Antimicrobial Activities of Phenolic Extracts Derived from Seed Coats of Selected Soybean Varieties

Soybean hulls or seed coats consist of complex carbohydrates, proteins, lipids, and polyphenols such as anthocyanidins, proanthocyanidins, and isoflavones. The polyphenolics in the seed coats give them various colors such as black, brown, green, yellow, or even a mottled appearance. In this study, the antimicrobial effects of phenolic extracts from the seed coats of different colored soybeans (yellow, dark brown, brown, and black) were evaluated against foodborne pathogens such as Salmonella Typhimurium, Escherichia coli O157:H7, and Campylobacter jejuni in broth‐cultures as well as on chicken skin. The highest total phenolic content was observed for the phenolic extract from soybean variety (R07‐1927) with black colored seed coat (74.1 ± 2.1 mg chlorogenic acid equivalent [CAE]/g extract) and was significantly different (P <0.0001) from the extract of the conventional soybean variety (R08‐4004) with yellow colored seed coat (7.4 ± 1.2 mg CAE/g extract). The extract from black colored soybean produced reductions of 2.10 ± 0.08 to 2.20 ± 0.08‐log CFU/mL for both E. coli O157:H7 and C. jejuni after 3 d when incubated in broth‐culture having 4‐log CFU/mL of bacteria, whereas a 6 d incubation was found to reduce S. Typhimurium and E. coli O157:H7 at 2.03 ± 0.05 and 3.3 ± 0.08‐log CFU/mL, respectively. The extract also reduced S. Typhimurium and E. coli O157:H7 attached to chicken skin by 1.39 ± 0.03 and 1.24 ± 0.06‐log CFU/g, respectively, upon incubation for 6 d. Soybean seed coat extracts may have a potency as antimicrobial agents to reduce foodborne bacteria contaminating poultry products.     

Assessment of the microbiological safety of edible dried seeds from retail premises in the United Kingdom with a focus on Salmonella spp.

Sesame seed products have recently been associated with a number of Salmonella outbreaks in the UK and elsewhere. Aside from sesame seeds, there is little published information on the prevalence of Salmonella spp. in edible seeds. A study of 3735 samples of retail edible dried seeds in the UK was therefore carried out between October 2007 and March 2008 to assess their microbiological safety in relation to Salmonella contamination and levels of Escherichia coli, an indicator of faecal contamination. Overall, Salmonella was detected in 23 samples (0.6%), of which over half (57%) were sesame seeds. Other seeds contaminated with Salmonella were linseed (1 sample), sunflower (1 sample), alfalfa (1 sample), melon (4 samples) and mixed seeds (3 samples). E. coli was detected in 9% of samples, with 1.5% containing unsatisfactory levels (≥10²/g). These included melon, pumpkin, sesame, hemp, poppy, linseed, sunflower and mixed seeds. The UK retailers affected by the detection of Salmonella in their products recalled the contaminated batches, and Food Standards Agency food alerts were issued to advise against the consumption of affected seed products. This study highlights the importance of good hygiene practices and effective decontamination procedures during the production of these products.     

Effect of Immobilization and Salt Concentration on the Growth Dynamics of Escherichia coli K12 and Salmonella Typhimurium

Up to now, it is generally observed that (i) the microbial growth domain is confined by structure‐induced stress, or (ii) a solid(‐like) environment can enhance microbial survival/growth. In most studies in solid(‐like) systems, structure is induced by the addition of gelatin. The aim of this study was to evaluate the effect of other structure‐inducing components on the growth dynamics. Both single and binary gel systems are used. Growth is studied when simultaneously exposed to salt stress. Experiments are performed in spectrophotometer tubes, filled with 1 mL of liquid, or structured inoculated brain heart infusion. Four different (combinations of) gelling agents are tested, that is, gelatin, xanthan gum, a 50% combination of xanthan gum and gelatin, and a 50% combination of carrageenan and gelatin. Experiments determine the growth behavior of both Escherichia coli (0% to 0.5% and 1%, 2%, 3%, 4%, and 5% NaCl) and Salmonella Typhimurium (0%, 1%, 2%, 3%, 4%, and 5% NaCl) at 23.5 and 27 °C. By means of plate counting, the growth dynamics are determined. At the studied conditions, growth of E. coli and Salmonella Typhimurium seems independent of the type of structure‐inducing component. However, at higher concentrations of salt (>2%), lag phases are typically shorter in solid(‐like) systems than in liquid media. For the conditions tested, the effect of a structured environment on growth rate and maximal cell density can be neglected.     

