Elution, detection, and quantification of polio I, bacteriophages, Salmonella montevideo, and Escherichia coli O157:H7 from seeded strawberries and tomatoes

Outbreaks, occurrence, and control of norovirus and hepatitis a virus contamination in berries: A review

Foodborne enteric viruses, in particular HuNoV and HAV, are the most common cause of the berry-linked viral diseases, and outbreaks around the world, and have become an important concern for health authorities. Despite the increased importance of berry fruits as a vehicle for foodborne viruses, there is limited information concerning the fate of foodborne viruses in the berry supply chain from farm to consumer. A comprehensive understanding of berry-associated viral outbreaks - with a focus on contamination sources, persistence, survival, and the effects of current postharvest and processing interventions and practices - is essential for the development of effective preventative strategies to reduce risk of illness. The purpose of this paper is twofold; (i) to critically review the published literature on the current state of knowledge regarding berry-associated foodborne viral outbreaks and the efficiency of berry processing practices and (ii) to identify and prioritize research gaps regarding practical and effective mechanism to reduce viral contamination of berries. The review found that fecally infected food handlers were the predominant source of preharvest and postharvest pathogenic viral contamination. Current industrial practices applied to fresh and frozen berries demonstrated limited efficacy for reducing the viral load. While maintaining best practice personal and environmental hygiene is a key intervention, the optimization of processing parameters (i.e., freezing, frozen storage, and washing) and/or development of alternative processing technologies to induce sufficient viral inactivation in berries along with retaining sensory and nutritional quality, is also an important direction for further research.

Effect of chemical sanitizers on Salmonella enterica serovar Poona on the surface of cantaloupe and pathogen contamination of internal tissues as a function of cutting procedure

Survival of Salmonella enterica subsp. enterica serovar Poona on surface and stem scar portions of inoculated cantaloupe following sanitizer application, transfer of pathogen from the rind to the flesh during cutting, and growth of Salmonella Poona on cantaloupe cubes over 15 days of refrigerated storage were investigated. Cantaloupes inoculated with a rifampin-resistant strain of Salmonella Poona (10(7) CFU/ml) for 3 min and dried for 12 h were washed with chlorine (200 mg free chlorine per liter, 3 min), lactic acid (2%, 2 min), or ozone (30 mg/liter, 5 min). Fresh-cut cantaloupe cubes were prepared by (i) cutting the cantaloupe and then removing the rind or by (ii) peeling the rind and then cutting the flesh into pieces. The numbers of Salmonella bacteria recovered were higher in the stem scar portion (6.3 ± 0.3 log CFU/cm(2)) than the surface (4.8 ± 0.2 log CFU/cm(2)). Surface treatment with tap water or chlorine did not reduce Salmonella numbers, while treatment with lactic acid or ozone reduced Salmonella by 2.5 or 2.3 log CFU/cm(2), respectively. The use of lactic acid to sanitize the cantaloupes resulted in less Salmonella transfer to flesh during cutting; Salmonella numbers decreased to below detectable levels over 9 days of refrigerated (4°C) storage. Cutting cantaloupes after peeling the rind was more effective at reducing transfer of Salmonella to the internal tissue than cutting of cantaloupes prior to rind removal. These data suggest that treatment of cantaloupe rinds with lactic acid or ozone may be effective at reducing Salmonella numbers, while lactic acid application resulted in reduction of Salmonella transfer to cantaloupe flesh.

Low-dose irradiation improves microbial quality and shelf life of fresh mint (Mentha piperita L.) without compromising visual quality

