out, and inoculation levels of 10(0) to 10(8) CFU/ ml were tested for each pathogen. Multiple replications of doses of UV light ranging from 1.5 to 30 mW/cm2 were applied to different cocktail concentrations, and doses of > 8.4 mW/cm2 resulted in a 5-log reduction of Escherichia coli O157:H7, while a 5-log reduction of Salmonella was observed with doses of > 14.5 mW/cm2. Results for both organisms yielded sigmoidal inactivation curves. UVC light is effective in reducing microbial populations of pathogens on agar surfaces.     

Validation of methods used to recover Escherichia coli O157:H7 and Salmonella spp. subjected to stress conditionst

Escherichia coli O157:H7, Salmonella spp., and Salmonella Typhimurium DT104 were stressed with lactic acid and cell-free supernatants from lactic acid bacteria and plated on three different media to determine if injured cells were recovered. A comparison of the susceptibility and recovery of antibiotic-resistant strains of the pathogens and nonresistant strains was also made. Acid stress conditions were created by adjusting the pH of a cocktail mixture (two to four strains) of the pathogen to 3.50 with lactic acid and holding for 18 h. The pathogen cocktail was also stressed with a cell-free supernatant of Lactobacillus lactis (pH 3.90) in a 4:6 ratio. Both nonstressed and stressed cocktail cultures were plated on Trypticase soy agar (TSA) and violet red bile agar (VRBA) for E. coli and xylose lysine tergitol4 (XLT4) for Salmonella. Repair of injured cells was evaluated by pour plating the stressed cells on a 5-ml thin layer of TSA and allowing a 2-h room temperature incubation followed by overlaying with VRBA or XLT4. There were significant reductions in the populations of both pathogens under both stress conditions when plating was done on nonselective media. Injured E. coli O157:H7 was not recovered on recovery or selective media compared with TSA. Numbers of cells of supernatant-stressed Salmonella spp. plated on selective and recovery media were similar to those on TSA. Acid-stressed cells for all Salmonella spp. were not recovered on TSA, selective, or recovery media at levels comparable to recovery on TSA. Antibiotic-resistant strains showed similar recovery patterns on all media evaluated. However, the antibiotic-resistant strains were less sensitive to both stress conditions. The use of antibiotic-resistant strains resulted in a greater recovery of stressed pathogens than the use of recovery media.     

Growth rates of Salmonella and Escherichia coli O157:H7 in irradiated beef.

Ground beef was irradiated to 0, 2, or 4 kGy and then inoculated with a mixed culture of four serotypes of salmonellae or five strains of Escherichia coli O157:H7. The ground beef was stored at either 15 or 25 degrees C, and the growth of the inoculated bacteria was monitored over time. Growth parameters were determined for both the salmonellae and the E. coli O157:H7 using the Gompertz equation. There was no significant difference in lag phase duration or generation time, irrespective of the dose to which the ground beef had previously been exposed. Furthermore, the lag phase durations and generation times determined in this study did not differ significantly from previously published values. This suggests that, although irradiation eliminates a significant portion of the spoilage microflora in ground beef, the absence of this microflora provides no competitive advantage to the growth of salmonellae or E. coli O157:H7 in ground beef.     

Essential oils reduce Escherichia coli O157:H7 and Salmonella on spinach leaves

The efficacy of cinnamaldehyde and Sporan for reducing Escherichia coli O157:H7 and Salmonella on spinach leaves was investigated. Spinach leaves were inoculated with a five-strain cocktail of Salmonella or E. coli O157:H7, air dried for ca. 30 min, and then immersed in a treatment solution containing 5 ppm of free chlorine, cinnamaldehyde, or Sporan (800 and 1,000 ppm) alone or in combination with 200 ppm of acetic acid (20%) for 1 min or with water (control). After spin drying, treated leaves were analyzed periodically during 14 days of storage at 4°C for Salmonella, E. coli O157:H7, total coliforms, mesophilic and psychrotrophic bacteria, and yeasts and molds. Treatment effects on color and texture of leaves also were determined. Sporan alone (1,000S), Sporan plus acetic acid (1,000SV), and cinnamaldehyde-Tween (800T) reduced E. coli O157:H7 by more than 3 log CFU/g (P < 0.05), and 1,000SV treatment reduced Salmonella by 2.5 log CFU/g on day 0. E. coli O157:H7 and Salmonella populations on treated spinach leaves declined during storage at 4°C. The 1,000SV treatment was superior to chlorine and other treatments for reducing E. coli O157:H7 during storage. Saprophytic microbiota on spinach leaves increased during storage at 4°C but remained lower on leaves treated with Sporan (800S) and Sporan plus acetic acid (1,000SV) than on control leaves. The color and texture of Sporan-treated leaves were not significantly different from those of the control leaves after 14 days. Sporan plus acetic acid (1,000SV) reduced E. coli O157:H7 and Salmonella on baby spinach leaves without adverse effects on leaf color and texture.