Inhibition of Three Pathogens on Bologna and Summer Sausage Using Antimicrobial Edible Films

Whey protein isolate (WPI) films (pH 5.2) containing 0.5 to 1.0% p‐aminobenzoic acid (PABA) and/or sorbic acid (SA) were assessed for antimicrobial and mechanical properties while in contact with sliced bologna and summer sausage that were inoculated with Listeria monocytogenes, Escherichia coli O157:H7, and Salmonella enterica subsp. enterica serovar Typhimurium DT104. WPI films containing SA or PABA decreased L. monocytogenes, E. coli, and S. Typhimurium populations by 3.4 to 4.1,3.1 to 3.6, and 3.1 to 4.1 logs, respectively, on both products after 21 d at 4 °C. Background flora was inhibited compared with controls. Film tensile strength decreased while % elongation remained unchanged following 72 h of product contact.     

The effects of X-ray radiation on Escherichia coli O157:H7, Listeria monocytogenes, Salmonella enterica and Shigella flexneri inoculated on whole Roma tomatoes

In the last two decades several foodborne disease outbreaks associated with produce were reported. Tomatoes, in particular, have been associated with several multi-state Salmonella outbreaks. Inactivation of inoculated Escherichia coli O157:H7, Listeria monocytogenes, Salmonella enterica and Shigella flexneri on whole Roma tomato surfaces by X-ray at 0.1, 0.5, 0.75, 1.0, and 1.5 kGy was studied. The main purpose of this study was to achieve a 5 log reduction in consistent with the recommendations of the National Advisory Committee on Microbiological Criteria for Foods. Moreover, the effect of X-ray on inherent microflora (mesophilic counts, psychrotrophic counts and yeast and mold counts) of untreated and treated Roma tomatoes, during storage at ambient temperature (22 °C) for 20 days was also determined. Mixtures of three or two strains of each tested organism was spot inoculated (100 μl) onto the surface of Roma tomatoes (approximately 7–9 log per tomato), separately, and air-dried, followed by treatment with X-ray doses at 22 °C and 55–60% relative humidity. Surviving bacterial populations on tomato surfaces were evaluated using a nonselective medium (tryptic soy agar) with a selective medium overlay for each bacteria; E. coli O157:H7 (CT-SMAC agar), L. monocytogenes (MOA), and S. enterica and S. flexneri (XLD). Treatment with X-ray significantly reduced the population of the tested pathogens on whole Roma tomato surfaces, compared with the control. Approximately 4.2, 2.3, 3.7 and 3.6 log CFU reduction of E. coli O157:H7, L. monocytogenes, S. enterica and S. flexneri per tomato were achieved by treatment with 0.75 kGy X-ray, respectively. More than a 5 log CFU reduction per tomato was achieved at 1.0 or 1.5 kGy X-ray for all tested pathogens. Furthermore, treatment with X-ray significantly reduced the inherent microflora on Roma tomatoes. Inherent levels were significantly (p < 0.05) lower than the control sample throughout storage for 20 days.     