The effects of low-dose irradiation (0.25 to 2 kGy) and postirradiation storage (at 4 degrees C) on microbial and visual quality, color values (L*, a*, b*, chroma, and hue [ degrees ]), and chlorophyll content (Chl a, Chl b, and total Chl) of fresh mint were evaluated. Samples inoculated with E. coli O157:H7, Salmonella, and MS2 bacteriophage were irradiated and evaluated. E. coli O157:H7 and Salmonella populations were reduced by 2 to 2.4, 3.5, and 5.8 log CFU/g, respectively, 1 d after treatment with 0.25, 0.60, and 1 kGy, respectively, and were completely eliminated at 2 kGy. None of the irradiation doses (P < 0.0001) reduced MS2 bacteriophage populations by more than 0.60 log PFU/g. Irradiation doses did not affect visual quality and samples remained of excellent to good quality (score 7.75 to 9) for up to 9 d of storage. Irradiation at 0.60, 1, and 2 kGy increased (P < 0.0001) Chl a, Chl b, and total Chl. Both total Chl and Chl a decreased significantly after 3 d of storage. Significant decreases in Chl b were not observed until day 12 of storage. Color values (L*, b*, and chroma) were not significantly different until day 6 of storage and hue ( degrees ) remained unchanged (179 degrees ) for the entire storage period of 12 d. Overall, irradiation did not change L*, a*, b*, or chroma. These results demonstrate that irradiation of fresh mint at 2 kGy has the potential to improve its microbial quality and extend its shelf life without compromising its visual quality and color.

PRACTICAL APPLICATION

Mints and other raw fresh herbs are widely used for flavoring as well as garnish in a variety of dishes without further cooking. However, mint is one considered as one of the high-risk herbs when it comes to microbial contamination. We have evaluated the use of gamma irradiation treatment at very low doses ranging from 0 to 2 kGy to eliminate seeded Salmonella spp, E. coli O157:H7, and MS2 bacteriophage, a surrogate of hepatitis A virus. We found that low-dose irradiation (1.0 to 2.0 kGy) appears to be a promising method for improving the microbiological quality of fresh mint without compromising its visual and color attributes. This method may be applied to many popular fresh culinary herbs that are commonly used as garnishes in Asian cuisine.

Bacterial Separation and Concentration from Complex Sample Matrices: A Review

The use of many rapid detection technologies could be expanded if the bacteria were separated, concentrated, and purified from the sample matrix before detection. Specific advantages of bacterial concentration might include facilitating the detection of multiple bacterial strains; removal of matrix-associated assay inhibitors; and provision of adequate sample size reduction to allow for the use of representative food sample sizes and/or small media volumes. Furthermore, bacterial concentration could aid in improving sampling techniques needed to detect low levels of pathogens or sporadic contamination, which may perhaps reduce or even eliminate the need for cultural enrichment prior to detection. Although bacterial concentration methods such as centrifugation, filtration, and immunomagnetic separation have been reported for food systems, none of these is ideal and in many cases a technique optimized for one food system or microorganism is not readily adaptable to others. Indeed, the separation and subsequent concentration of bacterial cells from a food sample during sample preparation continues to be a stumbling block in the advancement of molecular methods for the detection of foodborne pathogens. The purpose of this review is to provide a detailed understanding of the science, possibilities, and limitations of separating and concentrating bacterial cells from the food matrix in an effort to further improve our ability to harness molecular methods for the rapid detection of foodborne pathogens.

Electrolyzed water and its application in the food industry

Electrolyzed water (EW) is gaining popularity as a sanitizer in the food industries of many countries. By electrolysis, a dilute sodium chloride solution dissociates into acidic electrolyzed water (AEW), which has a pH of 2 to 3, an oxidation-reduction potential of >1,100 mV, and an active chlorine content of 10 to 90 ppm, and basic electrolyzed water (BEW), which has a pH of 10 to 13 and an oxidation-reduction potential of -800 to -900 mV. Vegetative cells of various bacteria in suspension were generally reduced by > 6.0 log CFU/ml when AEW was used. However, AEW is a less effective bactericide on utensils, surfaces, and food products because of factors such as surface type and the presence of organic matter. Reductions of bacteria on surfaces and utensils or vegetables and fruits mainly ranged from about 2.0 to 6.0 or 1.0 to 3.5 orders of magnitude, respectively. Higher reductions were obtained for tomatoes. For chicken carcasses, pork, and fish, reductions ranged from about 0.8 to 3.0, 1.0 to 1.8, and 0.4 to 2.8 orders of magnitude, respectively. Considerable reductions were achieved with AEW on eggs. On some food commodities, treatment with BEW followed by AEW produced higher reductions than did treatment with AEW only. EW technology deserves consideration when discussing industrial sanitization of equipment and decontamination of food products. Nevertheless, decontamination treatments for food products always should be considered part of an integral food safety system. Such treatments cannot replace strict adherence to good manufacturing and hygiene practices.