Efficacy of benzyl isothiocyanate for controlling Salmonella on alfalfa seeds and sprouts

The efficacy of benzyl isothiocyanate (BIT), a compound found in cruciferous vegetables, for controlling Salmonella on alfalfa seeds and sprouts was investigated. Alfalfa seeds were inoculated by individual Salmonella enterica serotypes Newport, Typhimurium, Tennessee, Montevideo, or Braenderup at two inoculation levels of 3 or 5 log CFU g⁻¹, followed by treatment with BIT (0.5–2%) or chlorine (2%) for 15 min. Treated seeds were sprouted in seed sprouters. Surviving Salmonella populations on the seeds and sprouts were determined. At both inoculum levels, 1.5% and 2% of BIT significantly reduced populations S. Typhimurium and S. Braenderup on seeds to a level comparable to the chlorine-treated seeds. Salmonella populations recovered from the sprouts germinated from 1.5% or 2% BIT-treated seeds were significantly lower than the control and chlorine-treated seeds at both inoculum levels (P < 0.05). The results of the study indicate that BIT can be used to control Salmonella contamination on alfalfa seeds and subsequent sprouting process.     

Attachment and Biofilm Formation by Selected Strains of Salmonella enterica and Entrohemorrhagic Escherichia coli of Fresh Produce Origin

This study compared the abilities of selected Salmonella enterica and enterohemorrhagic Escherichia coli (EHEC) strains of fresh produce origin to form biofilms on polystyrene surface and to attach to alfalfa and bean sprouts. Each of the 7 S. enterica and 4 EHEC inocula (2 mL; 10⁷ CFU/mL) was placed in 6 different broths in 24‐well polystyrene tissue culture plates at 28 °C for 1 to 7 d. Developed biofilms were quantified using the crystal violet binding assay. In a separate experiment, alfalfa and mung bean sprouts (5 g) were exposed to 25 mL inocula (10⁷ CFU/mL) of S. enterica or EHEC at 22 °C for 2 h with shaking at 40 rpm. Contaminated sprouts were thoroughly rinsed and homogenized in 0.1% peptone water, and bacteria attached to sprouts were enumerated. Biofilm mass accumulated on polystyrene surface increased with incubation time (P < 0.05). Among the microbiological media used, LB no salt (NaCl) broth better supported biofilm development (P < 0.05). Two EHEC strains formed more biofilms than the Salmonella and other two EHEC strains (P < 0.05). However, more Salmonella cells (5.66 log CFU/g) attached to sprouts than EHEC cells (3.46 log CFU/g). Both Salmonella and EHEC attached in higher numbers to mung bean, than alfalfa, sprouts (P < 0.05).     

Erythrosine B (Red Dye No. 3): A potential photosensitizer for the photodynamic inactivation of foodborne pathogens in tomato juice

The objectives of this study were to evaluate the efficacy of erythrosine B (ERY, Red No. 3)-mediated photodynamic therapy (PDT) for inactivating Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes in tomato juice. The inoculated tomato juice was subjected to xenon light (E − L+), ERY (E + L−), or xenon light and ERY combination (E + L+) treatments. Treatment with E + L+ for 15 min decreased the cell counts of E. coli O157:H7, S. Typhimurium, and L. monocytogenes by 6.77, 2.74, and 6.43 log CFU/mL, respectively, without generating sublethally injured cells. The cell count reductions of E. coli O157:H7 and L. monocytogenes in the E + L+ treatment group were higher than the sum of cell count reductions in the E − L+ and E + L− treatment groups, which indicated the synergistic activity of the treatment combination. The T_3d and T_5d values calculated by the Weibull model indicated that S. Typhimurium exhibited higher resistance to the E + L+ treatment than the other two pathogens. Compared with control group, the E + L+ treatment group exhibited higher lycopene content and a* (red) value, whereas the pH value and sensory attributes were not significantly (p > .05) altered. These results suggest that ERY-mediated PDT can be potentially applied to control foodborne pathogens in tomato juice products without negatively affecting the product quality.     