Applications of Chlorine Dioxide Gas for Control of Bacterial Soft Rot in Tomatoes

Chlorine dioxide (ClO₂) gas was generated from a mixture of sodium chlorite and ferric chloride plus water (impregnated into zeolite) in a Tyvek sachet over a 2- or 24-h period. The gas was distributed by a fan over wound-inoculated tomato fruit (Lycopersicon esculentum) enclosed in a sealed aluminum pressure cooker. Within 24 h of inoculation with 6 log₁₀ CFU of Erwinia carotovora subsp. carotovora per wound and storage at 22 to 24°C, bacterial soft rot was observed on >80% of the nontreated wounds (10 wounds/fruit and 4 or 6 fruit/treatment). By contrast, wounds that had been exposed to an atmosphere containing up to 99 mg ClO₂ during a 2- or 24-h period remained firm and dry with no evidence of bacterial activity or soft rot. After 72 h of incubation, wounds exposed to 88 mg ClO₂ produced over 24 h or 99 mg ClO₂ produced over 2 h were free of decay, whereas bacterial soft rot was observed in ca. 12% and less than 5% of wounds treated with 0.75 mg or 7.5 mg, respectively, for either 2 or 24 h. Wounds that had not been inoculated remained free of bacterial soft rot throughout the entire storage period. Wounds exposed to the highest doses of ClO₂, 88 mg/24 h or 99 mg/2 h, became bleached and sunken. Additionally, the stem scars on these fruit became cracked, sunken, and bleached. The intact cuticle was not visibly affected, and there was no observed change in overall fruit color. ClO₂ gas may be effective for controlling postharvest decays of fruit that have been inoculated prior to or during harvest.

Concentration of Bacillus Spores by Using Silica Magnetic Particles

Silica particles are mainly used for the concentration of nucleic acid for diagnostic purposes. This is usually done under acidic or chaotropic conditions that will demolish most of the living organisms and prevent the application of other diagnostic tests. Here we describe the development of a method for the capturing and concentration of Bacillus spores using silica magnetic particles to enable fast and sensitive detection. We have shown that capturing various Bacilli spores via silica magnetic particles is limited, with large differences between spore batches (42 +/- 25%). The hydrophobic exosporium layer of spore limits the capture by the hydrophilic silica beads. Partial removal of Bacillus exosporium increases capture efficiency. To increase capturing efficiency without harming the spores' viability, a cationic lipid, didecyldimethylammonium bromide (DDAB), was used as a coat for the negatively charged silica particles. DDAB treatment increased capture efficiency from 42% to more than 90%. Using this method, we were able to capture as few as 100 Bacillus anthracis spores/mL with 90% efficacy. Release of captured spores was achieved by the addition of albumin. The capture and release processes were verified by plating and by flow cytometry using light scatter analysis. The method is simple, efficient, easy to operate, and fast.

Variability of virus attachment patterns to butterhead lettuce

Enteric viruses account for most foodborne illness in the United States. The objective of this study was to determine whether the isoelectric point (pI) of viruses such as feline calicivirus (FCV), echovirus 11, and bacteriophages phiX174 and MS2 had any effect on their attachment to butterhead lettuce. The adsorption of virus particles to the lettuce was variable. Bacteriophage MS2 was the only virus that fit the current Derjaguin-Landau-Verway-Overbeek model of virus attachment. Echovirus 11 had the highest affinity to lettuce surface. Echovirus 11 appeared to exhibit reversible attachment above its pI, whereas below its pI strong adsorption was observed. Adsorption of FCV was at its maximum above its pI. Bacteriophage phiX174 exhibited the most complex adsorption pattern, with attachment occurring only at the pH extremes (pH 3.0 and 8.0). These results suggest the current model for virus adsorption to sediment does not adequately explain the attachment of virus to lettuce. Importantly, the results indirectly suggest that current sample processing methods to recover viruses from lettuce may differentially select for the recovery of only certain virus types.