A new 7-plex PCR assay for simultaneous detection of shiga toxin-producing Escherichia coli O157 and Salmonella Enteritidis in meat products

A 7-plex PCR assay was developed to achieve an effective detection and identification of serotype Enteritidis of Salmonella spp. and shiga toxin-producing type of Escherichia coli O157 in meat products. Six DNA sequences in the invA and sdfI genes of Salmonella Enteritidis as well as rfbE, eae, stx1, and stx2 genes of E. coli O157:H7 were employed to design primers. The multiplex PCR assay could specifically and sensitively detect and identify target pathogens. Applying the assay to meat samples, the multiplex PCR assay was able to simultaneously detect and identify the two pathogens at a sensitivity of three CFU/10 g raw meats after simple 16 h enrichment in buffered peptone water. Further applying in 21 retail meat samples revealed that two samples were positive for non-shiga toxin producing E. coli O157, one sample was positive for Stx2 producing E. coli O157 and five samples were positive for Salmonella enterica Enteritidis. Taken together, the 7-plex PCR assay is a rapid and reliable method for effectively screening single or multiple pathogens occurrences in various meat products, and could also identify the Salmonella enterica Enteritidis from all Salmonella spp. and shiga toxin producing type from all E. coli strains. Considering as a non expensive screening tool, the multiplex PCR assay has a great potential in complement for food stuff analysis by conventional microbiological tests.     

Reductionin Listeria monocytogenes,Salmonella enterica and Escherichia coli O157:H7 in vitro and on tomato by sophorolipid and sanitiser as affected by temperature and storage time

Increased consumption of produce by consumers has been attributed to perceived health benefits of postharvest produce. Pathogen control is crucial because periodic occurrences and contamination of tomato and leafy greens have exacerbated food safety risks for consumers. We investigated the effects of temperatures (5 and 25 °C), storage time (30 min and 24 h) for inactivation of Listeria monocytogenes, Salmonella enterica and Escherichia coli O157:H7 by sophorolipid (SL‐p) produced fermentatively using palmitic acid as a co‐substrate at different concentrations in vitro. Reduction in pathogenic bacteria on grape tomato by SL‐p, sanitiser (Lovit) and combinations of SL‐p and sanitiser was determined. Temperature and storage time significantly (P < 0.05) affected pathogen inactivations by SL‐p as pathogen reductions were greater at 25 °C and 24 h than at 5 °C and 30 min of storage. L. monocytogenes was the most sensitive to SL‐p treatment as reductions of 5 log relative to untreated controls were attained at 0.12% of SL‐p. Significant reductions in S. enterica (1.91–3.85 logs) and E. coli O157:H7 (0.87–4.09 logs) were recorded at 2–5% of SL‐p. Lower populations of Salmonella and E. coli O157:H7 were inactivated than L. monocytogenes. On grape tomato, pathogen populations inactivated increased at higher SL‐p levels at 25 °C. Sanitiser and sanitiser + SL‐p reduced bacterial populations on tomato by 5.29–5.76 logs and 0.71–3.3.66 logs, respectively. These results imply the interactions of temperature, storage time and SL‐p significantly (P < 0.05) affected pathogen strain reductions. The combination of SL‐p with sanitiser led to synergistic effect on E. coli O157:H7, but not L. monocytogenes and S. enterica.     

Prevalence of the main food-borne pathogens in retail food under the national food surveillance system in Japan

The National Food Surveillance System in Japan was formed in 1998 to monitor the contamination of retail foods with bacterial pathogens. Approximately 2000–3000 samples were tested annually, and the data from food categories that had more than 400 samples collected during 1998–2008 were analysed. With regard to meat, the frequency of positive samples for Salmonella in chicken for raw consumption and ground chicken was 12.7% and 33.5%, respectively. Moreover, Shiga toxin-producing Escherichia coli (STEC) O157 was found in ground meat, organ meat and processed meat, although at a low frequency (0.1%). The prevalence of Campylobacter jejuni/coli was 13.3% and 20.9% in chicken for raw consumption and ground chicken, respectively. In vegetables and fruit, Salmonella was detected in cucumber, lettuce, sprout and tomato samples at a frequency of around 0.1–0.2%. With regard to seafood, Salmonella was found in 0.5% of oysters for raw consumption. Seafood was not contaminated with STEC O157 or Shigella. Serotype Infantis was the most frequently detected serotype of Salmonella in seafood, followed by the serotypes Typhimurium, Schwarzengrund and Manhattan. In ground chicken, 72.2% of the strains were identified as the serotype Infantis. E. coli, as an indicator of food hygiene, was detected in all food categories. The results show the prevalence of the above-mentioned pathogens in the retail food supplied in Japan; further, they indicate that consumption of raw food carries the risk of contracting food-borne infections.     