Metabiotic associations of molds and Salmonella Poona on intact and wounded cantaloupe rind

Salmonella Poona, a serotype rarely implicated in human infections, has recently caused several cantaloupe-associated outbreaks of salmonellosis. Metabiotic associations of molds and foodborne pathogens on produce have been reported. We tested proteolytic activity and measured changes in the pH of cantaloupe rind caused by growth of Alternaria alternata, Cladosporium cladosporioides, Epicoccum nigrum, Geotrichum candidum, and Penicillium expansum. Survival and growth characteristics of Salmonella Poona co-infected with each mold on the surface rind and in wounded rind tissue as affected by temperature were determined. C. cladosporioides, G. candidum, and P. expansum, but not A. alternata and E. nigrum, showed proteolytic activity on agar media containing gelatin and/or casein, with concurrent increases in pH, thus favoring survival and growth of salmonellae. Intact and mechanically wounded tissue of cantaloupe rinds were inoculated with a five-strain mixture of S. Poona and/or test mold. Five inoculation schemes were used: mold only, S. Poona only, mold and S. Poona simultaneously, mold then S. Poona 3 days later, and S. Poona then mold 3 days later. The pH of cantaloupe rinds inoculated with molds and stored at 20 degrees C for 14 days was significantly higher (P < or =0.05) than on day 0. Only the pH of rinds inoculated with C. cladosporioides or G. candidum was significantly higher (P < or =0.05) on day 21 than on day 0, when cantaloupes were stored at 4 degrees C. An initial population of S. Poona increased from 3.3 log(10) cfu/sample (ca. 7 cm(2)) of cantaloupe rind to populations as high as 9.5 log(10) cfu/sample during storage at 20 degrees C for up 14 days, regardless of co-inoculation with molds. Populations of S. Poona decreased or remained constant at 4 degrees C for up to 21 days. Results demonstrate that persistence and growth of S. Poona on intact, wounded, and decaying cantaloupe rind are not markedly affected by the presence of molds.

Fate of Escherichia coli O157:H7 and Listeria monocytogenes in strawberry juice and acidified media at different pH values and temperatures

Survival and growth of Escherichia coli O157:H7 and Listeria monocytogenes in strawberry juice and acidified media at different pH levels (pH 3.4 to 6.8) and temperatures were studied. Sterile strawberry juice (pH 3.6) and acidified trypticase soy broth (TSB) media (pH 3.4 to 6.8) were inoculated with approximately 6.7 log CFU/ml E. coli O157:H7 or 7.3 log CFU/ ml L. monocytogenes, incubated for 3 days at 4 and 37 degrees C. Bacterial levels were determined after 2 h, 1 day, and 3 days using surface plating nonselectively on tryptic soy agar and selectively on sorbitol MacConkey agar for E. coli O157:H7 or modified Oxford agar for L. monocytogenes. A spectrophotometer (660 nm) was also used to study growth inhibition of L. monocytogenes in different TSB and strawberry juice media (pH 3.4 to 7.3). E. coli O157:H7 survived well at pH values of 3.4 to 6.8 at 4 degrees C, but the number of injured cells increased as pH decreased and incubation time increased. At 37 degrees C, E. coli O157:H7 was inactivated at pH of < or = 3.6 but could grow at pH 4.7. L. monocytogenes was quickly injured at pH of < or = 4.7 within 2 h of storage at 4 degrees C and then was slightly and gradually inactivated as storage time increased. L. monocytogenes survived well at pH 6.8 at 4 degrees C and grew well at 37 degrees C. Growth of L. monocytogenes at 37 degrees C was inhibited in TSB by 1% citric acid and 0.5% malic acids at pH 3.4 or by 50% strawberry juice at pH 4.7. Bacterial injury and inactivation appeared to be induced by the acids in strawberry juice. The acids, pH value, temperature, and time were important factors for bacterial survival, inactivation, and growth in the media tested.