Efficacy of Neutral pH Electrolyzed Water in Reducing Escherichia coli O157:H7 and Salmonella Typhimurium DT 104 on Fresh Produce Items using an Automated Washer at Simulated Food Service Conditions

The objective of this study was to determine the efficacy of neutral pH electrolyzed (NEO) water (155 mg/L free chlorine, pH 7.5) in reducing Escherichia coli O157:H7 and Salmonella Typhimurium DT 104 on romaine lettuce, iceberg lettuce, and tomatoes washed in an automated produce washer for different times and washing speeds. Tomatoes and lettuce leaves were spot inoculated with 100 μL of a 5 strain cocktail mixture of either pathogen and washed with 10 or 8 L of NEO water, respectively. Washing lettuce for 30 min at 65 rpm led to the greatest reductions, with 4.2 and 5.9 log CFU/g reductions achieved for E. coli O157:H7 and S. Typhimurium respectively on romaine, whereas iceberg lettuce reductions were 3.2 and 4.6 log CFU/g for E. coli O157:H7 and S. Typhimurium respectively. Washing tomatoes for 10 min at 65 rpm achieved reductions greater than 8 and 6 log CFU/tomato on S. Typhimurium and E. coli O157:H7 respectively. All pathogens were completely inactivated in NEO water wash solutions. No detrimental effects on the visual quality of the produce studied were observed under all treatment conditions. Results show the adoption of this washing procedure in food service operations could be useful in ensuring produce safety.     

Inactivation of Salmonella enterica serovar Typhimurium and Quality Maintenance of Cherry Tomatoes Treated with Gaseous Essential Oils

The antimicrobial activity of the essential oils (EOs) from cinnamon bark, oregano, mustard, and of their major components cinnamaldehyde, carvacrol, and allyl isothiocyanate (AIT) was evaluated as a gaseous treatment to reduce Salmonella enterica serovar Typhimurium in vitro and on tomatoes. In vitro tests showed that mustard EO and AIT had the greatest inhibition of Salmonella, followed by cinnamon EO and cinnamaldehyde, while oregano and carvacrol showed the least inhibition. Scanning electron microscopy images of S. Typhimurium on tomatoes suggest that the EOs and their major components damaged the bacteria, and the damage was more obvious after posttreatment storage at 10 °C for 4 and 7 d. Salmonella on inoculated tomatoes was reduced by more than 5 log colony forming units (CFU)/g by mustard EO and AIT, by 4.56 and 3.79 log CFU/g following cinnamon EO and cinnamaldehyde treatments, respectively, and 1.54 and 3.37 log CFU/g after oregano EO and carvacrol treatments, respectively. Mustard EO and AIT induced discoloration, softening, and loss of the vitamin C and lycopene during 21 d of storage at 10 °C, while treatment with cinnamon EO and cinnamaldehyde did not result in significant changes in tomato quality. Tomatoes treated with oregano EO had better quality than nontreated samples after storage. Therefore, treatment with cinnamon and oregano EO and their major components appeared to be feasible for inactivation of Salmonella on tomatoes and maintaining quality.     