Effects of recovery, plating, and inoculation methods on quantification of Escherichia coli O157:H7 and Listeria monocytogenes from strawberries

Effects of different recovery and inoculation methods on quantification of Escherichia coli O157:H7 and Listeria monocytogenes from strawberries were studied. Strawberries were spot or dip inoculated with 7 to 8 log CFU per strawberry of each pathogen, air dried for 2 h, and stored for 1, 3, and 7 days at 4 degrees C. The inoculated samples were stomached or washed with phosphate-buffered saline (PBS; pH 7.2) or with modified PBS (pH 8.4). Bacterial levels were determined using a direct selective plating, thin agar layer plating, or membrane-transferring plating (MTP) with tryptic soy agar and sorbital MacConkey agar (E. coli O157:H7) or modified Oxford agar (L. monocytogenes). Under most test conditions, washing with PBS followed by MTP had significantly higher (P < 0.05) recovery for both bacteria compared with other tested methods. Within a 7-day storage period for spot-inoculated strawberries, a stomaching step resulted in an injury of 0.9 to 1.4 log CFU for E. coli O157: H7 and 1.4 to 1.7 log CFU for L. monocytogenes. When a washing step was used instead, this resulted in an injury of only 0.2 to 0.6 log CFU for E. coli O157:H7 and 0.2 to 0.7 log CFU for L. monocytogenes. Both bacteria could survive on strawberry surfaces, but their recovered levels decreased with the increase of storage time at 4 degrees C for both spot and dip inoculation methods. Dip inoculation generally had a lower recovery than spot inoculation. An ideal protocol to recover and enumerate E. coli O157:H7 and L. monocytogenes from strawberries involved shaking and washing samples with 100 ml of PBS for 15 min at 22 degrees C coupled with a MTP enumeration method.

Decontamination of strawberries using batch and continuous chlorine dioxide gas treatments

Efficacy of chlorine dioxide (ClO2) gas in reducing Escherichia coli O157:H7 and Listeria monocytogenes on strawberries was determined using batch and continuous flow ClO2 gas treatment systems. Effects of continuous ClO2 gas treatment on total aerobic plate count, color, and residual ClO2 and chlorite on strawberries were also evaluated. Strawberries were spot inoculated with 7 to 8 log CFU per strawberry of each pathogen (E. coli O157:H7 and L. monocytogenes), stored for 1 day at 4 degrees C, and treated at 22 degrees C and 90 to 95% relative humidity with 0.2 to 4.0 mg/liter ClO2 gas for 15 or 30 min using a batch treatment system or with 0.6, 1.8, and 3.0 mg/liter for 10 min using a continuous treatment system. Surviving microbial populations were determined using a membrane-transfer plating recovery method. Increased ClO2 gas concentrations resulted in increased log reductions of each pathogen for both the batch and continuous systems. A batch treatment of strawberries with 4 mg/liter ClO2 for 30 min and continuous treatment with 3 mg/liter ClO2 for 10 min achieved greater than a 5-log reduction for both E. coli O157:H7 and L. monocytogenes. After continuous exposure to 3.0 mg/liter ClO2 gas for 10 min followed by 1 week of storage at 4 degrees C, no aerobic microorganisms were detected and the color of the strawberry surface did not change significantly (P > 0.05). Residues of ClO2 and chlorite on strawberries after the treatment were 0.19 +/- 0.33 mg ClO2 per kg and 1.17 +/- 2.02 mg Cl2 per kg, respectively, whereas after 1 week of storage no ClO2 residues were detected and residual chlorite levels were down to 0.07 +/- 0.12 mg Cl2 per kg. These results suggest that ClO2 gas treatment is an effective decontamination technique for improving the safety of strawberries while extending shelf life.