Efficacy of Integrated Treatment of UV light and Low‐Dose Gamma Irradiation on Inactivation of Escherichia coli O157:H7 and Salmonella enterica on Grape Tomatoes

The study evaluated the efficacy of integrated ultraviolet‐C light (UVC) and low‐dose gamma irradiation treatments to inactivate mixed strains of Escherichia coli O157:H7 and Salmonella enterica on inoculated whole grape tomatoes. A mixed bacterial cocktail composed of a 3 strain mixture of E. coli O157:H7 (C9490, E02128, and F00475) and a 3 serotype mixture of S. enterica (S. Montevideo G4639, S. Newport H1275, and S. Stanley H0558) was used based on their association with produce‐related outbreaks. Spot inoculation (50 to 100 μmL) on tomato surfaces was performed to achieve a population of appropriately 10^7–8 CFU/tomato. Inoculated tomatoes were subjected to UVC (253.7 nm) dose of 0.6 kJ/m² followed by 4 different low doses of gamma irradiations (0.1 kGy, 0.25 kGy, 0.5 kGy, 0.75 kGy). The fate of background microflora (mesophilic aerobic) including mold and yeast counts were also determined during storage at 5 °C over 21 d. Integrated treatment significantly (P < 0.05) reduced the population of target pathogens. Results indicate about 3.4 ± 0.3 and 3.0 ± 0.1 log CFU reduction of E. coli O157:H7 and S. enterica, respectively, per tomato with UVC (0.6 kJ/m²) and 0.25 kGy irradiation. More than a 4 log and higher reduction (>5 log) per fruit was accomplished by combined UVC treatment with 0.5 kGy and 0.75 kGy irradiation, respectively, for all tested pathogens. Furthermore, the combined treatment significantly (P < 0.05) reduced the native microflora compared to the control during storage. The data suggest efficacious treatment strategy for produce indicating 5 or higher log reduction which is consistent with the recommendations of the Natl. Advisory Committee on Microbiological Criteria for Foods.     

Adherence of probiotic bacteria to human colon epithelial cells and inhibitory effect against enteric pathogens – In vitro study

The aim of this study was to determine the anti‐adherence properties of three probiotic lactobacillus strains (Lb. rhamnosus 0900, Lb. rhamnosus 0908 and Lb. casei 0919), and their mixture against pathogens: Escherichia coli ATCC 10536, Salmonella enterica serovar Typhimurium ATCC 14028 and Candida albicans ATCC 10231 using Caco‐2 human colon adenocarcinoma cells. All strains of lactobacilli and the probiotic mixture to the greatest extent inhibited adherence of S. Typhimurium, up to 91%. Lb. rhamnosus 0900 inhibited E. coli by 75.9%, and Lb. casei 0919 decreased adherence of C. albicans by 49%. All pathogens activated the adherence of the mixture of probiotic bacteria.     

Salmonella enterica multilocus sequence typing and its correlation with serotypes

Salmonella enterica is a foodborne pathogen of significant public health concern worldwide. In Thailand, S. enterica has also been ranked among the top five most significant bacterial agents of foodborne illnesses by the Ministry of Public Health. Conventionally, biochemical tests and antigen-antibody agglutination have been used to identify and subtype S. enterica, respectively. The objective of this study was to identify the serotypes of 180 S. enterica isolates. Multilocus sequence typing (MLST) was used to deduce the S. enterica serotypes based on sequence type (ST) correlation as shown in the MLST database (http://mlst.warwick.ac.uk/mlst/). Initially, MLST was used to confirm serotypes of 53 previously identified isolates of S. Enteritidis, S. Typhimurium, S. Hadar, S. Virchow, and S. Infantis isolated in Thailand. MLST and serotype correlation confirmed 52 (of 53) known isolates. MLST was performed in 127 S. enterica isolates of unknown serotypes from various sources. Serotypes of all 127 S. enterica isolates were successfully deduced based on STs. With MLST and PCR-based identification, we have shown that the majority of isolates are of monophasic S. Typhimurium (ST34; 43 isolates) and serotype Rissen (ST469; 37 isolates), in agreement with the top serotypes commonly found in Thailand based on the WHO National Salmonella and Shigella Center. We have also confirmed that MLST is a powerful Salmonella subtyping method which could be used not only as a tracking tool for an outbreak investigation at nucleotide level but also as a serotype predictor for making correlations with food safety regulations.     