Survival of Salmonella Montevideo on tomato leaves and mature green tomatoes

Survival of Salmonella Montevideo on tomato leaf and mature green tomatoes was examined. When spiked on the surfaces of excised leaves from greenhouse tomato plants, Salmonella Montevideo survived poorly if the leaves were allowed to dry. After spot inoculation of 6.6 log CFU per leaflet and incubation for 48 h at 60% relative humidity, the leaflets were dried, and surviving Salmonella were reduced 2.8 to 3.7 log CFU per leaflet. However, when leaves spiked with Salmonella were supported on hydroponic nutrient medium and incubated at 100% relative humidity, there was no significant reduction of surviving bacteria for at least 6 days. Exposure of mature green tomatoes to ethylene (100 ppm at 100% relative humidity and 20 degrees C for 6 days) did not significantly affect the survival of Salmonella on their surfaces. The significance of these data to pre- and postharvest safety of tomato is discussed.

Efficacy of acidic electrolyzed water for microbial decontamination of cucumbers and strawberries

An examination was made of the efficacy of acidic electrolyzed water (AcEW, 30 ppm free available chlorine), ozonated water (5 ppm ozone), and a sodium hypochlorite solution (NaOCl, 150 ppm free available chlorine) for use as potential sanitizers of cucumbers and strawberries. AcEW and NaOCl reduced the aerobic mesophiles naturally present on cucumbers within 10 min by 1.4 and 1.2 log CFU per cucumber, respectively. The reduction by ozonated water (0.7 log CFU per cucumber) was significantly less than that of AcEW or NaOCl (P < or = 0.05). Cucumbers washed in alkaline electrolyzed water for 5 min and then treated with AcEW for 5 min showed a reduction in aerobic mesophiles that was at least 2 log CFU per cucumber greater than that of other treatments (P < or = 0.05). This treatment was also effective in reducing levels of coliform bacteria and fungi associated with cucumbers. All treatments offered greater microbial reduction on the cucumber surface than in the cucumber homogenate. Aerobic mesophiles associated with strawberries were reduced by less than 1 log CFU per strawberry after each treatment. Coliform bacteria and fungi associated with strawberries were reduced by 1.0 to 1.5 log CFU per strawberry after each treatment. Microbial reduction was approximately 0.5 log CFU per strawberry greater on the strawberry surface than in the strawberry homogenate. However, neither treatment was able to completely inactivate or remove the microorganisms from the surface of the cucumber or strawberry.

Evaluation of inoculation method and inoculum drying time for their effects on survival and efficiency of recovery of Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes inoculated on the surface of tomatoes

A study was undertaken to evaluate methods for applying inoculum and to examine the effect of inoculum drying time on survival and recovery of foodborne pathogens inoculated onto the surface of raw, ripe tomatoes. Five-strain mixtures of Escherichia coli O157:H7, Salmonella, or Listeria monocytogenes were applied to tomatoes by dip, spot, or spray inoculation methods. Inocula were dried for 1 or 24 h at 22 degrees C before tomatoes were treated with water (control) or chlorine (200 micrograms/ml). Significantly (alpha = 0.05) larger populations (CFU per tomato) of E. coli O157:H7 and Salmonella were recovered from dipinoculated tomatoes than from spot- or spray-inoculated tomatoes. This difference was attributed to larger numbers of cells adhering to tomatoes subjected to dip inoculation. Populations of E. coli O157:H7 and Salmonella recovered from spot- and spray-inoculated tomatoes containing the same initial number of cells were not significantly different. Significantly different L. monocytogenes population sizes were recovered from inoculated tomatoes (dip > spot > spray). Populations of pathogens recovered from tomatoes were significantly larger when inocula were dried for 1 h compared with 24 h. Significant differences (water > chlorine) were observed in the sizes of populations for all pathogens recovered from tomatoes treated with chlorine, regardless of inoculation method or drying time. Results indicate that inoculation method, drying time, and treatment affect survival and/or recovery of foodborne pathogens inoculated onto the surface of tomatoes. We recommend that spot inoculation with a drying time of 24 h at 22 degrees C be used with standard methods to determine the efficacy of chlorine and other sanitizers for killing foodborne pathogens on tomatoes.

An adapted ImmunoMagnetic cell separation method for use in quantification of Escherichia coli O157:H7 from bovine faeces

Detection of Escherichia coli O157:H7 organisms in food, clinical or environmental samples is necessary for diagnosis of infection and epidemiological investigations. However, this pathogen may be present in low numbers and difficult to identify among high numbers of other background bacteria. In order to increase the sensitivity of culture- and PCR detection, pre-enrichment of E. coli O157:H7 in broth culture combined with ImmunoMagnetic cell Separation (IMS) is routinely employed. These methods, although able to detect levels as low as 2 cfu/g (from 10 to 25 g samples), are qualitative detection strategies only. If the actual numbers of E. coli O157:H7 are to be quantified, growth enrichment must be excluded and the organisms isolated directly from the sample of interest. Such quantification is necessary, for example, to determinate contamination levels on beef carcasses and for determination of bacterial numbers in in vivo gene expression studies. In the present study, it was not possible to recover organisms from bovine faecal suspensions using the customary IMS system and so a range of alternative buffers and other paramagnetic beads was tested. Combination of a 6.2-microm diameter bead with a detergent-based buffer gave optimal recovery of E. coli O157:H7 organisms from faecal suspensions. This system was validated for recovery of E. coli O157:H7 by comparing it with that obtained with the standard Dynabeads IMS protocol, using both the traditional broth enrichment method and a quantitative detection approach. We conclude that a 6.2-microm diameter Aureon bead can be used for quantitative isolation of E. coli O157:H7 directly from bovine faeces and, for this purpose, is preferred to the 2.8-microm diameter Dynal bead.

Bacterial contamination of cucumber fruit through adhesion

In this study, the adhesion of bacteria to fresh cucumber surfaces in aqueous suspension was shown to be dependent on time of incubation, inoculum species and concentration, and temperature. The adhesion of bacteria to the fruit in wash water was less extensive at lower temperatures and shorter exposure times. Various species of bacteria were adsorbed to cucumber surfaces in the following relative order: Salmonella Typhimurium > Staphylococcus aureus > Lactobacillus plantarum > Listeria monocytogenes. Cells were adsorbed at all temperatures tested (5, 15, 25, and 35 degrees C) at levels that depended on incubation time, but the numbers of cells adsorbed were larger at higher incubation temperatures. Levels of adhesion of bacteria to dewaxed fruit were higher for L. monocytogenes and lower for Salmonella Typhimurium, L. plantarum, and S. aureus than were levels of adhesion to waxed fruit.

Tomato glycoalkaloids: role in the plant and in the diet

Tomatoes, a major food source for humans, accumulate a variety of secondary metabolites including phenolic compounds, phytoalexins, protease inhibitors, and glycoalkaloids. These metabolites protect against adverse effects of hosts of predators including fungi, bacteria, viruses, and insects. Because glycoalkaloids are reported to be involved in host-plant resistance, on the one hand, and to have a variety of pharmacological and nutritional properties in animals and humans, on the other, a need exists to develop a better understanding of the role of these compounds both in the plant and in the diet. To contribute to this effort, this integrated review presents data on the history, composition, and nutrition of tomatoes, with special focus on the assessment of the chemistry, analysis, composition, nutrition, microbiology, and pharmacology of the tomato glycoalkaloids comprising alpha-tomatine and dehydrotomatine; their content in different parts of the tomato plant, in processed tomato products, and in wild and transgenic tomatoes; their biosynthesis, inheritance, metabolism, and catabolism; plant-microbe relationships with fungi, bacteria, viruses, insects, and worms; interactions with ergosterol and cholesterol; disruption of cell membranes; tomatine-induced tomatinases, pantothenate synthetase, steroid hydroxylases, and cytokines; and inhibition of acetylcholinesterase. Also covered are tomato-human pathogen relationships and tomatine-induced lowering of plasma cholesterol and triglycerides and enhancement of the immune system. Further research needs in each of these areas are suggested. The overlapping aspects are discussed in terms of general concepts for a better understanding of the impact of tomato glycoalkaloids in the plant in general and in food in particular. Such an understanding can lead to the creation of improved tomatoes and to improved practices on the farm and in the consumption of tomatoes.