Prevalence and counts of Salmonella spp. in minimally processed vegetables in São Paulo, Brazil

Minimally processed vegetables (MPV) may be important vehicles of Salmonella spp. and cause disease. This study aimed at detecting and enumerating Salmonella spp. in MPV marketed in the city of São Paulo, Brazil. A total of 512 samples of MPV packages collected in retail stores were tested for Salmonella spp. and total coliforms and Escherichia coli as indication of the hygienic status. Salmonella spp. was detected in four samples, two using the detection method and two using the counting method, where the results were 8.8 × 10² CFU/g and 2.4 × 10² CFU/g. The serovars were Salmonella Typhimurium (three samples) and Salmonella enterica subsp. enterica O:47:z4,z23:- (one sample). Fourteen samples (2.7%) presented counts of E. coli above the maximum limit established by the Brazilian regulation for MPV (10² CFU/g). Therefore, tightened surveillance and effective intervention strategies are necessary in order to address consumers and governments concerns on safety of MPV.     

The evaluation of a PCR-based method for identification of Salmonella enterica serotypes from environmental samples and various food matrices

The most commonly used method for serotyping Salmonella spp. is based on the Kaufmann–White scheme, and is composed of serological reactions using antibodies to LPS agglutinins. The multiplex PCR used in this investigation was established by Kim et al. to serotype the 30 most common clinical Salmonella serotypes, as determined by CDC. The PCR assay consists of two five-plex reactions and a single two-plex PCR reaction, based on six genetic loci from Salmonella enterica serotype Typhimurium and four loci from S. enterica serotype Typhi. In this investigation, we further evaluated the method for serotyping Salmonella spp. using a reference collection, environmental samples collected from a Mid-Atlantic region tomato farm study, four food matrices spiked with different Salmonella serotypes and a proficiency test. The PCR assay was first evaluated using DNA isolated from pure cultures of isolates obtained from various clinical and environmental samples, and then DNA isolated from broth cultures of food matrices of “Red round” and Roma tomatoes, Romaine lettuce, green onions and Serrano peppers spiked with serotypes Newport, Typhimurium, Javiana and Saintpaul, respectively. The results showed that the PCR assay correctly serotyped Salmonella spp. from the clinical, environmental, spiked food matrices, and proficiency test samples. These findings are significant because the PCR assay was successful in the identification of Salmonella in the spiked samples in a broth culture containing other non-salmonella organism. This method may be a useful resource for the food safety community.     

Survival and High‐Hydrostatic Pressure Inactivation of Foodborne Pathogens in Salmorejo,a Traditional Ready‐to‐Eat Food

Salmorejo is a traditional tomato‐based creamy product. Because salmorejo is not heat‐processed, there is a risk of contamination with foodborne pathogens from raw materials. Even though bacterial growth in salmorejo is strongly inhibited because of its acidic pH (close to 3.9), the growth and survival of 3 foodborne pathogens in this food has not been studied before. In this study, 3 cocktails consisting of Escherichia coli O157, Salmonella enterica serovar Enteritidis, and Listeria monocytogenes strains were inoculated in freshly prepared salmorejo. The food was treated by high hydrostatic pressure (HHP) at 400, 500, or 600 MPa for 8 min, or left untreated, and stored at 4 °C for 30 d. Viable cell counts were determined on selective media and also by the triple‐layer agar method in order to detect sublethally injured cells. In control samples, L. monocytogenes viable cells decreased by 2.4 log cycles at day 7 and were undetectable by day 15. S. enterica cells decreased by 0.5 or 2.4 log cycles at days 7 and 15 respectively, but still were detectable at day 30. E. coli O157 cells survived much better in salmorejo, decreasing only by 1.5 log cycles at day 30. Treatments at pressures of 400 MPa or higher reduced viable counts of L. monocytogenes and S. enterica to undetectable levels. HHP treatments significantly (P < 0.05) reduced E. coli counts by approximately 5.2 to 5.4 log cycles, but also yielded surviving cells that apparently were sublethally injured. Only samples treated at 600 MPA for 8 min were devoid of detectable E. coli cells during storage.